Introduction
Influenza A virus (IAV) is a zoonotic pathogen with pandemic potential that infects a wide range of species, including companion animals. Although surveillance efforts have primarily focused on North America, Europe and Asia, data from South America remain scarce. This study evaluated the molecular and serological evidence of IAV circulation in dogs and cats from shelters and multi-pet households in central Chile.

Methods
Between June and November 2020, oropharyngeal swabs and serum samples were collected from dogs and cats in shelters and multi-pet households in central Chile. Samples were analysed by RT-qPCR, NP-ELISA and hemagglutination inhibition assay.

Results
IAV was detected by RT-qPCR in 3.2% (11/342) of dogs (95% CI: 1.3%–5.1%) and 5.8% (4/69) of cats (95% CI: 0.3%–11.3%). Serological analysis revealed IAV seropositivity in 55.5% (96/173) of dogs (95% CI: 48.1%–62.9%) and 50.0% (10/20) of cats (95% CI: 28.1%–71.9%). Additionally, pdmH1N1 antibodies were detected in 26 animals (25.7%; 95% CI: 17.2%–34.2%) out of 101 NP-ELISA-positive serum samples, with higher median titres for cats (median?=?160) compared to dogs (median?=?20). Low-level antibody titres against Canine/H3N2 (range?=?10–20) were identified in three dogs (3.0%; 95% CI: 0.0%–6.3%), whereas no antibodies were detected against Canine/H3N8 or Avian/H3N6. No significant associations were observed between seropositivity and animal age, sex, origin or area.

Conclusions
This study presents the first report of IAV detection in cats in South America and highlights a high level of IAV exposure among companion animals in central Chile. These findings underscore the importance of including pets in IAV surveillance efforts under a One Health approach and highlight the need for expanded monitoring and genetic characterization of circulating strains to assess zoonotic risk.