Cheyletiella Mites: Population on the move

Cheyletiella mites (walking dandruff) have become an epidemic in our Midwestern practice in the summer, with endemic numbers throughout the year.

If you think Cheyletiella is a mite of the past, think again. In our practice we see more Cheyletiella mites than we do fleas. Chances are, if you haven't diagnosed this mite you're probably missing it.

Cheyletiella has been around since 1878, when it was first diagnosed in a rabbit. The first diagnosis in a dog was in Austria. It has since been reported in dogs, cats, fox, badgers, humans and probably exists in other wild animals.

C. yasguri is found in dogs, C. parasitivorax in rabbits and C. blakei in cats. All species can transiently affect humans — as Cheyletosis. A former theory was that the mites were predators of other ectoparasites, such as fleas, lice and flies. It is now believed that Cheyletiella is a true parasite of the dog, cat and rabbit. One report claims most domestic rabbits carry Cheyletiella but are not symptomatic.

The mite is contagious by direct contact. It is non-burrowing and feeds on the keratin layer of the epidermis. It is most often found dorsally, yet C. blakei will feed on the hair coat of cats.

Cheyletiella mites are large (466 to 500 microns by 300 microns wide) and in some cases visible to the naked eye. They are yellow, with four pairs of legs and the characteristic heavy-curved palpal claws.

The eggs (190 to 260 microns long), sometimes embryonated, are fastened to hairs by cocoon-like strands and often are mistaken for hookworm eggs but are three times larger. The life cycle is 21 days and includes five stages: egg, pre-larva, larva, first- and second-nymph stage and adult.

Once exposure occurs, it can take three to five weeks for the infestation to develop. The female mite is able to live off the host in the environment for 10 days.

The most common clinical presentation in the dog is pruritus with dorsal truncal scaling. However, because it has been reported that there can be nasal sequestration of the mite, facial pruritus, excoriation, sneezing and periocular involvement have been seen. Young dogs may be more affected. In both dogs and cats, I have seen older patients with other internal medicine concerns affected more often.

Because it is contagious, be wary of patients that go to groomers or kennels where there is association with other pets. In cats, pruritus with lesions such as miliary dermatitis, eosinophilic granuloma complex lesions, facial pruritus and sneezing have been reported. Remember to check all the pets in the household because there may be asymptomatic carriers. We had one dog that was diagnosed as a "chronic hookworm carrier" that in fact had Cheyletiella mites and the mite eggs were mistaken for hookworm eggs in the fecal exam.

Humans may be affected with papular lesions, with an area of central necrosis.

Diagnostic methods

Diagnosis of Cheyletiella mites can be tricky because it depends on finding the mite or egg on the patient; that is less likely if they have just been bathed. Methods of diagnosis include combings/ brushings, acetate tape, fecal flotation, skin biopsy and the vacuum-cleaning test.

In the cat, combings can be negative 58 percent of the time. Using a flea comb, gather dander near the skin, not at the distal ends of the hair. Observe dander in oil under low power. Combings can be performed via a fecal-flotation method using centrifugation and observing the floated eggs/mites in oil after allowing it to rise to the top after 10 minutes.

The acetate tape method is more effective in detecting mites when there is a heavy infestation. Again, the scale next to the skin and not at the distal ends of the hair should be obtained. The sticky side of the tape with dander adhered is affixed to a glass microscope slide and observed under low power.

Fecal flotations may yield Cheyletiella eggs that resemble hookworm eggs but are three times larger. One report in Norway used a special vacuum-cleaner method to detect mites; they felt it was the most accurate of all the methods.

With a skin biopsy, if the mite is captured in the sample it is diagnostic. If not, it is only suggestive. Findings in a skin biopsy from a patient with Cheyletiella include epidermal acanthosis with moderate to severe orthokeratotic hyperkeratosis, mixed-inflammatory infiltrate of the superficial dermis with eosinophils, lymphocytes, histiocytes and plasma cells and variable edema. Eosinophil numbers may be downgraded, depending upon previous steroid therapy.

Therapies

There are various topical and systemic therapies for Cheyletiella mites. They should include treatment of all exposed animals as well as appropriate environmental treatments.

Topical treatments for both dogs and cats include lime-sulfur dips every five to seven days for three to four applications, pyrethrin shampoos weekly for three to four weeks or Frontline spray (1 spritz/lb body weight every three weeks for two applications).

Because of nasal sequestration of mites, systemic therapies are probably more effective.

Systemic therapy choices for dogs include:

• Ivermectin 200 mcg/kg SQ or orally once weekly for three weeks (The dog must be heartworm-negative first and not a herding breed or white German shepherd. Use cautiously in older dogs of any breed.)

• Interceptor at 1 mg/kg every other day for 14 days or 1 mg/lb body weight once weekly for three weeks (must be heartworm-negative before using)

• Advantage Multi once monthly for two months

• Revolution one tube topically every 15 days for three treatments

• Amitraz dips once weekly for three weeks or every two weeks for two dips

Systemic therapy choices for cats:

• Ivermectin 200 mcg/kg SQ once weekly for three weeks or every two weeks for two doses

• Interceptor 1 mg/lb once weekly for three to four weeks

• Revolution one tube topically every 15 days for three doses

Treatments for either species should take into account the pet's physical condition.

Patients with underlying internal medicine disease need to be prescribed the safest treatment for their condition.

Once thought to be uncommon, Cheyletiella mites have resurfaced in large numbers.

Because there have been strides in treating fleas with newer, easier and safer products, perhaps we are seeing a resurgence in these parasite populations.

I am certain that once you start routinely checking pets, even if it's just to flea-comb each patient, you may be surprised at what you find.

Dr. 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.