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Archives de fiches, 2010

La FAO contribue à la compréhension de la géographie et l'écologie des agents pathogènes émergents

©FAO/Arif Ariadi

27 août 2010 - The number of emerging infectious diseases at the animal-human interface is increasing. Among the more frequently cited global factors amplifying emerging infectious diseases events we note human population pressures and the enhanced mobility of people, climate change, food and agricultural dynamics, and the progressive encroachment of forest and game reserves. Still, the precise mechanisms by which these socio-ecological dynamics or disruptions translate into successful disease emergence are not well understood.

The ecology and evolution of emerging disease agents may be better understood through application of geographic and ecological invasion frameworks. Colonization dictates the pathogen-host interactions and the infection course and host specificity evolve in such a way that invasion is supported. Later, pathogen and host start to co-evolve and the parasite life-history is accordingly adjusted. The latter phase takes place during disease entrenchment.

Given that invading pathogens’ ecological strategies differ, generalist and specialist pathogens will behave differently: specialists adapt to a predictable host environment whereas generalists prevail in more dynamic host landscapes. Hence, pathogen subpopulations would evolve dynamically, adjusting their replication, survival, and dispersal rates to fit the most successful strategy at the time. The recent panzootic of highly pathogenic avian influenza H5N1 (H5N1 HPAI) supports this hypothesis.

The virulence jump and host radiation of avian influenza viruses generally demonstrates how twentieth century agro-ecological dynamics may have contributed to creating a novel avian host ecology and niche for the gene pool as circulating in wild waterfowl. For instance, in China, H5N1 HPAI first evolved in domestic waterfowl to eventually provoke disease flare-up at an intercontinental scale, followed by virus retraction and persistence in selected countries (e.g. Bangladesh, China, Egypt, Indonesia, and Viet Nam).

Previous studies by the Food and Agriculture Organization (FAO) suggest that local H5N1 HPAI niches are featured by the presence of rice-duck agriculture, broiler production, live mixed-bird markets, poor infrastructure and services, and wild waterfowl migration.

H5N1 HPAI, as a disease, has turned into an infection of the respiratory tract of domestic ducks and geese, whilst bringing generalized infection to terrestrial poultry, in settings where the broader agricultural, climatic, geographic and socio-ecological settings are conducive.

Details on these topics can be found in a recent book titled The Biogeography of Host-Parasite Interactions (Oxford University Press, 2010) and with applied sections on historical biogeography, palaeontology, phylogeography, landscape epidemiology, invasion biology, conservation biology, human evolution, and health ecology. FAO contributed a chapter, number 17, on the invasion ecology during pathogen emergence, taking H5N1 HPAI as an example.