Actinobacillus pleuropneumoniae (APP) has a lot of folks scratching their heads right now, said Alyona Michael of the Iowa State University Veterinary Diagnostic Lab during an interview with AgriTalk’s Chip Flory on Wednesday.
APP is the general name of a bacterium that can cause very severe disease, she explained. The bacterium can be divided into a number of subgroups based on the virulence factors and structural molecules bacteria possess.
“The reason that becomes important is there are various serotypes that are high and low virulence. So generally, distribution of low virulence strains can be pretty wide, but high virulence strains, like what we’re seeing right now, are uncommon,” she pointed out.
If it’s tough to spread, Flory asked, how is it being transmitted?
“Within a herd, APP tends to be transmitted from sows to the pigs, and then disease can emerge later in the grow/finish stage once maternal immunity wanes and pigs become immunosuppressed or naïve animals are introduced. What’s unusual about this APP serotype 15 is that we are seeing lateral transmission in systems that don’t share sow herds. Again, that’s quite unusual within the U.S.,” Michael said.
APP does not survive well outside of a pig. It’s typically transmitted by direct contact, but given how many sites and systems are affected and the fact these sites and systems are thought to be APP15 negative, it appears to be transmitting via some other mechanism, she added.
“Rendering trucks, repair crews and packer trucks are all on the list of potential sources. There’s a very active investigative effort being led by Swine Health Information Center funding and Dr. Derald Holtkamp at ISU,” Michael said.
A Complicated Situation
It’s a pretty complicated investigation, she explained. Field investigators are currently conducting interviews to figure out the potential routes of spread. On the molecular side, Michael and other researchers, including Marcelo Almeida at Iowa State University and Marcelo Gottschalk at the University of Montreal, are collaborating to compare genetic sequences from this outbreak to historical isolates from across North America to help figure out where the strain came from.
“Based on some of the accounts I’ve heard, Dr. Michael, it’s super scary. By the time you figure out you may have APP serotype 15, it’s probably too late, right?” Flory asked.
Hopefully you never have to see it, Michael responded. Biosecurity is critical in preventing introduction to swine herds.
“Once you realize it’s there, really aggressive treatment is about your only recourse,” she said.
Veterinarians involved in the APP 15 outbreaks have shared the best treatment is an injectable antibiotic. Although water and feed medications are convenient, once the pigs are sick, they are very sick, she said. Because of this, they might not drink enough water or consume enough feed to get a good dose.
What Should Producers Look For?
“For better or worse, it’s not a subtle disease. And for worse, definitely,” she said. “It attacks and destroys the lung tissues, so these pigs struggle to breathe. You might have open mouth breathing, but a lot of times pigs will just be found dead. They look fine one hour, and then you walk back through that barn and they’re unfortunately deceased. Other symptoms include fever and coughing.”
Another striking finding is a bloody discharge running from the pig’s nose. After that, she said it will depend on a necropsy to examine the tissues in that animal and submit them for culture and PCR testing.
What’s Next for APP?
In the U.S., vaccination isn’t commonly practiced.
“We put a lot of effort into keeping our sow herds free of virulent strains, limiting transmission to the piglets through early weaning can help. So yes, there are systems that will have what we call an endemic strain of APP, again not APP15 to our knowledge,” Michael said. “So those animals are used to seeing that bacterium and don’t develop clinical disease unless new strains are introduced or additional health challenges allow the bacterium to colonize the lung. But again, a lot more effort is put toward keeping herds negative.”
Although she can’t get into specifics for the purposes of confidentiality, Michael said the current outbreak is within a narrow geographic radius in Iowa and is primarily hitting finishers.
“Knock on wood, we haven’t seen more cases in the last couple of weeks. So hopefully, this is under control at this point. Historically, serotype 15 is very infrequently detected in the United States. Again, this is just a bizarre situation,” Michael said.
The most important thing producers can do is make sure they are increasing biosecurity efforts. Learn more here.
Learn more about disease trends, emerging syndromes and more at the Swine Health Information Center.
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