Everything
you ever wanted to know about the Zika virus and its spread across North
and South America. (Daron Taylor,Claritza Jimenez/The Washington Post)
By Lena H. Sun-April 13
This post had been updated.
By Lena H. Sun-April 13
This post had been updated.
Federal health officials confirmed Wednesday that the Zika virus causes a
rare birth defect and other severe fetal abnormalities, marking a
turning point in an epidemic that has spread to more than 40 countries
and territories in the Americas and elsewhere.
Scientists at the Centers for Disease Control and Prevention conducted a
careful review of existing research and agreed that the evidence was
conclusive, Director Thomas Frieden said. It is the first time a
mosquito-borne virus has been linked to congenital brain defects.
"It is now clear, and CDC has concluded, that the virus causes
microcephaly," Frieden said. CDC is launching more studies to determine
whether children with that rare condition, which is characterized at
birth by an abnormally small head, represent the "tip of the iceberg of
what we could see in damaging effects on the brain and other
developmental problems."
The outcome validates the growing research of past months that strongly
implicated Zika as the culprit behind a broad set of complications in
pregnancy. The pathogen is also increasingly linked to neurological
problems in adults. The CDC report, published in the New England Journal
of Medicine, focused only on reviewing the evidence linking Zika and
fetal anomalies.
Global health officials had already assumed the virus was to blame for
the problems being seen in various countries. Since January, many have
advised women who were pregnant or hoping to become so to avoid travel
to Zika-affected areas or to take steps to avoid Zika infection. That
medical advice expanded over time to include women's partners,
especially as it became clear sexual transmission of the virus was more
common than had been known.
The research released Wednesday won't change that advice, officials
said. But they are hoping it will help educate the public about the
virus and its potential for harm -- particularly in the United States.
"We do know that a lot of people aren't concerned about Zika infection
in the United States, and they don't know a lot about it," said Sonia
Rasmussen, director of CDC's division of public health information.
"It's my hope that we can be more convincing that Zika does cause these
severe birth defects in babies and hope that people will focus on
prevention more carefully."
The research is likely to help scientists developing a vaccine for Zika, she said.
Researchers said there was no "smoking gun" or single definitive piece
of evidence that confirmed the virus as causing microcephaly,
calcifications within the fetal brain and vision problems in newborns.
Rather, the findings of recently published studies and a thorough evaluation by CDC researchers using established scientific criteria led them to the conclusion. Frieden likened the process to putting together pieces of a puzzle.
Rather, the findings of recently published studies and a thorough evaluation by CDC researchers using established scientific criteria led them to the conclusion. Frieden likened the process to putting together pieces of a puzzle.
The World Health Organization had said in recent weeks that there was
scientific consensus about the virus and microcephaly as well as
Guillain-Barré syndrome, a neurological condition that can lead to
paralysis. Researchers in Brazil, the hardest-hit country, said this
week that Zika also may be associated with a second serious condition
similar to multiple sclerosis. In a few cases with adults, they found
swelling of the brain and spinal cord involving the coating around nerve
fibers.
CDC officials said they worked independently of the WHO. The U.S. agency
is conducting studies on Guillain-Barré syndrome, and officials said
they are also likely to make a conclusive link between that condition
and Zika. "I think we're on the same page as the WHO," Rasmussen said.
There are still many outstanding questions about the risk facing
pregnant women infected with Zika. A limited number of studies show the
risk ranges from about 1 percent chance of having a baby with
microcephaly to almost 30 percent of pregnant women having fetal
abnormalities. A study in Brazil identified that upper range, with
pregnant women having "grave outcomes," Rasmussen said.
Scientists also don't know whether miscarriages and stillbirths are the
result of an infection. Nor do they know what stage of pregnancy is risk
the greatest, or whether another infection that occurred at the same
time might affect the risk of birth defects, she said.
A two-week-old born with microcephaly is examined during a physical therapy session at a hospital in Campina Grande, Brazil. (AP/Felipe Dana)
CDC's assessment of the evidence began last October but included Zika
studies that were published as recently as last weekend, Rasmussen said.
The detailed clinical information shows the most severe forms of
microcephaly, also known as fetal brain disruption sequence. In some
instances, the babies' heads are much smaller than what clinicians would
normally see in microcephaly cases, she said.
Among the evidence the report cited to support the causal relationship between Zika and these serious birth defects included:
• Zika infection during critical periods of early pregnancy, usually the first trimester or early second trimester;
• specific, rare patterns of birth defects in fetuses or infants with presumed or confirmed congenital Zika infection;
• biological evidence, including the presence of Zika virus in the brain
tissue of fetuses and babies with severe microcephaly who had died.
• rare exposure to the virus and a rare birth defect.
The researchers cited the recent case of a Washington, D.C. woman who
tested positive for Zika 10 weeks after she likely contracted an
infection during a trip to Guatemala – far beyond what scientists have
thought is the case. Damage to the fetus did not show up on early
ultrasounds. But after her abortion at 21 weeks, virus was found in the
fetal brain and there were significant brain abnormalities.
Brazil normally has an average of 163 cases of microcephaly each year.
But since October, officials have confirmed at least 944 cases of
microcephaly or other neurological problems, according to the WHO.
After a Zika outbreak in French Polynesia, that island also had an
increase in microcephaly cases. It normally has no more than two cases a
year, but it saw eight cases during a four-month period in 2014. A
recently published study using data from the island estimated the risk
for the rare birth condition to be 95 cases of microcephaly for each
10,000 pregnant women infected in the first trimester.
