Keep Cats Clear
of Swine Facilities to Protect Pigs from Parasite, Researchers Say
Barlow, UI News Bureau
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
facilitieswith screened windows and no portals for cats to enterand
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
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. Weigels 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 experimenta compartment-prevalence
modelto 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 Surveys 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
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-Pinillas 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.