Psst- H5N1 DOES Travel in the Air Between Large Livestock Facilities...

Regulatory animal health officials have minimized risks for aerosol spread of influenza- it's time for complete candor and acknowledgement of the implications

Those who have read this column for a while know that I have fairly strong “confirmation bias” towards aerosol transmission of highly infectious viral infections in multiple species in large confined animal operations (see 7/20/24- H5N1 Aerosol Spread with Respiratory Infection Continues to be Underrated). Both the swine and poultry industries have dealt routinely with highly infectious viruses and high concentrations of animal production units in smaller geographical areas, forcing them to confront issues of “unexplained” area infectious disease spread. Whole genome sequencing combined with producers’ willingness to selectively share location, temporal, and sequence data for outbreak analysis have greatly aided in disease spread analyses.

This week I want to concentrate on a very well documented study based on an H5N1 outbreak in poultry in the Czech Republic in early 2024: Genetic data and meteorological conditions: unravelling the windborne transmission of H5N1 high-pathogenicity avian influenza between commercial poultry outbreaks

This is a rare paper that combines full geographical, temporal, meteorological, sequence, and epidemiological outbreak data on a small set of farms in a discrete area. This data together makes a compelling argument for aerosol spread of H5N1 2.3.4.4b genotype D1 virus within this cluster of largely mechanically ventilated farms. Please read the paper carefully before returning to my discussion section.

Locations of referenced farms

Aerial views of referenced farms with ventilation flows illustrated

Discussion of Findings

I found this section of the discussion section to be highly insightful:

The exposure of a dense population of chickens to such high air volumes might well lead to minute virus amounts being captured and subsequently enriched to levels sufficient to trigger illness. This is consistent with the observed slow disease progression. Thus, it is likely that the specific settings of the poultry houses at recipient site C facilitated the wind-mediated spread of HPAI. Conversely, this also explains why other backyard poultry in villages located between the donor and recipient farms, as well as the poultry in C2A, were unaffected; they lacked sufficient population density and/or the booster effect of tunnel ventilation.

We have seen other examples in the U.S. (Iowa in 2015, for example) where backyard flocks were relatively unaffected by HPAI, while mechanically ventilated layer houses were infected, anecdotally often initially under the air inlets. It may be that “minimal infectious doses” in air vary by how that air is delivered to the recipient animals. The authors speculate that we may lack sensitivity in current methodology to detect viral RNA at infectious levels under certain conditions in mechanically ventilated barns.

Another section of the discussion raised a point that may be of practical importance in timing depopulation and maximum biosecurity strategies to when an infected farm is at most risk for infecting other farms:

Overall, it seems that the recipient farms were infected relatively very early after the outbreak on the donor farm and before it was depopulated. These findings are in stark contrast to the conventional theory that dust generated during depopulation is the major risk factor for the secondary wind spread of HPAI. It appears that the smoother aerosols produced by an infected flock (live) are much more likely carriers than the far heavier dust particles that settle quickly within short distances of an outbreak farm (after depopulation).

This finding lends credence to the current industry urgency in the United States to expedite the depopulation process as quickly as possible to minimize risk of additional on-farm bird illness and mortalities and further spread to adjacent farms. It also places a large premium on early diagnosis. How much of our farm-to-farm spread of avian influenza in poultry and dairy herds (as well as in endemic swine) is occurring prior to diagnosis via clinical signs in the source herd? All too often we are sampling donor animals and herds much too late in the shedding process to get an accurate estimate for their aerosol contribution to lateral spread of infection.

Additionally, we are likely masking our personnel much too late in attempting to prevent zoonotic transmissions of influenza from incubating poultry, swine, or dairy cattle to caretakers. Conversely, are we over-protecting against non-viable virus on dust, in dead birds, or low-risk fomites? These are separate research questions; however, as resources tighten, we need to concentrate our mitigation efforts towards the highest risks for onward spread.

Finally, this paper begins to address possible mitigations for addressing viral intake into mechanically ventilated facilities:

It is therefore worth considering the integration of airborne control technologies with existing on-farm biosecurity protocols to effectively limit the introduction and spread of pathogens via the windborne route. Continued research and improved surveillance are essential to fully understand the risks associated with such transmission. The knowledge gained could then be used to develop more effective preparedness strategies and control measures that would better mitigate the effects of future outbreaks.

We have all seen offers to address this issue with UV-C light or other disinfecting technologies proposed at or near inlets. The swine industry has employed HEPA filtration in breeding-gestation-farrowing units where animal density and the consequences of PRRSv outbreaks combine to make the increased capital and operating ventilation costs feasible.

Alternative efficacious technologies may be waiting in the wings; however, there is one caution. Birds (or pigs) must be ventilated adequately. This paper describes air flowing through inlets in these buildings at up to 250,000 cubic meters per hour! Any technology must provide sufficient viral neutralization capacity at each inlet at the required volume of air flow during the periods of highest risk for viral transmission. These limitations are researchable; however, we can’t just assume that an intervention at the inlets will be efficacious in all applications with required large volumes of air flow.

Aerosol Spread Versus Animal Movement/Contact Transmission Spread - the Nevada H5N1 2.3.4.4b D1.1 Paradigm Breaker

The recent outbreak of H5N1 2.3.4.4b D1.1 in 6 cattle herds in northern Nevada illustrates the complexities in sorting out routes of transmission in muti-case outbreaks. Multiple risks for viral spread must be considered; investigators cannot credibly ignore any potential routes for initial infection and onward within and between herd transmission.

The biggest take-home from Nevada of course, is that genotype B3.13 was not a unique crossover event of H5N1 2.3.4.4b into lactating dairy cattle. Rather, all cattle are likely susceptible to mammalian spillover events from multiple H5N1 2.3.4.4b genotypes with a similar respiratory introduction and pathogenesis as shown in other mammals.

This Nevada infection was found through bulk tank sampling fairly rapidly in 6 herds in a single valley. Epidemiological questions are immediately raised regarding how this virus was spread between herds - independent introductions from wild birds, herd-to-herd through lax biosecurity, aerosol transmission between herds, or some combination of these routes?

USDA has repeatedly reassured the public that B3.13 spread can be traced to improper movements or biosecurity breakdowns from infected herds leading to new herd infections, despite repeated explosive epidemics of B3.13 in MI, CO, ID and CA. Overwhelming evidence of rapid uncontrolled area spread has erased trust in federal or state summary descriptions of “ongoing biosecurity breakdowns” that lack any robust independent assessments of epidemiological and phylogenetic evidence, similar to what the Czech researchers demonstrated in the paper above.

This lack of confidence has been amplified by past USDA refusal to openly consider that cattle viral spread within and between farms was possibly via the oronasal route, which requires a much broader epidemiological assessments of concentrated livestock areas plus lactating and nonlactating cattle on dairy farms. Political and proprietary data collection and analysis constraints have prevented a complete review by independent teams of qualified specialists.

Now USDA-APHIS has acknowledged that the Nevada cattle outbreak was initiated by a wildlife contact and affected animals showed signs of pneumonia along with positive bulk tank PCR results. Additionally, Arizona has now reported bulk tank positive milk sequenced as D1.1; more cases will surely follow in other states, given the high prevalence of this virus across the U.S. Hopefully the National Milk Testing Strategy implementation will continue to effectively find new infected herds. USDA-APHIS messaging may evolve under the guidance of new political leadership as cases continue to unfold.

Back to H5N1 Zoonotic Transmissions

Ohio Producer Released from Hospital

U.S. bird flu hospitalizations rise to 4 after Ohio discloses case - CBS News

Ohio's health department confirmed Saturday that a farmer in the state was discharged from the hospital after being sickened by bird flu, marking the fourth American to have been hospitalized with the H5N1 virus.

"The individual had respiratory symptoms. He was previously hospitalized and has since been released," a spokesperson for Ohio's health department told CBS News in an email Saturday.

Authorities in Ohio had previously refused to disclose the status of their bird flu case, which was first announced earlier this week in a man who had contact with sick poultry.

While the genotype of this human infection has not yet been disclosed, the widespread poultry outbreak in Ohio has been attributed to D1.1, making the human infection likely of this genotype. Hopefully, CDC will soon release complete sequence information on this isolate to the public and GISAID, similar to what has recently been done with the Nevada D1.1 human isolate (GISAID - Highly Pathogenic Avian Influenza Outbreak in the United States).

Wyoming Backyard Flock Owner Hospitalized in Colorado

Wyoming Public Health announced an out-of-state human hospitalization for zoonotic H5N1 influenza (Wyoming’s First Human Bird Flu Case Confirmed - Wyoming Department of Health). The Platte County resident, hospitalized in Colorado according to other sources, was exposed to a later diagnosed H5N1-infected flock 2 days prior to onset of influenza like illness. Her viral genotype and current condition have not been disclosed by Wyoming, Colorado, nor CDC officials at this point. According to notes provided by Alexander Tin, CBS News Correspondent, a spokesman for the Colorado Public Health Department stated on February 15th that the patient was hospitalized within the last two weeks, and exposure to sick poultry preceded her hospitalization by just a couple of days.

That would place the onset of poultry illness around February 1st or shortly thereafter. Neither Wyoming nor Colorado Public Health has stated when a presumptive positive human H5N1 diagnosis was made and whether in Wyoming or after transfer to the Colorado Hospital. On Saturday Wyoming Public Health announced that the CDC had confirmed the positive diagnosis. CDC may have a public announcement when re-opening on Tuesday after the holiday weekend.

Separately, the Wyoming Livestock Board on February 14th announced the NVSL-confirmed diagnoses of H5N1 2.3.4.4b infections in 3 separate backyard poultry flocks in three different counties-Platte, Sheridan, and Washakie (Wyoming H5N1 backyard flocks). In a separate e-mail exchange with CBS news reporter Alexander Tin, State Veterinarian Dr. Hallie Hasel confirmed that these backyard poultry flock infections were caused by strain (genotype) B3.13. EDIT AT 1:43 PM - COMMUNICATION WITH DR. HASEL STATES THAT B3.13 NOT CONFIRMED - 1 OF 3 FLOCKS CONFIRMED AS D1.1 - MORE TO COME

Detection of B3.13 (“dairy strain”) in these three geographically separated backyard flocks is WOULD BE an epidemiological mystery, since wild birds are not known to carry this genotype from cattle herds, and Wyoming has not reported H5N1 in dairy cattle since last July. The state is listed as conducting “State-Specific” herd surveillance in the USDA National Milk Testing Strategy Program, with a status of “Provisionally Unaffected”. (National Milk Testing Strategy | Animal and Plant Health Inspection Service)

There is likely more to come on this case, depending on the status of the hospitalized patient, the sequence of the virus isolated at CDC as compared to NVSL poultry isolate, and further bird and cattle epidemiological work in Wyoming to flesh out possible sources of virus for these infected flocks.

Zoonotic H5N1, Aerosol Transmission and Regulatory Credibility

USDA, our State Animal Health Officials, and our livestock industries have noble intentions to demonstrate effective control over domestic disease risks to our trading partners and the public while allowing business continuity in today’s animal protein industries with relatively unrestricted animal movements and concentrated, intermingled production infrastructure. This ever more complex and mobile infrastructure has relied upon an antiquated fig leaf of “regulatory control” of disease spread between farms. Traditionally, visual accredited veterinarian movement inspection and limited testing processes worked well enough to serve as a regulatory oversight framework for traditional diseases in an older, less concentrated infrastructure.

Narrowing this discussion to the example of H5N1 2.3.4.4b influenza, we now have wildlife-carried and wide-area aerosol spread of a:

1. cross-species

2. highly infectious

3. potentially zoonotic and

4. often asymptomatic disease agent.

Our regulatory agencies and production industries are paddling like hell to maintain the old regulatory paradigm by denying or minimizing new realities for risk and spread of this threat in highly concentrated animal production populations.

Frankly, informed participants, observers and trading partners now see the situation for what it is:

1. H5N1 2.3.3.4b is now endemic in U.S. wildlife and is an ongoing spillover threat to major domestic livestock species, requiring ongoing targeted surveillance to protect animal and human health where H5N1 viral pressure is significant.

2. Aerosol spread of H5N1 2.3.4.4b is a potential area spread risk, especially in larger production units in multiple livestock species, requiring area monitoring when H5N1 outbreaks are diagnosed in local poultry or dairy populations by HPAI poultry surveillance or bulk tank milk testing. Dairy and poultry-specific surveillance serve as sentinels for wider surveillance in additional susceptible species in affected areas.

3. People working with all of our livestock species are at risk for zoonotic transmission of H5N1 2.3.4.4b (or a variant) to or from them and onward into the community. Risks of such an event are uncertain and dynamic based on ongoing mutations and reassortments, but the consequences are potentially catastrophic for all of agriculture and the public.

As long as USDA, the SAHO’s, and the commodity industry groups choose to ignore or minimize these realities, their credibility will be severely compromised, with ongoing “happy talk” useful for their own stakeholders’ consumption only. “Fool me once” public relations messaging is now discredited by the educated public.

We will collectively engage in dialogue regarding a range of initiatives the new administration should advance in dealing with H5N1 in poultry and livestock, but the above 3 points describe where we start when considering livestock surveillance and vaccine alternatives for H5N1 2.3.4.4b. This virus family has firmly charted its unpredictable place in our current livestock production ecosystem. Posturing or politics will not change that!

The flock, herd, and human infections will continue- let’s get them all documented and collectively analyzed to gain that crucial common picture. Then we can move in determining our smartest response, Secretary Rolland and dear agricultural colleagues!

John