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News & features archive, 2009

FAO study on agro-ecological resilience shines light onto the dynamics of persistence of H5N1 HPAI

11 November 2009 – In late 2003 highly pathogenic avian influenza (A) subtype H5N1 (H5N1 HPAI) emerged in Southeast Asia causing poultry and economic losses on a large scale. Since 2004, the disease has spread to the rest of Asia, Europe and Africa. The virus is nowadays believed to persist in China, Indonesia, Viet Nam, Bangladesh and Egypt. Veterinary epidemiologists involved in influenza research remain struck by the degree to which H5N1 HPAI persists, producing repeated outbreaks despite interventions on many fronts, including public education, surveillance sampling, restrictions on livestock movement, improvements in farm biosecurity, live-bird market disinfection, culling rounds, and vaccination campaigns.

The Food and Agriculture Organization of the United Nations commissioned a study to examine the main drivers behind H5N1 HPAI persistence in different agro-ecological contexts across the globe. Previous research identified five variables that helped differentiate areas according to their level of persistence: chicken density, duck density, agricultural population density, purchasing power parity per capita, and chicken production output/input ratio. Localities that host the greatest persistence were characterized by high chicken and duck densities, high agricultural population densities, intermediate purchasing power per capita, and intermediate chicken production output/input ratios. These localities included, among others, Egypt, Viet Nam, Indonesia and several coastal Chinese provinces.

A more recent study indicates that localities may differ in ecological resilience –the capacity to absorb external shocks– including disease outbreaks. Although this study is still a work in progress, preliminary results derived from a stochastic multivariate autoregression model suggest that the agro-ecological variables that define H5N1 HPAI epidemiology may in some countries be more tightly interconnected than in others. Industrialized countries in the West appear to differ from countries undergoing progressive economic transition in the ways in which their agro-ecological variables are interconnected. Ongoing work aims to address the effects such differences may have on the spread and evolution of the virus.

The results so far obtained also suggest that emergence of new influenzas, including H1N1/2009, may depend on more than just the agricultural sector from which they arose. Influenza dynamics may encompass broader ecological contexts in which livestock farming takes place. If this is indeed the case, effective disease management cannot be achieved by veterinary services alone, thus warranting collaboration from a wide array of stakeholders. Interventions must therefore be directed towards policies and practices that help shape the ways in which agro-ecological variables interrelate across the landscape. Such interventions may help reorganize livestock production systems and their corresponding agro-ecologies in such a way as to minimize the potential impacts of influenza outbreaks.

This study is being carried out by Robert G. Wallace from the University of Minnesota and Lenny Hogerwerf from the Université Libre de Bruxelles, under the overall guidance of Jan Slingerbergh, Senior Animal Health Officer and Head of EMPRES at the Food and Agriculture Organization.