Tuesday, December 06, 2005

Reference - Bird flu and pandemic influenza: what are the risks? : The Department of Health - About us: Ministers and department leaders


A severe form of avian influenza or ?bird flu? ? called H5N1 ? has affected poultry flocks and other birds in several Asian countries since 2003. As of 30 November 2005, 133 people have also caught the infection, as a result of close and direct contact with infected birds. Sixty-eight of these have subsequently died. There is no firm evidence that H5N1 has acquired the ability to pass easily from person to person. However, concern remains that the virus might develop this ability, or that it might mix with human flu viruses to create a new virus. It is this ability of avian influenza, to change and to mix, that has given rise to the fear of a new human flu pandemic. This regularly updated feature explains the background to the disease, and assesses the nature of the risk to people living in the UK.

What is bird flu?

Influenza virus. Photo: Linda Stannard, 1995
"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).

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 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.

How can bird flu infect people?

People are rarely infected with bird flu viruses. 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.

The first documented cases of bird flu infecting people occurred in Hong Kong in 1997 and this was also the H5N1 strain of virus. Investigation showed that close contact with live infected poultry was the source of the infection.

H5N1 is able to infect people because it is able to cross the species-barrier. 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.

Person-to-person transmission

There is no firm evidence that the H5N1 strain causing the outbreaks in SE Asia has acquired the ability to pass easily from person to person or to sustain transmission.

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.

Outbreaks of bird flu affecting people

Until mid-December 2003 ? the start of the current outbreak in poultry ? highly pathogenic avian influenza (HPAI) was considered a rare disease of birds.

The first documented cases of bird flu in people appeared in Hong Kong in 1997, when 18 people infected with an H5N1 virus strain were admitted to hospital, six of whom died. The source of infection in most cases was traced to contact with diseased birds on farms and in live poultry markets.

As of 30 November 2005, 133 reported cases of H5N1 infection in people have occurred in five countries, Thailand, Vietnam, Cambodia, Indonesia and, most recently, China. Sixty-eight of these have been fatal. Regularly updated information about human cases of H5N1 is available on the WHO website.

The current outbreak in birds

The outbreak now concerning health experts is H5N1. It began in poultry in South Korea in mid-December 2003, and has affected birds in many countries in Asia, Russia, and most recently Turkey and Romania. It involves a variant of the same virus subtype as that associated with the 1997 Hong Kong outbreak.

EU and UK controls are in place aimed at preventing the occurence of bird flu in UK. Nonetheless, it remains a remote possibility that bird flu could be introduced to poultry through the migration of wild birds, the illegal importation of dead chickens for consumption, the illegal importation of live birds or the entry into the UK of a person who has acquired the illness in an infected area.

As a precautionary measure, the UK has banned imports of live chickens from the following countries (due to bird flu outbreaks in these countries): Croatia, Turkey, Romania, Russia, Kazakhstan, Thailand, Cambodia, China, Hong Kong, Laos, Indonesia, Vietnam, Pakistan, Malaysia, South Africa, and North Korea.

A temporary ban on imports of captive birds from outside of the EU was agreed on 25th October 2005 at the Standing Committee on the Food Chain and Animal Health (SCoFCAH). The ban on commercial bird imports is accompanied by restrictions on the import of pet birds.

The European Commission (EC) has banned imports of all poultry, poultry meat products, and eggs from Thailand. The importation of ostrich and ostrich products from South Africa has also been banned, along with imports of other birds of the ratite family (a type of flightless bird). Other non-poultry birds, including pet birds accompanied by their owners, have also been banned.

The World Organization for Animal Health (OIE) maintains an up-to-date list of countries affected.

Imports and avian flu (opens new window)International disease monitoring (opens new window)World Organisation for Animal Health (OIE) (opens new window)OIE update on Avian Flu (opens new window)

Risk of a human influenza pandemic

In December 2004, the World Health Organization (WHO) stated:

?WHO and influenza experts worldwide are concerned that the recent appearance and widespread distribution of an avian influenza virus, influenza A/H5N1, has the potential to ignite the next pandemic."

World Health Organization, 8 December 2004

"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 occuring 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:

adapt, giving it greater affinity for humans, or;
exchange genes with a human flu virus, thereby producing a completely new virus strain capable of spreading easily between people, and causing a pandemic.
By necessity, if a new strain were to occur then few people, if any, would have a natural immunity to it.

What else can be done?

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, whether due to an H5N1 or another new strain. 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.

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

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

Purchase of antiviral drugsUK Influenza Pandemic Contingency Plan Operational guidance for health service plannersPandemic influenza antivirals frameworkDH Pandemic Flu pagesExplaining pandemic flu - October 2005 edition


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.

In addition, on 20 July 2005 the Department of Health invited manufacturers to tender for a contract to supply a limited amount of H5N1 vaccine. The move is part of work to prepare for and reduce the impact of a possible flu pandemic.

The Department proposes to purchase two million doses of H5N1 vaccine. 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.

What can I do?

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

covering your nose and mouth when coughing or sneezing, using a tissue when possible;
disposing of dirty tissues promptly and carefully ? bag and bin them;
avoiding non-essential travel and large crowds whenever possible;
maintaining good basic hygiene, for example washing your hands frequently with soap and water to reduce the spread of the virus from your hands to your face, or to other people;
cleaning hard surfaces (e.g. kitchen worktops, door handles) frequently, using a normal cleaning product;
making sure your children follow this advice.

If you do catch flu:

stay at home and rest;
take medicines such as aspirin, ibuprofen or paracetemol to relieve the symptoms (following the instructions with the medicines). Please note: Children under 16 must not be given aspirin or ready made flu remedies containing aspirin;
drink plenty of fluids.
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.

Important information for you and your family

Advice to travellers

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.

Recommendations to travellers to areas experiencing outbreaks of the disease in poultry are:

Avoid visiting live animal markets and poultry farms.
Avoid contact with surfaces contaminated with animal faeces.
Do not attempt to bring any live poultry products back to the UK.

National Travel Health Network and Centre (NaTHNaC) (opens new window)

Bird flu and pandemic influenza: what are the risks? : The Department of Health - About us: Ministers and department leaders

1 Comments:

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