Manitoba hog producers, veterinarians and others in the industry are nearing the end of a battle against deadly porcine epidemic diarrhea virus that affected 80 operations between April 28 and Oct. 24 last year.
Dr. Glen Duizer, chief veterinary officer for Manitoba, said May 8 that 67 of those operations are “presumptive negative,” which means PED is no longer present, with the possible exception of manure storage.
Ten operations are in the transitional phase, with pigs consistently testing negative for the virus. The other three are still listed as positive but Duizer said they have no clinical or actively shedding pigs and in one of those cases, the premises are empty of animals.
“Our current trend or target is … a little bit longer than the month of May. We were still targeting for the end of this month to get most, if not all, of the remaining herds onto presumptive negative,” said Duizer.
The infected operations, many of which had multiple premises and barns, were almost entirely in southeastern Manitoba bordered by Highway 72, the Trans-Canada Highway, the U.S. border and Sandilands Provincial Forest. It’s an area generally centred near Steinbach, Man., with PED in three main pockets.
Duizer said that during the outbreak, 12 operations got PED when pigs thought to have recovered from the virus, and which had tested negative, were moved in.
“We believe that this was evidence of recurrence of shedding for one reason or another, or perhaps a small group of pigs that just did not fully recover but started shedding larger numbers of the virus at a later date.
“The reason that we believe this, is that in some cases some of those 12 premises had other naive pigs on site that never became infected. So, the pattern really suggests that … PED-recovered pigs, through one way or another … may start shedding the virus again.”
The outbreak had two peaks, one in early July and a second in September, said Duizer. Those coincided with a lot of animal movement to packing plants. No finisher pigs were shedding the virus at time of slaughter but exposure to equipment, dead stock and transport are thought to be factors.
Duizer did not provide figures on how many pigs died or were eradicated to control PED. However, he did note marketing numbers indicate fewer finisher pigs went to slaughter in late 2017 and the first quarter of this year, which means the total was significant.
As for how PED entered the region, Duizer cited a number of potential sources. The virus is transmitted in fecal matter and can travel on surfaces, including equipment, trucks, vehicle tires, clothing and boots.
“First and foremost was direct animal movement. Second would be recurrent shedding of PED virus from recovered pigs, biosecurity gaps on the farm … associated with some form of contact to the farm, area spread in weather, dead stock, manure and manure application, and feed and feed movement.”
Some 30 premises were infected by pigs moving from one operation to another and of those, 18 were infected by pigs moved before it was realized they had PED.
Twelve of the 30 were infected by pigs thought to have recovered from the virus, Duizer added.
“From this I think we reiterate that the best option, when you’re dealing with PED-recovered pigs, is movement to slaughter (for cull sows or finishers) … or to other already positive premises for nursery pigs or younger finishers that need to be finished out.”
Many of the affected operations share staff and Duizer said that has potential to spread PED among barns and operations. He and other veterinarians suggest that staff working in PED-infected barns remain in those operations and not work in other barns where no PED has been found.
One suspicion suggests that the virus could have moved into hog operations from passing transport trucks carrying PED-positive animals. Spring weight restrictions brought trucks nearer to some barns because alternative routes were needed.
Duizer said the industry has since worked to establish dedicated truck routes from assembly yards to American slaughter plants so there is no movement down other roads.
Pigs who died in the outbreak were kept out of the rendering stream to avoid potential contamination of trucks, scales and wash bays. Dead stock was instead taken to a City of Winnipeg landfill designed to handle specified risk materials.
The role of manure and its application from infected premises in PED spread remains a question, Duizer added. No link has been established between manure spreading and PED infection. The greater risk is contamination via equipment.
“We can consistently find test-positive manure from lagoons one, two and even three years after the lagoons have received manure from infected pigs. The question remains as to whether that is infective or whether we’re just detecting viral particles.”
Feed was not identified as a source of Manitoba’s recent outbreak.