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H5N1 Bird Flu: Understanding the Risk

Although highly pathogenic H5N1 avian influenza (commonly known as the bird flu), has been a public health concern for years, recent developments have heightened media attention and public awareness. In 2024, 66 people in the United States were diagnosed with H5N1 bird flu resulting from animal to human exposures (there have been no cases of human-to-human exposure). In most cases, symptoms were mild. On January 6, 2025, however, a Louisiana resident died from their infection marking the first H5N1 bird flu death of the current outbreak in the United States.

The wild bird H5N1 genotype was found in both the Louisiana patient who died after exposure to a sick backyard poultry flock, and a Canadian teen who was hospitalized in November. It appears that this genotype could be more hazardous to humans and is also dangerous to other animals. California has reported a few house cat deaths in animals exposed to raw pet food and raw milk.

To date, there have been no known human cases of H5N1 in Massachusetts. That said, the disease is widespread amongst bird populations nation-wide, making it essential that the public understands best practices on how to prevent spread of this potentially deadly disease.

H5N1, Birds, and Humans

The natural reservoir of H5N1 are wild waterfowl like ducks and geese. Wild waterfowl migrate around the globe and can infect some other species of animals. Once introduced within domestic poultry flocks, the virus spreads rapidly and kills quickly, hence the name “highly pathogenic avian influenza”. In February 2024, one backyard flock in Barnstable County tested positive for H5N1 and had to be depopulated to prevent spread. No people were infected.

H5N1, Dairy Cows and Humans

For the first time in 2024, the H5N1 virus was found to have mutated to infect and transmit between dairy cows. No infected cows have been identified in Massachusetts or New England, however, 16 states have reported infected cows. Genetic analysis suggests that after a cow was infected by wild birds (likely through water or feed contaminated with bird feces), the virus then mutated to be able to spread within herds. There is currently no evidence that wild birds are continuing to infect dairy cattle, however, the risk cannot be ruled out (1).

Concerningly, H5N1 virus has been found in the milk of infected cows, posing a risk to dairy ranchers. Workers should be especially vigilant for signs of illness in their animals and wear protective gear if animals are sick. As of this article’s publication, 40 people in the U.S. have been infected from dairy cows. Nearly all of these infections have been mild, with symptoms like conjunctivitis (pink eye). Fortunately, pasteurization has proven to effectively kill H5N1 virus, thereby eliminating risk to the pasteurized milk supply or consumers. Even before H5N1 public health has strongly discouraged drinking raw milk due to its risk for transmitting infectious diseases. The recommendation NOT to drink raw milk is even stronger now.

What’s the Risk to Cape Cod?

Cape Cod is home to many migratory bird species, which can carry the virus. The risk to the general public remains low, but those handling birds—like farmers or wildlife enthusiasts—should exercise caution. We detail steps to protect yourself on our webpage, but here are some key takeaways:

How to Protect Yourself:

  • Immediately Report Sick or Dead Poultry: Backyard flock owners and commercial enterprises should report unexpected illness or death immediately to the Division of Animal Health at (617) 626-1795 (2).
  • Wear Protective Gear around Sick Animals: Disposable rubber gloves, safety goggles, & more (3).
  • Avoid Contact with Wild Birds: Avoid direct contact with wild birds and observe them only from a distance, if possible. Report unusual bird deaths to local authorities.
  • Do Not Drink Raw Milk: Pasteurized milk has proven to be safe from H5N1 and many other infectious diseases like salmonella and campylobacter.
  • Get Vaccinated: While the seasonal flu vaccine doesn’t protect against bird flu, it reduces the risk of co-infections with a human seasonal virus and an avian virus. While very rare, this could give the bird flu an opportunity to become more transmissible and potentially more virulent.
Image describes how infected backyard poultry could spread bird flu to peole.
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By staying informed and taking simple precautions, we can protect our community from potential health risks. For updates, visit the Barnstable County Department of Health and Environment’s website.


Sources:

  1. https://www.avma.org/resources-tools/animal-health-and-welfare/animal-health/avian-influenza/avian-influenza-virus-type-h5n1-us-dairy-cattle
  2. https://www.mass.gov/info-details/avian-influenza
  3. https://www.cdc.gov/bird-flu/caring/index.html#cdc_caring_for_yourself_and_others_providing_care-recommended-ppe

Related: Avian Bird Flu on Cape Cod – Barnstable County

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