Colorado has highly pathogenic bird flu – also known as HPAI or bird flu – on a dairy farm, the ninth state with confirmed cases. The U.S. Department of Agriculture’s National Veterinary Services Laboratories confirmed the virus in a herd in northeastern Colorado on April 25, 2024.
According to the USDA, this farm is one of 35 dairy farms in the US with verified cases of bird flu in cattle as of May 7, 2024.
Bird flu is not new to Colorado. The state experienced an outbreak in poultry that started in 2022. Since then, the USDA’s Animal and Plant Health Inspection Service has reported that 6.3 million birds in nine commercial flocks and 25 backyard flocks have been affected by the virus. The most recent detection was in February 2024.
But this is the first time the disease has sickened livestock in Colorado.
I am a veterinarian and epidemiologist at Colorado State University focusing on infectious diseases in dairy cows. I have worked on a USDA incident management team for many years on multiple livestock and poultry disease outbreaks, and I am leading efforts at Colorado State University to study this new outbreak.
The first cases of bird flu in cattle
Bird flu was first identified in dairy cattle in Texas and Kansas in March 2024.
Colorado State University faculty responded to the outbreak by forming a multi-state group with state departments of agriculture, the USDA and other universities to gain a better perspective on how this virus is transmitted between farms and between cows. The team is coordinating sampling and testing of sick and healthy cows on affected farms to understand which animals are shedding the virus, making them more likely to spread the disease, and for how long.
We are also working to identify measures to control this disease. Our network of animal health specialists works with dairy producers and informs them weekly about new data.
Detecting bird flu in cattle
In February 2024, veterinarians and researchers began testing blood, urine, feces, milk and nasal swabs from sick cows. The virus was most commonly found in raw milk, suggesting the disease may have spread to other cows during the milking process.
More recent laboratory tests have also detected the virus in the nasal secretions of cows for a short time before the virus manifests itself in their raw milk.
In late April, the U.S. Food and Drug Administration and USDA began testing commercial milk samples. So far, authorities have not found any live virus in these samples.
That’s expected because the pasteurization process, which involves heating milk to at least 161 degrees Fahrenheit (72 degrees Celsius) for at least 15 seconds, kills the virus. Pasteurization times and temperatures used in the US are designed to kill bacterial pathogens, but they work against this virus.
Raw milk, as the name suggests, is not pasteurized. The CDC has linked drinking raw milk to many foodborne illnesses, including E. coli and salmonella. The presence of the virus that causes bird flu, H5N1, is an additional cause for concern.
Dairy producers are required to remove abnormal milk and milk from sick cows from the food supply to protect consumers.
In addition to milk, the USDA Food Safety and Inspection Service tested samples of commercial ground beef from states with sick cows. As of May 1, 2024, no virus had been found in beef.
Slowing the spread of the disease
At this early stage in the outbreak in dairy cows, researchers don’t know exactly how bird flu spreads among livestock, so recommendations for containing the flu may change as more is learned.
I have seen many infected cows and they look dull and depressed, similar to how humans feel during a viral infection. Many infected cows show symptoms similar to those of people with the flu, such as fever.
Many dairy producers separate sick cows into hospital pens, separate from healthy cows, so that sick cows can be easily monitored and treated.
Because the virus has been found in nasal secretions during early infection, it is possible that the herds’ drinking water tanks could be a source of infection. As a best practice, farmers should continue to clean these tanks at least weekly – and even more often in hospital cages.
Infected cows can recover
The good news is that most cows get better. Like people with the flu, they respond to anti-inflammatory medications and oral fluids.
A small percentage of cows develop secondary bacterial infections and die or are humanely euthanized. Some cows recover from the infection but stop producing milk and are removed from the herd and usually slaughtered for beef.
Because the virus is most commonly found in milk from sick cows, our team recommends dairy producers continue to follow best dairy farm milking practices, including disinfecting the cow’s teats before and after milking, even healthy cows.
In late March, only one case of human conjunctivitis due to bird flu was reported in a Texas dairy farmer. The worker was likely exposed through direct contact with milk from an infected cow or by rubbing their eyes with hands or gloves that had come into contact with contaminated milk. The CDC recommends that farmworkers wear personal protective equipment, including eye protection, when in direct or close physical contact with raw milk.
How dairy producers can protect herds
Viruses can enter farms through the movement of livestock, people, vehicles, equipment and wild birds.
The U.S. dairy industry has a Secure Milk Supply Plan that addresses foreign and emerging dairy diseases such as bird flu. The plan calls for better biosecurity practices on farms during disease outbreaks.
Biosecurity practices include limiting livestock movements on and off farms, allowing only necessary personnel to access livestock, preventing vehicles and equipment from other farms from entering livestock areas, and cleaning and disinfecting vehicles entering and leaving dairy farms. Following these practices should significantly reduce the opportunity for the virus to enter new herds.
Birds also carry the virus. They are more difficult to control due to easy access to feed and water on dairy farms. State and federal fish and game departments and wildlife agencies are working with farmers to reduce the risk of diseases spread by wild birds. These include programs to limit the number of birds attracted to dairy farms, while respecting rules protecting these species.
Producers who observe cows with clinical signs of avian flu should notify their veterinarians so that appropriate testing can be performed to confirm the presence of avian flu. If a test result is positive, the laboratory performing the test must report it to the USDA. As USDA and affected states continue to monitor the disease, an accurate estimate of affected farms will allow researchers to determine how the virus is spreading from farm to farm – and whether we are making progress in containing it.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Jason Lombard, Colorado State University
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Jason Lombard receives funding from USDA. He is affiliated with the National Mastitis Council and the American Association of Bovine Practitioners. He is a former USDA employee.