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The World Health Organization on Monday said that severe health complications associated with the spread of Zika virus constitute a global public health emergency, a move that could help officials galvanize more resources to respond to the outbreak.

The announcement puts the WHO, which was widely condemned for its slow response to the West Africa Ebola epidemic, in a leadership role as public health officials seek to better understand the connection between Zika and a spike in birth defects, among other issues.

The outbreak of mosquito-borne Zika began last May in Brazil, and has spread quickly through the Americas. Several dozen cases have been reported in the United States among travelers who have returned from countries where there is active Zika transmission.


On its own, Zika causes mostly mild flu-like symptoms and would not have been deemed a global health emergency, officials said Monday.

But a WHO panel of 18 outside experts advising the agency concluded that a coordinated global response was necessary given the suspected link between Zika and a rapid increase in two serious conditions: a severe birth defect called microcephaly, in which newborns have abnormally small heads, and Guillain-Barré syndrome, a neurological condition that triggers temporary paralysis.


The theory is that infection during pregnancy can in some cases induce microcephaly in the fetus. Brazil has reported more than 4,000 suspected microcephaly cases since October. It typically sees about 175 cases annually.

Brazil and a few other Latin American countries have also reported more modest increases in cases of Guillain-Barré syndrome. People who develop it generally recover, and recover fully, though some die.

“We need a coordinated international response to make sure we get to the bottom of this,” the WHO’s director general, Margaret Chan, said during a news conference from the agency’s headquarters in Geneva.

The announcement marked the fourth public health emergency of Chan’s tenure. Earlier emergencies were called to deal with the 2009 H1N1 flu pandemic, West Africa’s Ebola outbreak, and problems plaguing the polio eradication campaign.

The emergency committee on Zika recommended that the WHO call for ramped-up surveillance for microcephaly and Guillain-Barré syndrome and that the definitions used to diagnose both be standardized, so that all countries are using the same yardstick when assessing the incidence of cases of these conditions.

The committee also called for rapid development of Zika virus tests and vaccines — thought it listed the latter as a longer-term measure — enhanced risk communications aimed at women in affected countries who may become pregnant, and strengthened mosquito control measures.

The committee did not recommend — and the WHO did not issue — travel advice for pregnant women. Chan said the committee found no public health justification for restrictions on travel or trade.

The US Centers for Disease Control and Prevention, by contrast, has urged women who are pregnant to consider avoiding travel to more than two dozen countries and territories experiencing Zika outbreaks. On Monday, it added American Samoa, Costa Rica, Curacao, and Nicaragua to its list.

Some public health experts said the WHO’s decision not to issue travel guidance was a mistake.

“Parents concerned for the welfare of their daughters would advise them not to travel to affected areas if they are pregnant,” said Lawrence Gostin, faculty director of the O’Neill Institute for National and Global Health Law at Georgetown University in Washington.

Gostin, who had been publicly pushing the WHO to declare the Zika outbreak a global health emergency, noted that the CDC has also advised women considering becoming pregnant to talk with their doctor before traveling.

“That is the right thing to do from a public health and ethical perspective,” he said.

The Zika virus, once thought to be a wimpy cousin of the more severe dengue and chikungunya viruses, has gained global attention in recent weeks since Brazil began to voice fears that the country was experiencing a surge in cases of babies born with microcephaly.

A number of affected countries in Latin America are recommending that women delay pregnancy — advice that advocacy groups have denounced as unworkable in countries where access to contraceptives may be limited and where abortions are outlawed.

The Zika virus was first discovered in 1947 in the Zika Forest of Uganda. It has been studied little, however, because it was not seen as a widespread threat to humans. Four out of five people infected show no symptoms, and those who do experience something like the flu — fever and achy muscles and joints.

People who contract Zika may also develop a raised red rash and/or conjunctivitis, commonly known as pink eye.

The story has been updated with details throughout.