One year after a highly pathogenic strain of avian flu, H5N1, wiped out approximately 17,000 elephant seals and 97% of their pups in Argentina's Valdés Peninsula, these marine mammals have begun to breed again. However, only a third of the previous population has returned.
An international research team led by the University of California Davis and Argentina's National Institute of Agricultural Technology (INTA) has returned to the Valdés Peninsula to study the virus's transmission in 2023. Their findings, published in Nature Communications, reveal that H5N1 spread effectively among marine mammals, marking the first transnational outbreak of the virus across five countries in southern South America.
Genomic analysis from the study showed that upon entering South America, the virus evolved into distinct clades affecting birds and marine mammals, a phenomenon unprecedented in the region. Co-author Agustina Rimondi, a virologist from INTA, emphasized, 'This virus is capable of adapting to marine mammal species, as evidenced by consistent mutations found in viruses from this clade. Importantly, our study also indicates that marine mammal H5 viruses can jump back to birds, highlighting the urgent need for increased surveillance and research cooperation in the region.'
Continuous monitoring and research are crucial for understanding the virus's evolution, as its adaptability could have global repercussions for human health, wildlife conservation, and ecosystems.
The Wildlife Conservation Society (WCS) in Argentina, which has tracked the returning elephant seal population as part of a decades-long monitoring project, believes that the epidemic has reversed years of conservation efforts for the species. Co-author Valeria Falabella lamented, 'It is likely that more than half of the breeding population has died due to the virus. It will take decades for the numbers to return to the size they were in 2022.'
Although the team has sampled the seals for signs of H5N1, none have tested positive this season so far. However, questions remain regarding the transmission methods of the virus, whether through aerosol, saliva, feces, or other means, and whether surviving animals have developed resistance through protective antibodies.
In the past year, the virus has spread among wild birds and caused outbreaks in poultry and dairy cattle in the United States, with recent cases reported among dairy and poultry workers.
On October 30, the U.S. Department of Agriculture reported the first case of H5N1 in pigs. No human transmission cases are known.
The current variant of H5N1 from clade 2.3.4.4b began causing global issues in 2020, coinciding with the COVID-19 pandemic. While humans faced COVID-19, H5N1 began killing tens of thousands of seabirds in Europe before spreading to South Africa. By 2021, it reached the United States and Canada, and by late 2022, it had spread to South America. In 2023, the flu was detected in poultry for the first time in Argentina and quickly affected sea lions at the southern tip of South America, leading to fatal outcomes for marine mammals and seabirds.