A recent study by researchers from Emory University and their colleagues from California, Colorado, Michigan and Virginia found evidence of the H5N1 virus in the air and wastewater on affected dairy farms.
For the new study, the group conducted extensive air, farm wastewater and milk sampling from 14 of California’s outbreak farms across two different farming regions, according to a report from the University of Minnesota.
In the initial air sampling phase, the group used three different air-sampling devices, one of them an open-face polytetrafluoroethylene (PTFE) filter cassette worn on a backpack to model exposure to facility workers. On each farm, they collected aerosols and droplets from exhaled breath of individual cows or rows of cows, within milking parlors during milking and within housing areas. Of 71 air samples tested for viral RNA in sampling of exhaled breath in milking parlors and housing areas, six were positive, including one from the open-face PTFE filter sampler.
Additional testing on nine more farms, including some in southern California, done within days of milk bulk tank positives, found H5N1 viral RNA in 21 of 35 air samples, with infectious virus found in 4 of the samples.
To investigate whether wastewater was a potential mode of H5N1 transmission, researchers collected samples of reclaimed wastewater on multiple farms, which included water used to clean milking equipment and dairy parlors and samples collected at drains, sump pumps, fields, and manure lagoons.
H5N1 viral RNA was detected at each point of the waste stream, including in manure lagoons that are widely used by migratory birds and in fields with grazing cows, they found.
Of samples with high viral loads, two wastewater samples yielded infectious virus.
“These results demonstrate that H5N1 is prevalent in reclaimed farm wastewater sites across dairy farms and may serve as another source of H5N1 spread between cows, to humans, and to peri-domestic animals,” the researchers wrote.
In other experiments, the researchers found on-farm differences in viral variants, as well as evidence that suggests multiple modes of H5N1 transmission is likely on farms.
The findings support the need for multiple mitigations, including respiratory and eye protection for farm workers, disinfection of milking equipment, treatment of contaminated milk and wastewater to inactivate the virus, and identification of infected cows, even those that aren’t showing clinical symptoms.
