Key Findings from Recent Research

Recent research published in Nature reveals that H5N1 avian influenza viruses derived from U.S. dairy cattle possess unique features that may facilitate infection and transmission among mammals. Despite these traits, the virus does not efficiently transmit via respiratory droplets to ferrets, a model organism for human influenza studies.

Outbreak and Experimental Findings

In March 2024, an outbreak of highly pathogenic H5N1 (HPAI H5N1) was reported among U.S. dairy cattle. This outbreak led to fatal infections among cats on affected farms, spillover into poultry, and four reported infections among dairy workers. The viruses isolated from these cattle are closely related to H5N1 strains circulating in North American wild birds since late 2021.

A collaborative study by researchers from the University of Wisconsin-Madison, Shizuoka and Tokyo Universities in Japan, and the Texas A&M Veterinary Medical Diagnostic Laboratory aimed to understand the characteristics of these bovine H5N1 viruses. Their experiments involved administering the virus to mice and ferrets to evaluate its replication and disease-causing potential.

Severe Disease Induction in Mice and Ferrets

When administered intranasally, the bovine H5N1 virus caused severe disease in both mice and ferrets. Mice receiving higher doses of the virus died, while those given lower doses exhibited varying survival rates. The virus was detected in multiple organs, including the mammary glands and muscle tissues.

Ferrets infected with the bovine H5N1 virus displayed elevated temperatures and weight loss. High virus levels were found in their respiratory tracts and other organs, though not in their blood or muscle tissues, unlike in mice.

Limited Respiratory Transmission

To assess respiratory transmission, ferrets were exposed to the bovine H5N1 virus and H1N1 influenza. While both groups showed clinical signs of disease, only ferrets exposed to H1N1 developed clinical disease, indicating that the bovine H5N1 virus does not transmit efficiently via respiratory droplets.

The study also found that bovine H5N1 viruses can bind to both avian and human-type cellular receptors. This dual receptor-binding capability suggests a potential to infect cells in the human upper respiratory tract, though current transmission between animals or people via respiratory droplets remains inefficient.

Implications and Funding

The findings suggest that bovine H5N1 viruses differ from previous H5N1 strains and may have the potential for mammalian infection. However, the limited respiratory transmission observed in ferrets indicates that the risk to humans may currently be low.

This research was funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

Reference

Eisfield, A., et al. "Pathogenicity and transmissibility of bovine H5N1 influenza virus in mice and ferrets." Nature, 2024. DOI: 10.1038/s41586-024-07766-6.

Highlights

• Bovine H5N1 avian influenza viruses can induce severe disease in mice and ferrets.
• The virus binds to both avian and human-type cellular receptors.
• Limited respiratory droplet transmission observed in ferrets.
• Outbreak in U.S. dairy cattle in March 2024, leading to infections among animals and humans.
• Study funded by the National Institute of Allergy and Infectious Diseases (NIAID).

Data Source: https://www.nih.gov/news-events/news-releases/features-h5n1-influenza-viruses-dairy-cows-may-facilitate-infection-transmission-mammals