Highly pathogenic avian influenza (HPAI), otherwise known as bird flu, has insinuated itself into the wild bird and domestic fowl populations around the world since at least 1997.
Although there are several antigenic variants of the bird flu virus, H5N1 is the current dominant form.
A brief history
The first human case of H5N1 bird flu was identified in 1997. By the end of that year, 18 human cases had been confirmed.
The virus faded into the background until 2003/2004, when a large outbreak of H5N1 infections spread through poultry flocks in several Asian countries.
Between 2003 and February 2011, the virus infected millions of birds in multiple countries. During this same period, 528 human cases of H5N1 infections were reported in 15 countries in Asia and Africa. Of these, 311 died.
As H5N1 has spread into flocks of wild birds and domestic fowl around the world, so too has the risk of spread to humans increased.
The situation in the USA
Since February 2022, the US Department of Agriculture (USDA) has confirmed the presence of H5N1-infected birds in 1376 poultry flocks, including 623 commercial flocks and 753 backyard flocks. More than 130 million birds from all 50 states have been affected.
The virus also is widely distributed across the wild bird population. The USDA has confirmed nearly 11,000 cases of bird flu in multiple species of wild birds since January 2022.
During this same period, the USDA confirmed H5N1 in 418 mammals across the country, including deer mice, house mice, domestic cats, mountain lions, coyotes, bottlenose dolphins, foxes, skunks, raccoons, black bears, and other species.
In March 2024, the USDA reported the first confirmed case of H5N1 infection in a dairy herd. As of December 31, 2024, there were 916 confirmed cases in cattle in 16 states: California, Colorado, Idaho, Iowa, Kansas, Michigan, Minnesota, Nevada, New Mexico, North Carolina, Ohio, Oklahoma, South Dakota, Texas, Utah, Wyoming.
In 2022, a poultry worker in Colorado was infected with H5N1—the first reported case of a human H5N1 infection in the USA. The next case was identified in March 2024.
From March 2024 to December 31, 2024, the US Centers for Disease Control and Prevention (CDC) has confirmed 66 cases of human infection with the H5N1 virus in 10 states: California (37), Colorado (10), Iowa (1), Louisiana (1), Michigan (2), Missouri (1), Oregon (1), Texas (1), Washington (11), Wisconsin (1).
Sixty-three of the 66 infected individuals worked either with dairy herds or in poultry farms and culling operations. No person-to-person spread has been reported.
The situation in Canada
Since December 2021, the Canadian Food Inspection Agency (CFIA) has detected 517 infected poultry premises (commercial and non-commercial) in nine provinces: Alberta (86), British Columbia (235), Manitoba (24), New Brunswick (2), Newfoundland and Labrador (2), Nova Scotia (8), Ontario (56), Québec (58), Saskatchewan (46).
Seventy-six of the 517 premises are currently infected. The other 441 have been cleared and released.
To date, the H5N1 virus present in US livestock (dairy cattle) has not been found in domestic poultry flocks in Canada.
To date, 3439 instances of confirmed or suspect H5N1 cases in wildlife (birds and mammals) have been reported to the Canadian Wildlife Health Cooperative. Infected wildlife have been found in every province and territory.
As of January 4, 2025, no cases of H5N1 infections in either humans or cattle have been reported in Canada.
What is being done to protect the milk supply?
In Canada
In May and June 2024, CFIA labs studied the effectiveness of milk pasteurization to inactivate the H5N1 virus. The study concluded that standard pasteurization procedures currently in use are effective.
Between March and September 2024, the CFIA tested 1,211 retail pasteurized milk samples from across Canada. All of the samples were negative for H5N1.
As of December 19, 2024, CFIA labs have tested 1,432 samples of raw milk arriving at processing plants in all provinces across Canada. All of the samples tested negative for H5N1.
In the USA
In May 2024, the FDA conducted a surveillance study of retail dairy products. All 297 samples were negative for the H5N1 virus.
In June 2024, the FDA released the results of its study on the inactivation of H5N1 virus in milk by standard commercial pasteurization procedures. The report concluded that the commercial pasteurized milk supply in the US is safe.
In August 2024, the FDA released the results of a second surveillance study that included aged raw milk cheese, pasteurized fluid milk and products made from pasteurized milk, such as pasteurized cheeses, cream cheese, butter, and ice cream. All 167 samples were negative for H5N1.
In October 2024, the FDA invited states to participate in a voluntary “silo study.” Grade “A” raw cow’s milk from participating states intended to be pasteurized were be sampled from raw milk storage silos at dairy processing facilities, over a six-week period.
On December 23, 2024, the FDA announced that it would begin to collect and test aged raw cow’s milk cheese for the presence of viable H5N1 virus.
Several state departments of agriculture have initiated surveillance of raw milk for the presence of the H5N1 virus. In December 2024, the California Department of Public Health announced the recall of raw milk and cream from two producers of retail raw dairy products—Raw Farm, LLC and Valley Milk Simply Bottled—after finding viable H5N1 viruses in samples of the companies’ milk.
Finally, on December 6, 2024, the USDA announced a new National Milk Testing Strategy. As part of the strategy, the USDA announced it would immediately begin testing of raw milk silos at dairy processing facilities.
How to protect yourself from bird flu
The CDC recommends the following precautions:
- Protective actions around wild birds Avoid direct contact with wild birds and observe them only from a distance, if possible. Learn more.
- What to do if you find a dead bird Avoid contact with wild or domestic birds that appear ill or have died and call to report sick or dead birds. Learn more.
- Protective actions around other animals with H5N1 bird flu Avoid unprotected exposure to infected live or dead animals or surfaces contaminated by them. Learn more.
- Protective actions if you work with potentially infected dairy cattle Avoid unprotected direct physical contact or close exposure with cattle and materials potentially infected or confirmed to be infected with HPAI A(H5) virus. Learn more.
- Consuming Milk People should not eat or drink raw milk or products made with raw milk. Choosing pasteurized milk is the best way to keep you and your family safe. Learn more.
- Preparing food It is safe to eat properly handled and cooked poultry in the United States. There are recommendations around products from other animals with H5 virus infections, including cattle and milk. Learn more.
- Traveling to other countries CDC does not currently recommend any travel restrictions related to bird flu to countries affected by bird flu in birds, other animals or people. Learn more.
- If you have contact with infected birds or other animals and become sick Learn what to do if you have contact with infected birds or other animals and become sick. Learn more.
- Clinicians can visit CDC’s avian influenza (bird flu) information for health professionals for the latest guidance. Learn more.
- Public health professionals and laboratorians can visit CDC’s avian influenza (bird flu) information for public health partners for the latest guidance. Learn more.
- Get a seasonal flu vaccine Seasonal flu vaccination will not prevent infection with bird flu viruses, but can reduce the risk of getting sick with human influenza viruses and thus the risk for seasonal and bird flu co-infection. Learn more.
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