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Malaria and Tick-Borne Encephalitis in a Warming World
Rogers, D.J. and Randolph, S.E. 2006. Climate change and vector-borne diseases. Advances in Parasitology 62: 345-381.

What was done
As part of a major review of the potential impacts of global warming on vector-borne diseases, Rogers and Randolph focus on recent upsurges of malaria in Africa and tick-borne encephalitis in Europe, asking the question "Has climate change already had an impact?"

What was learned
Focusing first on malaria, the zoologists from the University of Oxford in England state that "evidence for increasing malaria in many parts of Africa is overwhelming, but the more likely causes for most of these changes to date include land-cover and land-use changes and, most importantly, drug resistance rather than any effect of climate," noting that "the recrudescence of malaria in the tea estates near Kericho, Kenya, in East Africa, where temperature has not changed significantly [our italics], shows all the signs of a disease that has escaped drug control following the evolution of chloroquine resistance by the malarial parasite." They then go on to explain that "malaria waxes and wanes to the beat of two rhythms: an annual one dominated by local, seasonal weather conditions and a ca. 3-yearly one dominated by herd immunity," noting that "effective drugs suppress both cycles before they can be expressed," but that "this produces a population which is mainly or entirely dependent on drug effectiveness, and which suffers the consequence of eventual drug failure, during which the rhythms reestablish themselves, as they appear to have done in Kericho."

With respect to tick-borne-encephalitis (TBE) in Europe, the two researchers conclude that "although changing climate factors may have played a role in the upsurge of TBE, none has yet been identified that can satisfactorily explain both the spatial variation and the major temporal discontinuities in the incidence of this disease."

What it means
It is easy to claim that global warming is causing a resurgence of malaria and various other vector-borne diseases, as many climate alarmists have done over the past several years. It is another matter altogether to prove it.

Reviewed 11 April 2007