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Avian Influenza (bird flu)

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Bird Flu

What is avian influenza ?

Avian influenza (commonly known as bird flu) is a virus infectionwhich occurs naturally in birds. Wild birds can carry the virus intestinally, without being affected. Avian influenza can be highly contagious among birds, and can be rapidly fatal to many, including chickens, ducks, and turkeys.

Infection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The 'low pathogenic' form may go undetected and usually causes only mild symptoms, but the highly pathogenic form spreads rapidly through flocks of poultry; the disease has a mortality rate that can reach 100%.

Where is avian influenza usually found?

The virus originated in Eastern Asia, and has tended to spread westward; new strains appear periodically, some classified as low pathogenicity avian influenza (LPAI), causing little harm to infected birds. Other strains are high pathogenicity avian influenza (HPAI); causing serious illness and death among infected birds, and similarly in people. H5N1 is currently the HPAI causing major concern; first isolated in the east, it reached Scotland in April 2006.

How common is avian influenza ?

Like human influenza, the avian form can reach epidemic form among birds, and the disease is endemic to the world's bird population. Low pathogenicity forms are more common than high, and the disease accounts for many laying birds being 'off color' with lower laying rates.

How is avian influenza transmitted?

Infected birds spread the 'bird flu' virus via saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated secretions or excretions or surfaces contaminated by infected birds. Domesticated birds may become infected through contact with infected waterfowl or other infected poultry, or indirectly by contact with contaminated items.

The disease is highly contagious among birds, being spread among domestic fowl by human behaviour, as well as mingling with wild birds; the shooting community probably have a case to answer, with millions of young birds crossing national borders in crowded containers, before release into the wild to spread disease in local populations before being shot for sport.

Migratory waterfowl are currently thought to be the key carriers of the severe strains of the disease.

Can avian influenza be spread from person-to-person?

The disease can be spread by infected birds to people, through direct contact with contaminated items. There have been no recorded cases of person-to-person spread, but viruses do alter their structures, especially when they co-exist in the same host. It is theoretically possible that if someone carrying a virus endemic in humans were to contract the disease, a mutated form of the virus could develop with the ability to 'cross the species barrier', readily infecting human beings.

Pigs are susceptible to both human and bird viruses. If a pig were infected with the bird flu virus at the same time as a human flu virus, the animal could become a "mixing vessel", allowing a new, form of the bird virus to arise with the ability to spread directly from one human being to another.

There is fairly strong evidence that such an event lead to the 1918 human flu epidemic that killed upward of 20 million people.

Who is most at risk?

Currently, only people who have close contact with infected birds are considered at risk. Over three years since the problem was recognized, about 200 human infections have been confirmed, and about 100 people have died, worldwide; mostly in cultures where people and domestic fowls live in very close proximity.

What are the symptoms of avian influenza ?

In birds, avian influenza can range from symptom-free, to ruffled feathers and general malaise, to rapid onset of breathing difficulties and death within two days.

In human beings, mild forms of avian influenza appear to be similar to typical human influenza, including fever, cough, sore throat, and muscle aches. More aggressive forms have included eye infections, pneumonia, severe respiratory distress and other life-threatening complications. The symptoms may depend on the virus strain involved.

How is avian influenza diagnosed?

Initial diagnosis may depend on the individual history, particularly recent travel and contact with birds or avian wastes. Confirmation will depend on laboratory tests of nose and throat swabs, plus sputum, and possibly blood tests.

Is there a treatment for avian influenza ?

The H5N1 'bird flu' virus that has caused human illness and death in Asia has become resistant to amantadine, an antiviral medication used for human influenza. However, oseltamavir (Tamiflu) and zanamavir (Relenza), may well be effective against the H5N1 virus, though further research is needed.

Is there a way to prevent infection?

'Bird flu' is still only a small risk to those who work with birds, their excreta, and untreated products (eg feathers). Appropriate protective gear; including gloves, and - in some cases - masks and goggles - couple with an educative approach, will usually be sufficient. For the general public, a health education campaign that highlights the dangers of close contact (eg feeding pigeons and ducks), and contact with dead animals, will be required. Outside of affected areas, that will probably be sufficient.

Where the risk is higher - where the H5N1 virus has been identified - much tighter measures will be required, specific to the local culture and assessed risks. These measures will include clear directions on risky behaviour, and rigid control of bird movement and care.

What is the mortality rate for avian influenza ?

Among birds, some strains of the disease have a mortality rate approaching 100%; death usually occurring within 48 hours of infection.

 
2003
2004
2005
Total
Cases
Deaths
Cases
Deaths
Cases
Deaths
Cases
Deaths
Cambodia
0
0
0
0
4
4
4
4
China
0
0
0
0
8
5
8
5
Indonesia
0
0
0
0
17
11
17
11
Thailand
0
0
17
12
5
2
22
14
Vietnam
3
3
29
20
61
19
93
42
Total
3
3
46
32
95
41
144
76

Country
January to March 2006
These tables show Confirmed Human Cases of Avian Influenza A (H5N1) Reported to WHO
Cases
Deaths
Azerbaijan
7
5
Cambodia
1
1
China
8
6
Egypt
4
2
Indonesia
13
12
Iraq
2
2
Turkey
12
4
Total
47
32

Is there an avian influenza vaccine?

There currently is no commercially available vaccine to protect humans against H5N1 virus that is being seen in Asia and Europe. However, vaccine development efforts are taking place. Research studies to test a vaccine to protect humans against H5N1 virus began in April 2005, and a series of clinical trials is under way. For more information about H5N1 vaccine development process, visit the National Institutes of Health website.

Can avian influenza be controlled environmentally?

While the disease is restricted to birds, with no confirmed human-to-human transmission, there is good reason to believe that environmental measures can contain the disease, and reduce the riskd to human beings from infected birds.

Measures vary from country to country, and include the following:

Restrictions on keeping poultry outdoor in areas of particular risk of avian influenza. This should ensure that wild birds have no contact with feed and water destined for poultry.

There is an EU-wide ban on the collection of birds on markets, shows, exhibitions and cultural events, unless specifically authorised on the basis of a positive risk assessment.

Birds kept in zoos may be subject to vaccination. All vaccinated birds must be identified and recorded, and trade in these birds will be prohibited except under specific authorisation.

Import restrictions of live birds (pets or poultry and unprocessed feathers) where there has been confirmation of an outbreak of H5N1 avian influenza.

Occupational health guidance to protect people working with infected birds has been prepared by a number of countries .

Surveillance measures to ensure early identification of the infection and biosecurity measures at poultry farms have been tightened up.

Experts are working on the available information on migratory bird species, in order to assist in early warning and risk assessment

Imports controls at national borders are being stepped up, with special measures to prevent illegal introduction of live birds and poultry products that might pose a risk for AI virus introduction.

Outdoor activities that bring people into contact with wild birds, such as hunting and ornithology, may need to be restricted where local outbreaks demonstrate a risk.

Normal hygiene measures after handling dead birds should be followed (hand washing, safe food preparation etc).

Any mass change in the behaviour of wild birds must be reported, to assist in identifying diseased birds. Any abnormal mortality of wild birds must also be reported.

People collecting such dead birds must be given appropriate training in hand hygiene after the contact with them, use of gloves, masks, cleaning and disinfection.

In the event the disease is confirmed or suspected in an area, activities such as bird hunting must be re-assessed and appropriate action taken.

Additional measures will probably added to this list as loopholes are found and exploited by hunters and others, risking the health of the whole community.

Is there legal protection for workers and others?

All workers who may have contact with wild birds, or domestic birds that have had contact with wild birds, are entitled to full training and education; sufficient for them to assess the risks to themselves, and for them to be able to work in a way that minimises or removes the risks to the community. Failure to provide full education and sufficient protective gear, including gloves, masks, eye shields, general protective clothing (as appropriate to the job) and handwashing facilities, would almost certainly be seen by the courts as negligence, particularly if this led to confirmed disease spread.

Bibliography and Further Information Sources

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

 

First Published: 22 April 2006
Last updated: 22 April 2006
© Andrew Heenan 2006
 

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