Influenza A (H6): An Underestimated Avian Influenza Virus That Is Now Causing Concern Among Experts

While global attention is focused on H5N1 avian influenza and its recent outbreaks in cattle herds and among humans, another strain is now drawing the attention of the scientific community: the influenza A virus of subtype H6. Classified as a so-called low pathogenic avian virus, it has remained on the periphery of public health concerns for decades. However, new data show that it has significant zoonotic potential and could pose a substantial threat to public health.  

Global and Increasing Circulation

A study published in August 2025 in the Journal of Infection analyzed more than 3,500 genetic sequences of the H6 virus from the international GISAID database. The results show that this subtype is currently circulating in at least 40 countries, with a predominance in Asia, which accounts for nearly 70% of the isolates. China leads by a wide margin, followed by the United States and Vietnam. Since the virus was first detected in turkeys in the United States in 1965, its spread has followed an upward trend, peaking in 2014.  

Multiple Hosts and Cross-Species Transmission

One of the key findings of this research is the diversity of infected hosts. The H6 virus is widely present in domestic and wild birds, but it has also been found in poultry. More concerning, a few isolates have been identified in mammals such as pigs and rats. Cross-species transmission has already been observed in humans: the first case of H6N1 infection was confirmed in Taiwan in 2013. A serological survey conducted in China among nearly 16,000 workers exposed to poultry revealed more than 60 positive samples, confirming the existence of zoonotic transmission.  

Well-Established Transmission Routes

The researchers used phylodynamic analysis to better understand the circulation patterns of this virus. Their results highlight two major lineages—Eurasian and North American—as well as about fifteen plausible interspecies transmission routes. Waterfowl, both domestic and wild, appear to be key intermediate hosts, facilitating the spread to other species. The analyses also reveal well-established migratory routes connecting China, East Asia, South Asia, Europe, and North America.  

A zoonotic risk that can no longer be ignored

Taken in isolation, human cases linked to H6 may seem insignificant. But their recurrence, combined with the demonstrated ability of certain variants to bind to human receptors, necessitates a reassessment of the risk. For the study’s authors, the H6 virus is a serious candidate for future episodes of spillover—that is, sustained transmission from animals to humans. They call for strengthening global surveillance within a “One Health” framework to anticipate developments in this inconspicuous but potentially dangerous virus.