Microcephaly is "now only one of several" birth abnormalities associated with the Zika virus, Margaret Chan, director-general of the World Health Organization, said during a press conference today. Fetal death, placental insufficiency, fetal growth retardation, and injury to a fetus' central nervous system are all associated with the virus. "We can now conclude that Zika virus is neurotrophic — preferentially affecting tissues in the brain and brain stem of the developing fetus," Chan said, before cautioning that proving a link between Zika and these birth defects will take more research.

The WHO director-general spoke to the press following the second meeting of the WHO's Emergency Committee on Zika. The Emergency Committee, which is composed of infectious disease experts, concluded its meeting by recommending that research into the relationship between clusters of neurological disorders and Zika virus should be intensified. Governments should also increase their efforts to control Zika's main mode of transmission, mosquitoes.

In most cases, the Zika virus isn't dangerous. Only 1 out of every 5 infected persons will go on to develop symptoms, which are similar to the flu and last about a week. There’s no vaccine or treatment for the Zika virus, however, which is concerning given that Zika has been linked to microcephaly — a birth defect that causes children to be born with abnormally small heads — as well as Guillain-Barré Syndrome, a severe neurological disorder that can cause temporary paralysis in people of all ages.

So far, an increase in microcephaly has been in only documented in two countries, French Polynesia and Brazil, Chan said. "However, intense surveillance for fetal abnormalities is currently underway in countries like Colombia."

The link between birth defects and Zika isn't defintive, but governments shouldn't wait for scientific proof to take action, Chan said. "It is important that [in] every country, including Brazil, that women should be provided with all the information to empower them to make the decision of whether they want to get pregnant or whether they want to defer pregnancy," Chan said in response to a question about women who are pregnant in Brazil. "And if indeed they are already pregnant, they are other means to protect themselves from mosquito bites." Chan made no mention of abortion — a practice that, barring certain circumstances, is currently illegal in Brazil.

About 150 cases of Zika have been reported in the US; of those, none were locally acquired though mosquito bites. However, local transmission has now been recorded in 31 countries and territories in Latin America and the Caribbean. And the virus' spread will likely intensify in the coming months, Chan said. Because of the rainy season — which lasts from January through May — "we can expect to see more cases and further geographic spread," she said.