Climate change and the resurgence of malaria in the East African highlands

Abstract

The public health and economic consequences of Plasmodium falciparum malaria are once again regarded as priorities for global development. There has been much speculation on whether anthropogenic climate change is exacerbating the malaria problem, especially in areas of high altitude where P. falciparum transmission is limited by low temperature. The International Panel on Climate Change has concluded that there is likely to be a net extension in the distribution of malaria and an increase in incidence within this range. We investigated long-term meteorological trends in four high-altitude sites in East Africa, where increases in malaria have been reported in the past two decades. Here we show that temperature, rainfall, vapour pressure and the number of months suitable for P. falciparum transmission have not changed significantly during the past century or during the period of reported malaria resurgence. A high degree of temporal and spatial variation in the climate of East Africa suggests further that claimed associations between local malaria resurgences and regional changes in climate are overly simplistic.

Figure 1

Number of months suitable for P. falciparum malaria transmission defined by the Garnham criteria (temperature > 15 °C and rainfall > 152 mm in two consecutive months). Shown are annual observations from 1901 to 1995 for Kericho (a), Kabale (b), Gikonko (c) and Muhanga (d).

Figure 2

Meteorological time series from Kericho. a, Minimum (bottom), mean (middle) and maximum (top) monthly temperatures, plotted with a 13-point moving average (thick line) to show the long-term movement in these data. b, Total monthly rainfall, plotted with a 13-point moving average (thick line). For a comprehensive version with time series for all four highland sites, see Supplementary Information.

Figure 3

Spatio-temporal variation in temperature and rainfall in East Africa. a, Mean monthly temperature for the 1901–95 period, and deviations from this long-term average by decade (1940–95). The four sites are indicated: 1, Kericho; 2, Kabale; 3, Gikonko; 4, Muhanga. b, Mean monthly rainfall for the 1901–95 period, and deviations from this long-term average by decade (1940–95).