Michigan bird flu spike raises concerns about dairy cattle, wild animals and human risk

Michigan's poultry flocks are facing a resurgence of bird flu after months of relative quiet. In mid-December 2024, state officials detected H5N1 in a commercial operation in Ottawa County—the first confirmed case in Michigan poultry in more than six months. That single detection opened a door. Since then, the U.S. Department of Agriculture has confirmed seven additional outbreaks across the state, hitting five commercial flocks and two backyard operations, with the most recent case appearing in Oakland County. The timing matters less than what it signals: the virus is circulating again, and this time it's not just a poultry problem.

The broader picture is grimmer. Across the country, nearly 11 million birds have died or been culled, and more than 900 dairy cattle herds have been infected. The virus has also killed wild animals—raccoons, skunks, foxes, bobcats, and marine mammals—as well as domestic cats. In early January 2025, the Centers for Disease Control and Prevention reported the first human death from bird flu in the United States, a person in Louisiana. The disease is no longer theoretical or distant. It is here, it is spreading, and it is killing.

What makes this outbreak unusual is that H5N1, traditionally an avian virus, has jumped into dairy cattle with unexpected success. The virus first appeared in U.S. dairy herds in March 2024 in Texas and has since spread to 15 states, including California. Infected cows develop fever and lethargy, lose their appetite, and experience a dramatic drop in milk production. Most recover on their own, but the virus concentrates in the mammary glands, making their milk highly infectious. Pasteurization kills the pathogen, but raw milk remains dangerous—a significant risk for dairy workers and for wild animals that consume it on farms. Researchers at Michigan State University and federal laboratories are working to understand how long cows shed infectious virus and how the infection spreads within and between herds, but the answers are still incomplete.

Genetic sequencing has revealed two distinct strains circulating. The B3.13 genotype is found in both cattle and poultry, and evidence suggests it originated from a single spillover event—likely from wild birds to a cow in Texas, then cow to cow. A separate strain, D1.1, is circulating in wild birds and domestic poultry. The distinction matters because influenza A viruses, the category H5N1 belongs to, are the only flu viruses known to have triggered human pandemics. The fact that this particular strain is now established in mammals raises a concern that has kept epidemiologists awake: prolonged circulation in cattle increases the risk that the virus will adapt further, becoming more capable of infecting humans.

The economic and logistical toll on farms is substantial. Infected herds experience production losses, and managing an outbreak requires separation of sick animals, supportive care, additional labor, and personal protective equipment for workers. The virus has also spread from dairy farms to poultry facilities through contaminated equipment, clothing, shoes, and trucks—vectors that carry raw milk residue into environments where birds are kept. For poultry, the consequences are severe. The current strain is classified as highly pathogenic avian influenza, or HPAI, because of the high mortality it causes in domestic birds.

Controlling the spread now depends on biosecurity—the unglamorous but essential work of preventing contact between infected and healthy animals. Farms must limit visitors, disinfect tools and footwear, isolate sick animals, and maintain strict separation between species. Every H5N1-positive sample is sent to the USDA for genetic sequencing to monitor for mutations that might increase the virus's ability to infect mammals. Michigan researchers are collaborating with state and federal officials and farmers to track the virus's movement and understand its behavior in a host it has only recently begun to exploit. The outbreak that began in 2021 in wild birds has evolved into something more complex and more threatening. The question now is whether biosecurity measures and surveillance can slow its adaptation before it becomes something the country is far less equipped to handle.