Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 1996
Publication Date: N/A
Interpretive Summary: Toxoplasma gondii is a single celled parasite that infects most warm- blooded animals and man. It causes mental retardation and loss of vision in congenitally infected children and abortion in livestock. It is also a frequent cause of death in AIDS patients, often from encephalitis. Based on limited information in rodents the parasite is considered to have an affinity for brain tissue. A scientist at the Beltsville Agricultural Research Center has found that T. gondii was found more often in muscles than in the brain of animals. This information will be useful to veterinarians, public health workers and scientists working with parasite.
The persistence of Toxoplasma gondii tissue cysts in organs of cats (definitive host) and rodents (intermediate hosts) was studied. Nine cats, 9 rats, and 12 mice were fed T. gondii oocysts and their organs were digested in pepsin and then bioassayed for bradyzoites in mice. Of 9 cats killed 37 or 51 days after feeding 100 (2 cats), 1000 (3 cats) or 10,000 (4 cats) oocysts of the VEG strain, tissue cysts were found in each cat; in the tongue of 9, in the heart of 5, in the brain of 4, and in the eyes of 1 cat. The dose had no effect on the distribution of tissue cysts in cats. Nine rats were each fed 100,000 oocysts of the VEG strain of T. gondii and killed 21, 29 and 64 days later. At each time period, organs of 3 rats were pooled and bioassayed in mice. Tissue cysts were found in the brain, skeletal muscle, heart and kidneys of rats at each killing time; in the lungs, intestines, mesenteric lymph nodes and liver in 2 of 3 instances; in the tongue, spleen, and eyes in 1 instance. Using the same procedures and the same 11 organs as used for rats, tissue cysts were seen in all organs except in the tongue and liver of 3 mice killed on day 82 after feeding the VEG strain. In 9 mice (3 with each strain) fed oocysts of the ME-49, GT-1, or P89 T. gondii strain and killed 62-130 days later, tissue cysts were found consistently only in the brain. Thus, in rats and mice, most tissue cysts were found in the brain and rarely in the tongue which was in marked contrast to cats.