It’s been a good year so far for PED in Manitoba’s hog barns.
The province has had only two cases of porcine epidemic diarrhea (PED) this year; one in the northeast and one in southeast Manitoba, both in nursery barns confirmed June 10.
This is in comparison to 60 cases by July 22 last year, when the province was in the midst of a record-setting PED outbreak.
Why it matters: After a historically high PED year in 2019, 2020 has, so far, offered a respite for the pork sector.
Dr. Glen Duizer of the province’s Chief Veterinary Office noted several possible reasons for the decline.
The last four years have seen a wave-like pattern of PED peaks and troughs, something Duizer says may be partially explained by residual immunity in breeding stock following an outbreak, but eventually falling prey to herd turnover and a relatively short immunity window within each animal.
“It decreases the chance of new infections and it also decreases the severity of the clinical signs, but when you look at the typical breeding herd, they’re obviously introducing new, and subsequently naïve, animals on a regular basis,” he said. “It doesn’t take very long for that population in the herd, herd immunity to drop.”
At the same time, he noted, PED does not “stimulate a long-lasting immunity in the affected animals.”
Manitoba had seen relatively little of the virus prior to 2017. In the first three years since PED was confirmed in Manitoba in 2014, only 10 cases were found.
In 2017, cases jumped up to 80 in a single year, leading the pork sector to adopt more rigid biosecurity and animal transportation procedures.
For the next year, those measures seemed to have paid off. Only 17 cases were reported in 2018, all in southeastern Manitoba, which has typically seen the bulk of the province’s PED issues.
Last year, however, saw another dramatic upswing. Barns in 2019 saw the largest outbreak to date, eventually topping out at 82 cases, including cases in the west-central part of the province and northeast, both previously untouched by the disease.
There are fewer naïve barns this year than in even 2018, given recent outbreaks, Duizer noted. Last year, 45 per cent of cases were in naïve herds.
Of the two cases so far this year, one was from a previously infected premise.
The province, however, is still cautious with the immunity explanation.
Outside of breeding stock, hog production does not carry animals over year to year to bring in residual immunity, Duizer noted. He added that vets are also worried that immunity might be making clinical signs harder to detect before the virus has already moved downstream.
“Does it seem like it’s offered some protection in the subsequent year? We kind of have two years so far of evidence of that, but I’m cautious. It’s pretty speculative on our part,” he said.
Spring weather may also help explain the decrease, according to Jenelle Hamblin, swine health programs manager with the Manitoba Pork Council.
“We had a bit of a later spring,” she said. “It was not nearly as dry. We had some pretty timely rains. I think that certainly could have played a role based on some of the models or some of the analysis we did in the last few years.”
The province identified dust as a probable source of infection in several cases in recent years.
Farmer awareness and communication within the sector has also played a critical role, she said. Producers are on guard against the virus after two major epidemics in the space of three years, and Hamblin says lessons from those epidemics continue to make their way through the sector.
About 75 per cent of pork producers now belong to the Manitoba Co-ordinated Disease Response program, an online portal meant to quickly spread information on any disease issues in the province, including spread of manure from recently infected farms, as well as offer resources for producers.
“Any changes that could have been made to protect the premises, the changes have been made and communicated out,” she said.
Producers are also attempting to get ahead of the virus every year, Duizer noted. Many barns may institute what he calls “war-time” biosecurity during the high transmission risk periods from April to June. In that period, Duizer said, biosecurity may be much stricter than could be maintained in the long term, but for that critical period, may well avoid infection in the spring. Likewise, he noted, farms may pursue dust control or other efforts to limit spring PED risk.
Experts are also honing in on how the disease transmits and where the risk factors for infection are.
Last year, the Manitoba Pork Council spearheaded a project looking at the longevity of the disease in manure lagoons, after some evidence suggested PED might last in manure much longer than first assumed.
The project, in co-operation with the University of Saskatchewan’s VIDO-InterVac, tested three lagoons, two from farms who had fought a PED infection in 2017, and one premise infected in 2018.
The study found that any remnants of the virus in the manure could not infect naïve pigs, good news for the industry.
“It certainly allows us to focus our efforts mainly on the 2019 lagoons,” Hamblin said, noting that it would be the first pump out for those farms since their infection. “Absolutely, there was diligence taken with previously PED-positive lagoons. However, with that study resulting the way it did, it gives a little bit greater peace of mind.”
The pork council wants future trials on the subject, she added, although she noted that those studies will have to wait, with staff at VIDO-InterVac occupied with developing a vaccine against COVID-19.
Reduced case numbers this year will help lessen the viral load in Manitoba’s manure lagoons, she noted.
There is no definitive data to say that COVID-19 measures, such as limiting the number of barns a staff member works at, have spilled over into the fight against PED, although Duizer said it is, “very reasonable to assume that if you have less overall contact to any livestock our poultry premises, then you decrease the risk of bringing in any disease, including PED.”
“We don’t know how much the frequency of contacts to the many swine premises have decreased during the pandemic,” he said. “We know it has, but we don’t know to what extent.”
The pandemic has shifted how farms deal with service providers and other potential human contacts that would be commonplace in any other year, he noted. Vets, for example, have told his office that they are doing more of their business over the phone.
While transmission from human contact is less likely than animal-to-animal transmission, such as livestock transport, he noted, the increased frequency of human contacts multiplies the risk.
Producers, “saw a lot less farm traffic,” Hamblin also said.
The COVID-19 pandemic and social distancing both heated up in mid-March, she said, about the same time that farms would be seeing increase risk of PED.
“Our spring months, where we traditionally have seen cases, there wasn’t a lot of movement period, not only with farm traffic, but people in general,” she said. “Did that contribute? I can’t say for certain, but less farm traffic, less traffic certainly could have played a role.”
While the first part of the spring and summer has been promising, the province may also not be out of the woods, Duizer cautioned. Last year’s outbreak saw a cluster of cases in fall, he noted, something he warned could still appear this year.
Nine of last year’s 82 cases were confirmed Sep. 10 or later.