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Toxoplasma gondii usually causes encephalitis in patients with AIDS and a CD4 count of less than 100 cells/ÁL, often in the absence of prophylactic therapy for PCP with TMP-SMX. The host for the toxoplasma parasite is the cat; intermediate hosts include cows, sheep, pigs, eggs, and man. Infection occurs by ingestion of cat feces and rare meat.

Prevention of Toxoplasmosis. Toxoplasmosis can be prevented by not consuming rare meat, avoidance of sand boxes (where cat feces may be present) and litter boxes, and by washing of hands after handling cats.

Clinical Evaluation of Fever and CNS Symptoms

Toxoplasmosis occurs in 5-10% of patients with AIDS, presenting with fever, altered mentation, seizures, and focal neurologic signs that develop subacutely over a few days. It is the most common cause of isolated CNS disease in HIV-infected patients.

Patients are more likely to have toxoplasmic encephalitis if they have a positive T. gondii serology (IgG antibody) and have at least two focal cerebral lesions on MRI or CT (a single lesion has a high probability of being due to lymphoma rather than to T. gondii).

A negative toxoplasmosis extremely antibody titer makes the diagnosis of toxoplasmosis encephalitis unlikely. The false negative rate of the antibody titer is only 1-2%. A brain biopsy to exclude lymphoma is necessary in these patients.

Patients who have responded both clinically and radiologically to 7 days of treatment are also more likely to have toxoplasmosis.

Toxoplasmosis may also cause pulmonary infection and disseminated disease (presenting as severe sepsis and a positive