A Liberian woman appears to have contracted Ebola from unprotected sex with a man who survived the virus, health officials said today.

The 44-year-old woman was diagnosed March 20, the first new Ebola case in Liberia in a month. Doctors were perplexed by her case, because she hadn’t been to a funeral or had any other contact with current patients, according to a report from the Centers for Disease Control and Prevention.

But the woman did have unprotected vaginal intercourse a few weeks earlier, with a 45-year-old Ebola survivor who has been free of the disease for months. The man developed the disease in September and was discharged from a treatment center in early October. That man also had sex with a second woman, who has not tested positive for Ebola, the CDC says.

Although doctors have known for some time that the Ebola virus can survive in semen long after a patient is considered cured, there has never been a clear, documented case of this happening, according to the CDC report.

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