Story highlights A man who had no idea he had Zika gave the virus to his female partner, the CDC says

The CDC urges pregnant women to take safe-sex precautions if exposure is possible

(CNN) A man who had no idea he had Zika has given the virus to his female partner during sex, the Centers for Disease Control announced today. It's the first documented case of a person with no symptoms sexually transmitting the virus to a partner who had not traveled to an area of active Zika circulation.

The announcement came the same day the Food and Drug Administration revised its guidance to recommend that all blood donations in the United States and its territories be tested for the Zika virus.

The asymptomatic Zika transmission "illustrates the need for careful precautions when visiting an area where Zika is circulating," said Dr. John Brooks, a medical epidemiologist with the CDC. "Be sure to wear insect repellent and appropriate clothing, and use CDC guidance on safe sex when you return. This is especially critical for women who are pregnant or trying to conceive and their partners.

"Pregnant couples need to defer unprotected sexual contact for the entire pregnancy, even if the exposed partner never develops symptoms of Zika. A few months of precautions can prevent devastating lifelong defects for the developing fetus."

Exposure to the Zika virus during the first trimester, including before a woman even realizes she is pregnant, has been linked to a devastating birth defect called microcephaly, in which the infant is born with a small head and underdeveloped brain. Infants with that disorder face overwhelming obstacles such as seizures, eye and hearing problems, failure to thrive and even death. Infants exposed later in pregnancy may escape microcephaly but can continue to have abnormal brain development and learning disabilities.

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