MANILA (Reuters) - Four more people in the Philippines have been discovered infected by the Ebola-Reston virus and the possibility of pig-to-human transmission cannot be dismissed, the government said Friday.

It was not a major health risk, Health Secretary Francisco Duque told a news conference, adding that the government was however widening testing of people who might have been in contact with sick pigs at hog farms placed under quarantine since October 2008.

“The Ebola-Reston virus is both an animal and human health issue, but we still consider this as a low risk situation to human health,” Duque said.

He said experts from the World Health Organization (WHO), Food and Agriculture Organization (FAO) and World Organization for Animal Health (OIE) had been asked to determine the source and risk of the Ebola-Reston virus in pigs and impact on food security.

It is the first time the virus has been found outside monkeys and the first time it has been found in pigs. The virus had previously jumped from monkeys to humans but it is the first case of a jump from hogs.

Ebola-Reston virus was found in the Philippines as early as the late 1980s and 25 people were found infected after contact with sick monkeys. But only one developed flu-like symptoms and later recovered.

Last week, the government said at least 50 workers in the two farms were exposed to the virus but only one person tested positive. This person has not shown any symptoms and has remained healthy.

Duque said four new cases had been found and these people possibly had direct contact with sick pigs. Three of them were farm workers while one was a butcher, he added.

“At this time, the possibility of pig-to-human transmission cannot be dismissed,” Duque said.

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“Contact tracing of all five positive individuals is ongoing. It is a standard procedure to determine health risks to humans who are in close contract with positive individuals.”

He said all the four men who were found positive remain healthy and have not been seriously ill in the past 12 months.

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FARM PRACTICES

Davinio Catbagan, director of the bureau of animal industry, said tissue samples from 140 pigs from the two quarantined farms had been sent abroad for tests.

Earlier tests on more than 1,000 blood samples from pigs in the two affected farms had yielded negative results.

“No current unusual pig illness has been detected in these two farms,” Catbagan said, adding only two pigs died when the Ebola-Reston virus was discovered in October 2008.

The country has more than 13 million heads of swine and the discovery of Ebola-Reston in two farms was isolated, the government said.

The government has called on the public to report unusual pig deaths or illness, cautioning consumers from buying cheap pork and to fully cook meat bought from reputable sources.

Duque said they also asked commercial and backyard farms to practice safe farming and biosecurity measures to prevent and contain any future outbreaks.