Avian (bird) flu
Novel influenza viruses have the potential to generate global pandemics if they are sufficiently transmissible among humans.
Avian (bird) flu is contracted by humans through exposure to infected poultry. Person to person transmission has not been confirmed.
Of the four types of influenza virus, only two trouble humans, A and B. Most regional epidemics are due to type B. However, human pandemics such as the catastrophic 1918 flu, reported to have killed twice as many people as World War I, are caused by type A. These have avian lineages, according to a recent flu review in American Scientist.
While there have been several pandemic 'false alarms' in recent decades, experts agree that a flu pandemic is well overdue. The trouble with the flu virus is that it is continually mutating and changing. An expert report on how to deal with a flu pandemic in Ireland was produced for the Department of Health recently. It is a serious concern.
The first documented human outbreak of avian influenza A (type H5N1) resulted in 18 hospitalisations and six deaths among Hong Kong residents in 1997.
Investigations of that outbreak concluded that close contact with live infected poultry was the source of human infection in all 18 cases. For this reason, the practice of marketing live poultry directly to consumers should be discouraged in areas which experience outbreaks of highly pathogenic avian influenza among poultry.
The 1997 outbreak in Hong Kong was examined in detail. However, information about the disease in humans and its modes of transmission have been limited by the relatively small number of cases to date.
In 1999, two World Health Organisation (WHO) laboratories confirmed avian influenza A (type H9N2) viruses for the first time in humans. The two patients were children hospitalised in Hong Kong.
In mid-December 2003, outbreaks of H5N1 avian influenza were confirmed in the Republic of Korea, Viet Nam, Japan, Thailand, and Cambodia.
The World Health Organisation warned about the danger that the bird flu could mutate or combine with other viruses to create a world pandemic.
Further outbreaks of the bird flu were reported in other parts of Asia in late January 2004. As a precautionary measure, the EU Commission suspended the importation of all poultry products from Thailand after the death of a chicken butcher there from the virus.
While laboratory tests confirmed the human infections, there was no evidence of person to person transmission. Like the 1997 virus, the new strain did not appear to contain sequences from human flu viruses that would speed its spread from person to person, thankfully lessening fears that a lethal pandemic flu was imminent.
Culling of poultry
Rapid culling of infected or exposed poultry is seen as the major line of defence for preventing further human cases of bird flu and possibly averting the emergence of a new influenza virus capable of causing an influenza pandemic.
While trade restrictions were put in place by some countries to protect animal health, arising from the 2004 scare, the WHO does not believe that any processed poultry products (whole refrigerated or frozen carcasses and products derived from them) and eggs in or arriving from areas experiencing outbreaks of avian influenza in poultry flocks pose a risk to public health.
It is well known that influenza viruses are killed by adequate heat. The WHO has reiterated the importance of good hygiene practices during handling of poultry products, including hand washing, prevention of cross-contamination and thorough cooking (70°C).
However, as with the SARS virus, the full picture of the avian flu has still to be determined by scientists.
*This article has been compiled using information from the WHO, the Centres for Disease Control and scientific publications.