LONDON — It would be funny if it were not so serious. As migratory birds carry the avian influenza virus west across Europe, Britain is following in the footsteps of Russia, Ukraine, Romania and Turkey and asking hunters to shoot down as many incoming ducks and geese as possible. They have been issued with bird-flu testing kits to see if their victims are carrying the dreaded virus, but they really have little to worry about: all the cases of direct bird-to-human infection, now over 100 in total, have occurred on family farms in Southeast Asia.
The panic over bird flu is not wholly misplaced. If the H5N1 strain that is currently ravaging wild bird flocks learns to pass between human beings easily while retaining even a tenth of its current lethality — the death-rate among people who catch it directly from birds has been as high as 50 percent — the world would face an influenza pandemic as grave as the one in 1918-19. That one, known as the “Spanish influenza,” killed up to 100 million people at a time when the world’s population was only a third of what it is now.
Recent research has shown that the 1918 virus was also a purely avian strain that jumped to human beings, but then changed enough to become highly infectious between people. Its peculiar pattern of mortality, with a much higher death rate than usual among healthy young adults (half the victims of the Spanish flu pandemic were between 18 and 40 years old), is reappearing in the cases of direct bird-to-human transmission of the past two years. If the current avian virus also develops the ability to move easily between people, the world is in trouble.
Only in the past couple of decades has it been widely understood that almost all the quick-killer infectious diseases that have emerged to ravage human populations since the rise of civilization come from our own domestic animals. Human beings in the wild, like other predators that live in small, isolated groups of a few dozen individuals or less, would rarely have fallen victim to the quick-killer viruses and bacteria whose natural habitat is animals that live in large herds.
Even if such a disease did jump from some prey animal to the hunters who killed it, and even if it then adapted enough to infect the other members of the hunter-gatherer band, the new, human-infectious form would usually die out when it had run through those few dozen people. Only when civilization brought people together in large groups, and those people began living in constant close contact with domesticated versions of herd-dwelling animals, did the quick-killer diseases that often devastate those species begin to adapt permanently to the human species.
Over the past three or four thousand years this process has given us a whole range of highly infectious new human diseases, including quite lethal ones like smallpox, cholera, typhoid and the Black Plague. Influenza, which colonized civilized human beings via their flocks of domesticated birds, is usually a relatively mild member of this family of diseases, but the flu virus mutates with great ease, and occasionally it assumes a highly lethal form.
As our population has grown into the billions, and the volume and speed of travel have soared, we have become more vulnerable to these “emergent” diseases, but they are unlikely to emerge on a British or even a Russian farm. Eighty years ago the “Spanish influenza” virus probably made its way from wild ducks into chickens and thence into human beings on a Kansas farm, but modern commercial farming does not involve people and their animals sharing the same living spaces. Moreover, if some disease does cross the species barrier anyway, its human victims are far more likely to get early treatment (and, if necessary, quarantine).
The places where the style of farming and the density of human and animal populations still favor the easy movement of diseases from animals into people are mostly in Asia, particularly in Southeast Asia. That is where all the new flu viruses have emerged in the past half-century, where the SARS virus came from two years ago, and where other emergent diseases are most likely to appear. As a first step, it would make sense to create a network of trained observers who would report on any unusual disease patterns among the local farm families or their animals.
This is being done in Thailand, and much poorer Vietnam is making a start, but Indonesia has done little, the Chinese refuse to say what they are doing, and some of the smaller countries have done nothing. The developed countries would be wise to support these reporting networks, since they offer the best chance of stopping a new disease before it reaches the rest of the world.
In the longer run, farmers throughout the region must be encouraged to change their long-established ways of raising poultry, pigs and other animals. That is a tall order, but similar shifts in farming practice have already happened elsewhere, and at least the region’s economy is developing fast enough that it can provide markets for a more commercial style of farming and nonfarm jobs for those no longer needed on the land.
The countryside wouldn’t be nearly so picturesque at the end of the process, but the world wouldn’t be facing so many new diseases, either.