Keep Cats Clear of Swine Facilities to Protect Pigs from Parasite, Researchers Say
by Jim Barlow, UI News Bureau

Findings from 10 years of field research and a complex computer simulation suggest that swine producers should keep cats out of swine housing facilities to avoid Toxoplasma gondii infection of pigs and, in turn, reduce a human health risk.

“The simple recommendation is that producers should deny cats access to pigs to prevent infection with Toxoplasma gondii,” says Dr. Ronald M. Weigel, professor of epidemiology in veterinary pathobiology and project principal investigator.

“The easiest way to accomplish this is to build total confinement facilities—with screened windows and no portals for cats to enter—and monitor cats when doors are open. If feed is stored in buildings of this type, there should be minimal risk of cat fecal contamination of feed.”

According to College researchers, keeping cats away from swine facilities, including feeding areas such as this, is the best way to reduce infection with T. gondii.

Cats are the only known full-life-cycle host of theprotozoan parasite, which causes toxoplasmosis, a disease that seriously affects immuno-compromised individuals and fetuses of newly-infected pregnant women.

Dr. Weigel, Dr. Nohra E. Mateus-Pinilla, and others began conducting field studies on pig farms in 1992 to identify risk factors for swine infection with T. gondii. As part of her doctoral research under Dr. Weigel’s supervision, Dr. Mateus-Pinilla conducted a field study of the effectiveness of a feline T. gondii vaccine in reducing T. gondii exposure for swine. This study suggested that the vaccine was capable of reducing exposure of pigs to T. gondii, but it was unclear if this was the result of natural trends in the prevalence of infection in pigs or the result of vaccinating cats.

“We decided to use a computer experiment—a compartment-prevalence model—to provide for control conditions that are almost impossible to attain in the field,” says Dr. Mateus-Pinilla, now a veterinary epidemiologist with the Illinois Natural History Survey’s Center for Wildlife Ecology.

With the help of Dr. Bruce Hannon, a professor of geography, and the National Center for Supercomputing Applications at the University of Illinois, they developed a model in which they used parameters from their field research and tested them in all possible scenarios.

They considered farms with 10 to 50 cats, in increments of 10. Based on previous data, they tested how the prevalence of T. gondii in cats impacted the rate of transmission to pigs. Their simulation considered all the various combinations. Contrary to expectation, the percentage of cats that were infected had little to do with rates of infection in the pigs.

The answer was in how infection works in cats. Only newly infected cats shed the oocysts (highly resistant forms of the parasite), for about two weeks beginning a week after infection. After shedding oocysts, cats enter a chronic but not infectious state.

“They will test positive to T. gondii, but they are done shedding and no longer contributing to infection on a swine farm,” Dr. Mateus-Pinilla says.

“We really feel very comfortable with this model, because it uses data based on known information obtained from swine farms in Illinois,” Dr. Mateus-Pinilla says. “While cat-management practices may be things that farmers could be doing, our study did not actually address their potential impact. The idea for those farm practices is to simply reduce the exposure of pigs to areas where oocysts are likely to be found.”

She also suggested that farmers reduce the availability of food to cats, avoid feeding strays and control rodent populations in an effort to reduce cat populations.

In their study researchers concluded, by way of computer simulation, that reducing cat populations reduces swine exposure to T. gondii better than vaccinating cats against the parasite. The computer simulation included data from a previous field study that found vaccination to be effective in decreasing infections in both cats and pigs.

The research, which was published in the September 10 issue of Preventive Veterinary Medicine, was part of Dr. Mateus-Pinilla’s doctoral studies in the Department of Veterinary Pathobiology. It was funded by grants to Dr. Weigel from the U.S. Department of Agriculture, Bayer Animal Health Laboratories, the National Pork Producers Council and the University of Illinois Research Board.