Avian Influenza: Dogs and Cats at the Center of a New Zoonotic Front

A report highlights the role of pets in the evolution of influenza A viruses and the risk of a pandemic. For a long time, dogs and cats were spared from the circulation of influenza viruses. Influenza viruses were prevalent among wild birds, in poultry and pig farms, and, of course, among humans. However, since the early 2000s, pets have become full-fledged players in the ecology of influenza A, with a risk potential that extends far beyond the veterinary sphere. The presence of canine influenza viruses and the increasing detection of highly pathogenic avian influenza viruses in cats have raised concerns about their potential role as intermediate hosts in the emergence of pandemics. The authors summarize 20 years of research on influenza viruses in dogs and cats, particularly the H3N2 (canine) and H5N1 (highly pathogenic avian influenza) subtypes. On the one hand, these viruses demonstrate a growing ability to adapt to mammalian hosts at the human-animal interface, in settings where contact is daily and prolonged. On the other hand, most of the observed indicators suggest a real but still largely manageable risk, provided that this reservoir is taken seriously within a “One Health” framework.  

Dogs: An Avian Virus That Has Become Endemic

The first turning point occurred in dogs. In 2004, an H3N8 influenza virus of equine origin was identified in racing greyhounds in the United States, with dog-to-dog transmission. In 2007, an H3N2 virus of avian origin emerged in dogs in South Korea, likely due to exposure to infected poultry. The newcomer succeeded where H3N8 had failed: it adapted, became stably transmissible, and established itself as an endemic virus in East Asia, causing epidemic outbreaks in animal shelters, boarding facilities, and dog breeding operations. Introduced to North America in 2015, this canine H3N2 triggered several outbreaks in U.S. shelters and kennels before disappearing locally, but it continues to circulate and re-emerge through successive reintroductions from Asia. The authors note that, since 2022, the H3N2 influenza virus has been the only specifically canine influenza subtype still circulating worldwide. At the molecular level, this virus carries a series of mutations characteristic of adaptations to mammals: changes in the polymerase genes that enhance replication, alterations in the hemagglutinin that optimize binding to respiratory tract receptors, and modifications to proteins that promote immune evasion… In other words, the dog is no longer merely a collateral victim of an avian influenza virus; it now harbors its own influenza lineage.  

Cats: H5N1, the looming shadow of a panzootic outbreak

In cats, the scenario is different and more concerning. The H3N2 virus has not managed to establish itself long-term. However, cases of infection with the highly pathogenic H5N1 virus have been on the rise since the emergence of clade 2.3.4.4b, which is responsible for the current global panzootic outbreak. Outbreaks, sometimes fatal, have been reported in domestic cats in Europe, Asia, and North America, often with severe neurological symptoms. The study notes that exposure occurs primarily through food and the environment. Several outbreaks in Poland, South Korea, and elsewhere have been linked to diets containing raw poultry: in some cases, the H5N1 virus was detected directly in cat food made from chicken or duck meat. In 2024 and 2025, clusters of cat deaths in the United States were linked to the consumption of raw milk from infected dairy cows, confirming that cats primarily contract the infection through their diet. Outdoor or stray cats become infected by hunting or consuming the carcasses of infected wild birds, or even by frequenting environments contaminated by their feces. A serological survey conducted in France between 2023 and 2025, cited by the authors, detected anti-H5 antibodies in approximately 2% of outdoor cats, with an increased risk among stray and hunting cats—a sign of infections that often go unnoticed.  

The Human-Animal Interface as a Source of Viral Hybridization

Virologists are concerned about the viral ecosystem harbored by infected animals. Dogs and cats share the same living space as humans, with close contact that bears no resemblance to that found in a breeding facility or herd. They may be exposed to avian viruses through their food or the environment, but also to human viruses carried by their owners, as seen during the 2009 H1N1 pandemic, with documented transmissions from humans to cats or dogs. The theoretical risk is well understood: if an animal is co-infected with an avian influenza virus and a human virus, the eight segments of the influenza virus genome can recombine to generate a hybrid virus, potentially possessing both a strong adaptation to the human respiratory tract and genes of avian origin against which our herd immunity is weak. For the time being, the authors emphasize, no influenza virus of this type has emerged in dogs or cats. However, several so-called adaptive mutations observed in feline and canine isolates are the same as those already associated with greater affinity for mammals in other influenza lineages. The study, however, qualifies this alarming finding. While precisely documented, cases of transmission from pets to humans remain rare, such as the episode involving the H7N2 virus transmitted by cats to healthcare workers in the United States. The main risk today lies in the silent accumulation of mutations and segments of diverse origin in hosts closely related to humans.  

Raw food diets, shelters, veterinary clinics: high-risk interfaces

Beyond the molecular mechanisms, the article highlights a few key points. Raw food diets are singled out. Diets based on raw meat or unpasteurized milk—which are very popular among some pet owners—provide the virus with a prime entry point, via poultry meat from slaughterhouses affected by H5N1, raw milk from infected dairy herds, frozen products in which the virus can persist for weeks, and so on. Several recent incidents (recalls of batches of raw cat food in the United States, cat deaths following the consumption of contaminated raw milk) confirm these concerns. Another high-risk setting: high-density dog shelters, boarding facilities, and dog breeding facilities. In these settings, the canine H3N2 virus spreads very efficiently through respiratory transmission, via aerosols and contaminated surfaces. A single introduction is often enough to trigger an outbreak. The authors note that this virus remains, at this stage, largely confined to dogs, but that each outbreak provides another opportunity for the virus to further adapt to mammals. Veterinary clinics also play an ambivalent role. They serve as sentinels—since they receive sick animals, collect samples, and can sequence viruses—but they are also sites of potential viral spread if biosecurity measures are inadequate. Hence the call to systematically include influenza A in respiratory diagnostic tests for domestic carnivores when the situation warrants it.  

Monitor Without Causing Alarm

The authors advocate for targeted surveillance of the highest-risk interfaces: supply chains for raw pet food, high-density shelters and boarding facilities, dairy farms exposed to H5N1, and veterinary clinics in areas heavily affected by avian influenza. For pet owners, the message remains simple and practical: avoid feeding dogs and cats raw poultry meat or raw milk during periods of high H5N1 virus circulation, limit unsupervised outdoor access in areas where dead wild birds are found, and consult a veterinarian promptly if unusual respiratory or neurological signs appear, especially if the animal lives near poultry farms or lakes frequented by waterfowl. For public health authorities, including pets in influenza A risk management scenarios does not mean opening a new front, but rather acknowledging the obvious: in a household where humans, dogs, and cats live together, an influenza virus is capable of conducting cross-species transmission and infecting all of these potential hosts. Ignoring this link, at a time when H5N1 is infecting mammals, would be a strategic mistake.