Brazil's top health official says the Zika virus outbreak is proving to be worse than believed because most cases show no symptoms.
Health Minister Marcelo Castro told Reuters that Brazil will start mandatory reporting of cases by local governments next week when most states will have labs equipped to test for Zika, the mosquito-borne virus that has quickly spread through Latin America. The virus has no vaccine or cure at present.
Earlier today, the World Health Organisation declared the Zika outbreak to be a global emergency, a decision that should help fast-track international action and research priorities.
In Brazil, believed to be the country hit hardest by Zika, the outbreak has sparked fear especially among pregnant women after local experts linked the virus to thousands of cases of microcephaly, or abnormally small heads and underdeveloped brains, in newborns.
"Eighty percent of the people infected by Zika do not develop significant symptoms. A large number of people have the virus with no symptoms, so the situation is more serious than we can imagine," Mr Castro said in an interview.
"Our big hope is finding a vaccine," he added.
The Zika emergency has also cast a shadow on Brazil's hosting of the Olympic Games in Rio de Janeiro in August.
The Dilma Rousseff government said there was no chance the Games will be called due to the health scare.
"We have to explain to those coming to Brazil, the athletes, that there is zero risk if you are not a pregnant woman," Ms Rousseff's chief of staff Jaques Wagner told reporters.