Diagnosis

Diagnosis of toxoplasmosis is usually made by detection of Toxoplasma-specific IgG, IgM, or IgA antibodies. There are several tests available that detect these immunoglobulin antibodies within several weeks of infection:

• dye test (DT)
• indirect fluorescent antibody test (IFA)
• enzyme immunoassays (ELISA, immunoblots)

If acute infection is suspected, the patient's serum should be tested for IgG and IgM Toxoplasma-specific antibodies. For a testing results algorithm, see CDC's DPDx Toxoplasmosis: Antibody Detection page.

Serologic tests are sometimes unreliable in immunosuppressed patients. Because of the persistence of Toxoplasma cysts and antibody in asymptomatic chronic latent infections, immunosuppressed persons with both positive PCR and serologic results should have their diagnostic testing results interpreted in relation to clinical features of an active infection. A negative PCR does not rule out active infection. PCR can also be performed on amniotic fluid which can be helpful in determining fetal infection following acute acquired infection of the mother.

Diagnosis can be made by direct observation of the parasite in stained tissue sections, cerebrospinal fluid (CSF), or other biopsy material. These techniques are used less frequently because of the difficulty of obtaining these specimens. Parasites can also be isolated from blood or other body fluids (for example, CSF) but this process can be difficult and requires considerable time.

Treatment

Treatment of immunocompetent adults with lymphadenopathic toxoplasmosis is rarely indicated; this form of the disease is usually self-limited. If visceral disease is clinically evident or symptoms are severe or persistent, treatment may be indicated for 2 to 4 weeks (adults: pyrimethamine 200 mg for one day as a loading dose, then 50-75 mg per day; plus sulfadiazine 1-1.5 g four times per day; plus folinic acid (leucovorin) 10-25 mg with each dose of pyrimethamine) followed by reevaluation of the patient's condition. Leucovorin protects the bone marrow from the toxic effects of pyrimethamine. If the patient has a hypersensitivity reaction to sulfa drugs,  pyrimethamine plus clindamycin can be used instead. The fixed combination of trimethoprim with sulfamethoxazole has been used as an alternative when the primary drugs of choice are unavailable.

Management of maternal and fetal infection varies depending on the treatment center. In general, spiramycin is recommended (for the first and early second trimesters) or pyrimethamine/sulfadiazine and leucovorin (for late second and third trimesters) for women with acute T. gondii infection diagnosed at a reference laboratory during gestation. PCR is often performed on the amniotic fluid at 18 gestation weeks to determine if the infant is infected. If the infant is likely to be infected, then treatment with drugs such as pyrimethamine, sulfadiazine, and leucovorin is typical. Congenitally infected newborns are generally treated with pyrimethamine, a sulfonamide, and leucovorin (see Montoya JG, Liesenfeld O. Toxoplasmosis . Lancet. 2004 Jun 12;363:1965-1976; for additional information regarding management in pregnant women, see Montoya JG, Remington JS. Management of Toxoplasma gondii infection in pregnancy. Clin Infect Dis 2008;47:554-566).

Persons with AIDS who are newly infected with T. gondii, or who have a recrudescence, need treatment that must be taken until a significant immunologic improvement is achieved as a result of antiretroviral therapy.

More on: Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents.