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Q. Can Ebola be transmitted through semen? Could a man infect a woman through sex before he overtly falls ill? In particular, could Dr. Craig Spencer, who spent several days with his fiancée after his return from Africa and before his infection was detected on Oct. 23, have infected her through sexual contact?
A. “We’re not supposed to say ‘never’ in public health, but I’d say it’s extremely, extremely, extremely, extremely unlikely,” said Dr. Daniel G. Bausch of the Tulane University School of Public Health and Tropical Medicine, who has studied levels of virus in Ebola victims and survivors.
Ebola virus has been found in the semen of male survivors for up to 101 days after the onset of symptoms, according to the Centers for Disease Control and Prevention. So health authorities — being cautious — usually recommend that men who recover use condoms or abstain from sex, including oral sex, for three months. However, there have been 20 outbreaks of Ebola since the disease was first discovered in 1976, and sex has never emerged as a major risk factor.
“Though multiple studies have shown that Ebola virus can persist in semen for longer than in blood or other body fluids, sexual transmission of Ebola has not been definitively established,” the agency concludes on its web page detailing the studies.
The highest levels of virus are consistently found in blood, vomit and feces, and the virus is usually detectable in them from the moment the patient tests positive. Virus levels in blood, vomit and feces are low when symptoms first appear, then rise rapidly to a peak at Day 5 or so, then start to go down and are low again by Day 15 (if the patient survives that long).
The virus starts to rise later in other fluids, including saliva and tears, but never to such intense concentrations as it does in blood, vomit and feces. It’s unclear whether there’s ever whole virus in sweat.
The number of men whose semen levels have been measured in studies is small. When the virus was found in semen in studies, it was usually at levels so low that it was not detected by standard viral culture tests, but only by polymerase chain reaction, or P.C.R., testing.
Also, Dr. Bausch explained, the testicles are one of several parts of the body, along with the eyes and the brain, that are “immunologically protected.” It is harder for pathogens to enter them, and harder for the immune system to clear those pathogens if they do get in. For that reason, he said, it is extremely unlikely that Dr. Spencer, or any man, has infectious levels of Ebola virus in his semen before the peak of his infection.
The salivary glands, in contrast, Dr. Bausch said, are not protected. So if there was any danger in intimate contact with Dr. Spencer, kissing was probably the greater risk, Dr. Bausch said. But because viral loads begin to rise in saliva days later than they do in blood, the risk was probably near zero, he added.