Beware of PRRS virus variants

Be prudent with biosecurity protocols to prevent illness from spreading.

By Kristen Lutz

Porcine reproductive and respiratory syndrome (PRRS) is a familiar ailment to pork producers. However, a new strain of the virus has filtered itself into barns south of the border, meaning Canadian producers should up their ante when it comes to biosecurity protocols.

While the virus can infect hogs throughout the year, it’s most common for infection rates to increase in the spring and fall with the change in weather. Plus, additional manure spreading can lead to airborne pathogen transmission.

A New Strain: PRRS 1-4-4 L1C

The new strain to be wary of is PRRS 1-4-4 L1C. To better understand this strain, Egan Brockhoff, DVM, veterinary counselor at Canadian Pork Council and veterinarian at Prairie Swine Health Services, explains the naming convention. “The naming system of PRRS virus is based off restriction length polymorphism. You can have many 1-4-4 strains that are completely unrelated because it’s just a way to name the open reading length of the gene,” he says.

The L1C portion of the name refers to the lineage or relation to other strains. “L1C is just a place on the dendrogram, like a family tree. The family tree shows how closely viruses are related to other viruses on the tree. This strain fits into the L1C Lineage, which makes it unique from all other viruses, slightly,” he says.

This new strain of PRRS has been majorly affecting Minnesota and Iowa and there’s been a small spread to surrounding midwestern states. “Every few years we get a strain of PRRS that is really pathogenic. Before this one, we had PRRS 1-7-4 that was pathogenic as well. These strains are extremely frustrating and difficult to manage, but we have dealt with them before,” Brockhoff explains.

PRRS signs & symptoms

The virus is complex; it can reduce fertility and cause abortion in gestating gilts and sows. It can also lead to other health issues, such as pneumonia. Al-though able to infect pigs at any age, it’s more present in younger pigs since they have a naïve immune system. Clinical signs can include “lethargy, anorexia; failure to thrive is typically present with a (high) fever,” says Brockhoff. “You may hear a cough, (witness) abortion and in young pigs, you’ll see scours.”

farrowing crate piglets
    Jodie Aldred photo

PRRS is a very adaptable, constantly changing virus, which can make it very hard to control on farms. “The virus will change; it’s an RNA virus. This means you can see the strain change over time, and you can see new introductions of the virus if biosecurity is an ongoing challenge,” Brockhoff explains.

“Farmers can have PRRS on their farm for years and years and (infection) depends on how the farm flows their pigs. Continuous flow (producers) always have piglets on their farm and are creating a new naïve immune system for the virus. So, we continue to see the virus circulating because of this new or naïve immune system.”

Disease transmission

Most producers assume it spreads through direct transmissions, such as pig-to-pig contact or person-to-pig contact. This would be most common when bringing in a new set of pigs carrying PRRS, or a worker moving between barns who wasn’t following biosecurity protocols.

Direct transmission of the virus can also occur through semen. “PRRS virus can move readily through semen and embryo transfer. So, testing semen before (pigs) entering the farm is very common. Boars (can) directly test positive for PRRS since it moves through the semen so well,” says Brockhoff.

Indirect transmission covers a wide variety of additional methods for disease transfer. “PRRS can move through bodily fluid. You can contaminate a transport truck, move it on your footwear, tools and equipment,” says Brockhoff. He continues to explain that even taking a clean transport truck with PRRS negative pigs to a processing plant and coming into contact with PRRS positive manure is a gateway to bringing the virus back to your farm. However, proper biosecurity protocols that ensure only clean and disinfected trucks are returning to the farm can help stop the spread.

PRRS can also be airborne. “There are some strains of the virus that are very effective at moving through arousal and some are not very good,” Brockhoff continues. “It is a virus that has been documented to travel almost 10 kilometers.”

piglet nursing
    Egan Brockhoff photo

The complexity of this virus is likely linked to its surface protein. These allow the virus to “camouflage itself, and it mutates its surface protein so the camouflage changes. It’s a very complicated virus,” Brockhoff says, perfectly summarizing the dynamic challenges this virus brings and why it can be so difficult to manage.

Vaccine effectiveness

A study was conducted and led by Scott Dee, DVM, director of Pipestone Research and former professor at the University of Minnesota. During a seminar at the Leman Swine Conference in St. Paul, Minn. on Sept19, 2021, Dee explained the study, as well as the results from the pre-published experiment.

This vaccine study consisted of three experiments total, but the most interesting one focused on the last pathogenic strain of PRRS, 1-7-4, and how effective vaccines were at control. This experiment consisted of three groups: the first was a control group with no vaccine given, and the remaining two groups were given one of two possible vaccines: Ingelvac PRRS or Prevacent PRRS. Vaccines were given according to label instructions and 28 days post-vaccination the pigs were challenged against PRRS using a well-documented PRRS challenge model. Results showed that both vaccines tested were effective against this PRRS virus.

“It reminds us that in the early days of disease outbreak, there is often speculation. It’s important to do these controlled trials so the veterinary community can use evidence-based decisions to help guide management decisions,” Brockhoff concludes.

“The vaccinated groups performed much better than the non-vaccinated groups. So, although there is a discussion on the effectiveness of the vaccines, these researchers found that both vaccines reduced all signs and symptoms of the disease: mortality, fever. And vaccinated pigs had a better average daily gain than unvaccinated pigs,” Brockhoff confirms.

Biosecurity protocols

Farmers are in control of direct transmission instances within their respective operations.

Biosecurity practices and protocols are more than capable of catching the virus and preventing further spread. “With new animals entering the farm, there should be a vet-to-vet (conversation) to discuss the source. There should be routine testing of the source to ensure it’s PRRS negative. When animals arrive at the farm, ideally, they are quarantined away from your pigs and then tested before they are released into your barn,” explains Brockhoff.

Indirect transmission can also be controlled on-farm, including routinely ensuring everyone is made aware of the biosecurity protocol and kept up to date with changes. Brockhoff explains that having an entryway that separates the outside ‘dirty’ things from the clean inside, and disinfecting things are key. “Make sure your transports are washed, disinfected and ideally thermal assist dried. Make sure all fomites (tools, boots, hands) entering the barn are disinfected. Whether this is by a fogging or disinfecting room, or spraying a disinfectant,” he continues.

People entering and leaving the barn should always shower and wash their hands. “There has been significant evidence to show that if you do something as simple as washing your hands with warm water and soap, you can eliminate the virus,” he states.

National surveillance

Canada is set up with a national surveillance system for swine and viruses like PRRS. The Canadian Swine Health Intelligence Network (CSHIN) is here to protect all pork producers from potential outbreaks.

CSHIN is “made up of four regional networks: the Atlantic Swine Network, RAIZO Quebec (Réseau d’alerte et d’information zoosanitaire), Ontario Animal Health Network and Canadian Western Swine Health Network,” Brockhoff explains. “These four regional networks, plus the national network, keep track of what’s happening in terms of PRRS emergence.

“They rely on veterinary diagnostic labs across Canada called CAHSN Labs (Canadian Animal Health Surveillance Network Labs).” CAHSN labs test and keep track of potential PRRS cases. The labs then feed information into their respective regional networks, which then relay that information to the national level.

Thanks to systems like these, the PRRS 1-4-4 L1C strain has not yet been found in Canada. However, veterinarians have been putting out information blasts to pork producers explaining the immediate importance of biosecurity right now.

The most likely method of transmission of the current PRRS strain would be from transports heading down to the midwestern U.S. where recent outbreaks have occurred. “We don’t bring a lot of pigs up from the U.S., but we do bring transports,” Brockhoff explains. “So, when the trucks go down to the states and unload pigs, before those trucks coming back to your farm they need to be properly cleaned and dried to stop the spread of any virus, not just PRRS.”

Combining knowledge and on-farm mitigations will help keep the virus at bay. Information blasts from CSHIN will have material on the spread of viruses and the preventative measures that can be taken.

“Biosecurity remains king, and external biosecurity is your big tool to keeping the virus off your farm,” Brockhoff says. “There are a lot of mitigation steps for direct or indirect virus exposure. Keep working with your vet and keep having discussions to keep up with your biosecurity.” BP

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