Monday, September 04, 2023

Nature: North American Wintering Mallards infected with HPAI Show Few Signs of Altered Local or Migratory Movements


Credit U.S. Fish & Wildlife

#17,656

Up until fairly recently, the role of migratory birds in the spread of Highly Pathogenic Avian Influenza (HPAI) was heavily disputed, with many conservation agencies (see BNHS Claims Migratory Birds Not Responsible For Outbreak) adamant that `sick birds don't fly'. 

The first major diaspora of H5N1 occurred in 2004-2005 with the emergence of a new clade 2.2, which eventually moved into Europe, Africa and the Middle East. Suddenly H5N1 was no longer just a problem in Southeast Asia. 

While HPAI H5 first emerged in poultry, it seemed obvious to many that wild and migratory birds were instrumental in spreading the virus (see Bird Flu Spread: The Flyway Or The Highway?). Still, others clung to the belief that it was driven primarily by the poultry trade. 

In 2014 new HPAI H5N8 virus appeared in South Korea. After their MOA blamed its arrival on migratory birds from Mainland China, the UN's Scientific Task Force on Avian Influenza and Wild Birds quickly issued a statement saying:

"There is currently no evidence that wild birds are the source of this virus and they should be considered victims not vectors."

They would modify their stance slightly in 2015 - after the subsequent arrival of HPAI H5 to North America - stating the `. . . spread of HPAI virus is via contaminated poultry, poultry products and inanimate objects although wild birds may also play a role'.

The following year (2016), Europe also saw its first major avian epizootic, which was caused by a newly reassorted H5N8 virus which was first detected around the Ubsu-Nur Lake in Russia (see map below), and was later carried to Europe by migratory birds.  

 

Since then, it appears that that HPAI H5 has only gotten better at spreading via migratory birds. 

A few studies and blogs include:

Viruses: Recurring Trans-Atlantic Incursion of Clade 2.3.4.4b H5N1 Viruses by Long Distance Migratory Birds from Northern Europe to Canada in 2022/2023
While it is now generally accepted that migratory birds play a large role in the spread of avian flu, there is a lot we don't know about its carriage by avian hosts.  Some birds obviously fall ill (and may die) from the virus, while others appear to carry the virus asymptomatically.  

Avian species that were previously rarely affected by H5, have now become susceptible (see DEFRA: The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK).  And more changes in behavior are always possible.

Today we've an open access study that looks at the impact of HPAI H5 infection on North American Mallards, which finds they tolerate the virus quite well, and that infection has little or no impact on their local or migratory behavior. 

I've only reproduced the abstract below.  Follow the link to read it in its entirety.  I'll have a brief postscript when you return.

Article

Open Access
Published: 02 September 2023
North American wintering mallards infected with highly pathogenic avian influenza show few signs of altered local or migratory movements

Claire S. Teitelbaum, Nicholas M. Masto, Jeffery D. Sullivan, Allison C. Keever, Rebecca L. Poulson,
Deborah L. Carter, Abigail G. Blake-Bradshaw, Cory J. Highway, Jamie C. Feddersen, Heath M. Hagy,
Richard W. Gerhold, Bradley S. Cohen &Diann J. Prosser

Scientific Reports volume 13, Article number: 14473 (2023) Cite this article

Abstract

Avian influenza viruses pose a threat to wildlife and livestock health. The emergence of highly pathogenic avian influenza (HPAI) in wild birds and poultry in North America in late 2021 was the first such outbreak since 2015 and the largest outbreak in North America to date. Despite its prominence and economic impacts, we know relatively little about how HPAI spreads in wild bird populations.

In January 2022, we captured 43 mallards (Anas platyrhynchos) in Tennessee, USA, 11 of which were actively infected with HPAI. These were the first confirmed detections of HPAI H5N1 clade 2.3.4.4b in the Mississippi Flyway. 

We compared movement patterns of infected and uninfected birds and found no clear differences; infected birds moved just as much during winter, migrated slightly earlier, and migrated similar distances as uninfected birds. Infected mallards also contacted and shared space with uninfected birds while on their wintering grounds, suggesting ongoing transmission of the virus. 

We found no differences in body condition or survival rates between infected and uninfected birds.

Together, these results show that HPAI H5N1 clade 2.3.4.4b infection was unrelated to body condition or movement behavior in mallards infected at this location during winter; if these results are confirmed in other seasons and as HPAI H5N1 continues to evolve, they suggest that these birds could contribute to the maintenance and dispersal of HPAI in North America.

Further research on more species across larger geographic areas and multiple seasons would help clarify potential impacts of HPAI on waterfowl and how this emerging disease spreads at continental scales, across species, and potentially between wildlife and domestic animals.

          (Continue . . . )

It is now September, and tens of millions of migratory birds that have spent their summer at their high latitude breeding spots - likely spreading and sharing a mixture of avian viruses  - will soon begin their annual southbound migration. 

Between antigenic drift and antigenic shift (reassortment), the virus that returns this fall could easily be more - or less - virulent, or biologically `fit', than what we saw in the spring.

Evolution is a double-edged sword, and what it adds it can also strip away. But there is one thing we do know; evolution never stops.  

Which is why we should be prepared for surprises.

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