Bird flu jumps to dairy cows, sparking fears of future pandemics

AMES, Iowa — In a surprising twist of events, highly pathogenic avian influenza (HPAI) H5N1, a virus typically associated with birds, has made an unexpected leap to dairy cattle (cows) in the United States. This development, first detected in March 2024, has sent ripples through the scientific community and raised concerns about the virus’s ability to adapt and spread to new species — potentially threatening the health of humans and animals around the globe.

The H5N1 virus, part of the broader family of flu viruses, has long been a concern in the poultry industry and among wild bird populations. Its ability to cause severe disease and high mortality rates in birds has earned it the “highly pathogenic” designation. However, its recent appearance in dairy cows marks a significant shift in our understanding of the virus’s capabilities.

Researchers from Iowa State University, led by Rahul Nelli and Todd Bell, conducted a study to understand how this avian virus could infect and replicate in mammals like cows. Their findings, published in the journal Emerging Infectious Diseases, shed light on the molecular mechanisms that allowed this cross-species jump.

At the heart of the matter are structures called sialic acid receptors. These receptors, found on the surface of cells, act like docking stations for viruses. Different types of sialic acid receptors exist, and traditionally, bird flu viruses prefer to bind to one type (α2,3-linked), while human flu viruses favor another (α2,6-linked).

The research team examined tissues from infected dairy cows and found that, surprisingly, their respiratory tracts and mammary glands contained both types of receptors. This dual presence potentially explains why these cows were susceptible to the avian flu virus.

What’s particularly concerning is the discovery that the virus could replicate in the cows’ mammary glands, leading to its presence in milk. This finding has triggered public health alerts and new testing requirements for dairy products, especially unpasteurized milk.

The infected cows showed signs of illness, including reduced milk production and unusual changes in milk consistency. Upon closer examination, researchers found evidence of the virus in both the lungs and mammary tissues of the affected animals.

This unexpected jump from birds to dairy cattle raises questions about the virus’s ability to adapt and potentially infect other mammalian species, including humans. While there’s no immediate cause for panic, the situation underscores the importance of ongoing surveillance and research in the field of zoonotic diseases – those that can pass between animals and humans.

The discovery also highlights the interconnectedness of animal and human health, a concept known as “One Health.” As viruses continue to evolve and adapt, understanding these complex relationships becomes increasingly crucial for public health preparedness.

As research continues, scientists and health officials are working to develop strategies to monitor and contain the spread of this virus in dairy cattle populations. This event serves as a reminder of the ever-present potential for new infectious disease challenges and the need for continued vigilance and scientific inquiry.