8 Cheyletiellosis
INTRODUCTION
Cheyletiellosis is a common ectoparasitic disease affecting dogs, cats and rabbits. It is caused by Cheyletiella spp. of mites and results in a pruritic, papular and variably scaling skin disease predominantly affecting the dorsal trunk, although the pruritus can be generalized. As with all parasitic diseases, demonstration of the mite confirms the diagnosis, although in about half of all cases that won’t be possible and trial ectoparasitic therapy will be necessary.
CASE HISTORY
The dog had been in the owner’s possession since it was a puppy. It was regularly wormed and vaccinated annually. Its diet consisted of a proprietary complete chicken- and rice-based dried food, with occasional scraps, biscuits and dog chews.
Over the previous year, there had been a progressive onset of, initially mild, dorsal pruritus, then increasingly severe scaling. There was no seasonality to the symptoms.
Other important history was as follows:
CLINICAL EXAMINATION
There were no abnormalities detected on physical examination. Examination of the skin revealed:
This was a long-standing dorsal pruritic skin disease in a young dog, which made ectoparasitic disease very likely. It would be very unusual for atopic dermatitis, or an adverse food reaction, to result in pruritus confined to the dorsal trunk. The degree and distribution of pruritus was not consistent with scabies, but was entirely consistent with cheyletiellosis. There was no history of direct contact with other dogs, or cats, but ectoparasitic disease could not be ruled out on this basis alone, as indirect transmission does occur. There was history of exposure to rabbits, which can carry Cheyletiella spp. of mites.
There was also a history of possible zoonosis, and pruritic papules on the forearms in an owner are suggestive of scabies or cheyletiellosis. Heavy flea infestations can also result in bites to owners, but they are usually on the distal limbs.
The differential diagnoses included:
CASE WORK-UP
The first step was to rule out any involvement of ectoparasitism. Close visual inspection, flea combing and coat brushing examinations are useful for the detection of fleas and flea faeces. Tape strips, microscopic examination of coat brushings and skin scrapes are useful for finding evidence of Cheyletiella spp. mites. A recent study reported a vacuum cleaning technique as also a very effective method of identifying Cheyletiella mites. The following tests were performed:
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