Air was sampled directly in the stream entering poultry houses through their air inlets and analysed by environmental DNA metabarcoding, looking for the hosts of avian influenza rather than the virus. Wild waterbird DNA was detected in air inside all three sampled farms and outside two of them, with sequences annotated at species level including swans and tufted ducks. The sampling covered 61 indoor and 60 outdoor measurements between December 2021 and April 2022 across two broiler farms and one layer farm.
The detail that gives this weight is the state of the farms. All three had recently been positive for H5N1, all had been cleared and decontaminated before sampling, and all were assessed as high biosecurity standard. Conventional biosecurity was in place and material from wild waterbirds was still arriving in the air entering the buildings. That moves the inlet from a theoretical pathway to a measured one, in a way that outbreak geography and dispersion modelling cannot.
Two things to keep straight when using it. Host DNA is a proxy: avian influenza virus itself was not recovered from the inlet air, so this demonstrates the pathway rather than a viral ingress event, and it should be stated that way. The second is a genuinely useful idea rather than a caveat. The authors propose the method as a way to audit biosecurity, testing whether an inlet arrangement is actually excluding outside material by looking for the species that carry the pathogen. For a building being evaluated rather than designed from scratch, that is a measurement worth knowing exists.