Ebola can cause deadly disease in some forms
A form of Ebola virus has been detected in pigs for the first time, raising concerns it could mutate and pose a new risk to humans.
Ebola-Reston virus (REBOV) has only previously been seen in monkeys and humans - and has not caused illness.
But researchers are concerned that pigs might provide a melting pot where the virus could mutate into something more menacing for humans.
The new discovery - in the Philippines - is featured in the journal Science.
However, the researchers, from the US Centers for Disease Control and Prevention, stress that the virus at present appears to pose no risk to humans.
It has been detected in farm workers who tend the infected pigs, and they have shown no signs of illness.
However, writing in Science, the researchers said: "REBOV infection in domestic swine raises concern about the potential for emerging disease in humans and a wider range of livestock.
"There is concern that its passage through swine may allow REBOV to diverge and shift its potential for pathogenicity."
REBOV belongs to the family of filoviruses which usually target primates.
These viruses cause viral haemorrhagic fevers, which cause extensive internal bleeding, and can be fatal.
The latest study examined tissue samples taken from pigs from different parts of the Philippines suffering from unusually severe respiratory infections.
Analysis showed that the animals were infected with widely varying strains of the virus, suggesting it may have circulated widely in pigs even before it was first discovered in monkeys exported to the US from the Philippines in 1989.
The researchers said it was possible that REBOV originally emerged in another, as yet unidentified, host. Fruit-eating bats have been suggested as one possibility.
Pigs are known to provide an ideal host for viruses to mutate. Experts say the potential risk is magnified because they are an essential part of the human food chain, and come into close contact with people.
Researcher Dr Michael McIntosh said: "We know this family of viruses are associated with fatal illnesses in humans.
"Even though there is no evidence at this time to suggest REBOV causes diseases in humans it does seem that it can infect humans, and be transmitted from swine to humans.
"The effect of such an infection on an immuno-compromised host - humans or swine - is also an unknown factor of concern."
The World Health Organization says that pork is still safe to eat, provided it is prepared and cooked properly.