In the first known case of what may be transmission of the Ebola virus from a pig to a human, a pig handler in the Philippines has tested positive for a strain of the virus, world health officials and the Philippine government announced Friday.

But the strain — Ebola Reston — is not known to be dangerous to humans, and the worker, who was infected at least six months ago, is healthy, officials said.

The development is worrying, because pigs are mixing vessels for other human and animal viruses, like flu, and because it shows that pigs may also be able to transmit the lethal strains of Ebola. Far more humans are in regular contact with pigs than with apes, monkeys or bats, the other known hosts.

But Dr. Juan Lubroth, chief of animal health at the United Nations Food and Agricultural Organization, said that there was “more need to investigate than to worry” and that many unanswered questions remained.