Defeating the airborne virus

Winging it: Although migratory waterfowl are the best carriers of bird flu, they are also the most resistant to it. Photo by Pte John Wellfare

Live-bird markets have been identified as one of the ways avian influenza is spread from bird to bird.

It is impossible to predict when a bird flu pandemic might, if ever, occur, but it is possible to be prepared, Sqn-Ldr Belinda Ball reports.

An influenza pandemic occurs when a new strain of influenza virus aemerges, spreading around the globe and infecting many people at once. An influenza virus capable of causing a pandemic is one that people have no natural immunity to, can easily spread from person to person, and is capable of causing severe disease in humans.

What is bird flu and is it going to cause a flu pandemic?

Bird flu, or avian influenza, is an infectious disease of birds caused by type-A strains of the influenza virus. There have been a number of outbreaks of bird flu recently in Asia and Europe. There have also been some cases of people catching bird flu as a result of close contact with sick poultry. Because the bird flu virus has infected a small number of people and because it causes severe illness or death, even in young, otherwise healthy people, it is being closely watched in case it undergoes genetic changes that would make it able to spread easily from person to person.

If these changes occur, then it could cause a pandemic. So far, this has not occurred. Organisations such as the World Health Organisation (WHO) and the Australian Government are concerned that this may happen in the future.

History of avian influenza

The natural reservoir of avian influenza viruses are migratory waterfowl – most notably, wild ducks – and these birds are also the most resistant to disease.

Domestic poultry, including chickens and turkeys, are particularly susceptible.

Domestic flocks coming into contact with wild migratory waterfowl have been implicated as a frequent cause of outbreaks and live bird markets have also played a significant role in the spread of epidemics.

It has been noted that there are about 16 sub-types of influenza virus known to infect birds, but to date, all outbreaks of the highly pathogenic form have been caused by the subtypes H5 and H7.

The most recent cause for concern occurred in December 2003 and January 2004, when laboratory tests confirmed the presence of H5N1 avian influenza virus in human cases of severe respiratory disease in Vietnam. Since then, there have been three waves of disease, affecting multiple countries in Asia. As of November 1, 77 human cases had been reported to the WHO, of which 31 deaths were attributed to the virus. Fortunately, none of the avian influenza viruses have developed the ability to spread easily from person to person, which is a prerequisite for a pandemic.

Sqn-Ldr Belinda Ball is a clinical policy nurse with Defence Health Services.

Frequently asked questions

What is an influenza (or flu) pandemic?

A flu pandemic is a worldwide outbreak of disease that occurs when a new influenza-A virus appears in humans, causes serious illness and spreads easily from person to person.

Is a flu pandemic different to the flu that occurs every year?

The seasonal outbreaks, or epidemics, of flu that occur each year are caused by subtypes of influenza viruses that are already circulating among people, so there is already a level of immunity in the community.

Because we know which viruses are circulating each year, we can also vaccinate people for them. Pandemic flu is caused by an entirely new virus sub-type, which no-one would have immunity to. The pandemic can spread very quickly before a vaccine becomes available, affecting a greater number of people and likely causing greater sickness and death than a seasonal flu.

Is bird flu or pandemic flu in Australia?

There are no current reports of bird flu in animals or humans in Australia. A truly pandemic virus has not emerged yet anywhere in the world.

What is the current level of threat of a pandemic in the world?

A close watch is being kept on the bird flu outbreaks. An expert group in Australia met at the end of May this year and determined that the threat level is Overseas-3. This means there are some human bird flu cases overseas, but the infection is limited and doesn’t appear to be readily passing from human to human. A pandemic would be declared if we reached Overseas-6 – that is, when there is increased and sustained transmission of human bird flu in the general population.

In a recent statement, the Commonwealth Chief Medical Officer said the accepted likelihood of an influenza pandemic in the next one-to- two years was about 10 per cent.

More bird flu questions answered next edition.

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