By Alan Mozes
And a related case report illustrates why this latest discovery is so concerning: Scientists from the U.S. Army Medical Research Institute for Infectious Diseases in Maryland found evidence in blood and semen samples that a male Ebola survivor from Liberia infected his female partner a full six months after his blood tested negative for the deadly virus. His semen sample tested positive.
The first study stems from an ongoing effort to track the fallout from last year's Ebola outbreak. According to the World Health Organization (WHO), the deadly virus has claimed the lives of more than 11,000 people, and infected an estimated 28,000 in three West African nations: Guinea, Liberia and Sierra Leone.
Researchers from the WHO, the U.S. Centers for Disease Control and Prevention, and the Sierra Leone Ministry of Health and Sanitation have spent the last year monitoring the bodily fluids of 93 male Ebola survivors whose symptoms have largely subsided.
In the Oct. 14 issue of the New England Journal of Medicine, a team led by Dr. Gibrilla Deen, from the Sierra Leone Ministry of Health, reported that more than one-quarter of the men who provided samples seven to nine months after the first sign of symptoms had semen that tested positive for Ebola. The case report appears in the same issue of the journal.
"I think this has really important implications, because we really know very little about this virus," said Dr. William Fischer, an assistant professor of medicine at the University of North Carolina School of Medicine in Chapel Hill.
"And this demonstrates that the problems inflicted by Ebola don't necessarily end with clearance of the virus from the blood," added Fischer, who was not involved in the study.
The study team first looked for signs of Ebola in semen samples obtained from nine Sierra Leone patients during the three months following their onset of symptoms. Ebola was found in 100 percent of those samples.
Another 40 men were tested four to six months later, and 65 percent of those semen samples tested positive. The most recent group of 43 men were tested between seven and nine months after symptom onset, and 26 percent had Ebola in their semen, the investigators found.
"We've seen this sort of thing with other diseases -- the compartmentalization of a virus," Fischer said. "The virus looks for parts of the body that the patient's immune system can't easily get to, what we call immune-privileged sites. And when a virus can get into those areas, it can actually persist."
Dr. Amesh Adalja, a senior associate at the Center for Health Security at the University of Pittsburgh Medical Center in Baltimore, put it this way: "These are essentially sanctuary sites, hideouts where the immune system doesn't have the same power it has in the blood or in the gastrointestinal tract."
Adalja, who was not a part of the latest investigation, added, "We've seen this happen in a patient's eyeball. And we've known for a while that Ebola can hide out in semen. But until now we didn't know that this could continue beyond six months. So, this is a very important finding. And it will have an influence on how we guide patients going forward, and how we determine when it's appropriate to give patients the all-clear."
But Fischer added: "It could be that what we're seeing here are just remnants of virus with a marked decrease in infectivity. And it could be that their ability to hide out doesn't last forever. This study does suggest that the risk that they can do this goes down with time."
Fischer added that there is probably "some level of immune response that can attack this hidden virus over time, though it may take a while to penetrate. But at this point it's hard to know."
Meanwhile, he said, "the concern that survivors can pass the virus on sexually is real."
Just how real remains unclear, the research team said. The investigators acknowledged that they are not yet able to characterize the level of infection risk posed by the amount of virus they've spotted in semen. And in their report, they pointed out that "although cases of suspected sexual transmission of Ebola have been reported, they are rare."
Nevertheless, as a practical matter, the WHO cautions that male survivors of the Ebola outbreak in West Africa should go in for routine viral testing and counseling, and refrain from all sexual contact, or use condoms, until their semen samples have twice come back negative for Ebola.