The H5N2 strain has never before been found in a human, health agency says, but stresses risk remains low.

The global health agency, in a statement on Wednesday, said the 59-year-old died in Mexico City in April after developing symptoms including a fever, shortness of breath, diarrhoea and nausea.

The man’s relatives said he had already been bedridden for three weeks for other reasons before the onset of his acute symptoms.

Mexico’s public health department said in a statement that the man’s underlying ailments included chronic kidney failure, diabetes and high blood pressure.

He sought hospital care on April 24 and died on the same day.

Initial tests showed an unidentified type of flu that subsequent weeks of lab testing confirmed was A(H5N2), the WHO said.

It was the “first laboratory-confirmed human case of infection with an influenza A(H5N2) virus reported globally”, the agency added.

Andrew Pekosz, an influenza expert at Johns Hopkins University in the United States, told the Reuters news agency that the man’s prior health conditions put him at “a risk of more severe influenza”.

But how this individual got infected “is a big question mark”.

The WHO said the source of exposure to the virus was unknown, although cases of A(H5N2) have been reported in poultry in Mexico. These include in a backyard chicken farm in Michoacan state, which borders Mexico State, where the man lived, but authorities have so far been unable to establish a connection.

The WHO said no further human cases have been discovered despite testing people who came in contact with the deceased at home and in hospital.

“Based on available information, WHO assesses the current risk to the general population posed by this virus as low,” it said.

Mexico’s Ministry of Health also said there was “no risk of contagion for the population,” noting that “all samples from identified contacts [of the patient] have been negative”.

Authorities are monitoring farms near the victim’s home and have established a permanent monitoring system to detect other cases in wildlife in the area, the ministry added.

A different variant of bird flu, A(H5N1), has been spreading for weeks among dairy cow herds in the US, with a small number of cases reported among humans.

Other bird flu varieties have killed people across the world in previous years, including 18 people in China during an outbreak of A(H5N6) in 2021, according to a timeline of bird flu outbreaks from the US Centers for Disease Control and Prevention.

Pekosz said that since 1997, H5 viruses have continuously shown a propensity to infect mammals more than any other avian influenza virus.

“So it continues to ring that warning bell that we should be very vigilant about monitoring for these infections because every spillover is an opportunity for that virus to try to accumulate those mutations that make it better infect humans,” Pekosz said.