CategorySwine Health - General Disease
Date Full Report Received09/24/2012
Date Abstract Report Received09/24/2012
Funded ByNational Pork Board
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. As several of these isolates were either undetectable by existing PCR assays or were identified as species typically regarded as poorly pathogenic, it is imperative that the potential virulence of these atypical isolates be determined for if these isolates are deemed pathogenic, the development of a diagnostic test that will correctly identify these strains is an urgent need. The ultimate goal of this study was to identify more consistent and accurate methods to confirm a clinical diagnosis of SD, and this study addressed the overall goal in three ways: 1) by utilizing a mouse model to assess the virulence potential of twenty-one Brachyspira strains including multiple atypical clinical isolates from pigs with gross and microscopic features consistent with SD as well as a group of nonpathogenic isolates and multiple isolates of B. hyodysenteriae, 2) based upon the results of the mouse experiment, eight isolates including both typical and atypical pathogenic strains as well as nonpathogenic strains were inoculated into pigs to confirm virulence and clinical manifestations in the target species, and 3) based upon the combined results of the mouse and pig experiments, the eight tested isolates were given a well-defined pathotype (virulent versus avirulent) and can be further compared by future genetic analyses in attempts to identify targets in the pathogenic strains which may form the basis for improved PCR assays for use in diagnostic laboratories.
In both the mouse and pig inoculation experiments, Brachyspira spp. that impart characteristic strong beta-hemolysis when cultured on blood agar were associated with the greatest degree of virulence as determined by the development of cecal and colonic inflammation in infected animals. Additionally, in pigs, the development of clinical SD was only observed 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 compatible with a clinical diagnosis of SD even if the isolate is not identified as B. hyodysenteriae, and that the cultural characteristics of Brachyspira spp. are a more sensitive indicator of the potential to induce SD that the molecular identification of the isolate alone.
Iowa State University Veterinary Diagnostic Laboratory
1600 South 16th St
Ames, IA 50011