Influenza A (H5N1)

Highly Pathogenic Avian Influenza - H5N1

Updated 2/10/2025

January 31, 2025: The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service reported the first detection of the H5N1 virus, subtype D1.1, in dairy cattle in Nevada. D1.1 is the current predominant genotype in migratory wild birds, and the Nevada cases represent the second spillover event from migratory wild birds to dairy cattle following the B3.13 event in late 2023/early 2024 (https://www.aphis.usda.gov/sites/default/files/dairy-cattle-hpai-tech-brief.pdf).

January 6, 2025: The Louisiana Department of Health reported a patient who had been hospitalized with the first human case of highly pathogenic avian influenza (HPAI), or H5N1, in Louisiana and the U.S. has died. https://ldh.la.gov/news/H5N1-death

December 18, 2024: The Centers for Disease Control and Prevention (CDC) reported the first case of severe avian influenza A(H5N1) virus ("H5N1 bird flu") infection in the United States in a hospitalized patient in Louisiana.

November 19, 2024: The California Department of Public Health (CDPH) has identified a suspected avian flu infection in a child from Alameda County who had mild upper respiratory symptoms and no known contact with infected animals.

November 13, 2024: The Public Health Agency of Canada (PHAC) confirmed a human case of avian influenza caused by influenza A(H5N1) virus in Canada.

In April 2022, an individual in Colorado was confirmed by the Centers for Disease Control and Prevention (CDC) as the first human case of HPAI A(H5N1) virus in the U.S. Human infections with avian influenza A viruses, including A(H5N1) viruses, are uncommon but have occurred sporadically worldwide.

However, in the United States, since 2022, HPAI A(H5N1) virus detections have been reported in more than 200 mammals. On April 1, 2024, the CDC confirmed a positive human case of influenza A(H5N1) virus in the United States in a person with exposure to dairy cows. It is the first known case of human infection from contact with an infected mammal.

Since April 2024, there have been 61 reported human cases of H5 bird flu reported in the United States.

As of December 2024, 866 dairy herds in 16 U.S. states have confirmed cases of H5 bird flu virus infections in dairy cows and 50 states have reported outbreaks in poultry.

The CDC tracks and reports confirmed cases, by state and source of exposure, in a table on its website: https://www.cdc.gov/bird-flu/situation-summary/index.html. The CDC has recommendations for clinicians on monitoring, testing, and antiviral treatment for patients with suspected or confirmed avian influenza A virus infections.

Read an opinion article by Jennifer B. Nuzzo, Lauren Sauer, and Nahid Bhadelia in the Washington Post discussing how "If many dairy farm workers contract H5N1, we risk a pandemic."

Unofficial Map of H5N1 cases around the globe by the University of Nebraska Medical Center's Global Center for Health Security