MICROBIOLOGY AND EPIDEMIOLOGY

Toxoplasmosis is caused by the intracellular parasite Toxoplasma gondii; cats and their prey are the definitive hosts. The primary route of transmission to humans is ingestion of tissue cysts from soil, food (e.g., undercooked meat), or water contaminated by cat feces.

• Roughly one-third of women who contract T. gondii during pregnancy transmit the parasite to the fetus, with a 65% risk of transmission if maternal infection is acquired in the third trimester.
• In the United States and most European countries, seroconversion rates increase with age and exposure. In the United States in 2009–2010, 13.2% of individuals >6 years old had serologic evidence of exposure; rates are higher in most other regions of the world.