Is Animal Agriculture Contributing to Bird Flu Spread?

It has been a bad flu season, and not just for humans but animals too. Seasonal influenza is raging across the United States, causing 24 million illnesses since Fall 2024. Birds have it even worse. Avian flu has affected 23 million poultry in the last 30 days. Bird flu originates in wild birds and spreads among commercial poultry, but don’t let the name fool you. This pathogen can infect more species than just birds, and that is where our story gets interesting.

The current strain of bird flu (also called H5N1 avian influenza) has raised alarm bells among public health experts because it has jumped into other species, including dairy cattle and humans. People who work on livestock farms have caught it, as have industry veterinarians. As of February 11, 2025, the Centers for Disease Control and Prevention reported that bird flu has affected 1,555 poultry operations and 967 dairy herds in the United States. There are 68 confirmed cases of animal workers and one human fatality in January 2025. 

In this episode we discuss the origins of bird flu, how it spreads, and the risks to our food supply and public health. Our guests: Drs. Meghan Davis and Erin Sorrell, both Associate Professors in the Department of Environmental Health and Engineering at the Johns Hopkins School of Public Health. Dr. Davis is a veterinarian and microbiologist who has first-hand experience with zoonotic diseases and worker safety. Dr. Sorrell is an expert in biosafety, biosecurity, and health systems who advises groups on how to control outbreaks as part of her work at the Johns Hopkins Center for Health Security. 

In our conversation, Dr. Davis comments on how bird flu risks are different for large industrial livestock operations compared to smaller pasture-based operations, and how industrial operations can serve as amplifiers for viruses to swap genes and become more virulent or transmissible in humans.  

A typical industrial livestock operation can house hundreds to thousands of dairy cattle, thousands of pigs, and tens of thousands of chickens— often in confined settings where the virus can spread quickly. Dr. Davis explains that infected poultry flocks are “depopulated” --that is, killed en masse--which at large farms can include over a million birds at a time. Dairy cattle can recover from the illness but can become reinfected, which has experts wondering if the virus could become endemic. Additionally, researchers have long been concerned that a new human influenza epidemic could arise from or be magnified by industrial livestock operations.

Bird flu impacts are rippling through food supply chains, causing egg shortages and price spikes. Dr. Sorrell elaborates on risks to the food supply and what the public can do to protect themselves from food that could potentially contain bird flu. For example, federal agencies are providing health advisories to properly cook meat and not to drink unpasteurized “raw” milk.  Backyard flocks are another way that people could be exposed to bird flu, which might make people think twice about starting a chicken coop this year. 

With a change in political administration comes new policies and priorities. We ask Dr. Sorrell to reflect on the Biden Administration's response, and what the Trump Administration should be doing to get bird flu under control. Sorrell and others are concerned that the Trump Administration is curtailing data sharing at CDC, which could hurt the ability of groups to prepare and respond to bird flu, and has withdrawn the United States from the World Health Organization, which hurts information sharing with other countries.

The potential for human-to-human spread of bird flu is top of mind for both Drs. Sorrell and Davis. The CDC says the risk of bird flu to the public is currently low, because human exposures are mostly limited to livestock and poultry workers and there has yet to be human-to-human spread. However, the situation can change quickly as the virus evolves. Just days after we recorded the podcast, a new strain of bird flu infected a dairy worker in Nevada, causing fresh concerns among groups that track the virus. This new strain does not appear to move from person to person, but perhaps next time we will not be so lucky.  

This is an evolving story, and one that we will revisit in the coming months.