GENEVA — International human and animal health experts warn the H5N1 avian influenza is evolving quickly and posing a global health threat as the virus is increasingly crossing species barriers and infecting a wide range of domestic and wild mammals. “These developments pose significant challenges to animal, human and environmental health,” Dr. Gregorio Torres, veterinarian and head of the science department at the World Organization for Animal Health, told journalists in Geneva Tuesday. He noted that avian influenza, commonly known as bird flu, has been reported in 108 countries and territories over five continents in the last three years. “And as of December 2024, the infection has been detected in over 70 species of domestic and wild mammals. This includes the ongoing detection of H5N1 in dairy cattle in the United States,” Torres said. “So far, the close monitoring of the virus has not found markers that could suggest effective mammalian adaptation, but we know this can change at any time,” he said. Most human cases in US The World Health Organization this week reported 76 people were infected with the H5 avian influenza viruses in 2024, most of them among farm workers. Sixty-one of these cases occurred in the United States, which has reported outbreaks in wildlife, poultry and, more recently, dairy cattle. “This is the first time we have seen the infections from dairy cattle to humans, and so many within the U.S.” said Dr. Maria Van Kerkhove, director of epidemic and pandemic threat management at WHO. “In the U.S., all but two have direct links with infected animals, whether this was working on farms, whether this was part of culling exercises,” she said. “We have not seen any detection of human-to-human transmission among these cases.” While much attention on the bird flu situation has focused on the United States this year, Van Kerkhove noted that Australia, Cambodia, Canada, China and Vietnam also reported outbreaks. Based on available information, she said that the H5N1 viruses have remained avian viruses and have not adapted to spread among people, stressing that follow-up epidemiologic, virologic and serologic investigations “so far have not reported or identified human-to-human transmission.” “However, this can change quickly as the virus is evolving, which is why we are actively assessing the situation and why surveillance is so critical,” she said. 300 million birds dead Although the WHO assesses the current risk of infection for the public as low, it considers the public health risk for farm workers and others exposed to infected animals to be low-to-moderate. The WHO advises exposed groups to use personal protective equipment such as coveralls, respirator masks, eye protection, gloves and boots to minimize the risk. Since October 2021, H5N1 has caused the deaths of more than 300 million birds worldwide, affecting the livelihood of millions of people. “In addition to the direct impact on livelihoods, the economic burden on farmers can lead to reduced investments in biosecurity measures,” said Madhur Dhingra, the U.N. Food and Agriculture Organization’s senior infectious diseases animal health officer. “This increases the risk and leads to a dangerous cycle of risk, vulnerability, and loss. … In regions heavily reliant on poultry as a primary protein source, HPAI [highly pathogenic avian influenza] poses a serious threat to food and nutrition security,” she said. “The impacts of HPAI have spilled over into wildlife, with more than 500 bird species and over 70 mammalian species affected, including endangered animals like the California condor and polar bears,” she said. “The biodiversity impacts, particularly among seabirds and marine mammals, and disruption of fragile ecosystems, such as the Antarctic region, are concerning.” Health experts agree that increased surveillance and close monitoring of the evolution of the H5N1 virus are essential to prevent the disease from spreading widely around the world. “We are in an interpandemic period right now where we have a number of different zoonotic viruses, with avian influenza, H5N1 one of several,” Van Kerkhove said. “While we are operating in a state of readiness, I think the world is not ready for another infectious disease, massive outbreak or pandemic because we have lived through COVID and it was incredibly traumatic, and it is still ongoing. “We are recommending to our member states and national authorities to increase surveillance and vigilance in human populations, especially those who are occupationally exposed, for the possibility for infection, and, of course, doing thorough investigations around each and every human case,” she said. In the meantime, she advised people to minimize their risk of becoming sick from bird flu by carefully watching what they eat and drink. “Cows infected with the H5N1 virus have been reported to have high viral loads in their milk,” she said, so, it is advisable that people “consume pasteurized milk.” “If pasteurized milk is not available, heating milk until it boils also makes it safe for consumption. Similarly, we recommend thoroughly cooking meat and eggs when in areas affected by avian flu outbreaks,” she said.