Current H5N1 Bird Flu Situation in Dairy Cows
Domestic Summary
A multistate 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 had been found in cows. On April 1, CDC confirmed one human HPAI A(H5N1) infection in a person with exposure to dairy cows in Texas that were presumed to be infected with the virus. This is thought to be the first instance of likely mammal to human spread of HPAI A(H5N1) virus. In May 2024, CDC began reporting additional, sporadic human cases in people who had exposure to infected dairy cows. That latest human case counts are available at H5N1 Bird Flu: Current Situation Summary | Avian Influenza (Flu) (cdc.gov).
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.
CDC Resources
News
- CDC Confirms Second Human H5 Bird Flu Case in Michigan; Third Case Tied to Dairy Outbreak Thursday, May 30, 2024
- Outbreak of Highly Pathogenic Avian Influenza A(H5N1) Viruses in U.S. Dairy Cattle and Detection of Two Human Cases — United States, 2024 Wednesday, May 29, 2024
- Study Shows Novel Influenza Virus Infections in Humans in the United States Would Likely be Detected Through Existing Health Care Surveillance Wednesday, May 29, 2024
- Technical Update: Summary Analysis of the Genetic Sequence of a Highly Pathogenic Avian Influenza A(H5N1) Virus Identified in a Human in Michigan Friday, May 24, 2024
- CDC A(H5N1) Bird Flu Response Update May 24, 2024 Friday, May 24, 2024
- CDC Reports Second Human Case of H5 Bird Flu Tied to Dairy Cow Outbreak Wednesday, May 22, 2024
- CDC A(H5N1) Bird Flu Response Update May 17, 2024 Friday, May 17, 2024
- CDC A(H5N1) Bird Flu Response Update Friday, May 10, 2024
- CDC’s Flu Surveillance Systems Can Detect Avian Influenza A(H5N1) Virus Infections Wednesday, May 8, 2024
- CDC A(H5N1) Bird Flu Response Update Friday, May 3, 2024
- Avian Influenza A(H5N1) U.S. Situation Update and CDC Activities Friday, April 26, 2024
- Technical Report: Highly Pathogenic Avian Influenza A(H5N1) Viruses Friday, April 26, 2024
- Avian Influenza A(H5N1) U.S. Situation Update and CDC Activities Friday, April 19, 2024
- Update: Human Infection with Highly Pathogenic Avian Influenza A(H5N1) Virus in Texas Friday, April 5, 2024
- Technical Update: Summary Analysis of Genetic Sequences of Highly Pathogenic Avian Influenza A(H5N1) Viruses in Texas Tuesday, April 2, 2024
- Highly Pathogenic Avian Influenza A (H5N1) Virus Infection Reported in a Person in the U.S. Monday, April 1, 2024
Guidance
- Key Public Health Prevention Recommendations for HPAI A(H5N1) | Fact Sheet [154 KB, 2 pages]
- Highly Pathogenic Avian Influenza A(H5N1) Virus in Animals: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations
- Updated Interim Recommendations for Worker Protection and Use of Personal Protective Equipment (PPE) to Reduce Exposure to Novel Influenza A Viruses Associated with Disease in Humans
- Considerations for Veterinarians: Evaluating and Handling of Cats Potentially Exposed to Highly Pathogenic Avian Influenza A(H5N1) Virus
- Health Alert Network (HAN) – 00506 | Highly Pathogenic Avian Influenza A(H5N1) Virus: Identification of Human Infection and Recommendations for Investigations and Response
- Information for Specific Groups
- Human Infection with Avian Influenza A Virus: Information for Health Professionals and Laboratorians
Communication Resources
- Factsheet: Protect Yourself From H5N1 When Working With Farm Animals [2 MB, 1 page] | Spanish [1.7 MB, 1 page] | K’iche’ [2.1 MB, 1 page]
- Fact Sheet: Information for Farm Workers Exposed to H5N1 Bird Flu in U.S. Dairy Cows or Other Animals [245 KB, 2 pages]
Related webpages
- What CDC Is Doing to Respond to Bird Flu Outbreaks in Dairy Cows and Other Animals in the United States
- H5N1 Bird Flu: Current Situation Summary
- Bird Flu Virus Infections in Humans
- Avian Influenza in Birds
- Bird Flu in Pets and Other Animals
Publications
- Detection of Novel Influenza Viruses Through Community and Healthcare Testing: Implications for Surveillance Efforts in the United States – Morris – 2024 – Influenza and Other Respiratory Viruses – Wiley Online Library
- Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in a Dairy Farm Worker, NEJM, 2024. Supplementary Appendix [520 KB, 2 pages]
- Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024 [245 KB, 2 pages]
- Recommendations to Minimize Influenza Transmission at Dairy Cattle Livestock Exhibitions (usda.gov) [194 KB, 5 pages]
- Federal Order to Assist with Developing a Baseline of Critical Information and Limiting the Spread of H5N1 in Dairy Cattle: Frequently Asked Questions (usda.gov) [320 KB, 4 pages]
- USDA APHIS Testing Guidance for Labs for Influenza A in Livestock [289 KB, 3 pages]
- USDA APHIS Requirements and Recommendations for HPAI H5N1 Virus in Livestock for State Animal Health Officials, Accredited Veterinarians and Producers [290 KB, 7 pages]
- USDA livestock case definitions [131 KB, 2 pages]
- USDA Confirms Highly Pathogenic Avian Influenza in Dairy Herd in New Mexico
- USDA, FDA and CDC Share Update on HPAI Detections in Dairy Cattle
- Federal and State Veterinary, Public Health Agencies Share Update on HPAI Detection in Kansas, Texas Dairy Herds
- Highly Pathogenic Avian Influenza (HPAI) Detections in Livestock
- Influenza: Not Just for the Birds (usda.gov) [286 KB, 1 page]
- APHIS Recommendations for Highly Pathogenic Avian Influenza (HPAI) H5N1 Virus in Livestock [292 KB, 6 pages]
Other Documented Mammalian Infections
In recent years, HPAI H5N1 infections have been detected in mammals including but not limited to wild or feral animals such as foxes, bears, and seals; stray or domestic animals such as cats and dogs; farm animals, such as goats, cows, and mink, and zoo animals such as tigers and leopards. A timeline, which includes mammalian detections of bird flu, can be found here: Highlights in the History of Avian Influenza (Bird Flu) Timeline – 2020-2024