Influenza A(H5N1) in Ferrets

I'm afraid I'm the bearer of bad news.

Since 2020, there has been unprecedented global spread of highly pathogenic avian influenza A(H5N1) in wild bird populations with spillover into a variety of mammalian species and sporadically humans.

In March 2024, Influenza A(H5N1) virus was first detected in dairy cattle in the USA, with subsequent detection in numerous states, leading to date to over a dozen confirmed human cases.

In a study, scientists employed the ferret model, a species that permits concurrent investigation of viral pathogenicity and transmissibility in the evaluation of A/Texas/37/2024 (TX/37) A(H5N1) virus isolated from a dairy farmworker in Texas[1].

The results show that the virus has a 'remarkable ability' for robust systemic infection in ferrets, leading to high levels of virus shedding and spread to naïve contacts. Ferrets inoculated with TX/37 rapidly exhibited a severe and fatal infection. The virus efficiently transmitted in a direct contact setting and was capable of indirect transmission via fomites.

Airborne transmission was corroborated by the detection of infectious virus shed into the air by infected animals, albeit at lower levels compared to the highly transmissible human seasonal and swine-origin H1 subtype strains. Our results show that despite maintaining an avian-like receptor binding specificity, A/Texas/37/24 displays heightened virulence, transmissibility, and airborne shedding relative to other clade 2.3.4.4b virus isolated prior to the 2024 cattle outbreaks, underscoring the need for continued public health vigilance.

Ferrets represent an invaluable model for the study of influenza virus pathogenicity and transmissibility in humans[2].

In conclusion: Influenza (H5N1), isolated from a farmworker, was tested in ferrets. All animals died as a result of an infection 2 to 3 days post-inoculation. High virus titers were detected in systemic tissues from all ferrets, including the brain. Airborne transmission was also detected.

In another study it was found that A/Texas/37/2024 transmits by respiratory droplets in mammals without prior adaptation[3].

This doesn't bode at all well for the future.

[1] Joanna Pulit-Penaloza et al: Transmission of a human isolate of clade 2.3.4.4b A(H5N1) virus in ferrets in Nature - 2024
[2] Thakur et al: Ferrets as a Mammalian Model to Study Influenza Virus-Bacteria Interactions in Journal of Infectious Diseases - 2024
[3] Gu et al: A human isolate of bovine H5N1 is transmissible and lethal in animal models in Nature - 2024.