Why the US Should Screen for Toxoplasmosis During Pregnancy

Imagine discovering that your newborn has brain swelling, blindness and severe seizures. Then imagine being told that these devastating outcomes might have been avoided with a straightforward test for the widespread parasite Toxoplasma gondii.

People can acquire Toxoplasma wherever an infected cat has passed faeces, including litter trays, sandpits, gardens and yards. Infection can also result from drinking contaminated water or eating undercooked meat or shellfish.

For most people, the illness is mild and the infection can be controlled.

But when someone catches Toxoplasma for the first time during pregnancy, the parasite can pass through the placenta, leading to miscarriage or severe congenital abnormalities. This pregnancy-related transmission from parent to baby is known as congenital toxoplasmosis.

As many as 4,400 babies could be born with congenital toxoplasmosis in the US every year.

I am a professor of microbiology at the Indiana University School of Medicine, where my laboratory investigates Toxoplasma biology. Blood tests can track the level of Toxoplasma antibodies in the pregnant parent.

Rising levels signal that an acute infection is occurring, placing the fetus at risk of congenital toxoplasmosis. Yet giving anti-parasitic medicines promptly to pregnant people who develop toxoplasmosis can help shield the fetus from the most severe effects of congenital toxoplasmosis.

For decades, several countries, including France and Austria, have tested for and treated toxoplasmosis in pregnancy. Brazil has recently introduced a comparable programme.

In the US, however, Toxoplasma testing is not part of routine prenatal screening.

Why screen for toxoplasmosis during pregnancy?

Toxoplasma is both common and difficult to detect. More than 40 million American adults carry the parasite, illustrating how readily it can be acquired. Because infection generally produces no obvious symptoms, many parents of affected babies cannot remember when or where they were infected.

Research from several countries has shown the advantages of identifying and treating toxoplasmosis while a person is pregnant.

Toxogest, the first randomised clinical trial to examine the effectiveness and safety of treatment for reducing prenatal toxoplasmosis transmission, released its results in 2018. The study ended because funding ran out, but its findings indicated that treatment reduced not only transmission, but also the seriousness of disease in infections that occurred despite treatment.

A meta-analysis covering 33 studies published between 2017 and 2021 likewise found that pregnant women who received the antibiotic spiramycin had significantly lower parasite-transmission rates to their unborn child than untreated mothers.

For Dr. Jose Montoya, a toxoplasmosis clinician and researcher at Sutter Health's Remington Laboratory, screening has an evident benefit. "In countries that perform prenatal screening for toxoplasmosis, the severity of congenital toxoplasmosis is far less than what is routinely observed in the US," he said.

Congenital toxoplasmosis may be more common than believed

Some critics contend that congenital toxoplasmosis occurs too infrequently to justify prenatal testing. However, the US already screens for conditions rarer than toxoplasmosis, including phenylketonuria.

The true rate of congenital toxoplasmosis could also be underestimated. No national toxoplasmosis surveillance data are currently available because the infection is not nationally notifiable in the US. As most states neither track nor report infection during pregnancy, researchers cannot establish how many miscarriages are caused by Toxoplasma or how many children are affected.

A 2021 report from the Centers for Disease Control and Prevention drew attention to weaknesses in US toxoplasmosis surveillance. It stated that standardised, routine pregnancy testing would generate essential data for assessing the scale of this danger to babies. It would also help researchers investigate the reasons for the high US stillbirth rate, which has a disproportionate impact on Black women.

Researchers have cautioned that Toxoplasma prevalence could increase as free-range, organically raised foods become more popular and climate change continues.

Animals reared free-range are more likely to encounter infectious Toxoplasma oocysts in outdoor grazing areas and water supplies, where contamination with cat faeces is more likely. Higher temperatures and stronger climate change-driven storms encourage oocysts to persist and spread through the environment - for instance, as greater soil erosion contaminates waterways.

Furthermore, reports that unusually virulent Toxoplasma strains are moving from South America could worsen congenital toxoplasmosis infections in the US.

Costs of toxoplasmosis during pregnancy

"This disease not only has a steep physical and emotional cost, but also an important economic one," said Dr. Rima McLeod, director of the Toxoplasmosis Center at the University of Chicago.

In a 2011 study, McLeod estimated that adopting France's prenatal screening and treatment approach could save U.S. taxpayers US$620 per child, or $2.5 billion annually.

New technologies developed by researchers have also eased concerns about the cost of testing.

McLeod's team created a low-cost finger-prick test capable of detecting Toxoplasma in 30 minutes. Other scientists have developed a test based on saliva.

How to avoid toxoplasmosis

Toxoplasma causes substantial, lifelong neurological and visual impairments in hundreds of babies born in the US each year. Prenatal testing and treatment protocols that are safe and simple to carry out could largely reduce congenital toxoplasmosis.

"Those who conducted the Toxogest clinical trial did not incorporate a placebo control because it was deemed unethical not to monitor and treat congenital toxoplasmosis," Montoya said.

"But currently, pregnant people in the US are being relegated into such a placebo group – denied simple, low-cost procedures that could save their children from birth defects."

Until systematic prenatal testing for congenital toxoplasmosis is introduced, pregnant people can best protect themselves by paying close attention to risk factors. Anyone who is pregnant should avoid cleaning litter trays and other places where cats may have passed faeces. Fruit and vegetables should be washed before eating, and meat should be cooked to the correct temperature.

Bill Sullivan, Professor of Pharmacology and Toxicology, Indiana University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.