Submitted to: International Society for Veterinary Epidemiology and Economics
Publication Type: Proceedings
Publication Acceptance Date: June 10, 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. It is estimated that up to 50% of the adult human population has been exposed to this parasite. However, there are no prevalence data for farmers in the U.S. Scientists at the Beltsville Agricultural Research Center and the University of Illinois report, for the first time, prevalence of T. gondii-antibodies in 54 of 174 (31%) of farm workers from 43 swine farms in Illinois. This prevalence rate is considered to be twice that in general population of the U.S. They discuss risk factors associated with toxoplasmosis in humans. These finding will be of interest to public health workers, veterinarians, and parasitologists.
An epidemiologic investigation of risk factors for T. gondii infection in workers and residents of swine farms was conducted on 43 swine farms in Illinois. Blood samples were collected from 174 adults on these farms in 1993. The modified agglutination test was used to test for antibodies to T. gondii, with a positive result at the 1:25 dilution as the threshold for rseropositivity. An interview was conducted for each participant, in which information was obtained on the handling of cats, litter boxes, animal feed, and raw meat, gardening, and washing of hands after these activities and before eating, to determine possible modes of acquisition of infection. Multiple logistic regression analysis was used to examine the association with T. gondii seropositivity of these behaviors, age of worker/resident, years working/residing on farm, as well as the following farm level risk factors: T. gondii infection in cats on the farm, detection of oocysts on the farm, feed storage in open containers, and rearing of pigs on pasture. The T. gondii seroprevalence rate for the farm workers and residents was 31% (54/174). The factors associated with increased risk of human T. gondii infection were the number of seropositive cats trapped on the farm (p=0.008), male sex (adjusted 0R=3.97, p=0.01), rearing pigs on pasture (aOR= 3.88, p= 0.03), and gardening (aOR=2.18, p=0.05). Reduction in human exposure to T. gondii on swine farms should focus primarily on reduction of the number of infected cats on the farm.