What is avian flu?
Avian influenza, also known as bird flu, is a contagious viral disease in animals, caused by a virus loosely related to human influenza. While all bird species and, less commonly, pigs are thought to be susceptible, domestic poultry flocks are especially vulnerable to infection, which can rapidly result in epidemics among their populations.
Since bird flu was first recognised there have been more than a dozen strains of the virus. Some are relatively harmless, while others result in death within hours.
What are the most dangerous strains?
The H5N1 form of bird flu is the most dangerous. But three versions of the milder H7 form have also spread to humans. Both H5N1 and H7 are referred to as "highly pathogenic", which means they are extremely contagious among birds. The disease spreads both by air and contact with bird droppings. Mortality is close to 100%, with many birds dying on the same day they were infected.
Where has it appeared?
Asia has suffered most heavily in the latest bird flu outbreak, which started in 2003. Millions of Asian birds have died after contracting the disease, or have been destroyed in measures to prevent it spreading.
H5N1 cases in animals have been recorded in more than 50 countries in Asia, Africa and Europe since 2003.
To what extent has Britain suffered?
There have been a handful of outbreaks involving H5N1 and H7 at poultry farms and bird sanctuaries. Each outbreak prompted a slaughter of the flocks involved.
If it just affects birds, why the panic?
According to the World Health Organisation (WHO) more than 300 people around the world have been infected by the H5N1 strain, of whom 216 have died.
So far, most of the human deaths have been in Asia, in communities in which people live in close proximity to poultry.
Although it does not easily infect humans, every time it does, it increases the chance that the virus could mutate into a form that could be passed from one infected human to another.
The WHO says that would probably be how a flu pandemic would start. Pandemics have occurred every 20 to 30 years, but it has been almost 40 years since the last one happened.
The most severe occurred in 1918-1919, and is estimated to have killed around 50 million people worldwide. On September 29 2005, David Nabarro, the WHO expert appointed to coordinate the international response to a pandemic, said a pandemic would cause anything from five million to 150 million human deaths.
The Department of Health's (DoH) national framework for pandemic flu predicts that up to 750,000 extra deaths could be expected in Britain within 15 weeks of a flu pandemic. A quarter to half of the population may be infected and up to 2.5% of those could die.
How does it spread?
WHO scientists believe it is likely that the virus is carried by migrating birds. Others, such as the Royal Society for the Protection of Birds and Birdlife International argue that there is strong evidence to suggest the poultry trade plays a large role in the spread of bird flu.
What measures is the UK taking?
In common with other countries, the British government's plan to tackle bird flu is characterised by surveillance and containment. The Department for Environment, Food and Rural Affairs has asked birdwatchers to help provide an early warning against the arrival of the infection and has issued guidelines accordingly. Scientists are also involved in examining bird droppings for signs of the influenza virus.
The EU says communication between the public, vets and doctors is essential in alerting authorities to any outbreak of flu.
When an outbreak is confirmed, authorities slaughter poultry in an attempt to contain the spread of the virus. Were it to mutate into a form contagious among humans, officials would begin a programme of mass treatment using antiviral drugs and flu vaccines.
The British government plans to treat half the population with Tamiflu and to buy 14.7m courses of antibiotics to treat infected people who suffer potentially lethal complications, such as pneumonia. The health secretary has also signed agreements with two pharmaceutical companies to provide enough flu vaccine to cover the entire UK population in the event of a pandemic. The vaccine would not be ready to tackle the first wave of a pandemic but it would protect people against any subsequent waves. There is also a stockpile of 3.3m doses of H5N1 vaccine for healthcare staff.
What drug treatments are available?
Tamiflu, made by the Swiss pharmaceutical company Roche, is the antiviral drug favoured by most governments.
It can be taken as a preventative treatment, but there is no evidence it will stop people being infected. Doctors believe it could relieve flu symptoms and help the body to fight the virus.
However, there have been concerns that H5N1 is developing resistance to Tamiflu. In December 2005, research published by the New England Journal of Medicine showed that two out of eight patients being treated for bird flu in Vietnam had died despite receiving Tamiflu. The drug is only available on prescription in the UK and, with governments around the world ordering it, has become very scarce. It might be possible to obtain online, but since prices have increased the British government has warned that fakes are in circulation.
Another antiviral drug, Relenza, is available but has to be inhaled and is harder to store over long periods.
Stockpiles of the vaccine against H5N1 could be a first line of defence for priority groups while scientists develop a vaccine against the exact strain responsible for the pandemic.
The British government will buy sufficient vaccine for the entire population should a pandemic begin and the strain of flu be identified, but it would take around seven to nine months to produce.
The government is briefing doctors on how to deal with any mass outbreak. The DoH has made information available to the public, as has the WHO.
What other measures are being taken?
The EU has banned imports of poultry products from countries with bird flu outbreaks. However, on October 17 2005, the then health secretary, Patricia Hewitt, told the Commons there was no danger to people of contacting bird flu by eating poultry.
The Food Standards Agency says there is no evidence to suggest bird flu can be passed on by eating poultry or eggs, but it recommends ensuring they are properly cooked.
The Australian government has recommended washing eggs before breaking them and washing hands afterwards.
What if the pandemic happens anyway?
The DoH would have the main responsibility for coordinating the UK's emergency response, with the support of the Health Protection Agency (HPA), the UK-wide authority responsible for combating the spread of infectious disease.
The DoH would establish a national operations room to support the local response to outbreaks, and would coordinate vaccine distribution to affected areas.
Devolved administrations in Wales, Scotland and Northern Ireland have been asked to coordinate the response in their regions. The HPA has also published an updated influenza pandemic contingency plan, which makes up part of the DoH's overall preparations.
In the event of a pandemic, the HPA would set up a strategic emergency coordination centre. It would coordinate clinical surveillance, provide infection control advice, analyse flu strains and issue information to the public and healthcare professionals. It would also advise the DoH on the use of vaccines.
In December 2005, a House of Lords science and technology committee report said it did not believe the DoH could provide strong enough leadership in the event of a flu pandemic. It recommended that the government appoint a cabinet-level minister to coordinate the implementation of the contingency plan.
How would the response work on the ground?
Strategic health authorities would receive support through regional public health groups, which would coordinate the work of primary care trusts and hospitals in responding to cases.
All hospital and ambulance service trusts would be expected to put in place the necessary resources to care for people affected by a pandemic in their area, as well as offering help to other NHS trusts.
It is likely that areas would be put under quarantine, travel restrictions imposed, schools closed and public meetings banned.
However, British peers have voiced concerns about whether the health infrastructure could cope with the 1 million new cases expected every day at the height of a pandemic.
Panic buying and food shortages are expected, and it is likely that the Cabinet emergency response team (Cobra) would be called into action to coordinate responses to the crisis.
Police would probably need to use stringent powers granted under the Civil Contingencies Act 2004 and the military could be called upon to replace police and other emergency service personnel too ill to work.
