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A study which analysed samples of the latest outbreak in Guinea has found that it appears not to be a fresh spill-over from nature - but rather has come from a survivor of the previous outbreak in West Africa - which was five years ago.

Scientists say this suggests the disease can be incubated within humans for years and we may need to start thinking of 'human reservoirs' of the disease as well as animal ones. They're calling for increased surveillance and vaccination programmes to contain outbreaks before they get out of control.

Michael Wiley is a virologist at the University of Nebraska Medical Center and CEO of PraesensBio who contributed to the report.

"When this first happened 90 days was a surprise, then 180, then 500 days was a surprise. I think this is still very shocking but not completely unexpected."

(Photo: A man walks past an Ebola awareness painting in Monrovia. Credit: EPA)