II. Cryptosporidiosis
III. Other Endoparasites
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.
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.
A. Nonpathogenic protozoa frequently observed in Guinea pigs include
the enteric coccidian (Eimeria caviae), and Balantidium caviae,
a large ciliate of the cecum and colon (see photo). 
B. The metazoan parasite commonly associated with Guinea pigs is Paraspidodera uncinata, a roundworm which resides in the cecum (A.). Typical roundworm ova ( B.) can be demonstrated by fecal floatation techniques. Piperazine has been reported to be an effective treatment. Ivermectin (.3-.5 mg/kg; SQ) may also be used, but efficacy studies are lacking.
C. Encephalitozoon cuniculi has been reported as a spontaneous
infection in Guinea pigs. The incidence of infection is unknown.
Lesions in the brain and kidneys are similar to those reported in rabbits.
Diagnostic tests for Guinea pigs are the same as for rabbits, and include
serologic assays for detection of antibody to E. cuniculi and histopathologic
demonstratioin of spores in infected tissues.
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