COS 61-9
Highland malaria moves up in altitude with warmer temperatures
The impact of global warming on vector-borne diseases and on highland malaria in particular remains controversial. Although temperature is known to influence transmission intensity through its effects on vector demography and pathogen development within the vector, its effects in long-term trends are confounded by those of other drivers potentially at play. Here, we take advantage of spatio-temporal data at a regional scale, to ask instead how the altitudinal distribution of Plasmodium falciparum malaria changes with the interannual variability of temperature. We analyze monthly cases from 124 municipalities in the Antioquia region in western Colombia for 1990–2005 and 158 kebeles in the Debre Zeit sector of central Ethiopia for 1993–2005. These analyses are based primarily on the cumulative altitudinal distribution of the cases, independently from their totals, and on the change in quantiles of these distributions as a function of temperature; in addition to clustering of localities with similar temporal dynamics and negative binomial regression.
Results/Conclusions
We demonstrate an expansion of the altitudinal distribution of malaria in warmer years in both highland regions. Specifically, the median elevation of the cumulative altitudinal distribution increases with mean temperature, with a larger fraction of the cases at higher elevations in warmer years. Comparison of the rate of change in cases with temperature over (1) interannual time scales and (2) a longer-term trend spanning two decades, indicates that warming per se can explain the increase in malaria burden from the beginning of the 1980s to the end of the 1990s. Similar increasing trends in both P. falciparum and P. vivax for the Debre Zeit region rules out a primary role of drug resistance. Our findings imply that climate change will, without mitigation, result in an increase of the malaria burden in the densely populated highlands of Africa and South America.