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.
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.