Toxoplasma gondii

Prepared by: Michael J. Huerkamp, DVM, Diplomate ACLAM
Date: June 30, 2003 (first written March 12, 1990)

Agent: Toxoplasma gondii

Toxoplasmosis is the third most common fatal foodborne disease and causes up to 4,000 cases of birth defects annually. It occurs in free-ranging or stray cats that are permitted to prey on wild rodents. Humans typically acquire toxoplasmosis by gardening without gloves in contaminated areas and then eating or preparing food or by eating dirt (children). The disease in humans is typically self-limiting but may occur as a brief flu-like disease. Should infection occur, consequences are greater in pregnant women where toxoplasmosis can cause birth defects in infants. Studies show that 15-25% of Americans have been exposed to toxoplasmosis.

Potential Hazard: Cats of unknown history (such as strays from a municipal pound) are at greatest risk of infection. After ingestion of infected rodents, cats begin to shed eggs 3 to 48 days later and do not show any signs of infection. Generally, shedding ceases within 30 days and the parasite is eliminated from the host. However, in some cases, cats may be latently infected and egg shedding may resume after a period of dormancy. The parasite eggs become infective 24 hours after shedding. Humans become infected with toxoplasmosis through ingestion secondary to exposure and poor personal hygiene.

Recommended Precautions: Infection can be prevented and eggs can be removed from the environment before they become infective by feeding cats only cooked commercial diets and changing litter boxes daily. Cat handlers should wear and laboratory coat or gown and gloves when handling cats or their excreta and should wash hands after removing gloves and before meals. Because of the short period of actual egg shedding, cats that have been in domestic colonies for a month or more are not likely to transmit the disease. Pregnant women and workers that are immunosuppressed should consult with their physician if their job involves handing cats or cleaning litter boxes.

References:
Biosafety in Microbiological and Biomedical Laboratories, 4th edition, CDC-NIH, 1999, p. 128.
CDC. Preventing congenital toxoplasmosis. MMWR 49(RR02): 57-75, March 31, 2000.