H5N1 Bird Flu Detected in Dairy Cows: What Scientists Know

The detection of Highly Pathogenic Avian Influenza (HPAI), specifically the H5N1 strain, in dairy cattle across the United States marks a significant and unexpected shift in viral behavior. For decades, scientists monitored this virus primarily in poultry and wild birds. The confirmed spread to livestock raises urgent questions about food safety, animal health, and the potential for human transmission.

The Unprecedented Jump to Cattle

In early 2024, the United States Department of Agriculture (USDA) confirmed a surprising development: dairy cows in Texas and Kansas tested positive for the H5N1 virus. This was the first time this specific influenza strain had been detected in cattle. Since the initial discovery, the virus has been identified in herds across multiple states, including Michigan, Idaho, New Mexico, Ohio, North Carolina, and South Dakota.

This event is biologically significant because cattle were not previously considered a likely host for this type of influenza A virus. The specific strain identified is H5N1, clade 2.3.4.4b. This variant has been circulating globally in wild birds since 2020 and has caused mass mortality in poultry and various mammal species like seals and foxes. Its ability to infect cows suggests the virus is adaptable and finding new mammalian pathways to survive.

Symptoms in Infected Cows

Unlike chickens, which often die rapidly from the virus, dairy cows appear to be more resilient. The mortality rate in cattle is low, and most infected animals recover within a few weeks with supportive care. Farmers and veterinarians have noted specific clinical signs in affected herds:

Decreased Milk Production: There is a sudden and sharp drop in the amount of milk produced by the herd.
Abnormal Milk Quality: The milk from sick cows often becomes thick and discolored, resembling colostrum.
Reduced Appetite: Cows eat significantly less and show signs of lethargy.
Fever: Affected animals run fevers and may exhibit dehydration.

Interestingly, the illness seems to affect older, lactating cows more severely than younger heifers or dry cows.

How is the Virus Spreading?

Understanding the transmission route is the top priority for the USDA and the Centers for Disease Control and Prevention (CDC).

Wild Birds as the Source

The primary vector remains wild migratory birds. Genetic sequencing of the virus found in cows is consistent with strains found in wild birds. Dead birds were reportedly found on several of the affected farms, suggesting the cows likely ingested the virus through contaminated feed or water sources.

Potential Cow-to-Cow Transmission

While the initial infections came from birds, there is evidence suggesting the virus may be spreading between cows. This transmission likely occurs mechanically rather than through the air. Scientists believe milking equipment acts as a vehicle for the virus.

The virus has been found in high concentrations in the milk of infected cows. If milking claws or lines are not thoroughly sanitized between cows, the virus can physically move from an infected udder to a healthy one. The movement of cattle between states has also correlated with the spread, reinforcing the need for strict biosecurity and testing before transporting livestock.

The Warning Sign: Farm Cats

One of the grim indicators of this outbreak was the impact on farm cats. On several affected dairies, cats that consumed raw milk or colostrum from sick cows died. The mortality rate among these cats was high (around 50 percent in some reports), and they exhibited severe neurological symptoms. This confirmed that the virus is present in the raw milk and can be fatal to other mammals that consume it.

Is the Food Supply Safe?

The most common concern for the general public regarding this outbreak involves the safety of milk and beef. The Food and Drug Administration (FDA) and USDA have been clear on this matter.

Commercial Milk is Safe

The commercial milk supply remains safe to consume. This is primarily due to pasteurization.

Pasteurization Effectiveness: This process involves heating milk to a specific temperature for a set period to kill harmful bacteria and viruses. The FDA has confirmed that standard pasteurization protocols effectively inactivate the influenza virus.
Diversion of Milk: Milk from sick cows is required to be diverted or destroyed. It does not enter the commercial food supply. Even if traces of virus were to slip through, pasteurization destroys them.

However, the FDA strongly advises against consuming raw (unpasteurized) milk. The high viral load found in the milk of infected cows poses a genuine risk to anyone drinking raw dairy products from affected herds.

Beef Safety

The USDA Food Safety and Inspection Service (FSIS) states that the meat supply is safe. Ground beef should always be cooked to an internal temperature of 160°F (71°C) to kill bacteria and viruses. Steaks and roasts should reach at least 145°F (63°C). There is currently no evidence that people can get infected by eating properly cooked meat from a healthy animal.

Human Risk and the Texas Case

The risk to the general public remains low. However, people who work directly with infected animals face a higher level of exposure.

In April 2024, a dairy worker in Texas tested positive for H5N1 after exposure to presumed infected cattle. This was only the second recorded human case of H5N1 in the United States.

The symptoms were mild:

The patient reported conjunctivitis (pink eye) as the only symptom.
They did not experience respiratory distress or pneumonia.
The patient recovered fully after antiviral treatment with oseltamivir (Tamiflu).

This case indicates that while the virus can jump to humans, it has not yet mutated to spread easily between people. The CDC continues to monitor the situation and analyzes the virus for any genetic changes that would increase human-to-human transmissibility.

Surveillance and Prevention

To contain the spread, the federal government has implemented new rules. As of late April 2024, the USDA requires mandatory testing for H5N1 in dairy cattle moving across state lines. Positive results restrict the movement of the herd until they recover. This helps prevent the virus from traveling to new regions via cattle transport.

Frequently Asked Questions

Can I get bird flu from drinking milk? No, provided you drink pasteurized milk. The pasteurization process kills the H5N1 virus. However, you should avoid raw milk, as live virus has been detected in unpasteurized samples from infected cows.

Does this affect egg prices or availability? While this specific article focuses on dairy cows, H5N1 outbreaks in poultry flocks have historically impacted egg prices. However, the infection in cows is separate. The dairy cow infections themselves do not directly impact egg supply, though the same virus circulating in wild birds poses a concurrent risk to poultry farms.

What should I do if I find a dead bird? Do not touch it. State wildlife agencies and the USDA track bird deaths to monitor the virus. Report the finding to your local state veterinarian or wildlife agency so they can collect it for testing if necessary.

Is the virus airborne between cows? Current evidence suggests the virus in cows is not spreading effectively through the air (respiratory droplets) like it does in humans or pigs. The primary route appears to be physical contact with contaminated milk or milking equipment. This limits the speed of spread compared to an airborne respiratory virus.