The risk of catching Ebola from a survivor is generally low since the virus disappears from the blood within weeks, but it may persist in semen for many months, researchers said Monday.
Until now, scientists have been uncertain of how to characterize the risk of catching the Ebola virus — which killed more than 11,000 people in West Africa — via social contact with survivors who have overcome their illness.
Ebola is known to spread by close contact with the bodily fluids of an infected person, and can cause fatal haemorrhage, vomiting and diarrhoea.
For the latest study, published in the journal PLOS Neglected Tropical Diseases, scientists pored over nearly 6,000 articles on Ebola to find those that documented the virus in survivors' blood, sweat, urine, semen, stool, vomit, vaginal fluids and breast milk.
"We wanted to know how long the Ebola virus persists in different body fluids after people have recovered — in order to assess how much of a transmission risk those survivors pose to their family, communities and medical professionals," said lead researcher Paul Hunter from the University of East Anglia's Norwich Medical School.
LOW INFECTIOUS RATE
They found that virus typically clears the blood — considered the major risk for transmission because blood carries a lot of the virus — within 16 days.
Just five percent of patients carried the virus in their blood after 16 days, and the longest period observed was 29 days.
The virus lingered in the semen of male survivors much longer — some 70 percent of semen samples from male survivors tested positive for the virus in the first seven months after illness.
In all, the study found just 17 survivors had given semen samples over the seven month period following the onset of infection.
"Apart from saliva and blood, there are potentially important gaps in the information on all bodily fluids," noted the study.
The US Centers for Disease Control and Prevention cautions people to use a condom or abstain from sex after an Ebola infection.
"Because it is not known how long Ebola might be found in the semen of male survivors, they should abstain or use a condom for all sexual activity," according to the CDC website.
The study in PLOS did not weigh in on how to avoid the risks of sexual transmission, but said that "apart from blood and semen, most other body fluids pose a low infectious risk."
Not enough evidence could be found to make a conclusion on breast milk.
Hunter added that the team found no evidence that the virus could re-activate in survivors and become infectious again — via non-sexual contact — after the initial illness had passed.
"Consequently transmission from social contact with an Ebola survivor is not something that is likely to be a problem, even if that person is suffering from longer term complications."