Cheyletiella: the under-diagnosed mite

In our practice we actually see more cases of Cheyletiella mites "walking dandruff" than fleas!

I am not sure of the reason except that with the advent of newer, safer, more effective methods of flea control, the majority of these products do not eradicate Cheyletiella as did older pyrethrin-based products. Because this mite seems to have gained a foothold, be sure to check for it in all pruritic patients.

Photo 1: A Greyhound with Cheyletiella mites that presented with face rubbing and sneezing. Note the periocular and perinasal erythema.

Cheyletiella dermatitis is produced by Cheyletiella species which are contagious surface-living mites most often affecting the dorsal trunk. Species affected by this mite include dogs, cats, rabbits, humans and possibly wild animals.

Three species can affect various hosts: C. yasguri usually affects dogs; C. blakei usually infests cats, and C. parasitovorax affects rabbits. All of these species can transiently affect humans. Experimental transfer of C. yasguri from dogs to rabbits is suggestive of non-host specificity.

The physical appearance of the large mite (385 micrometers) microscopically shows four pair of legs and prominent accessory mouth parts that terminate in hooks. The mites are surface dwellers and seldom burrow. They tend to reside on the dorsum of the animal, although anecdotal reports have mentioned their crawling into and out of the nares. The life cycle is 21 days with adult females able to live off the host for up to 10 days.

Diagnosis

Skin scrapings, combings or Scotch tape technique observed in oil under low power are effective diagnostic techniques. The large mite or the elliptically-shaped ova (resembles hookworm eggs) attaches to hairs by fine strands. Round fecal matter may be present. A fecal exam may contain hookworm-type eggs. Skin biopsies if not containing a mite may indicate superficial perivascular dermatitis with varying numbers of eosinophils. Be sure to check other pets in the household if you suspect Cheyletiella but do not find mites on the examined patient. Also be careful if the animal has just been groomed or bathed as mite numbers will be reduced. Asymptomatic carriers, particularly those with underlying disease, may exist. So if other pets in the household are not pruritic, it does not rule out Cheyletiella. Diagnostics can be negative in 15 percent of dogs and 58 percent of cats with Cheyletiella.

Photo 2: The typical presentation of Cheyletiella or walking dandruff.

Clinical appearance

Cats may present as a miliary dermatitis, eosinophilic granuloma complex lesions, or most commonly, a generalized flaking of the dorsal trunk.

Human lesions include papules with a central necrosis. Occasionally pruritus without lesions occurs, but mites can be found after a thorough search. Other symptoms include face rubbing and sneezing.

Cats may be responsive to steroid injections but become pruritic after the injection wears off. One canine patient presented with a "chronic hookworm problem" which was, in fact, an untreated Cheyletiella infestation. Dogs may have pruritus without lesions, sneezing or a dorsal truncal flaking. The most common breed we see affected is the American Cocker Spaniel, but any breed — particularly those around other pets or that have been groomed or kenneled — should be suspected.

Solutions

Options include one of the following: weekly bathing in pyrethrin shampoo, lime sulfur dips every five to seven days for three weeks, fipronil spray one spritz/lb body weight repeated again in three weeks, selamectin topically one dose every 15 days for a total of three doses, ivermectin 200 micrograms/kg every week for three weeks (must be heartworm negative first and not used in herding breeds or crosses thereof —I also avoid ivermectin in older patients), milbemycin 2 mg/kg once weekly for three weeks (one study treated for up to nine weeks). The environment must be treated with a house and carpet spray such as those that are used for fleas. Remember to treat any pet exposed to the affected animal and not just the affected animal.

Dr. Alice Jeromin is a pharmacist and veterinary dermatologist in private practice in Cleveland, Ohio. She is a 1989 graduate of The Ohio State University College of Veterinary Medicine and an adjunct professor at Case Western Reserve University's College of Medicine in Cleveland.