Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 1997
Publication Date: N/A
Interpretive Summary: Infections by the protozoan parasite Toxoplasma gondii are widespread in livestock and humans. It causes mental retardation and loss of vision in congenitally infected children and abortion in livestock. Humans and animals become infected with T. gondii by ingesting food and water contaminated with a resistant stage (oocyst) of T. gondii excreted in feces of infected cats or by eating undercooked meat from infected animals. Rats are considered an important source of infection for pigs and cats. A scientist at the Beltsville Agricultural Research Center has found that rats can be infected with few oocysts and that Toxoplasma encysted stage persists in rat tissues for over a year, perhaps for life. These findings will be useful in control of toxoplasmosis on swine farms.
Technical Abstract: Toxoplasma gondii infected rats are considered important in the epidemiology of toxoplasmosis because they can serve as a source of infection for pigs and possibly for cats. To study the distribution of tissue cysts, 10 Sprague-Dawley female adult rats were fed 1 oocyst (3 rats, group A) or 105 oocysts (3 rats, group B) of the VEG strain or 10,000 0oocysts of the GT-1 strain (4 rats, group C) of T. gondii. All rats in a group were killed at one time: 76 (group A), 240 (group B), and 443 (group C) days after oocyst inoculation (DAI). Tissue cysts were seen in the brains of all 10 rats by direct microscopic examination. Portions or whole organs from heart, lung, liver, spleen, small intestines, kidneys, skeletal muscle, eyes, mesenteric lymph nodes, stomach, uterus, and tongue from all rats in a group were pooled by organ, digested in acid-pepsin solution for 60 min, washed in saline, and then bioassayed in mice. Based on bioassay in mice, tissue cysts were present in 3 extraneural tissues of rats from group A, 6 extraneural organs of group B and in 10 extraneural organs of rats of group C. Tissue cysts were present in skeletal muscles and kidneys of all 3 groups. Thus, tissue cysts are formed both in neural and extraneural tissues of rats. Therefore portions of infected rats, excluding the head, can be a source of infection for pigs and cats.