Cheyletiella blakei Infection in Cats

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Cheyletiellosis is caused by large, nonburrowing mites found in the hair and on the surface of the skin. Cheyletiellid mites feed on keratin on the surface of the skin, and Cheyletiella blakei will also feed on the hair of the cat. Although the species of cheyletiellid mites most commonly identified in cats is C blakei, this mite is not thought to be highly host specific, and feline infestation with Cheyletiella yasguri and Cheyletiella parasitovorax, found more commonly on dogs and rabbits, respectively, is possible. The mites may be carried between hosts by fleas, lice, and flies.¹ It has been hypothesized that the prevalence of these mites has decreased as routine use of flea and tick preventives has become more common.² Recent studies have shown a prevalence of 0.15% in client-owned cats compared with 0.9% in free-roaming cats in Oklahoma.^3,4

Cheyletiella Parasite Life Cycle

Cheyletiella species mites complete their 35-day life cycle on the host. Ova are loosely attached to the hair via fibrillar strands. Eggs hatch into legless, nonfeeding prelarvae, then progress through larval and first and second nymphal stages before becoming large adult mites.¹ Although larvae, nymphs, and adult male mites die quickly after leaving the hosts, adult female mites may live off the host for 10 days or more.²

Diagnosis of Cheyletiella Mites

Presentation of infested cats may vary from excessive chewing leading to bald patches (barbering) and partial alopecia with absent or mild skin lesions to miliary dermatitis. Progressively more generalized scaling and hair loss may develop in untreated animals. Some cats may exhibit crusting at the tips of their pinnae. Pruritus severity can be variable and does not always correlate with ectoparasite load. Cheyletiellid mites are highly contagious, and other species (especially other cats, dogs, and rabbits in the home) may also exhibit clinical signs.² Pruritic papules in groups and bullous eruptions may develop on in-contact humans.⁵

Cheyletiella species mites and their eggs are most easily found by sampling the surface of the skin via flea combing, hair plucking (trichogram), superficial skin scraping, and taking acetate tape impressions to pick up surface debris. Flea comb and trichogram samples should be placed in mineral or immersion oil on a microscope slide; although a coverslip is not necessary, the author finds it easier to use one when examining the slides. To best visualize the mites, flea combing, trichogram, skin scrapings, and tape impression samples should be examined under low light and low magnification. Because cats are such fastidious groomers, finding mites on the surface of the skin may be difficult; fecal flotation may reveal mites that have been ingested during grooming.

Ova are nonoperculated, ovoid, and approximately 240 m long. Adult mites are roughly 500 µm long and are most distinguishable by their large palpal claws near their mouth parts.¹ Adult mites can be speciated by examining the sense organs found on the limb of the mites. On C blakei mites, the sense organ is conical; on C yasguri, y-shaped; and on C parasitovorax, globoid. However, the sense organs may be difficult to identify, and mite species does not affect treatment recommendations.¹

For some patients, diagnosis may need to be made by response to an empirical treatment trial. One case series reported that mites in skin and/or fecal samples were demonstrable for only 8 out of 15 affected cats living in the same home.⁶ Clinical signs in all cats and their owners resolved with acaricidal therapy.

Treatment of Cheyletiella Mites

There are no licensed veterinary products specifically labeled for treatment of Cheyletiella species infestation. However, several off-label treatments, such as commercially available products containing selamectin and fipronil applied monthly, have been found to be effective in cats.^6,7 A topical product containing a combination of 10% imidacloprid and 2.5% moxidectin has also been found to be effective in dogs.⁸ For cats that do not tolerate topical therapy, systemic ivermectin may be used at 200 to 300 µg/kg PO q7d or SC q14d.⁹ To ensure that any emerging larvae and nymphs are also killed, cats and any in-contact pet mammals should be treated for 6 to 8 weeks. To the author’s knowledge, no studies evaluating the efficacy of isoxazolines against Cheyletiella species have been published to date.

Because infestation with cheyletiellid mites is contagious, all pets in the home or in contact with the infested cat should receive treatment. Treating the environment is not required as long as all potential pet mammalian hosts are treated appropriately; however, treating the environment should be considered when clinical signs or demonstrable mites persist.⁶

Zoonotic Potential of Cheyletiella Mites

Although cheyletiellosis is fairly easy to treat and often causes only mild pruritus, infestation is zoonotic and may cause bullous lesions mimicking immunobullous diseases in humans. In rare cases, Cheyletiella species have been reported to cause arthralgia and peripheral eosinophilia in humans.⁵

Prevention of Cheyletiella Mites

For both treatment and prevention, routine monthly use of commercially available preventives containing fipronil, selamectin, and imidacloprid/moxidectin are effective.^6-8 Consistent flea prevention for all pet mammals in the home to kill or repel fleas may reduce the risk of fleas acting as fomites for the spread of Cheyletiella species.

Case Scenario

Signalment, History, and Physical Examination

A 3-year-old, spayed female domestic medium-haired cat was presented to an animal hospital for evaluation of a 1-month history of overgrooming. Two months previously, the clients had adopted a rabbit that was reported to have a mild amount of dandruff. When questioned, the clients also admitted that they felt itchier than normal and had noted red bumps on their skin. Physical examination of the cat revealed partial alopecia along the dorsum and lateral thorax with mildly increased scale and occasional papules in some of the affected areas (FIGURE 1).

Figure 1. Areas of partial alopecia and occasional papules on the dorsum of the affected cat.

Diagnosis

Acetate tape impressions were taken from the areas with increased scale. Trichogram samples were obtained from areas of partial alopecia. On the tape preparations, long mites with large palpal claws (FIGURES 2 AND 3) and nonoperculated, ovoid eggs were noted, but only 1 ovoid egg was noted on the trichogram samples (FIGURE 4). Mites and eggs were consistent with Cheyletiella species; however, speciation could not be determined by using the available microscope.

Figure 2. Adult Cheyletiella mite identified on an acetate tape preparation.

Figure 3. Large, palpal claws identified near mouth parts on adult Cheyletiella mite.

Figure 4. Single ovoid Cheyletiella egg identified on acetate tape preparation.

Treatment

A topical flea preventive containing selamectin and sarolaner (Revolution Plus; Zoetis, zoetisus.com) was applied to the cat during the visit, and another dose was sent home with the clients for application 1 month later. The clients were instructed to monitor the cat for any adverse effects (e.g., lethargy, skin lesions not associated with the application site, anorexia, pruritus, conjunctivitis, sneezing, alopecia, crusting at the application site) and to discontinue use if these signs were noted.

An appointment was made later that week to evaluate the pet rabbit for cheyletiellosis. At that appointment, Cheyletiella species were noted on the rabbit and appropriate topical therapy with a flea preventive containing selamectin was initiated.¹⁰ The clients were instructed to seek care from a physician to address their own skin lesions.

Outcome

Overgrooming in the cat resolved 3 weeks after the first dose of selamectin/sarolaner. Examination 6 weeks after initial presentation revealed significant hair regrowth, and an acetate tape preparation was unremarkable. The clients reported that their skin lesions had spontaneously resolved. The clients were instructed to continue monthly application of the flea preventive to both the cat and the rabbit to prevent reinfestation.

Summary

Cheyletiella species infestation is an uncommon but notable cause of pruritus, overgrooming, and miliary dermatitis in cats. Although the most common species of Cheyletiella mite found on cats is C blakei, cheyletiellid mites are highly contagious and not host specific; therefore, cats can also acquire infestation with C yasguri from dogs or C parasitovorax from rabbits. Diagnosis relies on identification of mites in skin or fecal samples. A positive response to an empirical treatment trial can also be considered diagnostic when mites have not been identified but clinical signs are compatible. There are no licensed veterinary products labeled for the treatment of cheyletiellid mites; however, flea preventives containing fipronil, selamectin, or imidacloprid/moxidectin effectively treat cheyletiellosis in cats. Control and prevention of Cheyletiella species infestation not only provide comfort for our patients but also help prevent transmission to in-contact humans.