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.”
“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
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.
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 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.
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.