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
“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
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
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.