Resolution of <i>Mycobacterium bovis</i> infection in wild brushtail possums ( <i>Trichosurus vulpecula</i> )

Abstract

Abstract The brushtail possum (Trichosurus vulpecula) is the principal wildlife reservoir of Mycobacterium bovis in New Zealand (Morris and Pfeiffer 1995 Morris, RS and Pfeiffer, DU. 1995. Directions and issues in bovine tuberculosis epidemiology and control in New Zealand. New Zealand Veterinary Journal, 43: 256–265. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). Tuberculosis in possums is a progressive, fatal infection. The complete resolution of infection in possums has not been reported. The purpose of this communication is to present two cases of complete and spontaneous resolution of tuberculosis in wild, naturally infected possums. During an 11-year (1989–2000) longitudinal study of a possum population at Castlepoint in the Wairarapa, 90 bacteriologically-confirmed cases of M. bovis infection were observed, and 88 of the tuberculous possums were either found dead or were presumed to have died when they ceased to be trapped. As the home range of adult possums is stable (Efford et al 2000 Efford, M, Warburton, B and Spencer, N. 2000. Home-range changes by brushtail possums in response to control. Wildlife Research, 27: 117–127. [Crossref], [Web of Science ®] , [Google Scholar]) it was assumed that if an adult possum could no longer be trapped, it had died. In many cases, the declining physical condition of a tuberculous possum prior to its disappearance supported the assumption. However, two cases survived and were euthanised, one 15 months and the other 30 months after they first showed clinical signs of infection. When examined post mortem, neither showed evidence of M. bovis infection. The case histories are described and the significance of the observations discussed.