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Cheyletiellablakei Smiley, 1970

(Figures 5-20 through 5-21)


ETYMOLOGY:Cheyle = lips and tiella, a diminuitive meaning that this is smaller than tia or tea; along with blakei for Dr. D.F. Blake, Department of Biology, Walla Walla College, Washington.


HISTORY: In 1878, Mégnin was the first to describe adult Cheyletiella mites, and he theorized that these mite preyed on other mites (Merchant, 1990); hence, he gave them the scientific name Cheyletusparasitivorax (Bronswijk and Kreek, 1976). It has been demonstrated, however, that members of this genus are true "mange" mites and not predatory on other mites (Merchant, 1990). The mite genus Cheyletiella was erected by Canestrini in 1885 to contain the genus described by Mégnin in 1878 as Cheyletusparasitivorax. In the beginning, there were some inconsistencies in the spelling of the generic name: Cheletiella, Cheiletiella, and Cheyletiella (Bronswijk and Kreek, 1976). Eggs of Cheyletiella species were not described until 1917. They were "...fixed to a hair... elongated, resembling the eggs of a louse in general appearance, but minute, and with a very delicate cuticle." (Hirst, 1917). Reed (1961) reported "nit-like objects" on the hair which could be interpreted as being either mites or eggs (Ewing, 1967). Hirst (1917) was the first to report that Cheyletiella occurred on cats. This was follwed by several other reports (Smiley, 1970) that recognized Cheyletiella, as Cheyletiellaparasitovorax, occuring on cats. Ewing et al. (1967) noted that the sensory organ on the leg of the mite from cats differed morphologically from that present on the mite from dogs; and Smiley (1970) described Cheyletiellablakei from cats as a new species using as types specimens recovered from a cat in Ithaca, New York. Human involvement with this mite was first reported by Lomholt in 1918.

GEOGRAPHIC DISTRIBUTION: Bronswijk and Kreek (1976) provided a synopsis of the worldwide distribution of cheyletiellosis in the rabbit, dog and the cat. Reports of feline infestation have originated from every continent. Recent reports of feline infestation have come from the United States (Keh et al., 1987), Italy (Faravelli and Genchi, 1984, Faravelli and Traldi, 1985, Dal Tio et al., 1990), Turkey (Dinçer and Karaer, 1985), and Yugoslavia (Wikerhauser and Pinter, 1987).

LOCATION IN HOST: Mite of the genus Cheyletiella are surface-dwelling (non-burrowing), residing in the keratin layer of the skin and in the haircoat of the definitive host. These mites thrive on keratin debris and tissue fluids. Cats typically exhibit scaling on the head, neck and dorsum, lesions easily confused with those of flea-allergy dermatitis and miliary dermatitis (Smith, 1988). Kwochka (1987) reports that these mites have also been observed to crawl in and out of the nostrils of cats.

IDENTIFICATION: Cheyletiellosis has been referred to as "walking dandruff" because the mites often resemble large, mobile flakes of dandruff. Cheyletiellid mites are unique among mites that parasitize domestic cats, possessing distinct key morphologic features. These are large [500 by 265 µm (Foley, 1991)] mites, visible to the naked eye. Utilizing the compound microscope, one can discern their most characteristic key morphologic feature, their enormous hook-like accessory mouthparts (palpi) (Fig. 5-20). These palpi assist the mite in attaching to the host as it feeds on tissue fluids (Schmeitzel, 1988). Kwochka (1987) reports that these mites also feed on skin surface debris. Members of the genus are also known for their characteristic body shape, a shape that has been reported as being like that of a "shield" (Kwochka, 1987) or that of "bell pepper" or a "western horse's saddle" when viewed from above.

Three species of Cheyletiella have been suspected of infesting cats: Cheyletiellablakei (most commonly), Cheyletiella yasguri (common on dogs), and Cheyletiellaparasitivorax (common on rabbits) (Grant, 1989). One of the characteristic features used to differentiate the various species in the genus Cheyletiella is the shape of the sense organ on the first pair of legs. This organ is reported to be conical in Cheyletiellablakei, heart-shaped in Cheyletiellayasguri, and globose in Cheyletiellaparasitivorax. Species identification, however, is often difficult due to the individual variation in the shape of this organ and to distortion during fixation and mounting for light microscopy (Schmeitzel, 1988). The male organ of sperm transfer, the aedeagus or penis, extends from between the thrid and fourth pair of legs to the posterior of the body of the amle mite and is a straight structure. The adeagus of Cheyletiella parasitovorax is highly curved and resembles the blade of a scythe. Scanning electron microscopy can be of considerable hel in the identification of species (Marchiondo and Foxx, 1978).

The eggs of Cheyletiella are often the means by which a diagnosis of cheyletiellosis is made, eggs being attached to the hair shaft at the pole (Grant, 1989). Eggs are 235 to 245µ long by 115 to 135µ wide (smaller than louse nits) and supported by cocoon-like structures bound to the hair shaft by strands of fibers (Ewing, 1967). Two or three eggs may be bound together on one hair shaft (Grant, 1989).

LIFE CYCLE: The life cycle is spent entirely on the cat. These are non-burrowing mites, residing in the keratin layer of the epidermis. They are never associated with hair follicles. There are five developmental stages in the life cycle of this surface dwelling mite: egg, larva, nymph I, nymph II and adult (Kwochka, 1987). The adult mite attaches eggs to hair (Foley, 1991). The larvae which emerge from the eggs have three pairs of legs while each subsequent nymphal stage and the adult stages possess four pairs. Should the motile stages of this mite leave the definitive host, they usually die within 48 hours, however female mites have been known to survive for as long as 10 days off the host under refrigerated conditions (Schmeitzel, 1988). The prepatent period for Cheyletiella species has been reported to range from 21 (Kwochka, 1987, Scheidt, 1987) to 35 days (Scott and Horn, 1987, Schmeitzel, 1988, Paradis et al., 1990, Foley, 1991).

The mites are very mobile and, as a result, are very contagious by direct contact. "Walking dandruff" can spread easily through a cattery (Foley, 1991). Mites of Cheyletiella species have been found on fleas, flies and lice, hypothesizing that these larger ectoparasites may play a significant role in the animal to animal spread of cheyletiellosis (Kwochka, 1987, Scott and Horn, 1987).

CLINICAL PRESENTATION AND PATHOGENESIS: The mites feed relatively superficially on the skin of their feline host (Fig. 5-21). The most characteristic clinical sign of an infestation with Cheyletiella species is the moving white flakes along the dorsal midline and head of the cat (Foley, 1991). Cheyletiellosis in cats has been described as a more localized dorsal crusting along the back with minimal or no pruritus. Cats will occasionally exhibit a diffuse miliary dermatitis that is characterized by reddish-yellow crusted lesions. Scaling may be present (Kwochka, 1987).

Cats are often asymptomatic carriers. This feature may be due to the meticulous grooming habits of the feline that may reduce the level of infestation (Schmeitzel, 1987; Paradis et al., 1990). Frequently the first sign of cheyletiellosis is the development on the owner of an erythematous, papular, pruritic dermatitis. These lesions typically affect areas of close contact with the cat, particularly on the arms or trunk (Grant, 1989). Infested cats may manifest variable degrees of dermatitis, or be asymptomatic carriers.

DIAGNOSIS: Magnifying loupes and selective removal of questionable flakes or hairs is perhaps the quickest method of diagnosing cheyletiellosis (Foley, 1991). Multiple, repeated skin scrapings may be required as the mites are especially difficult to demonstrate (Scheidt, 1987; Paradis et al. 1990).

The "flea comb and potassium hydroxide (KOH) technique" have proven to be a reliable diagnostic technique. In this procedure, a flea comb is used to collect epidermal debris from a 10 cm by 10 cm area over the lumbosacral area. Material is placed in 15 ml centrifuge tube with 1 ml 10% KOH and heated in a water bath until hair and remains are dissolved (approximately 30 minutes). Saturated sugar solution is added to form a meniscus, a coverslip is applied and the tube centrifuged at 1,500 rotations per minute for 10 minutes. The coverslip is then removed, placed on a glass slide, and examined microscopically under low power for eggs and the varied developmental stages of Cheyletiella species (Paradis et al., 1990).

Combing dandruff-like debris onto black paper often facilitates visualization of these highly mobile mites. Using clear cellophane tape to entrap mites collected from the haircoat often simplifies localization and viewing under the compound microscope (Merchant, 1990). Epidermal debris may be collected using a small vacuum cleaner and the debris subjected to examination (Schmeitzel, 1988).

Some fastidious cats may demonstrate mites and/or eggs on fecal flotation (Scheidt, 1987, Foley, 1991). Eggs observed in fecal flotation are large (230 by 100µ) and embryonated. They are three to four times as large as hookworm eggs. The egg is characteristic in that high-powered microscopical examination of the pole of the egg in which the anterior of the mite is developing will reveal two small arrowheads or harpoons protruding from the surface of the eggshell.

Skin biopsy reveals a perivascular dermatitis that is spongiotic and hyperplastic. The perivascular dermal infiltrate contains neutrophils, mononuclear cells and a few to many neutrophils. Sections of mites may be observed (Schmeitzel, 1988).

TREATMENT:Cheyletiella species are very sensitive to most insecticides. In warmer ecosystems where conventional, year-round flea control is practiced on animals, Cheyletiella spp. mites have been inadvertently eradicated. However, since these mites can live in the environment for up to 10 days, complete eradication in enzootic areas may be difficult, demanding the services of a professional exterminator (Scheidt, 1987).

Antiseborrheic shampoos are helpful in removing heavy scales and crusts prior to using an acaricide on the cat (Kwochka, 1987). Cheyletiellosis is usually treated by applications of topical acaricides in dip, powder or shampoo forms. Treatment must be repeated four to eight times at weekly intervals (Paradis et al., 1990). Pyrethrins, carbaryl, rotenone powder and lime sulfur dip are safe for use on cats (Foley, 1990). Due to the high degree of contagiousness with cheyletiellid mites, all of the animals in the household or cattery must be treated (Schmeitzel, 1988). The environment must be cleaned and treated with a residual acaricide to prevent reinfestation by any mites that might survive off the host. The services of a professional exterminator may be indicated (Scheidt, 1987).

Ivermectin has demonstrated good efficacy against Cheyletiella species in clinical trials at a dosage of 300 µg/kg BW once by subcutaneous injection. This dosage should be repeated in five weeks (Paradis et al., 1990). The owner must be made aware of the fact that ivermectin is not currently licensed for use in cats and a release agreement or owner's consent form should be signed prior to its administration (Jackson, 1977). The product should not be given to kittens (O'Dair and Shaw, 1991). Ivermectin may be especially effective in controlling infestations of Cheyletiella species in households with many cats, or used by owners who are physically disabled or used when conventional therapies fail (Paradis et al., 1990).

EPIZOOTIOLOGY: Sporadic outbreaks of cheyletiellosis are common. Severe infestations can occur in litters, catteries, breeding farms, or pet shops (Merchant, 1990). Cheyletiellosis demonstrates no perceptible age, breed, or sex predilection (Scott and Horn, 1987). It has been suggested that the incidence and severity of clinical signs in the feline are greater in long-haired cats (Scheidt, 1987). In a survey of feline skin disorders seen in a university practice, Scott and Paradis (1990) noted that Himalayan cats accounted for 50% of the cases of cheyletiellosis. These mites are transmitted by both direct and indirect contact. It has been hypothesized that fleas, flies and lice may play a transport role in the spread of Cheyletiella species from animal to animal (Scott and Horn, 1987). Fomites (e.g., grooming tools) have also been implicated in this transmission (Kwochka, 1987). With regard to age incidence, puppies and kittens appear to be most susceptible (Foley, 1991).

HAZARDS TO OTHER ANIMALS: This mite is extremely contagious and can affect rabbits, dogs and humans (Grant, 1989), however, it is highly likely that the species on the cat prefers a feline host even though these mites are not host specific (Prescott, 1984, Foley, 1991).

HAZARDS TO HUMANS: As mentioned previously, human infestation with Cheyletiella species was first reported in 1918 (Lomholt, 1918). Humans, especially cattery personnel, are highly susceptible to infestation by Cheyletiella species (Foley, 1991).

Human involvement has been reported to occur in 20 to 80 per cent of the cases in cats and dogs. Human cheyletiellosis lesions may begins as single or grouped erythematous macules. These rapidly evolve into papules. The lesions frequently become vesicular or pustular and in time develop a central necrotic area. Pruritus is intense. Parts of the body that may be affected include the arms, legs and torso. The face is rarely affected. Other lesions may include bullae, urticaria, erythema multiforme, and generalized pruritus without dermatitis (Scott and Horn, 1987). Skin scrapings from humans with Cheyletiella species are rarely positive. Diagnosis is often based on demonstration of mites or eggs, clinical history, clinical signs, and response to elimination of the mites. Cheyletiellablakei cannot complete its life cycle on humans. The induced dermatitis spontaneously regresses within three weeks following elimination of the mites (Scott and Horn, 1987).

CONTROL/PREVENTION: Since the mites are easily destroyed by most common insecticides, the owner often "cures" the pet when they treat the pet with flea control products. All in-contact animals must be treated (Kwochka, 1987).

Because the female mite can survive up to 10 days off of the host (Schmeitzel, 1988), the premises must be thoroughly cleaned and sprayed with a residual insecticide (acaricide) such as microencapsulated pyrethrins and microencapsulated chlorpyrifos. A professional exterminator should be consulted to ensure complete application. Foggers may be used to ensure that the furniture where cats may jump and sleep is properly treated (Kwochka, 1987).


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Figure 5-20. Cheyletiella. Note the large palpal claws

Figure 5-21. Cheyletiella. Histological section through a Cheyletiella blakei feeding on cat skin; the large palpal claw is evident in the section.