UK confirms world’s first case of H5N1 bird flu in a sheep

A sheep in the UK has tested positive for avian influenza H5N1, marking the first known case of the virus in the species worldwide, health officials confirmed.

The infection was identified in North Yorkshire during routine surveillance of livestock on a farm where avian influenza had previously been detected in captive birds, the UK’s Department for Environment, Food & Rural Affairs (Defra) and the Animal and Plant Health Agency (APHA) confirmed on Monday.

Following repeat positive milk tests, the infected sheep was humanely culled, and further testing of the remaining flock was conducted by the APHA at its national reference laboratory. No additional infections were found, and authorities believe this remains an isolated case.

“This is the first time this virus has been reported in a sheep,” Defra and APHA said in the joint statement. “While the risk to livestock remains low, all keepers must remain vigilant and maintain high biosecurity standards.”

UK Chief Veterinary Officer Christine Middlemiss said strict biosecurity measures have been implemented at the affected premises. “We have confirmed the detection of influenza of avian origin (H5N1) in a single sheep on a farm in Yorkshire,” she said. “While the risk to livestock remains low, I urge all animal owners to ensure scrupulous cleanliness is in place and to report any signs of infection to the APHA immediately.”

The case will be reported to the World Organisation for Animal Health (WOAH) and the World Health Organization (WHO) in line with international reporting obligations.

This development comes amid growing global concern over the spread of a newer subclade of H5N1, known as 2.3.4.4b, which has infected an increasing number of mammalian species, including humans, in recent years.

In the United States, outbreaks in dairy cattle have affected nearly 1,000 herds across 17 states as of March 18. Additional cases have been confirmed in swine in Oregon and alpacas in Idaho, according to data from the U.S. Department of Agriculture.

The same clade has also caused infections in 115 domestic cats in more than 20 U.S. states, with the highest concentration reported in California. Mass mortality events linked to H5N1 have been recorded among wild mammals including sea lions in Chile, Peru, Argentina, and Russia.

Other documented cases in mammals include dolphins, polar bears, foxes, skunks, coyotes, dogs, goats, and even rodents in non-laboratory settings.

The UK Health Security Agency (UKHSA) reiterated that bird flu remains primarily a disease of birds and that the risk to human health is very low. “Globally, we continue to see that mammals can be infected with avian influenza A(H5N1),” said Dr. Meera Chand, Emerging Infection Lead at UKHSA. “However, current evidence suggests that the avian influenza viruses we’re seeing circulating around the world do not spread easily to people.”

The Centers for Disease Control and Prevention (CDC) in the U.S. confirmed the first likely case of mammal-to-human transmission of H5N1 in April 2024, involving a dairy farm worker in Texas exposed to infected cattle. Sporadic human cases linked to dairy cow exposure have been reported since, though human-to-human transmission has not been observed.

LINK: A list of all human cases of H5N1 bird flu since 2021

The UK Food Standards Agency also reassured consumers that avian influenza poses a very low food safety risk. “Properly cooked poultry and poultry products, including eggs, remain safe to eat,” said Robin May, Chief Scientific Adviser at the FSA.

Authorities in the UK continue to monitor the situation and have urged livestock keepers to report any suspicious symptoms in animals immediately.