|Vianna, M C B|
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2005
Publication Date: 11/23/2005
Citation: Dubey, J.P., Hill, D.E., Jones, J.L., Hightower, A.W., Kirkland, E., Roberts, J.M., Marcet, P.L., Lehmann, T., Vianna, M., Miska, K.B., Sreekumar, C., Kwok, O.C., Shen, S.K., Gamble, H.R. 2005. Prevalence of viable toxoplasma gondii in beef, chicken, and pork from retail meat stores in the united states and risk assesment to consumers. Journal of Parasitology 91:1082-1093. 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. Scientists at the Beltsville Agricultural Research Center and Cenetrs for Disease Control, Atlanta, Georgis have determined the prevalence of viable Toxoplasma in retail meats in the U.S. The results will be of interest to biologists, parasitologists, public health workers, physicians, and veterinarians.
Technical Abstract: Prevalence of viable Toxoplasma gondii was determined in 6,282 samples (2,094 each of beef, chicken, and pork) obtained from 698 retail meat stores from 28 major geographic areas of the U.S. Each sample consisted of a minimum of 1 kg of meat purchased from the retail meat case. To detect viable T. gondii, meat samples were fed to T. gondii-free cats and feces of cats were examined for oocyst shedding. Initially, 100 g from 6 individual samples of a given species were pooled (total 600 g) and fed to a cat over a period of 3 days and feces were examined for oocysts for 14 days; the remaining meat samples were stored at 4 C for 14 days (until results of the initial cat fecal examination were known). When a cat fed pooled samples shed oocysts, individual meat samples were then bioassayed for T. gondii individually in cats and mice. Genetic characterization was performed using the SAG2 locus and 5 hyper-variable loci. In all, 7 cats fed pooled pork samples shed oocysts. Of these, T. gondii oocysts were detected microscopically in feces of 2 cats that were fed 600 g pooled pork samples; 1 isolate was Type II and the second was Type III. When these 12 individual samples were bioassayed in cats and mice (1 cat and 10 mice per sample), T. gondii was detected in only 3 samples (3 by bioassay in cats and in 1 by bioassay in mice); the genetic data indicated that only 2 T. gondii isolates were present in these pork samples. The remaining 5 isolates of T. gondii were obtained from feces of cats that were fed pools of 6 pork samples each; oocysts were so few in number that they were not detected by microscopic examination but were detected by mouse bioassay of cat feces; genetically of these 5 isolates from pooled pork samples, 2 isolates were Type III, 1 was Type II and 2 were Type I. These 30 individual pork samples could not be bioassayed individually because they had been discarded by the time results of cat feces bioassay were known. None of the cats fed chicken and beef samples shed oocysts. Overall, the prevalence of viable T. gondii in retail meat was very low. Nevertheless, consumers, especially pregnant women, should be aware that they can acquire T. gondii infection from ingestion of undercooked meat from retail meat stores. Fortunately, cooking meat until the internal temperature reaches 66 C kills T. gondii.