Evaluation of the effectiveness of a feline toxoplasma vaccine in reducing the exposure of swine to Toxoplasma gondii

The effectiveness of a feline Toxoplasma vaccine in reducing exposure of swine to T. gondii was evaluated in a 3-yr field vaccine trial conducted on 8 Illinois swine farms. These farms had been identified as 'high prevalence' (>2% T. gondii seroprevalence in finishing pigs) in a previous investigation (1992--93). Each farm was visited 3 times per year in 1994 and 1995, and once in 1996. During 1994 and 1995 cats were inoculated with the T. gondii vaccine. There was a mean decrease of T. gondii seroprevalence in finishing pigs from 4.61% from the pre-vaccination (1992, 1993) to 1.1% in the post-vaccination (1996) period. The seropositivity rate in mice decreased from 4% to 0%. The mean prevalence of isolation of T. gondii cysts from brain and heart tissues in mice decreased from 1.1% in 1994, to 0.8% in 1995, and to 0.5% in 1996.;The second study used a deterministic dynamic computer simulation model of the transmission of T. gondii in the swine farm ecosystem in a factorial experimental design to test the following hypotheses. T. gondii infection in finishing pigs decreases with (1) vaccination of susceptible cats, (2) increased cat capture rate (for vaccination), (3) decreased number of cats, (4) decreased T. gondii prevalence in cats, and (5) decreased oocyst survival time. Simulations were run for 10 years, with a weekly interval. Elimination of T. gondii in finishing pigs increased with a decrease in oocysts survival and a decrease in the number of cats in the farm. T. gondii prevalence in finishing pigs decreased with a decrease in the number of cats, a decrease in oocyst survival time, vaccinating and using an optimized vaccination schedule. Initial T. gondii prevalence in cats had no effect on outcome. Vaccination had less impact in decreasing T. gondii infection in finishing pigs than a decrease in the number of farm cats.