Highly Pathogenic Avian Influenza (HPAI) H5N1

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The highly pathogenic avian influenza (HPAI) H5N1 also known as the Bird Flu, is a zoonotic influenza that naturally occurs in wild aquatic/migratory birds. These waterfowl are the natural reservoir for this virus, and are the most resistant to infection.

It is a type A influenza, with surface glycoprotein subtypes H5 and N1, which dictate viral entry and release into host cells. It is spread by bird migration and since then, it has become the dominant strain in bird populations worldwide, and has jumped species to over 200 different mammals. Humans have no immunity to these viruses.

It was identified in China in 1996 and spread through migratory birds worldwide to at least 108 countries across five continents. The first human cases of A(H5N1) were in Hong Kong in 1997.  Since January 1, 2003, the World Health Organization (WHO) reports that as of July 1, 2025, there have been 986 cases of human infections with this virus, including 473 deaths from 25 countries. A case fatality rate (CFR) of 48%. 71 of these cases were in the United States with 2 deaths.

- There has been a resurgence in Cambodia since 2025 with 19 new confirmed cases and nine deaths (CFR 57.5%).

- The HPAI is widespread in wild birds worldwide and has also been detected in many backyard poultry flocks.

-  The virus is now found in poultry throughout the United States and continues to impact poultry farms with millions of birds being affected since 2021.

- It has been an ongoing multi-state outbreak in the U.S.  in dairy cattle. As of January 6, 2026, HPAI has been confirmed in in a total of 19 states with over 1000 confirmed cases. (Arizona, California, Colorado, Idaho, Iowa, Kansas, Michigan, Minnesota, Nebraska, Nevada, New Mexico, North Carolina, Ohio, Oklahoma, South Dakota, Texas, Utah, Wisconsin, and Wyoming.) 

- The HPAI H5N1 has also infected some mammals believed to have eaten infected birds. These include seals, bears, foxes, skunks; farmed mink; stray or domestic animals, such as cats and dogs; and zoo animals, such as tigers and leopards. It has also been reported to be in a pig in Oregon.

With the re-emergence of the highly pathogenic avian influenza (HPAI H5N1), scientists once again are watching for mutations that can cause another pandemic. 

This is a novel virus to which the world population has no immunity. The death rate of Covid-19 at its height was 1.2%. The death rate of HPAI H5N1 globally from January 1, 2003 is 48%.

It has jumped species and is able to infect over 200 other types of mammals. Scientists say it is out of control in wild animals. Because it is able to infect so many new species, it introduces a new complexity if it were to cause a pandemic. It would pose significant challenges for mitigation and control efforts.

Recent genetic changes show it is close to human-to-human transmission causing great concern. It’s been said that a pandemic caused by this virus would be like a global tsunami, similar to the 1918 Influenza.