Are autism and herpes linked?

Women actively infected with genital herpes during early pregnancy had twice the odds of giving birth to a child later diagnosed with autism spectrum disorder (ASD).

This is according to a study by scientists at the Center for Infection and Immunity at Columbia University’s Mailman School of Public Health and the Norwegian Institute of Public Health.

The study found an association between maternal anti-herpes simplex virus-2 (HSV-2) antibodies and risk for ASD in offspring.

What causes it?

“We believe the mother’s immune response to HSV-2 could be disrupting foetal 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.

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The authors do not believe that the risk is due to direct infection of the foetus because such infections are typically fatal. Instead, they suggest that neurodevelopmental outcomes are due to primary or reactivation of infection in mothers with inflammation in close proximity to the womb.

What is genital herpes?

HSV-2, also known as genital herpes, a highly contagious and lifelong infection usually spread through sex.

After an initial outbreak, HSV-2 virus lives in nerve cells and is often inactive, with flare-ups occurring with diminishing frequency as the body builds up immunity to the virus.

The study

The researchers sought to explore the link between maternal infection and risk for autism, focusing on five pathogens known collectively as ToRCH agents – toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex viruses type-1 and -2 – to which exposure during pregnancy can lead to miscarriage and birth defects.

Women actively infected with genital herpes during early pregnancy had twice the odds of giving birth to a child later diagnosed with autism spectrum disorder

They examined blood samples from 412 mothers of children diagnosed with ASD and 463 mothers of children without ASD enrolled in the Autism Birth Cohort (ABC) Study overseen by the Norwegian Institute of Public Health. Samples were taken at two specific times – at around week 18 of pregnancy and at birth – and analysed for levels of antibodies to each of the ToRCH agents.

They found high levels of antibodies to HSV-2, not any of the other agents, correlated with risk for ASD.

This link was only evident in blood samples taken at a time point reflecting exposure during early pregnancy when the foetal nervous system undergoes rapid development, not at birth. The finding mirrors earlier epidemiological data indicating that activation of the maternal immune system during early-to-mid-pregnancy is associated with long-term developmental and behavioural problems in offspring.

In all, 13 percent of mothers in the study tested positive for anti-HSV-2 antibodies at mid-pregnancy. Of these, only 12 percent reported having HSV lesions before pregnancy or during the first trimester, a likely indication that most infections were asymptomatic.

“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. “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.”

Source: Columbia University’s Mailman School of Public Health. Sciencedaily.com

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