Growing evidence linking Zika to microcephaly: WHO

The World Health Organisation said today it could still take months to determine for certain that the Zika virus causes the serious birth defect microcephaly, but said evidence was growing.

"There is an increasing accumulation of evidence now that these phenomena may be associated," Bruce Aylward, WHO chief on outbreaks and health emergencies, told reporters. The mosquito-borne Zika virus, which has been spreading explosively in Latin America especially, is strongly suspected of causing a rapid rise in the number of children born with microcephaly -- abnormally small heads and brains -- in the hardest-hit country, Brazil.

A hike in microcephaly cases was also registered following a Zika outbreak in French Polynesia three years ago. The virus is also believed to be tied to a rise in cases of the paralysis-causing Guillain-Barre syndrome in eight countries, including Brazil, Colombia, El Salvador and Venezuela.

Aylward said researchers would likely be able to prove more quickly that Zika causes Guillain-Barre than microcephaly, since surges in the syndrome are believed to be lagging only about three weeks after spikes in Zika infections.

By comparison, it will take much longer to register a spike in microcephaly in babies born to women infected with Zika at some point during their pregnancies, he said.

Meanwhile, "the virus is considered guilty until proven innocent," Aylward said, stressing "the need to be super aggressive" in trying to rein in the Aedes aegypti mosquito, which carries Zika and also dengue and chikungunya viruses.

The mosquito is endemic to tropical regions, and is already transmitting Zika in at least 36 countries worldwide -- 28 of them in the Americas -- and Aylward said there were indications that the virus was spreading in six additional countries.
"We are still dealing with a very much evolving situation," Aylward cautioned.