With the sting of a mosquito bite and a fever, many pregnant women may not know that they caught the Zika virus -- until it strikes their unborn child.
Now authorities in some Latin American countries are warning women to avoid getting pregnant, after thousands of cases of birth defects linked to the disease over recent months.
Babies across the region, and at least one in the United States, have been born with abnormally smaller heads, a condition doctors call microcephaly, which can cause brain damage.
The scare has struck hardest in Brazil, which hosts the summer Olympic Games in August.
It is one of 14 Latin American and Caribbean countries that the United States has warned pregnant women not to visit because of the Zika risk.
"I am very afraid," said Jacinta Silva Goes, a 39-year-old cleaning lady in Sao Paulo who is expecting her third child.
"For the moment I am not using mosquito repellent because the doctor has not told me to. He has not spoken to me about Zika," she told AFP.
Zika used to be thought just a poor relation of dengue, another mosquito-borne virus.
The World Health Organization (WHO) says it is transmitted by the same mosquito that spreads dengue, chikungunya and yellow fever.
But the WHO this week noted a surge in cases of microcephaly in Brazil, the country most affected by the current epidemic.
WHO spokesman Christian Lindmeier said today there were 3,893 suspected microcephaly cases in Brazil, which included 49 deaths. Before last year there were about 160 cases of microcephaly in Brazil on average.
"The link between the Zika and the microcephaly... Is still being investigated," Lindmeier said, but acknowledged that Zika "seems the strongest candidate.
