U.K. detects first human case of 'distinct' form of swine flu

Officials are racing to track the contacts of the United Kingdom's first human case of a "distinct" form of swine flu.

On Monday, the U.K. Health Security Agency (UKHSA) announced it had detected a single confirmed human case of influenza A(H1N2)v as part of routine national flu surveillance.

There have been dozens of human cases of that strain reported globally since 2005, but none of them are genetically related to the recently identified case, officials said.

"Based on early information, the infection detected in the U.K. is a distinct clade (1b.1.1), which is different from recent human cases of influenza A(H1N2) elsewhere in the world but is similar to viruses in U.K. swine," reads the UKHSA's statement.

Officials said the individual experienced a mild illness and fully recovered, but the source of their infection isn't yet known.

"We are working rapidly to trace close contacts and reduce any potential spread," Meera Chand, the UKHSA's incident director, said in a statement. "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."

That includes increased surveillance in surgeries and hospitals in North Yorkshire, a region of northern England.

H1N1, H1N2 and H3N2 are major subtypes of swine influenza A viruses in pigs and occasionally infect humans, usually after direct or indirect exposure to pigs or contaminated environments, UKHSA officials said in their statement.

A total of 50 human cases of influenza A(H1N2)v, the broader strain identified in the U.K. case, have been reported in various countries, including Canada.

Manitoba's Department of Agriculture and Resource Development reported one human case of variant H1N2 in the province to the Public Health Agency of Canada in late 2021, and said it appeared to be an isolated instance, with no evidence of human-to-human transmission.

The year before, Manitoba reported cases of variant influenza viruses found in two unrelated individuals in different communities. One was a case of human influenza A(H1N2)v and one was a case of human influenza A(H1N1)v, along with an unrelated case of H3N2 variant influenza.

In 2009, however, a different strain sparked a pandemic. That H1N1 influenza A virus contained genetic material from viruses that were circulating in pigs, birds and humans in the 1990s and 2000s, and it exploded globally, becoming known as "swine flu."

H1N1 is now circulating in humans seasonally and is distinct from the virus strains currently circulating in pigs.