The rapid spread of avian influenza among poultry and dairy farms has heightened concerns among health experts about the risks posed by the methods used to cull and dispose of infected birds. Recent practices, such as dumping carcasses in landfills and methods requiring close human contact, have raised alarms about the potential for further disease transmission, according to data obtained by Reuters and interviews with officials and disease experts.
Extreme heat during the carbon dioxide asphyxiation of chickens at a Colorado egg farm likely contributed to five bird flu cases among workers, marking the largest cluster of human cases in the United States, the Centers for Disease Control and Prevention (CDC) reported this week. The CDC’s Principal Deputy Director Nirav Shah emphasized the importance of systematic use of protective gear during the culling of infected animals during a Tuesday call with reporters.
Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, highlighted the risks workers face during the culling process. Inhaling the virus can lead to symptoms such as pink eye and respiratory issues. “Depopulation activities need to clearly focus on protection for these individuals,” he stressed. The Colorado Department of Agriculture, in collaboration with the U.S. Department of Agriculture (USDA) and the affected farmers, decides on the methods for killing birds.
Over the past 2.5 years, bird flu has spread to nearly every U.S. state, with nine cases among poultry and dairy workers reported since March. The virus’s spread among livestock increases the likelihood of human infections, although the general public’s risk remains low, according to CDC officials. Since February 2022, approximately 95 million chickens, turkeys, and other poultry have been culled and disposed of, USDA data shows. While 2022 was the deadliest year for bird flu, the number of chickens disposed of in 2024 is nearing last year’s total.
In Colorado, workers used mobile gas chamber carts to kill infected birds, accommodating between a dozen and 50 birds at a time. More than 150 workers were exposed to infected poultry, with 69 displaying symptoms and five testing positive, according to the Colorado Department of Public Health and Environment.
Most culled birds are composted on farms, a process involving covering the carcasses with materials like wood shavings, maintaining high temperatures, and occasionally stirring the compost piles. This process typically takes several weeks and is considered the safest to avoid moving carcasses and potentially spreading the virus. However, in rare cases, carcasses are transported to landfills. For instance, Michigan egg producer Herbruck’s Poultry Ranch disposed of nearly 2 million chickens in private landfills between April 15 and June 8.
Only 3% of poultry have been disposed of in landfills since 2022, with Herbruck’s disposal accounting for about two-thirds of that number. Following Herbruck’s disposal, a nearby dairy farm tested positive for bird flu, raising concerns among local farmers. However, whole genome sequencing revealed that the disposed carcasses did not cause the infection.
John Clifford, a former USDA chief veterinarian and current advisor for the USA Poultry and Egg Export Council, emphasized the importance of on-site composting to prevent virus spread. Myah Walker, compliance unit supervisor at the Minnesota Board of Animal Health, also supported on-site composting. In contrast, Brian Hoefs, Minnesota’s state veterinarian, cautioned against using landfills, describing them as a “restaurant for scavengers” and a potential disaster.
As wild birds continue to spread the virus between farms and species, the poultry industry must navigate these challenges to protect both human and animal health. The ongoing outbreak underscores the need for stringent biosecurity measures, proper disposal practices, and protective equipment for workers to mitigate the risks associated with avian influenza.
