CDC scientists conclude Zika virus causes microcephaly, other brain defects

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Scientists at the U.S. Centers for Disease Control and Prevention (CDC) have concluded that Zika virus can cause microcephaly and other severe fetal brain defects, ending months of uncertainty about the link between brain defects and Zika.

The results of a CDC study were published in the New England Journal of Medicine on Wednesday and used evidence from a number of recently published studies. It noted that it had no “single piece of evidence” to provide conclusive proof of a link.

The CDC’s conclusion means that women who are infected with Zika during pregnancy have an increased risk of having a baby with brain defects, though it is still unclear how great that risk is, as a number of infected women have delivered babies that appear to be healthy with no signs of brain defects.

“This study marks a turning point in the Zika outbreak. It is now clear that the virus causes microcephaly,” said CDC Director Tom Frieden. “We are also launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems.”

Frieden added that its study reaffirmed the agency’s recommendations to pregnant women and their partners to take steps to avoid Zika infection.

Zika virus was first isolated from a monkey in the Zika forest of Uganda in 1947 and the virus continued to affect mainly monkeys for nearly 5 more decades, causing only a mild illness when found in humans. That assessment began to change several years ago with outbreaks on Pacific islands, which preceded a larger outbreak in Brazil that has since expanded.

Local transmission of Zika has been reported in 62 countries and territories across all continents except Antarctica, according to the World Health Organization, which says further geographical spread is to be expected. Zika is spread mainly through mosquitoes but can also spread through sexual contact.

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