Submitted to: International Society for Veterinary Epidemiology and Economics
Publication Type: Proceedings
Publication Acceptance Date: May 28, 1997
Publication Date: N/A
Interpretive Summary: Infections by the protozoan parasite, Toxoplasma gondii are widespread in livestock and humans. Humans become infected by ingesting the parasite stage (tissue cysts) encysted in meat or by ingesting the resistant stage (oocyst) excreted in cat feces. There is no vaccine to control toxoplasmosis in humans and animals. Scientists at the Beltsville Agricultural Research Center and the University of Illinois report trials with a vaccine for cats on 6 Illinois farms. Vaccination of farm cats to reduce to prevent oocyst shedding resulted in no reductions in prevalence of T. gondii in cats, mice and sows but a significant decrease in the prevalence of T. gondii in finishing pigs. These findings will be of interest to public health workers, veterinarians, pigs farmers, and parasitologists.
A feline Toxoplasma vaccine consisting of live bradyzoites of the mutant T-263 strain, capable of preventing oocyst shedding by cats, was used in this study. A field trial was conducted on 8 commercial swine farms in Illinois to determine the effectiveness of this vaccine in reducing the exposure of finishing pigs to T. gondii. Each farm was visited 3 times in 1994, 3 times in 1995 and once in 1996. During the vaccination period (1994-1995), cats were trapped and inoculated orally with the T-263 vaccine. Blood samples were obtained from pigs, cats and mice. Antibodies to T. gondii were detected using the modified agglutination test. A total of 179 unique cats (95 adults & 84 juvenile) were trapped during the vaccination period. Prior to vaccination, 72.6% juvenile cats and 32.6% adult cats were seronegative. Recapture rates for adult and juvenile seronegative cats were 58.1% and 45.9% respectively. Change in prevalence from pre-vaccination to post vaccination period, was evaluated for all the farms and for all species tested. There was a non-significant decrease in seroprevalence to T. gondii in mice, cats and sows, and a significant decrease (mean=-3.9%) in finishing pigs. Seroprevalence in mice for all the farms, decreased from 4% in 1992/3 to 0% in 1996. There was a significant positive correlation (rho=1.000 p-0.0001) between the change in prevalence in juvenile cats and the change in prevalence in finishing pigs. This suggests, that the reduced exposure of pigs to T. gondii was related to the reduced exposure of cats to the parasite, indicating that administration of a Toxoplasma vaccine to cats on swine farms can reduce the exposure of pigs to T. gondii.