A year after an outbreak of bird flu highly pathogenic H5N1 killed about 17,000 elephant seals and 97% of their offspring, these animals have returned to breeding in the Valdés Peninsula (Argentina) although this time there are only a third of the number there used to be.
An international team of researchers, co-led by the University of California Davis and the National Institute of Agricultural Technology (INTA) of Argentina, has returned to the Valdés Peninsula to study the transmission of the virus in 2023.
The results were published this Monday in the journal Nature Communications.
The team has discovered that the H5N1 virus spread efficiently among marine mammals and that That outbreak was a link in the first transnational spread of the viruswhich spread to five countries in southern South America.
The study’s genomic analysis also found that upon entering South America, The virus evolved into separate clades of birds and marine mammals, which is unprecedented.
“We are showing the evolution of H5N1 viruses that belong to the B3.2 genotype over time since their introduction in South America at the end of 2022,” explains virologist and main co-author Agustina Rimondi, from INTA and currently also at the Robert Institute. Koch.
“This virus is capable of adapting to marine mammal species, as we can see from the mutations that are consistently found in viruses belonging to this clade. And what is very important, Our study also shows that H5 viruses from marine mammals are able to jump back to birds, highlighting the need for increased surveillance and research cooperation in the region”.
The authors emphasize that continued surveillance and research is vitally important to better understand the evolution of the virus, as its increased flexibility to adapt to new hosts could have global consequences for human health, wildlife conservation and ecosystems. .
Elephant seal census
The Wildlife Conservation Society of Argentina (WCS Argentina), which has tallied the population of returned elephant seals as part of a decades-long monitoring project, believes the epidemic has reversed decades of conservation efforts. species.
“More than half of the breeding population has likely died from the virus. It will be decades before numbers return to the population size of 2022″, laments co-author and director of coastal and marine conservation at WCS Argentina, Valeria Falabella.
The team has also sampled the animals for signs of H5N1, but so far, no elephant seals have tested positive this season.
However, last year’s outbreak continues to raise questions. For example, scientists do not know whether the virus was transmitted by aerosol, saliva, feces or other means, or whether surviving animals have developed resistance through protective antibodies.
In the last year, The virus has spread among wild birds and caused outbreaks in American poultry and dairy cows.with recent cases among workers in the dairy and poultry sector.
On October 30, the US Department of Agriculture reported the first case of H5N1 in pigs in the United States. There are no known cases of contagion between humans.
A pandemic among birds
The current H5N1 variant of clade 2.3.4.4b began causing problems globally in 2020. As humans faced the COVID-19 pandemic, H5N1 began killing tens of thousands of seabirds in Europe before moving to South Africa.
In 2021, it entered the United States and Canada, and spread to South America at the end of 2022. In 2023, the flu was detected for the first time in poultry in Argentina and by summer it was already affecting sea lions at the tip of South America since where it moved rapidly northward, with deadly results, first for marine mammals and then for seabirds.
In October 2023, the authors of the study inspected the Punta Delgada elephant seal breeding colony, on the coast of Peninsula Valdés, where they observed an unprecedented mass mortality from highly pathogenic avian influenza H5N1 in seals and several terns.