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The role of rabbits in the transfer of bovine johnes disease

In any disease control program eradication of disease depends upon the protection of disease free animals from potential sources of infection. Sylvatic hosts have the potential to thwart eradication campaigns Wild bovids and ungulates are a source of bovine tuberculosis for North American cattle herds. Two non-ruminant wildlife reservoirs, possums and badgers in New Zealand and England respectively, have hampered eradication of bovine tuberculosis. 

 The presence of a common wildlife reservoir of Johne's disease could render the eradication of Johne's disease impossible or compromise current control measures. In Scotland, rabbits have been demonstrated to be infected with M. paratuberculosis. In order to assess the risk posed to Johne's disease control due to wildlife this survey examined rabbits and another herbivore commonly found on Australian pastoral land, eastern grey kangaroos. 

European Rabbits 

The aim of the first part of this project was to survey European rabbits (Oryctolagus cuniculus) for the presence of Mycobacterium paratuberculosis in areas with endemic Johne's disease in sheep and cattle. In total 310 rabbits, 4 hares and 3 feral goats were examined by culture. No M. paratuberculosis was confirmed in any of the animals sampled. Eight of 314 samples demonstrated growth of organisms other than M. paratuberculosis. The lack of any evidence of Johne's disease in the rabbits in the Victoria survey would suggest that, under the conditions examined, rabbits are unlikely reservoir hosts for Johne's disease. 

The survey was designed to examine a sufficiently large sample of rabbits to detect infection if it occurred in relatively low levels of 3% with confidence limits of 95%. To "prove" that a disease does not exist in a population the entire population must be sampled with a test of 100% sensitivity and specificity. This survey does not rule out that rabbits may occasionally or rarely become infected with JD but that if it occurs it is likely to occur in low enough numbers as to not be a significant risk to resident populations of farmed livestock. Because of the limited range of farms and environments in the survey it is impossible to rule out the presence of a "focus" or "hotspot" of JD in rabbits as exists in Scotland. 

Large scale surveys for diseases that occur rarely are expensive and logistically difficult. A larger survey examining a wider range of environmental conditions over a larger number of farms with smaller numbers of rabbits per farm similar to the Scottish survey (Grieg et a11995) would be worthwhile. 

Eastern Grey Kangaroo 

Thirty-seven female and sixty-three males were sampled.  Five faecal samples had some growth which was shown to be due to contaminants, all other faecal and tissue samples were found to be negative. There was no evidence of M. paratuberculosis in the kangaroos examined. Although no animals were found to be infected with JD in this survey it does not rule out that eastern grey kangaroos could become infected with paratuberculosis.  It does however demonstrate that infection if it occurs is unlikely to occur at a significant level and eastern grays are unlikely to act as significant reservoirs of infection of Johne's disease.

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This page was last updated on 10/11/2014

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