Studies on the biology of Toxoplasma gondii (Nicolle and Manceaux, 1908), an important protozoan parasite of man and many animals

Abstract

An investigation was made on the biology of Toxoplasma gondii (Nicolle and Manceaux, 1908). The Beverley strain of Toxoplasma gondii was used in this study. Observations were made on the effect of desiccation on viability of Toxoplasma gondii oocysts exposed to different conditions for varying periods. The results showed that the suspensions of washed sporulated oocysts in experimental and control conditions remained viable for a longer periods of time as compared to the fecal suspensions and deposits of sporulated oocysts in experimental and control conditions. The fecal suspensions of sporulated oocysts in experimental and control conditions remained ineffective for a longer period of time as compared to the fecal deposits of sporulated oocysts except in the experimental condition in the refrigerator and the control condition in the shade. A comparison was made of the measurements of Toxoplasma oocysts obtained from kittens infected with Toxoplasma gondii cysts, and from kittens infected with T. gondii cysts obtained from mice infected with sporulated oocysts. The results showed statistically that the latter group of unsporulated and sporulated oocysts were larger than the first. Observations were made on the developmental stages of Toxoplasma gondii in small intestines of kittens and the appearance of oocysts in the feces. The results confirmed the occurrence and the nature of the newly described fecal form of Toxoplasma, and the transmission of toxoplasmosis by cat feces containing T. gondii oocysts. The characteristic schizogony and gametogony were demonstrated in the small intestine of kittens, particularly in the ileum. In this study, the sporulated oocysts in fresh cat feces were seen 48 hours after experimental infection. Attempts were made to establish the fecal form of T. gondii in various animals. Marmosets, mice, rats, golden hamsters, puppies, chicks, cotton rats and snakes infected orally with T. gondii cysts showed no Toxoplasma oocysts in the fecal material collected two to ten days after infection. Two marmosets which were infected orally with sporulated oocysts developed acute toxoplasmosis and extensive necroses on the submucosa of their small intestine, particularly the ileum. Observations were made on the effect of Toxocara canis larvae, Toxocara cati larvae, and Schistosoma mansoni on Toxoplasma gondii cysts in the brains of mice. Inverse correlations were indicated between the number of Toxocara canis larvae and Toxoplasma cysts; also, Toxocara cati larvae and Toxoplasma cysts. The cyst counts of experimental mice infected with S. mansoni and also with Toxoplasma cysts were about the same as the Toxoplasma cyst counts of control mice without blood flukes.