Researchers are one step closer to understanding the link between Zika, a mosquito-borne virus that has been spreading throughout central and South America, and the birth defect microcephaly.
In a new study, researchers examined eight cases of microcephaly that occurred during the 2013-14 outbreak in French Polynesia. Five of the pregnancies were terminated, and three resulted in live births.
By using data from previous studies that tracked the number of births, pregnancies, and suspected and confirmed cases of Zika and microcephaly during the outbreak, the researchers were able to create a mathematical model to assess Zika and microcephaly risk in six different scenarios.
Based on the model, which also factored in results from diagnostic tests that were used to look for signs of Zika, the researchers found that risk of microcephaly was the greatest during the first few months of a pregnancy. The researchers estimated that Zika-linked microcephaly can affect one in every 100 pregnant women who contract the virus within the first trimester. Microcephaly is a condition that is characterized by an abnormally small head paired with an underdeveloped brain.
"Our analysis strongly supports the hypothesis that Zika virus infection during the first trimester of pregnancy is associated with an increased risk of microcephaly," said Simon Cauchemez at Institute Pasteur in France, study co-lead investigator.
"The finding that the highest risk of microcephaly was associated with infection in the first trimester of pregnancy is biologically plausible, given the timing of brain development and the type and severity of the neurological abnormalities," the authors wrote in the study, which was published in The Lancet.
Cauchemez cautioned that it is unclear whether or not his findings apply to the current outbreak.
"Data from French Polynesia are particularly important since the outbreak is already over," said a co-author of the study, professor Arnaud Fontanet at Institute Pasteur. "This provides us with a small, yet much more complete dataset than data gathered from an ongoing outbreak. Much more research is needed to understand how Zika might cause microcephaly."
According to the U.S Centers for Disease Control and Prevention, Zika, which was declared a public health emergency by the World Health Organization, has been reported in 31 countries and territories since the outbreak began in Brazil. Health officials, researchers and country leaders have been working on finding ways to stop the virus from spreading.
In the United States, officials have plans to field test mosquitoes that have been genetically altered for the purpose of combating Zika. Although the Food and Drug Administration (FDA) considers the mosquitoes to be safe, a field test will not begin until the agency hears from the public first.
There has not been a single case of locally transmitted Zika within the continental U.S.
