Research finds that avian influenza can spread through milking
Juergen Richt, a researcher at Kansas State University, USA, has just published his findings linking milking practices to the transmission of the H5N1 avian influenza virus, which affects dairy cattle and was first detected in the country last spring.
As of 1 October 2024, H5N1 avian influenza had affected more than 200 dairy cattle farms across 14 states, with milking equipment and anthropogenic activities suspected of being involved in transmission, but without clear evidence of how this was occurring.
In a collaborative effort, research teams led by Richt, in partnership with Martin Beer of the Friedrich Loeffler Institute in Germany, experimentally infected both calves and lactating cows with the H5N1 clade 2.3.4.4b virus — the strain circulating in livestock in the USA — in order to investigate possible modes of transmission. They compared susceptibility and transmission in nine calves infected via oral and nasal inoculation and three lactating cows infected via mammary gland inoculation. In addition, the mammary glands of three further dairy cows were inoculated with H5N1 euDG, the clade 2.3.4.4b avian influenza strain circulating in Europe.
Infection in calves resulted in mild clinical disease, with moderate viral replication and no transmission to pen-mates. In contrast, dairy cows developed severe mammary gland infection characterised by fever, mastitis, and a sharp drop in milk production. Dramatic increases in viral load in milk were observed, but there was no evidence of systemic infection or nasal shedding of the virus. These findings indicate that milk and milking procedures, rather than respiratory spread, are the likely primary routes of H5N1 virus transmission among livestock.
According to Richt, it is imperative that we study the ways in which avian influenza is transmitted in dairy cows, since given the potential economic damage to the livestock industry and the human health risk posed by H5N1, this research demonstrates that establishing safe and hygienic milking systems is a substantial concern for this sector in the United States.
The study was funded in part by the Kansas State Bio and Agricultural Defense Facility National Transition Fund, and animal research was conducted at the K-State Biosecurity Research Institute and the Friedrich-Loeffler-Institut in Germany.