the threat from the sky that worries scientists – L’Express

the threat from the sky that worries scientists – LExpress

The threat is contained in four letters, or rather two and as many numbers: H5N1. Detected in 1996, this strain of avian flu that originated in China managed to colonize the entire planet: first in Russia, then in Northern Europe before attacking the south of the continent, leaving behind millions of bird carcasses. ducks, chickens and other farmed poultry. But in recent years the pattern has changed. A highly pathogenic variant of the virus – called HPAI H5N1 – appeared and was able to mysteriously pass from birds to mammals, particularly during its invasion across the Atlantic. At the end of Latin America, its passage leaves a landscape of desolation: more than 30,000 sea lions in Peru and Chile died between 2022 and 2023, as well as porpoises, dolphins and otters. In total, around fifty species are affected throughout the world. The virus then traveled along the Pacific coast, then up the Atlantic coast, passing through Argentina, Uruguay and Brazil. Last October, a real H5N1 “tsunami” caused the death of more than 17,000 elephant seals in Patagonia. But it was last March that the situation changed for another species: Man.

Avian influenza A(H5N1) has taken up residence in the United States on several cattle farms in Texas, infecting cows for the first time. Today, the ongoing outbreak has spread to more than 80 herds in at least 11 US states, and the virus has also been detected in the wastewater of several others. Where the situation gets complicated is that cows are an animal that we are close to. And what was supposed to happen happened: a new species barrier was crossed and three humans have, to date, been infected. All of them have in common that they work on a farm and are, in this context, exposed to infected cows.

READ ALSO: Avian flu: how the epidemic is slipping away from us

A first infection in Texas was announced on April 1. This was the first known worldwide case of avian flu in a human via a cow. A second case was reported in Michigan in mid-May, with eye symptoms developing after milk was thrown into the eyes. The third case, identified on May 30, is also in Michigan, but is an employee at a different operation. Neither employee wore protective equipment. But, while the first two patients had only presented mild symptoms in the eyes, this third person reported “more typical” symptoms of a respiratory illness, including cough (without fever). A chance when we know that, until now, the fatality rate of avian flu was around… 50%. So, a question arises: what if the next pandemic came from avian flu?

Worrying mutations of the virus

“The closer the virus gets to humans, the more it infects mammals and humans, the more likely it is to adapt,” says Hervé Fleury, professor emeritus at the CNRS and the University of Bordeaux and author of Emerging and re-emerging viruses (Elsevier Masson). A recent study also raises fears of the worst in this regard. Posted online Saturday June 1st – and not validated by peers at this stage – it was led by Marcela Uhart, researcher at the University of California at Davis. According to this, the genetic analysis of the H5N1 virus collected from elephant seals that died in South America shows that it would have acquired around twenty mutations allowing it to spread among mammals. This would prove for the first time that the pathogen has the ability to transmit between mammals, and therefore has the capacity to cause large-scale infections in other species, including humans.

READ ALSO: Avian flu: man protected from a pandemic, but for how long?

However, if certain mutations are considered “worrying” by the researchers responsible for this study, the absence of mutations observed in hemagglutinin (HA) is good news. This is the viral protein that attaches to receptors in humans and animals. However, according to several studies, modifications of hemagglutinin would be necessary to allow H5N1 to spread among humans, and these would be the prelude to other even more important adaptations. “What is important to follow is above all the continuum of persistence of certain mutations in the virus, and to know if some of them can combine and persist to adapt to another organism, including ‘Man,’ says Thibaut Crépin, CNRS researcher at the Institute of Structural Biology. “On the other hand,” he continues, “mutations that would be associated with the adaptation of a virus within a given animal species absolutely do not mean that this can be directly transposed to humans.”

There is currently no evidence of human-to-human transmission of H5N1.

© / Chilean Antarctic Institute / AFP

Still, the picture is not all black. In the United States, experts have so far not detected any mutation resembling an adaptation of the virus to cows. Furthermore, the American Centers for Disease Prevention and Control (CDC) are shouting it loud and clear: the risk for the population remains “low”. No evidence of human-to-human transmission of the H5N1 virus has been found, and no “unusual” signs of influenza in humans have been detected, such as an increase in emergency room visits. Likewise, a corner of the veil concerning the mystery of cow-to-human transmissions has been lifted in a recent study. According to new data put online on May 22, and relayed by the magazine Nature Thursday, May 6, the milking process likely caused viral transmission between cows, other animals and potentially humans. Indeed, researchers have revealed that the milk of infected cows contains an astronomical number of viral particles which can survive for several hours. If this were confirmed, it would be excellent news because aerosol transmission – as is the case with Covid-19 – is much more difficult to contain. In other words, changes in milking procedures could help control the epidemic and prevent human infections, for example by requiring farmers to wear coveralls.

The mechanics of runaway

Despite these discoveries, researchers still fear a runaway. “The worst-case scenario is more and more likely,” adds virologist Hervé Fleury. “The virus has adapted to marine mammals, so it can also, by circulating in farms, mutate to adapt to humans Recently, it has even managed to infect herds of llamas in the United States, so it is constantly evolving. Now, we are faced with two scenarios: either H5N1 adapts to the human species on its own; farmer who suffers from human influenza type A(H3N2) is superinfected by a cow contaminated with H5N1 What would happen? There would be a recombination which would form an H5N2 transmissible from human to human, and we would then have a. start of the pandemic This is not a far-fetched hypothesis, far from it.”

H5N2, this strain of avian flu, considered less pathogenic than its famous half-brother, made headlines on Thursday June 6 in Mexico, where it caused the death of a 59-year-old man, the first known death in the world today. In this country, cases of H5N2 had already been detected in farmed poultry in several states. The experts want to be reassuring, with the WHO deeming the risk of spread “low” and this death due to “multifactorial” causes. Nevertheless, this new piece of the puzzle in the threat posed by avian flu is of concern. Is the mechanics of the runaway already in motion? “What may be worrying is the coexistence of two viruses, H5N1 and H5N2 for example, which have been spotted in relatively close geographical areas, and which would combine their genomes. This would cause the emergence of a third virus with a more lethal potential. important, and this scenario is very difficult to anticipate,” assures Thibaut Crépin.

READ ALSO: Avian flu: Antarctica faces worst-case scenario

Faced with this situation, a phenomenon particularly worries health authorities: the consumption of raw, unpasteurized milk is increasingly widespread throughout the world, and particularly in the United States, praised on social networks and by certain pseudo- doctors. However, this practice could have serious consequences due to the H5N1 epidemic taking place across the Atlantic. According to a recent study published in the New England Journal of Medicine, Researchers from the University of Wisconsin-Madison and Texas A&M University fed droplets of raw milk from infected cows to five mice. The rodents developed signs of the disease, including some lethargy. Researchers then found high levels of the virus in their nasal cavities, tracheas, and lungs, as well as low to moderate levels in other organs. Similarly, many cats on American farms where cows are infected have contracted bird flu. According to scientists, it is therefore important to heat raw milk to high temperatures – as pasteurization does. This destroys almost all traces of the virus after a few seconds, and destroys the entire pathogen after several minutes.

In the worst-case scenario, if a human avian flu pandemic spreads, will humanity have learned the lessons of Covid-19? Thibaut Crépin answers bluntly: “No”. “But I sincerely hope that the vaccine manufacturers are ready because we will have to react very quickly if the worst happens!” His colleague Hervé Fleury is more optimistic. “The United States is closely monitoring the situation, they are studying the idea of ​​vaccinating cattle and they already have a federal stock of inactivated vaccines in their possession. Furthermore, Moderna is already preparing a messenger RNA vaccine against H5 which could be ready very quickly in the event of a crisis.” The virologist assures us: we are no longer in 1918, when the poorly named “Spanish flu” caused between 20 and 50 million deaths, according to thePastor Institute. It was already an avian strain…