Recent studies have revealed that avian influenza (H5N1), commonly known as bird flu, can infect horses without causing noticeable symptoms.  Researchers from the University of Glasgow detected antibodies to the virus in blood samples from horses in Mongolia, indicating asymptomatic infections.

This discovery raises concerns about horses acting as silent carriers, potentially facilitating the virus’s spread to humans.  The close interaction between horses and humans, especially in regions where H5N1 is prevalent, could increase the risk of zoonotic transmission.  Additionally, there’s apprehension that co-infection with equine influenza (H3N8) might lead to viral reassortment, resulting in new, potentially more virulent strains.

While H5N1 primarily affects birds, its recent transmission to various mammals, including cows, tigers, pigs, seals, house cats, and polar bears, underscores its expanding host range.  In the U.S., human cases have been reported, and the virus’s spread to cattle has been documented.  Experts warn that H5N1 may be just one mutation away from enabling human-to-human transmission, which could have significant public health implications.

In response to these developments, health agencies are enhancing surveillance and preparedness efforts.  The UK Health Security Agency, for instance, has ordered vaccines targeting the H5 family of viruses to mitigate potential human outbreaks.

Given the evolving situation, it’s crucial for those in close contact with horses, particularly in areas with known H5N1 outbreaks, to implement stringent biosecurity measures and remain vigilant for any signs of illness in animals.  Ongoing research aims to further understand the implications of H5N1 infections in horses and the potential risks to human health.

Sources:

Damdinjav, B., Raveendran, S., Mojsiejczuk, L., Ankhanbaatar, U., Yang, J., Sadeyen, J….Murcia, P. R. (2025). Evidence of Influenza A(H5N1) Spillover Infections in Horses, Mongolia. Emerging Infectious Diseases, 31(1), 183-185. https://doi.org/10.3201/eid3101.241266.

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