EXPRESS: Highly pathogenic avian influenza H5 clade 2.3.4.4 and human new pandemic H1N1 virus exposure in domestic cats with outdoor access in the Netherlands in 2024.
Duijvestijn MBHM, Broens EM, Schuurman NNMPNMP, Vernooij JCM, van den Brand JMA, Wagenaar JA, van Kuppeveld FJM, Verhagen JH, de Haan CAM · Journal of Feline Medicine and Surgery · 9 June 2026
Outdoor domestic cats show increased HPAI H5 exposure; dual viral infections warrant reassortant monitoring.
This Dutch study investigated seropositivity to highly pathogenic avian influenza H5 clade 2.3.4.4 (HPAI H5) and pandemic H1N1 (H1N1pdm09) in 254 outdoor domestic cats during 2024. Sera were tested using ELISAs and hemagglutination inhibition assays. HPAI H5 antibodies were detected in 2.8% of cats by ELISA but none by HAI, while H1N1pdm09 antibodies were found in 5.5% overall with 2.8% confirmed by HAI. Notably, 0.79% of cats showed dual seropositivity to both viruses. HPAI H5 prevalence in outdoor cats exceeded previous findings in domestic cats with unknown outdoor access (0.46%) but remained lower than in rural stray cats (11.8%). These findings suggest outdoor access increases HPAI H5 exposure risk in domestic cats and highlight their potential role as mixing vessels for influenza viruses with zoonotic implications.
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