Separation of Farms In Study
#18,616
While admittedly controversial, over the past 15+ years we've looked at a number of studies which strongly suggest that infectious avian influenza viruses may be carried - likely on `dust particles' - for extended distances by the wind.
How long these viruses may remain viable, and how far they might travel, is a matter of considerable debate. Viruses are subject to desiccation, and are easily killed by UV light, which makes them fragile outside of a living host.
A recent study (see 2023's The Role of Airborne Particles in the Epidemiology of Clade 2.3.4.4b H5N1 High Pathogenicity Avian Influenza Virus in Commercial Poultry Production Units) cast considerable shade on the notion, suggesting the the effective range of such transmission was likely 10 meters or less.
But we've seen other studies that suggest infectious influenza virus particles might successfully travel several kilometers.
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. And while some might consider it `fringe' science, we've seen a number of serious studies over they years.
- In December of 2012 (see Barnstorming Avian Flu Viruses?) we looked at a study called Genetic data provide evidence for wind-mediated transmission of highly pathogenic avian influenza that found patterns that suggested farm-to-farm spread of the 2003 H7N7 in the Netherlands due to the prevailing wind.
- Another study of the same outbreak, Modelling the Wind-Borne Spread of Highly Pathogenic Avian Influenza Virus between Farms (PloS One 2012), found that windborne transmission could have accounted for up to 24% of the transmission over distances up to 25 km.
- 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.
In 2022's Zoonoses & Public Health: Aerosol Exposure of Live Bird Market Workers to Viable Influenza A/H5N1 and A/H9N2 Viruses, Cambodia, researchers were able to extract viable avian flu viruses from the air in and around live bird markets in Cambodia.
We revisited this idea only a few weeks ago, in Osterholm Podcast: The Potential Environmental (Airborne) Spread of H5N1, where Dr. Mike Osterholm discussed the very real possibility that the H5N1 virus may be carried by contaminated `dust' from poultry farms, infecting other nearby farms, animals, and potentially even humans.
Today we've a preprint that provides data that strongly supports the idea that windborne spread of HPAI H5 virus particles may have spread the pathogen as far as 8 km between farms in the Czech Republic.
Furthermore, the authors believe this transmission occurred prior to the depopulation work at the index farm.
I've only posted the abstract, so follow the link to read it in its entirety. I'll have a bit more after the break.
Genetic data and meteorological conditions: unravelling the windborne transmission of H5N1 high-pathogenicity avian influenza between commercial poultry outbreaks
View ORCID ProfileAlexander Nagy, Lenka Černíková, Kamil Sedlák
doi: https://doi.org/10.1101/2025.02.12.637829
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Abstract
Understanding the transmission routes of high-pathogenicity avian influenza (HPAI) is crucial for developing effective control measures to prevent its spread. In this context, windborne transmission, the idea that the virus can travel through the air over considerable distances, is a contentious concept and, documented cases are rare.
Here, though, we provide genetic evidence supporting the feasibility of windborne transmission. During the 2023-24 HPAI season, molecular surveillance identified identical H5N1 strains among a cluster of unrelated commercial farms about 8 km apart in the Czech Republic.
The episode started with the abrupt mortality of fattening ducks on one farm and was followed by disease outbreaks at two nearby high-biosecurity chicken farms. Using genetic, epizootiological, meteorological and geographical data, we reconstructed a mosaic of events strongly suggesting wind was the mechanism of infection transmission between poultry in at least two independent cases.
By aligning the genetic and meteorological data with critical outbreak events, we determined the most likely time window during which the transmission occurred and inferred the sequence of infected houses at the recipient sites. Our results suggest that the contaminated plume emitted from the infected fattening duck farm was the critical medium of HPAI transmission, rather than the dust generated during depopulation.
Furthermore, they also strongly implicate the role of confined mechanically-ventilated buildings with high population densities in facilitating windborne transmission and propagating virus concentrations below the minimum infectious dose at the recipient sites. These findings underscore the importance of considering windborne spread in future outbreak mitigation strategies.
While some may still dismiss this idea, there are precedents with other agricultural diseases.
In 2014's BMC Veterinary Research article Evidence of infectivity of airborne porcine epidemic diarrhea virus and detection of airborne viral RNA at long distances from infected herds authors Carmen Alonso, Dane P Goede, Robert B Morrison, Peter R Davies, Albert Rovira, Douglas G Marthaler and Montserrat Torremorell wrote:Results indicated presence of infectious PEDV in the air from experimentally infected pigs and genetic material of PEDV was detected up to 10 miles downwind from naturally infected farms. Airborne transmission should be considered as a potential route for PEDV dissemination.Similarly, FMD (Foot & Mouth Disease) has been shown to spread from farm-to-farm over long distances, sometimes exceeding 60 km (see 2022's Airborne Transmission of Foot-and-Mouth Disease Virus: A Review of Past and Present Perspectives).
