Natal multimammate mice (M. natalensis) occur throughout sub-Saharan Africa, and are an important agricultural pest species and natural reservoir hosts for several microparasites that cause disease in humans, including Yersinia pestis (bubonic plague), leptospirosis and several arenaviruses including Lassa virus, which can cause severe haemorrhagic fever in humans [28–32]. Multimammate mouse demography has been studied thoroughly, which allows us to create a simple but accurate demographic model that will serve as a basis for transmission modelling (see below). In Tanzania, where most of the studies on its population ecology have been conducted, M. natalensis exhibits strong annual population fluctuations, with densities ranging from 10 ha−1 in the breeding season to greater than 300 ha−1 outside the breeding season . Importantly, we have recently quantified a contact–density relationship for this species, which provides us with a realistic biological background for fitting the transmission functions .