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Typically, influenza viruses are expected to remain viable - even under optimal conditions - for only a few hours outside of a living host (see Influenza Virus Survival At Opposite Ends Of The Humidity Spectrum).
But we've seen reports of much longer persistence in the environment, particularly of HPAI H5N1.
In the spring of 2006 we saw reporting on the H5N1-related deaths of 5 young people in Azerbaijan who reportedly were engaged in collecting swan feathers from dead birds. This except from a UN News report:
Over the weekend, a field investigation conducted jointly by WHO and the Azeri Ministry of Health found evidence that carcasses of numerous swans, dead for some weeks but not buried, may have been collected by residents as a source of feathers.
De-feathering of birds is a task usually undertaken by adolescent girls and young women. The WHO team is today investigating whether this practice may have been the source of infection in a village where the majority of cases have occurred in females between the ages of 15 and 20.
While infected birds normally shed H5N1 (depending upon species) for anywhere between 2 and 14 days, the ability of the virus to survive for weeks or even months in the environment provides additional opportunities for propagation.
A 2010 study conducted by researchers at the National Institute of Animal Health, Tsukuba, Ibaraki, Japan determined that the H5N1 virus may survive on the dropped feathers from infected ducks and may then spread to the environment.
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 (note: PCR detectable doesn't necessarily mean viable or infectious).
Another study from 2010 published PLoS One (Can Preening Contribute to Influenza A Virus Infection in Wild Waterbirds?) found that preen oil glands secretions, which waterproof the feather of aquatic birds, can allow avian flu and other pathogens to cling to the bodies of birds.
In addition to feathers:
- 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, in Proc. Royal Society B: Influenza A Viruses Remain Viable For Months In Northern Wetlands - USGS, researchers found 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.
Article: 2272644 | Accepted author version posted online: 17 Oct 2023
Immature feathers are known replication sites for high pathogenicity avian influenza viruses (HPAIVs) in poultry. However, it is unclear whether feathers play an active role in viral transmission. This study aims to investigate the contribution of the feather epithelium to the dissemination of clade 2.3.4.4b goose/Guangdong/1996 lineage H5 HPAIVs in the environment, based on natural and experimental infections of domestic mule and Muscovy ducks.During the 2016-22 outbreaks, H5 HPAIVs exhibited persistent and marked feather epitheliotropism in naturally infected commercial ducks. Infection of the feather epithelium resulted in epithelial necrosis and disruption, as well as the production and environmental shedding of infectious virions. Viral and feather antigens colocalized in dust samples obtained from poultry barns housing naturally infected birds.In summary, the feather epithelium contributes to viral replication, and it is a likely source of environmental infectious material. This underestimated excretion route could greatly impact the ecology of HPAIVs, facilitating airborne and preening-related infections within a flock, and promoting prolonged viral infectivity and long-distance viral transmission between poultry farms.
(SNIP)
By identifying another route of viral shedding for ducks, these results open the way to a paradigm shift in the epidemiology of avian influenza. Transmissibility is influenced by viral shedding and environmental stability [6]. Infectious virions shed by the feather epithelium may be protected from physical factors or even disinfectants, resulting in an unexpected persistence of infectivity in the environment. However, whether any particular resistance properties are associated with this route of excretion, thanks to the protection provided by cornified cells, endogenous or uropygial lipids, still needs to be clarified [16,47,48].
Combining natural and experimental infections, our findings support the environmental shedding and dissemination of H5 HPAIVs through the infected plumage of domestic ducks, which may constitute an underestimated route of transmission. Further investigations are needed to establish the importance of this alternative route compared to the fecal-oral and the respiratory-aerosol routes, and to define its impact in the implementation of biosecurity measures.
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Although the long-distance spread of avian influenza viruses via `poultry dust' remains controversial, we've seen numerous studies suggesting it may be possible. The science of all of this has a name; aerobiology – the study of how bacteria, fungal spores, pollen and even viruses can be passively transported in the air.
Over the past dozen years we've looking at a number of studies investigating long-distance airborne spread of avian flu, including:
- In the spring of 2015 during the North American H5Nx epizootic, the idea of farm-to-farm spread via infected dust was openly discussed by the USDA (see Bird Flu’s Airborne `Division’).
- In 2018, in Frontiers: Two Studies On The Epidemiology of Avian Influenza Viruses, we looked at a study that detected airborne HPAI viruses during the 2016-17 H5N8 epizootic in France, which saw more than 400 farms affected.
- And in 2019, in Nature: Airborne Transmission May Have Played A Role In Spread Of U.S. 2015 HPAI Epizootic, we saw a study that looked at air movement trajectories and viral concentrations during the epizootic and the probability of airborne transmission for the 77 HPAI cases in Iowa. While not definitive, long-range airborne spread was considered plausible.
- And in 2022, in HPAI (H5N8) Clade 2.3.4.4b Virus in Dust Samples from Poultry Farms, France, 2021 - published in the CDC's EID Journal - we saw evidence of virus-contaminated dust on and around poultry farms, and suggests sampling the dust - instead of swabbing birds - may be a more effective way to detect avian influenza outbreaks.
It isn't just avian flu. in 2020's study Nature Comms: Influenza A Transmission Via `Aerosolized Fomites', we looked at laboratory evidence that influenza A viruses (and probably others) can be transmitted via airborne or `aerosolized fomites'.
We have a long history of underestimating viruses, but they have evolved over ten of millions of years with only one purpose; to survive. And they've gotten exceedingly good at that.
Studies like today's remind us just how well adapted, and formidable, H5N1 has become. And it is only through a better understanding of how it functions that we can hope to contain it.
