APP Strikes with a Vengeance in Upper Midwest Pig Farms

Recent APP outbreaks in the Upper Midwest have resulted in increased morbidity and mortality across a pocket of production systems where it had previously been well controlled.
Recent APP outbreaks in the Upper Midwest have resulted in increased morbidity and mortality across a pocket of production systems where it had previously been well controlled.
(National Pork Board and the Pork Checkoff)

It was the Friday after Thanksgiving. A finishing supervisor walked into a barn in Iowa where he discovered a large spike in pig mortality. By the time his team finished removing the dead pigs and mass treating the site several hours later, the mortalities had tripled.

The culprit? Actinobacillus pleuropneumoniae (APP).

Recent APP outbreaks in the Upper Midwest have resulted in increased morbidity and mortality across a pocket of production systems where it had previously been well controlled. For one veterinarian, seven sites in their system have had lateral APP breaks since November that have affected late finishing pigs. Evaluation shows these breaks are all APP type 15. 

From a clinical picture, he said they are generally seeing a group of pigs that is fine one day, and then the next day they discover high acute mortality at the site. Sometimes they’ve seen a day or two with a moderate increase in mortality. If they can catch those early, they can avoid the big spike. 

He shared his experiences during a webinar offered by the Swine Health Information Center and the American Association of Swine Veterinarians, hosted by the Iowa State University Swine Medicine Education Center. 

Another veterinarian shared a similar experience that has occurred on eight farms he oversees since December. Pigs from multiple sow sources have been affected even though none of the sow herds are APP positive. To date, the affected sites have been late finishing phase animals prior to marketing activities. 

Rapid Infections

The sites have had normal mortality and performance leading up to the breaks, both veterinarians shared. The most common presentation has been sites that are clinically normal and break with extremely high mortality overnight. 

“We saw a sudden rapid increase of disease in the healthy general population animals. We also saw blood and froth from the oral and nasal cavities, and extremely severe lethargy with dog sitting, thumping and coughing in the barns. And we had several instances reported of animals coughing up blood and expiring within seconds or minutes of people seeing them coughing up blood,” one veterinarian described.

Some of the farms confirmed concurrent infection with the PRRS 1-4-4 strains leading up to the outbreak. This brings to light the question: Is this APP or PRRS driving the mortality?

Direct reaction time has been critical to the success of the treatment plan. Waiting even a few hours to start administering the medication can greatly affect the outcome, one veterinarian said.

How Does APP Spread?

APP is an obligate parasite, so it survives poorly outside of the host, explained Alyona Michael with the Iowa State University Veterinary Diagnostic Lab. However, environmental persistence can be increased by any wet conditions or higher organic load, she said.

One veterinarian noted all of his sites share a common rendering service, which is the same rendering service that other producers in his geography share as well. 

“There's a possible relationship with trailers or personnel moving between sites. It raises the question, ‘Is there potential for short distance aerosol spread of this virus?’ I know there's some suggestion that it could move a few hundred or several hundred meters potentially, but not much evidence of any specific demonstration of that, that I could find in literature,” he said. 

When it comes to how APP moves, this operation is focused on the mortality removal process, especially contaminated rendering trucks that could contaminate the outside of sites, and then that bacteria being tracked back into the barns. 

Mortality removal is the last task of the day and there is absolutely no reentry into the animal space. They are also making sure people enter sites properly and are boosting biosecurity protocol.

Vaccination Status

None of the flows would have been expected to have any APP issues, so both veterinarians said they have not used any APP vaccines in their herds.

“I’ve probably seen and heard about more lateral introductions of APP in the last two months than in my life before that combined. Normally it's rare to have a lateral introduction in my experience. We don't have any other herds that would be using any APP vaccine either,” one veterinarian said.

He’s hopeful they can get the area cleaned up by depopulation and repopulation with new pigs. All of their sites are wean-to-finish or grow-finish sites that would be all-in, all-out. Because of this, they don't expect any endemic issues.

Further Investigation

The APP serotype 15 is most frequently reported in Australia with some outbreaks documented in Japan and the United Kingdom. According to records, Michael said the earliest detection of serotype 15 in Iowa occurred in 2011. Up until now, detection of this serotype has been relatively infrequent, she said. 

“Until now, we've detected stereotype 15 outbreaks from over 19 sites and affecting at least nine separate systems. Furthermore, these affected sites are located within a very tight geographic radius of approximately 20 miles,” Michael said. “In addition to the spatial temporal cluster, we actually found a smaller spike of about four serotype 15 cases in early summer 2021. Curiously, these four cases are also geographically restricted to the area of the current outbreak.”

The investigation of this outbreak in comparison to historically detected strains is being pursued with funding support from SHIC and pending collaboration with Marcelo Gottschalk, an APP expert from the University of Montreal.

Michael, along with Marcelo Almeida of the Iowa State University Veterinary Diagnostic Lab, addressed APP biology, carrier state, transmission and development of clinical disease, pathogenesis, as well as serotypes and toxins. They shared diagnostic considerations describing the outbreak, general work up results from recent cases, an historical perspective based on ISU VDL serotypes, and the present outbreak of serotype 15. They also shared perspectives on surveillance and monitoring. 

Editor’s Note: Veterinarian names have been withheld to protect the farms involved.

More from Farm Journal's PORK:

How Could PRRS 1-4-4 1C Sneak into Your Herd?

Follow the Science to Beat PRRS 1-4-4, Lineage 1C

Think Twice About Feed Biosecurity on Your Pig Farm

Put PRRS Strain 1-4-4 Lineage 1C in Perspective

PRRS Strain 1-4-4: The Most Dramatic Strain I’ve Seen, Yeske Says

PRRS Virus: Uncovering a Hidden Enemy

PRRS: Deciphering the Mystery Disease 

 

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