A health worker fumigates a house as residents wait outside during a campaign against the Zika virus and other mosquito-borne diseases at Carabayllo district on the outskirts of Lima, Peru February 1, 2016. [Photo/Agencies]

Brazil has reported nearly 4,000 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.

Brazilian Health Minister Marcelo Castro said that the epidemic was worse than believed because in 80 percent of the cases the infected people had no symptoms.

As the virus spreads from Brazil, other countries in the Americas are also likely to see cases of babies with Zika-linked birth defects, experts believe.

The Pan American Health Organization says that Zika has now spread in 24 nations and territories in the Americas.