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The H5N1 strain of avian influenza has led to the deaths of over 17,000 elephant seals in a year and wiped out 95 per cent of the pups in 2023, new research has revealed.
The research, published in journal Nature Communications, pointed out that the virus spread along the coasts of Peru and Chile between 2022 and 2023, transmitted by porpoises, dolphins and other marine mammals.
In June 2023, the virus spread southwards in Chile, eventually reaching other South American shores. Since October 2023, it has caused record mortality among southern elephant seals (Mirounga leonina) at Península Valdés in central Patagonia, Argentina.
This location, a UNESCO World Heritage site, holds global significance for marine wildlife conservation. The outbreak has impacted the breeding population, with at least 35 subadult and adult seal carcasses recorded in the area.
“The mortality event led to significant changes in the elephant seal social structure, with a progressive replacement of mature alpha males by subadults and a rapid decline in the number of breeding females,” the study noted.
The peak in elephant seal pup mortality occurred between September and October 10, 2023.
“It is likely that more than half of the reproductive population died due to the virus,” said co-author, Valeria Falabella and director of coastal and marine conservation Wildlife Conservation Society (WCS ), Argentina in a press statement. “It will take decades before the numbers are back to the 2022 population size.”
The population will see an unusually low birth rate in 2024, even if a majority of adult females have survived, the study suggested.
Currently, no infected elephant seals have been identified in the new breeding season, though the study observed that both males and females had abandoned colonies, likely due to the spread of infection.
Additionally, scientists have revealed evidence of the evolution of a new marine mammal clade of the existing H5N1 Hhighly pathogenic avian influenza (HPAI) 2.3.4.4b clade virus, with mutations that may have enhanced its ability to infect mammals while retaining its capacity to spill over to avian hosts.
“Our viral genome data provides evidence for the evolution of a novel marine mammal clade of H5N1 (2.3.4.4b) HPAI virus that has spread among pinnipeds (seals) in several countries of South America, revealing mutations that may have enabled their ability to infect mammals while also retaining the ability to spillover to avian hosts,” the study observed.
The scientists identified that the H5N1 HPAI viruses in Argentina belong to the B3.2 genotype among the 11 virus sequences analysed.
“The B3.2 viruses introduced from North America into South America have a reassortant genotype with four segments from the Eurasian H5 lineage (PA, HA, NA, and MP) and four segments from low pathogenicity avian influenza viruses from the North American lineage (PB2, PB1, NP, and NS),” the paper stated.
Within this clade, Argentina’s poultry viruses are intermixed with viruses from other regions and wild bird hosts, suggesting frequent virus movement across national borders and spillover between wild birds and poultry.
A quantitative analysis conducted by the researchers showed that H5N1 HPAI was transmitted nearly four times from wild birds to marine mammals along the Pacific coast of South America.
The study further indicated spillback from marine mammals to coastal birds and a human in Chile. One wild bird virus from Chile and four terns were reportedly infected, suggesting four independent instances of spillback from marine mammals to birds.
Human and sanderling viruses within the marine mammal clade also appear to be independent spillover events from marine mammals. This conclusion is supported by the presence of PB2 mutations associated with mammalian adaptation in viruses within the marine mammal clade.
The authors warned that its mutation leading to increasing adaptation to mammals is a “potential public health concern”.
They demand the formation of holistic strategies considering the linkages of human, animal and environmental health along with safeguarding biodiversity, promoting sustainable practices, and improve global resilience against emerging infectious diseases.