THE DYNAMICS OF BOVINE TUBERCULOSIS IN POSSUM POPULATIONS, AND ITS ERADICATION OR CONTROL BY CULLING OR VACCINATION

1. A simple model is used to investigate the feasibility of eradicatin g bovine tuberculosis (Mycobacterium bovis Karlson and Lessel) from po ssum (Trichosurus vulpecula Kerr) populations by culling, or by distri buting a (hypothetical) non-transmissible vaccine; and of reducing the prevalence of tuberculosis to a defined level within a fixed time per iod. 2. The model suggests that tuberculosis could be eradicated from a possum population by reducing its density to 43% of the (no-disease) carrying capacity, which would require culling possums at a rate of 9 .2% per year; or by maintaining 40% of the population in a vaccine-imm une state, which would require vaccinating possums at a rate of 15% ye ar(-1). 3. The model suggests that the prevalence of tuberculosis coul d be reduced to 10% of its pre-control level within 5 years by culling possums at a rate of 12% year(-1), or by vaccinating possums at a rat e of 13% year(-1). 4. Taken together, these results suggest that culli ng possums to maintain a low population density may be the most effici ent method of preventing tuberculosis from establishing in an uninfect ed population, but vaccination could be as or more efficient as a mean s of removing tuberculosis from an infected population. Both of these statements are sensitive to changes in parameter values. 5. The cullin g rate needed to achieve eradication of tuberculosis is sensitive to t he maximum population growth rate, r, and to the logistic shape parame ter, theta. It is insensitive to whether density-dependent population regulation acts through the birth or death rates. 6. The disease dynam ics are sensitive to the shape of the contact rate function, which is determined by the relative importance of mating, den sharing (possibly sequentially), aerosols and marking, and other mechanisms in the tran smission of tuberculosis. 7. All results are sensitive to the increase d population mortality due to disease, alpha, which is difficult to es timate. 8. The results have been calculated under the assumption that immigration of possums from other areas does not occur. If it did it c ould change the results significantly.