Zika Virus a Global Health Emergency, W.H.O. Says

The World Health Organization declared the Zika virus and its suspected link to birth defects an international public health emergency on Monday, a rare move that signals the seriousness of the outbreak and gives countries new tools to fight it.

An outbreak of the Zika virus, which is transmitted by mosquitoes, was detected in Brazil in May and has since moved into more than 20 countries in Latin America, including two new ones announced Monday: Costa Rica and Jamaica.

The main worry is over the virus’s possible link to microcephaly, a condition that causes babies to be born with unusually small heads and, in the vast majority of cases, damaged brains. Reported cases of microcephaly are rising sharply in Brazil, ground zero for the disease, though researchers have yet to establish that Zika causes the condition.

At a news conference in Geneva, Dr. Margaret Chan, the director general of the W.H.O, acknowledged that the understanding of the connection between the Zika virus and microcephaly was hazy and said that the uncertainty placed “a heavy burden” on pregnant women and their families throughout the Americas. She said the emergency designation would allow the health agency to coordinate the many efforts to get desperately needed answers. Officials said research on the effects of Zika in pregnant women was underway in at least three countries: Brazil, Colombia and El Salvador.

“The evidence is growing and it’s getting strong,” Dr. Chan said. “So I accepted, even on microcephaly alone, that it is sufficient to call an emergency. We need a coordinated international response.”