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Swine disease-outbreak investigations identify hazards and on-farm risk events

Biosecurity has become the all-inclusive protector of swine herd health, attempting to shield pigs from exposure to detrimental viruses, bacteria and other pathogens. But even with all the biosecurity research, protocols and training, disease outbreaks remain a regular occurrence.

Why is that?

One reason, according to Derald Holtkamp, DVM, professor, veterinary diagnostic and production animal medicine, Iowa State University, “is because the industry, at least in the US, takes a ‘ready, fire, aim’ approach.” What he means by that is when research on a specific pathogen identifies likely transmission, producers and veterinarians place intense focus — or “open fire” — on addressing the problem area. “We have to remind ourselves that just because a certain situation can cause an outbreak doesn’t mean it occurs frequently,” he added. “We need to step back and look at what are the most frequent causes; where are the vulnerabilities to pathogen introduction and aim at those.”

One such example is porcine reproductive and respiratory syndrome virus (PRRSV). Research has shown that the virus can be transmitted through the air, yet even with more filtered barns, about 25% of the US sow herd breaks with PRRS in any given year. However, data from the Morrison Swine Health Monitoring Project at the University of Minnesota shows that PRRS cases have declined following other extreme disease episodes, such as when porcine epidemic diarrhea virus entered the US in March 2013 and spread throughout 2014. “Producers and veterinarians got very serious about biosecurity during that time, and there were carryover effects for PRRSV,” Holtkamp said. “The industry responded to a crisis, and in 2015, it was a very ‘quiet’ year for PRRS.”

However, biosecurity diligence eventually weakened, and PRRS cases started to rise again. The 2018 African swine fever (ASF) outbreak in China re-focused US producers’ and veterinarians’ attention and renewed their biosecurity commitment to keep the virus out of the country, which again produced benefits for PRRSV.

A better approach

“Ready, aim, fire” is a better approach to make more sustainable progress, Holtkamp told participants of Zoetis’ 2020 Peer Circle webinar series. In the past decade, Holtkamp has committed much of his work to bio-exclusion — meant to keep pathogens from entering a swine herd and infecting pigs. More specifically, he has developed, revised and refined a process for disease-outbreak investigations, designed to identify hazards that make farms vulnerable to the introduction of pathogens and prioritize biosecurity measures to address those hazards.

“We’ve found the best time to get producers and veterinarians interested in improving biosecurity is right after a disease outbreak occurred,” he noted. “In a sense, that’s a crisis for the producer, so they’re interested in knowing what went wrong and are eager to put effective measures in place.”

Outbreak investigations are not new in the US. They’ve been around for many years, but the process lacked consistency. In fact, too often, the investigation was dominated by preconceived ideas of what went wrong. “It’s hard to learn that way, so we’ve proposed a slightly different approach,” Holtkamp said. “That involves a standard form and a more systematic, consistent and comprehensive process to follow.”

The on-site visit

The process starts with an on-site interview, which includes the farm manager and herd veterinarian, and is directed by a veterinarian who is not associated with the farm. It can be beneficial to involve other employees and upper-level production management. “Through the process you often can see them change their mindset,” Holtkamp said. “They’re already thinking about hazards and where bad things can happen.”

An investigation interview takes 2 to 3 hours to complete and addresses the farm as well as the surrounding area. In the US, outbreak investigations have been used primarily for PRRS, but Holtkamp noted they could be applied to other diseases, including ASF.

The approach is based on the internationally recognized principles of the Hazard Analysis and Critical Control Points. “A big part of that is to list hazards at all steps of production, so that’s what we’ve done in detail,” he added.

The interview form is the foundation of the investigation and is available on the Swine Health Information Center website (under the emerging disease/rapid response tabs). There also are examples of completed forms, training materials and videos.

The form is categorized by swine movements, vehicles/deliveries, people movements, pork/food entry, manure removal, entry of other animals, air/water entry. Each category has a series of closed-ended questions, requiring yes, no or multiple-choice answers, organized by carrying-agent-entry events, which “is any event when a virus, bacteria or other pathogen can be carried into a herd,” Holtkamp noted.  “For example, when semen gets delivered to the farm that’s one event. So, the potential pathogen-carrying agents are the semen, the driver, the vehicle. Events tend to happen with multiple pathogen-carrying agents.”

There is a scoring system — high, medium or low — for the investigator to rate the likelihood that the entry event was responsible for the pathogen introduction and outbreak. The investigator follows the same order of questioning every time. The closed-ended questions are used to direct an open-ended discussion about the steps that occurred and where there could be potential hazards. For semen entry, there are questions related to the boar stud, which leads to a discussion about its location, biosecurity processes and such.

“We need to understand all the steps in the process — who, what, where, when and how these production activities are taking place,” Holtkamp said. “It’s important to look at the entire production process; to think beyond a list of biosecurity practices.”

No smoking gun

It’s also important to recognize that it’s unlikely for a single failure to be responsible for introducing a pathogen into a susceptible herd. Rather, it’s the result of a series of failures.

Holtkamp is a strong advocate of layering biosecurity measures. “We tend to spend too much time trying to get everything perfect. We should focus more on layers,” he said.  “If one fails, you have others to back it up. None are 100% effective; they all have holes if not followed correctly.” One such example of layers for employee entry is having a bench entry, a shower, cleaning protocols for the shower area and hand-washing stations.

From 2015 to 2017, 19 PRRS outbreak investigations showed that the carrying-agent-entry events that rated high most frequently were employee entry, cull-sow removal and repairs done inside the barn.

“With any event that happens frequently, there’s a risk of pathogen introduction,” Holtkamp said, “and employee entry is the most frequent carrying-agent-entry event, by far.” So, not only do you need to build prevention measures, but you need to engage employees and build their understanding of what, why and how to do things.

Holtkamp believes that biosecurity investments have been effective, but people’s attention and commitment to detail slip. Outbreak investigations can identify vulnerabilities, and producers and veterinarians can use that information to prioritize biosecurity measures to address the most significant hazards first.

“You can’t do everything at once, so invest resources where you would get the greatest effect,” he noted. “Also accept that biosecurity is an active and continuous process to control hazards; it will never be done.”



Editor’s note: The presentation referenced in this article was made to a group of swine health professionals in Asia as part of Peer Circles webinars hosted by Zoetis.



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Biosecurity has become the all-inclusive protector of swine herd health. But even with all the biosecurity research, protocols and training, disease outbreaks remain a regular occurrence. Why is that?

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Posted on January 31, 2021

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Challenges associated with controlling porcine reproductive and respiratory syndrome virus (PRRSV) have resulted in the increased use of molecular diagnostic tests and sequencing, according to Phillip Gauger, DVM, PhD, Iowa State University.

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