by By Jake Spring
SAO PAULO (Reuters) – The deadly H5N1 bird flu virus has spread more aggressively than ever in wild birds and marine mammals since it arrived in South America in 2022, raising the risk that it will become a greater threat to humans , according to interviews with eight scientists.
Of more immediate concern is the evidence that the disease, which was largely confined to bird species, appears to be spreading among mammals. This pressure has already killed a handful of dolphins in Chile and Peru, about 50,000 seals and sea lions along the coast, and at least half a million birds across the region.
To confirm mammal-to-mammal transmission, scientists would likely need to test infections in live animals.
“It’s almost certainly happened,” said Richard Webby, a virologist at St. Jude Children’s Research Hospital in Memphis, Tennessee. “It is quite difficult to explain some of these major infections and deaths without mammal-to-mammal spread.”
The strain has been shown in many bird species, including some migratory species, which can spread it across the region, scientists told Reuters.
As climate change increases, animals will be forced to move into new territories, mixing with each other in new ways and possibly encouraging further opportunities for virus mutations.
“It’s a matter of time before you find the first South American strain in North America,” said Alonzo Alfaro-Nunez, a viral ecologist at the University of Copenhagen.
HUMAN RISK
The growing concern prompted the 35 countries in the Pan American Health Organization (PAHO) to convene regional health experts and officials at a meeting this week in Rio de Janeiro.
The group plans to launch the world’s first regional commission to monitor bird flu and response efforts, a PAHO official told Reuters. This has not been previously reported.
Since the virus was first discovered in Colombia in October 2022, two cases have been identified in humans on the continent, one in Ecuador and one in Chile. Both came from exposure to infected birds.
Although those patients survived, H5N1 bird flu is fatal to humans in about 60% of cases worldwide.
The World Health Organization is unlikely to raise the level of risk to humans from its current “low” level without evidence of human-to-human transmission or mutations adapted to human receptors, experts said.
Drugmakers, including GSK and Moderna, have said they are developing bird flu vaccines for humans, and have the ability to produce hundreds of millions of doses within months using production lines used to for seasonal flu vaccines.
“We (the virus) are making very few evolutionary steps that are moving long-term toward potential human infection,” said Ralph Vanstreels, a University of California, Davis researcher studying South American variants of H5N1.
Every year, the closely packed elephant seals raise pups on Argentina’s Valdes Peninsula on the Atlantic coast.
Last November, the Vanstreels came upon a grim sight: hundreds of dead and rotting calves on the beach. Researchers estimate that 17,400 cubs died, almost all born in the colony that year.
It’s highly likely that all of those chicks will be infected by birds, scientists said. Cubs usually only have contact with their mothers, leading scientists to suspect that this is how it spreads.
Vanstreels is part of a group of scientists working to track the genetic mutations of the virus in South America.
In a draft paper posted on the website of the US Centers for Disease Control and Prevention, they analyzed samples from sea lions, seals and birds up the coast from Peninsula Valdes. Comparing the genomes from these samples to those collected in North America in 2022 and earlier in Asia, the team identified nine new mutations.
The same mutations were found in samples collected in 2022 and 2023 in Chile and Peru, which were also affected by mass die-offs of lions and seabirds.
“This is the first time that this virus is so adapted to wildlife,” Vanstreels said. “Obviously something happened in Peru and northern Chile where they got these new mutations.”
In the draft paper, researchers noted that the same mutations were present in one of the continent’s two human cases, a 53-year-old man who lived one block from the shore where seabirds were gathering.
Researchers said that case “shows the potential threat these viruses pose to public health.”
REGIONAL RESPONSE
As health officials and experts gather in Rio this week, Latin American countries will be pressured to step up disease surveillance in the wild.
Because of the region’s sparse data and limited resources, scientists are struggling to understand how the disease is spreading in the wild, and the number of cases is likely to be much higher than reported. Some cases are not being sampled or lab tested, scientists said.
Bolivia, for example, did not register a wild case last year, although the disease was detected in the surrounding countries, said Manuel Jose Sanchez Vazquez, epidemiological coordinator of the PAHO veterinary health center.
Managing the disease response can also be complicated, Sanchez noted. Threats to humans are dealt with by public health officers, while threats to poultry or livestock fall to agricultural or veterinary authorities. In the case of wild animals, the responsibility usually falls to environmental officers.
The new regional commission, which is expected to be announced on Thursday, would aim to set standard protocols for monitoring, handling and reporting of cases among various government agencies. It could also help pool lab resources, Sanchez said.
“We are worried and we are on alert,” said Sanchez. “If the virus adapts to mammals it is more likely to be transmitted to humans.”
(Reporting by Jake Spring; Editing by Katy Daigle and Bill Berkrot)
