Eating Raw Meat Tied to Toxoplasmosis in Japan

SAN FRANCISCO -- Toxoplasmosis was uncommon in a study of pregnant women in Japan, but infection occurred most often in a region where people often eat raw meat, researchers reported here.

About 2% of pregnant women had a history of Toxoplamsa gondii infection and one in 1,000 women may be at risk of becoming infected during pregnancy, but no infants in the study tested positive, according to Hiroyuki Moriuchi, MD, of Nagasaki University.

Some of the women who contracted T. gondii reported gardening or farming, but only one had a pet cat, he said at the Pediatric Academic Societies meeting here.

The protozoan parasite that causes toxoplasmosis is common worldwide, and the CDC estimates that more than 30 million people in the U.S. may be infected. Risk factors include eating under-cooked meat and contact with cat feces or contaminated soil.

"In the public perception cats are far over-emphasized as a cause of toxoplasmosis," Joshua Wolf, MBBS, from St. Jude Children's Research Hospital, who moderated the session, told MedPage Today. "Although cat litter exposure is frequently thought of as an important risk factor for toxoplasmosis, and should be avoided in pregnancy, consumption of rare meat is much more commonly the cause."

A healthy immune system can usually keep T. gondii under control, but it can cause severe illness in immunocompromised individuals. The parasite can cross the placenta and lead to cognitive and motor dysfunction in babies born to women infected during pregnancy.

Moriuchi's group looked at the prevalence of T. gondii infection among pregnant women, and congenital toxoplasmosis among their infants, in Nagasaki prefecture in Japan.

Between August 2014 and October 2016, all pregnant women in the city of Nagasaki and the island town of Gotoh were given an educational brochure about toxoplasmosis prevention and tested for T. gondii IgM and IgG antibodies by ELISA assay.

Women who tested positive for both IgM and IgG were assessed for antibody avidity. Low IgG avidity indicates probable new infection, while high avidity shows prior infection (as does isolated IgG positivity). Women who were only IgM positive were retested two weeks later.

Women with suspected primary infection were treated with spiramycin, which can prevent mother-to-child transmission of T. gondii. Their infants were repeatedly evaluated for congenital toxoplasmosis through 12 months, including serological tests, eye exams, and brain imaging. Those with abnormal findings or persistently positive IgG were treated with pyrimethamine, sulfadiazine, and leucovorin.

The study included 7,789 pregnant women, with an average age of 30.5 years. Most tested negative for both T. gondii IgM and IgG. However, 95 women (1.2%) tested positive for IgG only, 28 (0.36%) tested positive for IgM only, and 56 (0.72%) tested positive for both. Therefore, 1.9% had a history of T. gondii infection, Moriuchi said.

Twenty-one women were both IgM and IgG positive and had low IgG avidity, suggesting new infection; all were given spiramycin. None of the women with isolated IgM positivity became IgG positive during follow-up.

The prevalence of IgG positivity increased over time, reaching 3.2% among women age 40 or older, and with higher parity, reaching 3.5% among those who had three or more children. Based on these numbers, Moriuchi estimated that the annual seroconversion rate was 0.13%, suggesting that one in 1,000 women may contract T. gondii during pregnancy.

Looking at location, the researchers found that about a third of the women with evidence of current or past T. gondii infection were from the southern Kyushu area, southeast of the city of Nagasaki. A previous study of pregnant women in Miyazaki prefecture in this area showed a prevalence of 20.5% in the oldest age group, according to Moriuchi.

People in that region like to eat raw meat, including horse meat and chicken, he said. Among the 21 women with suspected new infection, 14 (67%) reported eating raw or under-cooked meat, four (19%) reported gardening or farming, one (5%) worked at a restaurant, and one (5%) had a cat.

Of these women, 16 had given birth, one had an induced abortion, and four were still pregnant. Ten of the babies tested negative for T. gondii infection, while the other six were asymptomatic and awaiting final test results.

"Until now, no infant has been shown to be congenitally infected with T. gondii, hopefully due to spiramycin therapy," Moriuchi's group concluded.

Wolf said the study shows that "although maternal toxoplasma infection is rare, there is an opportunity to intervene in early pregnancy and potentially affect transmission" by educating women about risk factors.

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