The G4 virus, the swine flu that fears a new pandemic

Barely detected and already feared: a new H1N1 virus identified in pig farms in China has characteristics that hover the risk of a new pandemic, according to a Chinese study published Monday, June 29. Explanations with two experts.

One pandemic after the other or both at the same time? A publication in the US scientific journal PNas (Proceedings of the National Academy of Sciences) on Monday, June 29, aroused the fear of this disastrous scenario and pushed the World Health Organization (WHO) to urge the scientific community to “not lower your guard”.

In the article in questionChinese scientists have revealed that they have detected a new virus in pigs that can be transmitted to humans and that would require “urgent action” to control it, as it has the properties of a “pandemic” threat.

Not everything is good in the pig

This newcomer to the virological scene, called G4, is the distant son of the H1N1 virus that caused the influenza A pandemic in 2009. He was discovered during an extensive test campaign on the pig population in ten Chinese provinces, conducted between 2011 and 2018.

Pig surveillance has become an important issue of public health in China, the world’s largest producer and consumer of this meat. Because everything is not good in the pig. In fact, this animal is “also allowed for bird flu virus [chez l’oiseau], for swine flu and human influenza, “emphasizes Manuel Rosa-Calatrava, research director at Inserm and co-director of the Virology and virology laboratory, contacted by France 24. The pig then acts as a large pot from which, through the interaction between mutations and exchange of Genes between influenza viruses that are present simultaneously, new pathogens emerge, this is called genetic re-evaluation.

This is what happened in 2013 in southern China, where the G4 virus was first observed. This strain then spread to become, from 2016, “the dominant form of the virus in the observed swine population”, note the authors of the article in Pnas.

This offspring of the H1N1 virus in 2009 is the result of the intersection of “three viral strains that have the specificity of having surface proteins [c’est-à-dire qui permettent de s’accrocher à l’hôte infecté, NDLR] that humans have not yet been exposed to, says Colin Butter, a researcher in animal biology at the British University of Lincoln, contacted by France 24. Therefore, humans have not yet been able to develop natural defenses against this new pathogen Vaccines against the H1N1 virus from 2009 or against seasonal influenza have also found to be ineffective, the Chinese researchers found behind the discovery.

An “explosive cocktail”

It is the first element of the “explosive cocktail” that represents the pathogenic agent G4, according to Manuel Rosa-Calatrava. In fact, “as the human population is a priori, completely naive to this new virus [c’est-à-dire qu’elle n’a pas développé d’anticorps, NDLR], the spread on the planet can be facilitated, “emphasizes the researcher at the VirPath laboratory.

But all this would remain anecdotal if there was no transmission to humans. Unfortunately, more than 10% of workers in controlled pig farms have tested positive for the occurrence of the disease. “This means that the virus is already spreading in the population in contact with carrier animals,” notes Colin Butter.

There is still the big unknown factor in the transmission between people. “At the moment, researchers do not seem to have observed any cases outside of people who have been close to pig farming,” concludes the British expert. But Chinese scientists have achieved potentially alarming results … in ferrets. Animals contaminate each other, both through direct contact and through the airways. An important result: “The ferret is a reference model for assessing human transmissibility, because it presents cellular receptors for human influenza viruses in particular,” concludes Manuel Rosa-Calatrava.

In addition, analyzes on these animals showed that “the damage caused to the lungs was more severe than the 2009 H1N1 virus, with edema, bleeding and bronchopneumonia more serious,” the authors of the Chinese study write.

Be extra vigilant

But what is true of ferocity is not necessarily true of man, although it is a good indicator. “There are a whole host of biological mechanisms that make it impossible to just translate results from one to the other,” says Colin Butter. More important to him is the fact that, in “six years of circulation in China, it has not yet been proven to transmit between people”. In addition, “the authors do not report serious clinical cases in humans,” this researcher notes.

These elements cause Colin Butter to consider the pandemic risk with caution. “I don’t think there is an urgent threat, and given our current knowledge of this virus, I can’t imagine a G4 virus pandemic besides Covid-19 this year,” he concludes. Still, it is important for him to double his vigilance to follow the evolution of the situation.

We are actually “with one or more mutations for human transmissibility”, recalls Manuel Rosa-Calatrava. “And the problem is that it is impossible to predict when and if they will take place. The French scientist realizes that the scenario of a short-term G4 pandemic is not the most likely, but it should not be completely ruled out in his eyes, considering that in a century the world has already faced four pandemics of influenza viruses (Spanish flu 1918-19, Asian flu 1957-58, flu in Hong Kong 1968-69 and bird flu 2009-2010), to his knowledge, this would be the first time that the world would have to deal with two pandemics at the same time.

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