The Manitoba Pork Council "has received new information that suggests many livestock truck washes based in the US and Canada use recycled water," said Miles Beaudin, the council's quality assurance manager, in a special notice last week.

"Cleaning livestock trailers using recycled water may pose a significant biosecurity risk."

Porcine epidemic diarrhea (PED) has now infected hogs at 199 sites in 13 states. There have been no cases detected or reported in Canada.

The council, among others, has for weeks urged truckers to wash, disinfect and dry all trucks and trailers returning from the US before going to a pig farm, assembly yard or pork packing or processing plant in Canada.

However, "it is important to select a truck wash that does not use recycled water," Beaudin said last week.

"Truckers should wash their truck and trailers with only fresh water, use an appropriate disinfectant and follow a sound wash process as prepared by the Canadian Swine Health Board."

Transportation link

Swine veterinarians, investigators with the US Agriculture Department and others are focusing on the nation's livestock transportation system as they try to determine how the virus is spreading from farm to farm and state to state.

Mexico said Tuesday it has restricted live pork imports from the United States, citing the risk of the virus spreading.

Mexico's agriculture ministry, which said it would review imports on a case by case basis, added it had not detected the virus in Mexico.

Pigs imported from the US prior to 17 May would be quarantined and closely observed, the Mexican ag ministry said, and it is checking all lots of pigs imported from the United States during the past three months.

PED was never seen in North America until it surfaced several weeks ago in the US hog herd. Most often fatal to very young pigs, the virus causes diarrhea, vomiting and dehydration. It also sickens older hogs, though their survival rates tend to be high.

Iowa, the largest US hog producer, has the most sites testing positive for PED at 102 as of 10 June. The state raises 30 million hogs each year on average, according to the Iowa Pork Producers Association.

Substantial increase

Researchers at veterinarian diagnostic labs, testing samples as part of a broad investigation into the outbreak, have seen a substantial increase in positive cases since early June, when data on the PED outbreak showed it at some 103 sites nationwide.

The data was compiled and released last week by Iowa State University, University of Minnesota, Kansas State University and South Dakota State University.

The virus does not pose a health risk to humans or other animals and the meat from PED-infected pigs is safe for people to eat, according to federal officials and livestock economists.

But the virus is proving harder to control than previously believed. In addition to Iowa, Oklahoma has 38 positive sites, Minnesota has 19 and Indiana has ten, according to the data.

PED has also been diagnosed in Arkansas, Colorado, Kansas, Illinois, Michigan, Minnesota, Missouri, Ohio, Pennsylvania and South Dakota.

Spread

PEDV is spread most commonly by pigs ingesting contaminated feces. Investigators are studying physical transmission, such as truck trailers marred with contaminated feces, or a person wearing dirty boots or with dirty nails.

Mortality among very young pigs infected with PED on US farms is commonly 50 per cent, and can be as high at 100 per cent, say veterinarians and scientists who are studying the outbreak.

The strain of the PED virus seen in the US is 99.4 per cent similar in genetic structure to the strain that hit China's herds last year, according to the US researchers.

After PED was first diagnosed in China in 2010, it overran southern China and killed more than a million piglets, according to the Centers for Disease Control and Prevention's Emerging Infectious Diseases Journal.

No direct connection has been found between the US outbreak and previously identified outbreaks in Asia and Europe, scientists and researchers said.