The most common cutaneous parasite of the guinea pig is Trixacarus caviae (Figs. 1a and b), a mite that has an appearance similar to that of Notoedres and a life cycle of 10-14 days. The parasite can remain asymptomatic for a long time (even months or years), but clinical signs usually appear 2-5 weeks after contagion. At first the infestation is present on the dorsal part of the neck and the back (Figs. 2a and b), but gradually extends to the rest of the body. The lesions are mainly due to self-harm caused by an intense pruritus, with erythema, ulcers, alopecia and, in chronic cases, lichenification (thickening of the skin) and yellowish-white scales. The guinea pig may show signs of irritability because of the pruritus and sometimes may even have convulsions erroneously interpreted as neurological signs. Asymptomatic carriers are common; recrudescence of signs may occur in the case of stress, old age, concomitant disorders or vitamin C deficiency.
The diagnosis is confirmed through examination of skin scrapings. However, the parasites are not easy to find, and if an infestation is suspected, it is worth trying treatment. The easiest and most effective treatment is ivermectin (0.3-0.5 mg/kg per os or subcutaneously at intervals of 2 weeks, until healing). The oral route is not advised in animals under 3 weeks old. Pregnant guinea pigs can be treated with ivermectin without risk of adverse effects. Topical selamectin (on the skin of the neck) is also effective at a dose of 6-12 mg/kg once a month. The administration of meloxicam may be of help in the most severe cases. This disease is a minor zoonosis: people in contact with infested guinea pigs may develop a pruritic dermatitis.
Other mites that can infest the guinea pig are: Sarcoptes scabiei, Notoedres muris and Myocoptes musculinus, which cause a pruritic dermatitis. Also in these cases the diagnosis is made from skin scrapes and the treatment of choice is ivermectin.
The guinea pig can be infested by two types of lice: Gliricola porcelli (Fig. 3), which is the more common, and Gyropus ovalis (Figs. 4a and b).
Usually there are no clinical signs, but in the case of massive infestation, there may be pruritus, alopecia and the formation of crusts. These parasites may be seen by the naked eye and identified by microscopic examination. Adhesive tape is useful for collecting the parasites.
Chirodiscoides caviae is an uncommon mite infesting the hair of guinea pigs and is usually asymptomatic. In the case of massive infestation there may be self-harm and ulcerative dermatitis and self-induced alopecia of the lumbosacral region because of the intense pruritus. The parasites can be identified by microscopic observation of hairs or through the scotch test.
The treatment for these ectoparasites is pyrethrine-based products for use in cats or ivermectin.
Demodex caviae is a rare parasite in the guinea pig and may be asymptomatic. The clinical signs include alopecia, erythema, papules and crusts with variable pruritus of the head, trunk and anterior limbs. It is detected fairly easily in deep skin scrapes; the diagnosis may also be made from skin biopsies. The treatment consists of baths with amitraz (250 ppm) once a week, until a month after the skin scrapes have become negative. Treatment with ivermectin (0.3 – 0.5 mg/kg subcutaneously, repeated after 8-10 days) has also been reported.
Guinea pigs can, occasionally, be infested by fleas. The treatment is pyrethrine-based powders for use in cats. Obviously all other animals, including those of other species, in contact with the infested guinea pig must be treated.