Cheyletiellosis

Cheyletiellosis is a contagious, parasitic skin disease of dogs, cats and rabbits caused by mites of Cheyletiella spp.

MORPHOLOGY AND LIFE CYCLE OF THE PARASITE

The mite has an oval-hexagonal body about 300-500 µm long with a well-developed rostrum and palps terminating with two prominent curved, opposing claws. The limbs are also developed and terminate in comb-shaped appendages (empodium) (Figs. 1 and 2).

Cheyletiella spp. show preferences for different host species: one species of Cheyletiella prevalently infests cats (Cheyletiella blakei), one prevalently infests dogs (Cheyletiella yasguri) and another prevalently infests rabbits (Cheyletiella parasitivorax), although there is not a real species specificity so the mites can infest species other than the one to which they are best adapted. The three Cheyletiella spp. differ by the morphology of their sensory organ (solenidium) located on the third segment of the first pair of limbs: this organ is heart-shaped in C. yasguri, conical in C. blakei and globular in C. parasitivorax.

The life cycle of the mite, carried out entirely on the host (permanent parasite), lasts about 3 weeks; the adults can survive for at least 10 days away from the host without feeding. Cheyletiella live on the corneal layer of the skin of the host, moving rapidly in pseudo-tunnels and feeding on skin detritus. The eggs, laid on hair shafts, are small and, unlike the eggs of lice (nits), are not operculated and are fixed weakly to the fur by loose, intertwined fibrillar filaments (Fig. 3).

Contagion occurs predominantly by direct contact, rarely from an infested environment and exceptionally by transport of the Cheyletiella on other parasites such as fleas, lice and flies. Transmission to humans is possible and the resulting lesions are itchy, crusted papules (Fig. 4).

CLINICAL SIGNS

Infested animals, usually puppies from breeding facilities or pet shops, have lesions predominantly on the dorso-lumbar region, characterized by dry flakes of various sizes (desquamative dermatitis) (Figs. 5 , 6 and 7).

During careful inspection of the skin in severe infestations it is possible to observe both the eggs and the moving mites among the skin flakes; the mites can, however, be mistaken for the exfoliated keratinocytes since it is not easy macroscopically to differentiate between the parasites and small skin flakes (Fig. 8). Indeed, English-speaking authors have given the infestation the name ‘walking dandruff disease’.

Pruritus, which may be absent in recent infections, is of variable intensity, being very severe in some cases. Some subjects develop crusted papular lesions (miliary dermatitis in the cat) and, in relation to the intensity of the pruritus, may have self-inflicted lesions (alopecia, excoriations, ulcers, scabs). Self-induced symmetrical alopecia is a common finding in infested cats and more rarely there may be eosinophil lesions grouped together in the so-called eosinophilic granuloma complex (eosinophilic plaque, eosinophilic granuloma). 

DIAGNOSIS

The diagnosis of cheyletiellosis is made from detecting the presence of the parasite or its eggs under a microscope. The technique of choice for identifying Cheyletiella is microscopic examination of material taken from brushing the animal’s fur (with a fine-toothed comb or directly with the hands) and collected from the examination table using transparent adhesive tape (scotch test) (Figs. 9, 10 and 11). When there are large numbers of parasites on the surface of the fur, they can be collected by applying the transparent adhesive tape directly to the skin of the animal.

Another diagnostic technique that can be used, particularly when there are few lesions and a small number of parasites, is to take a scraping of superficial skin.

DIFFERENTIAL DIAGNOSIS

• Other ectoparasitic diseases
• Leishmaniosis
• Disorders of keratinisation
• Allergic disorders
• Ringworm (cats)

TREATMENT

There are no compounds currently registered in Italy for the treatment of cheyletiellosis in dogs and cats; however, various products with acaricidal activity have been used both topically and systemically, with excellent results, in cats and dogs: fipronil as a spray twice a month in dogs and as a single spot-on administration in cats, selamectin given as two spot-on applications 1 month apart, injectable ivermectin (0.2-0.3 mg/Kg subcutaneously; two applications 2 weeks apart) and, in the dog, spot-on moxidectin, available in combination with imidacloprid (two applications 1 month apart). The acaricide treatment should always be extended to all animals in contact with the infested one.

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