#17,402
Over the past two decades we've seen ample evidence that - under the right environmental conditions - HPAI H5 viruses can remain viable for quite some time. A few examples include:
- In the August 2010 issue of Applied and Environmental Microbiology, researchers determined that the H5N1 virus may persist on the dropped feathers from infected ducks and may therefore spread to the environment (see Persistence of Avian Influenza Virus (H5N1) in Feathers Detached from Bodies of Infected Domestic Ducks).
- At 4°C (39F) the virus was detectable for 160 days, while at the higher temperature 20°C (68F), the virus was detected for 15 days.
- 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).
- 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).
- And in 2020 we looked at a study from researchers at the USGS (see Proc. Royal Society B: Influenza A Viruses Remain Viable For Months In Northern Wetlands - USGS), which found long-term survival of influenza A viruses in wetlands in both Alaska and Minnesota.
With tens of millions of infected poultry that must be safely disposed of, and millions more animal carcasses (both birds and mammals) decomposing in the wild, the ability of these viruses to be picked up and spread by scavengers is a genuine concern (see HPAI Confirmed As Cause Of Death For 3 California Condors).
All of which brings us to a study, published today in the journal Pathogens, which found a surprising lack of persistence (after 4 months) of detectable H5N1 RNA on an island seabird colony in the Shetland archipelago of Scotland, which had been the site of a mass mortality event during the summer of 2022 from avian flu.
The authors speculate that heavy rainfall in the region over those 4 months may have washed away the virus, although it isn't known how rapidly that occurred. I've posted the link, and some excerpts, but you'll probably want to read the report in its entirety.
Environmental Samples Test Negative for Avian Influenza Virus H5N1 Four Months after Mass Mortality at A Seabird Colony
Robert W. Furness , Sheila C. Gear ,Kees C. J. Camphuysen , Glen Tyler , Dilhani de Silva ,
Caroline J. Warren , Joe James , Scott M. Reid and Ashley C. BanyardPathogens 2023, 12(4), 584; https://doi.org/10.3390/pathogens12040584 (registering DOI)Received: 16 March 2023 / Revised: 6 April 2023 / Accepted: 11 April 2023 / Published: 12 April 2023
Abstract
High pathogenicity avian influenza (HPAI) profoundly impacted several seabird populations during the summers of 2021 and 2022. Infection spread rapidly across colonies, causing unprecedented mortality. At Foula, Shetland, 1500 breeding adult great skuas Stercorarius skua, totalling about two tonnes of decomposing virus-laden material, died at the colony in May−July 2022.
Carcasses were left where they died as Government policy was not to remove dead birds. The factors influencing risk of further spread of infection are uncertain, but evidence suggests that HPAI can persist in water for many months in cool conditions and may be a major transmission factor for birds living in wetlands.
We investigated risk of further spread of infection from water samples collected from under 45 decomposing carcasses and in three freshwater lochs/streams by sampling water in October 2022, by which time the great skua carcasses had rotted to bones, skin, and feathers.
No viral genetic material was detected four months after the mortality, suggesting a low risk of seabird infection from the local environment when the seabirds would return the next breeding season. These findings, although based on a relatively small number of water samples, suggest that the high rainfall typical at Shetland probably washed away the virus from the decomposing carcasses.
However, limitations to our study need to be taken on board in the design of environmental monitoring at seabird colonies during and immediately after future outbreaks of HPAI.
(SNIP)
This small study suggests that removing rotting carcasses during the nonbreeding season would be unlikely to reduce the risks of avian influenza reappearing. The unexpected contrast between these results and the in situ study in Alaska [4] could be a result of the high rainfall at Shetland resulting in the virus being washed away. Rainfall in Shetland was >100 mm in August and in September 2022 [18]. Nevertheless, experimental evidence has shown that water represents a good matrix for virus survival and the infection of Galliformes, although such outcomes are likely to depend on the virus isolate used and dose administered (APHA, unpublished data).
This leaves open the question of whether carcass removal early in an outbreak at a colony would reduce further transmission. It seems likely that removal of infected carcasses immediately after the death of the birds may reduce risk of spread of the infection. A more extensive assessment of water samples might be more informative, especially if sampling were able to occur during the outbreak event itself and at timepoints shortly after the apparent infection burnout.
In the absence of further data, we can only speculate as to which modes of transmission are most impactful on the maintenance of infection across different bird species in remote environments. However, it is possible to make some testable predictions based on knowledge of the ecology of this species. We know that diets of great skuas vary with the size of the colony, with more predation on other seabirds and scavenging around small colonies and more foraging on fish around larger colonies [19]. If scavenging on infected birds was the main route of infection for great skuas, then infections would be more likely to occur in smaller colonies.
In contrast, if a migrant carries the infection from the wintering area and infects neighbours at the colony, then the largest colonies would be at greatest risk because more birds would mean more possibility of an infected individual returning to the colony and starting a new outbreak. An analysis of the infections that occur in future at different sizes of the colony, and possibly the creation of phylogenies based on virus sequencing to identify likely transmission events between colonies and between nonbreeding areas and breeding areas may help to identify the key routes involved. This would help to identify likely mitigation measures to reduce the impact on seabirds of high conservation concern. As the HPAI outbreak among great skuas in 2021 and 2022 may have killed about half of the entire adult population of this globally scarce species [3,7], there is a pressing need for further work on these issues.
In hindsight, our water sampling in October was too late after the peak of infection in June−July to monitor decline in virus levels. We should have started water sampling at the peak of the infection, but that was not achieved because the outbreak of HPAI in seabirds was an unexpected and novel event, arranging logistics took time, and evidence suggested that the virus would survive in the water for some months. There is an urgent need to plan for more detailed environmental sampling at seabird colonies during and immediately after future outbreaks, as these seem likely to occur in 2023 and beyond. Future planning can learn lessons from our experience reported here.
The lack of viable H5 virus detection after 4 months on Foula is obviously good news for returning birds, but it doesn't negate the very real problem that H5N1 can remain infectious for days, week, or sometimes months in the environment.
