Specialities - Infectious Disease

New Rapid Test for Toxoplasma Gondii Infection Shows Promise in Preventing Fetal Transmission and False Positives

May 2024

Specialities - Infectious Disease

New Rapid Test for Toxoplasma Gondii Infection Shows Promise in Preventing Fetal Transmission and False Positives

May 2024

A breakthrough in the detection of infections caused by the parasite Toxoplasma gondii offers an inexpensive and highly accurate diagnostic test that can deliver results within 30 minutes from a finger-prick in a doctor's office or within an hour from a small blood sample tested in a local laboratory. This new test, developed by LDBIO Diagnostics of Lyon, France, is designed to identify false positives in other commercial diagnostic tests for toxoplasmosis, providing quick reassurance to uninfected pregnant women and their doctors and enabling timely interventions to protect fetuses in acutely infected mothers.

These findings are highlighted in a study led by toxoplasmosis specialist Dr. Rima McLeod, Professor of Ophthalmology and Visual Science and Pediatrics at the University of Chicago, published on May 23, 2024, in PLOS Neglected Tropical Diseases.

“By using this approach and test to monitor pregnant women monthly for Toxoplasma infections, beginning before or very early in pregnancy, we can help prevent infections of their babies,” stated Dr. McLeod. “This test can also contribute to solving the problem of false positives from other Toxoplasma tests, inexpensively, which can help reassure pregnant women and their doctors.”

Early detection of T. gondii in previously uninfected pregnant women is crucial for minimizing the damage of toxoplasmosis in unborn babies. Without proper diagnosis and treatment, acute toxoplasmosis in a fetus can be fatal or lead to premature birth, noted co-corresponding author Dr. Martine Wallon of the Institut des agents infectieux and Hôpital de la Croix-Rousse in France. In newborns, the infection can cause severe complications, including microcephaly, hydrocephalus, brain damage, and organ inflammation.

Prompt diagnosis and treatment can eliminate the risk of brain damage, emphasized co-author Jorge Gómez-Marín from the University of Quindio in Colombia.

The Toxoplasma ICT IgG-IgM point-of-care diagnostic test utilizes immuno-chromatographic paper, similar to the color-changing tests used for Covid-19, to deliver rapid results. The research team recommends that uninfected women should have their antibody status tested monthly during pregnancy, starting before the 12th week and continuing 4 to 6 weeks after delivery.

The study analyzed 12 new individual studies conducted by researchers in the United States, France, and Colombia. These studies assessed the feasibility of using the ICT in various clinical settings and examined the perceptions of patients, families, and health care workers.

“The ICT and gestational screening are well-received by patients, providers, and policymakers, suggesting it may become a valuable part of standard obstetrical practice,” Dr. McLeod said.

The ICT also serves as a back-up diagnostic tool to detect false positive results in standard commercial tests for IgM antibodies. The research compiled new and previous studies from multiple institutions, including the University of Chicago, Stanford University, and the Palo Alto Medical Foundation, and from countries such as France, Morocco, and Tunisia. The test demonstrated more than 97.5% sensitivity with blood samples and 99% sensitivity with serum, along with 100% specificity across various settings and populations. Over 5,500 individual samples were tested in conjunction with more than 20,000 separate assays using reference laboratory comparator tests, revealing the ICT's superior performance compared to other non-specialty reference laboratory tests.

Despite eight U.S. states requiring the reporting of toxoplasmosis cases to the CDC, routine screening for T. gondii in pregnant women is not common practice. In contrast, France and Austria have found cost-effective benefits in screening pregnant women for toxoplasmosis. The test, costing between $4 to $10, meets all World Health Organization ASSURED criteria and is already in use in several countries, including Martinique, French Guiana, and Morocco.

“Testing should be supervised by a knowledgeable health care provider because understanding the implications of the results requires medical knowledge of this disease and its treatment,” Dr. McLeod advised. “Proper use is critical since lifelong consequences of this infection are so significant for a family.”

Toxoplasma gondii spreads through parasites initially developed in cat intestines and excreted in cat feces, contaminating soil, water, and food. The parasite can also be contracted by consuming undercooked meat. Epidemics of highly virulent new strains are occurring in North and Latin America among humans and wildlife. Once established in the human body, T. gondii can survive in the brain in a latent, currently untreatable stage, potentially causing or exacerbating illnesses not previously linked to the infection.

By identifying seronegative women before pregnancy and diagnosing acute toxoplasmosis promptly in pregnant women, U.S. physicians can treat the infection before it affects the fetus. The test is also valuable in ophthalmology and neurology, where the parasite can cause significant damage to the eyes and brain.

The researchers hope that the new test will lead to more effective screening and treatment protocols, ultimately improving outcomes for mothers and their babies.