Influenza is a clever virus and one that deserves respect. Current concerns with the H5N1 avian influenza virus strain demonstrate why public health around the world continues to watch and monitor for impact on human health. Although the situation is not one that currently affects us on a day-to-day basis, it is important that we have a basic understanding of why this remains newsworthy.

Spread and evolution of H5N1.

Since its emergence, H5N1 has spread across multiple continents, affecting wild birds, poultry, and mammals. In late 2023, the virus was detected in Antarctica for the first time, raising concerns about its impact on native wildlife. By 2024, H5N1 had been reported in various regions, including Europe, Asia, and the Americas, leading to significant poultry losses and economic challenges.

In the United States, H5N1 has been detected in wild birds, poultry, and mammals across all 50 states. As of early 2025, nearly 70 human cases have been confirmed, primarily among individuals with direct exposure to infected animals. In December 2024, the Centers for Disease Control and Prevention (CDC) confirmed the first severe human case of H5N1 in Louisiana, involving a patient hospitalized with severe illness.

We have seen H5N1 move across nonhuman animal species, to situations where humans have become mildly ill after contact with animals, and now to situations where animal contact has resulted in severe human illness.

Since this particular strain of influenza has been detected in a variety of animals, but rarely in humans, what is the concern? The concern […]