There are two species of Demodex that inhabit the skin of hamsters – D. aurati (Figure 1) and D. criceti (Figure 2). These mites may be present in hamsters with no signs of skin disease. D. aurati (long-bodied) inhabits the hair follicles and D. criceti (short-bodied) inhabits keratin of the epidermal surface. Transmission from the mother occurs during suckling.
Most problems are caused by D. aurati, invariably occurring secondarily to an underlying problem associated with a diminished immune system. A diagnosis of underlying factors is therefore advisable, if possible, prior to attempting treatment.
For demodicosis in hamsters, underlying factors (Miller et al., 2013) include:
- Concurrent neoplasia
- Chronic renal disease
- Inadequate nutrition
- Immune system decline due to old age
A retrospective study of 102 hamsters with dermatological lesions in two academic settings (White et al., 2019) is the most recent substantial study of hamster skin diseases to be published. Of 65 hamsters seen in California, 54 percent had skin disease; and in Nantes, France, 67 of 164 hamsters (41 percent) had skin lesions. Demodicosis due to D. aurati, abscesses and neoplasia were the most common skin diseases. In California, six hamsters (18 percent) had neoplastic conditions, of which five were cutaneous lymphoma.
In this study it was noted that some rare diseases were diagnosed, such as hyperadrenocorticism and paraneoplastic alopecia. Underlying causes of demodicosis were not established in many cases.
Deciding what constitutes old age may prove to be a problem. If breeders of a line of hamster are known, they may be able to indicate the usual lifespan for their stock. It is useful to bear in mind average lifespans, especially when dealing with children’s pets. It is not uncommon to be presented with a demodectic hamster at the end of its normal lifespan, and treatment in these cases will be unrewarding and potentially upsetting to the owner if a poor prognosis has not been discussed.
Syrian hamsters, commonly kept as pets in the UK, will live on average between 2 to 2.5 years, with shorter or longer lifespans possible. The average lifespans of other species of hamster are:
- Roborovski hamster: 3 to 3.5 years
- Campbell’s dwarf hamster: 2 years
- Chinese hamster: 1.5 to 2 years
- Winter white Russian dwarf hamster: 1.5 to 2 years
Species and genetics as above, diet, exercise, husbandry, environment, quality of care and treatment of illness will likely affect a hamster’s lifespan.
Clinical signs of demodicosis are patchy alopecia, scaling and crusting (Figure 3). Lesions can be anywhere on the body but tend to be on the neck and dorsally in the initial stages, and more generalised late in the course of the disease. In early cases presenting with alopecia, the flank scent glands may become visible. Secondary infection can occur and an affected hamster may be systemically ill due to an underlying systemic problem.
- History and physical examination
- Tape preparations
- Skin scrapings
- Biopsy (the mites are not normally difficult to find; biopsy is rarely required and may not be permitted by the owner on cost grounds)
Ivermectin has been reported to be beneficial in many cases with variable dosage regimes. In one study (Tani et al., 2001), 56 hamsters with demodicosis were treated with ivermectin orally daily at a dose of 0.3mg/kg by mouth. Overall, 87.5 percent improved clinically, but in those cases with concurrent disease, the prognosis was poor.
Amitraz has been used to treat hamster demodicosis, with most authorities recommending a dilution of 100 ppm once weekly (Paterson, 2006).
A single report of demodicosis in a Syrian hamster treated with between 0.4 and 0.6mg/kg of doramectin subcutaneously for six weeks resulted in a dramatic improvement in skin lesions with negative skin scrapings. Initially, both D. aurati and D. criceti were identified. The hamster relapsed at 28 months of age with abdominal alopecia and pruritus. On this occasion, skin scrapings were positive for D. cricetialone. There was a response to a further eight injections of doramectin weekly at 0.6mg/kg, although at the end of this time (with the hamster now aged two years and six months) mites were detected (Sato, 2009).
In the largest study to date (White et al., 2019), several treatments were described with variable results. These included: topical amitraz; topical amitraz with metaflumizone; ivermectin subcutaneously and by mouth; topical selamectin; and moxidectin by mouth. A limitation of the study as emphasised by the authors is that not all treatment details and follow-ups were available on clinical records. The inclination not to spend money on a small rodent with a short lifespan often was a determining factor in the decision not to pursue diagnostic investigations or treatment.
Nevertheless, a useful conclusion is that cutaneous conditions in hamsters are common with the three main ones being demodicosis (described here), abscesses and cutaneous lymphoma. The latter could be considered as a possible underlying cause of demodicosis in some cases.