The deadly H5N1 bird flu virus has spread more aggressively than ever before in wild birds and marine mammals since arriving in South America in 2022, raising the risk of it evolving into a bigger threat to humans, according to interviews with eight scientists.

Of more immediate concern is evidence the disease, once largely confined to bird species, appears to be spreading between mammals. This strain has already killed a handful of dolphins in Chile and Peru, some 50,000 seals and sea lions along the coasts, and at least half a million birds regionwide.

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’s Children’s Research Hospital in Memphis, Tennessee. “It’s pretty hard to explain some of these large infections and die off without having mammal-to-mammal spread.”

The strain has shown up in dozens of bird species, including some migrating species, which can spread it beyond the region, scientists told Reuters.

As climate change escalates, animals will be forced to move into new territories, mixing with one another in new ways and possibly boosting opportunities for the virus to further mutate.

“It’s a matter of time before you will detect the first South American strain in North America,” said Alonzo Alfaro-Nunez, a viral ecologist at University of Copenhagen.

Human risk

The growing concern has prompted the 35 countries in the Pan American Health Organisation (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 oversee bird flu monitoring and response efforts, a PAHO official told Reuters. This has not been previously reported.

Since the virus was first detected in Colombia in October 2022, there have been two known cases in humans on the continent, one each in Ecuador and Chile. Both came from exposure to infected birds.

While those patients survived, H5N1 bird flu is deadly to humans in roughly 60% of cases worldwide.

The World Health Organisation (WHO) is unlikely to raise the risk level for humans from the current “low” 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 capacity to produce hundreds of million so doses within months utilising production lines used for seasonal flu vaccines.

“We’re seeing [the virus] doing little evolutionary steps that are on the long-term moving towards a potential human infection,” said Ralph Vanstreels, a University of California, Davis researcher studying South American variants of H5N1.

Every year, Argentina’s Peninsula Valdes on the windswept Atlantic coast teems with densely packed elephant seals rearing pups.

Last November, Mr. Vanstreels came across a grim scene: hundreds of dead and rotting pups on the beach. Researchers estimate 17,400 pups died, nearly all born to the colony that year.

For each of those pups to have been infected by birds is highly unlikely, scientists said. Pups usually have contact only with their mothers, leading scientists to suspect this is how it spread.

Mr. Vanstreels is part of a group of scientists working to trace the virus’ genetic mutations in South America.

In a draft paper posted on the U.S. Centres for Disease Control and Prevention website, they analysed samples from sea lions, seals and birds from up the coast from Peninsula Valdes. Comparing the genomes from these samples with those collected in North America in 2022 and Asia earlier, 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 hit by mass mortality of sea lions and birds.

“This is the first time this virus is so adapted to wildlife,” Mr. Vanstreels said. “Clearly something happened in Peru and in northern Chile where they acquired 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 seashore where seabirds congregated.

Researchers said that case “highlights the potential threat posed by these viruses to public health.”

Regional response

With health officials and experts meeting in Rio this week, Latin American countries will be pressed to boost disease surveillance in the wild.

The region’s patchy data and limited resources has left scientists struggling to understand how the disease is spreading in the wild, with the number of cases likely much higher than reported. Some cases are not being sampled or lab-tested, scientists said.

Bolivia, for example, did not register a case in the wild last year, though the disease has been detected in surrounding countries, said Manuel Jose Sanchez Vazquez, epidemiology coordinator for PAHO’s veterinary health centre.

Managing the disease response can also be complex, Mr. Sanchez noted. Threats to humans are dealt with by public health officials, while threats to poultry or livestock fall to agriculture or veterinary authorities. In wild animals, the purview typically falls to environmental officials.

The new regional commission, expected to be announced on March 14, would aim to set standard protocols for monitoring, handling and reporting cases among various government agencies. It could also help in pooling laboratory resources, Mr. Sanchez said.

“We are worried and we are vigilant,” Sanchez said. “The more adaptation of the virus to mammals, the more likely it is that transmission to humans could happen.” (Reporting by Jake Spring; Editing by Katy Daigle and Bill Berkrot)

Argentina’s economy minister and the anti-establishment upstart he faces in a presidential runoff next month began competing Monday to shore up the moderate voters they need.

Economy Minister Sergio Massa earned almost seven points more than chainsaw-wielding economist and freshman lawmaker Javier Milei in Sunday’s vote. Most polls had shown Mr. Massa slightly trailing, as voters had been expected to punish him for triple-digit inflation that has eaten away at purchasing power and boosted poverty.

On November 19, voters will either choose Mr. Massa, despite the economic deterioration that took place on his watch, or place their hopes in a self-described anarcho-capitalist who promises a drastic shake-up of South America’s second-largest economy.

Mr. Milei’s fiery rhetoric and radical proposals — like slashing subsidies that benefit a large swath of the population and replacing the local currency with the dollar — galvanised die-hard supporters, but cost him support among more moderate voters.

Mr. Massa focused his messaging in the latter part of the campaign on how Mr. Milei’s budget-slashing chainsaw would negatively affect citizens already struggling to make ends meet, with a particular focus on how much public transportation prices in Buenos Aires would increase without subsidies, said Mariel Fornoni of the political consulting firm Management and Fit.

That “had a significant impact and evidently instilled more fear than anything else,” Ms. Fornoni said.

Mr. Massa once again showed his Peronist party’s power to mobilise Argentine voters. A political movement named after former President Juan Domingo Perón that has both left- and right-wing factions but broadly believes in social justice and workers’ rights, Peronism has been a dominant force and in this election cycle emerged as the only viable left-leaning option.

Right-wing votes were divided between Mr. Milei, former Security Minister Patricia Bullrich of the main opposition coalition and another candidate, Cordoba province’s Governor Juan Schiaretti. Ms. Bullrich finished third in the field of five candidates, and the runoff will be decided by where her voters ultimately migrate.

She said in her concession speech Sunday night that she wouldn’t congratulate Mr. Massa on his victory because he was part of “Argentina’s worst government,” and that her coalition would never support “the mafias that have destroyed this country.” She stopped short of endorsing Mr. Milei, however.

During the campaign, Mr. Milei harshly criticised Ms. Bullrich as part of the entrenched elite that required purging, but he sought to appeal to her voters in a radio interview Monday, suggesting that they should focus on the bigger picture.

“Everyone who wants to change Argentina, who wants to embrace the ideas of freedom, are welcome,” Mr. Milei said. “It’s not a matter of labels; it’s a matter of who wants to be on this side.”

Asked in a news conference Monday whether he foresees challenges in siphoning support away from Ms. Bullrich, Mr. Massa responded that “leaders aren’t the owners of votes” and that several views espoused by Mr. Milei “have nothing to do with our culture and the values of the average Argentine citizen.”

Mr. Massa also said he would not want his government to be characterized as only Peronist.

“I believe it’s a mistake to suggest that the upcoming phase should be tied solely to Peronism. We are heading toward a government of national unity. I will call upon the best from various political forces, regardless of their origin,” Mr. Massa said.

Mr. Massa had already told voters that he inherited a bad economic situation exacerbated by a devastating drought that decimated exports. He reassured them that the worst was past.

With nearly all ballots counted Monday, Mr. Massa, 51, had 36.7% of the vote and Mr. Milei, 53, had 30%. Ms. Bullrich got 23.8%

In his radio interview, Mr. Milei characterised Mr. Massa’s results as the minister’s “ceiling” and said his showing marked a “floor”.

Mauro Salvatore, a 23-year-old programmer, said outside Milei’s campaign headquarters Sunday night that he is optimistic Mr. Milei will pick up the votes that went to Bullrich in the first round.

“We have a clear possibility. We find ourselves in a situation we knew wouldn’t be easy, but you can see the Argentine people are tired and really want change, independent of whether it will be Milei or Bullrich,” said Mr. Salvatore. “We have a lot of faith that some of Bullrich’s voters can be taken, given it’s understood they have more inclination toward Milei’s ideas than Massa’s.”

Analysts, however, questioned whether those votes would automatically transfer to him. Some of the more progressive elements of Ms. Bullrich’s coalition were already making clear Monday they would not support Mr. Milei, who has raged against the so-called “political caste,” vowed to eliminate half the government ministries and slash public spending.

And some analysts warned a runoff scenario may not be conducive to Mr. Milei’s combative style.

Mr. Milei is “an inexperienced candidate, lacking political expertise, who perhaps may not have the capacity to understand that the current scenario will require him to moderate, build political agreements, and appeal to voters who might ask for changes in his political proposal,” said Lucas Romero, head of Synopsis, a local political consultancy.

Mr. Milei’s casting himself as a culture warrior against the creep of the so-called “socialist agenda” appears to be a headwind, said Benjamin Gedan, director of the Latin America Program at the Washington-based Wilson Center. Mr. Milei has been endorsed by Brazil’s former far-right President Jair Bolsonaro and says he shares a common mission with former U.S. President Donald Trump. Some supporters wear hats that read “Make Argentina Great Again”.

Mr. Gedan described Milei’s opposition to abortion and gun control, among other positions, as “out of sync with Argentine society”.

Sovereign bonds plunged Monday and there was a selloff in Argentine equities as the market predicted that Mr. Massa’s first-round surprise means the government has little incentive to correct any of the economy’s imbalances for now. In the run-up to the vote, Mr. Massa boosted welfare programs and implemented tax cuts that benefited almost all registered workers, going against calls from the International Monetary Fund for austerity and removal of subsidies.

Mr. Massa “was able to build over the last two months through some tax holidays and other giveaways that could be fairly deemed populist,” said Brian Winter, a longtime Argentina expert and vice president of the New York-based Council of the Americas. “It’s going to be really interesting to hear what he says in the next few weeks, because he will need to win over some more moderate voters in order to win.”