Epizootiology of trypanosomiases: some aspects of mathematical modelling.

The formulation of trypanosomiasis transmission models is complicated by heterogeneity, due to (a) different feeding preferences of vectors for a range of host species, (b) the presence of different genetic lines in the parasite population, and (c) variations in susceptibility and infectivity among hosts and vectors. Simple models are used to explore qualitative effects of changes in host range of vectors on the basic reproductive rate (section 1), of migration of vectors on disease persistence (section 2), and of gradual acquisition of immunity to different trypanosome serodemes (section 3). Many implicit and explicit assumptions need to be validated by fitting models to field data as part of multidisciplinary projects.