Herpes doubles autism risk

New research suggests that women with genital herpes carry an increased risk of giving birth to a child with autism spectrum disorder. Jana Howden reports.

Electron micrograph of herpes simplex virus that can cause genital lesions and is now being linked to autism.
Lester V. Bergman/Getty Images

Women with genital herpes – a sexually transmitted disease affecting about one in five American females – have twice the odds of giving birth to a child with autism spectrum disorder, according to new research published in mSphere.

Antibodies to herpes simplex virus type 2, otherwise known as genital herpes, were found in blood samples taken from women during early pregnancy whose children were later diagnosed with autism spectrum disorder.

Led by a team of scientists from Columbia University in the US and the Norwegian Institute of Public Health, the research is the first to provide immunological evidence for the link between herpes infection during pregnancy and autism.

"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.

Autism spectrum disorder is a lifelong developmental condition that impacts a person’s ability to relate to their environment and to other people. It is generally more common in males, and affects roughly one in 68 children in the US.

“The cause or causes of most cases of autism are unknown,” says one of the study’s authors, W. Ian Lipkin, “but evidence suggests a role for both genetic and environmental factors.”

In an attempt to better understand what causes autism spectrum disorder, the team began by focusing on five pathogens known collectively as ToRCH agents – Toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex viruses type 1 and 2. Exposure to these ToRCH agents during pregnancy can cause miscarriage and birth defects.

The researchers took blood samples from 412 mothers of children diagnosed with autism spectrum disorder, and 463 mothers of children without the condition. Samples were taken at two time points – around 18 weeks into the pregnancy, and at birth – and the levels of ToRCH agents in the blood were analysed.

Of the five ToRCH agents tested for, it was only high levels of antibodies to HSV-2 that were shown to be correlated with risk for autism spectrum disorder. Because the herpes virus isn’t detectable in blood, the blood tests looked for HSV-2 antibodies – which the body produces to fight the virus – to determine whether or not an individual was infected.

The results indicate that women suffering from genital herpes early in their pregnancy – the time when the foetal nervous system is rapidly developing – double their chances of giving birth to a child with autism spectrum disorder.

After an individual is infected with herpes, it lives in nerve cells and is often inactive. Of the mothers that tested positive for herpes, only 12% reported having visible signs of the virus before their pregnancy, indicating that in most cases the infection was asymptomatic and most women involved in the study were infected without even knowing.

The results mirror previous studies that have found activation of a mother’s immune system early in her pregnancy is associated with long-term development and behavioural problems in her children.

While direct infection of a foetus with herpes normally results in death, the researchers suggest that in these cases the virus caused inflammation close to the womb, which then increased the probability of autism spectrum disorder presenting in the children.

The researchers express hope that future study will further analyse the link between genital herpes and autism, and determine if herpes suppression during pregnancy is needed.

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