What Is Bird Flu And What Are The Risks?

As officials work to determine whether the outbreak of bird flu at a farm in Yorkshire is an isolated case, Sky News examines the virus in more detail.

:: What is bird flu?

Avian flu, or bird flu, is an infectious viral illness that spreads among birds. There are 16 types.

In rare cases it can affect humans, with two strains having claimed hundreds of lives over the last 10 years.

It affects a number of species of birds, including geese, ducks, turkeys and chickens.

Because birds do not always get sick if they are infected with the illness, seemingly healthy birds can pose a risk to people who come into contact with them.

:: How does it spread to humans?

It is spread through direct contact with infected birds (either dead or alive), their droppings, or secretions from their eyes or respiratory tract.

The virus is not transmitted through cooked food.

The NHS says poultry and eggs are safe to eat in areas that have experienced outbreaks.

:: What risk is there of the virus spreading to humans?

Officials have been keen to stress the risk to human health from this outbreak is considered to be extremely low and there is no risk to the food chain.

:: What strain is this current outbreak?

The Department for Environment Food and Rural Affairs has confirmed the virus is the H5 strain, but has said it is not the H5N1 strain, which is the deadliest.

The exact strain won't be known until laboratory test results come back later this week.

:: When was the last case in the UK?

The last serious case in the UK was back in June 2008.

Hens in Banbury, Oxfordshire, were confirmed as having the H7N7 strain, and the outbreak was confined to just one premises.

:: How many people have died from bird flu?

According to the World Health Organisation (WHO) , by July 2013 633 people had been infected with the H5N1 strain and 377 had died. Indonesia, Egypt and Vietnam have been the worst-hit countries.

Reports began to emerge in March 2013 that people in China were being infected with H7N9 strain.

There were 134 confirmed cases and 43 people had died by July 2013, the WHO said.

Millions of birds have been killed to prevent the spread of the virus.