Nature Communications study finds very low H5N1 infectious dose in dairy cows
An open-access Nature Communications paper finds that H5N1 can establish robust mammary-gland infection in dairy cows at a very low dose, while still showing notable barriers to transmission.
Nature Communications published an open-access paper on May 24 examining experimental infection of dairy cows with highly pathogenic avian influenza A(H5N1). Researchers from The Ohio State University and St. Jude Children's Research Hospital say the virus shows a strong tropism for the bovine mammary gland, a finding that challenges existing assumptions about influenza A host range and tissue specificity.
The team studied the B3.13 genotype of H5N1 in female lactating dairy cattle. Their objective was to define the infectious dose, routes of exposure and factors linked to morbidity and mortality. Nature notes that the manuscript has been posted in an unedited early-access form ahead of final publication, but the data and conclusions are already publicly available.
The central result is that intramammary inoculation with as few as 10 TCID50 established a robust infection and led to shedding of high-titer virus in milk. In practical terms, the study indicates that a very small dose can infect the udder, reinforcing the importance of the mammary gland as the main target tissue in this experimental setting.
At the same time, the paper reports clear transmission barriers. Despite the low infectious dose, H5N1 did not readily transmit via contaminated milking equipment or by close contact with infected animals in the experiments. Respiratory and oral exposures were also much less likely to establish productive infection and associated morbidity than direct intramammary exposure.
The severity findings are equally important for dairy biosecurity. High-dose intramammary exposure resulted in severe disease and mortality, and the authors say this challenges current hypotheses about how H5N1 spreads on dairy farms. Their conclusion is that additional agent, host or environmental cofactors may be needed to explain real-world farm transmission, making the study directly relevant to surveillance, milking hygiene and outbreak-control strategies.