The World Health Organization announced Thursday that it will convene an emergency meeting to try to find ways to stop the transmission of the Zika virus – which officials said is “spreading explosively” across the Americas.

“The level of alarm is extremely high, as is the level of uncertainty. Questions abound. We need to get some answers quickly, ” Margaret Chan, director general of the WHO, said in Geneva during a briefing for member countries.

Aedes aegypti mosquitoes sit in a petri dish at the Fiocruz institute in Brazil. The mosquito is a vector for the proliferation of the Zika virus, now spreading throughout Latin America. The Associated Press

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The WHO said the pathogen, which was virtually unheard of in the region a year ago, is spreading so fast that it could infect as many as 3 million to 4 million people within 12 months. Chan said those numbers and the severity of the possible complications being reported – from a brain abnormality called microcephaly in children to paralysis in adults – make the situation dramatically different than what epidemiologists have seen with past outbreaks of the virus.

Health officials said 24 countries and territories are affected by mosquitoes that are transmitting Zika locally. The Centers for Disease Control and Prevention said the United States has 31 confirmed cases in 11 states and the District of Columbia. All are travel-related, said Lyle Petersen, director of CDC’s vector-borne disease division, and “this number is increasing rapidly.” There also are 20 additional cases because of local transmission in U.S. territories – 19 in Puerto Rico and one in the U.S. Virgin Islands.

In a separate briefing with reporters Thursday, U.S. officials said all states are now required to report Zika cases. As a result, they expect to see a sharp increase in cases involving a traveler infected while abroad who becomes symptomatic after returning home. But local outbreaks are unlikely here, officials said.

EDUCATING PUBLIC ABOUT RISKS

Global health authorities have already been criticized for not moving quickly enough to call an emergency meeting on Zika. Some public health experts accused the WHO of failing to learn lessons from the Ebola epidemic of 2014, when the organization delayed sounding the alarm for months.

Lawrence O. Gostin, a global health law professor at Georgetown University, said Chan needs to “urgently mobilize international resources” to curb Zika’s spread. “It is far better to be over-prepared than to wait until a Zika epidemic spins out of control,” he said in a statement.

“If the association between microcephaly and Zika virus is confirmed, there will be an ethical imperative to protect women of childbearing age from contracting the infection,” Gostin added.

At his daily briefing, White House press secretary Josh Earnest was asked if the U.S. and international response to the Zika virus was too slow.

“What you have seen from this administration is a response consistent with the kind of threat that could be out there. At this point, here in the United States, the risks of disease spread by mosquitoes are quite low,” he said. “The temperatures in North America right now are inhospitable to the mosquito population. Eventually that will change, and we have to be mindful of any possible risk here in the United States.”

Earnest noted that President Obama on Tuesday convened a group of scientists and public health officials to discuss efforts to combat the disease and noted travel warnings issued by the CDC and a public information campaign by CDC and NIH.

“We are in a stage right now where we want to educate the public about what the risks are,” he said. “For most people, the risks of the Zika virus are minimal.”

‘AN ABUNDANCE OF CAUTION’

Brazil is the epicenter of Zika, and public health officials are investigating the suspected link between the virus and the rare condition that affects fetal brain development, as well as a possible association between the pathogen and, in adults, a syndrome known as Guillain-Barre that can lead to paralysis.

During a briefing to the WHO executive board on Thursday, Brazil’s health minister, Claudio Maierovitch, said the country is investigating 12 confirmed deaths of babies born with microcephaly for potential linkage with Zika virus infection. The country has more than 4,000 suspected cases of microcephaly, and while some have turned out to be other conditions, many have been confirmed through ultrasound, he said. He did not provide a figure.

Pregnant women who tested positive for the Zika virus and later had babies with microcephaly had experienced a rash and fever during the “first and second parts of their pregnancy,” he said.

Several countries in Latin America and the Caribbean have been so shaken by the reports that they have taken extreme measures by advising women of childbearing age to wait six months to two years before trying to become pregnant. Bruce Aylward, assistant director-general of the WHO, said its position is that women who are pregnant should engage in “an abundance of caution” to avoid being bitten by mosquitoes.

Marcos Espinal, director of communicable diseases and health analysis for the Pan American Health Organization, said Zika is likely to spread to the same areas where dengue exists and predicted that “we can expect 3 to 4 million cases of Zika virus disease.”

That reach includes parts of the southern United States, according to a map he presented at the briefing.

The WHO said Zika appears to be spreading so rapidly for two reasons: One, because it is a new disease to the region and so the population does not have immunity, and two, because the Zika virus is primarily transmitted by a mosquito species known as A. aegypti, which lives in every country in North and South America except Canada and Chile.

CDC: U.S. OUTBREAK UNLIKELY

Previous outbreaks of Zika occurred primarily in areas with small populations – a distinction from the situation in Brazil, where the virus is circulating in densely populated urban areas.

CDC deputy director Anne Schuchat told reporters Thursday that living conditions in the United States, such as better air conditioning, more window screens and less crowding, are factors that make it much less likely for a widespread outbreak of Zika. But mosquito control is difficult even in this country, and she said state and local authorities need to be vigilant to “jump in” if there are locally transmitted cases.

She said the Food and Drug Administration is also looking into whether any additional guidance is necessary regarding blood donations. Zika virus stays in the blood for only a few days, she said.

There has been one reported case that the virus could have been transmitted through sex, and another case in the medical literature where the virus was found in semen two weeks after symptoms of infection, according to the CDC’s Schuchat.

“But the science is clear that Zika is primarily transmitted to people through the bite of an infected mosquito,” she said. “That is really where we are putting our emphasis.”

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