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Toxoplasma gondii is a coccidian parasite that is among the most common parasites that infect humans worldwide. Members of the feline species, domestic or wild cats, are the definitive hosts.


Cats ingest Toxoplasma in the form of tissue cysts (eg, eating infected rodents or oocysts) and excrete oocysts in their feces. The oocysts can remain viable in the soil in a warm and moist environment for as long as 18 months. Oocysts can sporulate within 1 to 5 days and become infectious by releasing sporozoites, becoming an ongoing source of infection for other mammals. Oocysts can also remain viable in salt and fresh water. T gondii can be found in nature in 3 forms: (1) oocysts excreted in cat’s feces; (2) bradyzoites in tissue cysts; and (3) tachyzoites, the active proliferative form that can infect several different types of cells, seen during acute infections or reactivation of chronic infections.

Humans can become infected by the following routes: (1) ingestion of viable tissue cysts in undercooked T gondii–infected meat; (2) ingestion of contaminated food from contact with contaminated surfaces/utensils; (3) ingestion of food contaminated with soil such as unwashed fruits or vegetables; (4) accidental ingestion of soil contaminated with T gondii (eg, while cleaning a cat’s litter box or during gardening); (5) congenital infection via mother-to-child transmission; (6) drinking contaminated water; (7) via organ transplantation with a T gondii–infected organ carrying tissue cysts; (8) rarely from blood transfusion as the duration of parasitemia after acute infection is usually short; and (9) after a laboratory accident with Toxoplasma-contaminated material. Additional risk factors recently associated with risk of T gondii infections include eating infected raw oysters, clams, or mussels and drinking unpasteurized goat’s milk. Toxoplasma tissue cysts in meat can be inactivated with cooking at high temperatures (eg, up to 74°C [165°F] for poultry meat) or freezing for at least 48 hours at –20°C (–4°F); processed infected meat that is smoked or dried can still be infectious. Drinking contaminated water has been the source for large community outbreaks. Commonly used water treatments do not efficiently inactivate oocysts. The T gondii seroprevalence rates vary in different parts of the world and can range from less than 10% in some northern European countries to 60% to 80% in South America and Africa. In the United States, the overall age-adjusted seroprevalence according to the National Health and Nutrition Examination Survey (NHANES) 2009–2010 survey was 12.4%. However, the seroprevalence in certain socioeconomic and racial subgroups can be as high as 20% to 25%. The age-adjusted seroprevalence of T gondii among women of childbearing age in the United States in 2009 to 2010 was 9%. The incidence of acute toxoplasmosis during gestation in the United States has been estimated to range between 0.2 and 1.1 acute infections per 1000 pregnant women, which translates to approximately 800 to 4400 pregnant women being acutely ...

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