MODELING OF PARASITIC POPULATIONS - CESTODES

The philosophy of mathematical modelling as it applies to the epidemio logy of cestode populations is reviewed. A model provides, via the ''t hreshold theorem'', a criterion for deciding in advance if a control p rogramme can succeed in eradicating the parasite. In order to use this criterion it is necessary to have an estimate of the basic reproducti on ratio, R0, which can only be obtained if reliable epidemiological d ata are available before the control programme is started. A model has been used to describe the population dynamics of Echinococcus granulo sus, Taenia hydatigena and Taenia ovis in sheep and dogs in New Zealan d. For these parasites, data from a 40-year longitudinal study, as wel l as short-term field and laboratory studies, were available. A model has also been used to evaluate a proposed control programme directed a gainst Echinococcus multilocularis in foxes and voles in France. Here the type and extent of control intervention is predetermined by the ex isting rabies control programme. These two examples, which demonstrate the different techniques required to model cestodes in domestic and w ild-animal populations, are reviewed, and the use of a model as the ba sis 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.