Suspected case of human influenza caused by an influenza A(H1N2)v virus of clade 1C.2.4 of swine origin in Brittany
Following the detection of a human case of infection with a swine-origin influenza virus in the Côtes d’Armor region, investigations are underway, and Santé publique France has developed a protocol to identify any potential cases of infection with this virus and enable the implementation of appropriate control measures.
Swine flu
thematic dossier
Influenza viruses that emerge and circulate in pigs all have zoonotic potential, meaning they can infect humans, and sporadic cases are regularly detected. No recent cases of human-to-human...
Update as of September 10, 2021
On September 3, 2021, the National Reference Center for Respiratory Infectious Viruses at the Pasteur Institute confirmed an infection in a man residing in the Côtes-d’Armor department caused by the swine-origin influenza A(H1N2)v virus, clade 1C.2.4. This is the first detection of this virus in a human in France.
The patient reported exposure to live pigs in the week prior to the onset of symptoms. The patient is in good health. To date, no symptomatic individuals have been detected among his close contacts.
What is known about the influenza A(H1N2)v virus?
The virus detected in this human case is genetically closely related to swine viruses recently detected in Brittany and elsewhere in France, identified as genotype “H1avN2 #E” by the National Reference Laboratory (LNR) for Swine Influenza (ANSES), containing an HA (hemagglutinin) gene belonging to clade 1C.2.4.
This clade was identified in 2020 as an emerging lineage spreading among the pig population in Europe (notably in France, Denmark, Italy, and Spain). It was detected in pigs in Brittany for the first time in February 2020. In areas where it is currently circulating actively, it has rapidly become the predominant virus among all influenza viruses detected in pig farms.
Virological and genetic analyses are underway at the CNR and the National Reference Laboratory for Swine Influenza Viruses (ANSES) to characterize this virus, and in particular to identify potential markers of adaptation to humans and virulence.
Due to the active circulation of this virus within the pig population in France, systematic screening for influenza viruses (type and subtype) should be conducted in any person exposed to pigs who presents with clinical symptoms consistent with acute respiratory infection and a negative test for SARS-CoV-2.
Cases of human infection with influenza viruses of porcine origin occur sporadically worldwide. Since January 2021, approximately ten cases of human infection with A(H3N2)v, A(H1N1)v, and A(H1N2)v viruses of swine origin have been detected in the United States, Canada, Australia, Taiwan, Denmark, and Germany. Human cases of infection with swine influenza viruses are generally mild, although a few severe cases have been reported. Several isolated events of human-to-human transmission of swine influenza viruses have been described or suspected in the past, but no sustained transmission chains (i.e., involving multiple generations of successive infections in humans) have been reported since the 2009 pandemic.
This event, occurring in a region of France characterized by a high density of pig farms, is therefore not an unexpected phenomenon. However, the characteristics of this A(H1N2)v virus of clade 1C.2.4, particularly its ability to adapt to humans, remain to be determined.
Questionnaire on Animal-Origin Influenza (Possible Case)
