Wednesday, November 07, 2018

WHO: Migratory Birds & The Potential Spread Of Avian Influenza


Although anticipated each fall by bird lovers, in recent years the annual southbound trek of migratory birds has also been associated with the arrival and spread of HPAI and LPAI viruses.

In 2015 - following North America's record HPAI H5 epizootic - we looked at a study (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl) which concluded that - while migratory waterfowl can briefly carry HPAI H5 - they were not a very good long-term reservoir for highly pathogenic avian flu viruses.
HPAI viruses, they posited, burned out fairly quickly in aquatic waterfowl populations - likely due to their immunity to LPAI viruses - and would therefore have to be reintroduced periodically.
That pattern appears to have changed recently when, in the fall of 2016, H5N8 returned to Europe after an 18-month absence and brought with it a number of genetic and behavioral changes attributed to a reassortment event that likely took place sometime in the spring of 2016 (see EID Journal: Reassorted HPAI H5N8 Clade - Germany 2016).
Among the changes noted in this reassorted HPAI H5N8 virus was enhanced virulence in wild birds, an expanded avian host range, and perhaps most notably, unusual environmental persistence into the summer.
Although last winter's arrival of HPAI to Europe and Asia was subdued compared to the previous winter, it did bring with it a newly reassorted HPAI H5N6 virus which arrived in Japan, South Korea, Taiwan and Northern Europe (The Netherlands) literally within days of each other (see EID Journal: Novel HPAI A(H5N6) Virus in the Netherlands, December 2017).
A study, published in 2016 (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1), suggests that waterfowl can pick up new HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way to their summer breeding spots - where they spread and potentially evolve -  and then redistribute them on their southbound journey the following fall.
We've also seen persistent H5N8 and HPAI H5Nx outbreaks over the summer in western Russia and Bulgaria, both of which lie beneath the Black Sea/ Mediterranean Flyway which funnels birds to Western Europe, the Middle East, and Africa.

While we don't have a good handle on what viruses may have circulated above the arctic circle over the summer, or what viruses migratory birds may have picked up on their journey south, we may find out in the coming weeks.

Although the following WHO report deals with Europe, North America and Asia are similarly at risk of seeing HPAI viruses carried in by migratory birds. 

Avian influenza could spread along wild birds’ migration routes this winter

This winter, health authorities and people living in countries of the WHO European Region located along wild birds’ migration routes should be particularly vigilant about avian influenza outbreaks in poultry and wild birds. Since some avian influenza viruses can infect humans, it is important that people in countries experiencing outbreaks take protective steps and avoid contact with sick and dead birds or contaminated environments.
Start of the autumn bird migration

In the European Region every autumn, wild birds migrate south-westwards to overwinter in warmer climates. Since June, the Russian Federation has experienced multiple avian influenza outbreaks in poultry along major bird migration routes. Given the presence of avian influenza viruses in the Region, their spread to other countries is likely.

Avian influenza outbreaks in the Russian Federation

Between mid-June and 1 October 2018, the Russian Federation reported 80 outbreaks of highly pathogenic avian influenza (HPAI) H5 virus and 1 outbreak of HPAI A(H5N2) virus among domestic poultry, to the World Organization for Animal Health (OIE). The Federal Service for Veterinary and Phytosanitary Surveillance of the Russian Federation has confirmed that the most recent outbreak was caused by a HPAI A(H5N8) virus. This virus is closely related to viruses that, in 2016–2017, caused the largest outbreak in poultry and wild birds ever recorded in the Region, resulting in millions of birds being culled and high economic losses. Migratory wild birds were identified as the likely vehicle bringing the virus to the Region. Therefore, vigilance of the public and close collaboration between the public health, veterinary and environmental authorities is important in the coming months to ensure rapid detection of avian influenza viruses in birds and to protect human health.

What should people do

A number of protective measures can be taken to prevent human infection with avian influenza viruses:

  • Stay informed about wild birds’ migration routes in your country, as communicated by relevant national authorities.
  • Avoid direct or close contact with any birds (poultry or wild birds) or contaminated environments and report sick or dead birds to responsible authorities.
  • Do not touch birds or carcasses with bare hands. If you must handle a carcass, wear gloves or use an inverted plastic bag to collect the bird. Make sure you wash your hands with soap and water or use a suitable disinfectant after handling.
  • Follow good food safety and food hygiene practices in line with WHO’s Five Keys to Safer Food Programme; for instance, cook poultry or wild birds thoroughly at sufficiently high temperatures. 
Avian influenza viruses and risk for human health

Human infection with avian influenza viruses is rare and is mostly linked to direct or close contact with live or dead infected birds or their environments. To date, no human infections with avian influenza A(H5N8) or A(H5N2) viruses have been reported. However, avian influenza viruses warrant close monitoring given their ability to change, potentially resulting in viruses that can pass from animals to humans. People in countries experiencing outbreaks are advised to adhere to the protective measures listed above.

For North Americans, our Arctic Refuge, where more than 200 bird species spend their summers, serves as a central hub, and funnels migratory birds south each fall via all four North American Flyways.

Credit U.S. Fish & Wildlife 

And as we discussed previously, these North American Flyways overlap with both Atlantic and Pacific flyways which could allow HPAI or LPAI carrying birds from Europe or Asia to reach our shores.

Some past blogs on that possibility include:

EID Journal: Introduction of Eurasian-Origin Influenza A(H8N4) Virus into North America by Migratory Birds

USGS: Alaska Still A Likely Portal For Introduction Of Avian Viruses 
EID Journal: Reassortment in Wild Birds in Alaska before H5 Clade Outbreaks

PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses

All of which makes enhanced biosecurity for poultry flocks the `new normal' for poultry flock owners around the globe. For more on biosecurity here in the United States, you may wish to visit the USDA's:

Biosecurity for Birds

Last Modified: May 14, 2018
Credit USDA

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