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News & features archive, 2010


Satellite telemetry supports determination of HPAI dispersal ranges and rates

© FAO/Saeed Khan

09 September 2010 - The Highly Pathogenic Avian Influenza H5N1 (H5N1 HPAI) epidemic that swept through Southeast Asia in 2004 has spread across Eurasia and into Africa. The specific details of transmission dynamics are still not well understood. In recent years, however, wildfowl have been suspected of contributing to the broad and rapid geographic spread of H5N1 HPAI. This suspicion arises because migratory birds, in their intercontinental flyways, can effectively carry and disperse zoonotic pathogens for long distances. Furthermore, experimental infection studies reveal that some geese, swans and wild ducks shed H5N1 HPAI asymptomatically and this makes them ideal candidates to spread the disease as they move from place to place.

 To gain a better understanding of wildfowl-specific transmission dynamics, a team of researchers from the Food and Agriculture Organization of the United Nations (FAO), CIRAD, the U.S. Geological Survey, and Wetlands International evaluated the dispersive potential of H5N1 HPAI through an analysis of the movement range and movement rate of birds monitored by satellite telemetry. The team analysed the movements of 228 birds from 19 species flying over disease affected regions of Asia, Europe and Africa that were monitored by satellite telemetry from 2006 to 2009; part of FAO’s Global HPAI Disease and Migration Ecology Programme that has fitted with transmitters, more than 500 birds to date. The results from this analysis confirms that individual migratory wildfowl have the potential to disperse H5N1 HPAI over large distances, thus being able to perform movements of up to 2,900 kilometres within timeframes compatible with the duration of asymptomatic infections.

 But closer examination of the data reveals that, for any given individual migratory bird, there are an estimated 5 to 15 days annually when infection could result in the effective dispersal of H5N1 HPAI over 500 kilometres. In view of this, therefore, long-distance virus dispersal by individual wildfowl is unlikely. Additionally, the study suggests that intercontinental virus dispersion would probably require relay transmission amongst a series of migratory birds that have been successively infected. This requirement lowers the likelihood of virus dispersal.

 One of the most significant applications of this quantitative assessment of the dispersive potential of H5N1 HPAI by selected migratory birds is that it challenges the assumption that free-living wildfowl will respond similarly to captive, experimentally-infected birds. It also questions the rationale that asymptomatic infection will not alter their ability to move freely.

 More about this study and other details in relation to this topic can be found in “Potential spread of highly pathogenic avian influenza H5N1 by wildfowl: dispersal ranges and rates determined from large-scale satellite telemetry” published at the Journal of Applied Ecology, summer 2010.

 The Wildlife Unit of the Emergency Prevention Systems for Transboundary Animal and Plant Pests and Diseases (EMPRES) at FAO contributed to this and many other scientific studies evaluating whether waterfowl habitat use or migration are spatially or temporally related to H5N1 HPAI outbreaks . FAO supports these studies in order to design, test and provide analytical frameworks for quantifying the risks of disease spread among livestock, wildlife and people, and in this case, specifically avian-borne diseases. Overall, FAO is working to address high-impact transboundary diseases that are emerging and re-emerging around the world.