Flies can carry the bird flu virus which has killed 46 people in Asia but there is no evidence they can spread the killer disease to other animals or humans, an animal health expert said on Wednesday.

Dewan Sibartie of the World Organisation for Animal Health (OIE) spoke a day after Japan’s Health Ministry said researchers found flies infected with avian influenza virus last year, the latest example of how the highly contagious virus can jump between species.

“Flies can carry the virus just like any other animal,” Sibartie told Reuters on the sidelines of a bird flu conference in Vietnam.

“But we don’t have any evidence to say that the virus will multiply in these flies and increase the danger. So I don’t think that it is really a specific problem to consider as regards to animals or even human beings,” Sibartie added.

The H5N1 bird flu strain was found in flies caught last March near a poultry farm in Kyoto in western Japan that had seen an outbreak of the virus the previous month.

A Japanese official said the possibility that flies could spread the virus among birds could not be ruled out and they should be exterminated in any future bird flu outbreaks.

“As a preventive measure such things (exterminating flies) are probably needed to ensure the safest measures,” Hiroshi Takimoto, who heads the ministry’s office of infectious disease information, said in Tokyo on Tuesday.

Sibartie said flies can “mechanically” carry the virus, but “we have not proved the virus can multiply in flies and create further problems”.

Besides having killed dozens of humans and caused the slaughter of 140 million birds across Asia, the H5N1 strain has been known to infect other species such as cats and leopards.

The World Health Organisation and health officials around the globe fear that the H5N1 strain might mutate into a lethal new virus that could spread rapidly among humans.