In this Dec. 23, 2015 file photo, 10-year-old Elison nurses his 2-month-old brother Jose Wesley, who was born with microcephaly, at their house in Poco Fundo, Pernambuco state, Brazil.

Pregnant women should avoid traveling to Latin America and Caribbean countries that have outbreaks of a tropical illness linked to birth defects, health officials said Friday.

The illness is caused by the Zika virus which is spread through mosquito bites. It causes only a mild illness in most people. But it’s been spreading around the world, and there’s mounting evidence linking it to a terrible birth defect, especially in Brazil.

Late Friday, US health officials said pregnant women should consider postponing trips to 14 destinations — Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Suriname and Venezuela.

They also advised women who are trying to get pregnant or thinking of getting pregnant to talk to their doctor before traveling to those areas, and to take extra precautions to avoid mosquito bites.

Zika is the name of a virus discovered in a monkey in the Zika forest of Uganda in 1947. It is native to tropical Africa, Southeast Asia, and the Pacific Islands. But infections have exploded recently in Latin America and the Caribbean. It is spread through bites from the same kind of mosquitoes that can spread other tropical diseases, like chikungunya and dengue fever.

Experts think that only about 1 in 5 people who are infected with the Zika virus develop any symptoms. For those that do, Zika illness usually involves fever, rash, joint pain, and red eyes, which usually last no more than a week. There is no medicine or vaccine for it. Hospitalizations are rare, and deaths from Zika have not been reported.

Two reasons. First, there’s been growing evidence linking Zika infection in pregnant women to a rare condition called microcephaly, in which the head is smaller than normal and the brain has not developed properly.

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