What is special about the current outbreaks in poultry?
The current outbreaks of highly pathogenic avian influenza, which
began in South-east Asia in mid-2003, are the largest and most
severe on record. Never before in the history of this disease have so
many countries been simultaneously affected, resulting in the loss
of so many birds.

The causative agent, the H5N1 virus, has proved to be especially
tenacious. Despite the death or destruction of an estimated 150
million birds, the virus is now considered endemic in many parts of
Indonesia and Viet Nam and in some parts of Cambodia, China,
Thailand, and possibly also the Lao People’s Democratic Republic.
Control of the disease in poultry is expected to take several years.
The H5N1 virus is also of particular concern for human health, as
explained below.


Which countries have been affected by outbreaks in poultry?
From mid-December 2003 through early February 2004, poultry
outbreaks caused by the H5N1 virus were reported in eight Asian
nations (listed in order of reporting): the Republic of Korea, Viet
Nam, Japan, Thailand, Cambodia, Lao People’s Democratic
Republic, Indonesia, and China. Most of these countries had never
before experienced an outbreak of highly pathogenic avian influenza
in their histories.

In early August 2004, Malaysia reported its first outbreak of H5N1 in
poultry, becoming the ninth Asian nation affected. Russia reported
its first H5N1 outbreak in poultry in late July 2005, followed by
reports of disease in adjacent parts of Kazakhstan in early August.
Deaths of wild birds from highly pathogenic H5N1 were reported in
both countries. Almost simultaneously, Mongolia reported the
detection of H5N1 in dead migratory birds. In October 2005, H5N1
was confirmed in poultry in Turkey and Romania. Outbreaks in wild
and domestic birds are under investigation elsewhere.
Japan, the Republic of Korea, and Malaysia have announced control
of their poultry outbreaks and are now considered free of the
disease. In the other affected areas, outbreaks are continuing with
varying degrees of severity.

What are the implications for human health?
The widespread persistence of H5N1 in poultry populations poses
two main risks for human health.

The first is the risk of direct infection when the virus passes from
poultry to humans, resulting in very severe disease. Of the few avian
influenza viruses that have crossed the species barrier to infect
humans, H5N1 has caused the largest number of cases of severe
disease and death in humans. Unlike normal seasonal influenza,
where infection causes only mild respiratory symptoms in most
people, the disease caused by H5N1 follows an unusually
aggressive clinical course, with rapid deterioration and high fatality.
Primary viral pneumonia and multi-organ failure are common. In the
present outbreak, more than half of those infected with the virus
have died. Most cases have occurred in previously healthy children
and young adults.

A second risk, of even greater concern, is that the virus – if given
enough opportunities – will change into a form that is highly
infectious for humans and spreads easily from person to person.
Such a change could mark the start of a global outbreak (a
pandemic).
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