Swine flu is a very contagious respiratory infection in pigs. The G4 virus is a multi-reassortant swine influenza virus (derived from a mixture of several viruses) that may be more pathogenic to humans than the porcine H1N1 virus which was the source of the 1 A / H1N2009 influenza pandemic and which has become seasonal in humans.

Swine flu is a highly contagious viral infection in pigs. This disease is very common in North and South America, Europe and parts of Asia. Swine flu viruses can affect other species, mainly humans, and other animals such as turkeys.

Evolution of the virus

These swine flu viruses, like all influenza viruses, change, evolve and undergo reassortment (exchange of genes between several viruses) frequently “but in pigs the antigenic evolution which follows mutations is slower than in human being ”specifies Gaëlle Simon, Deputy Head of the Porcine Virology Immunology Unit at the Ploufragan-Plouzané-Niort Laboratory of ANSES, and Head of the National Porcine Influenza Reference Laboratory.

When influenza viruses of different species infect pigs simultaneously, these viruses can reassort each other and give rise to new viruses made up of a mixture of viral material of porcine, human and / or avian origin, which can be transmitted to the Man. This is the case with the H1N1pdm virus which caused the 2009 pandemic. Since then, humans have himself transmitted this virus to pigs all over the world, in which it has undergone reassortment with other swine influenza viruses.

Thus, a porcine influenza virus containing certain genes of the H1N1pdm virus has been spreading in Chinese pig farms for several years. This multi-reassortant porcine influenza H1N1 virus, containing certain genes of the H1N1pdm virus, is called “G4 reassortant EA H1N1” and is more commonly known as the G4 virus (genotype 4).

The H1N1 influenza virus type A is transmitted from person to person through the air, by hand touching the nose, eyes or mouth after touching surfaces contaminated with respiratory secretions.

As for the G4 virus, it is transmitted from pigs to humans. This is called a zoonosis. Studies carried out in China suggest that 10,4% of workers in the pork sector in the sample of people tested would have been infected with this G4 virus and 4.4% of the general population. “We may be underestimating the passage of swine viruses from pigs to humans because swine flu is indistinguishable from normal flu. Only serious cases lead to the performance of tests which allow us to know the strain, ”indicates Gaëlle Simon.

At the moment there does not appear to be any human-to-human transmission of the G4 virus. New mutations in the virus could lead to transmission between humans. And we know that this G4 virus can infect ferrets and be transmitted between ferrets, which is worrying, the ferret being an animal model for the study of human influenza. This G4 virus is therefore closely watched because it could lead to a new pandemic.

Namely

There is no risk of catching swine flu from eating pork or pork products.

Swine flu is caused by influenza type A viruses. These are subdivided into several subtypes, the most common of which are H1N1, H3N2, H1N2. A new genotype of swine influenza virus subtype H1N1 has been identified in China since 2013: G4. All swine influenza viruses have zoonotic potential, which means that they can be transmitted to humans.

In humans, swine flu produces symptoms resembling those of seasonal flu, with upper airway involvement, acute respiratory illness or pneumonia. Influenza caused by the A / H1N1 virus is manifested by high fever, cough, body aches, and great fatigue.

The diagnosis of swine flu is made as for the diagnosis of Covid 19, by analyzes of a sample of secretions taken from the nose or throat, in pigs as in humans. “This PCR makes it possible to detect whether it is an influenza type A virus or not. Further PCR can then be performed to analyze the viral subtype (H1N1, H3N2).

If we want the genotype of the virus, we have to do the sequencing of the viral genome. This makes it possible to see if the virus is a virus resulting from a reassortment between two different viruses. »Explains Gaëlle Simon. “Generally, the test to detect swine flu is only performed in case of exposure to infected pigs or in case of development of a very serious form,” she explains.

Treatments for swine flu in humans consist of treating symptoms and resting. “Only serious cases require treatment with antivirals” informs Gaëlle Simon.

G4 virus: prevention by vaccination

In pigs, there are vaccines against certain swine flu viruses, including a vaccine against the H1N1pdm virus. There is a multivalent seasonal influenza vaccine in humans (which contains the antigens of two type A viruses, strains H1N1pdm and H3N2, and the antigens of type B viruses). There is no vaccine against the G4 swine strain.

Vaccines against seasonal influenza would a priori be ineffective against the G4 virus. “Studies in China have shown a weak antigenic relationship,” explains Gaëlle Simon.

The national “Résavip” network

In 2011 in France, “Résavip”, the national surveillance network for influenza A viruses responsible for influenza in swine, was set up. “It was born out of a desire in France on the part of the State and professionals in the pig industry to set up a long-term system to monitor the influenza viruses circulating in pig farms and to be able to alert in the event of discovery of a virus which could potentially be more at zoonotic risk and be able to take measures if ever there is an emergence of a particular virus ”informs Gaëlle Simon. The G4 virus has not been identified in France.