The Ebola virus has mutated in West Africa say scientists who fear it could mean the disease is becoming more contagious.
Researchers in France who first identified the current outbreak have been tracking the virus in Guinea, analysing hundreds of blood samples from infected patients.
"We know the virus is changing quite a lot," said human geneticist Dr Anavaj Sakuntabhai. "That's important for diagnosing (new cases) and for treatment. We need to know how this virus (is changing) to keep up with our enemy"
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Viruses mutate all the time so this is not unusual, says the BBC's global health correspondent Tulip Mazumdar. And Ebola falls into the same category of viruses as HIV and influenza, which have high mutation rates.
Researchers say they are concerned that some of those with the disease may not be displaying symptoms, which could make the disease more contagious.
"These people may be the people who can spread the virus better, but we still don't know that yet. A virus can change itself to less deadly, but more contagious and that's something we are afraid of," said Sakuntabhai.
Another concern is that the virus could mutate in a way which means airborne transmission could occur. However, scientists are keen to emphasise that there has been no evidence of this yet.
"For the moment the way of transmission is still the same. You just have to avoid contact (with a sick person)," said virologist Noel Tordo. "But as a scientist you can't predict it won't change. Maybe it will."
The study in Guinea is also expected to help scientists uncover why some people survive the disease and others do not. Ebola survival rates vary widely, ranging between 30 and 90 per cent, with the current outbreak killing around 40 per cent of those infected.
Ebola has so far claimed at least 8,641 lives and almost 22,000 people have been infected, although that number is expected to be much higher in reality.
