Scratching is a common skin problem in guinea pigs, and there are multiple causes. Some of the most common are parasites, including fleas, mites, and lice.
Ctenocephalides felis (the cat flea) is the most common flea affecting guinea pigs. They usually become infested when another pet in the house brings in the fleas from outside. As in other animals, fleas cause guinea pigs to scratch. Fleas may also cause hair loss (alopecia), crusty lesions on the skin, and even anemia, if the fleas are in high number.
A flea comb can be helpful in finding fleas. Comb the guinea pig and then look for fleas or dark brown granules. These granules are called "flea dirt," which is actually the feces of the flea, and is primarily digested blood. Along with the eggs, the female flea deposits a large amount of feces, which will serve as food for the larvae when they hatch. The flea dirt will dissolve into a red color when moistened.
For treatment, a pyrethrin-containing product suitable for cats is often used. The safety of many of the other treatments developed for cats and dogs has not been determined in guinea pigs. Contact your veterinarian before using any insecticide on your guinea pig. Other pets in the house, and the environment must be treated as well.
There are two mites that cause skin problems in guinea pigs. Trixacarus (Caviacoptes) caviae is the most common mite and the most common parasite that causes scratching. This mite is related to the mite in dogs that causes sarcoptic mange. The other common mite is Chirodiscoides caviae.
T. caviae causes severe scratching and self-trauma. There may also be hair loss, thickening of the skin, redness, and papules. This mite usually affects the head, shoulders, back, and flanks of the guinea pig, but may spread to the entire animal. Secondary bacterial infections can occur. The itching is so severe that some animals may appear to have seizures or other abnormal behavior. Severely infected pregnant guinea pigs may abort. Some guinea pigs may carry the mite, but show no signs. Then, if they are stressed by poor nutrition, cold temperatures, or other illnesses, they may develop disease. The mite is transmitted by direct contact, and can temporarily infest people.
An infestation with T. caviae can be diagnosed by a veterinarian performing a skin scraping. The mites can be difficult to find, and the veterinarian may prescribe treatment solely based on the clinical signs of disease.
The most common treatment is a series of ivermectin injections. Animals in contact with the infested animal should be treated, as well. The mites can survive in the environment, so it is recommended that the housing be cleaned and then soaked in a lime sulfur solution at a dilution of 1:40 (one part lime sulfur to 40 parts water). Dry everything thoroughly before placing the guinea pig back into his housing.
C. caviae is called the "guinea pig fur mite." Whereas T. caviae burrows into the skin, C. caviae is usually found on the hair, and more commonly affects the rump area. Signs of infestation include scratching, redness, hair loss, and flaking. The scratching is usually much less intense than that seen with T. caviae. Some animals, however, may groom continuously causing a rough appearance to the hair coat and even skin ulcers. This mite is also transmitted by direct contact.
An infestation with C. caviae is easier to diagnose. The veterinarian will collect some hairs through combing, or applying adhesive tape to the animal's fur. The hairs are examined under the microscope for mites.
The treatment for infestations with C. caviae is similar to that of T. caviae.
There are several species of lice that commonly affect guinea pigs. Especially in heavy infestations, lice can cause scratching, redness, papules, and scabs, usually around the head and ears. Some infested animals may not show any signs. Infestations of lice and the mite, C. caviae, are commonly found together. Lice are spread through direct contact, and sometimes through the bedding. The lice of guinea pigs do not affect humans.
Lice are larger than mites, and may be seen on the hairs with the naked eye or a magnifying glass. As with mites, ivermectin injections are the usual treatment. The housing should be cleaned, as well.