MANILA, Philippines?(UPDATE 4) A Philippine pig farm worker has tested positive for a strain of the Ebola virus that is not deadly to humans, the World Health Organization and the government said Friday.

Health Secretary Francisco Duque said the farm worker's blood carried antibodies of the Ebola-Reston virus, which was first detected in laboratory monkeys in 1989 and has recently spread to pigs.

"Otherwise, he is healthy and has no sign of any sickness," Duque said at a joint news conference with a WHO mission.

Duque said health authorities were still trying to find out how the farmer contracted the virus and could not be certain it had spread from pigs.

He said there was no cause for public alarm, noting that pork is safe to eat as long as it is properly handled and thoroughly cooked, and that the latest incident presented a "negligible risk to human health."

WHO expert on infectious diseases Julie Hall said the antibodies indicated the worker had been infected between six and 18 months ago, but that he had not suffered any serious illness in the past year.

She said the case was still under investigation pending results of tests carried out on samples sent to the US Centers for Disease Control in Atlanta, Georgia.

Dr. Eric Tayag, DoH epidemiology chief, urged the public to report any unusual pig deaths as a first step.

"Second, handle sick pigs with caution; third do not consume double dead meat and lastly always cook pork adequately," said Tayag in a text message to INQUIRER.net.

At the same time, Tayag denied the victim was a hog farmer.

"We never mentioned the person who was positive was a hog farmer until we find out how he was exposed," said Tayag, noting the victim could have been more likely exposed to the virus carrier at least six months ago.

"So we have to know what happened six months ago," he said.

"In the meantime because the person remains healthy and never claimed being sick in the past year and person has antibodies, then this person cannot make others sick," Tayag said.

Ebola-Reston was first detected in 1989 in laboratory monkeys sent from the Philippines to Reston, Virginia, in the United States. Unlike its African counterparts, it has not proved deadly.

The worker is not the first human case of the Ebola-Reston virus, although he is the first person found to have been infected in the latest outbreak.

Twenty-five people who came into contact with the infected laboratory monkeys in 1989 tested positive for the virus. Only one showed signs of sickness, suffering from flu-like symptoms, but quickly recovered.

The government quarantined farms in the northern Philippine towns of Pandi and Talavera after the Ebola-Reston virus was discovered in pigs in July 2008.

Agriculture Secretary Arthur Yap said the quarantine remained in place and the Philippines had banned the export of pig products.

He also said authorities were widening their monitoring to include all farms that had reported unusual incidences of sickness in swine.

Duque said only four of the 6,000 pigs tested had contracted the virus since it was first detected.

Fifty people from two affected pig farms have been tested and examined, the official said.

The identity and age of the infected worker and the location of the farm were not disclosed. With a report from Thea Alberto, INQUIRER.net