#17,743
Although we've known for decades that marine mammals (seals, whales, sea lions, otters, etc.) are susceptible to influenza viruses (see UK: HAIRS Risk Assessment On Avian Flu In Seals) - and have followed sporadic outbreaks (see here, here, here, and here) over the years - we've never seen anything like the losses due to HPAI H5 over the past 12 months in South America.Preprint: First Mass Mortality of Marine Mammals Caused by Highly Pathogenic Influenza Virus (H5N1) in South America
Chile: SERNSPESCA Reports > 4,300 Marine Animal Deaths
Argentina: SENASA Reports More Sea Lion Deaths From H5N1 - Issues Health Guidelines
Hundreds of thousands of birds have died, along with tens of thousands of marine mammals. But the numbers we get are undoubtedly major under-counts, as there are thousands of miles of remote, and hard to access shorelines up and down the South American Continent, and many mammals likely die unnoticed at sea.
Direct contact with infected birds is high on the list, but there are other pathways, including the concerning possibility of mammal-to-mammal transmission. Parsing out whether - or how often - that is happening, is no easy task.
Another concern, as we've seen with spillovers of HPAI H5 into terrestrial mammals (see Pathogens: Zoonotic Mutation of Highly Pathogenic Avian Influenza H5N1 Virus Identified in the Brain of Multiple Wild Carnivore Species), is the high incidence of neurological manifestations in these marine mammals.
From the same authors who penned the first report from Peru last February on the mass mortality of marine mammals in Peru, we get the following research letter published yesterday in the CDC's EID Journal.
This report covers their work during January–April 2023. Since then, the number of marine mammal deaths has expanded substantially - both in Peru - and throughout South America. Follow the link for photos and videos (viewer discretion advised), appendix, and references.
I'll have a brief postscript after the break.
Research Letter
Mass Mortality of Sea Lions Caused by Highly Pathogenic Avian Influenza A(H5N1) Virus
Víctor Gamarra-Toledo1, Pablo I. Plaza1, Roberto Gutiérrez, Giancarlo Inga-Diaz, Patricia Saravia-Guevara, Oliver Pereyra-Meza, Elver Coronado-Flores, Antonio Calderón-Cerrón, Gonzalo Quiroz-Jiménez, Paola Martinez, Deyvis Huamán-Mendoza, José C. Nieto-Navarrete, Sandra Ventura, and Sergio A. Lambertucci
Abstract
We report a massive mortality of 5,224 sea lions (Otaria flavescens) in Peru that seemed to be associated with highly pathogenic avian influenza A(H5N1) virus infection. The transmission pathway may have been through the close contact of sea lions with infected wild birds. We recommend evaluating potential virus transmission among sea lions.
The panzootic (2020–2023) caused by the highly pathogenic avian influenza (HPAI) A(H5N1) caused numerous global outbreaks in 2022 (1). At the end of the year, the H5N1 virus reached South America, causing alarming bird mortalities in Peru (2). Comprehensive surveys suggest the virus killed >100,000 wild birds by the end of March 2023 only in protected areas (and >200,000 birds including other areas); particularly affected were Peruvian boobies (Sula variegata), guanay cormorants (Leucocarbo bougainvilliorum), and Peruvian pelicans (Pelecanus thagus) (3). The large biomass of infected wild birds may have led to a spillover event affecting marine mammals cohabiting with them, as reported in other parts of the world (4). Here, we report the death of several thousand sea lions (Otaria flavescens) on the coast of Peru within a few months; the sea lions manifested neurologic and respiratory signs. Clinical signs we observed suggest they were affected by HPAI H5N1, which was later confirmed by government and scientific reports (5,6).
During January–April 2023, we performed detailed surveillance of dead and agonal sea lions in protected marine areas of Peru (Figure). We found 5,224 animals dead or dying on beaches (Table). The synchronized high mortality rate we observed was concerning; up to 100 dead animals were found floating together in the sea, and 1,112 animals died on 1 island that has one of highest populations of sea lions in Peru (San Gallan, Ica, Reserva Nacional Paracas; Table). Those unprecedented massive mortalities for this region and even the entire world killed ≈5% of Peru’s population of this species in a few months (Figure, panels A, B; Appendix Figure) (7).
National health authorities implemented restrictions regarding the manipulation of sick animals; for this reason, we were able to perform 1 necropsy, and the other observations were made by veterinarians at prudent distance. The clinical signs of agonal individuals were mainly neurologic, such as tremors, convulsions, and paralysis (Video 1; Video 2). The animals also showed respiratory signs such as dyspnea, tachypnea, and nasal and buccal secretions (Figure, panel C). The body condition of the necropsied sea lion ranged from good to very good. We observed substantial quantities of whitish secretions filling the upper respiratory tract (trachea and pharynx) (Figure, panel C). Lungs were congestive, with hemorrhagic focus compatible with interstitial pneumonia. Brain was also congestive, with hemorrhagic focus compatible with encephalitis (Figure, panel D).
Given the epidemiologic situation produced by HPAI H5N1 in wild birds that cohabit with the sea lions (2,3), the most plausible diagnosis causing this mass mortality event was acute disease caused by the virus. Clinical signs observed were similar to those reported in marine mammals infected with HPAI H5N1 in the United States (4). Official information from the Peru government and associated scientific research confirmed that not only birds but also sea lions tested positive for H5N1 virus (3,5,6). As of April 2023, sea lion deaths have surpassed 5,000 in Peru; thousands of sea lions with similar clinical signs died in Chile (8). This massive mortality event associated with HPAI H5N1 could be attributed to the large aggregations of sea lions that occur during the December–May breeding season (9).
In conclusion, sea lions in Peru experienced a deadly outbreak of disease that has caused mass deaths in several regions of the coastline (Figure). The sea lion mass mortality we described is compatible with systemic HPAI H5N1 that resulted in acute encephalitis and pneumonia. The source of the H5N1 virus affecting these sea lions was most probably the large number of infected live birds or their carcasses on the Peru coastline (2,3). Sea lions may be infected by close contact with those carcasses and through consuming them (Figure, panel E). The potential for direct transmission among sea lions from their colonial breeding behavior, in which they congregate by hundreds in the same area, should be evaluated, as should the large number of animals affected and the findings that many animals died simultaneously in groups in both Peru and Chile.
Recent research described potential mammal-to-mammal infection in minks (Neovison vison) (10). In fact, unique mutations that merit further surveillance were found through viral sequencing of some of the deceased sea lions we surveyed (5).
Further research is required to confirm the HPAI H5N1 virus as the main factor affecting the sea lions and to address the transmission pathway in this social species. We call for more attention to human–infected animal interaction in this geographic region (Figure, panel F) to identify any rise in infections and prevent a new pandemic.
Mr. Gamarra-Toledo is a biologist and research associate at the Museum of Natural History, Universidad Nacional de San Agustín de Arequipa, Peru. His primary research interest is wildlife conservation in coastal ecosystems of Peru. Dr. Plaza is a veterinarian and research associate at the Conservation Biology Research Group of the Laboratorio Ecotono, Instituto de Investigaciones en Biodiversidad y Medioambiente, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina. His primary research interests are wildlife health and epidemiology, human-wildlife interactions, and animal conservation.
Four months ago, in Avian Flu's New Normal: When the Extraordinary Becomes Ordinary, I wrote about the numbing effect that comes with the constant barrage of HPAI H5 reports from around the world.
As a result, Hundreds of dead sea lions on a South American beach from avian flu have gone from being an ominous warning sign to a grim statistic. The announcement last week that HPAI H5 had finally reached Antarctica was so anticipated that it had lost much of its impact.
Things that were nearly unthinkable two years ago (e.g. Repeated trans-Atlantic introduction of avian flu from Europe, the proliferation of HPAI H5 across the length of South America, or the repeated spillovers of H5 into mammalian species) have now become commonplace.
Although the future course and impact of HPAI H5 is unknowable, recent trends suggest that complacency is a luxury we cannot afford.
