Colombia is another Latin American country hard hit by Zika and that country's health minister said the effects of the virus there could have global relevance as scientists research the suspected link with microcephaly.

In contrast to Brazil, Colombia has yet to register any cases of the birth defect connected to Zika, Health Minister Alejandro Gaviria told Reuters.

Zika is primarily transmitted by a type of mosquito, meaning current efforts to control the outbreak are focused on protecting people, especially pregnant women, from bites and eradicating mosquito populations in affected areas.

However, research is under way on potential transmission by sexual contact. The WHO noted on Wednesday that "existing scarce evidence indicates that there may be a risk of sexual transmission."

But research studies are needed to assess the presence of the Zika virus in semen and other body fluids and potential sexual transmission as well as mother-to-child transmission, the WHO said.