Toxoplasma gondii is considered to be a significant pathogen of man and animals. T. gondii
is an obligate intracellular protozoan parasite, a coccidian, with worldwide distribution. In the
United States, serological studies have shown the incidence of antibody to T. gondii to range from
3% to 40% depending on the age group and geographic area surveyed. Toxoplasmosis in the
immunocompetent individual is usually asymptomatic. Acute infection induces both humoral and
cell-mediated immune responses which control the infection. With the appearance of the immune
response, certain of the toxoplasma organisms become encysted. There is little or no evidence
of host response to the cysts and they may remain dormant for many years. When toxoplasma infection
is acquired during pregnancy, there is a significant risk of infection to the fetus. It is generally
agreed that congenital infection takes place only when acute infection is acquired during pregnancy.
Women who have serological evidence of toxoplasma infection prior to becoming pregnant, rarely,
if ever, have infected neonates. It is the seronegative woman who becomes infected and seroconverts
during pregnancy who may give birth to an infected infant.
Toxoplasmosis has emerged as a serious complication in the immunocompromised host, particularly
in patients undergoing immunosuppressive therapy. These individuals exhibit more severe infections
upon primary exposure than do normal individuals and, if chronically infected, are more likely to
undergo endogenous reinfection. Primary infection with T. gondii is accompanied by the production
of antibody reactive with the organism. Antibodies of the IgM class appear within the first week
following infection, peak in 3 to 4 weeks, and generally become undetectable within 3 to 4 months.
Exceptions to this general pattern of IgM production have been noted in the form of early (3 week)
loss of detectable IgM or persistence of low titers of IgM for one year or more. IgG antibody to
toxoplasma usually becomes detectable within 3 weeks following primary infection and peaks between
2 to 6 months, depending on the serological test used for detection. Once peak titers occur,
they decrease slowly and persist at detectable levels throughout life. Serological tests are the
primary method used to diagnose toxoplasma infection. Several serological assays may be used to
demonstrate toxoplasma antibody, including the Sabin-Feldman dye test, the complement fixation test,
the indirect hemagglutination test, and the indirect immunofluorescent antibody (IFA) test.
Excellent correlation exists between relative titers obtained in the IFA test and those obtained
using the longer, more laborious procedures. In addition, the IFA test detects both IgG and
IgM-class antibody. If the test is positive using antihuman IgG, a monospecific antihuman IgM
fluorescein conjugate may be employed to distinguish the early antibody response characteristic
of primary infection.
ImmunoDOT TORCH test also includes a Toxoplasma gondii IgG dot as indicated in TORCH IgG testing.
This analyte is included as part of a comprehensive prenatal screening protocol. ImmunoDOT TORCH
test offers a simple simultaneous determination of the antibody status for the most common TORCH analytes.
GenBio also manufactures the indirect immunofluorescent antibody (IFA) tests, ImmunoFA Toxoplasma
gondii IgG test and ImmunoFA Toxoplasma gondii IgM test for the detection and titration of IgG
antibodies to Toxoplasma gondii in human serum.