Wednesday 5 March 2014

Influenza and chips: tracking bird movements using transmitters

Understanding bird migration is one important aspect to better understanding of influenza viruses. This is because water birds, including ducks, geese, swans, gulls, terns and waders are natural hosts for low pathogenicity avian influenza viruses (LPAI). High pathogenicity avian influenza (HPAI) viruses are mostly assembled in/found in poultry.

Little detail exists on the extent of wild bird movements from wintering areas to breeding grounds and back again, in both hemispheres. An interactive map that presents some of those data addresses some of this.  The map is located on a Food and Agriculture Organization of the United Nations (UNFAO) and United States Geological Survey (USGS; (1)) website here.

While this map does not include analysis of bird movements further southwards, it is clear that the tracked birds have distinct origins and endpoints. There is also visible overlap between different bird's flyways and endpoints. Such overlap represents chances for different viral passengers to be shed and acquired by the migrating birds, resulting in the production of new influenza virus subtypes and variants. At these endpoints there is also the possibility of local birds, poultry, pigs and perhaps other animals being infected by the visiting birds, also creating the possibility for new viral subtypes and variants to result.

Bird migration clearly involves countries all over the world. It is also seasonal. So just how big is the role for water bird movements in the "seasonality" of influenza outbreaks among poultry? I don't know but the answer is influenced by additional variables including the species and age of the birds, their interactions, their previous exposures to influenza viruses, health and immune status, differences between how and where wild birds exist, how and where poultry are farmed and caged and the health and environmental factors affecting virus survivability including humidity and temperature

From our human point of view, we sit at various points along this migratory transmission/acquisition chain, and that shows up when viruses spillover to us and cause overt disease. 

Amazing it doesn't happen more often really.

Links of interest...
  1. FAO-USGS Avian Influenza Projects at the USGS WERC
  2. H7N9 in wild birds...a review of the literature (VDU post)
  4. UN FAO Avian influenza telemetry studies
  5. Persistence of highly pathogenic avian influenza viruses in natural ecosystems.

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