Britain has been hit with its largest ever avian flu outbreak leading farms to cull more than one million birds.

The mutated H5N1 strain has rapidly spread across the country in recent months, leading to alerts being issued to bird owners.

An Avian Influenza Prevention Zone, requiring all bird owners to keep their flocks indoors, is in force across the UK, said The Department for Environment, Food & Rural Affairs (Defra).

While routine monitoring of sites by the Animal and Plant health Agency is ongoing.

Such visits led to pensioner Alan Gosling, from Buckfastleigh, Devon, testing positive and being forced to isolate.

Environment Secretary, George Eustice, told the House of Commons we are currently seeing “the largest ever outbreak in the UK of avian influenza”.

Defra has not confirmed the number of culled birds.

Bird to human transmission of avian flu is very rare and has only occurred a small number of times in the UK previously – though if caught can see around half of those infected die.

How did the new strain come about?

Avian flu is caused by the highly pathogenic causative agent called HPAI A(H5N1), a bird adapted strain of H5N1 (A/H5N1), itself a subtype of the influenza A virus.

The current mutated strain first appeared in Asia and is now spreading globally, killing tens of millions of birds and spurring the culling of hundreds of millions others to stop its spread.

It came to the UK by migratory wild birds from Europe, where high infection levels have also been recorded, reports the Guardian.

A rare white-tailed eagle was found dead in November on the Isle of Skye in Scotland before a postmortem confirmed it had avian flu.

Experts believe it may have caught the virus after eating infected greylag geese.

The UK’s Chief Veterinary Officer Christine Middlemiss said almost 300 wild birds had been found to have the strain in more than 80 locations and detections are continuing.

Where has it been detected in Britain?

The worst-hit area appears to be Lincolnshire, with the virus first confirmed there on December 11.

So far, a dozen outbreaks have been detected in the county and an estimated one million birds have been culled at farms there.

Professor Ian Brown, of the Animal and Plant Health Agency, said: “There is a high density of poultry farms in Lincolnshire and the virus has found its way in because it has been able to breach the biosecurity barrier of the farms.”

Exclusion zones have been put in place around Lincolnshire sites, including near Mablethorpe, Alford and South Elkington.

However, an outbreak was detected in North Yorkshire in November, while there have also been two outbreaks near Pocklington, East Yorkshire.

The latest outbreak of the virus was first discovered in North Yorkshire on 21 November, and was detected in Lincolnshire in December.

There have also been two outbreaks near Pocklington, in East Yorkshire.

An outbreak was also found at a premises near Highworth, north of Swindon, Wiltshire, in December.

All birds at the site were being humanely culled and temporary control zones were put in place, said Defra.

The UK’s Chief Veterinary Officer Christine Middlemiss added: “We are seeing a growing number of cases in birds on both commercial farms and in backyard flocks across the country. Implementing scrupulous biosecurity measures will help keep your birds safe.”

How did Alan Gosling catch it?

The 79-year-old duck expert had been looking after Muscovy ducks, which eventually moved to his home and became his pets.

Alan was ordered to test for the disease after a local flock of 160 local ducks came up positive and were culled last week.

Daughter-in-law Ellesha Gosling said: “The past couple of weeks have been hell for this family. He saw all of his ducks killed, and they were like his closest friends.

“He is often on the phone to us, asking what the doctors have said – but we can’t answer questions we don’t know the answers to.”

Ellesha said Alan first began to notice several ducks of his huge flock becoming sick a few days before Christmas.

The Muscovy ducks originally lived in a public area near Alan’s home.

After DEFRA and APHA got wind, more than 100 ducks living outside of Alan’s house on his property were culled in a bid to prevent the spread, shortly after Christmas.

Despite pleading against it, the 20 ducks which lived inside his home with him were culled on New Years Day by a team in Hazmat suits.

The family are keen to see the inside of the property cleared of contamination as they fear his condition could worsen, but say this has not yet taken place despite their pleas.

They say they have been told the cleaning of the inside of the house will have to be paid for by Alan – a further blow for the retiree.

Alan is now isolating alone as he mourns his pets and his family are worried about his health.

What are the symptoms?

Signs and symptoms of bird flu usually begin within two to seven days of infection, depending on the type.

In most cases, they resemble those of conventional influenza, including:

• Cough
• Fever
• Sore throat
• Muscle aches
• Headache
• Shortness of breath

Bird flu is usually caught by humans through contact with sick birds or with surfaces contaminated by their feathers, saliva or droppings.

People with bird flu can go on to develop life-threatening complications, including:

• Pneumonia
• Pink eye (conjunctivitis)
• Respiratory failure
• Kidney dysfunction
• Heart problems

Bird flu can kill 50 percent of the people it infects but contracting it for a human is very rare.

Professor Isabel Oliver, Chief Scientific Officer at the UK Health Security Agency, said: “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.

“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.”

What is the situation in Europe?

The German animal health institute Friedrich-Loeffler-Institut said the end of the epidemic is not yet in sight.

It is warning that the situation is developing more rapidly than last winter, with new cases coming in every day with a large distribution area.

Since October, the virus has been detected 675 times in wild birds, and 534 outbreaks have been reported in domestic (backyard and commercial) animals.

The virus has also been detected in mammals in several countries: in foxes in the Netherlands and Finland, in seals in Germany and Sweden, and in otters in Finland.

Kees de Jong, chairman of the poultry department of the agricultural and horticultural organization, LTO Nederland, said avian flu is no longer a seasonal concern as it once seemed.

He said solutions are needed beyond the culling of poultry and a vaccine is needed.

Ms Middlemiss added: “It used to be that we would have a reasonable-sized outbreak and then have two or three quiet years.

“But that’s not happening now. We’re seeing this across the whole of Europe. We need to understand better why we’re getting these ongoing infections every year.”