Parasite life cycles are complex and thought to develop over long periods with their hosts. This study reveals that parasites sometimes adapt rapidly to new hosts, indicating that host-parasite relationships may not always represent stable, long-term associations.

"Our findings raise the possibility that other parasites may also radically change their lifestyle by a similar mechanism and hence present new threats of infection" says study leader L. David Sibley, Ph.D., associate professor of molecular microbiology. The work is published in the Jan. 17 issue of the journal Science.

About 35 million people in the United States - and up to a quarter of the world's population - are thought to be chronically infected with Toxoplasma. However, only people with weakened immunity typically develop severe toxoplasmosis, a potentially serious disease that can lead to birth defects, brain inflammation and vision problems. The infection usually is acquired by accidentally swallowing spores from contaminated soil, water, cat litter or objects that have had contact with cat feces. The infection also can be acquired from eating raw or partially cooked meat, especially chicken, pork, lamb or venison.

While eating infected meat easily spreads Toxoplasma from animal to animal, related parasites have highly restricted life cycles and require that a specific carnivore eat a specific herbivore for transmission to occur.

Toxoplasma also is unusual in that worldwide there are only three main strains, whereas related parasites typically have many distinct strains. Research has shown that the three strains are highly similar genetically and arose from a single mating event between two
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Contact: Darrell E. Ward
wardd@msnotes.wustl.edu
314-286-0122
Washington University School of Medicine
16-Jan-2003