Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 27, 2001
Publication Date: N/A
Interpretive Summary: Infections by the single-celled parasite Toxoplasma gondii are widely prevalent in animals and humans. It causes mental retardation and loss of vision in children. Humans become infected by ingesting parasites encysted in meat or by ingesting food and water contaminated with the resistant stage of the parasite (oocyst) excreted in feces of infected cats. Oocysts swhen excreted in feces are unsporulated (not infective) and become infective after 1-2 days outside in the environment. Scientists at the Beltsville Agricultural Research Center and the Virginia Tech, Blacksburg have found that oocysts stored in refrigerator for 11 weeks were still capable of sporulating. These findings will be of interest to biologists, parasitologists and public health workers.
Toxoplasma gondii oocysts are excreted nonsporulated in the feces of cats into the environment. These oocysts must undergo sporulation to become infectious. Little is known about the factors that influence sporulation of T. gondii oocysts. The present study examined survival of nonsporulated oocysts under refrigerated conditions over an 11 week observation period. Microscopic examination of oocysts indicated that no visible development occurred under refrigerator conditions. The nonsporulated oocysts retained their ability to sporulate when placed at room temperature. The numbers of visually viable appearing oocysts decreased over time. Some oocysts in all samples were infectious for mice despite being refrigerated for up to 11 weeks before undergoing sporulation. Results indicate that nonsporulated oocysts can survive in the environment for at least 3 months and retain their ability to become infectious when placed under appropriate conditions.