Diagnosis, molecular epidemiology and control of avian intestinal spirochaetosis

Avian intestinal spirochaetosis (AIS) is a condition of laying and breeding hens resulting from colonisation of the large intestine with anaerobic intestinal spirochaetes of the genus Brachyspira. The main causative species in Australia are B. intermedia and B. pilosicoli. Infection with these species can lead to wet litter and reduced egg production. Currently, little is known about how these organisms enter flocks and spread, or how to control them. The economic losses to the poultry industry caused by AIS are thought to be significant, however problems with diagnostic techniques have resulted in this disease often being overlooked. The major aims of this thesis were to expand understanding of the epidemiology and cycles of transmission of B. intermedia and B. pilosicoli, measure the effectiveness of six disinfectants, develop faster and more reliable diagnostic identification methods, and to investigate effects of diet on colonisation by the spirochaetes. An epidemiological study on a laying hen farm detected infection with three different Brachyspira species, with multiple strains of these species being present. Infection appeared to have originated from other birds on the site rather than from environmental sources. Experiments showed that B. intermedia and B. pilosicoli survived in chicken faeces for between 2 and 17 hours at 37oC. B. intermedia tended to survive longer than B. pilosicoli, but the maximum survival time for both species at 4oC was only 72-84 hours. A study was then conducted into the efficacy of some common disinfectants in inactivating B. intermedia and B. pilosicoli. Six disinfectants were evaluated at their recommended working concentrations. All but alkaline salts inactivated two different concentrations of both spirochaete species in less than one minute in the presence of organic matter. Taken together, these results suggest that it should be relatively easy to break the cycle of infection by emptying, cleaning and disinfecting sheds between batches of birds. To improve diagnostic methodology, a two-step nested duplex PCR (D-PCR) was developed for detection of B. pilosicoli and B. intermedia, using DNA extracted from washed chicken faeces. The new test could provide results within 24 hours of sample receipt, and detected 4-5% more positive faecal samples than selective culture followed by individual species-specific PCRs. Finally, studies were conducted in experimentally-infected laying hens to investigate potential interactions between diet and colonisation with B. intermedia or B. pilosicoli. In the first experiment, the addition of zinc bacitracin or dietary enzymes to a wheat-based diet reduced colonisation by B. intermedia. In subsequent experiments, it was shown that diets based on wheat predisposed to colonisation with B. intermedia compared to diets based on barley or barley and sorghum. Subsequently, wheat variety Westonia was shown to increase susceptibility to B. intermedia but decrease it to B. pilosicoli, compared to a diet based on wheat variety Stiletto. There was no clear relationship between the soluble non-starch polysaccharide content of a given diet, the viscosity of the digesta in the ileum, or colonization with the spirochaete species. Addition of different dietary enzymes did not significantly reduce the digesta viscosity in the ileum, or significantly influence faecal water content. In flocks with persistent problems with AIS consideration should be given to modifying the diet, and, in particular, cereals other than wheat should be used. The wheat variety could be altered, but the addition of dietary enzymes to such wheat-based diets is not particularly reliable as a sole means of controlling AIS.