The World Health Organization has declared the mosquito-borne Zika virus to be an international public health emergency due to its link to thousands of suspected cases of birth defects in Brazil.
WHO Director-General Margaret Chan told reporters on Monday coordinated international action was needed to improve detection and speed work on a vaccine and better diagnostics for the disease, although curbs on travel or trade were not necessary.
The emergency designation was recommended by a committee of independent experts to the UN agency following criticism of a hesitant response so far. The move should help fast-track international action and research priorities.
Members of the committee agreed that the situation meets the conditions for a public health emergency of international concern. I have accepted this advice, Chan told a news briefing at WHO headquarters.
The WHO said last week the Zika virus, carried by the Aedes aegypti mosquito, was spreading explosively and could infect as many as 4 million people in the Americas. Brazil is due to host the Olympic Games in Rio de Janeiro in August.
The WHO was lambasted for reacting too slowly to the Ebola epidemic in West Africa which killed more than 10,000 people in the past two years, and has promised to do better in future global health crises.
US Centers for Disease Control and Prevention head Thomas Frieden said the declaration calls the world to action on Zika, while Jeremy Farrar, director of the Wellcome Trust medical charity, said the WHO should be congratulated for being far more proactive this time.
Derek Gatherer, a lecturer at Lancaster University, said the WHO's move was like a declaration of war ... on Zika virus.
Brazil has reported some 3,700 suspected cases of microcephaly, in which infants are born with smaller-than-usual brains. The Health Ministry has linked the condition to Zika, although the connection is not yet definitive.
Chan said the causal link was strongly suspected but not yet scientifically proven.