Europe is facing an unprecedented epizootic (this is the name given to epidemics that occur in the animal kingdom) due to the H5N1 flu virus. With 42 million cases reported in world organization for animal health in farmed poultry since October 2021 and millions of wild birds found dead in the wild, authorities have culled nearly 200 million domestic birds since 2021.
In France, since August 2022, more than 300 outbreaks in livestock have been detected, of which more than three quarters are concentrated in the Pays de la Loire region, a very dense area in terms of poultry farming. In addition, a notable increase in the number of infected wild birds found dead – notably seagulls and gulls on the coast of France – was noted during this same period.
The situation is worrying because whoever says affected birds, says risks for humans in contact, economic losses and tensions on the human food chain, but also animal health at risk since entire avian populations are decimated. As soon as farms are affected and animals slaughtered, farmers are threatened with economic precariousness, an entire sector affected by job losses and considerable waste.
In addition, if the situation is worrying today, it is that throughout the world, a large number of mammals have also contracted the H5N1 virus, in particular carnivorous mammals whose genetic proximity with humans is greater than with the birds. In France, the case of a chat tested positive has just been reported. Worldwide, cases have been described in sealsof the minksea lions or even sea lions.
Children, men and women have also recently been infected in Spain, the United Kingdom, the United States, China, Vietnam, Peru and Ecuador. No case has yet been diagnosed in France.
The H5N1 virus is not of recent emergence. It was first identified in 1996 in Southeast Asia. Since 2003 when the WHO has been counting human cases, 868 notifications were reported. The disease is particularly serious in humans, its lethality being estimated at more than 50%, even if the infection can sometimes be asymptomatic or paucisymptomatic [présentant très peu de symptômes, ndlr]. It is therefore an infection, clinically disproportionate to that of Covid-19 in terms of severity. There is no vaccine against H5N1 yet, neither for animals nor for humans. On the other hand, antiviral drugs such as oseltamivir are effective in the event of contamination.
Do mutations allow human-to-human transmission?
The question that fundamentally arises at this level is whether the mutations experienced by the H5N1 RNA virus now allow it to cross this species barrier which has held firm for almost thirty years because then we should fear of epidemics (in humans).
Let’s say it bluntly: today, we are not there yet. Nothing really new under the sun insofar as human-to-human transmission has not been proven and where, even in affected mammals, no chain of transmission has been demonstrated, but recent epizootics increasingly question this point. .
Let us first take the case of the epizootic which last October affected an intensive breeding of 52,000 minks in Galicia, in the northwest of Spain, by the sea. Two hypotheses confront each other and have not been decided to date. The first would be that a few minks were contaminated by seagulls carrying the virus that we could spot nearby (the cages in which the minks were being partially open and close to the beach) then that they then spread the virus to their congeners, thus creating real chains of transmission within the farm.
The second hypothesis would be that the sick mink were all individually contaminated by the virus-carrying seagulls near the farm. The investigation of this Spanish epizootic focus was able to reject a third hypothesis, that of food contamination, because the poultry that was served to the carnivorous mink came from properly traced farms in Spain and we could not find the avian virus in the food chain. The lethality of infected mink was close to 4%, due to multi-organ damage, pneumonia, encephalitis, and haemorrhagic hepatitis.
Similarly, in Peru, 3,400 sea lions were found dead from bird flu. Colonies of sea lions too, as well as seals, which were probably contaminated by seabirds. But it is difficult to rule out whether interspecies transmission has occurred because these animals, known to vocalize profusely they are among themselves, could also transmit the virus by aerosols, if mutations of the virus now allow this transmission.
H5N1 does not (yet) have the correct keys to enter
Of the 868 cases described since 2003, no case of human-to-human transmission has yet been described. THE tragic case of a little girl and his father affected by the virus in Cambodia last February did not invalidate this assumption despite initial fears.
The infected people have all been, it seems, through close contact with infected birds. Thus, even if people can be infected, they would represent vis-à-vis the virus what epidemiologists call a “cul-de-sac” in terms of transmission.
A virus cannot multiply without first infecting a cell. The virus uses the molecular material of the cell it contaminates to replicate, before emerging from the cell and infecting others. Only, in order to be able to infect a cell, the virus must be able to penetrate it. This occurs via complex molecular mechanisms of attachment of a virus envelope protein to a receptor on the target cell membrane. Still, when you don’t have the right key, you don’t enter through the door of the cell you want to invest.
This is what is happening so far with the H5N1 virus: it does not have the right keys to enter, or does not yet have them. Of course, appropriate mutations could shape the surface protein that acts as a bunch of keys, until a good key ends up allowing it to enter the cell and contaminate it. Then, the local environmental conditions of the virus must allow it to replicate. But there again, it is not won.
In the airways of birds it is much warmer (40 degrees) than in those of mammals (33 to 35 degrees in the human respiratory tree); neither are the acidity conditions the same, the pH is much higher in human cells; in short, all of this constitutes a species barrier that strongly protects mammals – including humans – from human-to-human transmission of avian influenza.
We know, however, that these barriers are not immutable, that the evolution of viruses through appropriate mutations sometimes ends up allowing them to spread to new populations of the living kingdom. But it can take a year, a century or a thousand years.
There is therefore no evidence to date of transmission of the H5N1 virus between mammalian species. The cat, contaminated in France, would have been via wild ducks carrying H5N1 and has not contaminated other cats to our knowledge, nor the human beings with whom it lives.
However, preventive measures to be taken
However, given the high circulation of the virus in birds and the number of mammals affected, as well as the virulence and lethality of the virus when it affects humans, it is important to ensure that precautions are taken. taken – especially since the more a virus circulates, the greater the risk of it mutating in a direction that is not necessarily favorable.
In this context, it is important to put in place preventive measures and it is in this sense that the WHO wrote in December 2022: “As these viruses are constantly evolving and spreading in animal populations, and with an increased risk of exposure to humans, there is an urgent need for increased vigilance and public health actions.”
These actions are of several orders:
- preserve the health and lives of people who come into contact with animals carrying the virus;
- preserve animal health and life;
- preserve ecosystems;
- preserve the employment of the professions concerned (breeders, technicians, veterinarians, etc.);
- reduce the risk that the virus will mutate or recombine with other viruses, particularly influenza, and end up adapting to humans.
It is therefore necessary to strengthen animal and human monitoring and to carry out concrete research actions on a large scale, as is the case with l’initiative Prezode. It now brings together one hundred international partners, and the membership of seven countries on four continents serves these objectives.
Recommendations were also made to professionals. Many scientists agree on the fact, for example, that it would be preferable to close mink farms, which have nothing absolutely essential, as long as the risk of epizootics is high as at present.
In addition, it is suitable:
- to remind walkers not to touch dead or injured birds on the public highway, in the forest, in the fields or on the beaches and to report them to French Office for Biodiversity or to the Fédération des chasseurs, and to inform the town hall;
- protect yourself individually with a mask and gloves when in contact with dead wild birds or during occupational exposures of farmed birds;
- to be vaccinated against seasonal flu, when you are a professional working in contact with wild or farmed birds, in order to reduce the risk of recombination between animal and human viruses;
- to consult a doctor in the event of flu-like symptoms or neurological disorders occurring within ten days of potentially risky contact.
Enemies whose plans we believe we know
The question of anticipating a future H5N1 pandemic arises. Due to the high lethality of the virus and the transmissible nature of human influenza viruses, it would already be a question of developing a vaccine against this H5N1 strain. It could be intended primarily for professionals particularly at risk, because they work in contact with the live animals concerned.
The research and development of a universal vaccine against influenza to protect against human and non-human variants of the influenza virus are sea snakes well known to researchers. But obviously we must not let our guard down or the investments here either: one day will we perhaps find the Holy Grail?
H5N1, like Covid-19, reminds us how important it is to think about human, animal and ecosystem health as a whole under the so-called One Health approach. English “One Health”, which aims to decompartmentalize research, monitoring and action against diseases at the interface between humans, animals and the environment.
Finally, because we cannot call on the population to remain in permanent hypervigilance, we must remember that the emergence of the H5N1 avian influenza virus does not date from yesterday, but from almost thirty years ago, and that it had already made the health authorities of Southeast Asia tremble in the early 2000s. We must even be wary of the new Maginot lines that we are often tempted to build against enemies whose designs we believe we know. While we feared in the first decade of the century an epidemic due to the humanized H5N1 virus coming from Southeast Asia, it is an A/H1N1 flu resulting from a recombination of an avian virus with that of the pig which came to us… from Mexico.
To date, and within living memory, only the H1N1, H2N2 and H3N2 viruses have caused pandemics in humans and it is not certain that this epidemiological landscape will change any time soon. We seem to be today in our observatories waiting for the H5N1 enemy, whose attack we foresee with some anxiety, but it could well be, vis-à-vis H5N1, that the enemy does not show up or that he never manages to open the well-sealed doors of the cells of our human organisms.
2023-04-26 05:20:33
#Avian #flu #fear #human #pandemic
