Health authorities have confirmed that bird flu is now consistently spreading between mammals, raising concerns about potential human outbreaks. Virologists have highlighted efficient and sustained mammalian-to-mammalian transmission of the highly virulent B3.13 form of the H5N1 virus, which has already led to the culling of 90 million domestic birds in the US since 2022. While the CDC states that the risk to the general public remains low, the virus’s ability to mutate and jump between species poses a significant threat.
Diego Diel, a virologist at Cornell University, highlighted that this is one of the first times evidence shows efficient and sustained mammalian-to-mammalian transmission of bird flu. The highly virulent B3.13 form of the H5N1 virus has led to the culling of 90 million domestic birds in the US since 2022. Although the Centers for Disease Control and Prevention (CDC) says the risk to the general public from the H5N1 strain is currently low, with the 11 infected individuals in the US experiencing mild symptoms, the virus remains a serious concern. A single confirmed death from the related H5N2 virus in Mexico underscores the potential risks if the pathogen evolves.
Diel explained that potential mutations could lead to adaptation in mammals, spillover into humans, and efficient human-to-human transmission in the future. H5N1’s ability to steal genes from other influenza viruses and jump between different mammalian species exacerbates these concerns. The virus has been detected in a wide range of mammals, including polar bears, otters, squirrels, dolphins, elephant seals, Antarctic fur seals, and goats.
Genetic Insights and Recent Outbreaks
Molecular virologist Daniel Perez noted the lack of understanding about why these viruses now infect many more species. The strain causing the US dairy cow outbreak was first genetically sequenced from a Canada goose in Wyoming on January 25, 2024. By March 25, 2024, dairy cows across multiple states had contracted this virus strain.
Genetic testing confirmed cow-to-cow transmission, with infections spreading to cats and a raccoon, presumably after consuming raw milk from infected cows. The virus appears to prefer invading mammary gland tissues, resulting in highly contaminated, discolored, and strangely textured milk.
Authorities worldwide are urging the public to maintain good hygiene around wild birds and report sightings of sick or dead birds. Australia and New Zealand, which currently have no reported cases of H5N1, are preparing for its inevitable arrival and the likely impact on their wildlife. Australia is also dealing with a mass poultry culling due to H7 bird flus, causing widespread egg shortages. In response to H5N1’s spread in dairy cows, the USDA now requires dairy cattle to test negative for the virus before interstate transport.
Vaccination Efforts and Future Research
To mitigate the impact on critically endangered species like the California condor, the US has started vaccinating these birds. Researchers are also working on developing a human vaccine. The recent cases highlight the zoonotic potential of the virus, emphasizing the need for robust measures to prevent and control the spread of H5N1 in dairy cattle and reduce the risk of the virus adapting to new mammalian hosts. This research has been accepted for publication in Nature.
