II. Dermatophytosis
III. Hypovitaminosis C (Scurvy)
IV. Pododermatitis (Bumblefoot)
A. Lice
Guinea pig lice, Gliricola porcelli (A.) and Gyropus ovalis
(B.) are chewing lice that commonly parasitize Guinea pigs. The lice
and their nits (C.) are distributed over the dorsum and perineum of the
body, and are large enough to be seen by visual exam of the pelt.
Lice may occasionally cause partial alopecia and pruritus in select animals.
Treatment is by persistent use of a synthetic pyrethroid flea powder 1-2
times per week.
B. Mites
1. Chirodiscoides caviae is a fur mite (see photo). Fur
mites may occasionally cause partial alopecia and pruritus in select animals.
They tend to distribute themselves over the dorsum of the host. Treatment
is by persistent use of a synthetic pyrethroid flea powder 1-2 times per
week. 
2. Trixacarus caviae is a sarcoptic mange mite of the Guinea
pig (see photo). This parasite occasionally can cause an intense
pruritus leading to self-mutilation, abnormal behavior, debility, and death.
Diagnosis is by skin scraping and identification of the mite. Reported
treatments include pyrethroid dusts, lime sulfur dipping, or washing with
a 1% lindane solution at weekly intervals until the infestation has been
eliminated. Ivermectin is effective at a dose of 0.3-0.5 mg/kg SQ; the
dose is to be repeated every 2 weeks until mite is eliminated. 
Public Health Significance: Trixacarus may cause scabies
in humans.
Trichophyton mentagrophytes is the most common dermatophyte isolated from guinea pigs. Prevalence of arthrospore carriage is quite high, though clinical disease is rarely seen. Transmission of ringworm is by direct contact with the spores. Young, aged, pregnant, and otherwise stressed animals are most susceptible to the disease.
C. Clinical signs: Lesions consist of irregular alopecia with
occasional crusts and broken hair shafts. Progression of lesions
occurs from the nose to limbs and back. Severe lesions may become
secondarily infected with bacteria. 
D. Diagnosis and Treatment: Diagnosis is based upon clinical signs and identification of the fungus on KOH cleared preps from inoculated dermatophyte test medium (DTM). Treatment includes clipping the area and griseofulvin (15 mg/kg s.i.d. PO, 2 to 4 weeks) or a topical antifungal cream applied b.i.d. for at least 4 weeks are probably equally effective. Griseofulvin should be used cautiously since it is derived from penicillium cultures. The environment should be evaluated because of unsanitary conditions and high humidity can increase the incidence of dermatophyte infections.
Public Health Significance: T. mentagrophytes has been reported
to spread by contact and fomites from animal to animal and from animal
to man.
III. Hypovitaminosis C (Scurvy)
A. Etiology: Guinea pigs lack the hepatic enzyme 1-gulonolactone oxidase, which is essential for the conversion of glucose to ascorbic acid. Vitamin C is involved in many biochemical processes in the body including the synthesis of collagen and of intracellular ground substance. If vitamin C is not supplemented in the diet or if the animal is anorexic, scorbutic lesions will rapidly develop.
B. Clinical signs: Scurvy is characterized by frequent vocalizations, weakness, anorexia, diarrhea, flaky to ulcerative skin lesions, stiffness, reluctance to move, petechia of the mucous membranes, subcutaneous hemorrhages and death in two to three weeks due to starvation or secondary infection. Other nonspecific but suspicious signs may include rough hair coat, delayed wound healing, teeth grinding, inactivity, stillbirths, and chronic disease.
C. Pathology: Necropsy findings may include fascial and
articular cartilage hemorrhages, petechial and ecchymotic bleeding on periosteum,
muscle, and gingiva. 
D. Diagnosis: A diagnosis can be made by dietary history, gross pathology, and serum ascorbate levels.
E. Treatment: Severely affected animals can be treated with 25-50 mg vitamin C IP s.i.d. until improvement is noted. Guinea pigs can then be given oral supplemental levels until the animal has recovered.
F. Control: Daily requirement of ascorbic acid is 15 mg/day, and this amount can be provided through supplemental feeding of a handful of cabbage or kale, a green pepper, a quarter of an orange, etc. Pregnant females should receive 30 mg/day. Vitamin C supplemented pellet research diets have an average shelf life of 6 months from the milling date when stored in a cool, dry place; shelf life can be prolonged by storage in a freezer. Commercial pet diets may have a shorter storage life of about 90 days after milling. If the vitamin is to be supplied in the water, a new solution at a dose of 200 to 400 mg/l drinking water should be mixed fresh daily due to instability of the vitamin in the presence of light and chlorine.
IV. Pododermatitis (Bumblefoot)
This disease is seen most frequently in Guinea pigs housed on rough,
unsanitized wire floors. Lesions occur on the palmar and plantar
surfaces of the feet and consist of granulomatous cellulitis or chronic,
fibrous granulomas with or without an exudative crust, of the feet.
Staphylococci have often been isolated from these lesions, probably as
secondary invaders. The best treatment is to transfer the affected
animal to a solid floored cage with dry shredded paper bedding. Resolution
of advanced lesions despite local and parenteral therapies is uncommon.
Soaking the feet in astringents or tamed iodine solutions and bandaging
the feet may be beneficial in severe cases.
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