Influenza A(H5N1) in Animals and Humans

Influenza A(H5N1) Virus was known as an Highly Pathogenic Avian Influenza (HPAI) virus. Most scientists were worried that, with some small mututions, the virus would be able to infect humans too. Cattle and goats, however, were assumed to be at low risk of contracting Influenza A(H5N1).

Now, in March 2024, both cattle and goats are reported to be infected across multiple states of the United States. Potentially worse, there are some signs that cow-to-cow transmission may already have occurred.

Influenza A(H5N1) is highly virulent and was first detected in dairy cows in Texas and Kansas at the end of March 2024. Since then the virus has spread to additional herds. As of early April 2024, cases have been reported among dairy herds in Texas (7), Kansas (2), Michigan (1), New Mexico (1), and Ohio (1).

Cattle impacted by Influenza A(H5N1) exhibit flu-like symptoms, including fever and thick and discolored milk accompanied by a sharp reduction in milk production. Economic impacts to facilities are ongoing as herds that are greatly impacted may lose up to 40% of their milk production for 7 to 10 days until symptoms subside.

Cattle is a known mixing vessel for Influenza. The virus will have mutated to better infect these cows and goats. Which means that Influenza A(H5N1) is one step closer to become virulent enough to infect humans on the large scale.

On April 1, 2024 news appeared that the first human case of Influenza A(H5N1) infection was found in Texas. Also, the next day, a cat was found positive for Influenza A(H5N1).

Sequences from the dairy cows matched with those from wild bird samples collected from Texas about the same time. However, the goat samples from Minnesota are most similar to a pheasant sequence from Colorado.

In humans
Worldwide, Influenza A(H5N1) virus infections have been reported in more than 890 people with an approximately 50% case fatality rate since 1997. Mild upper respiratory tract symptoms, lower respiratory tract disease, severe pneumonia with respiratory failure, encephalitis, and multi-organ failure have been reported.

Luckily, a vaccine is already in development[1].

[Source here - Last check 03jan25]

[Update 10 November 2024] First Canadian human case of Influenza A(H5N1) reported. See here and here.

[Update 15 January 2025] Since April 2024, 67 human cases of avian influenza A(H5N1) virus infection have been reported in the United States. Of these, 40 were associated with exposure to infected dairy cows, 23 were associated with exposure to infected poultry, one through other animal exposure (such as backyard flocks, wild birds, or other mammals), and three cases were of unknown origin. See here.

[Update 5 January 2025] Influenza A(H5N1) has mutated to infect (and kill) cats. Research suggests cats could serve as mixing vessels for reassortment of avian and mammalian influenza viruses[2].

[Update 6 January 2025] In the USA, the first patient died as a result of infection with the Influenza A(H5N1) Virus. See here. This fatal case - and the severe case in a teenager in British Columbia - are both linked to the new D1.1 genotype, which arrived in migratory birds during the fall of 2024. The majority of 'mild' cases in 2024 have been caused by the `bovine' B3.13 genotype.

[1] Beukenhorst et al: A pan-influenza monoclonal antibody neutralizes H5 strains and prophylactically protects through intranasal administration in Science Reports - 2024
[2] Chothe et al: Marked neurotropism and potential adaptation of H5N1 clade 2.3.4.4.b virus in naturally infected domestic cats in Emerging Microbes and Infections - 2025