Why the US Should Screen for Toxoplasmosis During Pregnancy

Imagine discovering that your baby has been born with brain swelling, blindness and disabling seizures. Then imagine finding out that these devastating problems might have been avoided through a straightforward test for the common parasite Toxoplasma gondii.

People can acquire Toxoplasma wherever an infected cat has passed faeces, including from litter trays, sandpits, gardens or 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 brought under control.

But when a person becomes infected for the first time during pregnancy, Toxoplasma can pass through the placenta, causing miscarriage or severe birth abnormalities. This transmission from mother to child during pregnancy is known as congenital toxoplasmosis.

As many as 4,400 babies could be born with congenital toxoplasmosis in the United States each year.

As a professor of microbiology at the Indiana University School of Medicine, I investigate the biology of Toxoplasma in my laboratory. Blood tests can track levels of Toxoplasma antibodies in the parent.

Rising levels signal an acute infection, placing the foetus at risk of congenital toxoplasmosis. Yet, giving anti-parasitic medicines promptly to pregnant people who develop toxoplasmosis can help shield the foetus from the most serious consequences of congenital toxoplasmosis.

Countries including France and Austria have screened for and treated toxoplasmosis in pregnancy for decades. Brazil has recently introduced a comparable programme.

Nevertheless, Toxoplasma testing is not part of routine prenatal screening in the United States.

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 mothers of infected babies cannot remember when or where they caught it.

Research from several countries has shown the advantages of identifying and treating toxoplasmosis during pregnancy.

Toxogest, the first randomised clinical trial to examine the safety and effectiveness of treatment aimed at reducing prenatal toxoplasmosis transmission, reported its results in 2018. While funding shortages stopped the trial, its findings indicated that treatment reduced both infection transmission and disease severity among breakthrough infections.

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

For Dr. Jose Montoya, a toxoplasmosis clinician and researcher at the Remington Laboratory at Sutter Health, the benefit of screening is unmistakable. "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

Critics have suggested that congenital toxoplasmosis is too uncommon to justify prenatal testing. However, the United States already screens for conditions that occur even less frequently than toxoplasmosis, including phenylketonuria.

The rate of congenital toxoplasmosis may also be undercounted. No national toxoplasmosis surveillance data currently exist because it is not a nationally notifiable disease in the United States. As most states neither track nor report infection during pregnancy, researchers cannot determine how many miscarriages are caused by Toxoplasma or how many children are affected by the infection.

A 2021 report from the Centers for Disease Control and Prevention drew attention to weaknesses in US toxoplasmosis surveillance, noting that routine, standardised testing in pregnancy would generate vital data for assessing the scale of this risk to babies. It would also help researchers understand the reasons behind the high rate of stillbirths in the United States, which disproportionately affect Black women.

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

Animals raised free-range are more likely to encounter infectious Toxoplasma oocysts in outdoor pasture and water supplies, where contamination with cat faeces is more probable. Higher temperatures and stronger storms linked to climate change encourage oocysts to persist and spread in the environment – including when greater soil erosion contaminates waterways.

Reports also suggest that unusually virulent Toxoplasma strains moving from South America could worsen congenital toxoplasmosis infections in the United States.

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 model of prenatal screening and treatment could save U.S. taxpayers US$620 per child, or $2.5 billion annually.

Researchers have also created new technologies that lessen concerns over testing costs.

McLeod's team produced a low-cost finger-prick test that identifies Toxoplasma in 30 minutes. Other researchers have developed a saliva-based test as well.

How to avoid toxoplasmosis

Toxoplasma causes substantial, lifelong neurological and visual impairment in hundreds of babies born in the United States every 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 only remain alert to the risk factors. Those who are 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 products 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.