Track Parasite Contamination
By Rosalie Marion Bliss
March 4, 2002
Scientists with the
Agricultural Research Service and the
Centers for Disease Control and Prevention (CDC) have been awarded a grant to study sources
of exposure to an insidious parasite. The study will provide the first risk
assessment of the likelihood of exposure to the parasite Toxoplasma
gondii by ingesting raw or under-cooked meat.
T. gondii is a single-cell parasite that infects about 23 percent of
the U.S. population. The annual cost from both acute illnesses and
complications due to toxoplasmosis is between $3.3 billion and $7.8 billion,
according to the latest estimates from the U.S. Department of
Agricultures Economic Research
Parasitologist Jitender P. Dubey and epidemiologist Delores E. Hill of
Biology, Epidemiology and Systematics Laboratory, Beltsville, Md., and
parasitologist H. Ray Gamble with the
National Academy of Sciences
are preparing to test 6,000 meat samples. The three-year study will look at
beef, chicken and pork.
Collaborators at the CDC now are in the process of selecting 28 major U.S.
metropolitan areas from which to take meat samples. According to the CDCs
Jeffrey L. Jones, the tests will provide a sense of how much T. gondii
there may be in meat and how that level differs throughout various regions
in the country. The $853,000 grant is from USDAs National Research
Cats are the only animal in which T. gondii completes its sexual
phase. A rodent- or bird- eating cat that becomes host to T. gondii
transmits millions of infectious-stage oocysts in its droppings for a week.
These hardy oocysts survive freezing temperatures in soil and sand. If the
oocysts come into contact with farm feed, they can infect farm animals during
feeding. When deposited in litter and sand boxes, the oocysts can infect
T. gondiis favorite hiding place in humans is inside brain and
muscle tissue. Although healthy people other than pregnant women can weather
T. gondii with few symptoms, it poses a risk to developing fetuses and
to persons with depressed immune systems.
ARS is the USDAs principal
scientific research agency.