Scientists have detected a new strain of Ebola virus in pigs for the first time giving rise to fears that it could mutate and pose a new risk to humans.

Although the strain of Ebola virus found in domestic pigs in the Philippines last year is not one linked to disease in humans its emergence in the human food chain is cause for concern.

The investigation published as a paper in the 10 July issue of Science, is a joint effort between scientists from the US Department of Agriculture at the Plum Island Animal Disease Center in New York, the US Centers for Disease Control and Prevention in Atlanta, and the Department of Agriculture in the Philippines.

The Ebola-Reston virus was found in pigs raised on farms near Manila, in Philippines after farmers reported high rates of sickness and deaths among their livestock in May 2008 who were experiencing an unusually severe outbreak of porcine reproductive and respiratory disease syndrome.

Although Ebola-Reston virus (REBOV) belongs to the family of filoviruses which usually target primates and has not caused illness to humans, researchers are concerned that pigs might be a means for the virus to mutate into something more menacing for humans.

The Ebola and Marburg viruses belong to the filovirus family, which cause hemorrhagic fever, characterized by bleeding, vomiting and diarrhea, and a 90% death rate.

Regarding the origins of the virus the researchers said it was possible that REBOV originally emerged in another, as yet unidentified, host and fruit-eating bats have been suggested as one possibility.

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."

The researchers, from the US Centers for Disease Control and Prevention, stress that the virus at present appears to pose no risk to humans.

Reston has not been found to cause deadly hemorrhagic fever in humans, but even though the farmers showed no symptoms when the researchers tested some of the pig farmers they found antibodies to Reston in their blood, suggesting pig-to-human transmission had taken place.

This has led to worries that the pig herds could be hosts for Reston to mutate into a form that does cause illness in humans, more so as pigs are known to provide an ideal host for viruses to mutate. If such an event does come to pass then perhaps pigs could also be hosts to other Ebola strains that do cause harm to humans.

The biggest cause for concern the researchers said was as pigs are in the human food chain and there is ample contact between pig herds and humans.

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 said that it is safe to eat pork provided it is prepared and cooked properly.