Avian influenza or 'bird flu' is a highly contagious disease of birds, caused by influenza A viruses. In birds, the viruses can present with a range of symptoms from mild illness and low mortality to a highly contagious disease with a near 100% fatality rate.

The bird flu virus currently affecting poultry and some people in Asia and other areas is the highly pathogenic H5N1 strain of the virus.

As the virus can remain viable in contaminated droppings for long periods, it can be spread among birds, and from birds to other animals, through ingestion or inhalation.

All bird species are thought to be susceptible to avian influenza. Migratory birds such as wild ducks and geese can carry the viruses, often without any symptoms of illness, and show the greatest resistance to infection. Domestic poultry flocks, however, are particularly vulnerable to epidemics of a rapid, severe and fatal form of the disease.

There are many different subtypes of influenza A virus. The most virulent are called highly pathogenic avian influenza (HPAI) and can reach epidemic levels among birds. Of these, subtype H5, and more particularly subtype H5N1 currently, pose the greatest concern for human health. Two other subtypes - H9 and H7 - have caused illness in people but neither has caused outbreaks in poultry as severe as H5N1-related ones.

According to the World Health Organization (WHO), there is mounting evidence that the H5N1 strain has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in people.

H5N1 is able to infect people because it is able to cross the species-barrier, although it does not do this easily. In human populations, where domestic pigs and wild and domestic birds live in close proximity with people, the mingling and exchange of human and animal viruses can more easily occur.

Those who have become infected have had close direct contact with infected birds. Historically, human infection with avian influenza viruses has usually caused mild conditions such as conjunctivitis (eye infection) and mild flu-like symptoms. More severe infections can lead to pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.

There are no confirmed cases of person to person spread in the outbreaks in Asia and Turkey. So far, while some instances of spread from one person directly to another have been reported, these have been isolated one-off occurrences with no further spread to people, and the route of transmission remains unconfirmed.

WHO does not at present recommend any restrictions on travel to any country currently experiencing outbreaks of bird flu in poultry flocks, including countries which have also reported cases in humans.

If you are visiting countries with reported outbreaks of H5N1 bird flu among poultry, you should observe the following measures:

Countries currently known to have had cases of H5N1 in birds are:

If you have been in contact with live or dead poultry in an affected country be aware of the symptoms of bird flu in humans. They are similar to ordinary flu symptoms and can appear suddenly. They may include:

If you have these symptoms whilst abroad and have been in close contact with live or dead poultry you should seek medical advice locally.

If you develop the above symptoms within seven days of leaving an affected country and you had close contact with live or dead poultry, it is very important that you seek immediate medical attention.

Either telephone your doctor, or ring NHS Direct on 0845 4647.

In February 2006, avian influenza H5N1 virus was found in a dead cat on the island of Ruegan (north Germany), where H5N1 has been identified in a number of wild birds including swans.

The German authorities have advised that people in areas where H5N1 has been detected in wild birds should not let their cats roam freely outside. 

This is not an unexpected finding, as it is known that cats can become infected with the virus. However, their role in onward transmission is not known hence the precautionary approach being adopted by the German authorities.

Defra is urgently seeking further scientific advice on transmission of infection to cats, but not currently advising cat owners in the UK of any need for precautionary measures, as there is no evidence of infection in the UK.

"Most experts believe that it is a matter of when, not whether, another influenza pandemic strikes."
Getting ahead of the curve: A strategy for combating infectious disease. A report by the Chief Medical Officer. January 2002 (p44).

"Wherever in the world a flu pandemic starts, perhaps with its epicentre in the Far East, we must assume we will be unable to prevent it reaching the UK. When it does, its impact will be severe in the number of illnesses and the disruption to everyday life. The steps we are setting out today will help us to reduce the disease's impact on our population."
Sir Liam Donaldson, Chief Medical Officer, 1 March 2005

But what is a pandemic, and what causes it? We are used to epidemics of 'ordinary' flu, which occur seasonally, every year, around the world. An epidemic is a widespread outbreak of disease occurring in a single community, population or region.

A pandemic, on the other hand, occurs on a much greater scale, spreading around the world and affecting many hundreds of thousands of people across many countries.

There are three main groups of flu viruses: influenza A, B and C. Influenza B and C viruses infect people only, however, influenza A viruses have the ability to cross the species barrier and infect people, birds, and animals such as pigs and horses. Among people, influenza A is the source of most 'ordinary' flu epidemics and has caused all previous flu pandemics.

Experts fear that the H5N1 subtype of avian influenza A could trigger the next pandemic, for several reasons. Firstly, it has already demonstrated an ability to infect people and cause severe disease - one of the key characteristics of a pandemic strain. Secondly, the virus has the ability to mutate and acquire genes from viruses infecting other species.

Experts are concerned that the virus could either:

By necessity, if a pandemic strain were to occur then few people, if any, would have a natural immunity to it.

The Chief Medical Officer's guide to pandemic flu, revised and published on 19 October 2005, has been produced for both members of the public and health professionals who wish to better understand the threat of pandemic flu.

The DH website provides further information on what the Government is doing to plan for an influenza pandemic as part of its overall contingency planning. The UK has had a national influenza pandemic plan since 1997 and was one of the first countries to publish a pandemic plan. The plan has been continually updated and the revised UK Influenza Pandemic Contingency Plan was published on 19 October 2005.

The revised plan outlines the actions that Government and other authorities are taking to prepare for a possible pandemic, and the actions that different organisations would take in the event of a pandemic, to slow down the spread of infection and minimise disruption. The plan is based on the framework recommended by the World Health Organization for national pandemic plans.

"This is a high quality plan, which shows that the UK continues to be at the forefront of preparations internationally for pandemic influenza. We hope that every country will develop their preparations to the same high degree."
Dr Asamoa-Baah, Assistant Director-General - Communicable Disease, World Health Organization

Antiviral drugs

There is some evidence that recent H5N1 viruses are susceptible to a class of antiviral drugs called neuraminidase inhibitors, although they appear to be resistant to the alternative antiviral drug, amantadine.

The Government is expanding its stockpile of antiviral drugs against the contingency of a flu pandemic. On 1 March 2005, the Health Secretary announced the procurement of 14.6 million treatment courses of the antiviral, Tamiflu - enough to treat a quarter of the UK population.

Vaccines

There are already several potential vaccines for protecting humans from infection with bird flu, at various stages of testing and production. Vaccine manufacturers and institutions working to develop and produce bird flu vaccines are using several candidate virus strains based on H5N1, which have been made available by the World Health Organization.

The UK's National Institute for Biological Standards and Control (NIBSC) is one of several organisations worldwide participating in the development of a vaccine to combat H5N1.

Whether these will be suitable for use against a new pandemic flu strain depends on how much the pandemic strain may have mutated and changed from the original H5N1 virus strain used to create the vaccine.

If the virus should substantially change, it is unlikely that existing vaccines would be effective, and a new one would have to be developed. Whilst the existence of an H5N1 vaccine could speed up the production of an effective vaccine, work on creating a vaccine could only begin once the new strain has been identified.

The Department of Health is finalising a contract for the purchase of 2-3 million doses of vaccine against the H5N1 strain currently circulating in Asia and other areas. This strategic stockpile could be used for research or as a first line of defence for priority groups, whilst a vaccine against the exact flu strain is manufactured. Experts will also be able to carry out further clinical studies on the H5N1 vaccine to learn more about how it works against the virus and how effective it could be.

Additional to this, the Chief Medical Officer announced on 20 October 2005 that the Department of Health is inviting manufacturers to tender for a contract to supply pandemic flu vaccine once the pandemic strain is known. The proposal to purchase, in advance, the capacity needed to make pandemic flu vaccine will make sure that an effective vaccine is available for use in the UK as quickly as possible after a flu pandemic starts. The UK will need approximately 120 million doses to be available as soon as possible.

General information aimed at local authorities, schools and other education establishments, essential services and the business sector, on the key issues to consider in planning for an influenza pandemic is available in the UK Influenza Pandemic Contingency Plan, at Annex J (pages 169 to 174).

Clear guidance will be issued by Health Departments based on the advice of the UK National Influenza Pandemic Committee, guidance from the WHO, or real time modelling should the need arise.

You can reduce, but not eliminate, the risk of catching or spreading influenza during a pandemic by:

If you do catch flu:

These measures are for your own health and to avoid spreading the illness to others.

Should a flu pandemic occur, more information will be given at the time through leaflets, websites and the media. Such information will tell you how you can protect yourself and your family and what to do if you think you are infected.

Some people will be recommended treatment – further information will be given at the time.

In addition to the specific webpages listed above, the following links are to websites (and website sections) that provide useful and regularly updated information on avian influenza.