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Veterinary student Steve VanRavenstein, in biosecure gear, with one of the pigs involved in the Brachyspira study. Photo: Roman Nosach.

Brachyspira strains not fitting the mold

It's 8 a.m. We enter the Level 2 disease containment area of the Western College of Veterinary Medicine's Animal Care Unit (ACU), ready to work with our research study's pigs. To our right are two shower rooms and a locker area; ahead of us is a bathroom. To our left is a hallway lined with doors leading to anterooms — small rooms where we gear up — that lead to the rooms housing our research project's pigs.

We hope these pigs will help us to answer questions about Brachyspira, a genus of intestinal bacteria that infects pigs, dogs, birds and other animals.

We know of six species of Brachyspira that infect pigs with multiple strains of each species. Traditionally, only B. hyodysenteriae has been known to cause bloody diarrhea. But in the past six years, barns in Saskatchewan and the U.S. Midwest have been reporting cases caused by other species of Brachyspira ­­— ones that don't normally cause any sickness.

The story began in 2009 when WCVM researchers Drs. John Harding, Janet Hill and Manuel Chirino began working on samples from a Saskatchewan swine farm. All of the samples came from pigs that had shown clinical signs of bloody diarrhea.

Staff at Prairie Diagnostic Services (PDS), the province's veterinary laboratory, initially analyzed the samples. But instead of finding B. hyodysenteriae, the strain that's usually associated with bloody diarrhea, PDS lab technicians could not match it to any known species.

The lab thought the samples might be either B. murdochii or B. intermedia. "We know that those two [Brachyspira] species do not cause bloody diarrhea in pigs," says Harding. Further testing on the submitted samples showed that the bacteria did not fit into either B. murdochii or B. intermedia and was in fact a novel species.

Soon after receiving these samples, other strains of Brachyspira were being isolated from swine barns in Alberta and Saskatchewan. These strains, like the ones submitted to PDS, didn't match any known species, but they seemed to be most closely related to a single isolate that was originally found in Britain during the 1980s.

In 2012, a WCVM research team launched a study to determine the prevalence of this new Brachyspira species, now called "B. hampsonii,"pigs of various ages in a commercial farm in Saskatchewan. As a result of this study the researchers discovered that atypical strains of Brachyspira, which were collected from clinically healthy pigs, were able to cause strong hemolysis (destruction of red blood cells) when cultured in the laboratory.

Researchers previously thought a trait of strong beta-hemolysis was a factor directly related to the virulence of the bacterial strain. That is, the more strongly hemolytic, the more likely the strain will cause disease.

But these new strains of Brachyspira bacteria don't seem to cause illness in pigs — and that's making it harder for veterinarians to diagnose and determine if a given strain will cause disease.

One of these strains, B. murdochii G79, is the subject of our current research trial. It was found in a healthy pig, but it caused hemolysis in the lab. If we can infect pigs with this strain and determine that it doesn't cause disease, we can conduct further testing to see how hemolysis and virulence are linked.

Wearing hospital scrubs, we walk to the anteroom of one of the pig rooms. We change our boots at the door, and then we put on a pair of gloves, don a surgical mask, hairnet, coveralls and one more set of gloves before going through the final door into the animal room.

The pigs are housed in pairs in pens, and one by one, we sedate each pig before we pass a feeding tube down its esophagus to feed it an inoculum containing Brachyspira murdochii strain G79.

We repeat this process three days in a row, and then follow up by collecting fecal samples and rectal swabs daily. Using these samples, we run PCR (polymerase chain reaction) tests to identify which species of bacteria are found in the feces. We also culture rectal swabs on blood agar to determine the hemolytic characteristics of the bacteria.

Months later, results from our study show that B. murdochii G79 did not cause significant disease in the pigs nor did it significantly affect their weight gain. As well, testing in the lab has indicated that this specific strain of Brachyspira causes intermediate hemolysis.

Research into other Brachyspira isolates is ongoing and characterization of the genome will enable researchers and veterinarians to predict which ones will cause disease and how hemolysis and virulence are linked. Results from these studies will hopefully lead to the development of a vaccine that will protect against this sickness in pig barns.

 

Steve VanRavenstein was one of several WCVM veterinary students who worked on research related to swine health and Brachyspira bacteria in 2014. Click on the students' names to read more about Gabrielle Paul-McKenzie and Stephanie Derbawka's experiences.

 

Steve Van Ravenstein of Surrey, B.C., is a second-year veterinary student who was part of the WCVM's Undergraduate Summer Research and Leadership program in 2014. Steve's story is part of a series of articles written by WCVM summer research students.
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