Habitat-related prevalence of macroscopic Mycobacterium bovis infection inbrushtail possums (Trichosurus vulpecula), Hohonu Range, Westland, New Zealand

AIM: To identify broadscale habitat factors influencing the prevalence of m acroscopic Mycobacterium bovis infection in brushtail possums ( Trichosurus vulpecula) at a site in Westland, New Zealand. METHODS: During 1973/74, 1989/90 and 1997, we undertook repeated cross-sect ional surveys of M. bovis infection in a possum population on the Hohonu Ra nge, Westland. Data were analysed to determine the influence of site-specif ic habitat characteristics (land form, aspect, slope, altitude), distance f rom forest-pasture margin and time since infection on the spatial and tempo ral prevalence of macroscopic M. bovis infection. RESULTS: The prevalence of M. bovis infection was highest in 1973/74 (13.4% ), compared with 1989/90 (3.1%) and 1997 (9.4%). The prevalence of macrosco pic M. bovis infection was significantly influenced by habitat, as indexed by altitude and slope in this study site. Every 100 m increase in elevation was associated with a 29% decrease in the odds of infection, and every 100 increase in slope was associated with a 20% decrease in the odds of infect ion. For possums caught in the lowland podocarp forest (altitude 100-200 m, average slope=5.7 degrees), the odds of infection were nearly 30-fold high er than those for possums caught in high-altitude hardwood forest near the tree line (atitude 900-1000 m, average slope=28 degrees). Whilst the preval ence of disease fluctuated markedly between surveys, its broadscale spatial distribution changed little over time. Proximity to the forest-pasture mar gin had no significant influence on the prevalence of disease, once the eff ect of habitat was taken into account. CONCLUSION: The prevalence of macroscopic M. bovis infection in possums was strongly influenced by habitat type, being highest in habitats that suppor ted the highest density of possums, and lowest in habitats where population density was low. There was no evidence of progressive spread of M. bovis i nfection in possums into forest away from pasture-forest margins over the 2 4-year period of these surveys.