Different Approaches to Modelling the Cost-effectiveness ofSchistosomiasis Control

This paper reviews three different approaches to modelling thecost-effectiveness of schistosomiasis control. Although theseapproaches vary in their assessment of costs, the major focus of thepaper is on the evaluation of effectiveness. The first model presentedis a static economic model which assesses effectiveness in terms of theproportion of cases cured. This model is important in highlighting thatthe optimal choice of chemotherapy regime depends critically on thelevel of budget constraint, the unit costs of screening and treatment,the rates of compliance with screening and chemotherapy and theprevalence of infection. The limitations of this approach is that itmodels the cost-effectiveness of only one cycle of treatment, andeffectiveness reflects only the immediate impact of treatment. Thesecond model presented is a prevalence-based dynamic model which linksprevalence rates from one year to the next, and assesses effectivenessas the proportion of cases prevented. This model was important as itintroduced the concept of measuring the long-term impact of control byusing a transmission model which can assess reduction in infectionthrough time, but is limited to assessing the impact only on theprevalence of infection. The third approach presented is a theoreticalframework which describes the dynamic relationships between infectionand morbidity, and which assesses effectiveness in terms of case-yearsprevented of infection and morbidity. The use of this model inassessing the cost-effectiveness of age-targeted treatment incontrolling Schistosoma mansoni is explored in detail, with respect tovarying frequencies of treatment and the interaction between drug priceand drug efficacy.