Pregnant women who have genital herpes infections have an increased risk of giving birth to a child with autism spectrum disorder, according to a new study.
The results, from researchers at Columbia University, are the first to link herpes simplex virus-2 — carried by more than 20% of women in the US — to autism in children. The study adds to a growing body of evidence that infections during pregnancy play a role in causing the disorder.
Though autism affects 1 of 68 children in the US, the causes behind most cases still remain unknown. Scientists have shown that there is a strong genetic component to autism, and suggested that infections during pregnancy also increase the risk of having the neurodevelopmental disorder.
“This is another really important piece of evidence showing that there is an association between infection during pregnancy and the risk for autism,” Kimberley McAllister, interim director of the Center for Neuroscience at UC Davis, who was not involved in the study, told BuzzFeed News.
(The authors of the study declined to speak to BuzzFeed News for this story.)
“This accumulating evidence that maternal infection poses this risk is something that we really need to start thinking about how to prevent,” McAllister said.
The study included 875 mothers who gave birth in Norway between 1999 and 2008. Analyzing blood samples drawn from mothers in the middle of their pregnancy and after they gave birth, the researchers searched for antibodies — generated by the body to fight infections — to several disease-causing agents including rubella virus, herpes simplex virus-1, and HSV-2.
They found that high levels of antibodies to HSV-2 were associated with more than double the risk for autism in boys, compared to mothers who did not have an infection during the pregnancy.
Though the effect was seen only in boys, this was likely due to the fact that the fewer girls with autism were included in the study.
“Fewer girls are diagnosed in general,” Alycia Halladay, chief science officer of the Autism Science Foundation, who was not involved in the study, told BuzzFeed News. “I’m not entirely convinced that the sex difference is really there.”
She also cautioned against exaggerating the results of the study. “The risk is still small — in the grand scheme of things, most kids who have mothers who have herpes won’t end up having autism,” she said.
It’s not clear why some infections increase the likelihood of having a child with autism. But the researchers suggest that it might be the mother’s own immune response, rather than the viruses themselves, causing the neurodevelopmental effects in babies.
“It may be the mom’s own response to the infection that’s actually priming the brain of the offspring for a greater likelihood of autism,” said McAllister, whose own work has shown that simulating viral infections in mice can cause changes in behavior and brain-wiring that mirror autism in humans.
“We’re trying to understand what that molecular pathway is, because if we do that then we can eventually go in and develop better treatments.”
Despite being disproven by dozens of studies in the last decade, the fact that vaccines have again been swept into the public conversation around causes of autism is deeply troublesome, Halladay said.
“There’s some sort of lingering obsession with vaccines and autism, and that’s a distraction from real causes like this,” said Halladay. “We need our eyes on the prize to think about the issues that really matter.”