Study links H5N1 to stranded porpoises and dolphins in Chile

A new study in Frontiers in Veterinary Science adds stranded porpoises and dolphins in Chile to the growing list of mammals affected by highly pathogenic avian influenza H5N1. The paper reports H5N1 detection in five stranded cetaceans along the Chilean Pacific coast, including two porpoises and three dolphins, during the country’s major 2022-2023 wildlife outbreak. The authors say the findings point to a likely epidemiologic link between cetacean strandings and the broader H5N1 wave in marine birds and pinnipeds, even if the virus’s exact pathogenic role in these animals remains unresolved. (frontiersin.org)

The backdrop is Chile’s unusually severe marine wildlife event. Earlier Frontiers research found the virus spread roughly 4,000 kilometers along Chile in about four months after December 2022, with infections reported in wild birds, domestic birds, and at least five marine mammal species. That same analysis described unprecedented mortality of more than 100,000 wild animals in Chile, including about 20,000 marine mammals, during the outbreak period. Chile’s human health authorities and WHO also linked the country’s first human H5N1 case in March 2023 to environmental exposure in an area with large numbers of dead wild birds and marine mammals, highlighting how wildlife events can spill into broader One Health concerns. (frontiersin.org)

In the new cetacean paper, four animals were identified through external swab testing, while a fifth, a long-beaked common dolphin, was only confirmed after internal tissues were tested at necropsy. That dolphin’s lung and brain were PCR-positive, and histopathology showed mild leptomeningitis consistent with lesions reported in H5N1 infection, although immunohistochemistry was negative. That detail matters because it suggests field swabbing alone may miss some infected animals, especially when infection is centered in internal organs or the central nervous system. (frontiersin.org)

The Chile findings also fit a wider regional and global pattern. WOAH states that clade 2.3.4.4b has caused significant mortality in wild birds worldwide and marine mammals in South America since 2021, and it now treats H5N1 in mammals as a meaningful animal health, biodiversity, and zoonotic issue. PAHO and WOAH reporting has tracked mammalian outbreaks across the Americas, while broader summaries of the panzootic now include cetaceans such as porpoises, common dolphins, bottlenose dolphins, and Chilean dolphins among affected species. (woah.org)

There’s also some practical field perspective behind the paper. Chile’s fisheries agency, SERNAPESCA, had already reported H5-positive dolphins during the 2023 response and warned of a sharp rise in dead stranded marine animals during the outbreak. Separately, WOAH’s marine mammal field guide, published in 2024 and co-authored by Mauricio Ulloa and other wildlife experts, stresses that all H5N1 strains should be treated as zoonotic risks and outlines biosecurity, sampling, and carcass disposal measures for responders. While I didn’t find a fresh independent expert quote reacting specifically to this paper, the institutional response has been consistent: unusual marine mammal strandings during H5N1 activity should be approached as both diagnostic opportunities and occupational exposure events. (sernapesca.cl)

Why it matters: For veterinarians, diagnosticians, wildlife clinicians, and public health partners, this paper is less about companion animal risk than about surveillance blind spots and response protocols. It reinforces that H5N1 investigations in marine mammals may require more than superficial sampling, that neurologic tissues can be important, and that strandings should be interpreted in the context of concurrent bird and pinniped mortality. It also supports a One Health approach: wildlife surveillance, necropsy capacity, PPE use, and reporting pathways all matter when a virus with known zoonotic potential is moving through mixed-species coastal ecosystems. (frontiersin.org)

The study is careful not to overclaim. The authors note that only a limited number of necropsies were performed, so they can’t definitively assign H5N1 as the cause of death in every stranded cetacean. That restraint is important, because marine mammal strandings are multifactorial, and positive PCR results don’t always settle causation. Still, the clustering of positive cetaceans alongside elevated mortality in birds and pinnipeds makes the association hard to ignore. (frontiersin.org)

What to watch: The next step is deeper characterization, especially more systematic necropsies, tissue-based testing, and viral sequencing to determine how often cetaceans are truly diseased by H5N1 versus incidentally exposed, and whether any mammal-adaptive changes emerge in these marine spillover events. (frontiersin.org)