Toxoplasma gondii

Toxoplasma gondii is a species of parasitic protozoa, belonging to the Apicomplexa, that can cause the disease toxoplasmosis in humans. The life cycle of Toxoplasma gondii has two phases, one taking place only in cats and the other in many other mammals and birds. In an infected cat, the parasite lives in the small intestine, reproduces and is passed with the feces. Animals that come in contact with the feces become infected, the parasite enters macrophages in the intestinal lining and is distributed via the blood stream throughout the body. Another animal (including a cat) that eats meat of an infected animal gets infected itself.

To keep the cycle going, the parasite evolved an ingenious scheme: infected rats lose their natural fear of cats.

Human prevalence

In the U.S. NHANES III national probability sample, 22.5% of 17,658 persons >12 years of age had Toxoplasma-specific IgG antibodies, indicating that they had been infected with the organism.

References

• M. Berdoy, J. Webster, D. Macdonald: "Fatal Attraction in Rats Infected with Toxoplasma gondii", Proceedings of the Royal Society of London, B267, pp 1591 - 1594, August 7, 2000.
• CDC document: Toxoplasma gondii Infection in the United States, 1999–2000