The study published in the journal PNAS (Proceedings of the National Academy of Sciences) on June 29 was relayed by several mainstream media and raised many questions about the possibility of an influenza pandemic in humans. The authors note the increase in the frequency of a strain of influenza virus in pig farms in China. This virus was named “G4 reassortant EA H1N1”. It was detected for the first time in 2013, but its proportion among the viral strains identified has increased since 2016. It comes from a reassortment of genes from several lines of swine influenza virus. The characteristic that alerted the researchers is that some of its genes are from the H1N1pdm virus, which caused a flu pandemic in humans in 2009. These genes could facilitate its passage to humans and its ability to be transmitted from human to human. An experiment on ferrets, an animal model used to study human flu, showed that it could be transmitted from one animal to another.
No immediate risk in humans
However, not all the characteristics are met for this virus to cause a pandemic in humans: first of all, only two proven cases of human contamination by the “G4 reassortant EA H1N1” virus have been identified (in 2016 and 2018). The two people concerned lived near farms and no human-to-human transmission has been identified around these cases. Moreover, the virus has only been detected in Chinese farms. Finally, this is not the first reassortment of a swine influenza virus with the pandemic H1N1pdm virus, other examples have been identified since 2010, without causing a pandemic. The Animal Health Epidemiological Surveillance (ESA) platform, in which ANSES researchers participate, has published a reading note on its website which analyzes the results of this research in more detail.
Monitoring influenza in swine
In France, surveillance of influenza viruses in pigs has been stepped up since the 2009 pandemic. . As such, he has several missions, including developing and validating methods for identifying influenza virus subtypes and lineages. The laboratory precisely analyzes the characteristics of these viruses detected by veterinary laboratories approved for the detection of influenza A viruses in pigs. It also provides health monitoring and keeps banks of samples, viral strains and serums. These missions are carried out in particular in conjunction with the national surveillance network for swine influenza viruses, Résavip (see box).
The laboratory also conducts research to understand the evolution of influenza viruses, as well as the factors influencing the severity of infection in pigs, particularly in the event of co-infection by other pathogens. Finally, the unit works to identify the viral characteristics that facilitate the transmission of influenza viruses from one species to another.
Recommendations to avoid pig-human transmission
People who work in contact with pigs are more at risk of being infected with a swine influenza virus than the general population. Conversely, they can transmit some human influenza viruses to animals. When co-infected, swine and human influenza viruses can exchange genes, sometimes leading to the emergence of a potentially more infectious and virulent virus.
It is therefore recommended that professionals in the pork sector respect barrier gestures, including:
- shower and change clothes before and after contact with animals;
- wear a suitable mask and ensure good hand hygiene if they themselves or the animals have a flu-like illness;
- prohibit access to farms for people sick with the flu.