The efficacy of bacille Calmette-Guérin vaccine in wild brushtail possums ( Trichosurus vulpecula)

Abstract

A population of wild brushtail possums ( Trichosurus vulpecula) in which bovine tuberculosis was endemic was vaccinated with live bacille Calmette-Guérin (BCG) to determine the efficacy of vaccination. The population on the 56 hectare site was monitored bimonthly over 2 years using a capture-release regime. During the study tuberculosis was diagnosed by clinical and post mortem examination. Possums were vaccinated with BCG by both intranasal aerosol and conjunctival instillation. Possums were revaccinated on average every 5 months. Over the 2 years, 300 possums were recruited to the study with 149 being allocated to the vaccination group. There were significantly fewer cases of tuberculosis in the vaccinated (4 cases) than in the unvaccinated group (13 cases; P=0.023). The vaccine efficacy was 69%. An attempt was made to increase the incidence of disease by releasing onto the site possums that had been experimentally infected with a strain of M. bovis unknown in the area. However, this did not result in any additional cases. BCG vaccine was shown to have a level of efficacy which could be of assistance in controlling tuberculosis in wild possum populations. The future use of vaccination for the control of tuberculosis in wild possum populations is discussed.