Dermatophytic infections are relatively common in the guinea pig. The main aetiological agents are Trichophyton mentagrophytes andMicrosporum gypseum. The clinical signs are erythema, alopecia, seborrhoea and formation of crusts; pruritus is variable, but usually mild or absent (Figs. 1 and 2). Many guinea pigs are asymptomatic carriers of the infection. The diagnosis is made from observation of the infected fur under an optical microscope (Fig. 3) and by cultures of the fungus.
Both topical and systemic treatments can be used. The topical products act on the micro-organisms in the hair, while the systemic ones act at a follicular level. It has been advised to combine the two types of treatment since this can greatly shorten the time necessary to cure the condition. However, whether to use both treatments, only systemic treatment or (for single and/or small lesions) only topical treatment should be evaluated case by case. Baths can be too stressful (and can induce shock in some animals) and prudence is, therefore, necessary in advising them; sponging may be tolerated better.
The doses for small, exotic mammals have been extrapolated from those for dogs and cats, but there are virtually no studies on the safety of the drugs used, so it is important that the owner is always warned of possible toxic or idiosyncratic effects.
Topical treatment
- Econazole shampoo 10 mg/ml; 1-2 applications every 7 days for 4-8 weeks
- Miconazole solution 100 mg/ml; diluted at a ratio of 2 ml/100 ml and applied by sponging every 4 days for four applications
- Enilconazole solution 100 mg/ml, diluted at a ratio of 2 ml/100 ml and applied by sponging every 3-4 days for four applications
- Chlorexidine 4% foam or shampoo. At this concentration chlorhexidine is a fungicide. Its use in small, exotic mammals has not been described; nevertheless, it is an active principle normally well tolerated by guinea pigs, even when modest amounts are ingested.
- F10 solution, shampoo, gel. This substance has fungicidal properties and it is considered safe for use in rodents. The solution is used at a 1:100 dilution.
One study showed that miconazole and chlorhexidine had a synergistic effect against dermatophytes in culture. These two products could, therefore have greater activity if used together as topical therapy.
The local use of creams, lotions and ointments for humans is not recommended because these have not been formulated to penetrate the hair follicles and hairs; furthermore, they are easily removed by licking and ingested.
Systemic treatment
- Griseofulvin. This needs to be given with a lipid-rich meal in order to be absorbed adequately. In the ultramicronised form, the dose is 5-10 mg/kg every 24 hours, while the dose of the micronized form is 50-100 mg/kg every 24 hours divided into two or three administrations, for 2-8 weeks. Overdosage can cause bone marrow suppression. Griseofulvin is teratogenic and must not, therefore, be used in pregnancy.
- Ketoconazole. This should be administered with food and, in order to absorbed, requires an acid environment. It is not recommended as routine treatment in reproducers (whether male or female) because it interferes with steroidogenesis. The dose is 10-15 mg/kg every 24 hours for 2-4 weeks.
- Itraconazole. This is the product of choice for the treatment of dermatophytosis; it is very well tolerated and can be used in young subjects and pregnant sows. The dose is 5-10 mg/kg every 24 hours for 1 month or until the cultures become negative. The syrup formulation for cats is practical for dosing also in small mammals.
- Terbinafine. The dose used experimentally in dogs and cats is 10 mg/kg every 24 hours. Studies demonstrating the safety and efficacy of this drug in small mammals are lacking.
There are anecdotal reports on the use of lufenuron per os; this treatment cannot be recommended as there is not yet proof of its efficacy.
The treatment for dermatophytes is continued for 2 weeks after the clinical resolution of the lesions and, in theory, until two or three cultures for the fungus, performed at weekly intervals, are negative.
The environment can be treated with enilconazole 0.2%; sodium hypochlorite, at a dilution of 1:10, is effective as a disinfectant.
The possible presence of stressful and predisposing factors, such as overcrowding and poor hygiene, should be evaluated. One cause of treatment failure is the presence of several animals, while only the one with clinical signs is treated. This can result in so-called “ping pong” infections, which perpetuate the presence of the dermatophytes because the carriers act as a reservoir and continue to transmit the disease to each other.
The owner should be warned that this is a zoonosis (dermatophytosis is the most common zoonosis transmitted by these rodents) and that other animals in the house could be affected.