Distribution of tissue cysts in organs of rats fed Toxoplasma gondii oocysts

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 10(5) oocysts (3 rats, group B) of the VEG strain or 10(4) oocysts of the GT-1 strain (4 rats, group C) of T. gondii. All rats in a group were killed at 1 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.