- A diagnostic plan for dermatitis in the small mammal should follow standard protocols including hematology, radiography, microbiology, cytology, and surgical biopsy as indicated.
- Sarcoptid fur mites such as Sarcoptes scabei and Trixacarus caviae affect a wide variety of mammals and guinea pigs, respectively. Both species can cause pruritus, scales, crusts, and alopecia.
- Humans that become infested with sarcoptid mites may develop dermatitis.
Ectoparasites are a common problem in small mammals. Ectoparasite infestations can be suspected based on physical examination, however further diagnostics, such as a tape preparation or skin scrape, are required to identify microscopic ectoparasites. Most species of mites and lice are species-specific, however take special precautions, such as wearing exam gloves, to minimize the spread of potentially zoonotic pathogens.
Ear mites are one of the most common parasites observed in our practice. Otodectes cynotis is the ear mite of the ferret. Affected ferrets (Mustela putorius furo) generally have dark, ceruminous wax within the external ear canal and may frequently scratch at their ears. Psoroptes cuniculi is the rabbit (Oryctolagus cuniculi) ear mite. This mite can cause severe, painful inflammation with red or brown crusting of the external ear canal.
Sarcoptes scabei infestation affects many mammalian species including ferrets, rabbits, guinea pigs (Cavia porcellus), rats (Rattus norvegicus), mice (Mus musculus), African pygmy hedgehogs (Atelerix albiventris), and humans. The mite burrows into the stratum corneum, and affected animals often develop severe, intense pruritus, scales, crusts, erythema, and alopecia. Inflamed, edematous paws and self-mutilation are common findings in ferrets.
Trixacarus caviae, a sarcoptid burrowing mite, is the common mite of the guinea pig. Guinea pigs infested with T. caviae are generally asymptomatic, however animals maintained in poor conditions or exposed to stressors may develop alopecia, intense pruritus, scales, crusts, and hyperkeratosis. Trixacarus caviae can be difficult to eliminate in guinea pigs.
Chorioptes sp. is a common ectoparasite of African pygmy hedgehogs, which punctures the skin and sucks lymph fluid. Affected animals may present with crusts, scales, and spine loss.
The rabbit fur mite, Cheyletiella parasitovorax, is an infrequent finding in pet rabbits. Infested rabbits appear to have “walking dandruff”, and some individuals develop pruritus and alopecia.
Demodex spp. may cause alopecia and pruritus in ferrets, guinea pigs, hamsters (Mesocricetus auratus), and gerbils (Meriones unguiculatus).
Fur mites of the mouse include Myocoptes musculinus, Myobia musculi, and Radfordia affinis. Affected mice may suffer from pruritus, alopecia, and exudative dermatitis. In rare instances, Radfordia affinis may also cause clinical disease in rats.
In the past, many dermatologic conditions in exotic mammals were treated empirically, however successful case management requires a thorough diagnostic work up just as it does in small animals. Although it may be hard not to focus on the specific skin problem, it is important to remember that many small mammals present with multiple medical problems. Obtain a complete medical history and perform a thorough physical examination to develop a complete problem list for the patient.
- Perform a complete blood count and biochemistry panel to evaluate the patient for systemic disease.
- Use microscopic examination of skin scrapings and/or acetate tape preparations to diagnose mites (Fig 1).
- Also evaluate skin lesions with impression smear cytology and trichograms as indicated.
- Use cytology results to guide sample submissions for bacterial and/or fungal culture.
- Full thickness surgical biopsies may be required in some cases. Collect samples from the lesion margin and include both healthy and affected tissues.
- Obtain survey radiographs to assess the extent of injury, particularly if secondary osteomyelitis is suspected.
Ivermectin, moxidectin (Cydectin, Fort Dodge), and selamectin (Revolution®, Pfizer) are effective treatments for ear mites and fur mites. Milbemycin (Interceptor®, Novartis Animal Health), a closely related parasiticide, has also been used (400 µg/kg PO in hamsters). Other agents that have been used to treat mite infestations include lime sulfur shampoos or dips and Amitraz (Mitaban®, Pfizer). Amitraz has been described for treatment of Demodex spp. in ferrets, hamsters, and gerbils. The topical thiabendazole-based medication, Tresaderm® (Merial) has also been used in ferrets with ear mites. See Agents used for Ectoparasite Control for treatment options in small mammal patients.
Sarcoptid mites can survive for up to 7 days away from the host, feeding on sloughed skin in the local environment. Therefore, fomites such as infested bedding can serve as a source of disease transmission, and the environment should be cleaned intensively and cage bedding should be replaced.
Most species of mites are host-specific, however take special precautions, such as wearing exam gloves, to minimize the spread of potentially zoonotic pathogens. Humans that become infested with S. scabei may develop wheals, vesicles, papules, and intense pruritus. Pet owners, especially children, may become infected with T. caviae from direct contact with infected guinea pigs. Affected individuals generally develop mild dermatitis.
Sarcoptes scabei affects a wide variety of mammals, while the sarcoptid mite Trixacarus caviae infests guinea pigs. Both fur mites can cause pruritus, scales, crusts, and alopecia. Successful management of dermatologic disease in exotic small mammals requires a thorough diagnostic work up just as it does in small animals. Obtain a complete medical history and perform a thorough physical examination to develop a complete problem list for the patient. A diagnostic plan for dermatitis may include hematology, radiography, microbiology, cytology, and surgical biopsy as indicated.