Sex and masturbation may be hampering efforts to completely eradicate the deadly Ebola virus in West Africa due to transmission through male semen.
The World Health Organisation (WHO) had hoped for an end to the deadly outbreak by the end of the year but isolated flare-ups continue in areas beleaguered by the disease.
Bruce Aylward, head of the WHO's Ebola response, said they advised all male survivors to be tested three months after the onset of symptoms and then monthly until they know they have no risk of passing on the virus through their semen.
But a forthcoming study in the New England Journal of Medicine, based on around 200 survivors, found that around half still had traces of the virus in their semen after six months, a clinician familiar with the study told Reuters.
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The clinician, who was not authorised to speak about the study and spoke anonymously, added that the risk might not only be from sex but also from masturbation.
'It's not the sex that is dangerous, it's the semen that is dangerous,' said Mr Aylward
Transmission through semen may explain why a few cases continue to occur even though the outbreak has been almost completely eradicated by an intense international effort.
'This virus and this outbreak in particular has a nasty sting in the tail,'Mr Aylward said. 'It's not finished, by a long shot.'