What is it and what is behind the epidemic?

Chicken saved

Chicken saved

The world is experiencing the worst bird flu epidemic ever.

The highly infectious H5N1 strain of the disease is responsible for the deaths of hundreds of thousands of wild birds and millions of domesticated birds.

What is bird flu and how deadly is it?

Avian influenza is an infectious disease of poultry and wild birds that has been around for a century. It usually flares up in the fall before fading away.

“It originated among ducks in Europe and Asia and spread to other birds,” says Paul Digard, professor of virology at the University of Edinburgh’s Roslin Institute.

The H5N1 virus, which is currently the most prevalent strain, was first reported in China in 1996 and has erupted sporadically since then.

However, this year the virus lasted much longer than usual.

The H5N1 strain is deadly and can spread through entire flocks of domestic birds in a matter of days, through bird droppings and saliva or through contaminated feed and water.

Scientist in Israel carries away the carcass of a seabird that died of bird flu

Scientist in Israel carries away the carcass of a seabird that died of bird flu

The current wave of bird flu is the worst ever recorded in Europe and the United States.

‘160 million pet birds worldwide have either been killed by this virus or had to be culled by farmers to contain it,’ says Professor Munir Iqbal of the UK’s Pirbright Institute, who specializes in animal welfare.

“That includes 100 million pet birds in the US and Europe.”

In Western European countries, such as the UK, it has led to egg shortages in stores and fears of a turkey shortage at Christmas.

A colony of Dalmatian pelicans on a lake in northern Greece

Bird flu has decimated pelican colonies in Greece

What is so unusual about this outbreak?

More wild birds than ever have been killed by bird flu this year, with seabirds particularly hard hit.

The current virus has affected 80 different bird species,” says Professor Iqbal. “For example, it has killed 40% of the skua population in Scotland and 2,000 Dalmatian pelicans in Greece.”

This “huge epidemic” has also spread to species such as seals and foxes, says veterinary expert Dr Louise Moncla of the University of Pennsylvania in Philadelphia, US.

“These outbreaks started in Europe, then spread to North America, and unlike past outbreaks, they haven’t died out,” he says.

We are in the midst of ‘an unprecedented epidemic of wildlife diseases, the scale and scope of which is staggering’, says Dr Rebecca Poulson of the University of Georgia in the US.

Scientists aren’t sure why this outbreak is so much worse than others. It may be that the virus has mutated to allow it to spread more easily from one bird to another or to remain in the environment longer.

Gannets on Rouzic Island off the coast of Perros-Guirec in Brittany, western France

The recent spike in bird flu has been particularly damaging to protected seabird species such as the gannet

Dr Nancy Beerens, an avian flu expert at Wageningen Bioveterinary Research in the Netherlands, who analyzes suspected avian flu samples, says the virus may now be ubiquitous in wild birds.

“As the virus has now infected many wild bird species, it is unlikely to disappear from the bird population again,” he says.

What is being done to counter the epidemic?

China has vaccinated its domestic poultry farms.

However, other countries avoid it because it is difficult to judge which birds have been made immune to the vaccine and which have not – and therefore meat and eggs from vaccinated farms cannot be sold abroad.

“There are strict export controls when a country decides to vaccinate,” says Dr. Maurice Pitesky of the School of Veterinary Medicine, University of California, Davis.

Instead, governments in EU countries and North America have generally told their farmers to cull all poultry on any farm where avian flu has broken out.

Farmers in the UK and France have also been told to bring flocks of free-range poultry indoors, to prevent them from becoming infected by wild birds.

A French vet injects a bird with the vaccine

France and other EU countries are trialling bird flu vaccines

Despite the commercial drawbacks of vaccinating poultry, the governments of France and the Netherlands have initiated vaccine trials to try to bring the avian flu epidemic under control.

Is bird flu a risk to humans?

In some cases, humans have contracted avian flu when they have come in close contact with infected birds.

“The current strain of H5N1 currently appears to be at low risk for this,” says Prof. Digard.

However, she says, “We need proper surveillance of how it is spreading, monitoring wild birds and getting reports from pet vets.”

Follow Helen on Twitter @hbriggs.

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