PEDv is spread most commonly by pigs ingesting contaminated feces. The virus, which is deadly to very young piglets, does not pose a health risk to humans or other animals and the meat from PEDv-infected pigs is safe for people to eat, according to federal officials.
Swine veterinarian James Lowe and a group of veterinary peers said they gathered swabs and environmental samples last month from 669 livestock trailers at seven Midwestern slaughter facilities - before and after animals were unloaded and moved into holding pens.
The researchers found that 17 percent of the trucks that pulled into the facilities during this time had trailers that were contaminated with PEDv, according to an abstract summarizing the researchers' findings that was released earlier this month. At some plants, as many as 69 percent of the trailers arriving on site were contaminated with PEDv.
Of the trailers that arrived free of PEDv, about one in 10 trailers - 11 percent - became contaminated while at these facilities.
"What happens is, the animals are unloaded on a common dock, then there's a lot of cross traffic of animals" and people, Lowe said. "It's the truck driver. It's the plant personnel. Everyone walks over the same ground or steps onto the tractor. ... So it gets on boots, on coveralls."
For every contaminated trailer that arrived at these plants, the researchers found that 1.2 contaminated trailers left the sites - moving the virus to new, previously uncontaminated locations.
While trailers can be cleaned and washed after they exit a plant facility, Lowe said, such sanitation is not mandatory. Even when equipment is cleaned, "getting rid of the PEDv off the trailer, that's physically quite hard. Then, you'd also have to make sure the boots are clean, the coveralls are clean."
The virus has proved more difficult to contain and kill than previously believed, say swine veterinarians, investigators with the U.S. Agriculture Department and others investigating how the virus is spreading from state to state.
The total number of pig deaths from the outbreak since the outbreak began this spring is not known. As of the week of July 14, researchers at federal and state veterinarian diagnostic labs had identified 378 positive cases of PEDv in 14 states.
Lowe and the other researchers gathered about 100 samples from each of the seven facilities during a seven-day period in mid-June. They then sent the samples to the Iowa State University Veterinary Diagnostic Laboratory to be tested for PEDv.