Toxoplasma gondii, an intracellular coccidian protozoan parasite.
Ingestion of soil, water, or food contaminated with cat feces, ingestion of undercooked meat, congenital transmission when a woman becomes infected during pregnancy, and contaminated blood transfusion and organ transplantation.
T. gondii is endemic throughout most of the world. Risk is higher in developing and tropical countries, especially when people eat undercooked meat, drink untreated water, or are extensively exposed to soil.
Incubation period is 5–23 days. Symptoms may include influenzalike symptoms or a mononucleosis syndrome with prolonged fever, lymphadenopathy, elevated liver enzymes, lymphocytosis, and weakness. Rarely, chorioretinitis or disseminated disease can occur in immunocompetent people. In severely immunocompromised people, severe and even fatal toxoplasmic encephalitis, pneumonitis, and other systemic illnesses can occur, most often from reactivation of a previous infection. Infants with congenital toxoplasmosis are often asymptomatic, but eye disease, neurologic disease, or other systemic symptoms can occur, and learning disabilities, cognitive deficits, or visual impairments may develop later in life.
Serologic testing for T. gondii antibodies. Eye disease is diagnosed by ocular examination. Diagnosis of toxoplasmic encephalitis in immunocompromised people (most often seen in people with AIDS) can be based on typical clinical course and identification of ≥1 mass lesion by CT, MRI, or other radiographic testing. Biopsy may be needed to make a definitive diagnosis.
Treatment is reserved for those with severe disease or who are immunocompromised. A number of regimens are available, including pyrimethamine, sulfadiazine, and leukovorin. Alternative treatment regimens include clindamycin, atovaquone, and azithromycin.
Food and water precautions (see Chapter 2, Food & Water Precautions). Avoid direct contact with soil or sand that may be contaminated with cat feces. If caring for a cat, change the litter box daily. If pregnant or immunocompromised, avoid changing cat litter if possible, and do not adopt or handle stray cats.
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