Human Tropical Diseases in a Changing Environment

A taxonomy of the human environment and of its components is set out as a basis for understanding the complex determinants of human diseases in the tropics. The scale, nature and trends of tropical diseases are related to changes in environmental components, life systems and habitats, and these are analysed, with emphasis on vector-borne diseases, especially malaria. Although it is feasible to predict the consequences of changing single climatic variables for specific parts of parasite and vector life cycles, the probable effects of simultaneously changing several variables are far more difficult to predict because many qualitative and quantitative determinants of disease are likely to be affected and the effects of covariance are poorly understood. Local and specific changes are likely to overshadow more global climatic changes. The effects of global temperature rise are explored, with particular emphasis on the basic case reproduction rate for two species of human malaria parasites. Even a 2 degrees C temperature rise greatly increases this rate at the lower end of the temperature range compatible with transmission. The importance of secondary vectors may increase. Implications for transmission in Europe and for imported tropical diseases are discussed.