The study published in the journal PNAS (Proceedings of the National Academy of Sciences) on 29 June was picked up by several mainstream media outlets and led to many questions about the possibility of a human influenza pandemic. The study authors noted the increasing frequency of an influenza virus strain in pig farms in China. This virus has been named "G4 reassortant EA H1N1". It was first detected in 2013, but has been increasing as a proportion of all identified virus strains since 2016. It results from a reassortment of genes from several lineages of swine influenza viruses. The researchers were alerted by the fact that some of its genes were derived from the H1N1pdm virus, which caused a human influenza pandemic in 2009. These genes could facilitate its adaptation to humans and its capacity for human-to-human transmission. An experiment on ferrets, an animal model used to study human influenza, showed that it could be transmitted from one animal to another.
No immediate risk to humans
However, this virus does not have all the characteristics that would cause a pandemic in humans: first of all, only two confirmed cases of human contamination by the "G4 reassortant EA H1N1" virus have been recorded (in 2016 and 2018). The two people in question lived near farms and no human-to-human transmission was identified around these cases. In addition, the virus has only been detected on Chinese farms. Lastly, 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 Epidemiological Surveillance Platform for Animal Health (ESA), in which ANSES researchers participate, has published a note (in French) on its website that analyses the results of this study in greater detail.
Monitoring influenza in pigs
In France, surveillance of influenza viruses in pigs has been stepped up since the 2009 pandemic. The Pig Immunology and Virology Unit of ANSES's Ploufragan-Plouzané-Niort Laboratory is the National Reference Laboratory for swine influenza. As such, it has several missions, including developing and validating methods to identify influenza virus subtypes and lineages. The Laboratory analyses specific characteristics of these viruses when identified by veterinary laboratories accredited for the detection of influenza A viruses in pigs. It also conducts health monitoring and maintains banks of samples, viral strains and sera. These missions are mainly carried out in conjunction with the National Surveillance Network for Swine Influenza Viruses, Resavip (see box).
The Laboratory also conducts research to understand the evolution of influenza viruses, as well as factors influencing the severity of infection in pigs, particularly in the case of co-infection with other pathogens. Lastly, the Unit works to identify viral characteristics facilitating the transmission of influenza viruses from one species to another.
Recommendations to avoid swine-to-human transmission
People who work in contact with pigs are at greater risk of becoming infected with a swine influenza virus than the general population. Conversely, they can also transmit certain human influenza viruses to animals. In the event of co-infection, swine and human influenza viruses can exchange genes, sometimes leading to the emergence of a potentially more infectious and virulent virus.
Professionals in the pig sector are therefore advised to comply with barrier gestures, including:
- showering and changing clothes before and after contact with animals;
- wearing a suitable mask and ensuring proper hand hygiene if they or the animals have a flu-like illness;
- not allowing people who are ill with flu to enter farms.
The Resavip network
The Resavip network (National Surveillance Network for Swine Influenza A Viruses) conducts surveillance of swine influenza viruses, based on the reporting of clinical suspicions of influenza in swine herds and the identification of viruses by laboratory analysis. This type of monitoring provides a broader understanding of the swine influenza viruses present in metropolitan France and their geographical distribution. One of the network's unique features is that its surveillance concerns an unregulated health hazard. It is coordinated by the French Agricultural Cooperation (La Coopération Agricole). The other partners are the Directorate General for Food (DGAL), ANSES, the French National Society of Veterinary Technical Groups (SNGTV), the French Association of Directors and Managers of Public Veterinary Analytical Laboratories (ADILVA) and the French Federation of Health Protection Groups (GDS-France).