General Morphology of Adults. Fleas are small, black to brownish-black insects, with complete metamorphosis. They are wingless, having lost their wings in the course of their evolutionary development. Adult fleas are 1 to 4 mm long, depending on the species, and are laterally compressed. They have stout, spiny legs, adapted for leaping, and short, 3-jointed, clubbed antennae that fit into depressions along the sides of the head. Fleas have piercing-sucking mouthparts (figure 46, C, chapter 4), the principal elements of which are the grooved labrum and a pair of sharp, swordshaped mandibles. The concave inner sides of the mandibles, together with the labrum, form the sucking channel (Ewing and Fox, 1943).
In some species, a conspicuous transverse row of spines is located just above the mouthparts, and is called the genal comb or ctenidium. In others, the pronotum bears a transverse row of heavy spines called the pronotal comb. When flea specimens are "cleared" in lactic acid for microscopic examination, the combs show up prominently, and can be used to identify species with the aid of low magnification. Figure 302 shows that the cat, dog, mouse, and rabbit fleas have both genal and pronotal combs. Certain species that infest rodents have the pronotal but not the genal comb, and the human, oriental rat, and sticktight fleas lack both combs. It has long been assumed that the combs or ctenidia assist fleas in locomotion through fur, hair, and feathers, but this is apparently not the case; locomotion is facilitated by the strong setae on the legs, projecting almost. at right angles. The combs serve to make dislodgement or capture by the host more difficult. They are admirably adapted to resist a backward pull, and so must have a considerable survival value (Humphries, 1966).
The Flea Life Cycle. A female flea will lay 4 to 8 eggs after each blood meal, and can usually lay several hundred eggs during her adult life. The smooth, oval or rounded, light-colored eggs (figure 303, C), about 0.5 mm long, are deposited on, but not firmly attached to, the body, the bedding, or the nest of the host. Although they are a little sticky, those laid on the host's body may fall or be brushed off. This accounts for their being found in crevices in the floor, under the edges of carpeting, in sofas, or in cat or dog boxes, kennels, etc., where they usually hatch in 10 days or less.
The small, hairy, wormlike larvae, (figure 303, B) are whitish, with a distinct, brownish head, and do not have eyes or legs. They have 3 thoracic and 10 abdominal segments, with a single row of bristles around each segment. The larvae are about 1.5 mm long when they emerge, finally becoming about 5 mm long. They move forward by using their backward-projecting bristles and a pair of hooked, chitinous processes located at the end of the abdomen by which they can obtain purchase on a surface. When disturbed, they may "flip" in circles to escape. The larvae of some species require dried blood for food, but others do not. Those that do not need blood can feed on the many kinds of organic debris that are present in the crevices in which the eggs commonly hatch. They also feed on their own cast skins. They require high humidity.
Within a week to several months, the larvae grow through 3 instars, then spin a pupal cocoon (figure 303, D) covered with grains of sand, dust, or organic debris, in which they are quite effectively camouflaged in their natural surroundings. The pupae are initially white (figure 303, E), but they change to brownish before the adults emerge. In the pupa, the appendages are not closely pressed to the body, and it has: the general shape and characteristics of the adult. Under favorable conditions, the adult emerges in a week or two, but under adverse conditions, the pupal period may be prolonged to as much as a year. The adult may remain in the cocoon for a long time until vibrations indicating the presence of a possible host stimulate it to emerge and become active.
The potentially long pupal stage, besides the fact that adult fleas can live without food for remarkably long periods, accounts for the fact that people may enter a house after it has been unoccupied by humans or pets for months, yet be rapidly and severely attacked by fleas. Depending on the species and weather conditions, 2 or 3 weeks to as many months, and rarely as long as 2 years, are required for many species of fleas to complete a life cycle.
Fleas most often bite people about the legs and ankles, and there are usually 2 or 3 bites in a row. The bites are felt immediately, but tend to become increasingly irritating, and are frequently sore for as much as a week. Flea bites may vary in their effects, from a transient wheal to prolonged symptoms that last for years, depending on the sensitivity of the victim. Children less than 10 years old were found to be more sensitive to the bites than older persons (Hudson et al., 1960b). The insects inject a hemorrhagic saliva that can cause severe itching, and repeated bites may produce a generalized rash. A small, red spot usually appears where the flea's mandibles have penetrated the skin. The spot is surrounded by a red halo, but there is never much swelling. Some relief from the itching can be obtained by applying cooling preparations, such as. carbolated vaseline, menthol, camphor, or calamine solution, or by placing a piece of ice on the affected area. For people who suffer severe allergic reactions, antigens are available that are sufficiently effective to cause the immunized person to be subsequently unaware of flea bites.
Probably the most dreadful calamity in all human history was the "Black Death," a series of plagues of the Middle Ages, particularly in the fourteenth century. Although not known at the time, the highly contagious disease was caused by a bacillus, Yersinia pestis (= Pasteurella), carried primarily by rats and transmitted by the fleas they harbored. The disease caused swellings of the lymph glands and subcutaneous hemorrhages that turned black. The plague first struck in Asia, and then spread to Russia, Persia, Turkey, North Africa, and Europe. The Encyclopedia Britannica estimates that one-third of the world's people perished. The most dangerous forms of plague are bubonic, septicemic, and pneumonic. Two types are named for the parts of the body infected. Bubonic plague, confined initially to lymphatic glands (buboes), is not so dangerous as the septicemic, and especially the pneumonic, phases, which are rapidly spread from person to person by airborne infection (Dubos and Hirsch, 1965). Bubonic plague is no longer a major scourge of mankind, but only because we now know how it is transmitted, and therefore how to prevent it. War and dislocation can still increase its potential, but not as in past centuries. The World Health Organization reported 1,318 cases of plague in 1968 and 864 in 1969, the majority from Vietnam, Treatment of the disease is quite effective with modern antibiotics. However, it can sometimes be dangerous, even with early diagnosis and treatment.
The oriental rat flea, Xenopsylla cheopis, is the most important vector of the plague bacillus, Yersinia pestis, from rat to man but at least 29 other species of fleas can transit the disease including the northern rat flea, Nosopsyllus fasciatus; the mouse flea, Leptopsylla segnis; the dog flea, Ctenocephalides canis; the cat flea, C. felis; and the human flea, Pulex irritans. Plague is transmitted while the infected flea is feeding, by regurgitation of the bacillus from the flea's alimentary tract through the proboscis into the new host. Yersinia pestis is rapidly eliminated from the proventriculus of the oriental rat flea when the mean monthly ambient temperature exceeds 28 °C (82 °F), and plague epidemics decline with the advent of hot weather (Cavanaugh, 1971).
"Sylvatic" or "endemic" is the designation used for the plague in wild rodents. Under certain ecological conditions in vacated squirrel burrows, fleas may continue to harbor the plague bacilli for many months, providing a reservoir for the infection. Fleas are particularly suitable for this purpose because of their remarkable longevity, for they can survive more than 6 months, even without food. Sylvatic plague occurs in many parts of the world, remaining somewhat localized in each area. A group of rodents maintains the infection, and if domiciliary rats or mice come in contact with such a focus of infection, the disease may be carried to human habitations and human cases may result. Likewise, if humans enter sylvatic plague territory, they may become infected.
Ground squirrels and chipmunks have been shown to be reservoirs for the plague bacillus in California. In the case of sylvatic plague, a person is more likely to become infected by contact with sick or dead rodents than by flea transmission. Since 1925, all the known cases of plague in the United States have been associated with wild rodents and the fleas that infested them. The United States Public Health Service reported 36 cases of human plague during the 6-year period 1965-1970. Twelve of these cases were reported in 1970. Eight cases have been reported in California since 1940. Areas in California where rodents are periodically killed by plague extend from the northeastern part of the state through the Sierra Nevada to the Tehachapis, and also in the coastal areas between San Francisco and Ventura County. People are warned not to handle sick or dead animals. Sometimes, a sudden widespread increase (epizootic) of a disease will occur among such rodents, and the chance for human infection will increase greatly. During epizootics, control has been attempted by placing bait boxes containing 10% DDT and peanut butter at 500-ft (150-m) intervals in the infested area. The rodents that enter a box to feed pick up not only enough insecticide to kill the fleas on them, but also the fleas living in their nests or burrows. (Anonymous, 1970a).
The oriental rat flea is also the principal vector of murine or endemic typhus that may be transmitted from rats to man. This disease is caused by the microorganism Rickettsia mooseri, and is widespread in rats and other rodents. The principal mode of transmission is believed to be by rubbing or scratching infected flea feces into wounds made by their bites. Murine typhus should not be confused with the more serious epidemic typhus, which has caused the deaths of millions of persons, but is transmitted by lice. The fatality rate for murine typhus, on the other hand, is only about 2%. In the United States, the disease is often confused with tickborne Rocky Mountain spotted fever, both diseases being characterized by rash and fever. However, Rocky Mountain spotted fever usually occurs during the spring and early summer, while murine typhus occurs in late summer and fall. Murine typhus cases in the United States dropped sharply from 5,193 cases in 1945, through a combination of rat control and insecticide dust for fleas. Also, new broad-spectrum antibiotics have been successful in the treatment of clinical cases of the disease (Pratt and Wiseman, 1962).
In California, murine typhus has remained endemic only in the 5 southern counties since 1919, when the first cases were recognized. In the 30 years from 1920 to 1949, there were 487 cases and 21 deaths from the disease. In the 20 years from 1950 through 1969, there were 79 cases and no deaths. Since 1960, there have been about 1.5 cases per year (CPHS, 1971).
Cats as Transmitters. About 75% of the 28 to 52 cases of murine typhus per year that occurred in the United States since 1945 were reported from Texas, particularly in 3 southern counties in which the disease was epidemic, and in some instances under circumstances in which the usual method of spread from rat to rat flea to man did not seem to occur. Prompted by this fact, the possible role of the domestic cat in the transmission of murine typhus to man was investigated. Rickettsia mooseri had been found in cat fleas, Ctenocephalides felis, in nature (Irons et al., 1944), and it was assumed that the cat fleas obtained the rickettsiae from their normal source, the rat. There is much circumstantial evidence that most of the murine typhus in southern Texas is transmitted via flea-infested cats or from flea-infested grass. (In southern Texas, grass is often so heavily infested with cat fleas that they are locally known as "grass fleas.") The greatest incidence of murine typhus in southern Texas has been noted to be in women and children, who spent more time at home where most of the illnesses were contracted (Older, 1970). The investigation in southern Texas confirmed the conclusion arrived at by Irons et al. (1944) that at least 5 cases of murine typhus in Austin in 1942, including 1 laboratory infection, were probably acquired through the agency of cat fleas harbored by kittens carried away from a feed store. In endemic areas, feed stores were said to be particularly serious foci of typhus.
Likewise in southern California, where 34 separate outbreaks of murine typhus were recorded from 1952 to 1969, 21 were in families that owned cats or had frequent contact with them. Again, as in southern Texas, most cases occurred among housewives and children. Seven outbreaks were intimately associated with either dogs, cats, opossums, or skunks, and 2 with rats. With greatly improved rat and flea control, there has been a shift in the incidence of murine typhus in man from central Los Angeles to foothill and orchard areas in eastern Los Angeles and Orange counties. Opossums in such areas are heavily infested with fleas, and are suspected of being responsible for some of the sporadic cases of typhus in man (Adams et al., 1970).
Fleas, particularly dog and cat fleas, can serve as intermediate hosts for the dog tapeworm, Dipylidium caninum (L.), and the rodent tapeworm, Hymenolepis diminuta (Rudolphi), which occasionally attack humans, particularly very young children.
Description. The female (figure 303, A) is 2.5 mm long, and the male is slightly smaller. The head of the female cat flea is twice as long as high when seen from the side, while that of the female dog flea as less than twice as long as high. In both species, the genal comb consists of 8 pairs of spines, and the pronotal comb also consists of 8 pairs (figure 302). With the aid of low magnification, it can be determined that the first 2 anterior spines of the genal comb of the cat flea are about equal in length, while the first spine is distinctly shorter in the dog flea (Ewing and Fox, 1943; Pratt and Wiseman, 1962).
The larvae of both species (figure 303, B) are nearly twice as long as the adults. They feed on particles of dry blood, excrement, and various organic substances collected in corners and crevices in the infested premises. When infestations are very heavy, the accumulations of grayish larvae and white eggs give the sleeping quarters of cats and dogs a "salt-and-pepper" appearance that easily identifies the infestation.
How Infestations Are Spread. Particularly in warm, humid areas, the exclusion of cats and dogs, or their proper management, is necessary to prevent flea infestations. Residential premises are sometimes so heavily infested that cats will leave to seek relief, and will carry the infestation to an uninfested home. If an infested stray cat has kittens under or near an uninfested home, the appearance of fleas within the house is very likely to follow. Fleas often also become established in the lawns of heavily infested residences. Fleas can jump vertically for 5 or 6 inches (about 15 cm), and can attach themselves to skin or clothing. Some pest control operators avoid being bitten by spraying insecticide onto their clothing.
In addition to cats, dogs, and humans, many animals, including the opossum, are attacked by cat fleas and dog fleas. Indigenous to the southeastern United States, opossums are now found throughout the country. They were introduced into California when some of the animals kept as pets escaped in San Jose in 1910, and they are now abundant throughout the state. When people live near wooded areas or stream courses, or where trees and shrubs are abundant, they may have opossums in the attics, wall voids, crawl spaces, or basements of their homes. These animals can then be sources of infestation.
Description. The human flea lacks the genal and pronotal combs characteristic of the cat flea and dog flea, and may be distinguished from the oriental rat flea by having its ocular bristle inserted beneath the eye instead of in front of it, as it is in the latter species (figure 302).
The western hen flea, Ceratophyllus niger Fox (Ceratophyllidae), is larger than the sticktight flea, and attaches itself only briefly while feeding. It breeds primarily in fowl droppings. Besides fowls, it readily attacks humans, cats, and dogs.
Flea Bites on the Beach
Fleas may occur on beaches, particularly if there are nearby residences. People using beaches may be bitten by these fleas or by stable flies (Stomoxys calcitrans), which can often be found in piles of seaweed. Small amphipod crustaceans (Orchestia), known as "sand fleas," also found under beached seaweed, are often blamed for bites, but they are in fact completely harmless.
Even if both pets and premises are free of fleas, the pets can become reinfested if they are allowed to roam about in infested areas and associate with infested animals in the neighborhood. Other animals from outside sources that enter the treated premises can also cause reinfestation.
Treatment of Pets. Dusts are safer than sprays to use for treating pets, because no solvent is present to carry the toxicant into the skin. The safest insecticides are the botanicals (pyrethrum or rotenone). Some pyrethrum dusts may merely paralyze the fleas, allowing them to recover later. To prevent recovery and reinfestation, paralyzed fleas should be combed out of the pet's fur into a piece of newspaper and burned. Several brands of 1% and even 2% pyrethrins, plus 10% piperonyl butoxide (a synergist), and substantial quantities of base oil, incorporated into silica aerogels, are readily available. These preparations have extremely high insecticidal potency, and good results have been reported when they were thoroughly applied.
Another relatively safe insecticide is malathion; 3% malathion dust was used on a female cat and 3 successive litters of kittens with no apparent harm to the animals. Each treatment controlled the fleas for 7 to 10 days (Pratt and Wiseman, 1962). Insecticide dusts should be applied with a shaker, or be rubbed into the fur by hand, keeping the dust out of the animal's eyes, nostrils, and mouth. Treatment should be particularly thorough around the ears and beneath the forelegs. As much as 1 oz (30 cc) of dust is required for a large dog. Particularly when the dust contains pyrethrum, the fleas move about actively for a while, causing the animal some discomfort.
The following insecticides have been suggested for flea control on pets: (1) carbaryl dip or wash 0.5%, or dust 2 to 5%; (2) coumaphos dip 0.2 to 0.5%, spray 1%, or dust 0.5% (the coumaphos dust also contains 1% trichlorfon); (3) lindane dust 1% (neither lindane nor coumaphos should be used on cats or on dogs under 2 months old); (4) malathion dip 0.25%, spray 0.5%, or dust 4 to 5%; (5) pyrethrum spray 0.2% plus 2% synergist, or dust 1 %; and (6) rotenone dust 1 % (Anonymous, 1970a). Ronnel as a 0.25% solution can also be used to dip and sponge dogs and cats. Mallis (1969) warned against the use of rotenone on canaries, for it might cause them to contract pneumonia. He suggested a powder containing pyrethrum only. Pigs are also known to be particularly susceptible to rotenone (Anonymous, 1970a).
Dips or washes should be used under the supervision of a veterinarian. He can also treat dogs and cats by oral administration of 25 mg of ronnel per lb (0.45 kg) of body weight of the animal every other day, or trichlorfon tablets at 34 mg per lb of body weight twice weekly.
Flea Collars. Registration has been obtained for dichlorvos-impregnated flea collars for dogs (except whippets and greyhounds), and cats (except Persian), and the collars have been effective (CDC, 1972). Some animals suffer an adverse reaction, initially indicated by a reddening of the skin under the collar. The skin under the collar should be examined frequently, particularly when the collar is being used for the first time. For dogs, the collar should be loosely fastened, to allow for good separation between collar and skin. For cats, it must be fitted tightly, to avoid possible strangulation when the animal is climbing. To prevent deterioration of the insecticide, the collar should not be allowed to become wet. If the skin under the collar does become irritated, it sometimes takes weeks or even months to heal. In most cases, simply removing the collar and topically applying a medicated ointment to the affected area will be all that is needed. Occasionally, a person may be so hypersensitive to dichlorvos that the handling of the flea collar will cause dermatitis in the contacted areas of skin (Anonymous, 1970h).
Control of fleas with no risk of dermatitis and with no other clinical effects appeared to be possib!e when disks of 20% dichlorvos in plastic containers with ventilation holes were hung on dog collars. These plastic containers resulted in complete control of fleas within 120 hours on all dogs tested. Ticks were not killed, but dogs initially without them remained free for the 92-day period of the test (Quick, 1971).
Treatment of Premises. Fleas are most concentrated in and around kennels or other places where animals sleep, and in rugs or under porches where they rest. Infested animal bedding should be burned, or else laundered in hot, soapy water. It should not be left unlaundered for long periods while the animals are away, such as during vacations.
Sometimes accumulations of lint and dust contain flea eggs, larvae, and pupae that can be removed with a vacuum cleaner. The cleaned area can then be sprayed with 0.5% lindane or, if the fleas happen to be resistant to organochlorine insecticides, 2% malathion or ronnel or 0.5% diazinon may be used. The relatively new insecticide Gardonals, of very low mammalian toxicity, is said to be effective for flea control. Baseboards, moldings, bed frames, floor areas, and rugs should be lightly sprayed. If oil-base spray contacts asphalt tile, it should be wiped up immediately. The author prefers oil-base sprays, for a very fine mist can be generated and there is less chance of staining, but open flames should be avoided. A fine, light mist with oil-base is particularly desirable for treating upholstered furniture.
When an area is not easily accessible or where it is not practicable to remove rubbish and clutter, a 0.2% spray of dichlorvos may be desirable because of its fuming action. Pest control operators sometimes add a small amount of dichlorvos to the residual spray. Insecticide dusts are suggested for the treatment of inaccessible places where spraying may be difficult or impossible. Silica aerogel dust (Dri-die¨ 67) is useful for the treatment of attics and wall voids because it can be so easily and uniformly blown throughout any enclosed area. Because it is inorganic, silica aerogel remains effective indefinitely. The homeowner should make the attic, wall voids, and underarea (crawl space) rodentproof before treatment. Also, stray cats, dogs, and other animals should be kept out of the subfloor area, for they may infest it with fleas.
The author has rapidly and effectively treated a home by allowing a fog from a Hi-Fog machine (figure 21, chapter 3) to drift lightly over the entire area inside the house-over carpeting, under beds, sofas, and other furniture, and into closets, using 2% malathion or 20% ronnel. Using a hose attachment sprayer, the entire yard area was sprayed with 1 % diazinon emulsion, with special attention to the lawn. Fleas were found to be particularly abundant around garbage cans. Most modern insecticides are remarkably effective against fleas, and failure to control them can usually be attributed to faulty application.
The ticks constitute the superfamily Ixodoidea of the order Acarina, which includes the mites, but their larger size and leathery cuticle distinguish the ticks from the mites. The Acarina can be distinguished from insects by the head, thorax, and abdomen being fused together, by the absence of antennae, and by the nymphs and adults having 4 pairs of legs. However, the larvae have 3 pairs of legs, as do full-grown insects. There are 2 families of ticks: the "soft" or "softbacked" ticks (Argasidae), with about 20 species in the United States, and the "hard" ticks (Ixodidae), with about 55 species. The latter are of greater economic importance.
Description and Biology. Instead of a true head, ticks have a capitulum (see figure 305, for hard ticks). This consists of a basal portion, the basis capituli, to which the hypostome, the chelicerae, and the 4-segmented palps are attached. The hypostome is not only a piercing organ, but also possesses rows of backward-projecting spines that anchor the tick to the skin of its host. The insertion of the hypostome is facilitated by the chelicerae, that serve as cutting agents. At the extremity of each chelicera is a pair of digits, used to lacerate the skin of the host (figure 305).
Both male and female ticks are bloodsuckers. After engorgement, fertilization takes place. The male then dies, and the female drops to the ground and seeks a sheltered place for oviposition. After the period of several days required for the eggs to develop, she lays her eggs and also dies.
For their first blood meal, the 6-legged tick larvae or "seed ticks" must depend on chance meetings with suitable hosts, so as might be expected, they are able to live for long periods without food. In nature, the tendency of ticks to congregate along animal paths and roads, drawn by the scent left by passing animals, increases their chances of finding hosts. After engorging, they molt and become 8-legged nymphs.
The "soft ticks" may have several nymphal instars, and may have to endure a period of prolonged starvation each time they await a new host, but the "hard ticks" have only 1 nymphal instar. In either case, the mature nymphs may have to endure months of starvation before finding a suitable host upon which to feed, molt, and become adult. The adult leaves the host to lay eggs on the ground. Upon emerging from the eggs, the larvae commonly climb up on grasses or shrubs in order to be more readily contacted by passing animals.
Economic Importance. Few tick species are ever found in the home, but they may infest dogs and are important pests of livestock. Tick bites can cause great discomfort to humans. They remain attached for long periods of feeding, and therefore have the opportunity to inject large amounts of their venom, causing symptoms ranging from mild irritation to paralysis. If not soon removed, some species (wood ticks) can cause a form of paralysis known as "tick paralysis."
Among the soft ticks, only species of the genera Ornithodoros and Argas are important as vectors of disease. Argas spp. are important poultry parasites, but seldom attack man. Ornithodoros can be distinguished by the rounded sides of the body, in contrast to the distinct marginal border of Argas, which is always visible, even when the tick is fully engorged.
The female of O. hermsi is 5 to 6 mm long and 3 to 4 mm wide. The male is slightly smaller, but is similar in appearance. Unengorged ticks are light sandy in color. Freshly engorged specimens are dull, deep garnet, with a grayish-blue tint a few days after feeding. Absence of food greatly prolongs the life cycle. The larvae may live as long as 95 days without food, the nymphs even longer, and the adults more than 7 months. With occasional feeding, they have been kept alive in a pillbox for over 4 years (Herms, 1939). The duration of the life cycle varies from 202 to 314 days at 30 °C (86 °F) to 364 to 602 days at 21 °C (70 °F) (Pratt and Littig, 1962).
Ornithodoros turicata and O. talaje (Guérin-Meneville) transmit relapsing fever in southern areas, between Florida and California and northward to Kansas, Colorado, and Utah, and O. parkeri transmits the disease in the northwestern area.
Relapsing Fever. Relapsing fever is caused by host-specific spirochetes (slender, spirally undulating bacteria). The disease is characterized by chills, fever, sweating, generalized pains, and usually nausea, vomiting, and headache. Ticks not only remain infective for life, but pass the spirochetes to their offspring through the egg. Not only ticks, but also their rodent hosts, serve as reservoirs for the spirochetes. Ornithodoros hermsi transmits the spirochete Borrelia hermsi and O. parkeri transmits B. parkeri without crossinfections between the 2 species (Davis, 1939, 1948; Pratt and Littig, 1962).
Mountain cabins in areas where tickborne relapsing fever occurs should be rodent-proofed to exclude small rodents. Avoid soiling the fingers with the blood of chipmunks or squirrels. Infection can take place by contamination of a wound in the skin, although it is known that Ornithodoros hermsi, O. turicata, and O. parkeri definitely infect by their bites (Hunter et al., 1960).
Description. The pajaroello is a large tick, leathery, rough, and granulated (figure 304), and the whole surface, above and below, is a dirty yellowish-earthy color, and has rusty-red spots irregularly distributed (plate VIII, 6). The capitulum and palps are light yellow, and the legs are gray-brown. The unengorged tick is 10 to 12 mm long, rounded at the posterior end, and pointed anteriorly. The sides are parallel,. with only a slight median constriction.
Life Cycle. The female deposits large, spherical eggs, sometimes more than 1,000 per season, that hatch in 3 or 4 weeks. The very active larvae attach readily to a host. The ticks become sexually differentiated after the fourth molt, requiring about 4 months, or sometimes not until after the fifth molt. They usually molt once for each feeding (engorgement), but sometimes there are 2 molts between feedings.
Effect of a Bite. Herms (1939) described the symptoms of a victim bitten twice by a pajaroello,14 days apart. The first time, the tick was partly engorged, and the second time, it was fully engorged when dislodged. The second bite, on the left leg, was the more severe one. The engorged tick was about 20 mm long and 12 mm wide. A bright-red spot was visible at the point of the tick's attachment, surrounded by an irregular, purple ring about 20 mm in diameter. After 3 hours, the lower leg was greatly swollen, and a clear lymph exuded freely from the lesion.
Description and Biology. The female hard tick has a hard plate or shield on the anterior region of the back (figure 305, B), the remainder of which is smooth, and the body can be greatly extended by feeding. The shield covers the entire back of the male. The mouthparts are visible from above, projecting in front of the body, whereas in the soft ticks they are under the body, and are not visible from above. The pedipalpi (figure 305, B, palpus) are rigid, and are varied in form. The spiracles are situated behind the fourth pair of coxae. The coxae and tarsi are generally armed with spurs, which are absent in soft ticks. Pulvilli are always present in hard ticks, but are absent or rudimentary in soft ticks. The females feed only once, and lay one large batch of eggs often several thousand.
Hard ticks are scarce in forests being more abundant in shrubby areas, especially along trails or paths, to which they are attracted by the scents left by animals. Larvae hatching from eggs that have been deposited in some sheltered place will climb to the tips of grass blades or twigs near the trail used by their potential hosts, often clinging together in clusters of 100 or more. Any vibration of their resting place caused by a passing host animal stimulates the larvae to wave their legs about. If the animal brushes against them, they cling to its fur. "One-host ticks" [e.g., the winter tick, Dermacentor albipictus (Packard)] develop to maturity on the host. "Three-host ticks" (e.g., D. andersoni, D. variabilis, and Amblyomma americanum) drop from the host to molt. They may then crawl to a perch near a trail, responding to vibrations as did the larvae, and again cling to the fur of a passing animal. They engorge, and again drop off the host to molt, most species overwintering as unfed adults. Hard ticks cannot stand as much desiccation as soft ticks, and the latter generally survive in much drier situations.
Description of Adults. The adult male (figure 306, C) is about 4.5 mm long and 2.5 mm wide. The dorsal shield is dark brown, marked with a variable pattern of white. The unfed female (figure 306, D) is slightly larger than the male. Her shield, which is restricted to the anterior portion of the dorsum, is much more extensively marked with white than in the male. The male does not become larger as he feeds, but the female enlarges (figure 307) to about 13 mm long by 10 mm wide. The size of the shield does not change, but it becomes inconspicuous in relation to the greatly expanded remainder of the body (Smith et al., 1946).
Life Cycle. Over a 14- to 32-day period, the female lays masses of 4,000 to 6,500 ellipsoidal, yellowish-brown eggs, and then dies. The eggs normally hatch in 36 to 57 days. The larvae (figure 306, A) lack spiracles, have only 3 pairs of legs, have red markings near the eyes, and lack white markings on the shield. Unfed larvae are yellow, and about 0.6 mm long; engorged specimens are slate gray to black, and are about 1.2 mm long. The unfed larvae crawl about, seeking hosts, and can live for more than a year (maximum, 540 days) without food. In a simulated meadow, larvae became engorged on mice in an average of 4.4 days, then dropped from their hosts to seek protected places in which to molt. The nymphs lacked a genital opening and the white markings on the shield that characterized the adults. The unfed nymphs (figure 306, B) were light yellowish brown, with red markings near the eyes, and were about 1.5 mm long. The engorged nymphs were slate gray, and about 4 mm long. As with the larvae, they crawled about seeking hosts. The engorging period ranged from 3 to 11 days; the greatest number dropped on the sixth day, and found protected places in which to molt. They molted after 3 weeks to several months. Nymphs also could live for more than a year without food; the maximum period was 584 days (Smith et al., 1946).
Unengorged adults may live for more than 2 years if they do not find dogs or other large animals to which they can attach themselves. The engorgement of females requires 5 to 13 days, and mating takes place on the host. In the absence of suitable hosts the life history of the American dog tick may be prolonged to 2 or more years, but under favorable conditions, it may not take more than 3 months.
Hosts. In the field in Massachusetts, meadow mice were the most important hosts of the larvae and nymphs, while dogs were the most important for adults. Dogs can pick up hundreds of ticks in a day, and horses and cattle also suffer some annoyance (Smith et al., 1946).
Shoshone Indian braves exposed their squaws to the "evil spirits" believed to be associated with gophers in the foothills of the Rockies, and the braves avoided areas shown by this pragmatic test to be inhabited by the evil spirits. When white men brought large, domesticated animals into the foothills, the tick population multiplied closer to fixed settlements, and Rocky Mountain spotted fever became a much greater problem to white men than it originally had been to the Indians. What originally was thought to be a regional nuisance has now been shown to be a world-wide problem, for RMSF has been recognized in North and South America, and similar infections have occurred in Europe, South Africa, India, and Australia (Aikawa, 1966).
Biology. Nymphs and adult ticks spend the winter among grass and leaves on the ground, without feeding, and not until the first warm days of spring do they climb up on the brush to become attached to passing hosts. They feed only from about the middle of March to the middle of July, and this is the only period when people contract spotted fever.
Biology. In Oklahoma, engorged females seldom appear on hosts before mid-March, and maximum numbers of fed females drop from domestic livestock and deer during late April, May, and early June. After a lapse of 5 to 16 days, the dropped females oviposit under available ground litter, frequently depositing over 5,000 eggs per egg mass. The eggs generally hatch in about 30 days. The larvae climb to the tops of plants. Heavy rains and strong winds tend to dislodge them, and over 90% apparently perish under such circumstances. Lone star ticks overwinter in the fed larval stage, unfed nymphal stage, and 2 forms of adults: unfed adults, or fed nymphs that become adults during the winter after exposure to adequate warmth.
The ticks normally contact their hosts when the latter brush up against them on the tips of tall grasses and shrubs. However, if the host remains in the area for a considerable time without contacting them, nymph and adult ticks may become stimulated by heat and carbon dioxide from the host's body, and will then fall to the ground, find the host, and climb onto it. Larvae depend almost entirely on the host to make contact with the larval mass as it hangs from the tips of vegetation; they seldom seek a host (Hair and Howell, 1970).
The bite of the wood tick is not felt immediately, even though the tick remains attached, but the bite causes more or less inflammation later. If the tick is not removed with care (see "Removal of Ticks," farther on), its mouthparts usually remain in the skin and cause an ulcer that can become, infected. Another possible consequence of the bite, if a gravid female tick attaches at the back of the neck or base of the skull and feeds there for a week or so, is a disease known as tick paralysis. A paralysis develops, and if the tick is not removed, death by respiratory failure may result. Human beings, particularly children, have been affected, but more frequently domestic range animals are the victims. In North America, tick paralysis has been most common in the Pacific Northwest, where it had been known since the first decade of this century, and by 1954, 332 human cases had already been recorded. Dermacentor andersoni was almost always the tick that was implicated. The mortality rate was 11.7%, despite the fact that there is usually a latent period of about 5 days before D. andersoni can produce enough toxin to cause paralysis, and paralysis can be avoided by removal of the ticks during that period. For some 12 to 24 hours before the onset of actual paralysis, there may be vague complaints, irritability, tiredness, and pain or paresthesia (sensation of prickling, tingling, or creeping on the skin), in the lower extremities. There then occurs a loss of coordination, followed in a few hours by flaccid paralysis in the lower extremities. In another 12 to 24 hours, the paralysis ascends to the arms if the ticks are not removed. If the ticks are removed, recovery is rapid (Rose, 1954).
Not all female ticks can cause paralysis, and the reason for this is not known. Tick strains in some areas are more dangerous than in others. Using hamsters as experimental animals, Hughes and Philip (1958) found that ticks (D. andersoni) from British Columbia caused a much higher rate of paralysis than ticks from the Bitter Root Valley of Montana. This may account for the statistics presented by Rose (1954), showing about 72% of the cases of tick paralysis in the Pacific Northwest to be from British Columbia.
In California, D. andersoni occurs in the northeastern part of the state and southward along the eastern slope of the Sierra Nevada to Mono County. Instances of tick paralysis in deer and cattle, but not humans, are known from California. All clinically observed human cases have been acquired in Oregon or elsewhere (R. F. Peters, correspondence). However, the potential for tick paralysis, as well as the tick fevers (described following) would appear to exist. Vacationers in tick-infested areas should examine themselves daily to make certain that a tick has not embedded itself anywhere on the body. In the eastern and southern states, tick paralysis was not reported until 1938 (Costa, 1952). The species of ticks implicated have been Dermacentor variabilis, Amblyomma americanum, and A. maculatum Koch.
Colorado Tick Fever
T'he "Colorado type" of tick fever is caused by a virus, and is known to occur in western Canada and in Washington, Oregon, Idaho, Montana, California, Nevada, Utah, Wyoming, Colorado, and South Dakota. It is described as "an acute, febrile, dengue-like disease, usually without rash; a brief remission is usual, followed by a second bout of fever, each lasting 2 or 3 days. Characteristically mild, but may be severe in children, occasionally with encephalitis or tendency to bleed; deaths are rare." The reservoirs for the virus of Colorado tick fever are many species of ground squirrels, chipmunks, mice, wood rats, and other rodents. Ticks also serve as long-term reservoirs (CPHS, 1971).
The distribution of Colorado tick fever in California has coincided with that of its usual vector, Dermacentor andersoni. In 1957-1970, there were 115 laboratory-confirmed cases of Colorado tick fever in California, the majority acquired in that state but some in endemic areas from other states (CPHS, 1971). Since 2 tick fevers - Colorado tick fever and Rocky Mountain spotted fever - occur in California and other western states, the 2 diseases should be differentiated, and each should be given its full name in scientific papers and news releases.
Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is endemic throughout the United States outside of New England, particularly in mountainous regions, as well as in Canada and some parts of Mexico and South America. RMSF, first known in the Bitter Root Valley of Montana as early as 1872, is no longer a regional curiosity, and Aikawa (1966) suggested that it be called "rickettsial spotted fever," honoring the name of H. T. Ricketts, the most active and effective early investigator of the disease. In the West, the Rocky Mountain wood tick, Dermacentor andersoni, is the principal vector, both male and female ticks being infective; and in the East, the American dog tick, D. variabilis, is the most important vector (Larson, 1955). The rabbit tick, Haemaphysalis leporispalustris (Packard), is also a vector in the West, and the Pacific Coast tick, D. occidentalis Marx, is suspected, The lone star tick, Amblyomma americanum, is considered to be a probable vector in parts of the eastern United States, and in Texas, Oklahoma, and Arkansas (Pratt and Littig, 1962). It appears that any tick that infests the approximately 40 hosts of rickettsia is a potential vector. Birds are believed to be important factors in dissemination of ticks that harbor rickettsial agents, including Rickettsia rickettsia, the RMSF pathogen (Clifford et al., 1969). Rickettsias are a group of microorganisms about the size of small bacteria, and on the biologic scale they lie between the viruses and the bacteria. Besides the various spotted fevers, they are the causal organisms for the typhus fever group of rickettsial diseases, scrub typhus, fever, and probably trench fever.
Symptoms. RMSF is a severe, acute, infectious disease of the small peripheral blood vessels. It is said to cause greater damage to tissues on the surface of the body and to those of the brain than does any other rickettsial disease. Mortality to humans is commonly 20% or more (Rivers and Horsfall, 1959; Aikawa, 1966). A rash appears about the second to fifth day after a bite, on the wrists, ankles, and less often on the back, later spreading to all parts of the body. This rash is the most characteristic symptom of RMSF. The rash is sometimes preceded by a mottled appearance of the skin. The spots may become necrotic on the extremities. At the outset, the patient complains of frontal and occipital headache, intense aching in the lumbar region, and marked malaise. The incubation period may be 3 to 12 days in the milder infections and 2 to 5 days in the more severe ones. Before the initial chill, only minimal evening fever is experienced, but after the chill, the temperature continues to rise, reaching 102 to 104 °F (39 to 40 °C) on the second day, and then rises gradually to a maximum of 104 to 105 °F (40 to 40.6 °C) in the second week. In the virulent cases in the Bitter Root Valley of Montana, the temperature may reach 106 to 107 °F (41 to 41.6 °C), and may remain this high until the patient dies. The pulse rate may reach 150 and the respiratory rate 60 per minute in the terminal phase of the disease (Aikawa, 1966).
Transmission. Ticks transmit Rickettsia rickettsii from any small mammal to man during frost-free periods of the year. The organism enters the gut of a tick with the blood it sucks from its host and then spreads to all parts of the body, including the salivary glands. Fortunately, the disease is not transmitted unless the tick remains attached to its host for 2 hours or more. The disease is passed from one generation of ticks to the next via the egg, without decrease in virulence (Price, 1953). Despite transovarial transmission of R. rickettsia, the tick apparently suffers no ill effect, and the vertebrate vectors also appear to be in symbiotic relationship with the tick and suffer no evident clinical disease (Aikawa, 1966).
Vaccination. A high degree of protection to people who are frequently exposed to tick bites is afforded by vaccination - initially 3 injections at 5- to 7-day intervals and each year thereafter a booster shot. As a result, the number of reported cases of RMSF is steadily decreasing (Pratt and Littig, 1962; Aikawa, 1966).
Another rickettsial disease sometimes transmitted to man by ticks is Q fever (query fever), also known as coxiellosis or nine-mile fever, the causal organism for which is Coxiella burnetii. It has been reported from all continents, and in the United States, outbreaks have occurred most commonly among stockyard workers. Transmission to man is usually by inhalation of dust. Milk can be a source of infection. Tick species that have been found infected are Dermacentor andersoni, Amblyomma americanum, Otobius megnini, and many others (Horsfall, 1962; Pratt and Littig, 1962). Vaccination of persons liable to be exposed to infection has been effective (Hunter et al., 1960).
This is a disease caused by the bacillus Francisella tularensis, that occurs in the continental United States, Alaska, Canada, northern Europe, Japan, and many other parts of the world. In the United States, it was first reported in Utah in 1919 and was called "deer fly fever," but was later reported among various rodents in Tulare County, California.
Rabbits are important reservoirs for this bacillus, and it is mechanically transmitted from rabbit to rabbit by the deer fly Chrysops discalis (Francis and Mayne, 1921). However, ticks may be more important than deer flies in the transmission of this disease (James and Harwood, 1969). In fact, at least 54 species of arthropods can harbor the tularemia bacillus (Steinhaus, 1946). Besides existing in rabbits, tularemia is also known to be carried by meadow mice, ground squirrels, beavers, coyotes, sheep, and various game birds. When transmitted to humans by deer flies, exposed body surfaces are bitten, and the on set of pain and fever is sudden. Lymph glands become inflamed and swollen. The fever lasts for 3 to 6 weeks, and the patient generally convalesces slowly (Francis, 1919).
Tickborne (Endemic) Relapsing Fever
Louseborne relapsing fever and tickborne relapsing fever are both caused by spirochetes of the genus Borrelia, and they cannot be distinguished with certainty on the basis of clinical manifestations. (See comment in the earlier section on lice.) Most authorities believe that the spirochetes transmitted by lice and ticks are variants of the species Borrelia recurrentis, but many "species" have been identified by geographic location and by their argasid tick vectors, and were listed by Dubos and Hirsch (1965). It is reasonable to suppose that the isolation resulting from the burrow- or den-infecting habits of argasid ticks may have led to the development of different strains of a single pathogen. Tickborne relapsing fever tends to be endemic, and is completely so in the United States.
In California, relapsing fever is most commonly contracted from the bites of argasid ticks, generally Ornithodoros hermsi, and usually at elevations ranging from 5,000 to 8,000 ft (1,500 to, 2,400 m). Ticks in rodent-infested mountain cottages are common sources of the spirochetes (Herms and Wheeler, 1936). Infected ticks (O. hermsi, O. turicata, O. parkeri, and O. talaje) have been found in California, Arizona, New Mexico, Utah, Idaho, Montana, Colorado, Kansas, Oklahoma, Texas, and Florida. In Texas alone, 100 cases of tickborne relapsing fever were diagnosed from June, 1942, to May, 1949 (Dubos and Hirsch, 1965), and in California, there were 65 recorded cases from 1950 through 1970 (CPHS, 1971). In both states, many additional cases probably escaped detection.
The sensory physiology and behavior of I. ricinus were investigated in great detail by Lees (1948). The data are worth recording because they may hold for ticks in general. While crawling, the unfed female waves its first pair of legs like antennae. It uses these legs for crawling when it is not hungry. On the tarsi of its legs is Haller's organ, which contains sensilla stimulated by odor and humidity. As already stated, ixodid ticks climb to the tops of grass blades and twigs and wave their forelegs about when stimulated to do so by an approaching animal, and will cling to the passing host. The tips of the pedipalps of I. ricinus have sensory pads used for selection of a suitable feeding site on the host. Ixodes ricinus spends most of its life in microclimates of very high humidity, so desiccation forces the tick to periodically move down to the moist base of the herbage upon which it has climbed so that it can absorb moisture through its cuticle. One is reminded of similar periodic trips of subterranean termites, via their shelter tubes, from dry structural timbers to moist subterranean galleries where they can replenish their body moisture by cuticular absorption.
Description of Adults. The male is about 3 mm long, flat, uniformly reddish brown, and has tiny pits scattered over the back. The female (figure 308) before feeding resembles the male in size, shape, and color. When engorged with blood, she can reach about 12 mm in length. The engorged part of the body then changes in color to grayblue or olive.
Life Cycle. The engorged female falls off the dog, and seeks a sheltered place in which to lay a mass of 1,000 to 3,000 tiny, dark-brown eggs. These may be deposited in any available place, but because she tends to crawl upward, they are likely to be deposited in cracks or crevices in the roofs of kennels or the ceilings of porches. The female then dies, and her eggs hatch in 19 to 60 days. Cool and/or dry weather tends to prolong the hatching period. The minute, 6-legged, lightbrown larvae or "seed ticks" move to the lower parts of walls, and attach themselves to a dog at the first opportunity, but can survive as long as 8 months without food or water. After finding a host, they engorge themselves in 3 to 6 days changing from flattened to globular in shape: about 2 mm in diameter, and become bluish in color. They then drop, hide in cracks to molt, and in 6 to 23 days become 8-legged, reddish-brown nymphs.
After a few days of inactivity, the nymphs are ready to attach themselves to a dog, but like the larvae, they can live for months without food or water. Once attached, they engorge in 4 to 9 days and become oval, about 3 mm wide, and dark gray. They then drop off the dog, hide, and molt in 12 to 29 days. They are then adults, for among the hard ticks there is only a single nymphal instar. The adults will attach themselves to a dog at the first opportunity, but they can live as long as 18 months before attachment. They then engorge themselves with blood in 6 to 50 days, mate, and the females drop off to oviposit and repeat the life cycle (Bishopp, 1939). Under favorable conditions, the life cycle may be completed in 63 days at 85 °F (29 °C). However, under the usual environmental conditions and delays in attachment to the host, there are seldom more than 2 generations per year in the North and 4 in the South. The brown dog tick prefers warm, dry situations, and seldom develops in large numbers outdoors in the United States.
Obnoxious Features. Besides infesting dogs, the brown dog tick can be a serious nuisance in the home, where it may be seen emerging from numerous hiding places. Even if ticks are eliminated from a dog and its kennel, as well as from the home, it can pick up ticks from other infested residences in the neighborhood, from a boarding kennel, or when taken along on a vacation. A dog can pick up ticks that have dropped from another dog, but cannot become infested by direct contact, because a feeding tick drops off and molts before attaching itself to a new host. Ticks may attach themselves anywhere on a dog, but are most often found on the ears and neck and between the toes. Larvae and nymphs are often found in the long hair on the back. By sucking large quantities of blood, ticks can reduce a dog's vitality and cause it to be irritable. They transmit a canine disease known as piroplasmosis in various parts of the world. The causal organism is a protozoan, Babesia canis, that infects red blood cells, but the disease is rare in the United States.
Removal of Ticks Attached to the Body. It is desirable to remove attached ticks without leaving the capitulum embedded in the skin. Pratt and Littig (1962) recommended as follows:
If ticks become attached, the simplest method of removing them is by a slow, steady pull that will not break off the mouthparts and leave them in the wound. There is no certain way to make a tick detach its mouthparts. A drop of chloroform, carbon tetrachloride, ether, benzene, vaseline, or fingernail polish rubbed over it will help remove the tick. Several minutes to a half-hour later, when the tick has withdrawn its mouthparts, it can be removed with less damage to the skin. Touching the tick with the lighted end of a cigarette (or a hot needle) sometimes causes it to release attachment. An antiseptic should always be applied to tick bites just as to open wounds. If the hands have touched the tick during removal, wash them thoroughly with soap and water, since the tick secretions may be infective.For the removal of Ixodes ticks, Busvine (1966) suggested that, after dabbing them with chloroform or ether, the capitulum should be pressed inward to loosen the "teeth," and then the tick should be gently pulled away. Some ticks, such as Amblyomma and Ixodes, have longer mouthparts than others, such as Dermacentor. Their mouthparts penetrate more deeply, even through socks, and the ticks are harder to remove.
All types of repellents may be rendered relatively ineffectual by the tendency of ticks to crawl underneath clothing and attach themselves to untreated portions of the body. Therefore, treatment of clothing is recommended. Good protection is afforded by M-1960, Indalone, diethyl toluamide, dimethyl carbate, dimethyl phthalate, or benzyl benzoate (Pratt and Littig, 1962). In areas having frequent visitors, such as city parks, it should be borne in mind that ticks do not travel far after having a blood meal and dropping off their hosts. Therefore, the greatest numbers are found along walks and the edges of lawns. Adequate economical control might be obtained by applying pesticides in swaths 10 to 20 ft (3 to 6 m) wide along paths, roadsides, and the edges of lawns and gardens, where most of the ticks occur and where most exposure of humans is likely (Pratt, 1962; Pratt and Littig, 1962).
Control of ticks in areas having heavy plant growth can be obtained with dust, suspension, or emulsion formulations of various recommended residual pesticides, applied by hand or power equipment, or in certain situations by aircraft. Sprays are generally applied to grassy and brushy areas adjacent to human and domestic animal habitations, along roadsides and footpaths, vegetation surrounding camping and picnic sites, or wherever ticks may be present and annoying. Contamination of feed or foodstuffs, fishbearing water, or blossoms visited by bees should be avoided. A spray consisting of Gardona 75 wettable powder at a concentration of 0.5% of actual toxicant has been recommended for tick control when an insecticide of low mammalian toxicity and without long-lasting residues is desired, such as in recreation areas. The spraying can begin in the early spring when ticks first appear, and can be repeated if necessary. In recreation areas, the first spraying should be done shortly before the early summer influx of visitors (Hair and Howell, 1970).
Park Maintenance. In parks and other recreation areas, grass should be mowed periodically, for grass over 6 in. (15 cm) high offers considerable protection for ticks against the sun and dryness. Also, mowing will dislodge and disperse masses of "seed ticks," after which most of them succumb to desiccation. Tall grass also has the disadvantage of providing cover for host animals. An excessive "overstory" of trees and shrubs should be avoided in heavily infested areas, so that from 50 to 80% of the ground in a park is exposed when the sun is in any one position.
Control in Buildings
The brown dog tick is the species the homeowner is most likely to have to deal with, although the American dog tick and other species also enter the home on pets. The present recommendations pertain to the brown dog tick, which accounts for the emphasis on organophosphorus pesticides. It is necessary to use pesticides of long residual efficacy, because tick eggs may be protected from the spray in cracks or behind baseboards and moldings. Even if they are hit by the pesticide, they are not always killed, so the residue left by it must be able to kill the larvae hatching from the eggs after they start crawling about. Resistance to chlorinated hydrocarbons is now widespread in the United States, and they are no longer generally recommended. Oil solutions or water emulsions of 1% propoxur, 0.5% diazinon, 0.5% dioxathion, 0.5% chlorpyrifos, 1.5% fenthion, 1 or 2% malathion, 2% ronnel, or a dust containing 5% carbaryl have been suggested (CDC, 1973). Except for malathion and ronnel, when these pesticides are used indoors they should be applied only as "spot treatments" to the usual harborage sites.
Sometimes ticks are present in subfloor crawl spaces, under porches, and in other areas accessible to the dog but difficult to treat with a spray. Dust formulations containing the pesticides just mentioned can then be used most effectively.
When treating for the brown dog tick, the objective should be to, apply the spray or dust to areas frequented by the dog, paying special attention to its sleeping quarters, as well as to baseboards, doorways, window casings, floor and wall crevices, and beneath the edges of carpets. If the dog is permitted on overstuffed chairs, the cushions should be removed and all crevices and seams treated. In warmer climates, if the dog spends much time outside, the yard also should be treated, along with the doghouse, subfloor crawl spaces, and other areas accessible to it. Retreatment may be necessary 1 or 2 weeks later for severe infestations. When the premises are treated, the dog must also be treated, or reinfestation will occur. The owner may do this himself, or have it done by a veterinarian. Recommended treatments are washes of 1 % coumaphos or 0.5% malathion, or dusts of 5%, carbaryl, 0.5% coumaphos, 1% trichlorfon, or 3 to 5% malathion. Better penetration of the dog's fur may be obtained with liquid washes. The coumaphos wash or trichlorfon dust should not be used on dogs under 2 months of age. Veterinarians may use animal dips containing 0.1% dichlorvos, 0.2% naled, 1% carbaryl, 0.15% dioxathion, or 1%, ronnel. Veterinarians have also reported success with the oral use of ronnel (CDC, 1973).
Mites (order Acarina) are very small arthropods, with head and thorax fused into a cephalothorax. They have sucking mouthparts, no antennae, and those of interest as household pests have 4 pairs of legs as adults. Although most of these species have only 3 pairs of legs in the first (larval) stage after hatching from the egg, they gain a fourth pair in the second (nymphal) stage. The life cycle generally consists of the egg, larval stage, one or more nymphal instars or stages, and an adult stage. The life cycle usually requires only 2 or 3 weeks, and results in rapid increase and huge populations of mites under favorable conditions. A thorough discussion on the morphology and development of the free-living mites, on their role as parasites of animals and plants, and as vectors of disease, may be found in Mites, or the Acari by T. E. Hughes (1959).
Description. The members of the suborder Trombidiformes are characterized by the respiratory system, when present, opening in the region of the gnathosoma, the portion of the body bearing the mouth and its appendages. Chiggers are very small, 150 to 300 microns (0.15 to 0.3 mm) long when unengorged, and are red to pale yellow or white, depending on the species. Like all mite larvae, they have 6 legs. They are parasitic, but later stages are free-living, 8-legged mites. Only the larvae are harmful and only they are correctly referred to as "chiggers." The adults are bright red, hairy, or granular (Michener, 1946; Wharton and Fuller, 1952; Baker et al., 1956). The various stages of the trombiculid mites in general are adequately represented by figure 309, which shows an unengorged and engorged larva, a nymph, and an adult of Trombicula batatas (L.).
In some regions, this mite is a.pest of chickens and turkeys, affecting the younger birds most seriously. When heavily parasitized, the birds become droopy, refuse to feed, and may eventually die from starvation and exhaustion (Baker et al., 1956). A much more important chigger pest of chickens and turkeys, however, is Neoschongastia americana (Hirst), which ranges across the southern United States from California to Georgia, but does not attack man (Kunz et al., 1969).
Description. Chigger larvae are 0.15 to 0.25 mm long before engorgement, and are red to reddish orange, rarely white. Their mouthparts include 2 pairs of grasping palps provided with forked claws. The nymphs are much more hirsute than the larvae. The body is constricted behind the second pair of legs, giving them and the adults the characteristic shape of trombiculid mites shown in figure 309. The adults are much larger than the nymphs, and are even more hirsute. They are 0.9 to 1.1 mm long, and brilliant red (Jenkins, 1949; Baker et al., 1956).
Life Cycle. The spherical eggs, approximately 0.1 to 0.2 mm in diameter, are usually laid in the soil. The larva crawls about on the surface of the soil until it finds a suitable vertebrate host. It attaches to the host by means of its chelicerae and sucks blood, but as a rule does not burrow under the skin. Engorgement usually takes about 3 days. The larva then drops, enters the soil, and changes, via the nymphochrysalis, to the nymphal stage. The nymphs probably feed on the eggs and young instars of small arthropods. The adult emerges from a dorsal split in the imagochrysalis and nymphal cuticle (Baker et al., 1956).
The life cycle may require 2 to 12 months or longer, depending on the temperature. There may be 1 to 3 generations per year in temperate climatic zones, but reproduction may be continuous throughout the year in warmer regions, with as many as 6 generations. Females kept at suitable temperatures and supplied with water and food were observed to live more than a year and to produce larvae throughout that period. The time when chiggers are active varies from 2 months in Minnesota and Massachusetts to the entire year in southern Florida. Chiggers are most abundant during rainy spells in the area from Kansas to Texas, and may disappear during hot, dry weather (Jenkins, 1948).
Some Related Species
Trombicula splendens Ewing is a related species in the eastern United States. It prefers moister habitats, such as swamps and rotten logs or stumps. It is one of the most common causes of trombidiosis in the southeastern states.
Trombicula lipovskyana (Wolfenbarger) may be found in similar places in Tennessee, Kansas, Oklahoma, and Arkansas.
Trombicula belkini Gould is widely distributed in California, and has also been collected in Utah. Reptiles seem to be its favored hosts, but it also infests rodents and ground birds. It sometimes annoys humans and their pets (CEIR, 1960). This species is closely related to T. alfreddugesi, but the larvae lack nude, whiplike setae on the tarsus of leg II (Baker et al., 1956; Gould, 1956).
Trombicula batatas (L.) (figure 309) is common in Central and South America, the state of Puebla, Mexico, and has been reported from the southeastern United States (Michener, 1946; Jenkins, 1948). It has been collected on humans and many domestic and wild animals. One 12-year-old boy had 138 attached larvae (Michener, 1946). It has been reported to attack humans in the San Joaquin Valley of California (Doetschman and Furman, 1949).
Gould (1956) published an extensive monographic study of the larval trombiculid mites of California.
Favored Habitats. Chiggers are most abundant in areas that support thickets or scrub-type vegetation and where the ground is undisturbed, supporting many rabbits, other rodents, and various small host animals. They are generally eliminated automatically by habitat destruction in areas that are heavily populated or intensively farmed. In new urban subdivisions, however, chiggers may persist in lawns for several years. To determine the exact area of chigger infestation, a piece of black cardboard can be placed edgewise on the ground where an infestation is suspected. If chiggers are present, the tiny yellow or pink larvae will crawl rapidly over the cardboard and accumulate on the upper edge. Chiggers can also be easily detected on black, polished shoes (USDA, 1963). Jenkins (1948) suggested the possibility that chiggers might be of value in decreasing mosquito populations. The adults were often abundant in depressions in the ground which had become temporary pools containing Aedes and Psorophora larvae in the spring. Mosquito eggs laid in such depressions probably were serving as food for Trombicula adults.
Repellents. In areas where chiggers are known to be a problem, the avoidance of their favored habitats is, of course, a way of minimizing infestation. Protective clothing and repellents are recommended as already described for protection against mosquitoes and ticks. If infested, a thorough soapy bath as soon as possible is a highly effective treatment. Repeat the lathering and rinsing several times. Most of the chiggers, attached or unattached, will be killed.
Among the best repellents for chiggers are those containing diethyl toluamide (OFF), ethyl hexanediol (6-12), and dimethyl phthalate, applied to the skin and clothing around the ankles, waist, and armpits. To apply dusting sulfur to skin and clothing is an old but effective method of preventing chiggers. Repellents should be applied particularly to the legs, ankles, cuffs, waist, and sleeves. Some relief from itching can be obtained by applying a solution of 5% benzocaine, 2% methyl salicylate, 0.5% salicylic acid, 73% ethyl alcohol, and 19.5% water. This can be prepared by a druggist. It may be applied to each welt with a piece of cotton. Each treatment gives relief for an hour or more (USDA, 1963).
Control. Good control of chiggers in the field can be obtained for 1 or 2 months with toxaphene at 2 lb (0.91 kg) or lindane at 0.25 lb (0.11 kg) of actual toxicant per acre, preferably as emulsions. The amount of water used as a carrier of such quantities depends, of course, on the type of spray equipment available. A given quantity of insecticide can be used with either a large or small quantity of water, as long as the toxicant is thoroughly and uniformly distributed. The following quantities (stated as emulsifiable concentrates) of 4 insecticides that are effective against chiggers as well as insects have been recommended (Anonymous, 1970d).
|Insecticide and formulation||For 1,000 sq ft (93 sq m)||For 1 acre (0.405 ha)|
|Chlordane 45%||10 tsp (50 cc)||3 pt (1,440 cc)|
|Toxaphene 60%||7 tsp (35 cc)||2 pt (960 cc)|
|Diazinon 25%||0.5 pt (240 cc)||2.50 gal (9.50 1)|
|Malathion 57%||0.5 pt (240 cc)||2.50 gal (9.50 1)|
A convenient way to treat 1,000 sq ft (93 sq m) of lawn would be to mix any one of the formulations shown in the table with 3 gal (11 L) of water, but if weeds or tall grass were present, the same quantities of insecticide could be more effectively applied in 6 gal (22 L) of water. To spray an acre (0.405 ha), at least 25 gal (95 L) of water are required. Malathion treatments may need to be repeated because malathion is nonpersistent. There are also dust formulations of these insecticides that can be used effectively for chigger control. (Consult appropriate authorities about pesticides currently authorized.)
Description. The female is an almost microscopically small,. elongate mite (figure 310), 0.22 mm long and white to yellow in color. When gravid, she becomes greatly distended behind the fourth pair of legs, and attains a length of up to 2 mm. Her abdomen shows traces of lateral segmentation, and she has clublike hair between the first and second pairs of legs. The male is only 0.16 mm long, but is wider than the female.
Life Cycle. This mite has a strange and unusual biology. The males wander continuously over the distended body of the pregnant female, feeding on it parasitically. The large eggs hatch, and 206 to 300 mites develop to adulthood within the female's enlarged abdomen. They are extruded at the rate of about 50 per day. Only some 3% are males, but they emerge first and remain clustered around the genital opening. With the aid of their hind legs, they drag the females through the opening, even though they can emerge unassisted, and copulation takes place immediately. The females then search for hosts. Only 6 to 10 days are required from the time of fertilization to the hatching of eggs. The mites are active during the warmer months of the year at 80 °F (27 °C) or above (Baker et al., 1956; Scott and Fine, 1963).
Distribution of Bites. The bites of straw itch mites are characteristically distributed almost exclusively on clothed portions of the body, although they occur rarely on other areas, with the exceptions of the palms, soles, and mucous membranes. There is no tendency for the mites to be grouped, although this sometimes occurs fortuitously. A person may feel a prickling sensation at the time of the bite, but otherwise no immediate reaction seems to occur. The period between the time of the bite and the delayed reaction has been variously reported as 10 to 16, 16, 27, and 17 to 28 hours (Fine and Scott, 1965).
Straw Itch Mite Dermatitis. A considerable number of epidemics of dermatitis have been traced to infestation by Pyemotes ventricosus. Since many such outbreaks have not been recorded or correctly diagnosed, it is likely that this ailment is more common than is generally realized. Straw itch mite dermatitis is usually associated with sleeping on straw mattresses, harvesting grain, or otherwise handling or coming in contact with grain, straw, hay or other substances such as those just mentioned. The possibility of infestation is particularly strong if there are large numbers of the mites' host insects present, such as the Angoumois grain moth (Sitotroga cerealella) and the wheat jointworm (Harmolita tritici). The host insect need not necessarily be a species associated with hay or grain. For example, cases of straw itch mite dermatitis have been associated with severe infestations of furniture beetles (Anobium punctatum) in the floor joists of houses. The recurrence of such cases during the same season for 3 successive years led investigators to conclude that the mites migrated in search of new hosts as the adult beetles emerged and left the wood. The mites apparently were not able to penetrate the thick exoskeletons of the beetles when the latter were in the pupal and adult stages, and therefore they left and sought new hosts. In one house, the mites were controlled by treating the floors with 2% deodorized malathion emulsion (Fine and Scott, 1963, 1965; Scott and Fine, 1963).
Treatment and Prevention. The treatment of symptoms is not the solution to the problem. Either a person must avoid infested areas, or the mites and their host insects must be eliminated.
When rats occur in a house, their fecal pellets may be found in the attic, and can often be seen from the crawl hole. When rats are killed, the mites leave their bodies and may travel great distances, particularly along the heating pipes in the walls, for when they are not engorged with blood they are very active. When searching for mite infestations, a flashlight should be used and warm areas such as those near hot-water and steam pipes should be examined with particular care.
Description. The tropical rat mite is gray to pale yellowish gray, changing to red or black when engorged with blood (figure 311, inset). The females vary in length from about 1.15 mm when unfed to 1.41 mm when engorged. The males are about two-thirds as long as the females. A useful taxonomic character is the single dorsal plate, which is relatively narrow and does not cover the entire dorsal surface, even in specimens that have not fed. The dorsal plate bears pairs of long setae, more numerous on the anterior half and in most specimens with only 6 or 7 pairs on the posterior half (Skaliy and Hayes, 1949; Baker et al., 1956).
Life Cycle. After the adult female engorges, her first eggs may be laid within 2 days at ordinary temperatures (68 to 72 °F; 20 to 22 °C). They are deposited on debris in rat nests and burrows, but apparently not on the rats themselves. They hatch in about 36 hours. The larvae do not feed, and within a day they molt to enter the first nymphal stage, the protonymph. The protonymphs attach to a host and obtain a blood meal before dropping off and molting to become deutonymphs. In this stage they do not feed, but in 24 to 36 hours molt to become adult males or females. They mate and engorge within 3 days. Unfertilized females reproduce parthenogenetically. Four or 5 blood meals are required for the completion of the entire life cycle. The life of an adult female was found to average 61.9 days; the number of eggs laid, 98.8; and the life cycle from egg to egg, 10 to 12 days (Sheimire and Dove, 1931; Bertram et al., 1946; Baker et al., 1956).
Tropical Rat Mite Dermatitis. When the mites are abundant, they may be found anywhere in the house, and both nymphs and adults may attack people. Their bites produce irritation, and sometimes a painful dermatitis will continue for 2 or 3 days, leaving red spots on the infested areas (figure 311). Scratching may result in secondary infections.
Within some households certain individuals are affected while others are not. Sometimes, much time and money will be spent on ineffective medication and it is usually difficult for the infested person to obtain a correct diagnosis. This acariasis cannot be distinguished from flea bites, and is sometimes misidentified as scabies.
Control. The complete control of rats would, of course, eventually result in the elimination of tropical rat mites from infested premises. However, rat control often proves to be difficult, and "ratproofing" an attic may also be difficult and very expensive. It should also be borne in mind that trapping or otherwise killing rats may increase the attacks on the inhabitants of the house for a time because of the suddenly increased number of mites that leave the bodies of the dead rats. Unfed protonymphs have been observed to survive for as long a period as 43 days without food (Sudd, 1952).
Acaricides that depend on toxic action lose their toxicity too rapidly, particularly in the high summer temperatures of an attic. Reinfestation may then occur. HCN gas fumigation has been used successfully, but it is expensive and leaves no residue.
The successful results of a fluorinated silica aerogel dust, blown into attics for the prevention of drywood termites (Incisitermes minor) suggested a similar use of this material for the control of the tropical rat mite (Ebeling, 1960). In 5 infested houses and 1 2-story apartment house, in each of which 1 or more inhabitants had been attacked by rat mites for prolonged periods, the silica aerogel Dri-die 67 was blown into the attic at the rate of 1 lb to 1,000 sq ft (0.45 kg to 93 sq m) of attic area. For 4 of the houses, the dust was also blown into the crawl space under the house at the same rate (for floor space) as that for the attic area. An electric duster with a 1-gal (4-L) hopper was used to apply the dust. In the attic, the dust was applied entirely from the crawl hole, and under the house, from 1 or 2 crawl holes or a larger number of foundation vents. Since in all cases the mites were already distributed throughout the dwelling, some dust was applied with a small bellows hand duster under mattresses, on the spring supports of beds, along the edges and in the 4 corners of bed frames, into the junctures of seats and back or arm rests and under the pillows of sofas and lounges, under furniture and other out-of-the way places, and in a few spots along the floor boards and ceiling moldings.
The decision to make use of Dri-die 67 dust was made in an effort to bring about the immediate cessation of mite attacks. Principal reliance was placed on the dusting of the attic for longterm control.
Rat mites may live as long as 63 days with no food (Scott, 1949), so those not coming into contact with the dust may continue to infest the inhabitants of a house. In all the buildings treated, severe infestations had been experienced up to the date of treatment, but ceased immediately afterward, and were never resumed except in 1 house where the housewife received a few more bites after treatment. In this instance, she applied more dust behind the electric outlet plates and various other areas that had not been covered the first time. Control was soon obtained, and no reinfestation occurred. Conventional liquid acaricides could have been applied in the living spaces of the treated houses, for people usually try to avoid leaving an unsightly residue. However, dusting is appropriate in attics, wall voids, and other inconspicuous areas. The dusting should be done before rat control is attempted, so that mites leaving the bodies of dead rats will contact the dust and will not be able to reach the living space and infest its occupants.
Importantly, there is also considerable circumstantial evidence that it can transmit rickettsial pox, caused by Rickettsia akari (Baker et al., 1956).
Description. Unengorged mites are 0.65 to 0.75 mm long, and engorged females may reach a length of 1 mm or more. Their color may range from red to blackish, depending on how recently blood meals have been taken; they cause the mites to appear black. This species has 2 dorsal plates on the adult female, but even on unengorged specimens, the plates do not cover the entire dorsal surface. The anterior plate on the dorsum is 10 times larger than the posterior plate, and bears several pairs of setae, whereas the posterior plate bears only 1 pair. The chelicerae are long and whiplike (Baker et al., 1956).
Life Cycle. As with most macronyssid mites, there is an egg, larva, protonymph, deutonymph, and adult stage. Unlike the tropical rat mite, both protonymph and deutonymph require blood meals.
The life cycle occupies 17 to 23 days, and unfed females have been observed to live as long as 51 days. The adult mite leaves its host after feeding, and may be found crawling about in mouse nests, runways, or on the walls and ceilings of infested buildings (Baker et al., 1956).
Control. Control measures are the same as for the tropical rat mite.
The human itch mite has a legitimate claim to fame in the history of biology. The original description of the life cycle and habits of this mite and the proof that it was the cause of scabies were accomplished by the Italian pharmacist Diacinto Cestoni and the relatively obscure young physician Giovan Cosino Bonomo. This was in the seventeenth century, when endo- and ectoparasites were usually considered to be produced by spontaneous generation. The observations made by Cestoni and Bonomo became generally known through a letter written by Bonomo to Francesco Redi (1626-1697), an experimental entomologist best known as a debunker of the "spontaneous generation" myth. The letter was reproduced in facsimile by Lane (1928). It has been described as "the birth certificate of parasitology" (Sadun, 1969).
Buxton (1921a) made a detailed study of the external anatomy of the equine itch mite, Sarcoptes scabiei var. equi (Gerlach, 1857). A subsequent study of the anatomy of the human itch mite, Sarcoptes scabiei De Geer, 1778, var. hominis (Hering, 1880), revealed certain minute differences in scales and spines, but these differences were not constant and measurements overlapped. Buxton (1921 b) concluded that it was convenient to regard the 2 forms as varieties, but that this was more justifiable on physiological than on morphological grounds. For practical purposes, Buxton's (1921a) drawings and descriptions of the variety equi serve for the variety hominis. Heilesen (1946) made a detailed study of the anatomy of all stages of hominis, as well as an investigation of the biology of the species scabiei.
Description. Itch mites (figure 313) are broadly oval, somewhat hemispherical, and so small that even the adults are barely visible to the unaided eye. Adult females are 0.33 to 0.45 mm long, and the males, 0.20 to 0.24 mm. The mites are a translucent, dirty-white color, with the more highly chitinized portions brownish. The integument is finely striate over most of its surface. In living specimens, the body is seen to be divided into 2 regions by a fold in the integument; the posterior portion bears the last 2 pairs of the 4 pairs of very short legs. The last 2 pairs of legs do not extend as far as the margins of the body. The anterior 2 pairs of legs on females and all but the third pair on males are provided with delicate, stalked, terminal suction pads. In the females the posterior 2 pairs of legs, and in the males the third pair, terminate in bristles. The adults lack eyes and many special respiratory organs. Characteristic spines and bristles on the dorsal surface aid in identifying the species. The spines are directed backward, and may serve to anchor the mite in position when it is digging burrows in the skin (Munro, 1919; Buxton, 1941b; Hand, 1946; Heilesen, 1946).
Life Cycle. Both sexes and all stages of the itch mite tend to burrow into the skin immediately when placed on it, but the nymphs and males make only small, temporary holes, and move about frequently. The largest and longest burrows are made by the egg-laying female. The female always burrows in folds of the skin, preferring the deeper furrows and cracks. She can be induced to enter when a fine scratch has been made with a needle in the surface of the skin. She may also place herself in the acute angle between a sloping hair and the surface of the skin to gain support for initiating the burrowing (Heilesen, 1946). The winding burrow may reach a length of 5 to 15 mm. It is excavated in the deeper part of the horny epidermal layer, rarely as far as the granular layers (Buxton, 1941b; Heilesen, 1946).
Munro (1919) believed that, if undisturbed, the female would lay all her eggs in 1 burrow (figure 313). A second mating does not take place; she dies in the burrow. It appears from the observations of various authors that the adult life of the mite is from 2 to as many as 6 weeks. It is difficult to determine the number of eggs laid by a female in her lifetime, but it is usually estimated to be between 40 and 50. Munro also observed that the period between the beginning of burrow formation and the finding of the first larva varied from 71 to 78 hours. He also found that 9 eggs removed from burrows and kept at 29 °to 30 °C (about 85 °F) hatched in 68 to 80 (average 74) hours. He gave the following numbers of days for the duration of the various life stages of the female: egg, 2.5 to 3.5; larva, 1.5 to 3; first nymph, 1.5 to 2.5; and second nymph, 2 to 4. He concluded that the life cycle required from 9 to 15 days. The numbers of days for the various life stages of the female, as determined by Heilesen (1946), were as follows: egg, 3 to 4; larva, 3; first nymph, 3 to 4; second nymph, 3 to 4; and from copulation to oviposition, 2; a total of 14 to 17 days. The developmental period for the male was only 9 to 11 days. The male has only 1 nymphal stage, whereas 2 are recognized in the female. In the second nymphal stage, the female can be fertilized by the male, even though the orifice (tocoptome) by which the eggs are laid has not yet been formed (Warburton, 1920).
Means of Transmission. The ease of transmission of body lice via infested clothing and bedding has led many people to assume that itch mites could be transmitted in the same way. An important difference, however, is that body lice live on their host's clothes and contact his body only to feed, whereas itch mites spend most of their lives beneath the host's skin. In experiments with 63 male volunteers, in none of 31 men were itch mites transferred via blankets previously used by infested men, and in only 2 cases out of 32 were mites transmitted when uninfested men used underclothing immediately after it had been used by infested men (Mellanby, 1941). Merely putting clothing away for 2 or 3 days at ordinary room temperature should be sufficient to rid it of mites. Two persons in a bed gave the greatest opportunity for the spread of itch mites. However, transmission is also possible through "dancing, flirtation, and ordinary intimate contact between members of a family" (Heilesen, 1946).
Body Regions Infested. Munro (1919) observed the burrowing procedures of egg-bearing females. The suckers of a female's anterior pair of legs were fixed onto the skin, and she propped her body up with the bristles on her posterior pair, assuming an almost perpendicular position. With her chelate mouthparts she commenced to cut the skin and bore in, becoming completely concealed in as little as 2.5 minutes. (This was a much shorter period than the one recorded by Heilesen, who found that 6 adult females burrowed into his skin in 15 to 40 minutes.) She ceased burrowing at a low temperature or when the body of her host was cold, and recommenced with a slight rise in temperature or warming of the body. Munro was able to activate burrowing of female mites in his wrist by passing from a cold room to a warm one, and was able to regulate the rate of burrowing by alternately warming and cooling an infested wrist over a radiator or other source of heat. He observed that under normal conditions, the burrowing period corresponded more or less to the time spent in bed. He stated:
The parts of the body selected by the ovigerous female are the interdigital spaces; the wrists and the ulnar margins of the wrists; the elbows and the anterior folds of the axillae; the penis, scrotum, and buttocks; the back of the knee; and the ankles and toes. In young children, the egg burrows may occur on any part of the body, and in women, the undersides of the breasts are very commonly selected.
Localization of Infestation. In an examination of 886 soldiers, 9,978 adult female mites were found and removed, an average of slightly over 11 per patient. About 52%, had fewer than 6 mites and only 3.9% had more than 50. One patient had 511. The percentages of mites found in the various areas of the body were: hands and wrists, 63.1; elbows (extensor aspect), 10.9; feet and ankles, 9.2; penis and scrotum, 8.4; buttocks, 4.0; axillae, 2.4; and in the remaining regions of the body, a total of 2 (Johnson and Mellanby, 1942). In another investigation, among 119 women the percentages of mites in various body areas were as follows: hands and wrists (excluding palms), 74.3%; palms of hands, 7.5% (none were found on the palms of men); elbows, 5.8; feet and ankles, 8.8; buttocks, 1.1; and in all other areas, 2.5. Among 18 children, itch mites were found to be more uniformly spread over many parts of the body, As indicated by Munro (1919), with many mites on their ankles and feet (Hartley and Mellanby, 1944).
Active stages of mites confined in cells on parts of the body other than the foregoing will burrow into these parts, but if the cells are removed, they will leave them for the nearest sites usually selected. When Munro confined female mites on his forearm, they always burrowed into his skin enough for concealment, but left these burrows and were recovered on the wrist in from 20 minutes to 2.5 hours.
Symptoms of Infestation. Whereas in animals large numbers of mites give rise to "sarcoptic mange," in humans relatively small numbers of mites can cause unpleasant symptoms, and the disease is known as "scabies." At a certain stage, the irritation may become so severe that the patient becomes frantic and suffers from lack of sleep. If the infestation is long continued, or if a later infestation occurs, an allergic reaction develops, with intense itching and a redness, or rash of follicular papules over much of the body. The rash may develop on areas such as around the armpits, the wrists, the waist, inside the thighs, and backs of the calves, but these areas do not necessarily coincide with those of mite infestation. The rash may occur over much of the body, even though only a few mites may be present in restricted locations between the fingers (Pratt, 1963). In an investigation of 55 volunteers who had not been infested with itch mites before, Mellanby (1944) observed that during the first month of itch mite infestation, there were few or no symptoms and no erythema. Infested persons might even be unaware that mites were burrowing into their skin.
Symptoms began to be evident in about a month, and in about 6 weeks the irritation was sufficiently severe to cause some loss of sleep. Then the itching grew progressively worse, and after 100 days it was practically continuous and almost unbearable. However, when secondary infections and impetigo developed, the mite population decreased, and was sometimes completely eliminated. (If secondary infections are neglected, they may themselves require prolonged medical treatment.) When volunteers already infested were treated and then reinfested, intense local irritation was felt within 24 hours, and a patch of erythema surrounded each mite. This apparently caused an adverse environment for the mites, for in another 2 days most of them had disappeared, some scratched out by the patient and others leaving the burrow. Relatively few mites reached maturity when compared with the original infestation.
Medical Treatment. It is important to diagnose scabies correctly, for neither the irritation nor the liability to skin diseases can cease until the mites have been eliminated. Look for the burrow of a female in such places as between the knuckles and in folds of the wrist and elbow, and then gently prick the burrow open. Toward the end of the burrow, the mite can usually be distinguished as a dull-white spot. Remove it with a needle. A bath before treatment is desirable for hygienic reasons. Thorough treatment is essential, and is best done by a physician or a reliable nurse or orderly. Treatment consists of application of ointments or liquid preparations. Ramsay (1969) prescribed either 25% benzyl benzoate emulsions, Kwell® (1 % lindane) cream or lotion, or Eurax® cream or lotion. The latter contains 10% of crotamiton (N-ethyl-o-crotonotoluide). Ramsay recommended that these preparations be applied in the evening after the patient had taken a warm bath, and that the application be left in place until the next evening, when the treatment would be repeated. All areas of the skin below the neck should be treated, including body folds, palms, and soles. A cleansing bath should be taken 48 hours after the second application. Some tingling of the skin is to be expected after treatment, and it may last as long as 10 to 14 days. Calamine lotion or emulsion may be applied to alleviate this condition. Instructions on the package in which the medication is sold should always be read and followed carefully. Secondary infections may require the skills of a medical doctor or dermatologist. If the treatment is satisfactory and reinfestation occurs, an effort should be made to find untreated persons with whom the patient may have had contact.
Description. This broadly oval mite is very small about the size of the human itch mite. As in the human itch mite, in both sexes the anterior 2 pairs of legs and, in the male, also the fourth pair, have delicate, terminal, stalked suction pads. In the females, the posterior 2 pairs of legs, and in the males the third pair, end in bristles. Characteristic spines and bristles on the dorsal surface aid in identifying the species.
Life Cycle. The female lays her eggs in burrows she makes in the skin. They hatch in 3 to 5 days, and a complete life cycle requires 8 to 17 days (Smith and Claypoole, 1967).
Symptoms on Dogs. The eruption begins with small, white or erythematous (reddish, inflamed) papules, initially appearing, in the groin and "armpit" areas and on the periphery of the ears. The papules may become so numerous that they appear to be contiguous, especially on the relatively hairless portions of the body. Crusts form, composed of dried exudates of serum and blood. The skin becomes lichenous, scaly, and corrugated in appearance. The eruption spreads, but is usually most severe on the ears, head, abdomen, and in groin and "armpit" areas. Hair is lost, or can be easily pulled out in patches. The remaining hair becomes dull and lusterless, and the animal develops a characteristic "mousey" odor. Intense generalized itching accompanies the eruption, and if untreated, the animal may become emaciated and even die of exhaustion from the itching and extensive chronic inflammatory reaction, often with a secondary infection. Canine scabies occurs most commonly in undernourished puppies, particularly if they are suffering from internal parasites (Smith and Claypoole, 1967).
Symptoms on Humans. A rash develops on some persons after only brief contact with an infested dog, but the most severe cases develop in those with prolonged close contact. The eruption is most often in the form of pimples, but may be characterized by blisters and inflammation. There is frequently a sloughing away of the skin. Lesions are most common on the forearms, lower region of the chest, and on the abdomen and thighs, but may be generalized. The distribution of symptoms usually differs from that of human scabies, in that the finger webs and the genitalia are usually not affected, but both these areas may be involved if the infestation is severe. The face is not affected except in children. In view of the facts that (1) the sarcoptic mite can live for 4 to 5 weeks, (2) in no cases have symptoms lasted longer than this, and (3) burrows have not been found in human skin it appears that Sarcoptes scabiei var. canis does not reproduce on human skin, but this could be definitely proved only by prolonged observation on heavily infested human volunteers - an unlikely development (Smith and Claypoole, 1967).
Control of Mange on Dogs. In mange or scabies control on dogs, advantage has been taken of the fact that male mites do not do any significant boring into the skin, and may be controlled by continuous exposure to toxic vapors. In one experiment, a dichlorvos resin strip (NO-Pest Strip¨) was placed in the bedding inside the doghouse of a beagle, 3 x 1.5 x 2 ft (90 x 45 x 60 cm) in area. Within 2 weeks, the dog's skin, which had been red on the lower half of the body and on the legs from a severe case of sarcoptic mange, lost its redness, and new hair began to appear. The strip was moved to one side of the doghouse, and the dog's condition continued to improve; he recovered completely in 6 weeks. Whereas mites were taken from all skin scrapings before treatment, none were taken 6 weeks later. The dog had chewed the edges of the dichlorvos strip, but no ill effect was noted (Whitney, 1969).
The specialist who conducted this experiment had used dichlorvos resin strips for several years to protect dogs and cats from flies and mosquitoes, and had observed no sarcoptic mange or fleas on 60 beagles and 36 cats that had been kept in kennels and a cat room where the strips had been used.
Treatment for Scabies or Mange. Both dogs and humans have been effectively treated with "gamma benzene hexachloride cream." Humans were cured with 1 application. The patient should avoid further close contact with the pet until it is cured (Smith and Claypoole, 1967). The old NBIN lotion for a combination treatment for lice and scabies (Eddy, 1946) is still available under the name of Topocide, but may be procured by prescription only.
Figure 304. The pajaroello, Ornithodoros coriaceus.
Figure 305. External morphological features of hard ticks (Ixodidae). A, ventral aspect of capitulum; B, dorsal aspect of female; C, ventral aspect of male; D, leg. (From Pratt and Littig, 1962.)
Figure 306. American dog tick, Dermacentor variabilis. A, dorsal aspect of larva; B, nymph; C, adult male; D, adult unengorged female. (From Smith et al., 1946.)
Figure 307. Engorged female of the American dog tick, Dermacentor variabilis. (From Smith et al., 1946.)
Figure 308. Brown dog tick, Rhipicephalus sanguineus
Figure 309. A chigger mite, Trombicula batatas. A, unengorged larva; B, engorged larva; C, nymph; D, ventral view of preadult; E, adult. (From Michener, 1946.)
Figure 310, Straw itch mite, Pyemotes ventricosus. From left, male; female; gravid female. (From Fine.and Scott, 1963.)
Figure 311. Back and neck of a woman, showing maculae caused by bites of the tropical rat mite, Ornithonyssus bacoti. Inset: Engorged mite. (From Ebeling, 1960.)
Figure 312. Northern fowl mite, Ornithonyssus sylviarum (left), and chicken mite, Dermanyssus gallinae.
Figure 313. Top, dorsal and ventral views of the human itch mite, Sarcoptes scabiei var. hominis. Left, female; right, male; bottom, egg burrow with 9 eggs and a female mite at the end of the burrow. (Arranged from.Munro, 1919).