Evidence is growing of a link between the Zika virus and potential birth defects in babies, the World Health Organization said on Friday, though this could take four to six months to prove.
In autopsies, doctors in Brazil have found evidence of the virus in the brains of babies born with the neurological disorder microcephaly, said the director of the WHO's outbreaks and health emergencies department, Doctor Bruce Aylward.
"This does not still prove causation... but it is an increasing accumulation of evidence in terms of the temporal–geographic association of the virus and the consequences that we are worried about," he told a news briefing. "We are seeing a lack of other explanatory causes."
The WHO declared the Zika outbreak, which has spread to nearly 30 countries and territories, an international health emergency on Feb. 1.
Aylward said it would move early next month to accelerate research on developing diagnostic tests and vaccines against Zika by convening international experts. This was "very similar to what we did early days of Ebola," he said.
Microcephaly is a neurological condition marked by unusually small heads that can result in developmental problems.
Brazil said it has confirmed more than 500 cases and considers most to be related to Zika infections in the mothers. It is investigating more than 3,900 additional suspected cases.
Pregnant women in Colombia confirmed as being infected by the Zika virus will deliver babies in coming months, which is an opportunity for gathering further evidence, Aylward said.
"It will probably be somewhere (around) four to five or six months before we can say with some certainty," he said of the link.
In its Feb. 1 declaration, the WHO cited a "strongly suspected" relationship between the Zika virus, which is carried by mosquitoes, and infection in pregnancy and microcephaly.
"A lot can be done in terms of reducing the intensity of Zika transmission and the accumulating evidence is that this has got to be done and done very, very urgently," Aylward said.
The WHO is also convening experts in vector-borne diseases in the next three to four weeks to study "innovative tools" to control mosquitoes that carry the virus, WHO's expert Pedro Alonso said.
These included the use of genetically-modified mosquitoes whose larvae die quickly or other means to reduce the lifespan of mosquitoes or make them sterile, he said.