H5N1 Bird Flu in Cattle

The emergence of Highly Pathogenic Avian Influenza (HPAI), specifically the H5N1 strain, in United States dairy cattle marks a significant biological shift that has captured the attention of virologists and agricultural officials alike. While bird flu has decimated poultry populations for years, its jump to cows was unexpected. This article outlines the current facts regarding the spread, the safety of the commercial milk supply, and what this means for human health.

The Unprecedented Jump to Mammals

In late March 2024, the United States Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC) confirmed a surprising development. Dairy cattle in Texas and Kansas tested positive for H5N1. This was the first time this specific influenza virus had been detected in cows.

Historically, cows were not considered susceptible to Highly Pathogenic Avian Influenza A viruses. The virus, identified as clade 2.3.4.4b, has been circulating globally in wild birds and poultry since 2022. However, the virus found a way to infect cattle, likely starting through contact with infected wild birds or their droppings contaminating feed and water sources.

Since the initial detection, the virus has spread well beyond the Texas panhandle. As of mid-2024, infections have been confirmed in dozens of herds across multiple states, including:

  • Texas
  • Kansas
  • Michigan
  • New Mexico
  • Idaho
  • Ohio
  • North Carolina
  • South Dakota
  • Colorado

This geographic spread suggests that the virus is not only jumping from birds to cows but also moving between cows. Evidence points to transmission through shared milking equipment or the movement of asymptomatic cattle between states.

Symptoms and Impact on Dairy Cows

Unlike poultry, where H5N1 acts as a swift and lethal plague requiring the culling of entire flocks, the impact on cattle is different. It is generally not fatal for cows. The USDA describes the illness in dairy cattle as distinct and manageable, though economically damaging for farmers.

Farmers should look for the following clinical signs, specifically in older, lactating cows:

  • Drastic Drop in Milk Production: This is often the first warning sign. High-producing cows suddenly produce very little milk.
  • Changes in Milk Consistency: The milk may become thick and discolored. It often resembles colostrum (the first milk produced after birth), appearing yellow or concentrated.
  • Reduced Appetite: Affected cows eat significantly less feed.
  • Lethargy and Fever: Animals appear tired and may run a fever.

Most cows recover with supportive care, including isolation and hydration, within two to three weeks. Because the cows recover, mass culling (killing animals to stop the spread) has not been the standard protocol for cattle as it is for chickens and turkeys.

Is the Milk Supply Safe?

The most pressing question for consumers is whether the milk in their refrigerator is safe to drink. The Food and Drug Administration (FDA) has conducted extensive testing to answer this.

Commercial Milk is Safe The FDA and USDA maintain that the commercial milk supply is safe. This safety relies on pasteurization. Pasteurization is the process of heating milk to a specific temperature for a set period to kill harmful bacteria and viruses.

In April and May 2024, the FDA released results from a national survey of retail dairy products. While they found genetic fragments of the H5N1 virus in roughly 20% of retail milk samples, further testing confirmed that these were merely non-infectious remnants. The pasteurization process effectively inactivated the virus. Finding viral fragments is evidence that the virus was present in the raw milk, but the heating process successfully destroyed its ability to infect humans.

The Danger of Raw Milk The guidance changes completely regarding unpasteurized products. The FDA strongly advises against consuming raw milk or raw milk cheeses. Cats living on dairy farms that consumed raw milk from infected cows suffered severe illness and high mortality rates. This indicates that the live virus in raw milk is dangerous to mammals.

Human Health Risks and Worker Safety

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

Since the outbreak began in cattle, there have been confirmed cases of human infection linked specifically to dairy farms. For example:

  • Texas Case (April 2024): A dairy worker developed conjunctivitis (pink eye) after exposure to sick cows. The patient was treated with oseltamivir (Tamiflu) and recovered without complications.
  • Michigan Cases (May 2024): Two workers tested positive. One experienced only eye symptoms, while the other reported upper respiratory symptoms such as a cough.

These cases suggest that while the virus can jump to humans, it has not yet mutated to spread easily from person to person. The CDC continues to monitor the virus for any genetic changes that would increase the risk of human-to-human transmission.

Government Response and New Regulations

To contain the spread, the federal government has implemented strict measures. The USDA’s Animal and Plant Health Inspection Service (APHIS) issued a Federal Order in April 2024.

Testing Requirements: Lactating dairy cattle must test negative for Influenza A viruses before they are moved across state lines. If a test comes back positive, the animal cannot be moved until it has recovered and completed a waiting period.

Financial Support: The USDA has allocated funding to assist affected farms. This includes financial support for:

  • Heat treatment of waste milk.
  • Veterinary costs for testing.
  • PPE (Personal Protective Equipment) for farm workers.
  • Biosecurity planning to prevent future outbreaks.

Beef Safety

While the focus has been on milk, consumers also worry about beef. The USDA’s Food Safety and Inspection Service (FSIS) has tested ground beef samples from retail outlets in states with confirmed outbreaks. All samples tested negative for the virus.

Furthermore, cooking meat to a safe internal temperature serves as a final barrier against pathogens. Ground beef should always be cooked to an internal temperature of 160°F (71°C), which is sufficient to kill the H5N1 virus.

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, health agencies strongly warn against drinking raw (unpasteurized) milk, as it may contain live virus.

What happens if a cow tests positive? The cow is isolated from the rest of the herd to prevent spread. Her milk is diverted from the food supply and destroyed. The cow is given supportive care and usually recovers within a few weeks.

Are eggs safe to eat? Yes. While the virus affects poultry, proper cooking of eggs (cooking until the yolk and white are firm) kills bacteria and viruses. The FDA and USDA monitor poultry flocks and infected flocks are not used for food production.

Is there a vaccine for cows? Currently, there is no approved H5N1 vaccine for dairy cattle in the United States. Several pharmaceutical companies and the USDA are researching potential vaccines, but biosecurity (cleaning boots, controlling traffic, isolating sick animals) remains the primary defense.

How is the virus spreading between cows? While the exact mechanism is still being studied, evidence suggests it spreads through direct contact and mechanical vectors. This includes shared milking machines that may transfer virus-laden milk from one cow to another, or workers carrying the virus on clothing and boots between barns.