The first human case of a new strain of swine flu has been detected in the United Kingdom and health officials are trying to determine the origin of the virus.
On Monday, the UK Health Security Agency (UKHSA) verified that one person tested positive for influenza A H1N2v, a different but similar virus to flu viruses that spread among pigs across the country.
According to preliminary data, H1N2 infection in the UK is genetically unique from other recent human cases globally, specified by its clade or form, 1b.1.1.
“We are working quickly to trace close contacts and reduce any potential spread,” says UKHSA Incident Manager Meera Chand.
“In accordance with established protocols, investigations are being carried out to find out how the individual acquired the infection and to evaluate whether there are other associated cases.”
Following the onset of respiratory symptoms, the patient’s doctor in North Yorkshire tested him for flu on November 9 as part of standard national flu surveillance. Subsequently, genome sequencing and PCR testing identified H1N2.
Details about the patient’s age or general health have not been made public, but it is known that the patient had a mild illness and has made a full recovery.
Outbreaks of swine flu, a respiratory disease of pigs caused by influenza A viruses, occur frequently in pigs and occasionally people become infected.
Influenza viruses that normally circulate among animal populations (such as birds, horses, or pigs) and only sporadically infect humans are known as variant influenza viruses. This is represented by a lowercase v at the end of the subtype’s hemagglutinin (H) and neuraminidase (N) protein descriptors.
Human infections with influenza A subtypes, H1N1v, H3N2v, and H1N2v, have been previously identified, and the CDC reported this year’s first human cases in the United States in August.
Although H1N2v has never been found in humans in the UK before, the UKHSA says that since 2005, 50 human cases have been reported in other parts of the world.
Virologist Ian Brown of the UK Animal and Plant Health Agency explains in an expert reaction to the UKHSA report: “These viruses generally lack the ability to be transmitted from person to person and these events are usually explained by direct contact or indirectly with pigs.
While swine flu viruses have the potential to inflict widespread disease in pig populations, they typically cause only a small number of deaths. Infected pigs may show symptoms of respiratory disease, although these are usually mild or not present at all.
According to experts, this case is not cause for alarm, although more information about the strain is necessary to assess the risk.
University of Glasgow molecular virologist Ed Hutchinson warns that influenza A viruses can occasionally establish themselves in new host species.
“Human and animal influenza A viruses can ‘reproduce’ if they enter the same host, producing hybrid offspring that are well adapted to growth in humans but are not recognized by our immune responses to previous human influenza infections or vaccinations. (a process called genetic change)”, he explains.
“Because of this, it is particularly important to monitor the spread of influenza A viruses.”
Strains of influenza A subtype H1N1 have been responsible for several outbreaks in recent history, including the swine flu pandemic of 2009. Human infections with the virus spread rapidly around the world in a matter of weeks.
That particular strain, A(H1N1)pdm09, is now circulating seasonally in humans and is no longer called swine flu. It is different from the viruses currently circulating in pigs.
To limit the spread of flu viruses between pigs and humans, CDC recommends washing hands before and after contact with pigs, not eating or drinking near them, and avoiding contact with pigs that show signs of illness.
UK health authorities are tracking close contacts of the confirmed case and advising what action they should take.
For anyone experiencing respiratory symptoms, the UKHSA reiterates that anyone with such symptoms should avoid contact with other people, especially those who are elderly or vulnerable due to existing medical conditions.
