The development of analytical models for human trypanosomiasis.

The idea of biological equilibria is presented and applied first to the case of single species populations. Difference and differential descriptions of population changes over time are compared and contrasted. The complications that arise when describing interactions between species are then illustrated for the case of vector-borne diseases, such as malaria. A simple model for malaria is explored and later extended to the case of the African trypanosomiases where more than one vertebrate host species is involved. Appropriate parameter values obtained from the literature are listed, and equilibrium predictions given. These predictions broadly coincide with field experience. A brief description of the analysis of age-prevalence data is given and applied to several sets of data from sites in West, Central and East Africa. In each case the force of infection is extremely low, indicating that a non-human reservoir must be involved in the maintenance of the disease throughout Africa. A final plea is made to integrate the modelling exercise into on-going programmes for disease control or eradication.