Maternal infection with genital herpes, or other pathogens, during early pregnancy could increase risk of autism, or other neurodevelopmental disorders, says a new study.
Scientists looking for an association between maternal infections and risk of autism studied blood plasma samples from 875 moms during mid-pregnancy and after delivery. The results of the study, conducted by researchers at the Center for Infection and Immunity at Columbia University and the Norwegian Institute of Public Health, appear in the journal mSphere.
Since 2000, the rate of diagnosis of an autism spectrum disorder has risen from one in 150 children to one in 68. Once blamed for the increase, vaccines have been cleared, and researchers are looking to other factors, and combinations of factors, to unravel the mystery of the disorder and its increase in diagnosis.
Senior author on the study, and director of the Center for Infection and Immunity, W. Ian Lipkin, notes in a press release, "The cause or causes of most cases of autism are unknown, but evidence suggests a role for both genetic and environmental factors."
Among women in the United States, genital herpes simplex, or HSV-2, is the most commonly sexually transmitted disease. Most people who have the genital herpes virus do not know it, and the Centers for Disease Control and Prevention estimates one in six people, ages 14 to 49, carry the virus. You can be infected through oral, anal, or vaginal sex.
An existing infection by genital herpes is a pregnancy risk factor by increasing the possibility of miscarriage, early labor, and neonatal infection, among other issues. The study investigates the impact of new HSV-2 infection during early pregnancy.
Maternal infections (conditions suffered by the mother during pregnancy) are considered to be a risk factor for the development of neurological and other disorders in an unborn child. In this study, scientists looked at maternal infections caused by several pathogens, including genital herpes, to understand possible associations with later diagnosis of an autism spectrum disorder in the child.
One of the reasons autism spectrum disorders are difficult to diagnose is the lack of biomarkers to its path of development. In this study, scientists looked for antibodies to five infections known to cause serious consequences during pregnancy.
The infections, collectively called ToRCH agents, are toxoplasmosis, rubella virus, cytomegalovirus, and herpes simplex viruses HSV-1 and HSV-2. These infections are known to have the capability to cause miscarriage, brain damage, visual impairment, intrauterine growth restriction, and other fetal dysfunction when the mother is infected during pregnancy.
Using blood samples from mothers enrolled in the Norwegian Autism Birth Cohort (ABC), researchers genetically and statistically analyzed 1,781 blood samples at two points during pregnancy and made these findings:
- Review of the data "suggests that the presence of high levels of anti-HSV-2 antibodies at midpregnancy increases the risk of ASD." Women were twice as likely to give birth to a child later diagnosed with autism when they experienced an active genital herpes infection during pregnancy. There were no correlations between autism and the other infectious agents.
- As noted in the study, higher levels of antibodies occur during a recently acquired infection, or result from "reactivation of latent (existing) infection."
- The study mentions infection with HSV during pregnancy accounts for between four and nine percent of HSV cases that are diagnosed after birth.
- Overall, study authors suggest the "possibility that general immune activation" caused by maternal infection, instead of a particular pathogen, could pose difficulties for the developing fetus. This shifts focus toward the effects of inflammation and an immune response by a mother's body on the unborn child.
- Noting the study involved too small of a sample to draw gender conclusions, authors did note the diagnosis of autism spectrum disorders in this study skewed toward male babies.
In the press statement, postdoctoral research scientist and lead author Milada Mahic stated, "We believe the mother's immune response to HSV-2 could be disrupting fetal central nervous system development, raising risk for autism."
Researchers do not believe the HSV-2 virus directly infects the fetus, but during early pregnancy, the developing child suffers from the immune response of its mother when she is infected. Like listeria or Zika, mom may not even know she is infected.
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