ARS | Publication request: Determining Resistance of Toxoplasma gondii Oocysts to UV Disinfection Using Cell Culture and a Mouse Bioassay

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2010
Publication Date: August 1, 2010
Citation: Ware, M.W., Augustine, S.A., Erisman, D.O., See, M., Wymer, L., Hayes, S.L., Dubey, J.P., Villegas, E.N. 2010. Determining Resistance of Toxoplasma gondii Oocysts to UV Disinfection Using Cell Culture and a Mouse Bioassay. Applied and Environmental Microbiology. 76:5140-5147.

Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating undercooked meat from infected animals and food and water contaminated with oocysts. This paper reports on methods to kill oocysts in the environment. The results will be of interest to biologists, parasitologists, public health workers, and veterinarians.

Technical Abstract: The effect of UV exposure on Toxoplasma gondii oocysts has not been completely defined for use in water disinfection. This study evaluated irradiated oocysts by three assays: a SCID mouse biassay, an in vitro T. gondii oocyst plaque assay (TOP-assay), and a quantitative reverse-transcriptase real-time PCR (RT-qPCR) assay. The results from the animal bioassay show that 1 and 3 log10 inactivation is achieved with 4 mJ/cm2 UV and 10 mJ/cm2 UV, respectively; but 4 log10 inactivation is not achieved with even higher UV exposures. TOP-assay results, but not RT-pPCR results, correlate well with bioassay results. In conclusion, a 3 log10 inactivation of T. gondii oocysts is achieved by a 10 mJ/cm2 UV, and the in vitro TOP-assay is a promising alternative to the mouse bioassay.