TOXO IgM Reagent – Jaj International

Toxoplasma gondii is an obligate intracellular parasite capable of infecting a wide variety of intermediate hosts including man (see reference 1 for a comprehensive review of toxoplasmosis). Infected definitive hosts (cats) shed oocysts in feces which rapidly mature in soil and become infectious. When ingested by intermediate hosts, tachyzoites form and multiply rapidly with eventual development of cysts containing the slower growing, but infectious bradyzoites.

Thus, toxoplasmosis is acquired by man via ingestion of cat feces or undercooked meats infested with cysts. Infection of the normal adult is commonly asymptomatic. In those cases with clinical manifestations, the most common of the symptoms is lymphadenopathy which may be accompanied by an array of other symptoms making differential diagnosis difficult.

On the other hand, severe to fatal infections do occur in adults immunocompromised by cancer chemotherapy or immunosuppressive treatment and in patients with AIDS. Infections in the immunocompromised adults are thought to be reactivation of latent acquired infections and usually involve the central nervous system although involvement of other sites has been reported.

Transplacental transmission of the parasite resulting in congenital toxoplasmosis can occur during the acute acquired maternal infection. The risk of fetal infection is a function of time at which acute maternal infection occurs during gestation. Maternal infections acquired before conception present very little, if any, risk to the fetus. However, the incidence of congenital toxoplasmosis increases as pregnancy progresses; conversely, the severity of congenital toxoplasmosis is greatest when maternal infection is acquired early during pregnancy.

A majority of infants infected in utero are asymptomatic at birth, particularly if maternal infection occurs during the third trimester, with sequelae appearing later in life. Congenital toxoplasmosis results in severe generalized or neurologic disease in about 20-30% of the infants infected in utero; approximately 10% exhibit ocular involvement only, and the
remainder (about 70%) are asymptomatic at birth. Subclinical infection may result in premature delivery and subsequent neurologic, intellectual, and audiologic defects.

Prospective studies of pregnancies have shown that prenatal diagnosis of infection followed by prenatal therapy reduces the frequency and the severity of congenital toxoplasmosis. Serologic tests can be used to identify those pregnancies at risk; women who are seronegative at the time of diagnosis of pregnancy can be monitored during pregnancy.

Seroconversion is indicative of T. gondii infection and establishes gestational age when maternal infection occurred. Serologic tests specific for T. gondii IgM antibodies are useful aids in the diagnosis of both congenital and acute acquired toxoplasmosis. Levels of IgM antibody increase rapidly following acute acquired infections and begin to decline after several months but can persist at detectable levels for a year or more.19-21 Since persisting IgM levels may be detected
long after the onset of acquired infection, the use of a single serological test result must be used with caution in those cases when it is critical to establish the time of infection.

This applies to the diagnosis of acute T. gondii infection acquired during pregnancy. Determination of the date of infection based solely on the results of detectable IgM antibody to T. gondii is not recommended. That determination should include clinical history and previous serology, since low levels of IgM antibody may persist for a year or more.19-21 The use of a test to determine a rise in IgG antibody to T. gondii may provide additional information as to the date of infection. The AxSYM Toxo IgM assay is a method for the measurement of T. gondii specific antibodies in human serum and plasma (EDTA, heparin or sodium citrate).

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