8 August 2022

4 minute read

By: Kyle Baldwin

North America

Dr. Derald Holtkamp, professor with the College of Veterinary Medicine at Iowa State University, spoke with The Pig Site’s Sarah Mikesell at the 2022 Iowa Swine Day held in Ames, Iowa, USA. Dr. Holtkamp discussed the 2021-2022 outbreak of APP in Iowa and the results of their investigation.

“Actinobacillus pleuropneumoniae (APP) is a bacteria that's been around for a long time. It hasn’t generally caused a lot of problems in the US over the last few decades, but it does occasionally raise its head and we oftentimes serotype those bacteria,” Holtkamp said. “This one happens to be a serotype 15, but we want to caution that those conventions that we use to put a name on bacteria and we do the same thing with viruses.”

Not all serotype fifteens are the same; each has unique traits that researchers are trying to understand, he said.

“Dr. Marcelo Almeida and Dr. Alyona Michael are working on sequencing to sort out what may be unique about these particular serotype 15 bacteria, and so far, they found the ones that caused this recent outbreak are very tightly clustered together,” he said. “So, it does seem like this is a slightly different APP serotype 15 than we've dealt with in the past. We really think something has changed with what we still call serotype 15, and it's causing a little bit more problems than it has historically.”

Dr. Holtkamp says the APP serotype 15 has occasionally popped up in the US since 2010 but hasn’t really caused a significant problem until now.

“Starting in 2021, there was a slight increase in the incidence of cases submitted to the Iowa State University Veterinary Diagnostic Lab where they came back and it was serotype 15, so it wasn't enough to really raise any flags at that point,” he explained. “But then starting in late November to early December of 2021, we saw a fairly rapid increase in the number of cases being sent to the Iowa State Veterinary Diagnostic Lab. And we checked around with the other labs to see if they were having some similar pattern, and they weren't. Everything seemed to be coming here.”

An investigation was conducted by Iowa State and it was determined that the APP serotype 15 cases came from a small geographic area north of Ames, Iowa.

“And that happened for about two months from the end of November 2021 through end of January 2022. Every case that came in was positive for that serotype 15, and they were all in that very small, clustered area,” he described.

Dr. Holtkamp says that a total of seven sites, each from a different production company, were investigated.

“We approached the investigations from the standpoint of what we call a hazardous analysis and epidemiological investigation,” he said. “We wanted to understand what happened on those farms in a two week period before the outbreaks occurred on each farm. We wanted to document the death loss they experienced. We also asked them about how they treated the pigs to get a good assessment of what was going on.”

The investigation team had to look at a lot of questions specific to this outbreak to understand what happened.

“We were asking ourselves: why just in that small area? Why didn't it spread to other locations during those two months?” Holtkamp said. “So, we looked at things like market loads or market pigs, and three of the seven that we investigated were in the marketing phase, so they were sending market trucks around all around Iowa. But why did it just stay here?”

A common link between some of the sites gave the investigation team some insight on what could’ve caused the outbreak.

“We did find that five of the seven sites that we investigated used rendering and the other two used composting. Of the sites that were rendering, they all used the same company,” he explained. “We ended up learning some things about how the rendering company organized the trucks and fit together that it probably contributed to the outbreak. I'm not saying it's the sole way it was being transmitted, but I think it was probably a pretty significant part of the transmission and why it occurred in that small geographic area for two months.”

Dr. Holtkamp reflects on this discovery as it can be applied to other foreign animal diseases.

“As we worry about African swine fever and other foreign animal diseases getting in this country, it does highlight the need to address that a lot of these companies want to continue to use rendering,” he stated. “And that's a good thing from a resource use standpoint, but we need to figure out how to do it more safely, and it’s something that we shouldn't wait until we have a foreign animal disease introduction to try to figure out.”