The race is on to find a vaccine, as the mosquito-born Zika virus takes hold in the Americas.
It is being linked to severe birth defects. Around four thousand suspected cases of microcephaly have been reported here in Brazil.
Zika is now present in 23 countries and territories in the Americas, with Brazil hardest hit.
The Aedes aegypti mosquito is thought to be the sole species transmitting the virus.
But scientists are also investigating whether another more common type, the Culex, might be spreading it too.
“We’re losing the battle against the mosquito. As long as the mosquito keeps reproducing, each and every one of us is losing the battle against the mosquito. So we have to mobilise so we do not lose this battle,” said Dilma Rousseff, Brazilian President.
The World Health Organization predicts as many as four million people could become infected in the Americas.
There is no treatment for Zika infection and a vaccine suitable for widespread use is months, if not years away, developers are warning.
Most of those who get Zika show no symptoms, making it tough for pregnant women to know if it’s in their system.
The WHO – criticised over its response to West Africa’s Ebola epidemic – is holding an emergency meeting on Monday, to decide on what action to take.