Bird flu: What is it and what's behind the outbreak?

The satellite is going done its worst-ever outbreak of vertebrate flu.

The highly infectious H5N1 strain of the illness is liable for the deaths of hundreds of thousands of chaotic birds and millions of home ones.

Bird flu is an infectious illness of poultry and chaotic birds that has been astir for a century. It usually flares up successful autumn earlier fading away.

"It originated amongst ducks successful Europe and Asia, and dispersed to different birds," says Paul Digard, a prof of virology successful the Roslin Institute astatine Edinburgh University.

The H5N1 virus, which is the astir prevalent strain now, was archetypal reported successful China successful 1996 and has breached retired sporadically ever since.

However, this twelvemonth the microorganism has persisted for overmuch longer than usual.

The H5N1 strain is deadly and tin dispersed done full flocks of home birds wrong a substance of days, done birds' droppings and saliva, oregon done contaminated provender and water.

The existent question of vertebrate flu is the worst 1 ever successful Europe, and successful the US.

"160 cardinal home birds worldwide person been killed by this virus, oregon person had to beryllium culled by farmers to incorporate it," says Professor Munir Iqbal of the UK's Pirbright Institute, which specialises successful carnal welfare.

"This includes 100 cardinal home birds successful the US and Europe."

In occidental European countries, specified arsenic the UK, it has led to ovum shortages successful the shops and fears of a turkey shortage astatine Christmas.

More chaotic birds than ever earlier person been killed by vertebrate flu this twelvemonth - with oversea birds being particularly hard hit.

The existent microorganism has affected 80 antithetic vertebrate species," says Professor Iqbal. "For example, it has killed 40% of the skua colonisation successful Scotland, and 2,000 Dalmatian pelicans successful Greece."

This "huge outbreak" has besides dispersed into taxon specified arsenic seals and foxes, says veterinary adept Dr Louise Moncla of the University of Pennsylvania successful Philadelphia, US.

"These outbreaks began successful Europe, past dispersed to North America, and dissimilar past outbreaks, person not died out," she says.

We are successful the mediate of an "unprecedented wildlife illness outbreak, the breadth and scope of which is staggering", says Dr Rebecca Poulson of the University of Georgia, US.

Scientists are unsure wherefore this outbreak is truthful overmuch worse than others. It whitethorn beryllium that the microorganism has mutated to alteration it to dispersed much readily from vertebrate to bird, oregon to bent astir longer successful the environment.

Dr Nancy Beerens, vertebrate flu adept astatine Wageningen Bioveterinary Research successful the Netherlands, which analyses suspected vertebrate flu samples, says the microorganism whitethorn present beryllium ubiquitous successful chaotic birds.

"As the microorganism present has infected galore chaotic vertebrate species, it becomes improbable that it volition vanish again from the vertebrate population," she says.

China has been vaccinating its home poultry flocks.

However, different countries debar this due to the fact that it is hard to justice which birds person been made immune by the vaccine and which ones person not - and truthful the nutrient and eggs from vaccinated flocks cannot beryllium sold abroad.

"There are strict export controls erstwhile a state decides to vaccinate," says Dr Maurice Pitesky of the School of Veterinary Medicine, University of California, Davis.

Governments successful EU countries and North America person alternatively mostly told their farmers to cull each the poultry successful immoderate flock successful which vertebrate flu has breached out.

Farmers successful the UK and France person besides been told to bring escaped scope poultry flocks indoors, to halt them being infected by chaotic birds.

Despite the commercialized drawbacks of vaccinating poultry, governments successful France and the Netherlands person begun trials of vaccines to effort and bring the vertebrate flu epidemic nether control.

In immoderate instances, humans person caught vertebrate flu erstwhile they person travel into adjacent interaction with infected birds.

"The existent strain of H5N1 presently seems to beryllium debased hazard for this," says Prof Digard.

However, helium says: "We request due surveillance of however acold it is spreading, by monitoring chaotic birds and getting reports from vets dealing with home animals."

Follow Helen connected Twitter @hbriggs.