DYNAMIC-MODELS OF SCHISTOSOMIASIS MORBIDITY

Previous attempts to assess the health impact of schistosomiasis contr ol programs on community morbidity have been limited by a lack of a th eoretical framework that describes the dynamic relationships between i nfection and morbidity. In this paper a model of schistosomal morbidit y is developed and parameterized. Morbidity is divided into that due t o current heavy infection, and early and late stages of chronic diseas e. The model was parameterized using data showing resolution of diseas e after treatment, correlations between prevalence of disease and inte nsity of infection and using age-morbidity profiles. The fitted parame ters suggest that early manifestations of disease such as hepatomegaly in Schistosoma mansoni and S. japonicum infections would resolve rela tively quickly following treatment whereas later forms of disease such as liver fibrosis resolve very slowly or not at all. Similar general conclusions were obtained with data on early and late forms of urinary tract morbidity in S. haematobium.