Bird flu (avian influenza)

What is bird flu?

Avian influenza, or bird flu, is an infectious disease that is caused by a type of influenza virus. As the name implies, the disease mostly affects birds, but it can also affect humans, as well as animals such as cats and pigs.

The first cases of bird flu in humans were reported in 1997 in Hong Kong. Since then, there have been several isolated outbreaks among humans in various parts of the world, with most infections traced to contact with sick birds. Many of the cases of bird flu in humans have occurred in Asia. This is thought to be mainly due to traditional farming methods used in many Asian countries, where people live in close contact with animals.

While there have not been any reports of human infections with bird flu in Australia, several outbreaks have occurred among commercial flocks of birds. The most recent outbreak was in New South Wales in 1997. All outbreaks of bird flu among poultry in Australia have been successfully contained and eradicated. Avian influenza of the H5N1 subtype (see below) has never occurred in Australia.

Are there any current outbreaks of bird flu?

Since late 2003, there have been several reported outbreaks of bird flu among domestic poultry in Asia. More recently there have been infections discovered in poultry and wild birds in Europe, Asia, the Middle East, Africa and Russia. These outbreaks are ongoing, and millions of birds have been culled in an attempt to eradicate the disease from domestic bird populations.

Why has there been so much media interest in the recent outbreaks?

There are different subtypes and strains of the virus that causes bird flu, and some cause more severe disease than others. The subtype of the virus that has caused the recent outbreaks of bird flu in Asia is called influenza A (H5N1) virus, or simply H5N1 virus. The H5N1 subtype of the bird flu virus is very aggressive, and can cause serious infections in both birds and humans. Nearly 100 per cent of susceptible birds die from this infection, and of the small number of human cases, more than half of those infected have died. In 2008, cases of H5N1 bird flu among humans have been reported in Indonesia, China, Vietnam, Egypt and Bangladesh.

How is it spread?

Bird flu is highly contagious, and can infect all types of birds. Wild birds, especially water birds such as ducks, are the natural hosts of the virus. They often have no symptoms or only mild disease, but can pass the infection to domesticated birds (such as chickens and turkeys), who can develop severe disease. The disease can be passed between birds by direct contact, or carried between farms by contaminated objects, such as cages, clothing or feed.

Human infections with bird flu are not common, but it is possible for people to catch bird flu from infected poultry or surfaces contaminated with droppings, saliva or feathers from infected birds. Human cases of bird flu generally coincide with outbreaks in poultry.

There have only been a small number of cases of bird flu being passed from one human to another.

Why are health authorities concerned?

Type A influenza viruses, which are the type of influenza viruses that cause bird flu, are able to change over time. There are 2 main ways that the virus can evolve and change, known as antigenic drift and antigenic shift.

• Antigenic drift. When influenza A viruses replicate, their genetic material changes slightly, so that new strains of the virus are constantly replacing older strains. This process, known as antigenic drift, causes only small changes in the genetic makeup of viruses.
• Antigenic shift. The virus can also mix its genetic material with other subtypes of the influenza A virus, resulting in a completely new and different subtype of virus from either of the original viruses. This is known as antigenic shift.

Scientists are worried because the H5N1 subtype of the bird flu virus is able to mutate rapidly, and can readily mix with viruses that infect other animal species. If the H5N1 virus were to mix with the human flu virus through the process of antigenic shift, a highly infectious new virus could form, which could easily spread from one human to another.

The human population would not have any natural immunity to this entirely new viral subtype. Health officials are concerned that a virus that no-one had immunity to, which could be easily passed from one person to another, could result in an influenza pandemic (worldwide outbreak of disease), with high rates of illness and death.

What are the symptoms?

In most people, the initial symptoms of avian flu are similar to the symptoms that you experience when you have the regular form of the flu — fever, muscle aches and pains, and cough. The symptoms generally appear within 3 to 7 days of being infected with the virus.

Those people who are infected with aggressive, or virulent, subtypes of the virus (such as H5N1) may develop complications such as pneumonia. Another serious complication is a condition known as acute respiratory distress syndrome, which causes life-threatening breathing problems due to the lungs filling with fluid rather than with air.

How is bird flu treated?

Oseltamivir (brand name Tamiflu) and zanamivir (brand name Relenza) — antiviral medications used to treat regular flu — may be helpful in the treatment of bird flu. However, their effectiveness against the H5N1 subtype of the virus is uncertain, and there are also concerns about the availability and cost of these medications. To have any effect, these medications need to be taken within 2 days of the symptoms first appearing.

Is there a bird flu vaccine?

In June 2008, the Australian Therapeutic Goods Administration (TGA) approved the registration of a vaccine, known as Panvax, for use in the prevention of influenza caused by a pandemic strain of avian influenza virus. Panvax can be used only when an influenza pandemic has been officially declared by the Australian Government in consultation with the World Health Organization.

How can I avoid catching bird flu while travelling?

If you are travelling overseas, especially in Asia, take the following steps to protect yourself:

• avoid domesticated birds, poultry farms and live bird markets;
• regularly wash your hands or use alcohol-based hand sanitisers;
• wash your hands thoroughly after handling any uncooked poultry or eggs;
• avoid eating any foods that contain raw or undercooked eggs; and
• if you are eating chicken, make sure it is thoroughly cooked (proper cooking destroys the virus in poultry and eggs).

It may also be a good idea to have a flu shot before you leave. Although it won't protect you from bird flu, it can prevent simultaneous infection with both regular flu and bird flu viruses.

If you do become unwell or experience any flu-like symptoms on your return to Australia, you should see your doctor. Make sure you tell your doctor that you have been travelling, and which areas you visited. Your doctor also needs to know if you visited any open-air markets or farms.

What is being done to prevent bird flu entering Australia?

The government has implemented measures to prevent bird flu entering Australia, including:

• banning the import of live poultry or uncooked poultry products (including eggs);
• improving surveillance at all ports of entry into Australia; and
• increasing sampling of domestic flocks of birds for evidence of disease.

myDr, 2005
© Copyright: myDr, UBM Medica Australia, 2000-2010. All rights reserved.

Last Reviewed: 15 August 2008