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17 years of detective work, shared experiences helping pork industry get ahead of PRRS

31 October 2018

Poultry Health Today

The evolution of knowledge about porcine reproductive and respiratory syndrome (PRRS) is now enabling pork producers and their veterinarians to make headway combating this difficult and costly disease.

“You might lose a battle now and then, but overall, I’d say we’re winning the war,” said Scott Dee, DVM, PhD, director of research, Pipestone Applied Research, Pipestone, Minnesota.

Dee recalled the time in 1990 he encountered his first case of “mystery swine disease,” or what was later dubbed PRRS.

A distraught producer had summoned him to a sow farm where all the sows had aborted and many had died. The setting was eerie, Dee recalled, because there were no animal sounds. All he could hear was the producer, who was on his knees crying at the devastation.

The virus hadn’t yet been identified and diagnostics revealed no etiology. “It happened over and over, and I couldn’t do anything about it,” Dee said.

The good news was that although he was distressed and depressed by the carnage, it prompted him to search for answers.

Not long afterward, the virus was identified, and the disease’s name had been changed to “swine infertility and respiratory syndrome.” Dee continued to meet with colleagues and researchers and attend lectures about the disease.

Virus Transmission

The veterinarian focused on the persistent infection that characterises PRRS — “the fundamental mechanism of this virus” that makes PRRS so difficult to manage — and decided to investigate the disease from all angles. In the process, he learned about in utero infection of piglets, PRRS virus shedding and viral shedding in semen. Most important, he learned about PRRS virus transmission from persistently infected pigs. By then polymerase chain reaction, or PCR, testing and the swine bioassay had come into play.

Less was known about indirect PRRS virus transmission, however, so Dee, by then on faculty at the University of Minnesota, and his colleagues embarked on a series of sometimes quirky experiments, including one he called “the snowball from hell,” designed to determine if the PRRS virus could be moved from place to place.

Using a seemingly random combination of carriers — Dee’s SUV, work boots and the bathroom in Dee’s house — they demonstrated how the PRRS virus on a snowball dropped off the wheel well at a truck wash could be picked up by boots and transmitted to another farm, packing plant or anywhere the producer travelled, particularly in cold weather. In warm weather, Dee said, they learned it was possible but not as easy to transmit the virus.

In other experiments conducted by Dee’s students, he learned that certain strains of the PRRS virus — in this case MN184 — could also be transmitted via air and that flies could transmit it too.

Great Innovations

Fast-forwarding some 17 years, Dee said, “Oral-fluid sampling was a significant discovery in the battle against PRRS and for monitoring transmission. There’s really nothing more simple yet so sophisticated.” He added, “I put this at the top of the list of the innovations that have come forward. Just think how great our lives are now versus bleeding all those pigs.”

Blood swabs are still important, however, along with oral-fluid sampling and quarantine to help protect the herd from PRRSV transmission when new stock is brought to the farm. He added, “Blood swabbing boars and oral-fluid sampling are two of the most effective means of determining whether risk is occurring through direct animal movement or semen.”

Dee also pointed to early research showing the benefits of cleaning, disinfecting and drying trailers to prevent PRRS virus transmission. Recognized worldwide for his expertise in PRRS, he was also involved with a 4-year project showing that PRRS virus infections took significantly longer to become established in barns with airfiltration systems (Figure 1).

The cost of filtering a new construction project, he said, is about $1.50 per pig, and the return on investment if there’s an annual PRRS break is about 4:1. “So, it’s a very, very good decision to make from the business standpoint if you are getting infected in a hog-dense region.”

Dee noted the importance of having a room on the farm specifically for disinfection and drying — important components of biosecurity — along with quarantine and testing, sanitation of trailers and transport as well as air filtration.

Although PRRS remains the No. 1 disease target in the pork industry, he concluded, it can be successfully controlled and eliminated on a large scale. It requires an unwavering commitment from leadership, a significant investment, discipline, teamwork and a comprehensive approach toward biosecurity that considers all types of spread.

“You’ve got to have the whole package, with teams that will carry out protocols without fail,” Dee said.



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