Cats as sentinels of mammal exposure to H5Nx avian influenza viruses: a seroprevalence study, France, December 2023 to January 2025.

Circulation of clade 2.3.4.4b highly pathogenic avian influenza H5Nx viruses has intensified in recent years, increasing epizootics and mammalian exposure. Cats, bridging wild and domestic environments, are key for studying cross-species transmission. To assess their exposure in France, we screened 728 outdoor cats (December 2023-January 2025). Seropositivity was 2.6% (19/728), with an estimated seroprevalence at 1.8%. Absence of hunting behaviour was a significant protective factor. These findings highlight high recent exposure and the need for targeted surveillance in cats.