The relationship between prevalence of Mycobacterium bovis infection in feral ferrets and possum abundance

AIM: To determine the relationship between the prevalence of macroscopic My cobacterium bovis infection in feral ferrets (Mustela Aro) and the abundanc e of brushtail possums (Trichosurus vulpecula). METHODS: The predictive power of a previously reported positive association between the prevalence of macroscopic M. bovis infection in ferrets and po ssum abundance was examined by undertaking surveys of M. bovis infection in ferrets at sites of low and high possum abundance. The association was the n tested by a manipulative experiment that measured changes in the prevalen ce of macroscopic M. bovis infection in feral ferrets after reducing possum abundance. RESULTS: The positive relationship between the prevalence of macroscopic M. bovis infection in ferrets and possum abundance remained valid for new sur vey data, although the goodness of fit of the relationship was reduced. Exp erimentally reducing possum abundance reduced the odds of macroscopic M. bo vis infection in ferrets by 80% in the years immediately following possum c ontrol (Odds Ratio=0.23, p=0.003). CONCLUSIONS: There is a causal link between possum abundance and the preval ence of macroscopic M. bovis infection in feral ferrets in areas in which M . bovis infection is known to occur in ferret populations. This suggests th at possum-to-ferret transmission of disease occurs and accounts for most of the disease evident in ferret populations, though does not determine wheth er ferrets are spillover or maintenance hosts of M. bovis. Management to re duce the prevalence of M. bovis infection in ferrets should consider reduci ng possum abundance as a control tactic.