Swine dysentery makes an unwelcome comeback

Just when US pork producers thought swine dysentery was a problem of the past, it has re-emerged for an unwelcome encore in a slightly different form.

Swine dysentery was first reported in 1921, but the etiology remained unknown until 1971, according to the Iowa State University Swine Manual. Most of the research on the disease was reported during the 1970s and 1980s. Until recently, the disease had not been a significant problem for producers since the early 1990s, Matheus Costa, DVM, an assistant professor at the University of Minnesota, told Pig Health Today.

“Swine dysentery is closely associated with Brachyspira hyodysenteriae, a bacterium we have known for decades,” Costa said. “Brachyspira hampsonii causes the exact same disease, but it is a different bacterium. It made an appearance in the early 2000s, but with the change in lower antibiotic use, the bacterium is definitely making a comeback.”

The antibiotic, carbadox, was previously used in grow-finish feeds regularly and was also used at higher levels to control swine dysentery, or “bloody scours.” Producers don’t use the medication in the same way they did years ago, but it’s not just the different use of one medication that creates a problem.

“The fact that we don’t have a variety of drugs available for veterinary use anymore has really limited what we can use to suppress the disease,” Costa said. “As we progress to herds with higher health, we know some diseases will make a comeback.”

It’s hard to pinpoint one specific reason for increased incidence, but Costa said swine dysentery is “a real concern” in Europe and is becoming more of a concern in Canada. If the US government implements stricter regulations on antibiotic use, he said swine dysentery is likely to become more of a problem here as well.

Control measures

No commercially available vaccines exist for the control of swine dysentery, unfortunately. “The only way we have to control and prevent it, or even try to eradicate it, is with antibiotics,” Costa said. “We can depopulate and try to get rid of it that way, but it’s very hard to keep it out of the barn.”

Rodents can keep the bacterium alive and shed it, he explained. Birds can also be carriers, and the bacterium can survive in organic matter.

It’s a challenging task, but living with the problem is not a viable option, Costa said.

A different presentation

The disease doesn’t look the way it did 25 years ago, Costa has learned. Clinical presentation in the past was bloody diarrhea, but now there are gradients leading up to bloody scours. The feces will change color from green to red and go from being watery to mucoid.

“It’s not a strict bloody diarrhea anymore — you can see a gradient in it,” he said. After weaning, any pig is susceptible, so the grower and finisher phases are especially important, he added.

“We don’t fully understand swine dysentery, to the point that we don’t even know if just Brachyspira is enough to cause disease,” Costa said. “Some studies from the 1970s show that if a completely sterile pig is given Brachyspira hyodysenteriae, it does not develop swine dysentery. We believe something else needs to be present, but we don’t know exactly what that is.”

Part of Costa’s current research program involves trying to understand what leads to swine dysentery.

“It could be just a random combination of bacteria, or it could be a specific combination of bacteria,” he said.

Costa’s program is looking specifically at whole-pathogen microbiome interactions. He is studying how the pig is affected by Brachyspira and how it interacts with other bacteria. It appears Brachyspira actually controls what bacteria grow and what don’t grow within the pig’s microbiome.

“We’re exploring that as a possible control target, where we actually stopped Brachyspira from [controlling] the gut microbiome,” he said. “This way, Brachyspira would essentially just be another bacterium within the whole microbiome: Harmless, but present.”

There is also research showing that if feed is modulated and some ingredients are changed, the incidence and severity of swine dysentery can be decreased, he said. Again, the answer could be in the microbiome.

“We know that when we change feed ingredients, the bacteria that were thriving in the micro-environment change. No one has shown the link yet, but it’s not an impossibility,” he said.

What to look for

Costa said diagnostics are the first step if swine dysentery appears to be in the herd. Laboratory diagnostics can accurately identify Brachyspira, so veterinarians should send samples for culture and polymerase chain reaction (PCR) tests.

“Culture is definitely more sensitive, so don’t rely just on PCR,” Costa advised.

After the diagnostics confirm the presence of swine dysentery, producers and their veterinarians should discuss with farm managers and staff how to deal with the disease in terms of biosecurity, antibiotics and a plan to minimize losses.