United States health officials have confirmed the worst fears of many pregnant women in the US and Latin America by saying there is no longer any doubt the Zika virus causes babies to be born with abnormally small heads and other severe brain defects.
Since last year, doctors in Brazil have been linking Zika infections in pregnant women to a rise in newborns with microcephaly, or an unusually small skull. Most outside experts were cautious about drawing such a connection. But now the Centers for Disease Control and Prevention (CDC) says enough evidence is in.
“There is no longer any doubt that Zika causes microcephaly,” CDC Director Dr Tom Frieden said. The CDC said it is also clear that Zika causes other serious defects, including damaging calcium buildups in the developing brain.
Among the evidence that clinched the case were signs of the Zika virus, which is spread primarily through mosquito bites and can also be transmitted through sex, found in the brain tissue, spinal fluid and amniotic fluid of microcephaly babies.
The CDC and other health agencies have been operating for months on the assumption that Zika causes brain defects, and they have been warning pregnant women to use mosquito repellent, cover up, avoid travel to Zika-stricken regions and either abstain from sex or rely on condoms. Those guidelines will not change.
But the new finding should help officials make a more convincing case to the public for taking precautions. Some experts hope it will change public thinking about Zika the way the 1964 surgeon general's report convinced many Americans that smoking causes lung cancer.
“We've been very careful over the last few months to say, 'It's linked to, it's associated with.' We've been careful to say it's not the cause of,” said the CDC's Dr Sonja A Rasmussen. “I think our messages will now be more direct.”
The World Health Organisation (WHO) has made similar statements recently. A WHO official applauded the CDC report.
“We feel it's time to move from precautionary language to more forceful language to get people to take action,” said Dr Bruce Aylward, who is leading WHO's Zika response.
The CDC announced its conclusion in a report published online by the New England Journal of Medicine.
Zika has been sweeping through Latin America and the Caribbean in recent months, and the fear is that it will only get worse there and in the US with the onset of mosquito season this spring and summer.
Public health authorities have mounted aggressive mosquito-eradication efforts, including extensive spraying and campaigns to eliminate the sources of standing water in which mosquitoes breed. Those can include flower pots, swimming pool covers, discarded tires and pet water bowls.
The virus causes only a mild and brief illness, at worst, in most people. But in the last year, infections in pregnant women have been strongly linked to fetal deaths and devastating birth defects, mostly in Brazil, where the Health Ministry said on Tuesday that 1,113 cases of microcephaly have been confirmed since October.
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