Host-parasite relations and implications for control.

This paper considers the various measures available to control several of the neglected tropical diseases (NTDs). To develop the optimum methods for controlling the parasites that cause these NTDs, knowledge of the life cycles of both the parasites and their vectors are essential. Each NTD requires its own strategy for control based on detailed knowledge of the life cycle, and vector control, chemotherapy, better water supplies and better hygiene are all components that may be appropriate. For some diseases, improved drugs are urgently required, for some the tools are available for elimination, while uniquely guinea worm could be eradicated without any chemotherapeutic drug being used. Several NTDs lend themselves to mass drug administration (MDA) in which human populations are annually offered safe, effective and usually donated drugs with a view to morbidity control and/or elimination. The drugs could and should be used to improve the quality of millions of lives, prevent suffering, stigma, disfigurement and early death. The role of pharmaceutical companies who have donated their drugs for the treatment of millions of disadvantaged people in the developing world is acknowledged. One result of such drug pressure however is that evolutionary change may result, and it is incumbent on scientists during monitoring and evaluation of control programmes to ensure that such changes are recognised. One other unfortunate development is that a paucity of newly trained vector-borne disease experts may constrain future control efforts.