#18,851
Towards the end of the first world war French Prime Minister Clemenceau reportedly complained that `generals are always preparing to fight the last war', and much the same could be said about the way we are currently trying to combat HPAI H5N1.
The HPAI H5N1 clade 2.3.4.4b virus - which really only began its world tour a little over 3 years ago - has demonstrated several new traits that set it apart from earlier versions of the H5 virus, including infecting a broader range of avian species, the unexpected spilling over into cattle, and producing severe neurological manifestations across a wide range of mammals.
At the same time, we are seeing uncharacteristically mild illness in many (but not all) humans confirmed with the virus.
The virus is spreading via migratory birds at a furious rate, and infecting large numbers of poultry operations. Although most human infections have been linked to occupational exposure to poultry or cattle, the infectious source of a handful remain unknown.
And while currently the `official count' of cases in the United States is < 70 - given the limits of testing and surveillance - the real number is likely to be substantially higher (see Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers).
So far, we've attacked this current epizootic using pretty much the same tactics that have been used in the past, including during the (relatively brief) HPAI H5 epizootic of 2015.
But that first battle was won largely because the virus wasn't yet `fit' enough to maintain itself in wild birds (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl), not because of our stellar control efforts.
This time, we are dealing with a more persistent, more biologically `fit' virus; one that's become endemic in wild birds, and other hosts, in North America. And the longer it remains in the environment, the more opportunities it will have to evolve and adapt.
In this week's podcast, CIDRAP director Dr. Michael Osterholm discusses 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.
While this isn't a new idea (I'll have a review after the break), it has not exactly been universally embraced by the scientific community (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).
This hour-long podcast covers a lot of subjects, including controversial changes ordered during the first week of the Trump administration, but this topic begins about 25 minutes into the podcast.
A few excerpts from the transcript, but you'll want to listen to the full podcast.
And if you've ever seen large numbers of migratory birds on farm fields, you can understand how much bird feces are produced and what that means. Now, I was involved in 2015 with H5N2 work, in which we had to depopulate a number of poultry barns here in Minnesota. I also was involved with a company that is the largest egg laying company in North America. And that work convinced me that what was happening was many of these poultry production facilities, whether they be for egg laying or for actual production of chickens for slaughter, that in fact, these barns have only slats, curtains that shut, so that in fact, that is the protection against cold weather. They're not airtight at all. Many times. The slats are open in warmer days and keep the birds from contact with other wildlife or in fact, wild birds.
Today, I am certain that we are seeing clouds of dust with bird feces in that, and we are beginning to see what I would consider to be almost an environmental type disease, similar to the transmission that we see with Coccidioidomycosis, what we call Valley fever, where in fact that's a fungus that grows in the environment. And then on windy days it blows with the dust and you inhale it. I think we're going to see the same thing with H5N1. That's why so many of these barns are now positive.
(SNIP)
The second thing is H5N1 is not going away. This is a brand-new type of virus activity within wild birds spilling over into domestic production and as well as into humans. I know that my description today of a world with lots of migratory waterfowl poop blowing in the wind with virus attached to it may not seem appealing to many, but I think it's real.
I think it's exactly what's happening. And we're going to see more human cases related to that. The poultry industry is doomed to have challenge after challenge if they don't change the way they house these birds. They're going to have to find a way to have airtight buildings with only HEPA filter air coming in the intake and HEPA filter air being sent out the backside. If that doesn't happen, I convince eggs are going to be an expensive commodity for a long time to come.
A number of times over the past 15 years we've looked at the world of aerobiology; the study of how bacteria, fungal spores, pollen and even viruses can be passively transported in the air.
In 2010 (see Viruses Blowin’ In The Wind?) we saw a report in the journal Environmental Health Perspectives, that suggested that it was possible for H5N1 (or any Influenza A virus) to be transported across long (hundreds of kilometers) distances in the air.
Although researchers demonstrated influenza RNA could be detected in ambient air samplings, they didn’t establish that the virus remained viable over long distances.In December of 2012 (see Barnstorming Avian Flu Viruses?) we looked at a study in the Journal of Infectious Diseases 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 wind borne transmission could have accounted for up to 24% of the transmission over distances up to 25 km.
During the 2014-15 avian epizootic in the United States, airborne spread between farms miles apart was considered possible, although never conclusively proven see APHIS: Partial Epidemiology Report On HPAI H5 In The US) .
In Asia we've seen numerous instances where the `dust’ (desiccated chicken manure, feathers, etc.) from chicken farms has been strongly suspected as having spread bird flu – at least for a distance of several hundred yards. For some human bird flu cases in Indonesia and China, the only known exposure has been listed as living near, or simply walking past, a poultry farm or live market.
While still controversial, since 2015 the notion of long-distance spread of viable viruses has gained additional traction.
- 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.
- Also in 2022, in Zoonoses & Public Health: Aerosol Exposure of Live Bird Market Workers to Viable Influenza A/H5N1 and A/H9N2 Viruses, Cambodia, a study found that a `large percentage' of airborne viruses detected were viable.
Whether H5N1 has the ability to spark a pandemic remains unknown, but even if it can't, it can still do tremendous damage to agricultural interests and to the economy.
