Estimating disease transmission in wildlife, with emphasis on leptospirosis and bovine tuberculosis in possums, and effects of fertility control

1. We present methods for estimating disease transmission coefficients in wildlife, using Leptospira interrogans infection (a bacterial disease transmitted predominantly during social contacts) in brushtail possums Trichosurus vulpecula as a model system. 2. Using data from a field experiment conducted on a naturally infected possum population, we estimated disease transmission coefficients assuming either 'density-dependent' or 'frequency-dependent' transmission. 3. A model-selection approach determined that density-dependent transmission was the most appropriate form of the transmission of L. interrogans infection in brushtail possums. 4. We used the chosen model of transmission to examine experimentally the effect of tubally ligating female brushtail possums on the epidemiology of L. interrogans. The estimated transmission coefficient was 28% higher (P = 0.16) in populations subject to tubal ligation, raising the possibility that fertility control of this type may increase disease transmission rates. 5. Altering mating behaviour through fertility control may have the potential to control diseases such as bovine tuberculosis in brushtail possums, although the potential of fertility control techniques to change disease transmission coefficients and disease epidemiology requires further investigation. This would require models that examine the combined effects of fertility control on population dynamics, social behaviour and disease transmission coefficients simultaneously.