Infectious Agent

Toxoplasma gondii, an intracellular coccidian protozoan parasite.


Ingestion of soil, water, or food contaminated with cat feces, ingestion of undercooked meat or shellfish, congenital transmission from a woman infected during or shortly before 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 or shellfish, drink untreated water, or have extensive soil exposure. Congenital transmission can also occur if a woman is infected during pregnancy.

Clinical Presentation

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 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 tests for T. gondii antibodies are available at commercial diagnostic laboratories; however, because of the inherent difficulty in diagnosing acute toxoplasmosis, physicians are advised to seek confirmatory testing through the reference laboratory at Sutter Health Palo Alto Medical Foundation Toxoplasma Serology Laboratory ( 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 or MRI. Biopsy may be needed to make a definitive diagnosis.


Treatment is reserved for acutely infected pregnant women and those with severe disease or who are immunocompromised. A number of regimens are available, but the recommended regimen includes pyrimethamine, sulfadiazine, and leucovorin (folinic acid). Alternative treatment regimens include clindamycin, atovaquone, and azithromycin, but these have not been extensively studied. The recommended treatment regimen for acutely infected pregnant women depends on the timing of infection during gestation; physicians are advised to seek consultation with a specialist before initiating therapy in these patients.


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. Wash hands with soap and water after gardening, contact with soil or sand, and after changing cat litter.

CDC website:


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Anne Straily, Susan Montgomery