Highly pathogenic avian influenza (HPAI) has entered a concerning new phase, demonstrating its adaptability by spreading from birds to dairy cows. This marks the second recorded spillover of HPAI into dairy herds, highlighting the virus’s increasing ability to infect mammalian hosts.

Avian flu has been spreading at an increasingly alarming pace for the past year. It’s the infamous reason why eggs are so expensive. We have followed the virus since 2021, when it was detected in North American migratory birds. Over time, it mutated and changed, spilling over to dairy cattle between 2023 and 2024.

Now, it has happened again. According to a new technical brief from the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, avian flu has acquired a genetic change that makes it easier to jump to mammals.

From birds to cows

When a virus jumps from one species to another, it doesn’t necessarily mean it is well-adapted to the new host. Initial spillovers often result in limited infections, as the virus may struggle to replicate efficiently or spread. However, if the virus can sustain infections, it may accumulate mutations that improve its ability to replicate and transmit within the new species.

In January 2025, this strain was detected in dairy cattle in Nevada. These cases were first detected through routine milk sampling, not clinical symptoms. Initially, the infected cows showed no signs of illness. Unlike poultry, where HPAI outbreaks often cause mass die-offs, dairy cattle appear to be more resilient, allowing the virus to persist undetected for longer periods. This could create a hidden reservoir where further mutations could occur, increasing the risk of a zoonotic spillover to humans.

Only after HPAI was confirmed through genetic sequencing did farmers report unusual health issues in their herds. This silent transmission poses a major challenge to containment efforts.

The presence of the mutation in dairy cattle is a red flag for virologists and public health officials. While no human cases have been linked to this outbreak so far, the potential for HPAI to further adapt and become more infectious to mammals is a serious concern. The fact that this mutation has not been observed in wild birds or poultry but has emerged in cows suggests that once the virus enters a mammalian host, it may undergo further adaptations that make it more suited for mammalian transmission.

Can the virus jump to humans?

The virus has already been wreaking havoc on animal populations, leading to major culls of millions of animals — and counting. It’s also caused several human infections, including at least one severe case. But what is particularly concerning is that this variant, with the mammal adaptability, is now the dominant genotype in migratory birds.

The fact that it has successfully jumped into dairy cattle suggests that the virus is actively adapting to exploit new hosts. Given its rapid evolution, the possibility of future spillovers into other livestock or even humans cannot be ignored. Additionally, the silent nature of the infection in cattle suggests that the virus could circulate undetected for extended periods, increasing opportunities for further genetic changes.

If HPAI continues to evolve in dairy cattle or other mammals, it may acquire additional mutations that improve human infectivity or even enable human-to-human transmission, raising the risk of a future influenza pandemic. While there is no evidence yet of human-to-human spread, the threat is so great that we need to act preemptively.

This development underscores the need for rigorous surveillance, swift containment measures, and continued research into how HPAI is adapting. The virus’s ability to exploit new hosts is a stark reminder that nature is constantly evolving — and so must our efforts to combat emerging infectious diseases.