What are the diagnostic tests for toxoplasmosis (Toxoplasma gondii infection)?

From the Guidelines

Testing for toxoplasmosis in pregnant women should involve screening for both Toxoplasma IgG and IgM antibodies, as recommended by the PAMF-TSL, to capture cases of early seroconversion and prevent congenital toxoplasmosis 1. The most common tests for toxoplasmosis include IgG and IgM antibody tests, which detect antibodies produced in response to Toxoplasma gondii infection.

• A positive IgM antibody test suggests recent infection, while a positive IgG test indicates past infection and immunity.
• For pregnant women, testing is particularly important as toxoplasmosis can cause serious birth defects if transmitted to the fetus.
• Testing is recommended for pregnant women who have been exposed to cat feces, consumed undercooked meat, or show symptoms like swollen lymph nodes and flu-like illness.
• For immunocompromised patients, testing is also crucial as they're at higher risk for severe disease. Some key points to consider when testing for toxoplasmosis include:
• The timing of infection matters greatly in pregnancy, with first-trimester infections posing the highest risk to the fetus but being less likely to transmit, while third-trimester infections transmit more frequently but typically cause less severe disease.
• If IgM antibodies are detected, additional tests like PCR of amniotic fluid may be recommended for pregnant women to determine if the fetus is infected.
• Treatment decisions are based on test results, with pyrimethamine, sulfadiazine, and leucovorin being the standard treatment regimen for active infection, as noted in a study on treating opportunistic infections among HIV-exposed and infected children 1. It's also important to note that:
• The PAMF-TSL panel for pregnant women at ≤16 weeks of gestation includes Toxoplasma IgG and IgM tests, as well as the Toxoplasma IgG-avidity test 1.
• For women at a gestational age of >16 weeks, the PAMF-TSL panel includes Toxoplasma IgA ELISA, the Toxoplasma IgE ELISA, and the Toxoplasma IgG-avidity test 1.
• A study published in 2017 discussed the diagnosis, treatment, and prevention of congenital toxoplasmosis in the United States, highlighting the importance of testing and treatment for pregnant women 1.

From the Research

Testing for Toxoplasmosis

• Toxoplasmosis is a serious infection that can be transmitted from mother to fetus during pregnancy, potentially causing severe neurological or ocular disease, as well as cardiac and cerebral anomalies 2.
• Routine universal screening for toxoplasmosis is not recommended for pregnant women at low risk, but serologic screening should be offered to those considered to be at risk for primary Toxoplasma gondii infection 2.
• Several commercial immunoassays are available for detecting immunoglobulin G (IgG) and IgM antibodies to Toxoplasma gondii, including the Behring Diagnostics OPUS Toxo G and Toxo M, Abbott Diagnostics IMX Toxo-IgG 2.0 and Toxo-IgM, and bioMérieux Vitek VIDAS Toxo IgG and IgM 3.
• Enzyme-linked immunosorbent assay (ELISA) can be used to determine IgG, IgM, and IgA antibody responses in human toxoplasmosis, with IgM antibodies appearing during the earliest phases of infection and disappearing within 1-6 months 4.
• The dot enzyme-linked immunosorbent assay (Dot-ELISA) and ELISA have been compared with the immunofluorescent antibody test (IFA) for detection of IgM- and IgG-specific antibodies to human toxoplasmosis, with the Dot-ELISA correlating well with the IFA test 5.

Diagnosis and Treatment

• Suspected recent infection in a pregnant woman should be confirmed before intervention by having samples tested at a toxoplasmosis reference laboratory, using tests that are as accurate as possible and correctly interpreted 2.
• Amniocentesis should be offered to identify Toxoplasma gondii in the amniotic fluid by polymerase chain reaction (PCR) if maternal primary infection is diagnosed, or if serologic testing cannot confirm or exclude acute infection 2.
• Spiramycin should be offered for fetal prophylaxis to prevent spread of organisms across the placenta from mother to fetus, and a combination of pyrimethamine, sulfadiazine, and folinic acid should be offered as treatment for women in whom fetal infection has been confirmed or is highly suspected 2.