A non–peer-reviewed examine revealed on the preprint server bioRxiv means that extremely pathogenic avian influenza (HPAI) virus shed in poultry droppings may be transmitted by the wind, a chance that different consultants say cannot be dominated out however can also be very troublesome to show.
The report facilities on a February 2024 outbreak of H5N1 avian flu amongst unrelated industrial poultry farms situated about 8 kilometers (5 miles) aside within the Czech Republic through the 2023-24 HPAI season.
For the reason that newest H5N1 epidemic started in February 2022, the virus has led to the deaths of greater than 150 million US birds.
Ideally suited climate for transmission
The cluster was recognized after avian flu killed 5,000 fattening geese inside 2 days at a basic-biosecurity 50,000-bird farm close to a lake frequented by wild geese, the possible reason for the outbreak; the remainder of the poultry had been culled. Per week later, lethal outbreaks with a slower illness course occurred at two high-biosecurity rooster farms, the place useless birds had been discovered primarily close to the barns’ air-intake vents; the whole inhabitants was culled. All farms had their very own wells.
Consultants hypothesize that the slower illness course within the rooster barns could also be attributable to decrease H5N1 transmissibility in chickens, waning concentrations of the virus over distance from the duck farm, or housing circumstances.
The researchers, from the State Veterinary Institute Prague, used genetic, epizootiologic, meteorologic, and geographic information to reconstruct occasions suggesting that wind was the mechanism of H5N1 transmission between poultry on not less than two of the farms. Three H5N1 strains collected from birds in any respect three farms had been genetically an identical, no giant waterways had been close to the rooster farms, and the duck farm did not share workers or contractors with the rooster farms.
Our outcomes counsel that the contaminated plume emitted from the contaminated fattening duck farm was the essential medium of HPAI transmission, somewhat than the mud generated throughout depopulation.
What’s extra, meteorologic information revealed a breeze within the course of the rooster farms, cloudy circumstances that might have stored the solar’s ultraviolet mild from killing the virus, and virus-supporting cool air. The staff did not conduct air sampling.
“Our outcomes counsel that the contaminated plume emitted from the contaminated fattening duck farm was the essential medium of HPAI transmission, somewhat than the mud generated throughout depopulation,” the examine authors wrote. “Additionally they strongly implicate the function of confined mechanically-ventilated buildings with excessive inhabitants densities in facilitating windborne transmission and propagating virus concentrations beneath the minimal infectious dose on the recipient websites.”
Airborne not solely or main mode of unfold
Lead examine creator Alexander Nagy, PhD, instructed CIDRAP Information that he and his staff turned satisfied concerning the function of windborne transmission in these outbreaks once they confirmed the an identical id of the H5N1 pressure within the donor and recipient farms, the practically superb climate circumstances through the transmission occasion, and the gradual illness development within the rooster barns characterised by feed and water consumption earlier than medical indicators appeared.
“Moreover, the affected birds [dead chickens] had been situated in sections closest to the air inlets,” he mentioned. “Lastly, we excluded all different believable explanations.”
Michael Osterholm, PhD, MPH, director of the College of Minnesota’s Heart for Infectious Illness Analysis and Coverage (CIDRAP), writer of CIDRAP Information, mentioned airborne transmission may be crucial, “that means that that is essentially the most logical clarification for when you have got many barns with outbreaks in a single geographic space the place human biosecurity can’t be implicated as a motive for transmission.”
Up to now, he mentioned, the poultry trade has been reluctant to acknowledge airborne transmission due to the implications it could have for its practices: “The trade’s reluctance to simply accept this chance will not be that dissimilar to what we noticed with the shortage of some within the medical and public well being communities to acknowledge that SARS-CoV-2 transmission was additionally airborne.”
Whereas the researchers did an excellent job of laying out their speculation and supporting information, their conclusion needs to be interpreted with warning, mentioned David Swayne, DVM, PhD, a poultry veterinarian who retired as an avian flu researcher with the US Division of Agriculture (USDA) Agriculture Analysis Service.
“I believe we, as veterinarians who take care of avian influenza and different infectious illnesses, would acknowledge that there’s some airborne—and I am going to use the phrase dissemination—and that will result in transmission,” he mentioned. “However now we have to be cautious to ensure folks perceive that it doesn’t suggest that it is the solely means, nor that it is the main means. And every particular person facility goes to be completely different.”
Montserrat Torremorell, DVM, PhD, chair of the Division of Veterinary Inhabitants Drugs on the College of Minnesota, known as the researchers’ argument for airborne transmission “compelling.”
“Meteorological circumstances, timing of an infection, housing circumstances of the animals, susceptibility of the animal populations that turned contaminated and the shortage of different epidemiological hyperlinks between the premises are supportive of airborne transmission on this case,” she mentioned in an e mail.
Throughout an avian flu outbreak in Minnesota, Torremorell collected air samples inside and out of doors amenities housing three contaminated turkey and three egg-laying rooster flocks. Air samples from 5 of six flocks examined optimistic for big portions of H5N1 virus, all of them within the energetic an infection stage. The damaging pattern was from a flock within the superior stage of depopulation.
“The bigger variety of optimistic samples had been inside the power and on the exhaust fan (~5 m [meters; 16 feet] away from the power), and the variety of positives decreased with distance, however even with that we recognized some suspects (traces of RNA materials) at about 150 m and 1 km[kilometer;roughlyahalfmile)”shesaid”Viablevirus(throughvirusisolation)wasfoundinsidethefacilitiesattheoutsideoftheexhaustfanandatabout100m”[kilometer;roughlyahalfmile)”shesaid”Viablevirus(throughvirusisolation)wasfoundinsidethefacilitiesattheoutsideoftheexhaustfanandatabout100m”
Entry mechanism difficult to determine
David Stallknecht, PhD, professor emeritus at the University of Georgia’s College of Veterinary Medicine and a wildlife expert, said the study provides additional circumstantial evidence to several studies suggesting windborne viral spread. But he added that the mechanism of disease transmission into a poultry house is hardly ever identified, because there is no way to control for variables.
“It basically says that it could have happened, and I would not dispute that,” he said. “But to actually come down with concrete proof like you would in an experimental controlled experiment, there’s too much going on.”
“Influenza can be transmitted by a million different ways, probably many of them we don’t even know about,” he added. For example, whether the virus entered the poultry house via a raccoon, bird, person, or a person’s shoes, “those kind of details never really get resolved.”
Stallknecht said he and his team tried to research water-based avian flu transmission associated with ducks. “And we got to the point where we just had to quit because the numbers and the probabilities were so extreme,” he said. “You can’t do an experiment to pick up a one-in-a-trillion event.”
Swayne said that moving equipment and people in and out of poultry barns has to be done at a very high level of biosecurity to prevent viral transmission: “Yes, you could have movement of the virus by the wind, but it may be that it’s tracked in to the barns by the contamination around the outside, either from wild birds depositing fecal material there as they eat, spilled feed off of grain silos, etc.”
He added that just because a virus is transported via the wind doesn’t necessarily mean it will enter a barn that way. “The virus can move on particles or water droplets by the wind for a distance, and then it could land and contaminate the environment.”
Authors were initially skeptical, too
Nagy acknowledged that airborne spread isn’t typically considered a primary route of infection in poultry, and windborne spread requires “a constellation of many specific conditions” that behooves further research.
“However, when all conditions align, windborne transmission becomes a feasible mode of spread and could play a more significant role than previously thought, especially in densely populated poultry areas,” he said. “The windborne route is important to consider in cases when the infection emerges in new locations without obvious links to other farms or when illness and mortality are first observed near the air inlets.”
Poultry operations typically consist of confined, mechanically ventilated buildings with high population densities, a situation unlikely to change.
