Transmitting PRRS via Transportation

Sunday, October 16, 2022

Vehicles play a significant role in the virus's spread.

By Becky Dumais

"Porcine reproductive and respiratory syndrome virus (PRRSV) remains one of the most economically significant viruses in North American pig production and global pig production. PRRS is a beast," says Egan Brockhoff, veterinary counselor with the Canadian Pork Council.

"It's a very costly disease. An outbreak is one of the most devastating things a big farm can go through, so it makes a lot of sense to focus on it. PRRSV can be a much more expensive disease than a porcine epidemic diarrhea (PED) virus outbreak.

"Transport is always considered the top of the indirect contamination route," he says, discussing a recent study conducted by researchers at North Carolina State University (NCSU).

Models of study

Brockhoff says that it's been known for years that vehicles transmitted disease.

"There isn't just a single transportation event on a farm," he says. There are trailers dedicated to moving pigs from the sow barn to the nursery or the sow barn to the nursery grow-finish, for example.

"Those transports have a different risk profile than a transport that moves your pigs from the finisher to the slaughterhouse, or from the sow barn to the cull sow assembly yard.

"So what I like about this (study) is that it tries to provide further nuances to those details, and to establish a risk profile for the slightly different contamination pathways within the big category of animal transport."

Then there are other categories – "feed transport, people's transport, deadstock pickup. Transport itself is a great big space, but animal transport can be further divided into these smaller spaces," Brockhoff says.

The NCSU study, he adds, "gives us a tool to be a little more nuanced in terms of understanding."

The NCSU study modelled nine different potential transmission routes for PRRS. It found that trucks used to move animals, as well as farmworkers and feed, can be prevalent carriers for disease spread, and in an article outlining the results published on NCSU's website, writer Tracey Peake agrees with Brockhoff. PRRS is "the most economically significant disease affecting U.S. swine production."

A "novel mathematical model" was created, which includes potential transmission routes that, according to Peake's article, haven't been explored in depth.

Gustavo Machado, assistant professor of population health and pathobiology at NCSU, and corresponding study author and senior postdoctoral researcher Jason Galvis modeled nine modes of between-farm transmission of PRRSV based on the data taken from three swine farms.

Modes studied were: farm-to-farm proximity; transmission between farm animals; "re-breaks" for farms with a previous outbreak; between-farm vehicle movements; and animal by-products in feed ingredients.

The model was used to estimate the weekly number of outbreaks and their locations. Estimates were then compared to available outbreak data so that the researchers could calculate the contributions of each transmission route.

Results indicated that while pig movements and farm proximity remained the leading causes of disease transmission, the vehicles used to transport pigs were a major contributor to PRRSV spread – up to 20 per cent of infections.

"If I have a farm and receive an infected pig, that will only affect my farm," Galvis says in the article. "But if the same truck that brought me that pig then travels to other farms, it can carry that contamination with it. This is the first time we've included vehicle transmission in our model, and it does have an impact."

The NCSU study results confirm already-established knowledge, in Brockhoff's opinion, "that transport remains our No. 1 cause of indirect PRRSV (transmission) – and PED virus would be the same."

Interconnected continent

The overall goal of the model, according to the NCSU researchers, is to help producers target the areas where enhanced biosecurity and intervention would be helpful.

"If improving truck sanitation practices or adding cleaning stations could reduce PRRSV transmission, then that's much more cost-effective than treating the outbreaks when they occur," Machado says in the article.

The North American swine transport sector is extremely interlinked. "Everything in this paper is completely relevant to the Canadian story," Brockhoff says. "And when we do PRRSV transmission research here, it's relevant to our American colleagues too."

Brockoff says Canada moves about 100,000 pigs to the U.S. every week.

"It's a daily thing to see pig transports leave Canada, cross into the U.S., and return to Canada. I think of southern Ontario's cull sow assembly yards – those are the largest in Canada – and they're moving into the States all the time. We're so interconnected.

"And the reason why we wash and disinfect and dry trailers is because there's overwhelming agreement that contaminated transports are a major player," he says.

Hauling hotspots

When there are pigs within a trailer shedding the virus, the trailer then "really becomes a hotspot," Brockhoff says.

Although people can get PRRSV on their clothes, hands or body, they're not actively shedding it like pigs do. "They act as a fomite, as a mechanical vector.

"Pigs are the ones producing and shedding viruses, so when we haul a load of pigs that are shedding PRRS or PED, that trailer is red hot. We can move virus on people, but it's a spark compared to a trailer," he says.

There can be difficulty cleaning a trailer containing 2,400 nursery pigs or 150 finishers with potentially infected pigs, and yet biosecurity is vital. "Those trailers, when they're red hot like that, your wash, disinfect and dry has to be so effective." The problem, Brockhoff says, often lies in the lack of infrastructure.

More infrastructure

Vehicles are helping harbour – and deliver – the disease from place to place, but the issue doesn't necessarily lie within the current biosecurity protocols – it's more to do with a lack of facilities to clean the trucks.

Brockhoff coincidentally received an email the morning of this Better Pork interview from U.S. colleagues wanting to form a consortium on truck-wash biosecurity. "Because it's so important to all of North America and we don't have enough infrastructure in Canada and the U.S. to wash everything to the best possible level," he notes.

"This paper is timely but it doesn't change the fact that we probably need more resources too."

And while it's well recognized that washing your transports is one of the most effective things producers can do to reduce the indirect transmission of viruses like PRRSV (and PED), according to Brockhoff, the infrastructure issues are complicated.

"Building a truck wash is extremely expensive. Once you get it built, it's labour-intensive. It can take two people up to 2.5 hours just to wash a single trailer. Operating it is cost-intensive. There are layers of challenges within it.

"I don't think there are many people who wouldn't recognize the importance – but despite recognition, there are obstacles."

The highlight of it all, he says, is that it's going to take some innovation.

"We've seen more and more truck washes being built in the last 20 years. And in that time, we've seen more drying bays being built. In the last 15 years, we've seen more of these high-temperature baking bays being built.

"But we still don't have enough of them, and it adds a lot of cost to the sector, and we haven't had the most lucrative years. I think everyone would love access to something like that, but it's not always affordable." BP