Highly pathogenic avian influenza (also known as HPAI or bird flu) has been detected on a dairy farm in Colorado, making it the ninth state where cases have been confirmed. The U.S. Department of Agriculture’s National Veterinary Services Laboratories confirmed the virus was in a herd in northeastern Colorado on April 25, 2024.
This farm is one of 35 dairy farms across the U.S. where cases of bird flu in cattle have been confirmed as of May 7, 2024, according to the USDA.
Bird flu is not new to Colorado. The state experienced an outbreak in poultry that began in 2022. Since then, 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 last detection occurred in February 2024.
But this is the first time this disease has sickened cattle in Colorado.
I am a veterinarian and epidemiologist at Colorado State University studying infectious diseases in dairy cows. I spent years on the USDA incident management team working on numerous cattle and poultry disease outbreaks, and I am leading efforts to investigate this new outbreak at Colorado State University.
First cases of bird flu in cattle
Bird flu was first detected in dairy cattle in Texas and Kansas in March 2024.
Colorado State University faculty responded to the outbreak by forming a multi-state group of state departments of agriculture, USDA and other universities to gain a better perspective on how this virus is transmitted between farms and among cows. The team is coordinating the sampling and testing of sick and healthy cows on affected farms to understand which animals shed the virus, i.e. how long they are more likely to shed the disease.
We are also working to identify mitigation steps that will help control this disease. Our network of animal health experts works with dairy producers and keeps them informed with new data on a weekly basis.
Detection of bird flu in cattle
In February 2024, veterinarians and researchers began testing blood, urine, feces, milk and nasal swab samples from sick cows. The fact that the virus is most frequently detected in raw milk suggests that the disease may have spread to other cows during the milking process.
More recent laboratory tests also detected the virus in cows’ nasal secretions shortly before the virus appeared in raw milk.
In late April, the U.S. Food and Drug Administration and USDA began testing commercial milk samples. To date, authorities have not detected any live virus in these samples.
This is to be expected because the pasteurization process, which heats milk to a temperature of at least 161 degrees Fahrenheit (72 degrees Celsius) for at least 15 seconds, kills the virus. The pasteurization times and temperatures used in the United States are designed to kill bacterial pathogens, but they do not work against this virus.
Raw milk is not pasteurized, as the name suggests. The CDC has linked drinking raw milk to many foodborne illnesses, including E. coli and salmonella. The presence of the H5N1 virus, which causes bird flu, is an additional concern.
Dairy producers need to remove abnormal milk and milk from sick cows from the food supply to protect consumers.
In addition to the milk, the USDA Food Safety and Inspection Service also tested commercial ground beef samples from states where sick cows were found. As of May 1, 2024, the virus was not detected in beef.
Slowing the spread of the disease
At this early stage of the epidemic in dairy cows, researchers do not know exactly how bird flu spreads in cattle; therefore, recommendations for controlling avian influenza may change as more is learned.
I have seen many infected cows and they look dull and depressed, similar to what humans feel during a viral infection. Most infected cows have symptoms similar to those of people with the flu, such as fever.
Many dairy producers separate sick cows from healthy ones in hospital pens so that sick cows can be easily monitored and treated.
Since the virus is also found in nasal secretions in early infection, water tanks used for the herds’ drinking water are likely to be the source of infection. Farmers should continue to clean these tanks at least weekly, or even more frequently in hospital pens, as a best practice.
Infected cows can recover
The good news is that most cows recover. They respond to anti-inflammatory medications and oral fluids like a person with the flu.
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 often slaughtered for beef.
Since the virus is most frequently detected in the milk of sick cows, our team recommends that dairy producers continue to follow best milking practices on the dairy farm; This includes disinfecting the cow’s teats before and after milking, even in healthy cows.
Only one case of human conjunctivitis due to bird flu was reported in a dairy farmer in Texas in late March. The worker was likely exposed through direct contact with milk from an infected cow or by rubbing his eyes with hands or gloves that came into contact with contaminated milk. The CDC recommends that farm workers use personal protective equipment, including eye protection, when in direct or close physical contact with raw milk.
How can dairy farmers protect herds?
Viruses can reach farms through the movement of cattle, people, vehicles, equipment and wild birds.
The U.S. dairy industry has a Safe Milk Supply Plan to address foreign and emerging dairy diseases such as avian influenza. The plan calls for increased biosecurity practices on farms during disease outbreaks.
Biosecurity practices include limiting the movement of cattle on and off the farm, allowing only essential personnel to access cattle, preventing vehicles and equipment from other farms from entering cattle areas, and cleaning and disinfecting vehicles entering and exiting dairy farms. Following these practices will greatly reduce the likelihood of the virus entering new flocks.
Birds also carry the virus. They are more difficult to control on dairy farms due to their easy access to feed and water. State and federal fish and game agencies and wildlife agencies are working with farmers to reduce the risk of diseases spread by wild birds. These include programs that limit the number of birds attracted to dairy farms while respecting rules that protect these species.
Producers who observe cows showing clinical signs of avian influenza should notify their veterinarian so that appropriate tests can be performed to confirm the presence of avian influenza. If the test result is positive, the laboratory that performed the test must report it to the USDA. As the 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 news organization providing facts and authoritative analysis to help you understand our complex world. Written by Jason Lombard Colorado State University
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Jason Lombard receives funding from USDA. He is a member of the National Mastitis Council and the American Cattle Practitioners Association. He is a former USDA employee.