One person in the south-west of England has bird flu, the UK Health Security Agency has said.
The risk to the wider public continues to be very low, the agency said, but it urged people not touch sick or dead birds.
“Bird to human transmission of avian flu is very rare and has only occurred a small number of times in the UK previously," the health protection body said.
“The person acquired the infection from very close, regular contact with a large number of infected birds, which they kept in and around their home over a prolonged period of time.
“All contacts of the individual, including those who visited the premises, have been traced and there is no evidence of onward spread of the infection to anyone else. The individual is currently well and self-isolating.”
The UK has recently had a large number of bird flu outbreaks among animals, with chief veterinary officer Christine Middlemiss issuing warnings to bird owners over hygiene.
There are 64 cases of avian influenza H5N1 in England, the Department for Environment, Food and Rural Affairs says, with new cases being confirmed on a daily basis.
There are also cases in Wales, Scotland and Northern Ireland.
The whole of the UK is covered by avian influenza prevention zones, which require bird keepers to take measures try to stop the disease’s spread.
They include housing or netting for all poultry and captive birds to keep them away from wild birds, and disinfecting clothing and equipment.
Some strains of bird flu can pass from birds to people, but this is extremely rare, the agency says. It usually requires close contact with an infected bird, so the risk to humans is generally considered very low.
Human-to-human transmission of bird flu is also very rare, the organisation said.
The case was detected after the Animal and Plant Health Agency identified an outbreak of the H5N1 strain of bird flu in a flock of birds.
The infected birds have all been culled. As a precaution, the health security agency swabbed the person involved and detected low levels of flu.
Further lab analysis showed that the virus was the H5 type found in birds.
The authority said that, at this point, it has not been possible to confirm that this is a H5N1 infection (the strain that is circulating in birds in the UK).
But the agency has notified the World Health Organisation, which continuously monitors avian and other zoonotic influenza viruses through its Global Influenza Surveillance and Response System.
It said this is the first human case of this strain in the UK, although there have been cases elsewhere around the world.
“While the risk of avian flu to the general public is very low, we know that some strains do have the potential to spread to humans and that’s why we have robust systems in place to detect these early and take action," said Prof Isabel Oliver, chief scientific officer at the health security agency.
“Currently there is no evidence that this strain detected in the UK can spread from person to person, but we know that viruses evolve all the time and we continue to monitor the situation closely.
“We have followed up all of this individual’s contacts and have not identified any onward spread.”
Ms Middlemiss said: “While avian influenza is highly contagious in birds, this is a very rare event and is very specific to the circumstances on this premises.
“We took swift action to limit the spread of the disease at the site in question. All infected birds have been humanely culled, and cleansing and disinfection of the premises is under way.
“This is a reminder that stringent cleanliness when keeping animals is important.
“We are seeing a growing number of cases in birds on commercial farms and in backyard flocks across the country. Implementing scrupulous biosecurity measures will help keep your birds safe.”
The agency calls high-risk contacts of an infected person each day to see if they have developed symptoms.
People are also offered anti-viral treatment after exposure to infected birds to stop the virus reproducing in their body.
Swabs are also carried out on people, even if they do not have symptoms.
“This is clearly going to be big news but the key thing is that human infections with H5N1 are really rare [fewer than 1,000 worldwide since 2003] and they almost always occur as a result of direct, long-term contact with poultry," said Prof Mike Tildesley, from the University of Warwick.
“It can result in a nasty infection for the individual concerned but there has never been any evidence of sustained human-to-human transmission of H5N1, so at present I wouldn’t consider this to be a significant public health risk.”
Paul Wigley, professor of avian infection and immunity at the University of Liverpool, said: “Whilst avian influenza has the potential to be transmitted from poultry to humans, it is very rare and, as in this case, usually due to close and long-term contact with infected birds.
“Avian influenza such as the H5 serotype is largely adapted to infect birds and so is very unlikely to be transmitted from person to person.
“The advice given by APHA and UKHSA over contact with infected birds is sensible and should be followed. The risk of wider infection in the general public remains low.”