Elephant seal numbers drop after avian flu outbreak: First report of transmission between marine mammals
The sounds of barking elephant seals are again in the air along the breeding grounds of Península Valdés, Argentina—but it's quieter. Almost exactly a year after a massive outbreak of H5N1 highly pathogenic avian influenza ...
"It's beautiful to walk the beaches now and hear elephant seals again," said Marcela Uhart, director of the Latin America Program at the UC Davis Karen C. Drayer Wildlife Health Center within the UC Davis School of Veterinary Medicine. "At the same time, we're walking among piles of carcasses and bones, and seeing very few elephant seal harems, so it's still disturbing."
A study, published in the journal Nature Communications and co-led by UC Davis and the National Institute of Agricultural Technology (INTA) in Argentina provides evidence of mammal-to-mammal transmission during the 2023 outbreak.
It found that H5N1 spread efficiently among marine mammals. The outbreak in elephant seals was a stepping stone amid the first transnational spread of the virus in these species, extending across five countries in southern South America.
The study's genomic analysis further found that, upon entering South America, the virus evolved into separate avian and marine mammal clades, which is unprecedented.
"We're showing the evolution of H5N1 viruses that belong to genotype B3.2 over time since their introduction in South America in late 2022," said virologist and co-leading author Agustina Rimondi of INTA and currently also with Robert Koch Institute.
A subadult male elephant seal can be seen near sea lions in October 2024. Subadult elephant seals and sea lions frequently intermingle at rookeries along Península Valdés in Argentina. Close contact between pinniped species may have facilitated the spread of HPAI in 2023. Credit: Ralph Vanstreels, UC Davis
Elephant seal carcasses line the beach at Punta Delgada in Argentina on Oct. 10, 2023 following an outbreak of HPAI avian influenza that killed about 97% of all pups born that year. Credit: Ralph Vanstreels, UC Davis
Scientists survey a seabird colony for signs of HPAI outbreak in early October 2024. This colony was heavily affected in 2023, particularly the terns. Staying vigilant to detect signs of disease is critical for early detection of HPAI cases in wildlife. Credit: Marcela Uhart, UC Davis
On occasion, elephant seals breed among sea lions. Here, an adult male elephant seal and a female with her black-coated pup in the background, are surrounded by sea lions in October 2024. Dynamics of contact and beach sharing between these species was disrupted in 2023 during the massive HPAI outbreak in Península Valdés, Argentina. Credit: Ralph Vanstreels, UC Davis