Federal health officials have confirmed Zika virus can cause microcephaly and other brain abnormalities in infants.
Centers for Disease Control and Prevention (CDC) leaders said while many questions remain, they hope this determination will help improve communication and prevention efforts as they continue to study the virus.
“This is an unprecedented association,” CDC Director Tom Frieden, M.D., M.P.H., said. “Never before in history has there been a situation where a bite from a mosquito could result in a devastating malformation.”
The CDC’s findings were published in the New England Journal of Medicine.
“As with much scientific research, there’s no single piece of evidence that provides conclusive proof of this connection,” Dr. Frieden said. “Rather mounting evidence from many studies and a careful review of causal criteria was needed to determine Zika causes microcephaly and other birth defects.”
The CDC found the evidence met four of the necessary criteria to establish causality: the exposure to Zika occurred at a critical time during pregnancy, there was a specific birth defect or pattern associated with it, there were both a rare exposure and rare defect, and the causal link was biologically plausible, according to lead author Sonja A. Rasmussen, M.D., M.S., FAAP, director of the CDC’s Division of Public Health Information and Dissemination.
Still, CDC leaders said many questions remain, including what percentage of infants are at risk, what other birth defects may be linked to Zika, levels of risk at different times during pregnancy and other factors that may impact a fetus. They also are continuing to study whether Zika causes Guillain-Barré syndrome.
“Now that we’ve confirmed a causal relationship between Zika and certain birth defects, we can use this information to redouble our efforts to prevent Zika, more narrowly focus our research and communicate even more directly about the risks of Zika,” Dr. Rasmussen said.
The CDC recently held a Zika Action Plan Summit to help states prepare for the possibility of Zika virus spreading in the continental U.S. as summer approaches. The virus currently is being transmitted by Aedes aegypti mosquitoes in more than three dozen countries and territories in Latin America and the Caribbean.
The CDC has requested $1.9 billion from Congress to combat the virus and is borrowing $589 million, largely from Ebola funds, while it awaits a decision.
Health officials have not changed their guidance on protecting pregnant women and their babies from Zika. They recommend that pregnant women avoid travel to areas where Zika virus is spreading as no vaccines are currently available. All travelers to areas where Zika is being transmitted should take steps to avoid mosquito bites, and men who have been exposed to Zika should use condoms or abstain from sex with a woman who is pregnant or could become pregnant.
For the 20% of those infected who display symptoms, the illness is mild and may include fever, rash, joint pain and conjunctivitis. The infection is a nationally notifiable disease and should be reported to state, tribal, territorial or local health departments to facilitate testing.
The CDC has created a Zika Pregnancy Registry to track outcomes of infants with congenital Zika infection or who were born to women with Zika virus. Pediatricians should report clinical information on infants at birth, 2, 6 and 12 months of age. More information is available at http://www.cdc.gov/zika/pdfs/pregregistry-pediatricians-fs.pdf.
Pediatricians also can discuss suspected cases in newborns through the CDC Zika Pregnancy Hotline at 770-488-7100 or by emailing ZikaPregnancy@cdc.gov.