Removing the Pork Connection For a People ParasiteBy
Human infections with Toxoplasma gondii have dropped in recent
years, thanks to changes in personal hygiene, swine production and household
cooking and freezing of meat. But Agricultural
Research Service scientists won't be happy until the potential for
swine-transmitted toxoplasmosis is zero.
ARS researchers recently cloned pig genes they suspect play a major role in
enabling the animals to resist T. gondii, according to ARS
immunogeneticist Joan Lunney. She described their progress Sunday, Jan. 18, at
the Plant and Animal Genome VI International Conference in San Diego, Calif.
Overall, the studies will help identify the genes that endow natural
resistance against specific parasitic infections or help newborn pigs more
rapidly resist many infectious diseases. Lunney is based at the
Disease Resistance Laboratory in Beltsville, Md.
T. gondii usually doesn't make pigs or people sick, but it can cause
birth defects when a woman becomes infected during pregnancy. It can also be a
serious problem in AIDS patients and others with a suppressed immune system. In
the U.S., about 10 percent of young adults have T. gondii cysts in their
tissues, increasing to 40 percent of older people. Improperly cooked meat
appears to be an important source of infection as are cat feces. Although only
about 2 percent of market pigs carry the parasite, the lifetime chance of
ingesting a contaminated serving is high. But the parasite can be easily killed
by freezing meat or by cooking it thoroughly.
Lunney and colleagues have found genetic differences among pigs in the
ability to prevent T. gondii from getting a toehold. With further
research, they expect to identify pig genes responsible for T. gondii
resistance. This information will help swine breeders select more
They have so far cloned pig genes for seven cytokines--substances that
enable immune cells to talk to one another. They suspect cytokines play a big
role in resistance to T. gondii and many other diseases because they
coordinate the body's immune response to infection.
Scientific contact: Joan K. Lunney,
Disease Resistance Laboratory, Beltsville, MD 20705, phone (301) 504-8201,
fax (301) 504-5306, firstname.lastname@example.org.