* WHO expert says flu viruses can survive freezing
* Blood of H1N1 infected pigs may also contain virus
* Meat from sick pigs or pigs found dead must not be eaten
* Existing food safety, trade checks offer ample protection
(Recasts with more comments on food safety standards)
By Tan Ee Lyn
HONG KONG, May 6 (Reuters) - Meat from pigs infected with H1N1 flu should not be eaten by humans, a WHO official said on Wednesday, while stressing that existing checks were sufficient to safeguard the food supply from the new virus strain.
Jorgen Schlundt, director of the World Health Organisation's Department of Food Safety, Zoonoses and Foodborne Diseases, said care must be taken to ensure that pigs and their meat were checked for all diseases, including the H1N1 virus that may be present in the blood of infected animals.
"Meat from sick pigs or pigs found dead should not be processed or used for human consumption under any circumstances," he told Reuters.
It is possible for flu viruses such as the new H1N1 strain to survive the freezing process and be present in thawed meat, as well as in blood, the expert said. But he stressed that there was no risk of infection from eating or handling pork so long as normal precautions were adhered to.
"While it is possible for influenza viruses to survive the freezing process and be present on thawed meat, there are no data available on the survival of Influenza A/H1N1 on meat nor any data on the infectious dose for people," he wrote in an email reply to questions from Reuters about risks from the respiratory secretions and blood of infected pigs.
Schlundt said it was still unclear whether and how long the virus, which is commonly known as swine flu but also contains human and avian flu pieces, would be present in the blood and meat-juices of animals which contracted it.
"The likelihood of influenza viruses to be in the blood of an infected animal depends on the specific virus. Blood (and meat-juice) from influenza H1N1-infected pigs may potentially contain virus, but at present, this has not been established," he said.
The WHO has urged veterinarians, farm hands and slaughterhouse workers to exercise caution in their contact with pigs to avoid contamination until more is known about how it manifests in the animals.
"In general, we recommend that persons involved in activities where they could come in contact with large amounts of blood and secretions, such as those slaughtering/eviscerating pigs, wear appropriate protective equipment," Schlundt said.
The Food and Agriculture Organisation (FAO) and World Organisation for Animal Health (OIE) have said import bans on pigs and pork are not required to safeguard public health because the disease is not food-borne and does not pose a threat in dead animal tissue.
While acknowledging technical questions remain about the conditions in which the virus may be present, Schlundt stressed that the WHO had not changed its basic guidance that pork is safe to eat.
International trade and food safety guidelines -- drawn up well before the latest flu scare -- provide ample protection and ensure meat is not sourced from sick animals, he said.
"Sick animals should not enter the food chain. If you are following existing guidelines it (the virus) will not get into the human food chain," he said.
The Paris-based OIE has also said the new flu strain does not require supplemental care or checks besides those in place for other diseases, and stressed live pigs can continue to be traded using normal health inspection standards.
The new H1N1 swine flu virus is being transmitted from person to person, not from pigs to people.
Its global spread has prompted many countries to limit pork imports, however. As many as 20 governments have imposed import bans on live pigs and meat from affected countries to prevent exposure to the virus.
Such fears increased after Canadian authorities said on Saturday a herd of swine was infected by a farmer who had returned from Mexico.
The WHO said its laboratories have confirmed more than 1,500 cases of the flu virus in 22 countries.
While the strain is mainly spread from person to person through coughing and sneezing, experts do not know for sure how this virus came to be, which animal passed it to the first human patient and when that occurred.
But the case of the farmer infecting the pigs in Canada fuelled fears of the virus yet again jumping the species barrier -- this time from pig to human -- and possibly becoming more virulent in the process. (Additional reporting by Laura Macinnis in Geneva; Editing by Alison Williams)