Today one in 42 boys is diagnosed with Autism Spectrum Disorder. Girls are less likely to receive the diagnosis.
Scientists don't know what causes it, but new research points to a specific virus that becomes active in the mother during a certain time during her pregnancy.
Women with active infections of herpes simplex virus type 2 during pregnancy had twice the odds of giving birth to a child who was later diagnosed with autism. This, according to research from Columbia University where scientists discovered the virus, also called genital herpes, was most problematic if the flare-up occurred in the beginning stages of pregnancy.
"We believe the mother's immune response to HSV-2 could be disrupting fetal central nervous system development, raising risk for autism," says lead author Milada Mahic, a post-doctoral research scientist with the Center for Infection and Immunity and the Norwegian Institute of Public Health.
One in five American women carries herpes simplex virus type 2. It's contracted sexually, and stays in the body for life: sometimes active, sometimes inactive. Symptoms include blisters and sores but often there are no symptoms, so many people don't even know they have it.
Researchers in this study relied on blood samples during pregnancy to detect active infection. Later, when the children of more than 400 of those women were diagnosed with Autism Spectrum Disorder, their mothers' blood samples from pregnancy were compared to the blood samples from pregnancy during of approximately 400 mothers from the same study who gave birth to children who were not later diagnosed with ASD.
Researchers discovered a direct correlation to autism if the pregnant women had HSV-2 in the early stages of pregnancy. Scientists looked at the possibility of links between autism and other types of viruses such as herpes simplex virus type 1 and rubella but found none.
According to the authors, further study is needed to determine if screening and suppression of HSV-2 infection during pregnancy is needed.
"The cause or causes of most cases of autism are unknown," says senior author W. Ian Lipkin, director of the Center for Infection and Immunity and the John Snow Professor of Epidemiology at Columbia's Mailman School. "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."