The Western Canadian hog herd has remained almost free of the virus that has killed more than eight million pigs in the United States and sent pork prices soaring.

But pig producers in Manitoba, Saskatchewan and Alberta fear their farms could be devastated after a move by the Canadian Food Inspection Agency (CFIA) to require hog transport trailers be cleaned at U.S. wash facilities, that experts believe are contaminated with the disease, before returning to the provinces.

Manitoba Pork, the group that represents farmers in Canada's biggest pig producing and exporting province, has declared it a "crisis point," and says the federal government is ignoring expert advice from swine veterinarians and farmers.

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"We're raising the risk as a result of CFIA's obstinate approach in this thing," Andrew Dickson, general manager of Manitoba Pork, said.

Porcine epidemic diarrhea (PED), which kills almost all piglets and weakens larger ones, began sweeping through the U.S. hog industry in 2013 and was found in Ontario barns soon after. Amid a shortage of hogs for slaughter, pork and bacon prices in Canada and United States rose by 60 per cent. PED is generally spread through manure carried on the trucks that move among the farms, slaughterhouses and feedlots on both sides of the border.

But Western Canada has seen only a handful of cases of PED, a fact experts attribute to tough measures that include heightened on-farm biosecurity and the construction of about six advanced truck disinfecting stations in Manitoba.

Unlike many of the U.S. washes, the Manitoba truck washes do not recycle water and use high-temperature air to "bake" the trailer and kill the virus.

"Our first line of security has always been the border. That's why we introduced this emergency measure of bringing the trucks in and washing them at special stations here," Mr. Dickson said.

The system was approved in 2014 as an emergency measure by the CFIA, which temporarily allowed it to replace the long-standing rules requiring all livestock trucks be washed before returning to Canada.

"Having certified truck washes that could guarantee that we weren't going to get the virus was awesome," said Egan Brockhoff, a veterinarian at Prairie Swine Health Services in Alberta, who has worked extensively on the disease in Canada and abroad. "Taking clean Canadian trailers into exposed and contaminated U.S. truck washes really concerns us."

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However, the CFIA nullified the emergency measure on May 2 and pig trucks returning from U.S. farms must be cleaned at U.S. facilities.

"The CFIA has reviewed the situation and has concluded that the outbreak of PED in Canada no longer merits an emergency response," said the CFIA, which did to grant an interview.

A spokesman for Agriculture Minister Lawrence MacAulay said the minister would not intervene and declined an interview request.

Manitoba is home to pork giants Maple Leaf Foods Inc. and HyLife Ltd. and hundreds of independent farms. Every week, about 65,000 pigs from the western provinces – mostly babies – and 120 trucks cross into the U.S. at Emerson, Man. The trailers return empty.

"If Manitoba has healthy pigs then the rest of us have healthy pigs because it's an interconnected industry," Dr. Brockhoff said.

The Manitoba industry has launched a monitory program, testing the returning trailers for the virus. It is too soon to say if any have returned positive for the virus, Dr. Brockhoff said.

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Meanwhile, transport companies and pig farmers are continuing to ensure the trucks are washed in Canada after visiting the U.S. cleaning stations, a process that is slow, expensive and, most worrisome, optional.

"We feel we have an obligation to our customers. If I send that trailer into another farm, I could be putting their livelihood at risk," said Angie Hurst, co-owner of Luckhart Transport Ltd., a livestock trucking company based in Ontario and Manitoba that hauls pigs all over North America. "And if they don't have their business then I don't have their business."

The Maritimes has eradicated the disease. Quebec farms are PED-free, but it has been found at plants that slaughter pigs from Ontario, where at least nine new cases have been found since December.

Farms in Manitoba, Saskatchewan, Alberta and B.C. are PED-free, which Dr. Brockhoff credits to biosecurity measures including Manitoba's truck washing program.

PED is present in about 50 per cent of the U.S. sows and found throughout U.S. packing plants and feedlots. The disease is well-entrenched in Asian herds, he said, and a constant frustration for pig producers there.