Proc. Royal Society B: Influenza A Viruses Remain Viable For Months In Northern Wetlands - USGS

#15,447

Not so very long ago (see 2014's  Bird Flu Spread: The Flyway Or The Highway?), there was still heated debate over whether migratory birds can carry and deliver HPAI (highly pathogenic avian influenza) viruses over long distances.

HPAI was commonly associated with poultry, which presumably evolved from low path (LPAI) viruses carried asymptomatically by wild birds.  

The `sick birds don't fly' argument finally bit the dust following the 2016 H5N8 epizootic in Europe, followed closely by the arrival of HPAI H5N8 in the Middle East and Africa (see 2016's Migratory Birds & The Spread Of Highly Pathogenic Avian Flu).  While some wild birds do die from HPAI, many others appear to carry these viruses with little apparent effect. 

While this helps to explain the intercontinental spread of HPAI viruses, we've also seen studies suggesting that many wild birds clear HPAI infections relatively quickly (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl), making them only short-term carriers of these viruses. 

Another study, published in 2016 (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1), posited that waterfowl can pick up new HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way to their summer (high latitude) breeding spots - where they spread, amplify, and potentially evolve - only to redistribute them on their southbound journey the following fall.

While this `chain of custody' of HPAI viruses in migratory birds might fully explain the spread of HPAI globally, for years researchers have also been looking at the environmental persistence of influenza A viruses in the wild - and how that might affect both the ecology and evolution of LPAI and HPAI viruses. 

Normally influenza viruses are expected to remain viable - under optimal conditions -  for only a matter of hours (or sometimes days) outside of a living host (see Influenza Virus Survival At Opposite Ends Of The Humidity Spectrum). 

But we've also seen reports of much longer persistence in the wild, particularly of HPAI H5N1.

As H5N1 is primarily a gastrointestinal malady in birds it is believed that the virus is commonly spread in the wild via shared feces-contaminated pond and lake waters (see Bogor: H5N1 Detected In Retention Pond). 

A 2010 study conducted by researchers at the National Institute of Animal Health, Tsukuba, Ibaraki, Japan determined that the H5N1 virus may also persist on the dropped feathers from infected ducks and may therefore spread to the environment.

Applied and Environmental Microbiology, August 2010, p. 5496-5499, Vol. 76, No. 16
0099-2240/10/$12.00+0 doi:10.1128/AEM.00563-10

Persistence of Avian Influenza Virus (H5N1) in Feathers Detached from Bodies of Infected Domestic Ducks

Yu Yamamoto, Kikuyasu Nakamura, Manabu Yamada, and Masaji Mase

At 4°C (39F) the the H5N1 virus was detectable in feathers for 160 days, while at the higher temperature 20°C (68F), the virus was detected for 15 days.

Detectable doesn't necessarily mean viable, however.  RT-PCR tests can often pick up remnants of inactivated viruses. 

In 2012's EID Journal: Persistence Of H5N1 In Soil, we looked at several studies that found H5N1 could remain viable on various surfaces, and in different types of soil, for up to 13 days (depending upon temperature, relative humidity, and UV exposure).

And in 2017, researchers showed that - when refrigerated - H5N1 infected poultry could remain infectious for months (see Appl Environ Microbiol: Survival of HPAI H5N1 In Infected Poultry Tissues).

Today we've a new study, from researchers at the USGS, which finds long-term survival of influenza A viruses in wetlands in both Alaska and Minnesota, suggesting theses waters could potentially serve as an over-wintering environment for for AI viruses. 

This is particularly important, as Alaska is considered the likely entry point of Asian avian flu strains to North America (see USGS: Alaska - A Hotspot For Eurasian Avian Flu Introductions).

While the full study is behind a paywall (follow the link), we have the following abstract that provides the gist. I'll return with a brief postscript.

Influenza A viruses remain infectious for more than seven months in northern wetlands of North America

Andrew M. Ramey, Andrew B. Reeves, Judith Z. Drexler, Joshua T. Ackerman, Susan De La Cruz, … See all authors 

Published:09 September 2020https://doi.org/10.1098/rspb.2020.1680

Abstract

In this investigation, we used a combination of field- and laboratory-based approaches to assess if influenza A viruses (IAVs) shed by ducks could remain viable for extended periods in surface water within three wetland complexes of North America. In a field experiment, replicate filtered surface water samples inoculated with duck swabs were tested for IAVs upon collection and again after an overwintering period of approximately 6–7 months. 

Numerous IAVs were molecularly detected and isolated from these samples, including replicates maintained at wetland field sites in Alaska and Minnesota for 181–229 days. In a parallel laboratory experiment, we attempted to culture IAVs from filtered surface water samples inoculated with duck swabs from Minnesota each month during September 2018–April 2019 and found monthly declines in viral viability.

In an experimental challenge study, we found that IAVs maintained in filtered surface water within wetlands of Alaska and Minnesota for 214 and 226 days, respectively, were infectious in a mallard model. Collectively, our results support surface waters of northern wetlands as a biologically important medium in which IAVs may be both transmitted and maintained, potentially serving as an environmental reservoir for infectious IAVs during the overwintering period of migratory birds.

Footnotes

Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.5097100. 

Although the transfer of avian influenza viruses from these contaminated waters to other migratory birds passing through is the primary concern, birds aren't the only potential recipients. 

Just over a year ago, in Nature: Semiaquatic Mammals As Intermediate Hosts For Avian Influenza, we looked at a study that warned that mink - and possibly other semiaquatic mammals (like raccoons, otters, etc.) - could be at risk of infection as well. 

In 2017, in H2N2: Everything Old Is Flu Again, we saw a study published in The Journal Of Veterinary Medical Science, which detailed the finding of H2N2 in Siberian Muskrats in 2014. (see Genetic characterization of an H2N2 influenza virus isolated from a muskrat in Western Siberia).

The authors wrote:

Results suggest that interspecies transmission of LPAIVs from wild water birds to semiaquatic mammals occurs, facilitating the spread and evolution of LPAIVs in wetland areas of Western Siberia.

H2N2 is of particular concern because it sparked the Asian Flu pandemic of 1957, and reigned as the sole circulating human influenza A virus until 1968, when it was supplanted by H3N2.  While absent in humans for over 50 years, it remains high on our watch list (see H2N2: What Went Around, Could Come Around Again).

Taken together, these studies indicate the ecology and evolution of avian influenza viruses in the wild are almost certainly far more complex, and interconnected, than we currently know.