The transmission of infections can be sensitive to changes in population density, especially in the case of fluctuating wildlife populations [1–3]. When modelling disease transmission, the probability of encountering an infected individual is typically assumed to be either independent of (frequency-dependent) or linearly dependent on (density-dependent) population density . Sexually transmitted infections are generally described using frequency-dependent transmission because the number of sexual contacts is assumed to remain constant, regardless of population density . Infections that are transmitted through regular ‘every-day’ contacts are often assumed to be density-dependent .