Preprint: The canine respiratory epithelium is a permissive ecosystem for influenza interspecies transmission and emergence

 

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Until 2004, dogs were considered relatively immune to influenza, but that changed abruptly when an equine H3N8 virus spilled over to dogs at a Florida racetrack, and began its world tour.

Three years later, an avian H3N2 virus spilled over to dogs in South Korea, and spread across Asia, eventually arriving in the United States in 2015.

In 2010, in Morens & Taubenberger on Influenza’s History, we looked a a fascinating 11-page historical review of Influenza outbreaks amongst a variety of hosts (human, avian, equine, porcine, canine, etc.) going back more than 3,000 years by Jeffrey K. Taubenberger and David Morens.

They cited a number of pandemics where anecdotal accounts mentioned dogs falling ill, either before - or concurrent to - when human cases emerged.

Since then we've looked at a lot of studies on dogs and flu, including: 

• In late 2012, in China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs, we looked at a study that found a newly emergent avian origin H3N2 virus prevalent in pet and farmed dog populations in southern China.

• In 2015, in Korea Finds More Dogs With H5N8 Antibodies, we saw evidence of HPAI infection in dogs. 

• Also in 2014, in Study: Dogs As Potential `Mixing Vessels’ For Influenza - we looked at the ability of different influenza strains (canine, equine and human) to infect, and replicate in, canine tracheal tissues. 

• In 2015, researchers reported finding Influenza A(H6N1) In Dogs, Taiwan

• Again in 2015, in Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China, we looked at the discovery two H3N2 CIVs possessing high homology with human/swine influenza viruses.

• In 2023 we looked at a lengthy (57-page) preprint called Increased Public Health Threat of Avian-origin H3N2 Influenza Virus During Evolution in Dogs from researchers in China who warned on the continued evolution of canine H3N2, which appears to be moving towards becoming a more `humanized' virus.

• More recently (2025) we looked at A Brief History of Influenza A in Canines & Canadian Report On A Recent Fatal H5N1 Dog Infection.

While dogs are more apt to have less severe flu illness than cats - making infections easier to miss - there is little doubt they are susceptible.  Unknown, however, is whether they are mostly a dead-end host, or if they are capable to transmitting the virus to others. 

Today we've got a preprint from researchers in the UK which attempts to better understand the risks. Using canine lung explants, they find that dogs are a plausible host for influenza reassortment, as they contain both human-type (α2,6) and avian-type (α2,3) receptor cells.

The caveats being that this is an ex vivo study, and is subject to a number of limitations (see below), and there is currently no evidence that novel influenza viruses are spreading efficiently among canines. 

But the only constant with influenza viruses is that they change, making today's status tenuous at best.  Due to its length, I've only posted some excerpts. Follow the link to read the report in its entirety.  

The canine respiratory epithelium is a permissive ecosystem for influenza interspecies transmission and emergence
Hanting Chen, Jack Hassard, Jiayun Yang, Callum Magill, Toby Carter, Jean-Remy Sadeyen, Aimi Ito, Clio Duerr,  Hannah Rose Montgomery, Savitha Raveendran, Kieran Dee,  Maximillian N J Woodall, Grace B Tyson, Maria M Afonso, Verena Schultz,  Claire Mary Smith,  Margaret J Hosie, Stuart Haslam, Munir J Iqbal,  Pablo R Murcia

doi: https://doi.org/10.64898/2026.06.04.730051
This article is a preprint and has not been certified by peer review 

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Abstract

The outcome of virus spillover ranges from dead-end infections to pandemics and is underpinned by host-pathogen interactions as well as evolutionary and epidemiological processes. The emergence of novel influenza A viruses (IAVs) has been associated with reassortment events involving multiple species, highlighting the importance of reservoir and intermediate hosts in viral emergence.

Highly pathogenic H5N1 IAVs of the 2.3.4.4b genotype have caused a panzootic affecting a broad range of mammals. The role of dogs -arguably the most popular companion animal and a natural host of IAVs- in the ecology of IAVs under this new zooepidemiological scenario is unknown. To address this, we characterised the glycome of the dog respiratory epithelium, infected canine tracheal explants with multiple IAVs (including canine H3N2 and H3N8, equine H3N8, avian H3N8 and H5N1, swine H1N1, human H1N1 and H3N2, and bovine H5N1 viruses), and determined their cellular tropism.

We show that the respiratory tract of dogs presents abundant sialylated glycans known to act as IAV receptors. Further, most IAVs (including 2.3.4.4b viruses) infected and replicated in dog tracheas, targeting mainly ciliated cells. Serological testing showed evidence of influenza spillover infections in dogs from the UK.

Overall, our results show that the canine respiratory tract can provide a suitable environment for the generation of new IAVs. Given the multi-host contact networks of dogs in nature, they could act as recipients, bridging hosts, and/or mixing vessels for multiple IAV lineages, playing a central role in the ecology of influenza emergence.

(SNIP) 

Our results suggest that dogs could act as a bridging species for the emergence of novel IAVs, including the H5N1 2.3.4.4b genotype. Serological studies in North America and Europe show that hunting dogs are routinely exposed to H5N1 IAVs 53,54. 

Vaccination of high-risk dog subpopulations could reduce the risk ofinter species infections (avian-to-dog and dog-to-human) and should be considered as preventative measures. 

This study has various limitations. Tracheal explants represent a significant portion of the airways, but this experimental system does not include the upper respiratory tract, the bronchial tree, nor the pulmonary parenchyma, which are likely to exhibit different virus/host interactions due to the presence of different cell types.

Further, explants lack systemic responses that are normally mounted during viral infections. Despite these limitations, our results are consistent with observations reported in field studies 59,60 and experimental in vivo infections 26,27

In sum, influenza spillover and emergence require a succession of processes that occur at different scales8. As the canine respiratory tract is a suitable ecosystem for IAV infection and reassortment and dogs routinely interact with multiple species that support endemic IAVs, dogs could facilitate the flow of virus between sympatric species. Targeted approaches to reduce the risk of IAV infections in dogs should be part of preparedness efforts to control influenza cross-species switching. 

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