The Government has issued a warning to all animal owners after the first case of bird flu in a sheep was confirmed at a Yorkshire farm. The case was identified during a routine inspection of the premises after an outbreak of avian flu among captive birds and marks the first time the H5N1 strain has been detected in an English sheep. The infected sheep was humanely culled to allow for "extensive testing", the Department for Environment, Food and Rural Affairs (DEFRA) said.

"Strict biosecurity measures have been implemented to prevent the further spread of disease," UK Chief Veterinary Officer Christine Middlemiss added. "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 Animal Plant Health Agency immediately." Ms Middlemiss stressed that there was "no evidence to suggest an increased risk to the nation's livestock population".

It comes after avian influenza was identified in dairy cows in the US, with the strain's first human casualty confirmed as a 65-year-old with underlying health conditions in January.

They reportedly contracted the disease following exposure to a personal flock of birds, including some of wild origin.

Despite this, authorities in Louisiana assured the public that general danger to humans remained low - although "people who work with birds, poultry or cows, or have recreational exposure to them, are at higher risk".

The H5N1 strain has already proved adept at jumping between species, having spread to mammals including foxes, bears, raccoons and seals in America alongside over 60 other human cases.

DEFRA has enforced an "avian influenza protection zone" for the whole of England to prevent the flu spreading, with 13 regions also subject to mandatory housing measures, meaning that birds must be kept inside.

Dr Meera Chand, Emerging Infection Lead at the UK Health Security Agency, said: "Globally, we continue to see that mammals can be infected with avian influenza A (H5N1).

"However current evidence suggests that the avian influenza viruses we're seeing circulating around the world do not spread easily to people - and the risk of avian flu to the general public remains very low."

"UKHSA has established preparations in place for detections of human cases of avian flu and will respond rapidly with NHS and other partners if needed," she added.