BACK in 1796, an English country doctor named Edward Jenner carried out the experiment that was to make him famous. He took pus from a cowpox pustule on the hand of a milkmaid and transferred it to an open cut on the arm of 8-year-old James Phipps. Later, he injected the boy with smallpox virus, and though the youngster became ill he recovered with no lasting effects.
Jenner鈥檚 experiment, the first vaccination, was the start of a process that has progressively isolated humans from micro-organisms. Vaccination was followed by urbanisation and sanitisation. Over the intervening centuries, water and food have been purged of infectious agents, children in rich countries contract fewer childhood diseases, and smallpox itself disappeared from the natural world.
Then, in the late 1980s, came hints that things had gone too far. The world was in the grip of an epidemic of allergies: teachers鈥� desks were filling with asthma inhalers, hay fever ran riot, and nut allergies appeared as if from nowhere. The cause, argued a group of immunologists, was that children鈥檚 immune systems were no longer being primed by childhood infections. In consequence, they overreacted when faced with harmless allergens such as house dust mites and grass pollen.
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The 鈥渉ygiene hypothesis鈥�, as it became known, did not last long in its original form. It is being supplanted by the idea that the allergy epidemic arises not from a lack of nasty infections, but from the non-appearance of some old friends. Today, researchers believe the innocuous microbes that children used to pick up from water, dirt and animals help to educate the immune system to identify threats and respond appropriately. This notion is backed by a completely new vision of how the immune system regulates itself (see 鈥淔ilthy friends鈥�).
It is an intriguing theory. If true, it demonstrates how intimately we are entwined with the world of micro-organisms. Just as the brain of a child raised without social contact and language will never develop normally, so a young immune system deprived of common microbes will fail to function properly.
But it also raises difficulties. We need to identify which of the millions of microbe species we used to be close to are important. And is vaccination the only way to introduce them? Then there are questions over whether a one-off exposure will be enough, and if only young children will benefit.
It is an exciting challenge. To rid the world of serious allergies would be an immense achievement. And there are already strong hints of where to look for beneficial bacteria. The incidence of allergies in people who grow up on farms with animals is way below that in the rest of the population. There may be more health-giving influences on farms than Jenner could ever have imagined.
