Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1433 page)

TOXOPLASMA SEROLOGY SCREEN (
TOXOPLASMA GONDII
, IgG AND IgM)

   Definition

   
Toxoplasma gondii
is an obligate intracellular parasite capable of infecting most mammals, including humans. Toxoplasmosis usually is asymptomatic, but primary infection during pregnancy can result in congenital disease. The domestic cat is the only definitive host for
T
.
gondii
and is the reservoir of the infective oocysts that are passed in the feces. Human infection may be acquired by consuming cysts in uncooked or undercooked meat of infected animals or by contact with oocysts from the feces of an infected cat.

   Acute
Toxoplasma
infection can pose a serious threat to immunocompromised individuals and newborns who acquire the infection in utero. Immunosuppressed patients may develop encephalitis, myocarditis, or pneumonitis. Congenital infections usually result as a consequence of asymptomatic acute maternal

infection. This infection can cause premature delivery, spontaneous abortion, or stillbirth.

   Management of toxoplasmosis requires serologic monitoring of infected individuals, as the organism is not readily available for culture.

   
Normal range:
Negative.

   Use

   Aids in the diagnosis of toxoplasmosis.

   First-line test in endemic areas for identifying
T
.
gondii
infection in pregnant women.

   Testing for the presence of
Toxoplasma
IgG can be useful to determine prior infection and indicate reactivation of the infection.

   Testing for the presence of
Toxoplasma
IgM is useful to determine acute infection.

   Interpretation

   Positive in
Toxoplasma
infection.

   Individuals infected with the
Toxoplasma
organism typically exhibit detectable levels of IgM antibody immediately before or soon after the onset of symptoms. IgM titers normally decline within 4–6 months but may persist at low levels up to a year. Patients with active
Toxoplasma
chorioretinitis usually have undetectable levels of IgM.