Abstract
The anaerobic intestinal spirochaete Brachyspira hyodysenteriae colonises the large intestine of pigs and causes swine dysentery (SD), a severe mucohaemorrhagic colitis. SD occurs worldwide, and control is hampered by a lack of vaccines and increasing antimicrobial resistance. B. hyodysenteriae strains typically produce strong beta-haemolysis on blood agar, and the haemolytic activity is thought to contribute to the pathogenesis of SD. Recently, weakly haemolytic variants of B. hyodysenteriae have been identified in Europe and Australia, and weakly haemolytic strain D28 from Belgium failed to cause disease when used experimentally to infect pigs. Moreover, pigs colonised with D28 and then challenged with virulent strongly haemolytic strain B204 showed a delay of 2–4 days in developing SD compared to pigs not exposed to D28. The current study aimed to determine whether Australian weakly haemolytic B. hyodysenteriae strain MU1, which is genetically distinct from D28, could cause disease and whether exposure to it protected pigs from subsequent challenge with strongly haemolytic virulent strains. Three experimental infection studies were undertaken in which no diseases occurred in 34 pigs inoculated with MU1, although mild superficial lesions were found in the colon in 2 pigs in one experiment. In two experiments, significantly fewer pigs exposed to MU1 and then challenged with strongly haemolytic virulent strains of B. hyodysenteriae developed SD compared to control pigs not previously exposed to MU1 (p = 0.009 and p = 0.0006). These data indicate that MU1 lacks virulence and has potential to be used to help protect pigs from SD.
Highlights
Swine dysentery (SD) is a severe mucohaemorrhagic colitis of pigs that classically results from infection of the caecum and colon with the anaerobic strongly betahaemolytic intestinal spirochaete Brachyspira hyodysenteriae [1]
Of the pigs in group A that were inoculated with weakly haemolytic strain MU1, one pig was positive 10 days after the first day of inoculation and all were colonised by 24-days post-inoculation
Avirulent or weakly virulent strains of B. hyodysenteriae have been known to exist for many years [23,24,25,26], and mutants that have been attenuated in different ways to reduce their virulence have been engineered [13, 27]
Summary
Swine dysentery (SD) is a severe mucohaemorrhagic colitis of pigs that classically results from infection of the caecum and colon with the anaerobic strongly betahaemolytic intestinal spirochaete Brachyspira hyodysenteriae [1]. In North America and Europe, SD has occurred in pigs either naturally or experimentally infected with members of two other strongly haemolytic Brachyspira species, Brachyspira hampsonii and Brachyspira suanatina [2, 3]. Of the latter two, infections with B. hampsonii occur most commonly, in North America [4], whilst infections with B. suanatina are rare. A weakly haemolytic strain (D28) from a herd in Belgium did not induce disease in experimentally infected pigs. 28 of the 30 pigs in both groups succumbed to SD within 30 days, so there was not significant protection against disease [17]
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