Modelling of parasitic populations: cestodes.

The philosophy of mathematical modelling as it applies to the epidemiology of cestode populations is reviewed. A model provides, via the "threshold theorem", a criterion for deciding in advance if a control programme can succeed in eradicating the parasite. In order to use this criterion it is necessary to have an estimate of the basic reproduction ratio, R0, which can only be obtained if reliable epidemiological data are available before the control programme is started. A model has been used to describe the population dynamics of Echinococcus granulosus, Taenia hydatigena and Taenia ovis in sheep and dogs in New Zealand. For these parasites, data from a 40-year longitudinal study, as well as short-term field and laboratory studies, were available. A model has also been used to evaluate a proposed control programme directed against Echinococcus multilocularis in foxes and voles in France. Here the type and extent of control intervention is predetermined by the existing rabies control programme. These two examples, which demonstrate the different techniques required to model cestodes in domestic and wild-animal populations, are reviewed, and the use of a model as the basis for a benefit/cost analysis of control options is discussed. These techniques could, in principal, be used to design control programmes for Taenia saginata or Taenia solium in humans.