Thu Jul 9, 2009 3:14pm EDT

HONG KONG (Reuters) – Researchers are worried about a type of Ebola virus spreading in pigs in the Philippines and have warned that it could mutate in the swine population and become more dangerous for people.

The Philippines had tested 141 people, the researchers said, and six of them who either worked on pig farms or with swine products were found with antibodies to the Ebola-Reston virus, which means they might have been infected by pigs at some time.

Although none of them fell ill, the scientists from the Philippines and the Centers for Disease Control and Prevention in the United States warned the virus could change.

“REBOV (Ebola-Reston virus) infection in domestic swine raises concern about the potential for emerging disease in humans and a wider range of livestock,” they wrote in a paper published in the latest issue of Science.

“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 target primates. These viruses cause viral hemorrhagic fevers, which result in bleeding and coagulation, and can lead to death.

In their study, the scientists examined blood and tissue samples taken from pigs suffering unusually severe respiratory infections in different parts of the Philippines and found they contained widely varying strains of the virus.

This suggests that the virus may have circulated widely in pigs even before it was first discovered in monkeys exported to the United States from the Philippines in 1989, they wrote.

“It is possible that REBOV spilled over to monkeys and swine from an as yet unidentified host. Bats have been implicated as reservoirs for other filoviruses … and may also represent a candidate reservoir for REBOV,” the wrote.

The Philippines slaughtered 6,000 pigs at a hog farm north of the capital Manila to prevent the spread of the virus earlier this year. That was the first time the virus had been found outside monkeys and the first time in pigs.

The appearance of new or potentially dangerous microbes in farmed animals, like pigs, is always a worry because they make up the food chain and come in close physical contact with people.

(Reporting by Tan Ee Lyn; Editing by Sugia Katyal)