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Although
migratory waterfowl are the best carriers of bird
flu, they are also the most resistant to it.
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Photo
by PTE John Wellfare
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AN
INFLUENZA pandemic occurs when a new strain of influenza
virus emerges, 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.
Squadron Leader 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 an 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 few
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 met in Australia 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.
