One pandemic after another, or both at the same time? A publication in the American scientific journal Pnas (Proceedings of the National Academy of Sciences), Monday, June 29, aroused the fear of this catastrophic scenario and prompted the World Health Organization (WHO) to call on the scientific community to “not not lower your guard. ”
In the article in question, Chinese researchers revealed that they have discovered a new virus in pigs capable of being transmitted to humans and which would require “urgent action” to control it, because it has the characteristics of a threat ” pandemic “.
Not everything is good in the pig
This newcomer to the virological scene, baptized G4, is the distant son of the H1N1 virus which caused the influenza A pandemic in 2009. He was discovered during a vast campaign of tests on the pig population in ten Chinese provinces, conducted between 2011 and 2018.
Monitoring pigs has become a major public health issue in China, the world’s largest producer and consumer of this meat. Because all is not good in the pig. This animal is, in effect, “permissive as well for avian flu viruses [chez l’oiseau], for those of the swine flu and those of the human flu “, underlines Manuel Rosa-Calatrava, director of research at Inserm and co-director of the Virology and human pathology laboratory VirPath, contacted by France 24. The pig then acts as a kind large pot from which, through the interplay of mutations and exchange of genes between influenza viruses present at the same time, new pathogens emerge, this is called genetic reassortment.
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 pig population observed”, note the authors of the article in Pnas.
This descendant of the 2009 H1N1 virus is the result of the cross between “three viral strains which have the particularity of having surface proteins [c’est-à-dire qui permettent de s’accrocher à l’hôte infecté, NDLR] to which man has not yet been exposed “, underlines Colin Butter, researcher in animal biology at the British university of Lincoln, contacted by France 24. The human being has, therefore, not yet been able to develop natural defense against this new pathogen. The vaccines against the H1N1 virus of 2009 or against the seasonal flu have also been shown to be ineffective, found the Chinese scientists 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. Indeed, “as the human population is, a priori, completely naive in the face of this new virus [c’est-à-dire qu’elle n’a pas développé d’anticorps, NDLR], the spread on a planetary scale could be facilitated “, underlines the researcher of the laboratory VirPath.
But all this would remain anecdotal if there were no transmission to humans. Unfortunately, more than 10% of workers in controlled pig farms have tested positive for the presence of the disease. “This means that the virus is already widespread among the population in contact with carrier animals,” notes Colin Butter.
There remains the great unknown factor in the transmission between humans. “For the moment, scientists do not seem to have observed any cases outside of people who have been close to pig farming,” summarizes the British expert. But, Chinese researchers have obtained potentially worrying results … in ferrets. Animals do contaminate each other, both through direct contact and through the respiratory tract. An important result: “The ferret constitutes a reference model for assessing transmissibility between humans because it presents, in particular, cellular receptors for human influenza viruses”, summarizes Manuel Rosa-Calatrava.
In addition, analyzes carried out on these animals showed that “the damage caused to the lungs was more severe than that of the H1N1 virus of 2009, with edema, hemorrhages and bronchopneumonia more serious”, write the authors of the Chinese study.
Be extra vigilant
But what is true for the ferret is not necessarily true for the human, even if 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, there has not yet been a proven case of transmission between humans”. In addition, “the authors do not report serious clinical cases in humans”, notes this researcher.
These elements lead Colin Butter to consider the pandemic risk with caution. “I do not think there is an urgent threat, and, given our current knowledge about this virus, I do not imagine a pandemic of G4 virus in addition to that of Covid-19 this year “, he concludes. It is nonetheless important for him to redouble his vigilance in order to follow the development of the situation.
We are, in fact, “with one or more mutations for transmissibility between humans,” recalls Manuel Rosa-Calatrava. “And the problem is that it is impossible to predict when and if they will take place. The French researcher recognizes that the scenario of a short-term G4 pandemic is not the most likely, but it is not to be completely excluded in his eyes, considering that in a century the world has already faced four pandemics of influenza virus (Spanish flu in 1918-19, Asian flu in 1957-58, Hong Kong flu in 1968-69 and avian flu in 2009-2010) .This would be, to his knowledge, the first time that the world would have to deal with two pandemics simultaneously.
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