Investigation and Characterization of Differences in Atypical Brachyspira spp. Isolates Versus Classic Strains

April 3, 2013 — 

Swine dysentery (SD), or bloody scours, has historically been associated with the presence of the strongly beta-hemolytic spirochete Brachyspira hyodysenteriae. However, Brachyspira spp. not identified as B. hyodysenteriae by polymerase chain reaction assays (PCR) have recently been recovered from pigs with clinical SD. The goal was to identify more consistent and accurate methods to confirm a clinical SD diagnosis. The study addressed this by: 1) utilizing a mouse model to assess the virulence potential of 21 Brachyspira strains, including multiple atypical isolates from pigs with features consistent with SD, as well as nonpathogenic isolates and multiple isolates of B. hyodysenteriae; 2) using the mouse experiment results, eight isolates, including typical and atypical pathogenic strains as well as non-pathogenic strains, were inoculated into pigs to confirm virulence and clinical manifestations; 3) based upon combined results of the mouse and pig experiments, the eight isolates received a well-defined pathotype (virulent versus avirulent) and can be compared by genetic analyses to identify targets in the pathogenic strains to develop improved PCR assays for diagnostic testing. In both the mouse and pig experiments, Brachyspira spp. that impart characteristic strong beta-hemolysis were associated with the greatest degree of virulence as determined by the cecal and colonic inflammation in infected animals. In pigs, clinical SD was observed only following infection with strongly beta-hemolytic spirochetes, with disease also occurring following infection by strongly beta-hemolytic isolates not identified as B. hyodysenteriae by PCR. These data suggest that the isolation of a strongly beta-hemolytic spirochete from feces or colonic tissues of pigs with bloody scours should be interpreted as a clinical diagnosis of SD even if the isolate is not identified as B. hyodysenteriae. Also, the cultural characteristics of Brachyspira spp. are a more sensitive indicator of the potential to induce SD than the molecular identification of the isolate alone.

Key Points:

• Polymerase chain reaction assays (PCR) have failed to identify some isolates (Brachyspira spp.) causing swine dysentery (SD).
• More details about the potential virulence of atypical or poorly pathogenic isolates were needed.
• In the case of Brachyspira spp., cultural characteristics are a more sensitive indicator of the potential to induce SD than the molecular identification of the isolate alone.
• A more consistent and accurate test is needed to confirm all potential clinical SD diagnosis.

Principal Investigator: Dr. Eric Burrough, Iowa State University

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Source: Pork Checkoff Research Review, March-April, 2013