these scenarios that scientists fear – L’Express

Could the scenario of the end of 2019, with the emergence of a pandemic in China, happen again in the coming weeks, from the United States this time, because of the avian influenza A(H5N1) virus? ) ? We are not there yet, far from it. But scientists fear it, looking towards this pathogen that comes from birds and which, slowly but surely, is making its nest in mammals, including humans. Avian flu first appeared in 1996, but since 2020 the number of outbreaks in birds has exploded and more and more species have been affected. A turning point came in March when infections were detected in several dairy herds across the United States. In this closed environment, the virus grew until it was able to contaminate humans, mainly farmers. And now the epidemic seems to be spreading little by little. On November 22, a child tested positive for the first time in Alameda County, in the San Francisco Bay Area. To date, 55 human cases have been detected in the United States in 2024, including 29 in California, according to the American Centers for Disease Prevention and Control (CDC).

Another alert, further north, in the plains of British Columbia, Canada, attracts the attention of researchers. On November 2, a teenager positive for avian influenza subtype H5 presented worrying symptoms, and was urgently hospitalized on November 8. In critical condition, the minor suffers from acute respiratory distress. Health authorities quickly discovered that he was positive for influenza A subtype H5. But this virus differs from that observed so far in the United States, according to the first published data. “Geneticists studying avian flu sequences are looking for a series of genes that might be associated with greater human-to-human adaptation or increased virulence of the virus. And in this case they noted changes in some of these areas that are concerning,” says Meghan Davis, associate professor at Johns Hopkins University.

This could indicate that the H5N1 virus has the ability to resemble a human virus more than an avian virus, but it is not yet known whether this change is significant and more dangerous for our species. The virus may have mutated during the adolescent’s illness: additional sequencing could reveal more about its evolution. Especially since, for the moment, we do not know precisely how he became infected. Although there have been outbreaks of H5N1 among poultry in British Columbia, the young man was not exposed to it, although he had contact with several domestic animals, including dogs, cats and reptiles. It is possible that one of these animals itself encountered a dead bird or animal and transmitted the virus to the teenager, according to Canadian health authorities. A mystery that remains to be solved.

At present, however, let us be reassuring: there is no evidence of human-to-human transmission of this virus. Members of the infected child’s household in California tested negative for bird flu; the same in Canada where no other cases were detected among the adolescent’s contacts, including family, friends and health professionals. “It’s not clear what the real-world consequences will be, but all of these things are certainly a wake-up call,” Meghan Davis said. “We really need to pay attention to it and we really need to try to reduce the number of human infections as much as possible.”

In Canada, researchers hope the mutated virus will disappear without being transmitted to others. Systematic isolation of potential new cases could put this virus in an evolutionary dead end, but if the mutation happened once, it could happen again. “This is a particular concern among less well-monitored populations,” said Meghan Davis. Here again, a race against time is on to identify human infections as early as possible, in order to isolate them before they spread this mutation. “The possibility of a more contagious virus is a red flag,” says Richard Webby, virologist in the department of infectious diseases at St. Jude Children’s Research Hospital. This “underscores the need to do something about this virus. We need to get it under control.”

An infected pig and a risk of spillover

Since its emergence in March in dairy cows in the United States, the H5N1 virus has already undergone several developments. “Influenza A H5N1 is a virus with pandemic potential. What we are currently seeing are sporadic cases of more severe illness globally – linked to poultry or wild birds, where we know how the patient was exposed – and more frequent cases of mild illness among workers exposed to the dairy strain, says Meghan Davis If we start to see documented human-to-human transmission or more frequent serious illness among exposed workers or other high-risk groups. , “this would serve as a wake-up call that the virus may be adapting in ways that could increase its pandemic potential.”

For the moment, this is not the case. But researchers are vigilant because the virus is still circulating across the Atlantic. “We need to monitor this situation as closely as possible. Any warning we can receive about new viruses causing these types of changes will allow us to be warned,” assures Richard Webby. He continued: “The United States does not adequately test and monitor cases of avian flu, which means scientists could miss mutated cases like the one in Canada.”

Because this is where the researchers’ concern lies. If H5N1 has existed for decades, the current “clade” 2.3.4.4b has caused an epizootic (Editor’s note: global pandemic in animals) since 2020, affecting dairy cows or marine mammals en masse. “In detail, there are many different genotypes within this ‘clade’, and some of them are associated with more serious human diseases. This is what is worrying!, continues Meghan Davis. Because the virus has many possibilities for further evolution and adaptation.”

The recent infection of a pig on a farm in Oregon is particularly worrying, because these animals are known to be able to be contaminated by swine influenza viruses but also by human or avian influenza viruses. This co-infection can facilitate the emergence of new so-called “reassortant” influenza viruses: by combining the genes of several influenza viruses of different origins, they could become more virulent or facilitate their transmission to other species. The 2009 H1N1 influenza pandemic was created and initially spread by this species.

So many signals indicating that the virus is spreading at high speed, which offers it so many possibilities to mutate, or even to recombine with other viruses present in an intermediate host such as the pig or another mammal. Virologist Tulio de Oliveira, director of the Center for Epidemic Response and Innovation in South Africa, wrote on November 19 in the New York Times that the United States’ response “appears inadequate and slow, with too few genomic sequences of H5N1 cases in farm animals made public for scientific analysis.” “The failure to combat H5N1 in the US herd could have global consequences, and this requires urgent attention. The United States has done little to reassure the world on the fact that they succeeded in containing the epidemic.

The world is looking at the United States

For now, efforts to control the outbreak, which is spreading among dairy cows, are focused on quarantining facilities, which include both dairy and poultry farms, infected with this “clade.” But this is not enough according to several specialists. First, the genome sequences of H5N1 cases in animals in the United States are not being quickly made available, which could prove essential to understanding the threat and giving the world time to prepare, including by developing antivirals and drugs. vaccines. Then, Tulio de Oliveira calls for testing all animals on a farm where an individual is sick, which is not done systematically, in particular for economic reasons linked to the meat and milk lobby.

Because traces of the virus have been detected in several bottles of raw milk sold in supermarkets, particularly in California. Here again, the authorities’ response seems insufficient to say the least, and can be summed up as follows: “Don’t drink this milk!”. No removal from shelves of this product for the moment, nor restrictions in the promotion of this drink. “The cornerstone of an effective response is understanding the biology and epidemiology of the virus and using effective technologies like testing, treatments and vaccines to protect the population,” said Joshua Sharfstein, vice-president. dean for public health practice and community engagement at Johns Hopkins University. In Europe, the H5N1 virus has not disappeared, but it has not yet contaminated any cattle or humans.

Although France has vaccinated its poultry and is carrying out massive slaughters, recent cases have been identified in the United Kingdom. “Beyond the risks for its citizens, the United States must remember that the country where a pandemic breaks out can be accused of not doing enough to control it, continues in the new york times Tulio de Oliveira. We still hear that China has not done enough to stop the Covid-19 pandemic. None of us would want a new pathogen labeled ‘American virus,’ because it could be very damaging to the reputation and economy of the United States.”