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Week 35: Migratory bird behaviour shapes 

where and when avian influenza spreads

 

A study published on 26 August investigated the factors that influence the spread of highly pathogenic H5 avian influenza during waterfowl migration. The researchers compiled 43 potential factors and tested 28 of them using a geographically detailed, individual-based simulation model.

Species: Wild migratory waterfowl. The findings are also relevant to domestic ducks, geese and chickens, as infection can spread from wild birds.

What did the researchers find?

  • How easily the virus was transmitted and how long a bird remained infectious had the greatest impact on the overall extent of spread and the risk of infection reaching domestic poultry.
  • When large numbers of birds gathered at the same stopover sites, the risk of transmission increased.
  • More diverse and less overlapping migration routes could allow the infection to persist for longer and spread across a wider area.
  • The characteristics of the virus mainly influenced how many birds became infected and the risk of transmission to domestic poultry. The birds’ migratory behaviour primarily influenced when, where and for how long the infection spread.
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Credit to : Royal Society Publishing
 

Strength of evidence

Moderate for mechanisms and risk assessment. This is a comprehensive, peer-reviewed modelling study using systematically selected parameters, but it is not a field study that can determine the exact level of risk for a specific flock or farm. The model results depend on assumptions regarding factors such as transmissibility, environmental transmission and bird movements.

What does this mean for backyard flocks?

The recommendation to protect your birds’ feed and water from wild birds still applies. However, the study shows that the risk of infection does not depend solely on how many wild birds are passing through an area. The risk may be particularly high when large numbers of ducks and geese gather at nearby lakes, wetlands or stopover sites.

It may therefore be wise to strengthen your flock’s biosecurity when large numbers of wild waterfowl gather in the surrounding area – rather than focusing only on specific times of the year.

Migration season does not carry the same level of infection risk throughout. Local stopover sites, large concentrations of birds and changes in migration routes can all influence when the risk is at its highest.

Credit to : Royal Society Publishing

Sources

Royal Society Publishing