Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 1996
Publication Date: N/A
Interpretive Summary: Infection by the protozoan parasite, Toxoplasma gondii is widely prevalent in man and animals. It causes mental retardation and loss of vision in children and abortion in livestock. Humans become infected with Toxoplasma by ingesting meat infected with tissue cysts or by ingesting food and water contaminated with feces of infected cats containing the resistant (oocysts) of Toxoplasma. Toxoplasma oocysts are highly resistant to environmental influences and can survive outside the body for months. Scientists at the Beltsville Agricultural Research Center and the Eastern Regional Research Center, ARS, Wyndmoor, PA have determined that oocysts can be killed by low doses (0.25kGy) of irradiation with cessium 137 and that vaccination with irradiated oocysts can induce protection in mice. These results will be useful to understand the mechanisms of protection against T. gondii.
Technical Abstract: Toxoplasma gondii oocysts are highly resistant to environmental influences. To study the effect of gamma-irradiation on the viability of T. gondii oocysts, 1 million sporulated oocysts of the VEG strain were irradiated to absorbed doses of 0.10, 0.15, 0.20, 0.25, 0.30, 0.40 and 0.50 kGy at 5 C with a 137Cs gamma-irradiation source. Treated oocysts were bioassayed for viable T. gondii in mice. Viable T. gondii was not found in brains of mice 2 mo after oral inoculation with oocysts irradiated at levels > 0.25 kGy. Therefore, gamma irradiation is an effective means of killing T. gondii oocysts. Mice inoculated orally with oocysts irradiated at 0.20 and 0.40 kGy were partially protected when challenged orally with lethal doses of nonirradiated oocysts.