Cats are the definitive host for Toxoplasma gondii. The organism completes its life cycle in the intestinal epithelial cell, and oocysts are shed in feces. T. gondii also infects several intermediate hosts (including humans, sheep, pigs, cattle, rabbits, mice, and monkeys) by selectively infecting muscle and brain tissue, causing a variety of neurologic symptoms and signs. In humans, symptoms can be masked or delayed for many years and can be life-threatening (750 deaths in 1999). Toxoplasmosis is one of the most frequent severe neurologic infections among persons with AIDS. Infection is the result of ingestion of viable oocysts during exposure to infected raw or undercooked meat or cat feces. IgG antibodies to T. gondii appear early, peak within 6 months, and are detectable for life. The National Health and Examination Survey (NHANES 1999-2000) tested 4234 people 12 to 49 years of age to determine the prevalence of T. gondii antibodies. Now continual, this study was compared with an earlier one (NHANES III 1988-1994) that tested 17,658 people. The 2 studies used a representative sample of the U.S. civilian population in a stratified, multistage, probability cluster design (age adjusted, 95% confidence limits). Data were gathered on health care and household conditions and from standardized physical examinations, and blood samples were collected at mobile centers and analyzed.

In the NHANES 1999-2000 study, 15.8% (638 people) were antibody-positive for T. gondii. Antibody prevalence was higher among nonHispanic black persons than among nonHispanic white persons and increased with age. Statistics were similar for men and women. No statistically significant differences were found between the 2 studies, indicating that T. gondii antibody prevalence has remained stable over the past 10 years.

COMMENTARY: Toxoplasmosis is emerging as an important zoonotic disease that often goes unrecognized. Recent studies suggest that T. gondii may also be responsible for some intractable behavioral conditions, such as schizophrenia. Elucidating risk factors and focusing on preventive education will be challenges for the future.

Toxoplasma gondii infection in the United States, 1999-2000. Jones JL, Kruszon-Moran D, Wilson M. EMERG INFECT DIS 9:1371-1374, 2003.

Toxoplasma gondii and schizophrenia. Torrey EF, Yolken RH. EMERG INFECT DIS (serial online); 2003.