Global Seroprevalence and Prevalence of Influenza A in Dogs and Cats: A Systematic Review and Meta-Analysis
Influenza A virus (IAV), long recognized for its impact on human and animal health, has increasingly been identified in companion animals such as dogs and cats. While their role in the zoonotic transmission of IAV has often been underestimated, growing evidence suggests that these species may play a more significant part in the ecology of influenza viruses than previously thought.
A recent systematic review and meta-analysis, conducted in accordance with PRISMA guidelines, offers the most comprehensive global estimate to date of the prevalence and seroprevalence of IAV in domestic dogs and cats. The study synthesized data from 79 studies in dogs (n = 35,895) and 34 in cats (n = 2,882), providing critical insights into the geographical and temporal distribution of IAV among companion animals.
Prevalence and Seroprevalence: Key Findings
The pooled prevalence of active infection with IAV was estimated at 12.04% in dogs (95% CI: 3.96–23.28) and 1.73% in cats (95% CI: 0.00–7.10). Seroprevalence, reflecting prior exposure, was found to be 12.07% in dogs (95% CI: 4.4–22.49) and 7.39% in cats (95% CI: 3.17–13.12).
Significant geographic differences were observed. Dogs in the Americas and Asia showed higher prevalence rates compared to those in Europe. Additionally, infection in dogs was found to be more common during the spring and summer months, potentially reflecting seasonal dynamics of viral transmission.
Interestingly, meta-regression analysis revealed no significant associations between prevalence and factors such as clinical signs, ownership status, or broad geographic region. However, substantial heterogeneity among studies suggests that methodological variables—such as diagnostic techniques, sample types, or local epidemiological factors—may influence reported prevalence rates.
Virology and Cross-Species Transmission Potential
Influenza A viruses belong to the Orthomyxoviridae family and are characterized by a segmented, negative-sense RNA genome. The viral surface proteins hemagglutinin (HA) and neuraminidase (NA) define the subtype, with 18 known HA and 11 NA variants identified to date.
In dogs, several IAV subtypes have been documented, including H3N8, which originated from horses and was first identified in U.S. dogs in 2004, and H3N2, an avian-origin subtype first detected in Korea in 2006. Experimental infections have demonstrated canine susceptibility to avian subtypes such as H5N1, with viral shedding observed in respiratory secretions, raising concern over potential interspecies transmission—including to humans and poultry.
Cats, although historically considered resistant to IAV, are now recognized as potential reservoirs. Natural infections with pandemic H1N1 (2009) and experimental susceptibility to both human and avian subtypes (including H5N1, H7N3, and H9N2) have been documented. The role of felids in transmission is especially concerning given their close cohabitation with humans and other domestic animals, and their potential for acting as bridge hosts in zoonotic events.
Clinical and Epidemiological Implications
While clinical disease in infected dogs and cats may range from subclinical to severe respiratory illness, the broader implications lie in their epidemiological role. The capacity for influenza A viruses to mutate and reassort increases the risk of novel strain emergence—especially in multi-host environments.
Given the potential for zoonotic transmission, and the public health risks posed by highly pathogenic strains such as H5N1, ongoing surveillance in companion animals is essential. This study underscores the need for standardized seroepidemiological studies, including consistent diagnostic protocols and global data sharing.
Moving Forward: A One Health Approach
Influenza A virus is a prime example of a One Health challenge, where human, animal, and environmental health intersect. The study's findings reinforce the importance of including companion animals in IAV monitoring programs—not only to protect animal health but also to anticipate and mitigate zoonotic threats.
Veterinarians play a key role in this effort, through:
Encouraging reporting and testing of suspected influenza cases in pets.
Supporting surveillance initiatives and research collaborations.
Promoting biosecurity and vaccination strategies (where applicable).
Educating clients on the potential risks of interspecies influenza transmission.
As our understanding of IAV ecology evolves, so too must our strategies for prevention and control. Integrating dogs and cats into global influenza surveillance is no longer optional—it is a critical step toward better preparedness and a more comprehensive public health response.
