Bovine HPAI H5N1 Viruses May Have Features That Facilitate Transmission Among Mammals

A series of experiments, whose findings were published in Nature, have revealed that bovine HPAI H5N1 viruses “may differ from previous HPAI H5N1 viruses and that these viruses may possess features that could facilitate infection and transmission among mammals. However, they currently do not appear capable of efficient respiratory transmission between animals or people.” NIH's website has the release.

Researchers conducted experiments on the strain of HPAI H5N1 that was reported among U.S. cattle in March of 2024 in order to “determine the ability of bovine HPAI H5N1 to replicate and cause disease in mice and ferrets, which are routinely used for influenza A virus studies.” First, mice were intranasally administered doses of influenza of increasing strength. All the mice that received the higher doses of infection died; “some of the mice that received lower doses survived, and those that received the lowest dose experienced no body weight loss and survived.”

High levels of H5N1 virus were also observed in “respiratory and non-respiratory organs, including in the mammary glands and muscle tissues,” compared to an H1N1 influenza virus, which was “found only in the respiratory tissues of the animals.”

The researchers also tested to see if transit among mammals would be observed via respiratory droplets. Groups of ferrets were infected with H5N1 and then placed near uninfected ferrets. Only ferrets “exposed to the H1N1-infected group showed signs of clinical disease, indicating that the cow influenza virus does not transmit efficiently via respiratory droplets in ferrets.”