The Ebola virus only spreads through direct contact with a sick person's body fluids. including blood, saliva, sweat, vomit, urine, faeces, breast milk, and semen. It's the last one that has doctors concerned: it's likely that for one Liberian woman, Ebola was a sexually-transmitted disease.
The woman came down with the virus after she had unprotected sex with a man who had recovered from the disease five months earlier. In an article about the public health implications of the discovery at Nature, Declan Butler describes the genetic detective work that identified the source of the woman's infection. Starting with the male survivor's semen, researchers...
...generated an almost complete sequence of the Ebola virus genome from his semen and showed that it differed by just one mutation from the sequence of the virus in the woman. And three mutations shared by the woman and the survivor had not not been seen in the 796 other sequences of Ebola in West Africa. "I think that we can move the 'probable' to 'confirmed', based on all available evidence," says Gustavo Palacios, one of the authors of the study and a researcher at the Center for Genome Sciences.
Although the risk of sexually transmitted Ebola infection is low, it's clearly not zero. Researchers are still trying to determine how long Ebola virus can live in semen and other tissues after victims recover. Based on this new case, they're recommending that Ebola survivors either abstain from sex or use condoms for at least six months, or until they test negative for the disease twice.