Public Health and Epidemiological Considerations For Avian Influenza Risk Mapping and Risk Assessment

Avian influenza viruses are now widely recognized as important threats to agricultural biosecurity and public health, and as the potential source for pandemic human influenza viruses. Human infections with avian influenza viruses have been reported from Asia (H5N1, H5N2, H9N2), Africa (H5N1, H10N7), Europe (H7N7, H7N3, H7N2), and North America (H7N3, H7N2, H11N9). Direct and indirect public health risks from avian influenzas are not restricted to the highly pathogenic H5N1 “bird flu” virus, and include low pathogenic as well as high pathogenic strains of other avian influenza virus subtypes, e. g., H1N1, H7N2, H7N3, H7N7, and H9N2. Research has shown that the 1918 Spanish Flu pandemic was caused by an H1N1 influenza virus of avian origins, and during the past decade, fatal human disease and human-to-human transmission has been confirmed among persons infected with H5N1 and H7N7 avian influenza viruses. Our ability to accurately assess and map the potential economic and public health risks associated with avian influenza outbreaks is currently constrained by uncertainties regarding key aspects of the ecology and epidemiology of avian influenza viruses in birds and humans, and the mechanisms by which highly pathogenic avian influenza viruses are transmitted between and among wild birds, domestic poultry, mammals, and humans. Key factors needing further investigation from a risk management perspective include identification of the driving forces behind the emergence and persistence of highly pathogenic avian influenza viruses within poultry populations, and a comprehensive understanding of the mechanisms regulating transmission of highly pathogenic avian influenza viruses between industrial poultry farms and backyard poultry flocks. More information is needed regarding the extent to which migratory bird populations to contribute to the transnational and transcontinental spread of highly pathogenic avian influenza viruses, and the potential for wild bird populations to serve as reservoirs for highly pathogenic avian influenza viruses. There are still uncertainties regarding the epidemiological and ecological mechanisms that regulate “spill-over” and “spill-back” transmission of highly pathogenic avian influenza viruses between poultry and wild bird populations, and the interspecies transmission of avian influenza from infected birds to humans and other species of mammals. Further investigations are needed to evaluate the effectiveness of poultry vaccination programs for the control and eradication of avian influenza in poultry populations at the national and regional level, and the effect of long term poultry vaccination programs on human public health risks from avian influenza viruses. There is a need to determine risk factors associated with the extent of direct human involvement in the spread and proliferation of avian influenza viruses through commercial supply chain and transportation networks, and specific risk factors associated with domestic and international trade in live poultry, captive wild birds, poultry food products, (meat, eggs), poultry by-products (feathers, poultry meal), poultry manure, and poultry litter. Addressing these issues will greatly enhance our ability to implement economically and ecologically sustainable programs for the control of avian influenza outbreaks in wild and domesticated birds, increase our capability for promoting the protection of wild bird populations from disease and disruption, and help improve food security and public health in countries worldwide.