El Salvador is the latest country in Latin America to be put on alert over the “mosquito-borne Zika virus”:
The authorities there are advising women to try to avoid pregnancy for the the next two years to avoid passing on complications to babies.
Women already pregnant are being advised to do what they can to reduce the risk of mosquito bites.
The authorities in the US are warning pregnant women about the risk of traveling to the region.
“We are quite concerned about the potential complications to the fetus of a Zika virus infection of pregnant women and so we really are advising that pregnant women seriously consider postponing travel to these areas if possible,” said
Dr Beth Bell of the Center for Disease Control and Prevention in the US.
The Zika virus causes relatively mild symptoms but the Pan American Health Organisation says it may be linked to cases of brain damage in newborn babies in Brazil, one of the hardest hit countries.
It has spread quickly through large parts of Latin America and the Caribbean affecting 21 nations so far.
In northeast Brazil there has been a marked increase in cases of microcephaly, a neurological disorder in babies that scientists think may be linked to Zika.