“Don’t give up. … Just keep the faith. … We just have to keep up our spirits.”
That is advice from veterinary microbiologist Scott Dee to hog producers as they face yet another strain of porcine reproductive and respiratory syndrome — labeled by some as the “worst strain of PRRS we’ve ever had” in field observations. Dee spoke during a National Pork Board webinar this fall.
Dee, director of research for Pipestone Applied Research, said he heard earlier this year of breaks of the PRRS 144 Lineage 1, Sub lineage C. “We were worried that people were giving up,” he said. “There was a defeatist attitude in the industry, and that’s not normal for pork producers and swine veterinarians. We’re usually quite the opposite.”
With that, Dee and others on his team — statistician Roy Edler and director of research operations Dan Hanson — worked with Amanda Sponheim, Reid Philips and Justin Rustvold with Boehringer Ingelheim Animal Health to study the extent of PRRS 144-1C in the field.
The research team sought to answer the industry’s questions:
- Is this the worst strain ever?
- Do vaccines work anymore?
- Are biosecurity protocols ineffective?
- How is it transmitted?
- Can a spread be prevented?
Studies were done in four rooms of the Pipestone research barn, a biosafety Level 2 facility. Boehringer Ingelheim’s involvement brought added expertise as well as cost-sharing, since “we didn’t have time to write a grant because we were working in real time,” Dee said.
Comparison of strains
To determine if 144 is indeed the worst PRRS strain ever, the team compared its impact to that of PRRS 174, once considered the worst strain before the emergence of 144.
Research consisted of infecting groups of pigs with either the PRRS 144-1C virus or the 174 strain. The challenged pigs were split into three groups: non-vaccinated, vaccinated with the Boehringer Ingelheim’s Ingelvac PRRS MLV (Vaccine A) or vaccinated with Elanco’s Prevacent PRRS (Vaccine B).
To first answer the vaccine efficacy question, Dee presented impacts of the two vaccines on average daily gain, percent mortality and fever, as well as pigs infected with 144 and 174 with no vaccinations:
Average daily gain. ADG improved by:
- 1.39 pounds for Vaccine A group
- 1.38 pounds for Vaccine B group
- 1.20 pounds for 144-infected, non-vaccinated group
- 1.21 pounds for 174-infected, non-vaccinated group
Percent mortality. The figures were:
- 5.3% for Vaccine A group
- 4% for Vaccine B group and 144-infected, non-vaccinated group
- 13.3% for 174-infected, non-vaccinated group
Fever. Normal rectal temperature for a pig is 102.5 degrees F. The pigs’ body temperatures at 14 days post-challenge were:
- 103.8 degrees for Vaccine A group
- 104.7 degrees for Vaccine B group
- 104.9 degrees for 144-infected, non-vaccinated group
- 105.2 degrees for 174-infected, non-vaccinated group
“You see there’s significantly better growth rate in the vaccinated groups,” Dee said. “No difference between A or B, but both of those groups of pigs grew better than the non-vaccinated challenges. There’s a trend toward significance there with more mortality in the 174 group.”
Researchers also look at the serum viral load at three, seven, 14, 21, 28 and 35 days post-challenge to discover “how much virus is being produced inside these pigs,” he said.
“Day 14 and 21 was kind of when the fire was burning the hottest,” he said. “There’s quite a bit of virus in these pigs, quite a bit less is the vaccinated pigs, and there’s more virus in the 174 pigs.”
On Day 14, the 174 pig group had a virus load at 6.61×107, while the 144 pig group had virus at 4.57×105. “So we’re starting to see some differences that the vaccines are actually doing a pretty good job,” Dee said.
Pigs were also closely monitored for behavioral differences between the same four groups, and again the vaccinated pigs scored better than the non-vaccinated, infected pigs with the 174-infected pigs showing more of a negative impact when researchers observed the pigs’ attitudes, physical activity and respiratory rate.
Since the emergence of porcine epidemic diarrhea in 2013, the hog industry has learned the effectivity of stepped-up biosecurity measures on farms, in feed mills and for farm suppliers.
Two disinfectants were put to the test, and researchers found that the 144 strain was neutralized after one hour of contact. It was also discovered that PRRS 144 could indeed be transmitted through contaminated feed when fed naturally to pigs. However, two feed mitigants — Guardian and Sal Curb — when added to feed prevented infection.
PRRS 144 proved to survive in hog manure slurry for 14 days, but not for 21 days.
Research also shows that 144 was detected on hands, boots and coveralls of personnel following 30 minutes of contact with infected pigs. Also, in the absence of a shower and changing of clothes and footwear, the virus was transmitted to contact controls. However, the virus was not transmitted to contact controls after personnel showered and changed their clothes and footwear.
As with most diseases on pig farms, filtration appears to be effective against the spread of 144, as PRRS RNA was detected in 28% to 43% of interior air samples during the challenge period, but there was no detection in exterior air samples.
PRRS 174 is more pathogenic that 144. The modified-live vaccines are effective, and Dee recommends continuing to use the vaccines per label. “These biosecurity protocols work,” he said. “They work just fine. Aerosols and feed may be some risk factors for this virus, but the risk is reduced through filtration and feed mitigation.”
Dee sees hope. “This is highly pathogenic virus — no question. But we know how to deal with it. We’ve dealt with these viruses before. We have all the tools we need to be ready for this fall and getting into cold weather.”
More information on PRRS, along with the webinar, can be found at porkcheckoff.org.