Understanding the Current Avian Influenza Outbreak in Dairy Cattle and Risk to the Public

A Q&A with AGNR’s Team of Experts

Image Credit: Edwin Remsberg

May 23, 2024

May 22, 2024, a second human case of avian influenza contracted from cows was confirmed in Michigan. This comes two months after avian influenza was confirmed on a farm in Texas for the first time ever in dairy cattle. Days later a dairy worker caught the disease from a sick cow, becoming the first person in the world confirmed to have contracted avian influenza from a mammal. Soon after, two farm cats contracted it from drinking raw milk from infected cows.

These are concerning developments, but the virus causing this current bird flu outbreak is not a broad threat to human health at this time. HPAI H5N1 as it is called remains primarily an animal illness. However, the CDC is watching the situation closely for signs that bird flu could evolve to pose a greater risk to humans.

We spoke with the following experts from AGNR’s Department of Veterinary Medicine to better understand this current outbreak and the potential risks to humans.

  • KC: Kristen Coleman researches airborne infectious diseases specializing in the surveillance, epidemiology, and transmission of respiratory viruses.(She also holds a faculty position in the UMD School of Public Health)

  • MG: Mostafa Ghanem is an epidemiologist and poultry specialist developing advanced techniques for surveillance, prevention, and control of infectious diseases.

  • JP: Jaekeun Park researches the mechanisms of infection and immune response to influenza viruses in lung tissue and is developing improved animal models for vaccine development.

  • NT: Nathaniel Tablante is a biosecurity expert with extensive experience in managing avian influenza in poultry.

How do people get Avian Influenza?

MG: Most human cases of Avian Flu have been from infected poultry, but people can get it through exposure to other infected animals or an environment or products contaminated with the virus like feathers and carcasses of infected birds or raw unpasteurized milk from infected cows.

How dangerous is it to humans?

KC: Although human infections appear to be rare at this point, infections with certain avian influenza viruses can be fatal. While some people experience mild symptoms, approximately half of the people reported to be infected with certain strains of avian influenza virus have died.

JP: This high mortality is related to specific lineages of avian influenza viruses within H5 HA and H7 HA subtypes. The HPAI H5N1 viruses currently present in the US belong to this particular H5 lineage. Human infections from other avian influenza virus subtypes have been reported to cause milder diseases.

Does it spread between humans?

JP: While there have been a few reports suggesting direct human-to-human transmission of different strains of avian influenza over the last two decades, those were presumably from close contact with an infected person.

Although sustained transmission from person to person has not been seen, and the chance seems to be low, the more exposures people have to the virus, the more opportunities the virus has to adapt to a human host.

Could the virus evolve to spread between humans?

KC: There are certain mutations in the virus genome that could make it easier for it to infect humans, and be transmitted between humans. For example, if the virus acquires the ability to readily infect certain cells in the human respiratory tract, it could spread from person to person through exhaled respiratory aerosols. This is known as airborne transmission and it is how other contagious respiratory illnesses, such as COVID, are spread.

Why has this suddenly become a problem? Has the virus changed?

JP: It is not clear how, but this virus acquired the ability to transmit more effectively among migratory birds, which made it more prevalent and significantly increased the likelihood of other animals being exposed through contact with migratory birds and their secretions, primarily feces. That had not happened at this rate before.

We have recently seen this virus spread within new host species, such as seals and cows. Studies are still underway to understand the mechanism behind this virus spreading within these species. While it is unclear if these developments increase the risk to humans, it is certainly an alarming trend, especially with new host species that have frequent human contact, such as cows.

MG: If the virus successfully maintains itself in cattle (rather than going extinct after several rounds of transmission), this could mean that it is one step closer to humans as it already made the jump to a mammal. Therefore, controlling the current outbreak in cattle and limiting further spread is the first line of defense to reduce the risk for humans.

Is bird flu only a concern on farms where cows are kept?

KC: While farms with infected cows have a higher risk to workers, the threat is not limited exclusively to farms or rural areas. Avian influenza circulates mostly in wild birds, and a recent study detected the virus in four species of birds collected in New York City. The USDA also has a list of over 200 mammals, such as opossums, squirrels, and skunks that have been affected.

MG: That being said the risk for the general public remains low according to CDC.

KC: In addition to cows, cats have also been getting infected. This can happen when a cat eats a sick or dead bird, or drinks contaminated raw milk from infected dairy cattle.

How can people protect themselves and their pets from the disease?

KC: Do not touch or allow your pet to touch sick or dead animals, and do not consume or feed your pet raw meat or milk. Also, do not let your pets roam unsupervised as they can come into contact with droppings from infected birds.

Dairy workers should practice strict biosecurity at all times, including strict hygiene and sanitation on the farm and when handling milk and milk products.

Is there a risk of catching bird flu by drinking milk and eating meat?

NT: There is no risk of humans catching flu from pasteurized milk or properly cooked meat. Pasteurization of milk and proper cooking of meat inactivates avian influenza. People should avoid handling or drinking raw and unpasteurized milk.

Do we have effective vaccines against the H5N1 strain?

MG: While there is not yet a vaccine for this specific flu strain in this outbreak, the World Health Organization (WHO) maintains a list of candidate vaccines that offer protection against closely related H5N1 and can be mass-produced. Additionally, some countries, including the United States, have stockpiles of vaccine doses for at-risk populations, such as front-line workers. The cases from animals and birds are being closely monitored and the virus is being studied for any changes that would make it more dangerous or less susceptible to current antiviral drugs or vaccines.