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ARS Home » Research » Publications at this Location » Publication #32417
Title: KILLING OF DIFFERENT STRAINS OF TOXOPLASMA GONDII TISSUE CYSTS BY IRRADIATION UNDER DEFINED CONDITIONS

Author
item DUBEY JITENDER P - 1265-55-00
item Thayer, Donald

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Infection by the protozoan parasite, Toxoplasma gondii, is widespread in livestock and humans in the United States. It can cause mental retardation and loss of vision in children. Humans become infected by ingesting food or water contaminated with oocysts (resistant form of Toxoplasma) passed in feces of cats and by eating undercooked meat from infected animals. Among the ways to kill Toxoplasma in meat are cooking until internal temperature has reached 66 C (152 F), freezing, and by irradiation. ARS scientists at Beltsville and Philadelphia have tested the killing of tissue cysts of Toxoplasma of over 100 isolates. They found that Toxoplasma parasites of all isolates were killed by 50 Krads of cessium- 137. The findings provide guidelines for killing Toxoplasma in meat by irradiation.

Technical Abstract: To study the effect of gamma irradiation on the viability of Toxoplasma gondii tissue cysts, brains of mice inoculated with 95 newly isolated strains of T gondii from pigs, and 10 other laboratory isolates were pooled, flattened, packed in vacuum, and irradiated to absorbed doses of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.9 kGy at 5 C ( 0.5 C) with a cessium-137 gamma irradiation source. Treated samples were bioassayed for viable T gondii in mice and/or cats. Tissue cysts of all strains were rendered nonviable at 0.4 kGy. To study the effect of temperature on inactivation by irradiation, tissue cysts were irradiated at -4, 0, 4, 8, 12, and 16 C ( 0.5 C) at 0.25 kGy. Temperature during irradiation had no marked effect on the viability of tissue cysts.