Bird flu: everything you need to know

The avian virus will inevitably reach Britain, doctors say. But just how worried should we be - and what precautions can we take?Jeremy Laurance answers the questions we're all asking

Yes. At its worst a pandemic of avian flu could have a devastating global impact, greater than a terrorist attack, nuclear accident or environmental disaster. The World Health Organisation estimates that a mild pandemic could cause between 2 million and 7.5 million deaths. David Nabarro, the United Nations co-ordinator on avian and human flu, said the death toll could rise as high as 150 million in a severe pandemic. Last year's Boxing Day tsunami killed around 250,000.

Would a pandemic be more likely if bird flu reached Britain?

A pandemic depends on the bird flu that has infected humans mutating so that it acquires the capacity to spread from human to human like ordinary winter flu.

It does not matter where in the world this happens - in eastern England or north Vietnam - because once the new virus takes hold in the human population it will be spread round the world by international air travel. Flu is many times more infectious than Sars (Severe Acute Respiratory Syndrome) and Sars went round the world in weeks after it was first detected in Hong Kong in early 2003.

Is a pandemic inevitable?

Sir Liam Donaldson, the Government's chief medical officer, says that it is a question of when, not if, this happens. But he added that it was "less likely" to occur this winter because, in one scenario, the virus would have to undergo a series of mutations which could take a long period of time. (In a second scenario, the virus could undergo a genetic "reassortment" - a major mutation - to create a pandemic strain in a single event.)

What if bird flu arrives (in birds) in the UK?

The confirmation last week that birds infected with the H5N1 strain of avian flu have died in Turkey and Romania demonstrates that the disease is moving westwards, probably carried by migratory birds. If avian flu reached these shores and infected British poultry it would spell economic disaster for all of the farms affected.

Would humans be at risk?

Yes, if they have close contact with infected poultry, through living or working on poultry farms. So far there have been 117 cases of humans directly infected with H5N1 avian flu of whom 60 are known to have died, reported to the WHO.

This is not the first time that avian flu viruses have infected humans, but the H5N1 strain of avian flu has been the most lethal, causing the largest number of cases of severe disease and death. The cases are from four countries in South-east Asia - Vietnam, Thailand, Cambodia and Indonesia - where people traditionally live closely with their poultry.

Is it only those working closely with poultry who would need to worry this time around?

So far there have been no confirmed cases of human to human transmission of H5N1, (though there are a number of suspected cases). So the risk to anyone who does not have close contact with poultry would be minimal.

But there is a second greater risk - that someone working with poultry becomes infected with the avian H5N1 virus at the same time as they contract ordinary human winter flu. The two viruses would then mix and there is a possibility that they could genetically "reassort" to create a new strain that would spread from person to person, triggering a pandemic. This is the event, which could happen anywhere in the world, for which the WHO is waiting.

If bird flu arrives in Britain, what can I do to protect myself and my family?

Stay away from infected poultry farms. They would be quarantined anyway as soon as bird flu was detected. The virus is transmitted in the birds' faeces and the highest risk is believed to be during the slaughter, feather-plucking and butchery of the birds. Children should be kept away from areas that could have been contaminated by infected birds. Ducks should be avoided because they can be "silent carriers" - they are infected with the avian flu virus and can pass it on but do not fall sick themselves. Wash your hands if you have contact with live birds or touch anywhere that live birds have been.

Would it be safe to eat poultry and eggs?

Cooking destroys the virus so there should be no risk from eating cooked poultry or eggs. However, handling raw infected poultry could transmit the virus. Close monitoring by the authorities is therefore essential to ensure that an outbreak of avian flu in Britain is detected and dealt with before chickens from an infected farm enter the food chain. The European Union announced last week that it was banning imports of chicken from Turkey.

What are the symptoms of avian flu?

They are indistinguishable in their early stages from ordinary winter human flu. Coughing, sneezing and fever are the first tell-tale signs. However, while ordinary human flu is usually a mild respiratory illness, avian flu is more aggressive, commonly leading to pneumonia and multi-organ failure.

Who would be at greatest risk?

Most cases of human infection with avian flu have so far occurred in children and young adults. This is different from ordinary winter flu, which tends to be worst in the elderly and chronically sick. It depends on the nature of the virus and is impossible to predict. If a pandemic strain of flu emerged that targeted children it would increase global alarm.

DO THE DRUGS WORK?

Is there a vaccine?

Existing flu vaccines would be useless against avian flu. Scientists have developed a generic H5N1 avian flu vaccine that would not prevent infection with the virus but might lessen the impact of the illness and save lives. However, early testing suggests that it would have to be given in a high dose, and limited manufacturing capacity would mean that only a tiny proportion of the world's population could be protected. Further research is urgently needed.

Can avian flu be treated?

Antiviral drugs, such as Tamiflu, are the only medical defence. The Government is stockpiling 14.6 million courses of Tamiflu, enough for a quarter of the population, but has so far only taken delivery of 2.5 million. The rest will be delivered over the next year.

How effective is Tamiflu?

Unlike flu vaccine, anti-viral drugs can be used for any strain of flu. However, their effectiveness is limited. The drug must be started within 48 hours of the onset of symptoms, and it should lessen the severity of the illness, helping to save lives. One tablet must be taken morning and night for five days. The NHS cost for a five-day course of Tamiflu (10 tablets) is about £18. It can also be used as a preventative treatment, following exposure to birds or humans infected with avian flu, but in that case the course would have to continue for a minimum of seven days and up to six weeks during an epidemic.

Does Tamiflu work in children?

Yes, when given after the development of symptoms, to lessen the impact of the illness. However, it has not been tested as a preventative treatment in children under 12 and its safety or efficacy in that role are unknown.

Are there any problems with Tamiflu?

There has been one case of a Vietnamese girl with avian flu who was treated with Tamiflu and who did not respond. She had a resistant strain of the virus, researchers from Tokyo University reported last week in the journal Nature. The disclosure is a blow to global plans to stockpile the drug as it suggests that it may not work if resistance to the drug grows. The researchers recommend that countries consider ordering other antiviral drugs, such as Relenza, which is similar to Tamiflu but more difficult to use because it is inhaled.

Should I buy Tamiflu over the internet?

Demand for Tamiflu has soared as concern about bird flu has grown. It is only available on prescription, but some websites have been offering it with an online consultation with a doctor. However, most genuine suppliers are sold out and the Department of Health has warned that counterfeit Tamiflu is circulating.

If a pandemic in humans should strike, is there anything I can do?

When the epidemic is at its height, the only defence will be to keep your distance from other human beings. That means avoiding crowded places such as buses and trains; keeping your children out of school; and trying not to touch places other people have touched (the virus can survive for some hours on door handles and surfaces). During the Sars outbreak in Hong Kong in 2003, people wore surgical masks and carried tissues with which to open doors when they were out shopping. We could see the same happening in London if pandemic flu arrives at Heathrow.

SHOULD WE WORRY NOW?

No, unless you are a poultry farmer. There are three strands to this story and they tend to be confused. There is bird flu in birds; there is bird flu in humans; and there is the threat of a human pandemic.

Bird flu in birds has spread through poultry flocks in the Far East, causing economic devastation to poultry producers. It has now reached the borders of Europe, and it could arrive in Britain at any time.

More than 100 humans have been infected with bird flu in Asia through direct contact with infected birds. More than half of the human cases have died.

This much has already happened, and it is bad enough. However, the lethal strain of flu that could spread from human to human and cause a pandemic has not yet emerged.