Just when most of us thought it was safe to go back into the water (or at least eat chicken and turkey), H5N1 raises its black dorsal fin and reminds us that it has unfinished business with the human race. Although hypotheses abound, virologists have yet to understand avian flu's enigmatic behaviour: burning like a wildfire one season, going to ground the next. However, since the original outbreak in Hong Kong in 1997, one trend remains consistent: after each hibernation or disappearance, H5N1 re-emerges with its virulence intact and its geographical and species ranges extended.
A decade of breakneck research, driven by the fear that another 1918 influenza catastrophe (50-100 million dead in three months, the most murderous event in human history) was close at hand, has provided little solace. The daring laboratory resurrection of the 1918 virus has shown that H5N1 may be only a few amino-acid substitutions away from acquiring transmissibility at pandemic velocity. A pandemic already exists among wild birds and domestic poultry, and we saw a terrifying demonstration of its spreading power during the winter of 2005-06, when outbreaks emerged helter-skelter across western Asia, Europe and Africa - often with little clue as to the source of the infection.
Now H5N1 has resumed its mysterious and seemingly irresistible march with new human victims in China, Indonesia, Egypt and Nigeria, and a spectacular outbreak among English factory turkeys that raises troubling questions about the biosafety of the corporate poultry industry.
The World Health Organisation, meanwhile, is grimly mobilising to confront imminent worst-case scenarios. The proposed response remains the same as last year: rely on local early-warning systems to quickly identify sustained human-to-human transmission and then squelch it with massive saturation of the exposed population with the antiviral Tamiflu. This strategy is based on a dubious perfect-world model of pandemic emergence and medical response, and is overwhelmingly contradicted by the WHO's own recent experiences in the field.
In the first place, Roche's wonder-drug Tamiflu is no longer a magic bullet: several recent deaths in Egypt have been attributed to a Tamiflu-resistant strain and this resistance is likely to spread through the larger population of H5N1 subtypes. Second, the elaborate system of outbreak surveillance, immediate poultry slaughter, and isolation of human victims that has been painstakingly established in China, Vietnam and Thailand simply doesn't exist in many areas of recent outbreak, and will never come into being without a massive, urgent international effort.
In most of sub-Saharan Africa, for example, avian flu has simply flown off the radar screen. Nigeria is the current epicentre in the region only because a minimal surveillance effort exists. It is possible that large-scale outbreaks already rage elsewhere among poor Africans' ubiquitous chickens, but we will only know when their children start dying.
Africa's vulnerability to a new pandemic is horrifying, since avian flu would follow the grim furrows already ploughed by HIV/Aids. Infections synergise with one another: a macabre precedent is the case of the Indian subcontinent in 1918, where - thanks to pre-existing famine, malnutrition and malaria - pandemic influenza killed 10-20 million in less than three months.
The prospect of a new plague unleashed in the shantytowns of Lagos, Kinshasa or Nairobi, in other words, is virtually apocalyptic; yet the avian flu researchers I have recently spoken to are more worried about the potential for a global pandemic to erupt first in the suburbs of Jakarta or elsewhere in Java.
Bluntly put, years of heroic work in Vietnam to contain an explosive H5N1 outbreak that most experts feared was the likely pandemic trigger have been more or less annulled by the rampant and preventable spread of the disease across Indonesia's thousands of islands over the past 18 months. This has been a defeat for the WHO's containment strategy. For fear of losing their base of operations in the country, the WHO and other international agencies acquiesced in the Indonesian government's negligent failure to aggressively cull infected birds or to contain the early human outbreaks. Critics of the disastrous and failed campaign were censored and, in the case of the most senior foreign expert on the scene, even purged for leaking details of the fiasco to the international science press.
As a result, H5N1 is ineradicably entrenched in Indonesian poultry and the human toll has steadily increased, with a number of suspicious "family clusters" that suggest limited person-to-person transmission. Moreover, the virus is killing people within Jakarta itself, where high population densities favour accelerated disease evolution. The recent flood abets the danger. Be more worried, in other words, about the chickens in Java than the turkeys in Suffolk. While it is unnerving to have such a notorious virus unmasked in East Anglia, killer influenza is still most likely to reach London via Heathrow as a result of failed containment efforts elsewhere.
Avian flu will be the first plague in history to be preceded by a vast and lurid advertising campaign; yet despite all the warning signs, the rich countries have entirely failed to back up their rhetoric with sufficient aid to the poor frontline countries, or any genuine effort to develop a "world vaccine".
Mike Davis is professor of history at the University of California, Irvine, and the author of The Monster at Our Door: The Global Threat of Avian Flu.
© Guardian News and Media Limited 2007