Canadian politicians and health officials were demanding answers Monday from China over the country's ban on Alberta pork.

Xinhua news agency first reported the ban by the Chinese government on Sunday, which came after the revelation that 220 pigs at an Alberta farm had been infected with the H1N1 virus.

Accusing China of operating "outside of sound science," Agriculture Minister Gerry Ritz said Canada is considering taking China to the World Trade Organization if it doesn't lift the ban.

At least 10 other countries have shut out Canadian pork imports, including the Philippines, Ukraine, El Salvador, Honduras and South Korea.

So far, 20 countries have imposed a world-wide ban on imports of pork -- most of them affect products from Mexico and the U.S.

"This is an industry that has sales of over $15 billion and employs 45,000 people (in Canada)," said Liberal agriculture critic Wayne Easter in the House of Commons, "so the impact could be huge."

International Trade Minister Stockwell Day called China's ban on Canadian pork "disappointing and unwarranted," while Liberal foreign affairs critic Bob Rae went further, calling it "illegal."

The pigs caught the virus after having contact with a farm worker who had recently been to Mexico.

It was the first documented case of the H1N1 virus being transferred from a human to another species.

Day said Canadian officials in Beijing are attempting to "clarify" the situation with the Chinese government.

"All scientific evidence indicates the H1N1 flu virus is not passed by eating pork," Day said in an email to The Canadian Press Monday.

"There is no food safety concern related to the discovery of H1N1 Influenza in the herd in Alberta."

Scientists, including those at the World Health Organization, have been telling the public that the virus cannot be transmitted in food.

"Therefore (there is) no justification for the imposition of trade measures on the importation of pigs or their products," Day said.

Easter said the Tories need to be very aggressive in ensuring that countries don't ban Canadian pork.

"We export a lot of the byproducts of the hog to China that Canadians just don't eat... it's a very important market to us," Easter told CTV Newsnet from Ottawa on Monday.

Easter said hog prices are dropping at a time when the industry is already facing problems. He said producers will face "economic disaster" if the ban continues.

Paul Hodgman, executive director of Alberta Pork, said there is much at stake for Canada's pork industry.

"It's actually bigger on the export front than the beef industry is, which comes to the surprise of a lot of people," Hodgman told CTV Newsnet from Edmonton. "We export about 60 per cent of what we produce -- we're in the top three exporting nations in the world, and we export to about 100 countries."

In addition to China, at least eight other countries have put restrictions on Canadian pork since the H1N1 outbreak, Jurgen Preugschas, the president of the Canadian Pork Council, told The Canadian Press.

Alberta's chief veterinarian, Dr. Gerald Hauer, says there are no indications that people can get sick with H1N1 from eating pork.

"Pork is known to be safe to eat," Hauer told CTV's Canada AM in a phone interview from Alberta on Monday morning.

"All the organizations agree that properly prepared and handled and cooked pork will not cause any problems with swine influenza."

Hauer said the affected pigs have since been quarantined and the farm has been restricted from moving any of its pigs, on or off the farm, without permits from the Canadian Food Inspection Agency.

Authorities are also monitoring the health of other pigs within the region, he said.

Hauer said pigs are affected by the H1N1 virus similarly to the way that humans are.

"It causes a mild disease that generally just passes on its own," Hauer said.

Hauer said it is "not terribly surprising" that a farm worker passed the H1N1 virus onto the herd of Alberta pigs, but health officials have advised pig farmers to increase their bio-security measures as a precaution against the disease.

He said the fact that the pigs in Alberta have been infected does not increase the risk that the H1N1 virus will evolve into a more dangerous type of flu.

Infectious disease specialist Dr. Neil Rau told CTV's Canada AM the idea that the infected pigs will inevitably cause the H1N1 flu to become more virulent is "completely speculative."

"Mutations could also make the virus less virulent," Rau said in an interview in Toronto on Monday morning, noting that the "odds are that it will be less virulent."

With a report from CTV's Robert Fife and files from The Canadian Press and The Associated Press