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Zika spread through sex by symptom-free man

U.S. health officials on Friday reported the first case of Zika spread through sex by a man with no symptoms of the disease.

In the other 21 U.S. cases of sexual transmission, the virus was spread by someone who at some point had symptoms.

The report details the case of a Maryland man who went to the Dominican Republic, where there is a Zika outbreak. He didn’t get sick during the trip or when he returned. But his sex partner, who hadn’t traveled, did get sick with Zika and recovered.

Zika and sex: New research and avoiding the risk

Zika is mainly spread by mosquitoes. Most infected people don’t get sick. It can cause a relatively mild illness, with fever, rash and joint pain. But infection during pregnancy is particularly dangerous because it can lead to a severe brain-related birth defect, called microcephaly, in babies. Microcephaly is a condition where a baby’s head is much smaller than expected, and it often involves brain damage to varying degrees. Children with the condition may suffer from seizures, developmental delays and lifelong intellectual disability. 

Doctors believe the transmission of the virus from an infected person with no symptoms is extremely rare; it may be that they have smaller amounts of virus in their blood and bodily fluids and are less infectious.

The Centers for Disease Control and Prevention advises couples to use condoms for two months after a partner without symptoms has returned from a Zika​ outbreak area if the woman is of child-bearing age. For men with symptoms, the CDC advises using condoms for at least six months.

The Maryland case is unusual and doesn’t warrant a change in advice when it comes to protection during sex, said the CDC’s Dr. John T. Brooks.

French researchers in April reported a similar case of a couple without symptoms who both tested positive for Zika. However, both had visited a Zika area so infection from mosquito bites couldn’t be ruled out.

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