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Prevalence, pathogenicity and control of avian intestinal spirochaetosis in Australia

Stephens, Carol Pauline (2008) Prevalence, pathogenicity and control of avian intestinal spirochaetosis in Australia. PhD thesis, Murdoch University.

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      Abstract

      Avian intestinal spirochaetosis (AIS) is a relatively recently recognized disease of commercial layer and meat breeder chickens resulting from colonization of the gastrointestinal tract by anaerobic spirochaetal bacteria of the genus Brachyspira. AIS is characterised by delayed and/or reduced egg production and chronic diarrhoea. This thesis describes an investigation into the prevalence, pathogenicity and control of species of avian intestinal spirochaete in Australia. Faeces samples from chickens in 22 flocks of laying hens, 19 broiler flocks and 28 breeder flocks in Queensland, New South Wales, Victoria, Tasmania and South Australia were subjected to selective anaerobic culture for Brachyspira species. Spirochaete isolates then were speciated using phenotypic characteristics and specific polymerase chain reaction amplifications. A highly significant association was found between colonisation with Brachyspira species and the occurrence of wet litter and/or reduced production in both broiler breeder and layer flocks in eastern Australia. Multilocus enzyme electrophoresis (MLEE) then was used to help confirm the identity of the spirochaetes, and to examine their genetic relationships and disease associations. MLEE divided the isolates into five known Brachyspira species groups: Brachyspira murdochii, B. intermedia, B. pilosicoli, B. innocens, and “B. pulli”. Three new MLEE groups each containing single isolates were also identified. All farms with production problems or wet litter were colonised with the pathogenic species, B. intermedia and/or B. pilosicoli. The pathogenic potential of single isolates of B. pilosicoli and B. innocens then were experimentally evaluated in adult broiler breeders, confirming that infection with B. pilosicoli can result in serious egg production losses, whilst B. innocens is non-pathogenic. Antimicrobial susceptibility testing showed that the pathogenic spirochaetes B. pilosicoli and B. intermedia were both susceptible to tiamulin, lincomycin, metronidazole and tetracycline, while a lack of susceptibility to tylosin was found in some isolates of B. intermedia and B. pilosicoli. Some isolates of B. pilosicoli were not susceptible to ampicillin. Additional studies showed that zinc bacitracin, a common feed additive, can increase susceptibility to colonisation with B. pilosicoli. Both tiamulin and lincomycin were shown to be effective in treating infection with B. pilosicoli in adult birds.

      Publication Type: Thesis (PhD)
      Murdoch Affiliation: School of Veterinary and Biomedical Sciences
      Supervisor: Hampson, David
      URI: http://researchrepository.murdoch.edu.au/id/eprint/685
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