Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 1999
Publication Date: N/A
Interpretive Summary: Infections by the single celled parasite, Toxoplasma gondii are widely prevalent in man and animals. It causes abortion in livestock and mental retardation and loss of vision in congenitally infected children. Humans become infected by ingesting T. gondii encysted in meat of infected animals or food or water contaminated with oocysts from infected cat feces. There is no vaccine to prevent T. gondii infection in animals. Scientists at the Beltsville Agricultural Research Center and the University of Illinois conducted the first field trial of a T. gondii vaccine in cats on swine farms in Illinois. Vaccinated cats did not shed oocysts and there was a reduction in the prevalence of T. gondii in pigs. The results will be of interest to pig farmers, veterinarians, public health workers and biologists.
A 3 yr field trial was conducted on 8 commercial swine farms in Illinois to determine the effectiveness of a feline Toxoplasma gondii vaccine in reducing the exposure of swine to T. gondii. A vaccine consisting of live bradyzoites of the mutant T-263 strain, capable of preventing oocyst shedding by cats, was used in this study. Each farm was visited 3 times in 1994, 3 times in 1995 and once in 1996. Cats were trapped and inoculated with the T-263 oral vaccine during 1994 and 1995. On each visit, the following samples were collected: blood from pigs, cats, and mice for detection of serum antibodies to T. gondii, feces from cats to detect oocysts, and heart and brain tissues from rodents to determine presence of T. gondii tissue cysts. The modified agglutination test (MAT), with a positive titer set at the 1:25 dilution, was used to determine serum antibodies. At first capture 72.6% (61/84) of juvenile cats and 32.6% (31/95) of adult cats had no detectable antibodies (seronegative), indicating no prior exposure to T. gondii when they received their first vaccine. Of these first time seronegative cats, 58.1% (18/31) of adult and 45.9% (28/61) of juvenile cats were recaptured and received a second dose of vaccine. Changes in the prevalence of T. gondii infection were evaluated from the pre-vaccination (1992, 1993) to the post-vaccination (1996) period. Eleven cats (5%) were detected shedding oocysts between 1994-1996, of which 10 (90.1%) shed during 1994. The last detection of oocyst shedding by cats was during the first farm visit in 1995. There was a significant decrease in T. gondii seroprevalence for finishing pigs (p<0.05, Wilcoxon Sign Rank test).