Trends, priorities and policy directions in the control of vector-borne diseases in urban environments.

The habitats available in urban environments tend to be rather lacking in diversity compared to those in the countryside, and relatively few species are able to exploit them. Those that can, however, often find themselves relatively well provided with food and places to live, and relatively free of competitors and predators. This applies not only to such well-known species as the house-sparrow, but also to most of the important mosquito vectors of human disease in urban areas. Human city dwellers thus tend to be exposed to a different spectrum of disease than their rural counterparts. This review describes how the physical and social changes associated with urbanization have altered the transmission of vector-borne disease. It concentrates on the important mosquito-borne infections: malaria, dengue and filariasis. Dengue virus vectors breed in relatively clean water in man-made containers, while urban filariasis vectors breed in highly polluted water, and these mosquitoes have now been spread by man's activities to almost every tropical city. With important exceptions, anopheline malaria vectors have not generally succeeded in adapting to urban life, but malaria can still be a problem where there are rural pockets in the middle of town. Each of these problems requires control using different technologies and timing. The following policy implications are stressed. The areas of responsibility between different sectors of the local services (health, water supply, sanitation), and between these and the public, need to be clearly defined. Due to the biological complexities of vector-borne disease, decentralized primary health care systems are generally incapable of ensuring that control efforts are adequately targeted in time and space. Community support is essential but specialized technical skills are also required.