Epidemiology of Malaria and a New Proposal of the Control Principle Based on the Evolutionary Ecology of its Agents and Vectors.

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  • IKEMOTO TAKAYA
    Department of Microbiology, School of Medicine, Teikyo University
  • TAKAI KENJI
    Department of Immunology and Medical Zoology, School of Medecine, St. Marianna University

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Other Title
  • マラリア原虫とそのベクターの生態学論からみたマラリア流行の疫学と対策
  • マラリア ゲンチュウ ト ソノ ベクター ノ セイタイガクロン カラ ミタ マラリア リュウコウ ノ エキガク ト タイサク

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We have a long history of struggle against human malaria and have failed to see any sign of its extinction despite the modern development of medicine and control methods. After malaria emerged among human, its early extension appeared to start in the Paleolithic period followed by human migration and habitat expansion. And in the end of the 19th to the beginning of the 20th century, it covered geographically a relatively wide area over the globe. However, in the latest hundred year, it seems to have shown a distributional attenuation to result in a restricted coverage mainly in the tropical or subtropical areas. Because there was a global warming in this period, about 0.6°C in the average surface temperature on the earth, the warming would have had the effect of deterioration on the malaria distribution, if it solely had the direct influence. It was examined whether the diminution of distribution of malaria could be considered as one of evolutionary aspects of the parasite, in the phase of specific decline in the longer history of its evolution. Meanwhile, anopheline mosquitoes as malaria vector species have much longer history of evolution than the parasites and their human hosts. They were expected to require correspondingly longer periods to the processes of speciation and global distribution as well. It may be insightful to see as follows. Even if some vector species appeared to succeed in the temporary settlement of new colonies where they had been artificially delivered, they would possibly face to ecological difficulties to subsist. Many ecological factors appear to operate on the side of expulsion of the invader. Based on these considerations, a new malaria control principle was proposed. Malaria control principles in the past have not ever been conclusive yet, then it was propounded to attain specifically a reduction of mortality owing to malaria. This principle stems from the Ewald's (1994) adaptive severity hypothesis for pathogens. He developed this hypothesis on the rigorous analysis on the evolution of virulence of pathogens with the focus on their manner of transmission. If malaria mortalily, brought about by Plasmodium falciparum, could be reduced effectively, with some measures according to this principle, malaria would drop off the main public health problems.

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