By Ricci Shryock and Joe Bavier
MONROVIA/ABIDJAN, Feb 24 (Reuters) - Musa Pabai left an Ebola treatment center in Liberia in November, grateful to have survived a disease that has killed nearly 10,000 people across West Africa but fearing he still could pose grave danger the person closest to him.
By Valentine's Day, nearly three months later, the 23-year-old had not yet returned to Hannah, his girlfriend and mother of his young son.
"I don't want to be tempted by her ... It would be a problem," he said in the capital Monrovia, where he spent his self-imposed exile, afraid that he could still infect her through sexual contact despite his clean bill of health.
Research has shown traces of Ebola in semen of some survivors for at least 82 days after the onset of symptoms and in vaginal secretions for a much shorter period.
Scientists say testes are a reservoir for Ebola because white blood cells, which protect the body against disease, are unable to effectively destroy the virus there.
Although there is no conclusive scientific proof these traces are infectious, anecdotal evidence of several cases in West Africa and confirmed transmission of Marburg, another viral haemorrhagic fever, have led experts to warn of the potential risk of sexually transmitted Ebola.
With the disease typically taking 15 to 21 days to run its course, this means traces of Ebola can remain in semen for around two months after recovery.
This has raised the prospect of new infections, even in areas free of the disease, just as the year-long epidemic appears to be receding across the region.
Health officials declare Ebola outbreaks officially over after countries complete 42 days -- twice the incubation period for Ebola -- without recording new infections.
"We are saying that the outbreak is over after 42 days but technically it could be longer because of the risk of sexual transmission through contaminated semen," said Philippe Maughan, at the humanitarian branch of the European Commission.
The World Health Organization (WHO) advises Ebola survivors to abstain from sex during a 90-day period following recovery, or, failing that, to practice safe sex.
Worries over sexual transmission risk adding to the stigmatization Ebola survivors already face, and are protracting the emotional burden of families often struggling to overcome the deaths of relatives.
While men like Pabai have taken the WHO's advice a step further by separating themselves from their loved ones, some traumatized communities have imposed more draconian measures.
"We've got people being treated horrendously," said Margaret Harris, a spokeswoman on Ebola for the WHO. "In Sierra Leone particularly male survivors have been put in a form of concentration camp."
Harris said men had been detained in Bombali, a district northeast of the capital Freetown, highlighting how public hysteria had become a real danger.
"This will further stigmatize anyone with symptoms of Ebola and is likely to drive infections underground just at a time when we're getting the upper hand," she said.
Infections are now receding, potentially freeing up resources to test the semen of male survivors for the virus.
A positive test result would still not confirm if the traces of Ebola remain infectious, but a negative result could bring welcome relief.
"It's entirely possible to do this," said Michel Van Herp, an epidemiologist with medical charity Medecins Sans Frontieres. "At least we could reassure an individual that his semen is negative and he is not contagious."
Late last week Musa Pabai finally went home to Walakor, his village just outside Monrovia. He flirted, somewhat hesitantly, with Hannah but still worried for her health.
"They told me three months (of abstinence), but I am going to make it five months," he said. "That's my decision." (Additional reporting by Derrick Snyder in Monrovia and Emma Farge in Dakar; Editing by David Lewis and Robin Pomeroy)