Autism rates are increasing faster than our understanding of what causes the disorder, but a new study may help even the score. The research suggests that autism risk may be influenced by a viral infection, in addition to genetic and environmental factors. The report found that women with herpes simplex 2, the virus that causes most cases of genital herpes infections, had increased risk of giving birth to a child with autism spectrum disorder, although the precise reason for this remains unclear.

The study, now published online in MSphere by researchers from Columbia University, found that high levels of antibodies to HSV-2 were associated with more than double the risk for autism in children, compared to mothers who did not have an infection during their pregnancy, Buzzfeed News reported. This risk was only seen in male children, not girls.

Read: Herpes Symptoms In Men: Painful Sores, Swollen Lymph Nodes, And Other Signs

"We believe the mother's immune response to HSV-2 could be disrupting fetal central nervous system development, raising risk for autism," said lead author Milada Magic in a recent statement on ScienceDaily.

For the study, the team followed 875 mothers (412 mothers of children diagnosed with ASD and 463 mothers of children without ASD) who gave birth in Norway between 1999 and 2008. Blood samples were drawn from mothers both in the middle of their pregnancy and after they gave birth. Although the researchers analyzed the presence of several different antibodies in the mother’s blood, such as toxoplasma gondii, rubella virus, cytomegalovirus, the presence of HSV-2 was the only virus associated with increased ASD risk.

While HSV2 causes genital herpes, it is possible to carry antibodies for the virus without ever having a herpes outbreak. In fact, of the13 percent of mothers who tested positive for HSV-2 antibodies at mid-pregnancy, only 12 percent had ever had genital herpes symptoms in their life. According to the study, this shows that most HSV-2 infections are asymptomatic, meaning that women may carry the infection without ever realizing it.

As for the lack of ASD risk observed in girls, the team believe this may be due to the small amount of girls involved in the study. ASD is more common in males, and there simply may not have been enough girls with ASD involved in the study to show an accurate connection. However, this does not mean that HSV-2 is gender specific in its ASD risk.

In addition, the researchers emphasize that HSV-2 may be one of many risk factors contributing to ASD risk.

"The cause or causes of most cases of autism are unknown," said senior author W. Ian Lipkin in a statement. "But evidence suggests a role for both genetic and environmental factors. Our work suggests that inflammation and immune activation may contribute to risk. Herpes simplex virus-2 could be one of any number of infectious agents involved."

The findings could have important implications, seeing that as many as one in four American women are believed to be infected with HSV-2, Just Herpes reported. Of these, only about 20 percent will ever experience an outbreak. More research will be done to further investigate the connection between HSV-2 and ASD.

Source: Mahic M, Mjaaland S, Bovelstad HG, et al. Maternal Immunoreactivity to Herpes Simplex Virus 2 and Risk of Autism Spectrum Disorder in Male Offspring. mSphere . 2017

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