The first human case of a new strain of swine flu has been detected in the UK, and health officials are trying to determine the virus's origin.

On Monday, the UK Health Security Agency (UKHSA) verified that a person tested positive for Influenza A H1N2v, a distinct but similar virus to the flu viruses spreading in pigs across the country.

According to preliminary data, the 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 rapidly to trace close contacts and reduce any potential spread," says UKHSA's incident director, Meera Chand.

"In accordance with established protocols, investigations are underway to learn how the individual acquired the infection and to assess whether there are any further associated cases."

Following the onset of respiratory symptoms, the patient's doctor in North Yorkshire tested the patient for the flu on November 9 as part of standard nationwide flu surveillance. Genome sequencing and PCR testing later identified H1N2.

Details about the patient's age or general health haven't been publicly released, but it is known that the patient had a mild illness and has fully recovered.

Outbreaks of swine flu, a respiratory illness of pigs caused by type A flu viruses, occur frequently in pigs, and people occasionally get infected.

Influenza viruses that typically circulate through populations of animals – such as birds, horses, or pigs – and which only sporadically infect humans are known as variant flu viruses. This is represented by a lower-case v at the end of the subtype's hemagglutinin (H) and neuraminidase (N) protein descriptor.

Human infections with Influenza A subtypes, H1N1v, H3N2v, and H1N2v, have been identified previously, with the CDC reporting this year's first US human cases in August.

Though H1N2v has never been found in humans in the UK before, the UKHSA says that since 2005, 50 human cases have been reported elsewhere around the world.

Virologist Ian Brown from the UK's Animal and Plant Health Agency explains in an expert reaction to the UKHSA report: "These viruses generally lack the ability to spread human to human and such events are usually explained by direct or indirect contact with pigs."

While swine flu viruses have the potential to inflict widespread illness in pig populations, they typically only result in a small number of their deaths. Infected pigs may show symptoms of respiratory illness, though these are often mild or not present at all.

According to experts, this case does not warrant alarm, though further information regarding 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 'breed' if they get into the same host, producing hybrid offspring that are well-adapted to growing in humans but which aren't recognised by our immune responses to previous human influenza infections or vaccinations (a process called genetic shift)," he explains.

"Because of this, it's particularly important to monitor spillovers of influenza A viruses."

Strains of influenza A subtype H1N1 have been responsible for a number of outbreaks in recent history, including the 2009 swine flu pandemic. Human infections with the virus swiftly spread across the world within weeks.

That particular strain – A(H1N1)pdm09 – is now making seasonal rounds in humans and is no longer called swine flu. It's different from the viruses presently circulating in pigs.

To limit the spread of flu viruses between pigs and humans, the CDC recommends hand-washing before and after contact with pigs, not eating or drinking around them, and avoiding contact with pigs showing signs of illness.

Health authorities in the UK are following up close contacts of the confirmed case and advising what actions they should take.

For anyone experiencing respiratory symptoms themselves, the UKHSA reiterates that anybody with such symptoms should avoid contact with others, especially those who are elderly or vulnerable due to existing medical conditions.