By Stephanie Nebehay and Ben Hirschler
Suspected links between the Zika virus and two neurological disorders, microcephaly in babies and Guillain-Barre syndrome, should be confirmed within weeks, says the World Health Organisation.
A sharp increase in birth defects in Brazil has triggered a global health emergency over the mosquito-borne virus, which had previously been viewed as a relatively mild illness, and has spurred a race to develop a vaccine and better diagnostic tests.
The WHO said on Friday (local time) US government scientists and an Indian biotechnology firm were currently front-runners in the race to develop a vaccine. The UN agency for the first time advised pregnant women to consider delaying travel to Zika-infected areas.
Brazil, centre of the Zika outbreak that has spread to more than 30 countries, is hosting the Rio 2016 Olympics, an event expected to draw hundreds of thousands of athletes, officials and spectators.
"It seems indeed that the link with Zika [and microcephaly] is becoming more and more probable, so I think that we need a few more weeks and a few more studies to have this straight," Marie-Paule Kieny, WHO Assistant Director-General for Health Systems and Innovation, told a news briefing.
Studies of pregnant Latin American women who are confirmed as having had the Zika virus and due to deliver their babies soon should yield evidence, Kieny said, adding data also was being collected from studies in French Polynesia and Cape Verde.
Kieny said areas hit by the Zika virus had also seen increased cases of the neurological disease Guillain-Barre, adding: "The direct causality has still to be demonstrated but the association in time and in location seems to be clear."
Guillain-Barre syndrome, in which the body's immune system attacks part of the nervous system, causes gradual weakness in the legs, arms and upper body and sometimes total paralysis.
Researchers in Brazil are scrambling to determine whether Zika has caused a big rise in the number of cases of microcephaly, or abnormally small heads in newborns, with more than 4000 suspected cases of the condition reported to date.
Brazil has confirmed more than 400 of those cases as microcephaly and has identified the presence of Zika in 17 babies but a link has yet to be proven.