Governments in a dilemma over bird flu
Uncertainty over the risk posed by bird flu to human health has left policy-makers in a dilemma: how can governments justify committing already scarce public health funds to an unpredictable but potentially catastrophic event?
Experts have warned that the widespread occurrence of the highly pathogenic avian influenza virus, H5N1, could ignite a pandemic capable of killing millions of people around the world. However, calculating with any precision the risk or when it will strike is impossible, and yet the consequences of failing to respond to this uncertain threat could be dire.
“There is no way of predicting when the next pandemic will occur,” said Professor Maria Zambon, Head of the Respiratory Virus Unit at the United Kingdom’s Health Protection Agency.
“Risk assessment in this instance is qualitative, not quantitative. Therefore the margins for error and limits of confidence are wide,” Zambon said.
There were three influenza pandemics last century. The worst was the 1918–19 Spanish flu that killed 20–40 million people worldwide. The Asian flu of 1957–58 killed about one million globally and the 1968–69 Hong Kong flu was responsible for a global death toll of between one and four million lives.
The three strains involved in these outbreaks are thought to have originated in birds. Of the 15 known avian influenza virus subtypes, H5N1 is of particular concern. It has affected poultry populations in eight countries, three of which — Cambodia, Thailand and Viet Nam — have reported a combined total of 79 human infections of which 46 were fatal.
“Never before have we seen so many countries so widely affected by this disease, and with such devastating economic consequences, for rural farms and households as well as for the poultry industry,” said Dr Anarfi Asamoa-Baah, WHO’s Assistant Director-General for Communicable Diseases, referring to flu caused by the H5N1 virus.
The H5N1 virus has already shown two characteristics of previous pandemic flu strains: the ability to infect and to cause severe disease in people. It has not yet shown the third: the ability to pass easily between people. Sustained human-to-human transmission would signal the onset of an influenza pandemic and would trigger activation of national pandemic influenza contingency plans.
However, experts fear that the virus, which is known to mutate, could develop the ability to pass easily between humans either through adaptation to its human host or through genetic exchange with a human flu virus. At present, the main source of infection in humans is direct contact with live or contaminated poultry.
“There has been no evidence of any sustained human-to-human transmission but there were short, dead-end infectious chains which are typical for an avian influenza virus which is not adapted to humans,” said Dr Klaus Stöhr, Coordinator of WHO’s Global Influenza Programme, adding that since every cluster of cases could signal the beginning of a pandemic, every case has to be investigated immediately.
While experts agree that the unprecedented scale and spread of H5N1 has significantly heightened the risk of another influenza pandemic, estimates of the number of people it could kill range from 2 million to 50 million.
With today’s frequent international travel and cross-border flow of goods, once a pandemic strain does emerge, it will be impossible to prevent it from spreading globally.
“People who are infected with the real pandemic virus will be capable of infecting others even before they have any symptoms and therefore, unlike those infected with SARS (severe acute respiratory syndrome), would be impossible to identify at airports,” Stöhr said.