In Australia, studies of intestinal spirochaetal infections in commercial poultry flocks have showed that colonisation with the pathogenic species Brachyspira intermedia and Brachyspira pilosicoli is common. Moreover, these spirochaetes are recovered significantly more frequently from layer and broiler breeder flocks with diarrhoea and reduced egg production than from clinically normal flocks.

Experimental infection studies in broilers and layer hens has shown that strains of both B. intermedia and B. pilosicoli isolated from Australian chickens can cause disease and loss of production.

The purpose of the current project was to seek means to improve control of infections with the two main species associated with disease in Australia. The study was a collaborative effort involving Professor David Hampson, Nyree Phillips, Tom La and John Pluske at Murdoch University in Western Australia, and Carol Stephens at the Toowoomba Veterinary Laboratory in Queensland.

The project had two main components. First, on-farm studies were conducted to investigate determinants of the infections, including identifying patterns of infection with different strains and species of the bacteria, looking for potential reservoirs of the bacteria and examining their survival in the environment of the production house. This new information should help when trying to devise means to break the cycle of infection on individual infected farms. Second, a serious of experimental studies were conducted in layer hens fed different diets and infected with the spirochaetes. This was done in an attempt to identify potential dietary influences on the infection. The ability to reduce or modify the infections by using specific diets, without having to recourse to antibiotics, would improve the capacity of individual producers to control the infections.

On-farm epidemiological studies
Detailed studies were undertaken on a broiler breeder farm and on a layer farm to investigate possible sources of spirochaete infection. The broiler breeder farm had a past history of a wet litter problem associated with infection with B. pilosicoli. Unfortunately, in both cross-sectional and cohort studies conducted on this flock in the current investigation, no spirochaetes were isolated. Furthermore, no spirochaetes were isolated from environmental samples examined in the sheds. The reason for the absence of spirochaetes in a previously-infected farm was unclear, especially as no specific measures had been instigated to control or eradicate the infection. It could be deduced that the infection is likely to cycle between groups of birds on a farm, and does not persist in the environment, nor often become introduced from outside sources such as from wild birds or rodents. These observations are very encouraging in relation to developing means to control AIS on infected farms.

Cross-sectional and cohort studies were conducted on a layer farm with a past history of wet litter associated with AIS. Birds were found to be commonly infected with B. intermedia, but there was also evidence of infection with B. pilosicoli and another species – which was subsequently identified as the proposed species "Brachyspira pulli". Multiple strains of B. intermedia were recognised by using strain-typing techniques, and individual strains were not confined to single sheds of birds.

Hence cross-infection between sheds appeared to be occurring. The youngest birds had the least infection, and this supported the idea that infection was initially acquired from older birds housed in other sheds on the farm. It appeared that infection with B. intermedia became amplified and more common the longer birds were kept in a shed. Again, no environmental sources of infection were identified, and it appeared that infected birds on the farm were the prime source of infection for new birds introduced to the farm.

Spirochaete survival
This part of the study aimed to evaluate the efficacy of some common disinfectants in inactivating B. intermedia and B. pilosicoli, and to examine spirochaete survival in chicken caecal faeces held at different temperatures. Six disinfectants were evaluated at their recommended working concentrations: alkaline salts, quaternary ammonium, iodine as an iodophor, chlorine from a chlorine-release agent, glutaraldehyde and hydrogen peroxide. All but alkaline salts inactivated two different concentrations of both spirochaete species in less than one minute in the presence of organic matter. Both spirochaete species at three different cell concentrations survived in caecal faeces at 37oC for between 2 and 17 hours. B. intermedia tended to survive for longer than B. pilosicoli, but the maximum survival time for both species at 4oC was only 72-84 hours. This part of the study demonstrated that avian intestinal spirochaetes are rapidly inactivated by several common disinfectants, and their survive time in chicken caecal faeces is much less than has been reported for porcine intestinal spirochaetes in porcine faeces. It should be relatively easy to break the cycle of infection between batches of laying birds by resting sheds for a few days, and by using disinfectants on any residual faecal matter. Prevention of subsequent cross-infection from older birds in other sheds by the use of appropriate biosecurity measures would then ensure that the new birds remained free of infection.

Dietary influences on spirochaete colonisation
Previous work in pigs and chickens has suggested that there may be dietary influences on spirochaetal colonisation, and a previous study showed that addition of exogenous dietary enzymes to diets may reduce the susceptibility of birds to infection. It was believed that dietary fibre (non-starch polysaccharide or NSP), particularly soluble NSP, increases the viscosity of the digesta in the intestinal tract, and that this increases colonisation with intestinal spirochaetes.

To explore these effects, four experiments were conducted using layer hens fed on different diets and then experimentally infected with spirochaetes. In the first experiment, birds received diets based on two different wheat varieties that varied in their NSP content. They were then infected with a strain of B. intermedia. A significant dietary effect on colonisation was observed. Birds fed wheat variety Westonia were more commonly colonised than those fed variety Stiletto (although this could be a wheat batch effect rather than a variety effect), and the ileal contents of the former birds were significantly more viscous than those of the latter. This suggested a link between increased digesta viscosity and increased colonisation with B. intermedia. Unexpectedly, the total sNSP values for the two diets were similar, and there was no obvious explanation for the differences in the viscosity of the ileal contents that were observed.

The second experiment was a repeat of the first, except that a strain of B. pilosicoli was used to infect the birds rather than B. intermedia. The diets of these birds also were supplemented with 50 ppm zinc bacitracin to enhance colonisation by B. pilosicoli. Again there was a significant dietary influence on colonisation, but in this case colonisation was more common in the birds fed wheat variety Stiletto.

There were no significant differences in digesta viscosity, and no obvious explanation for the dietary effect on colonisation. The apparent different behaviour of B. intermedia and B. pilosicoli in the gastrointestinal tract in relation to the diet fed requires further investigation to confirm the effects seen.

The third experiment was designed to determine whether addition of dietary enzyme to the diet based on wheat variety Westonia would influence colonisation by B. intermedia. Unfortunately, in this experiment there was a very low colonisation rate in groups of birds either receiving or not receiving the dietary enzyme, and hence it was difficult to determine whether the enzyme preparation was useful in reducing colonisation. Interestingly, the enzyme had little effect on the viscosity of the ileal contents.

In the fourth experiment, three diets based on cereals with different NSP contents were used, each fed with or without the addition of commercial dietary enzymes (ie six groups of birds). The diets were based on wheat, barley or barley plus sorghum. The barley-based diets had around twice the sNSP content of the wheat-based diets, and resulted in the greatest viscosity of the ileal digesta. The barley plus sorghum diet had a little more sNSP than the wheat-based diet. All birds were experimentally infected with B. intermedia, and again a significant dietary effect on colonisation occurred. In this case birds fed both the wheat-based diets had more colonisation than birds on the other diets.

Addition of enzymes to the mash diets had no significant effects on the viscosity of the ileal contents, or on colonisation rates, and there was no clear association between the total sNSP content of the diet and the ileal viscosity. This experiment suggested that diets based on wheat may predispose to infection with B. intermedia, and that the total sNSP content of these diets per se may not be responsible for this effect. Consistent with this, dietary enzymes may not have a significant effect on colonisation and cannot be recommended for use as a main means of controlling AIS caused by B. intermedia.

Recommendations

• In order to control AIS at the flock level, incoming birds should be from a source that is not infected with intestinal spirochaetes, sheds should be thoroughly cleaned, disinfected and rested between batches of birds, and strict biosecurity measures implemented to prevent transmission of infection from sheds of older birds to new flocks.
• In flocks with persistent problems with AIS consideration should be given to modifying the diets being used. However, the outcome would appear to be somewhat unpredictable. Where possible, cereals other than wheat should be used.
• Addition of dietary enzyme is not recommended as a sole means of controlling AIS.

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Last updated: 19 December 2004Copyright RIRDC
http://www.rirdc.gov.au/reports/CME/04-141sum.html