Current H5N1 Bird Flu Situation in Dairy Cows

Domestic Summary

A multi-state outbreak of HPAI A(H5N1) bird flu in dairy cows was first reported on March 25, 2024. This is the first time that these bird flu viruses were found in cattle. CDC confirmed one human HPAI A(H5N1) infection that had exposure to dairy cattle in Texas that were presumed to be infected with the virus. While thought to be rare, this exposure to HPAI A(H5N1) bird flu virus is the first instance of likely mammal to human transmission.

In the United States, since 2022, USDA APHIS has reported HPAI A(H5N1) virus detections in more than 200 mammals.

Background

While rare, mammals can be infected with highly pathogenic avian influenza (HPAI) A(H5N1) (“H5N1 bird flu”) viruses. Reports of these sporadic infections in mammals have occurred globally amid widespread outbreaks of bird flu infections in wild birds and poultry.

Mammals can be infected with H5N1 bird flu viruses when they eat infected birds, poultry, or other animals and/or if they are exposed to environments contaminated with virus. Spread of H5N1 bird flu viruses from mammal to mammal is thought to be rare, but possible.

Global Summary

Globally, sporadic HPAI A(H5N1) virus infections in mammals have been reported across the continents of Asia, North America, South America, and Europe. More information about the global impact of avian influenza can be found here: Avian Influenza – WOAH – World Organisation for Animal Health.

Specifically, recent HPAI A(H5N1) infections in mammals have been detected in sea lions in Peru and Chile, sea elephants in Argentina, and foxes in Canada, France, and other countries. A list of significant HPAI outbreaks, including in mammals, can be found here: Highlights in the History of Avian Influenza (Bird Flu) Timeline – 2020-2024.

Risk to Humans

The wide geographic spread of HPAI A(H5N1) viruses in wild birds, poultry, and some other mammals, including in cows, could create additional opportunities for people to be exposed to these viruses. Therefore, there could be an increase in sporadic human infections resulting from bird and animal exposures, even if the risk of these viruses spreading from birds to people has not increased. CDC believes the current risk to the general public from bird flu viruses is low. People who have job-related or recreational exposure to infected birds or animals, including cows, are at greater risk of contracting HPAI A(H5N1) virus. CDC has recommendations related to testing, treatment of HPAI A(H5N1) infection and prevention of exposure to these viruses: Highly Pathogenic Avian Influenza A(H5N1) Virus in Animals: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations.