The U.S. Centers for Disease Control and Prevention on Friday advised pregnant women not to travel to the Aug. 5-21 Olympic Games to be held in Rio de Janeiro, citing the mosquito-borne Zika virus.

The health agency said these recommendations also hold for the Paralympic Games, scheduled for Sept. 7-18.

CDC said women who are pregnant may be at risk for sexual transmission of Zika and should use condoms the right way, every time, or not have sex during pregnancy.

A growing number of international athletes in recent weeks have said they are concerned about Zika, a virus that has been linked in Brazil to more than 4,000 suspected cases of microcephaly, a rare condition that causes abnormally small heads in infants and can lead to developmental problems.