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Global warming and malaria: knowing the horse before hitching the cart

Publication date:
P. Reiter
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This article criticises predictions that climate change will lead to more cases of malaria and its spread to higher latitudes and altitudes in the coming decades. Mathematical models that support this theory are criticised for having limited application because they side step four factors that are key to the transmission and epidemiology of the disease. These four factors are: the ecology and behaviour of humans, and the ecology and behaviour of the vectors. Case studies and a historical view of the disease are given as evidence that these four factors have been and will remain the principal determinants of malaria prevalence and incidence. The importance of ecology and behaviour in the decline of malaria in the temperates (regardless of temperature increases) is illustrated using the following examples:

ecological change owing to improved drainage and the reclamation of swampy areas for cultivation resulted in the elimination of mosquito habitat
the combination of selective breeding of livestock and introduction of new fodder crops resulted in larger farm building for stocks and larger numbers of livestock. This diverted mosquitoes from human habitation as they found attractive sites for resting (farm buildings) and feeding (livestock)
industrialisation and improvements in construction (for example non-use of thatch roofing) led to more people living in mosquito-proof housing.

Incidence and prevalence of malaria in the tropics is explained by the following factors:

the stable endemic malaria phenomenon is observed in areas where transmission rates are very high and local inhabitants exhibit immunity owing to repeated re-infection. Most people in sub-Saharan Africa live in regions of stable transmission
high birth rates have resulted in higher attack rates due to higher densities of people, and greater vulnerability because of the higher proportion of infants and children in the population
forest clearance creates habitats for the malarial vectors that breed in open sun lit pools
the proliferation of various impoundment has increased vector habitat area
movement of infected people to malaria rare areas and movement of non-immune people to areas of transmission
political and economical factors such as degradation of the health infrastructure, war and civil strife that erode the capacity of authorities to deal with the disease.

The conclusion is that traditional and new malaria control strategies should be pursued irrespective of future climate change.