herpes virus
The herpes simplex virus 2 causes genital herpesGetty Images

Women infected with genital herpes during pregnancy have higher chances of giving birth to baby boys suffering from autism spectrum disorder (ASD), a study has shown. They find that the problem may not be the virus itself, but the kind of immune activation it triggers in expectant mothers.

Genital herpes is a common sexually transmitted infection caused by the herpes simplex virus 2 (HSV-2). The World Health Organisation estimates that just over one in 10 people aged between 15 and 49 years old are infected globally.

The majority of infections are asymptomatic, but can sometimes lead to long-term complications. In recent years, animal and epidemiological studies have looked at the impact of maternal infection on the health of babies. There is now relative consensus that immune activation linked to infections in pregnancy are associated with an elevated risk of neurodevelopmental disorders, such as psychosis and ASD.

"The consensus so far is that it is probably not a specific infection that we have to worry about, but about immune activation in response to an infection. If you look at animal models, similar results are observed following exposure to say the influenza virus and non-specific immune stimulators", Grainne McAlonan, a Clinical Reader at King's College London told IBTimes UK.

To date, the exact causes of ASD remain elusive. It is thought that a mix of genetic and environmental factors play a part. The research published in the journal mSphere, suggests that immune activation in response to a HSV-2 infection during pregnancy is an environmental risk-factor for male offspring to be diagnosed with ASD.

Cause or correlation?

This is the first study to report an association between maternal anti-HSV-2 antibody
levels and risk of ASD in offspring. The scientists examined the data of 442 mothers of a child diagnosed with ASD and 464 controls. They had access to plasma samples taken during pregnancy and / or after delivery which enabled them to monitor antibody levels.

The researchers' interpretation of the data is that the presence of high levels of anti-HSV-2 antibodies at mid-pregnancy increases the risk of ASD in boys. For girls, the numbers are too small to reach a conclusion.

The study, which is based on a small sample of individuals, doesn't highlight a causal link between the virus and autism, it just identifies an interesting correlation.

"In their study, there was no difference in the number of mothers in each group that had HSV2 antibodies. But their data suggested that higher levels of antibodies are associated with a risk of ASD", McAlonan said.

"So maybe the question is not whether the HSV-2 exposure increases the risk of autism, but why mothers who have children diagnosed with ASD have a heightened immune response to exposure?That is, is there something which increases the risk of autism which also increases the response to infection? Here, one problem is that the researchers only look at this association in one direction", she added.

Autism
Causes of autism remain unclear despite years of researchGetty

The study's authors say other pathogens should be tested in future to see if the results with the herpes virus can be replicated. In the meantime, their study could prompt renewed efforts to monitor women more closely for gestational infections. However, more research, with a larger amount of data is needed before scientists can reach a definite conclusion about the role of immune response.

"We already knew that there is something about the immune response in ASD that we need to be looking at in greater detail, but we still need a lot more data; and more efforts to characterise the role of immune response in pregnancy and in individuals with ASD before we suggest interventions", McAlonan said.

Ian Dale, Head of Research at the National Autistic Society, also commented:

"No-one should draw any firm conclusions from this study, which claims that women who are infected with genital herpes early in their pregnancy may be more likely to have a child on the autism spectrum. We urge people not to worry unnecessarily about this study" (...) "What's most important for the 700,000 people on the autism spectrum in the UK today is to make sure that they have access to the right support from people who understand autism."