A virus strain similar to a form of swine flu circulating among pigs has been detected in the UK for the first time.
Influenza A(H1N2)v was found in a person as part of routine national flu surveillance undertaken by the UK Health Security Agency (UKHSA) and the Royal College of General Practitioners (RCGP).
The person was checked by their GP after experiencing mild respiratory symptoms, but they have since made a full recovery.
An investigation is now underway to find the source of the infection, with people who have been in close contact with the patient being offered testing, and treatment if they end up testing positive.
Meanwhile pig-keepers have been urged to report any suspicions of swine flu to their vets immediately, as some strains of the virus can be passed to humans.
The UKHSA said it is "increasing surveillance within existing programmes involving GP surgeries and hospitals in parts of North Yorkshire".
Its incident director, Meera Chand, said: "We are working rapidly to trace close contacts and reduce any potential spread... Investigations are underway to learn how the individual acquired the infection and to assess whether there are any further associated cases."
Swine flu: First case of swine flu strain H1N2 found in humans in North Yorkshire (The Yorkshire Post)
What are swine flu symptoms?
Symptoms of swine flu, otherwise known as H1N1, usually develop within one to four days of being exposed by the virus.
Here are the most common symptoms, according to the Mayo Clinic:
Fever, but not always
Chills and sweats
Runny or stuffy nose
Watery, red eyes
Tiredness and weakness
Feeling sick to the stomach, vomiting, but this is more common in children than adults
Is there a swine flu vaccine?
Two vaccines have been developed to protect against the virus that causes swine flu - under the brand of Pandemrix and Celvapan.
Most people given the Pandemrix vaccine will only need one dose. People who have the Celvapan vaccine will need two doses, at least three weeks apart, according to the NHS.
The vaccine is different to the seasonal flu vaccination offered every year, which does not protect against swine flu.
Where did swine flu come from?
The current H1N1 swine flu strain has genetic roots in an illness that infected pigs at the 1918 Cedar Rapids Swine Show in Iowa, USA, according to researchers at the University of Pittsburgh Graduate School of Public Health.
In a research paper, published online in 2009, they say: "At the same time the 1918 flu pandemic was rapidly spreading among humans, pigs were hit with a respiratory illness that closely resembled symptoms seen in people.
"Early experiments confirmed that this 1918 swine virus and a human strain emerged about the same time. Since then, this ancestor virus has re-assorted genetically with other influenza strains at least four times, leading to the emergence of the new 2009 strain, which has retained some similarities to the original virus."
The US Centers for Disease Control and Prevention (CDC) adds: "Subsequent research indicates that descendants of the 1918 virus still persists enzootically in pigs. They probably also circulated continuously in humans, undergoing gradual antigenic drift and causing annual epidemics, until the 1950s."
Is swine flu dangerous?
The majority of people can fight off swine flu on their own, as its symptoms are similar to those of regular flu, according to the Cleveland Clinic.
Symptoms last about eight days on average, and those who experience worsening or longer symptoms are encouraged to seek medical help.
A study following the 2009 H1N1 flu pandemic suggested clinical symptoms were similar to seasonal influenza, with the exception of vomiting.
It said mortality rate was higher in 2009 H1N1-infected patients with pneumonia, co-morbid conditions, and patients who required ventilatory support.
The World Health Organisation says 250,000 to 500,000 people die of seasonal flu annually.