No evidence of influenza A virus infection in marine mammals stranded in Basque Country coast (Northern Spain) in the context of H5N1 clade 2.3.4.4b expansion

Influenza A infection has been frequently detected in marine mammals causing different grade mortality events. In the last years, the highly pathogenic avian influenza (HPAI) H5N1 virus (Clade 2.3.4.4b) has been rapidly expanding and infecting a new variety of avian and mammal species, including marine mammals. In this new epidemiological context, the objective of this work was to evaluate the influenza A virus infection of marine mammals stranded in the Basque Country coast. 39 marine mammals were studied (2012-2024), most of them (77%) being dolphins (Striped Dolphin, Common dolphin, and Common Bottlenose Dolphin). But including Harbour Porpoise, Long-finned Pilot Whale, Cuvier's Beaked Whale, Northern Minke Whale, Pygmy Sperm Whale and Grey Seal. At necropsy, samples were collected from the lung, the intestine, and the central nervous system when possible. During 2024, serum samples and oropharyngeal, blowhole/nasal and rectum swabs were also collected. Real-time RT-qPCR was applied for influenza A virus detection in tissue and swab samples and commercial ELISA was used to detect antibodies against influenza A viruses. All samples were negative by PCR and ELISA, even though we detected 32 wild birds (mainly Northern gannets and gulls) infected with HPAI H5N1 in the Basque Country between 2022 and 2023. Despite the negative results obtained, we consider the continuation of the monitoring of influenza viruses in marine mammals essential, establishing collaboration networks and systematized protocols that allow us to gain insight into the epidemiology of influenza viruses in these species.
Funding: MCIN/AEI/10.13039/501100011033, FEDER-UE, FSE+ (PID2023-149441OR-C31 and PRE2022-101762); Basque Government.

Ane López-Morales1, Denis Benito2, Xeider Gerrikagoitia1, Vega Alvarez1, Xabier Lekube2, Manu Soto2, Jose Luis Lavín1 y Marta Barral1 1 Animal Health Department. NEIKER – Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA). 48160 Derio (Bizkaia). SPAIN 2 Research Centre for Experimental Marine Biology & Biotechnology. University of the Basque Country (PiE-UPV/EHU). 48620 Plentzia (Bizkaia). SPAIN

Avian influenza in mammals, pandemic preparedness, and one health