By Philip Whiteside, international news reporter
Ebola is a virus that causes a serious illness that often leads to death if it is not treated.
It was first identified in 1976 in the Democratic Republic of Congo in a community alongside the Ebola River.
During the outbreak, 318 cases were identified, but 88% of the victims died. The mortality rate makes it one of the most deadly diseases in history – much worse than the estimated 30-60% of Europeans who died of bubonic plague in the Middle Ages.
In 1967, as a result of a possibly related outbreak of DR Congo, the disease killed 151 people in what is now South Sudan.
Since then, there have been at least 25 outbreaks – most of whom have killed nearly 11,000 people in Guinea, Sierra Leone and Liberia between 2014 and 2016.
Some outbreaks have occurred in the West, but the vast majority have affected countries in a large part of Sub-Saharan Africa.
All have reached their peak and have subsequently disappeared and many are years apart and often hundreds or thousands of miles apart.
It is only recently that scientists have discovered that the movement of Ebola over great distances and its tendency to disappear and return is due to its natural home in the animal kingdom.
Professor Daniel Bausch, director of the British Rapid Support Team for Ebola and a senior figure in organizing the British response to the outbreak in West Africa, told Sky News why the disease can travel so far.
"We think it is probably kept in nature in bats," he said.
"When Ebola started near the small town of Gueckedou in West Africa in 2013, there was evidence that the first person who was infected was a small child playing around a tree where bats lay on their burrows.
"So you can imagine that it was a direct infection of the stool or that, for example, the bat munched on a mango and that the mango falls and the boy chews on the same fruit, and it is passed on by the saliva.
"Bats are the reservoir for several other sister viruses for Ebola, so that's the predominant theory.
"People can therefore become infected in different ways, they can become infected by accidental accidental contact, via stick excrement, saliva or food.
"Even though for many of us it seems a culturally strange thing, bats are a food source in many parts of the world – people catch bats and cook them.
"It is probably not the intention that people cook and eat the bats because the virus is inactivated during cooking, so it is the person who would catch and slaughter the animal that is most at risk.
"Then there is a third way, instead of the bat chewing on the mango and a man chewing the mango, it can be a monkey, or something like that, that gets infected by that process and then man goes hunting to that animal (like a monkey) with the Ebola virus and the person who is a butcher, that animal is infected. "
He said that bats are known to travel long distances, but are also very social animals, so the potential for Ebola to spread from bat to bat is very high.
"Bats can have large migration patterns," he said.
"It remains speculation how the tension of Ebola ended up in Guinea, but it is not that one bat or even a colony of bats all have to migrate to West Africa in one go.
"It may be that the process that eventually led to the bat being infected in Guinea started a decade ago – a colony of bats went from one cave in central Africa to a cave a bit more to the northwest and as the time passed by virus to other colonies, with the result eventually, perhaps years later, that bats are infected in Guinea.
"Bats fly with mammals, some can cover great distances.
"It is possible that it can go wherever the bats can be located, but it is also possible that viruses are very specifically linked to specific species. We think they have evolved together for thousands of years. There are no bats in the US. or the UK, so there would be no introduction of bats in those countries. "
He said that scientists had found evidence of at least three species of bats carrying Ebola, but it was not known which man had ended up with humans.
But the gaps in outbreaks can be explained by the probability that ebola-carrying bats will move and only occasionally come into contact with people that leads to cross-infection.
"There have been 10 outbreaks in the DRC," Prof Bausch said. "From this we can conclude that they each represent different events where introduction from the wild took place.
"If you want to use the term" latently ", it lies dormant in the bat population, it is not that it lurks in humans and then comes out. & # 39;
Despite Ebola's wide reach and ability to come back, Prof Bausch said he was confident that it would not evolve into a form that is more dangerous than it is at present.
He said: "This is a contagious disease, but if you compare it with other diseases, it is not really dangerous to catch it, people often confuse how transmissible a virus is with how deadly it is.
"For example measles – if someone in a room has measles, you are much more likely to catch it if you are in the same room or plane because it can be in the air.
"With Ebola you have to have direct contact and it has to be in the later stages of the disease If you are standing a few meters away from someone with Ebola, even if they have a very serious case, if you do not have contact with their blood or body fluids, your risk is essentially zero.
"There may be other types of the Ebola virus, but if it had incredible mutations, then those mutations might be so different that they could not replicate in animals.
"A certain amount of mutation that you could see, but I do not think there is the risk of what you sometimes see in the film, that the Zaire virus will suddenly change to be in the air, or will be maintained by another animal, that's something you see in Hollywood. & # 39;