GENEVA » The World Health Organization declared an international emergency today over the explosive spread of the mosquito-borne Zika virus, which is linked to birth defects in the Americas, saying it is an “extraordinary event.”

The U.N. health agency convened an emergency meeting of independent experts in Geneva to assess the outbreak after noting a suspicious link between Zika’s arrival in Brazil last year and a surge in the number of babies born with abnormally small heads.

“After a review of the evidence, the committee advised that the clusters of microcephaly and other neurological complications constitute an extraordinary event and public health threat to other parts of the world,” WHO Director-General Margaret Chan said.

WHO estimates there could be up to 4 million cases of Zika in the Americas in the next year, but no recommendations were made to restrict travel or trade.

“It is important to understand, there are several measures pregnant women can take,” Chan said. “If you can delay travel and it does not affect your other family commitments, it is something they can consider.

“If they need to travel, they can get advice from their physician and take personal protective measures, like wearing long sleeves and shirts and pants and use mosquito repellent.”

The last such public health emergency was declared for the devastating 2014 Ebola outbreak in West Africa, which killed more than 11,000 people. A similar declaration was made for polio the year before.

Such emergency declarations are meant as an international SOS signal and usually trigger increased money and efforts to stop the outbreak, as well as prompting research into possible treatments and vaccines.

Maria Cheng reported from London.