The UK Health Security Agency (UKHSA) has sought to reassure the public that the threat to humans from avian flu is low.

The annoiuncement comes as bird keepers must implement strict biosecurity measures to stop the virus spreading.

The Department for Environment, Food and Rural Affairs (DEFRA) said it is the country’s largest ever bird outbreak.

But the risk to human health from the virus remains very low, UKSA has said.

Chief veterinary officers in Great Britain have declared an avian influenza prevention zone (AIPZ) to halt the disease’s spread amongst poultry and captive birds.

Across the UK, 190 cases have been confirmed since late October 2021 – but more than 30 of these have ben confimed since the beginning of this month.

Prof Christine Middlemiss, the UK’s chief veterinary officer, told the BB: “We’ve never had to do this before, we’ve never had this level of environmental infection going on before that’s posing such a risk.”

The Food Standards Agency said that avian influenzas posed a very low food safety risk for consumers. The FSA said properly cooked poultry and poultry products, including eggs, are safe to eat.

The restrictions apply to keepers with more than 500 birds – ie large scale poultry businesses – with rules to limit access to non-essential visitors.

Avian flu is transmitted from wild to domestic or farmed birds.

It can be more prevalent at this time of year when natural migrations occur.

A statement from the chief veterinary officers said: “Bird keepers have faced the largest ever outbreak of avian flu this year and with winter brings an even more increased risk to flocks as migratory birds return to the United Kingdom.

“Scrupulous biosecurity and hygiene measures is the best form of defence.”

More than 20 birds were reported dead by the Wiltshire Wildlife – mostly Canada geese and two swans.The deaths are suspected to have links to avian flu.

Dave Turner, estates manager at the Wiltshire Wildlife Trust, told the BBC he had stopped all fishing and river access at the reserve, as well as educational activities including pond-dipping.

The public is being asked to stay on footpaths and to avoid walking through bird faeces.

He said: “It’s very hard with wild populations. You can’t control where they come from. We have large numbers of Canada geese and lapwings and more, and you don’t know what could be potentially coming and going from site.

“From a wildlife perspective this is the worst we’ve ever seen,” he said. “It could be a very long winter unfortunately.”

Clinical signs can vary between species of bird and some species (for example ducks and geese) may show minimal clinical signs.

Highly pathogenic avian influenza (HPAI) is the more serious type. It is often fatal in birds. The main clinical signs of HPAI in birds (which can include any or a combination of the following) are:

• sudden and rapid increase in the number of birds found dead
• several birds affected in the same shed or air space
• closed and excessively watery eyes
• lethargy and depression
• recumbency and unresponsiveness
• incoordination and loss of balance
• head and body tremoring
• drooping of the wings and/or dragging of legs
• twisting of the head and neck
• swelling and blue discolouration of comb and wattles
• haemorrhages on shanks of the legs and under the skin of the neck
• loss of appetite or marked decrease in feed consumption
• sudden increase or decrease in water consumption
• respiratory distress such as gaping (mouth breathing), nasal snicking (coughing sound), sneezing, – gurgling or rattling
• fever or noticeable increase in body temperature
• discoloured or loose watery droppings
• cessation or marked reduction in egg production