GENEVA, Switzerland (WPVI) --After an emergency meeting of independent experts, the World Health Organization declared an international emergency on Monday 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 experts were called to Geneva or onto the phone, 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 didn't make any recommendations on restricting 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."
This is the fourth public health emergency the WHO has declared in the past 7 years.
The most recent was for the devastating 2014 Ebola outbreak in West Africa, which killed more than 11,000 people.
A similar declaration was made for polio in Africa and Asia earlier the same year.
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.
WHO officials say it could be six to nine months before science proves or disproves any connection between Zika and the spike in the number of babies born in Brazil with abnormally small heads.
WHO, which was widely criticized for its slow response to the 2014 Ebola crisis in West Africa, has been eager to show its responsiveness this time.
Despite dire warnings that Ebola was out of control in mid-2014, WHO didn't declare an emergency until August, when nearly 1,000 people had died.
At the height of the Ebola outbreak, the WHO had predicted 1 million deaths to Ebola.
The official toll was 11,000.
Officials say that up to 4 million cases of Zika could turn up in the Americas within the next year.
Zika was first identified in 1947 in a Ugandan forest but until last year, it wasn't believed to cause any serious effects; about 80 percent of infected people never experience symptoms.
The virus has also been linked to Guillain-Barre syndrome, which causes muscle weakness and nerve problems.
Brazil's president today signed a measure allowing health officials access to any building to eradicate breeding grounds for a mosquito spreading the Zika virus.
It allows health officials access to all homes, public and private buildings- even if the property's owner cannot be located.
Officials can also request backup from police to raid any building suspected of being a mosquito breeding ground.
Brazil has sent about 220,000 troops to battle the Aedes aegypti mosquito that transmits Zika, dengue, chikungunya and yellow fever.
What we know so far is that the only microcephaly cases we see currently are from Brazil," Lindmeier said, noting that abnormally small heads in newborns can have many causes - such as the effects of herbicides, alcohol use, or drugs and toxins.
"This is exactly what is the concerning question: why do we see this in Brazil?"
World Health Organization spokesman Christian Lindmeier said the UN agency learned important lessons from its response to Ebola.
"That's why we are trying to bring in the best experts we can gather for this event, to try to establish what steps to take and what the way forward should be."
Late today, the Centers for Disease Control added 4 destinations to the list of those pregnant women are urged to avoid.
Commonwealth of Puerto Rico
United States Virgin Islands