A recent publication in Nature* confirms the pathogenicity of H5N1 virus derived from lactating dairy cows in ferrets and mice. Studies were conducted at the University of Wisconsin, Madison, Tokyo University and Texas A&M University Veterinary Medical Diagnostic Laboratory in conjunction with the National Institute of Allergy and Infectious Diseases.
It is evident that the avian-origin virus currently circulating in dairy cattle has undergone changes that allow it to infect mammals as evidenced by outbreaks in both marine and terrestrial animals from 2022 onwards. Farmed mink, cats, skunks, racoons and free-living mice are susceptible to the virus.
Under experimental, controlled conditions, the virus induced clinical signs in ferrets including elevated temperature, inappetence and loss in body weight. The virus could be isolated from both the upper and lower respiratory tracts following infection. Similar changes occurred in mice with viremia and a dose-dependent response ranging from mild signs to death
At present the bovine-adapted H5N1 virus does not appear to be transmitted by the aerogenous route on droplets from infected to susceptible ferrets. In contrast, H1N1 influenza virus is contagious in both ferrets and mice.
Laboratory housing to investigate transmission of respiratory viruses among ferrets. |
The authors concluded that the bovine-origin H5N1 influenza virus posses both human and avian receptor binding specificity but at this time is not contagious in ferrets, a standard research animal for influenza viruses.
It is possible that given both time and concentration of dairy cattle in large affected herds, strains of bovine H5N1 virus that appear to be transmitted by the droplet route among dairy cows may develop the capability to infect the respiratory tracts of humans representing a potential epidemic strain. It is therefore essential to develop epidemiologic data and understand mechanisms of transmission in the U.S. dairy industry in order to develop recommendations to prevent spread and to protect workers.
*Eisfeld, A. et al Pathogenicity transmissibility of bovine H5N1 influenza virus in mice and ferrets. Nature. DOI: 10.1038/s41586-024-07766-6 (2024)