I. Cryptosporidiosis
II. Inclusion Body Conjunctivitis
III. Mites
IV. Salmonellosis
A. Etiology: A major protozoan parasite in the Guinea pig is Cryptosporidium wrairi.
B. Clinical signs: Intestinal colonization by this organism may
cause weight loss in adults and diarrhea and/or poor growth rates in weanlings
and juveniles. 
C. Pathology: The organism is most common in the ileum where flattened
and irregular villi along with a granulomatous infiltrate in the lamina
propria and absorptive epithelium are the main pathologic features. Parasites
can be visualized in parasitophorous vacuoles (arrows) at the apical portion
of infected enterocytes. 
D. Diagnosis: Fresh mucosal scrapings of the ileum with observation of the mature schizonts (4 micrometers in diameter) by phase contrast microscopy or by light microscopic exam of IFA stained wet mount preps (commercial kits are available) provides the most rapid method of diagnosis. Histopathologic exam of intestinal biopsies or PCR of mucosal scrapings are other methods for diagnosis of this condition.
E. Treatment: Outbreaks of clinical disease can be partially controlled by the addition of 0.2% sulfamethazine to the water supply.
Public Health Significance: Cryptosporidium wrairi appears to be species specific, so the risk of zoonotic transmission may be low.
II. Inclusion Body Conjunctivitis
A. Etiology: Chlamydia psittaci is enzootic in some Guinea pig colonies.
B. Clinical signs: Chlamydia psittaci may cause conjunctivitis in one to three-week-old animals. Infected Guinea pigs may have reddened eyelids, chemosis, a serous exudate, or photophobia.
C. Diagnosis: Diagnosis is made by demonstrating the elementary bodies within epithelial cells from a conjunctival scraping.
D. Treatment: The infection normally resolves spontaneously by the time animals have reached four weeks of age. In severe cases topical broad spectrum antibiotic ophthalmic solutions can be used. Oral or parenteral antibiotics should be avoided due to its enterotoxemic affects.
E. Control: A serologic test (FA) is available.
Public Health Significance: Chlamydiosis is not a species-specific disease. Although there is no documentation that transmission of chlamydial infection from Guinea pig to man has occurred, the risk of zoonosis may be possible.
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.
Salmonella enterica serovar Typhimurium has been shown to infect guinea pigs. Acute deaths are occasionally seen in very young, very old, or stressed animals; diarrhea is not characteristic of the clinical picture, but nonspecific depression, anorexia, weight loss and unthriftiness are commonly noted. Abortion storms have been reported. No lesions are apparent in acute cases, but carriers and chronically infected animals may have enlarged livers, spleens, and lymph nodes containing small white necrotic foci. Identification of both acute cases and carriers depends on isolation of a Salmonella sp. from feces or mesenteric lymph nodes. No treatment is recommended. Animals that are culture positive for Salmonella should be removed from the facility. Elimination of a colony is recommended if numerous carriers are identified.
Public Health Significance: Humans ingesting Salmonella -
contaminated food or water experience a transient diarrhea. Children
or immunosuppressed adults are susceptible to more serious clinical disease
from Salmonella infection. Exposed personnel must be advised
of any apparent risks.
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