Cheyletiella species

Dogs and cats each have their own species of the mite fur Cheyletiella, which appear to be host-specific — C. yasguri in dogs and C. blakei in cats.  

Cheyletiella occurs on these hosts around the world.  The entire life cycle of the mites occurs on the host.  In general, dogs are more likely to show clinical signs (primarily pruritis, scaliness and eczema-like skin lesions around the face), than are cats.  These surface mites can be easily seen moving around in the haircoat - "walking dandruff".  Cheyletiella transmits readily to people, who can show clinical signs in the absence of signs in the pet, or before such signs develop.

 

Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Acari
Order: Prostigmata

Cheyletiella species are in the same Order as Demodex and Neotrombicula, which is different from that containing Sarcoptes, Notoedres, Psoroptes, Chorioptes and Otodectes, and from that containing Dermanyssus and Ornithonyssus.

Adult Cheyletiella have eight long legs, are approximately 0.5 mm in length, and their mouthparts include two large, prominent, curved, palpal claws that point inwards.  The species of Cheyletiella that occur on dogs and cats can be differentiated on the basis of the shape of the sense organ on each of the front pair of legs: in C. yasguri of dogs it is heart-shaped, and in C. blakei of cats it is conical. In C. parasitivorax of rabbits and other small mammals the sense organs are conical. This differentiation among the species is not usually necessary in veterinary practice, but may be in some cases of human infestation.

Cheyletiella yasguri occurs in dogs, C. blakei in cats and C. parasitivorax in rabbits around the world. There appears to be some degree of host specificity, but transient cross-infections are possible. In addition, some related free-living cheyletid mites, for example Cheyletus eruditis, occasionally infest dogs and cats but apparently do not cause clinical signs. These free-living mites can be differentiated microscopically from the species of Cheyletiella.

Cheyletiella species mites complete their entire life cycle on the host.  The mites can often be seen moving around in the hair coat - "walking dandruff". Although they are surface mites, the adult mites may make pseudo-tunnels in the keratinized layer of the epidermis. They pierce the skin and ingest tissue fluids. Adult female mites lay eggs attached to the hairs by fine threads. A six-legged larva develops within each egg, which then hatches and the released larva moults through two eight-legged nymphal stages and then to an adult. The entire life cycle can be completed in approximately three weeks.

Life Cycle: Cheyletiella species

Infestations with Cheyletiella species mites are very contagious, particularly among young animals or those that are immunosuppressed or in other ways stressed. Although the larvae and nymphs are not thought to be able to survive off the host for more than a few days, adults may survive for longer (maybe a few weeks), and it is possible that bedding and other fomites may act as sources of infestation.  In some instances, eggs of Cheyletiella in the environment might be a source of infestation for pets.

Infestation of dogs and cats with Cheyletiella is more common than are clinical signs associated with the mites. Clinical signs are thought to be associated with the feeding activities of the mites, and in some cases involve a hypersensitivity reaction. The first sign of Cheyletiella in dogs and cats is often a dry, usually non-pruritic scurfiness along the back. This scurfiness may then worsen and extend to affect other areas of the body, with hair loss, pruritus in some animals, and small red lesions, often with necrotic centres. Clinical progression is often slower and the signs less severe in cats, probably because the grooming activities of these hosts tend to control mite population size.

Some infested dogs and cats have few mites, but very severe clinical signs, particularly pruritus. These animals may have developed a hypersensitivity reaction and may develop exfoliative erythroderma, or lesions that mimic scabies. Cats sometimes develop miliary dermatitis or develop dorsal hypotrichosis without skin lesions.

Diagnosis of Cheyletiella infestation is not always easy, particularly in cats, because it may be very difficult to recover mites, even from animals showing typical clinical signs. The history and clinical signs can be very suggestive that Cheyletiella is present. Infestation with Cheyletiella species mites is often referred to as “walking dandruff”, as the mites can often be seen moving in the hair coat, especially if a magnifying glass is used.

To recover mites, the animal can be stood on a dark plastic sheet, brushed or combed against the lie of the coat, and the material collected then examined, either directly after immersing in mineral oil (to prevent the live mites from escaping) or following a potassium hydroxide digest as used for routine skin scrapings. Rather than brushing, skin debris can be collected on clear adhesive tape and examined as above, or a vacuum with an in-line filter can be used. Vacuuming the animal using a filter and examining the debris collected is very effective for Cheyletiella, in part because most or all of the external surface of the animal can be examined. Standard skin scrapings are not very effective for Cheyletiella, primarily because they are surface mites.

The presence of typical Cheyletiella skin lesions on the owner, or on other people in contact with an affected animal, sometimes in the absence of clinical signs in the animals, may be the first sign that the dog or cat has the mites. Failure to recover mites from a pet with compatible clinical signs and history should not rule out the diagnosis of cheyletiellosis.

There are no products approved in Canada for Cheyletiella in dogs and cats, but several are used extralabel, particularly macorcyclic lactones such as selamectin. Isoxazolines are likely to have efficacy against Cheyletiella, as for other mites. Repeat treatment, especially with older, topical products, may be necessary within 2-4 weeks. 

With Cheyletiella it is very important to effectively treat all in-contact animals (including dogs, cats, rabbits etc) even if they are asymptomatic and to remove or thoroughly clean any potential fomites, for example bedding. Effective treatment of Cheyletiella can be difficult because of the often large numbers of mites present and the possibility of re-infection from the environment. Also, resolution of the clinical signs does not always mean that the animal is mite-free, and so in some cases it might be advisable to continue treatment until several periodic examination of the haircoat and skin surface are negative for mites.

People can acquire Cheyletiella from dogs or cats as accidental hosts. Sleeping with an infested pet is probably a good means of encouraging zoonotic transmission. There is no evidence that the parasite can be transmitted person-to-person.  Sometimes lesions and symptoms may be present in the owner but not in the pet.

Among the primary signs in people are an intense pruritus and grouped erythematous macules. These develop a central papule which becomes vesicular, then pustular, then bursts to produce a yellow crust. The lesions are most often on the arms and trunk.

Arther RG (2009) Mites and lice: biology and control. Veterinary Clinics of North America Small Animal Practice 39: 1159-1171.

Curtis CF (2004) Current trends in the treatment of Sarcoptes, Cheyletiella and Otodectes mite infestations in dogs and cats. Veterinary Dermatology, 15: 108-114.