A 65-month longitudinal study of Mycobacterium bovis infection in a wild possum (Trichosurus vulpecula ) population

The epidemiology of Mycobacterium bovis infection in brushtail possums at a 21ha site at Castlepoint in the Wairarapa, New Zealand was studied using capture-mark-recapture. The mean annual adult population density was 8.7 per ha, and features of the population were high density and fecundity and early age breeding. Period prevalence of M. bovis infection was 10.2% for males and 11.7% for females and 10.8% overall. Incidence density was 2.8 per 100 months for both sexes. Tuberculous possums were recorded continuously throughout the study and four different restriction endonuclease (REA) types of M. bovis contributed to the infection dynamics. Two REA types were endemic, and infected possums were associated with distinct denning areas. The study clearly showed possums to be the reservoir host in livestock and wildlife with transmission most likely occurring by aerosol and associated contact during encounters. Transmission also occurs between females and their pouch young during rearing. Transmission through wounds caused by agonistic interactions was of minimal or no influence. All possums were examined post mortem for tuberculosis during the depopulation which followed and 6.07% were culture positive. Repopulation was then monitored and four REA types (Types 2, 3, 8 and 10) re-established.