"At this time we have seen no data that would indicate that pigs are in any way involved in spreading the current strain of H5N1 influenza virus," said FAO's Peter Roeder, a veterinary virologist and animal health expert. "FAO would advise caution in the interpretation of diagnostic results that have been generated by tests that do not conform to the standards established by the Office Internationale des épizooties (OIE)."
Nonetheless, scientists have expressed fears that swine - which suffer from a wide variety of diseases that also infect people - could become a vessel for the lethal avian flu strain to combine with human influenza, creating a deadly new virus that could spread easily from person to person.
In urging for calm, the FAO points to the findings of a recent study on Vietnamese swine, which showed no evidence of the presence of the H5N1 virus in swine.
"Right now, there is no justification for saying there is H5N1 virus infection in pigs in Vietnam," said author professor Robert Webster. "At this stage nothing has been proven. Until either a virus is isolated from within an animal or there are antibodies to show infection the question of transmission remains wide open."
Webster's investigation on pigs living in close contact with infected poultry produced no evidence of transmission between the two species, although virologists have known for many years that influenza viruses can pass between species, including swine and poultry.
"It would not be a surprise because the potential susceptibility of pigs to avian influenza virus is well known," the Paris-based OIE said.
FAO will continue to monitor and investigate the situation closely and will inform countries if there is any reason to believe that the situation is changing. Recent guidelines produced by a joint expert consultation with the World Health Organisation (WHO) and the OIE are available on the FAO website.But while the FAO continues to urge for calm, jitters about the potential infection of pigs still managed to send Thailand's stock market down 3 per cent on Friday, ending three days of rise.
Avian flu has ravaged Thailand's poultry industry, the world's fourth largest poultry exporter. More than 27 million chickens have been culled in Thailand, while in Vietnam, which has banned the transport and sale of poultry, 14 million chickens have been culled.