POC test offers low-cost way to screen for toxoplasmosis during pregnancy

Prenatal Testing Nhgri Flickr
NHGRI via Flickr. Credit: Ernesto del Aguila III

Gestational screening programs might benefit from a new clinical laboratory point-of-care (POC) diagnostic test that hunts for a toxoplasmosis-causing parasite that can be transmitted during pregnancy.

Toxoplasmosis is a zoonotic parasitic disease that represents a danger to pregnant women with compromised immune systems, according to the Centers for Disease Control and Prevention (CDC). Caused by a single-celled parasite called Toxoplasma (T.) gondii, toxoplasmosis is a foodborne illness but can also be caught from infected cat feces, according to the CDC.

Congenital T. gondii infections often have no symptoms at birth, but infected children can develop symptoms such as vision and neurological problems, according to the CDC.

However, a University of Chicago research team, whose latest collection of T. gondii studies was published May 28 in the journal Plos Neglected Tropical Diseases, has been testing a new lateral immunochromatographic test (ICT) for serum and whole-blood samples. The test is designed to enable diagnosis within an hour and could potentially allow early treatment of T. gondii to prevent toxoplasmosis complications such as microcephaly, hydrocephalus, damage and inflammation in the brain, heart, lungs, and eyes, and liver and spleen enlargement, according to the researchers.

Developed by French-based LDBIO Diagnostic, the Toxoplasma ICT IgG-IgM test captures IgG and/or IgM antibodies. What makes this test different from predicate tests, according to Ying Zhou, Karen Leahy, Andrew Grose, Dr. Joseph Lykins, and others affiliated with the University of Chicago departments of ophthalmology and visual science, is that "the ICT identifies likely false positives or raises suspicion that a result is truly positive."

The researchers suggested that incorporating the test into monthly gestational screening programs could have a "14-fold cost savings" for care, but would only cost between $4 and $10 each.

Presence of a positive ICT makes it likely that IgM is truly positive, and a negative ICT makes it likely that IgM will be a false-positive without infection, according to Zhou and colleagues who penned the article for Plos. These results create a new paradigm for rapid diagnosis and validation of results with a second-line test, they said.

For a University of Chicago blog article, toxoplasmosis specialist Dr. Rima McLeod, professor of ophthalmology and visual science and pediatrics at the University of Chicago, said the test is useful for early toxoplasmosis intervention.

"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," McLeod said. "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."

The researchers noted that starting as early as possible, uninfected women should have their antibody status tested once a month during pregnancy, beginning before the twelfth week and then four to six weeks after delivery. The tests would involve a finger prick in a doctor's office or blood sample collected by a local medical laboratory. Positive results influencing clinical care would still require clinical reference laboratory confirmation.

The Plos paper includes collation of the new, previously unpublished research with earlier studies from the University of Chicago, Stanford University, and the Palo Alto Medical Foundation in the U.S., France, Morocco, and Tunisia. The latest research analyzes 12 new individual studies conducted by scientists in the U.S., France, and Colombia.

Researchers examined the feasibility of using the ICT in multiple clinical circumstances and types of medical care as well as how it was perceived by patients, families, and frontline healthcare workers. Previous research in 2017 and 2018 provided the proof-of-principle studies demonstrating that the ICT could perform accurately with serum and whole blood, according to the researchers.

“Testing should be supervised by a knowledgeable healthcare provider because understanding the implications of the results requires medical knowledge of this disease and its treatment," McLeod said.

Toxoplasmosis is not a nationally notifiable illness in the U.S., according to the CDC, so no national level surveillance data are available. However, the researchers noted that eight states do require reporting toxoplasmosis cases to the CDC.

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