Although Finance Minister Jim Flaherty said it remains unclear how the spreading swine flu will affect the economy, some of Canada's industries are already feeling the pinch and experts have warned about serious challenges ahead.

"It's definitely nothing to play down lightly ... This threatens to exacerbate what is already the most serious downturn of the post-war period," said Bank of Montreal economist Douglas Porter.

Canada has so far confirmed 13 mild cases of human infection of the swine flu. Chief public officer of health David Butler-Jones has warned that more severe cases may appear and may even result in deaths.

Agriculture and travel industries are among the biggest victims of the outbreak. On Monday, investors' worries already sent shares of pork producers lower on the stock markets, ignoring reassurances that the meat is not the source of the flu.

"They could've called it anything they wanted, but they've called it swine flu, so of course, it hits the hog industry real hard," said pork farmer John Pruen from southern Manitoba, which province produces a large share of Canada's pork.

"It could do a lot of damage to our industry," Jodi Bakke, director of policy and communications for Alberta Pork told reporters on Wednesday, adding precautions have been taken in the industry including keeping people with flu symptoms away from pigs.

Producers worry the swine flu will devastate hog farmers in the same way bovine spongiform encephalopathy, commonly known as mad cow disease, affected cattle farming a few years ago.

Reports say many countries including China and Russia are already banning the import of North American pork, which relies a lot on exports. The province of Manitoba alone exports four million hogs a year.

Even worse than the pork industry, the swine flu outbreak could have a disastrous effect on Canadian agricultural producers, many of whom rely on Mexican workers to plant and harvest crops.

More than 15,000 Mexican workers are entering Canada this year under a seasonal farm workers' program. Although Canada has not banned Mexican workers from coming, it is tightening admissions by asking all workers to be checked and undergo test before entering.

A reduction in farm workers could result in a disastrous season for the agricultural industry and for consumers, according to Doug Connery, the labor chairman of the Vegetable Growers Association of Manitoba.

Connery, who farms asparagus, carrots, green onions and broccoli on more than 300 hectares, usually brings in 80 migrant workers each year. He said he stands to lose half of his revenue if he cannot use workers from Mexico.