PED mystery unsolved, but outbreak may have ended

Alberta’s lead veterinarians are cautiously optimistic the spread of a deadly hog virus has slowed — or maybe even stopped entirely.

“It’s now been eight weeks since our last case of porcine epidemic diarrhea virus (PEDv), and we’re ever hopeful that we will not be getting any more cases for the next while,” said Dr. Julia Keenliside, provincial veterinary epidemiologist.

Alberta was first hit by the virus — which spreads rapidly within herds and can be deadly in suckling pigs — on Jan. 7 when a farrow-to-finish operation near Calgary discovered the disease within its herd. A farrow-to-finish operation came next, on Feb. 1; then a farm 30 kilometres away on March 1; and finally, on March 15, a farrow-to-finish operation located just eight kilometres from the third infected site.

But since then, the virus has not been found in the province, despite increased surveillance of high-traffic pig sites, Keenliside said during a ‘town hall’ webinar on May 14.

Testing at 10 high-traffic pig sites across the province — three abattoirs, three assembly yards, and four truck washes — has ramped up by 110 per cent across the province since the first outbreak, and between Jan. 7 and May 9, at least 11,881 samples from these sites have been tested for the virus.

None came back positive.

“We’re pretty confident that none of our assembly yards or slaughter plants are a factor at this stage,” said Keenliside.

“While one negative environmental sample from one of these sites doesn’t mean there’s no PED there, having done weekly samples for 18 weeks and having them all remain negative does give us a better picture of what’s happening — and what’s not happening — in Alberta.

“The fact that we’re not seeing any positives tells us that we don’t likely have any other farms out there that are infected with this disease. This is all very good news for Alberta.”

Culprit still not found

The bad news is that officials are no closer to determining the source of the disease.

“Our first case of PED was over 1,300 kilometres away from the nearest case of PED that we can figure — that’s a long way that virus had to travel,” said Keenliside.

“So it’s a bit like being a police investigator — looking at all the different possibilities this virus could have taken advantage of when it moved.”

Officials are looking to recent outbreaks in other provinces for answers. In December, Ontario had three cases of the disease, followed by three more in February and two in April. Manitoba had its own outbreaks in December, February, and March, as did Quebec.

“We’ve been looking for the connection — why now and why in so many provinces?” said Keenliside. “But we’re not seeing any obvious connections yet.”

The National Centre for Foreign Animal Disease in Winnipeg has been sequencing the genome of the virus found in Alberta and comparing it to those from Ontario, Manitoba, Quebec, and the U.S. to see how closely related the strains are.

“Our preliminary results show that the virus closely matches both the Ontario and Manitoba strains, so we’re going to need to analyze more to see if we can draw conclusions.”

But other sources have been ruled out, including slaughter plants and assembly yards, said Keenliside.

“The timing just wasn’t right on the movements. None of these four farms moved pigs outside the province before they were infected.”

Feed ingredients have also been tested, as all four of the infected farms mix their own feed. The ingredients they used came from 10 countries in total, five different provinces, and four American states, including ones with PEDv infections. But testing those ingredients has been “really, really difficult.”

“You have a large volume and you’re looking for only a few virus particles within the feed. That’s a really tough one to prove or disprove,” said Keenliside.

One possibility is transport via ice on trucks travelling during the winter.

“On our first farm, we know we had trucks coming direct from the U.S. and Manitoba right to the feed mill to deliver their ingredients, right outside the door of the pig barn,” she said, adding that’s “pretty common” on pig farms.

“Maybe it’s a long shot, but potentially the virus could have come from the outside of the truck and then tracked into the barn if people weren’t changing their boots between the feed mill and the barn.

“People should be looking at feed mill biosecurity and thinking about where those trucks are coming from when they show up at the feed mill.”

Two of the farms also fed porcine plasma, and while the biosecurity around producing, processing, transporting, and storing plasma is stringent, none of the test results were conclusive, so there’s a “pretty remote possibility” the virus came in with the plasma.

A manure agitator on one of the farms that came from Manitoba is another suspect.

“Again, this is a long shot, but it was moved in the winter when the virus was frozen, so we’re still looking into whether it could have had contact with a PED-positive farm there,” said Keenliside. “At this point, I think everyone needs to critically look at their transport links for both feed and equipment and see if they came from regions where there is PED.”

Progress on infected farms

Meanwhile, vets are working to get all four farms to a ‘presumptive negative status,’ meaning the disease is no longer present in the animals or the barns.

Keith Lehman.
photo: Supplied

“An important part of our disease response plan was to make sure that we allowed these farms to get back into business as quickly as possible, while balancing the disease risks associated with a possible infection,” said Dr. Keith Lehman, chief provincial veterinarian.

The first infected farm opted to depopulate all its infected pigs through marketing, and disinfection on that barn is nearly complete. The other three, however, maintained their pig production — all three are farrowing again and have started to move market hogs to slaughter.

“All three farms that did keep animals were able to resume marketing of their pigs domestically through the contracts that they had in place prior to the disease detection,” said Lehman.

So far, that’s worked well for all three farms, added Keenliside.

“We know from Ontario that a number of farrow-to-finish operations have successfully eliminated the virus while continuing production,” she said. “We’ve been monitoring them to make sure that’s going well.”

Manure spreading now taking place at three out of four of the farms is also being monitored.

“We know that the virus can remain in the manure for several months, if not years, so we need to be very careful with how manure is spread,” she said.

“We’re lucky in Alberta that our farms are very far apart, so manure spreading has less risk here than it would in an area like Manitoba, where the farms are very close together. But even so, caution should be taken at manure-spreading time.”

And that same caution should extend to the rest of the farm as well, she added. All high-traffic hog sites should be treated as if they were contaminated, particularly transport trailers, barn entrances, and barns themselves. That means boot changes need to be enforced for every person every single time they enter or leave the barn, and trailers need to be washed, dried, and disinfected before and after transporting animals.

“You still need to keep up your biosecurity,” she said. “This is a good reminder that if there’s any unusual diarrhea, you need to make sure that is followed up with a veterinarian and that samples are taken.”