EPIFIL - A DYNAMIC-MODEL OF INFECTION AND DISEASE LN LYMPHATIC FILARIASIS

The lack of a quantitative framework that describes the dynamic relati onships between infection and morbidity has constrained efforts aimed at the community-level control of lymphatic filariasis. In this paper, we describe the development and validation of EPIFIL, a dynamic model of filariasis infection intensity and chronic disease. Infection dyna mics are modeled using the well established immigration-death formulat ion, incorporating the acquisition of immunity to infective larvae ove r time. The dynamics of disease (lymphodema and hydrocele) are modeled as a catalytic function of a variety of factors, including worm load and the impact of immunopathological responses. The model was paramete rized using age-stratified data collected from a Bancroftian filariasi s endemic area in Pondicherry in southern India. The fitted parameters suggest that a relatively simple model including only acquired immuni ty to infection and irreversible progression to disease can satisfacto rily explain the observed infection and disease patterns. Disease prog ression is assumed to be a consequence of worm induced damage and to o ccur at a high rate for hydrocele and a low rate for lymphodema. This suggests that immunopathology involvement may not be a necessary compo nent of observed age-disease profiles. These findings support a centra l role for worm burden in the initiation and progression of chronic fi larial disease.