Avian Flu: New Strain in China Infects Dogs and Poses a Potential Risk to Humans
A recent discovery from the Leizhou Peninsula in China has raised concerns about a new strain of avian influenza, H3N2, which appears to infect dogs more severely than before and has developed traits that make it more adaptable to humans.
A study published in Frontiers reveals that the common influenza A virus has jumped species, spreading from ducks to dogs. It has since recombined with other subtypes, increasing its ability to infect humans. While the virus is currently classified as low pathogenicity, scientists warn that H3N2 has already been circulating in China, South Korea, and the United States since at least 2023, with its current state remaining unknown. Researchers are now urging the establishment of a comprehensive surveillance system involving veterinary hospitals, shelters, and pet trade markets to monitor its evolution.
From Dogs to Humans?
The H3N2 virus has been present in dogs for decades, causing cold-like symptoms, coughing, and, in severe cases, death. However, recent mutations have made it capable of triggering intense respiratory symptoms and, in rare instances, neurological complications in humans.
Previously, it was believed that canine and human influenza viruses were distinct and could not infect each other. However, new evidence suggests otherwise.
Professor Zhao Zhihui of Guangdong Ocean University in Zhanjiang, China, explains: "The analysis of six isolated strains has shown that their genomes have reassorted with H1N3, H3N8, H5N6, H6N2, H7N7, and H9N2 subtypes. Our study reveals the health risks posed by H3N2 and highlights the importance of continuous monitoring of the influenza virus circulating in poultry."
The Evolution of H3 Strains
Until two decades ago, dogs and cats were thought to be largely immune to influenza A. That perception changed when hundreds of tigers in Southeast Asia died from H5N1 after consuming contaminated poultry. More recently, domestic cats have shown susceptibility to the highly pathogenic strain of avian flu that is spreading globally.
In dogs, concern arose after the equine influenza virus H3N8 mutated and spread among greyhounds at a Florida racetrack. Researchers believe that H3N8 was transmitted directly from horses to dogs without recombination, and it remains a canine-specific virus with no reported cases in humans.
However, a different strain—H3N2 avian influenza—has since become endemic in dogs in South Korea. Analysis of the original strain, identified in 2007, revealed that its genetic material closely matched that of poultry and pigeons infected in South Korea in 2003.
Dogs as "Mixing Vessels" for Influenza
Experts now believe that dogs could act as "mixing vessels" for different strains of influenza, potentially facilitating the evolution of new variants that could infect multiple species, including humans.
"H3N2 influenza viruses have been a major cause of outbreaks and have widely spread among humans since 1968," Chinese researchers note. "The H3N2 influenza subtype is present in humans, dogs, ferrets, pigs, and both domestic and wild birds. While currently classified as low pathogenicity, it actively circulates in human populations."
Recent studies have identified 12 avian-origin H3N2 strains isolated from dogs in northern China. Genetic analysis suggests that these strains originated from southern China and South Korea.
Increasing Risks for Humans
This newly identified H3N2 strain, which originated in ducks in Leizhou and later infected dogs, has acquired three additional human-like amino acid substitutions compared to previous strains. This suggests an evolutionary shift that could make it more dangerous for humans.
"These results indicate that H3N2 is evolving over time, and if it accumulates enough human-like mutations, it could gain the ability to spread efficiently among humans," the study warns.
While the precise impact of these mutations remains unclear, researchers emphasize that genetic changes are already facilitating viral replication in mammalian cells. "Our study indicates that H3N2 continues to circulate among dog populations in China, persistently acquiring human-like mutations, which poses a potential public health risk," concludes Professor Zhao Zhihui.
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