Author(s): Anne Straily, Susan Montgomery

Infectious Agent

Toxoplasma gondii, an intracellular coccidian protozoan parasite, causes toxoplasmosis.

Transmission

T. gondii transmission occurs through ingestion of food, soil, or water contaminated with cat feces; ingestion of undercooked meat or shellfish; congenital transmission from a person infected during or shortly before pregnancy; and contaminated blood transfusions or organ transplantation.

Epidemiology

T. gondii is endemic throughout most of the world. Risk for infection is greater in developing and tropical countries, especially when people eat undercooked meat or shellfish, drink untreated water, or have extensive soil exposure. Congenital transmission also can occur if a person is infected shortly before becoming pregnant or during pregnancy.

Clinical Presentation

Incubation period is 5–23 days. Symptoms can include influenza-like symptoms or a mononucleosis syndrome with prolonged fever, elevated liver enzymes, lymphadenopathy, 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 often are asymptomatic, but eye disease, neurologic disease, or other systemic symptoms can occur, and cognitive deficits, learning disabilities, or visual impairments could develop later in life.

Diagnosis

Serologic tests for T. gondii antibodies are available at commercial diagnostic laboratories; because of the inherent difficulty in diagnosing acute toxoplasmosis, however, 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 who are not receiving appropriate prophylaxis, can be based on typical clinical course and identification of ≥1 mass lesion by CT or MRI. Biopsy might be needed to make a definitive diagnosis.

Treatment

Treatment is reserved for acutely infected immunocompromised or pregnant people and people with severe disease. The recommended treatment regimen includes pyrimethamine, sulfadiazine, and leucovorin (folinic acid). Alternative treatment regimens include pyrimethamine with atovaquone, azithromycin, or clindamycin, but these have not been studied extensively. For the acutely infected pregnant person, recommended treatment depends on the timing of infection during gestation; seek consultation with an infectious disease specialist before initiating therapy in these patients.

Prevention

Travelers should adhere to safe food and water precautions (see Sec. 2, Ch. 8, Food & Water Precautions). In addition, travelers should avoid direct contact with sand or soil that could be contaminated with cat feces; if caring for a cat, change the litter box daily. Immunocompromised or pregnant people should avoid changing cat litter, if possible, and should not adopt or handle stray cats. Travelers should wash hands with soap and water after gardening, after contact with sand or soil, and after changing cat litter.

CDC website: Toxoplasmosis