Summary

It’s complicated. Tropical diseases have unusually intricate life cycles because most of them involve not only a human host and a pathogen, but also a vector host. The diseases are predominantly tropical due to their sensitivity to local ecology, usually due to the vector organism. The differences between the tropical diseases mean that they respond to environmental degradation in various ways that depend on local conditions. Urbanization and water pollution tend to limit malaria, but deforestation and dams can exacerbate malaria and schistosomiasis. Global climate change, the largest environmental change, will likely extend the range of tropical climate conditions to higher elevations and near the limits of the tropics, spreading some diseases, but will make other areas too dry or hot for the vectors. Nonetheless, the geographical range of tropical diseases will be primarily determined by public health efforts more than climate. Early predictions that malaria will spread widely because of climate change were flawed, and control efforts will probably cause it to diminish further. The impact of human disease on economic development is hard to pin down with confidence. It may be substantial, or it may be misattributed to other influences. A mechanism by which tropical disease may have large development consequences is its deleterious effects on the cognitive development of infants, which makes them less productive throughout their lives.