The germ of an idea

LOUIS PASTEUR, the 19th-century French microbiologist and chemist, is credited with confirming that microbes cause disease. When studying ailing silkworms, he made two vital observations. The first was that la flacherie, as the worms' illness was called, was contagious. This led to the germ theory of disease and, ultimately, to the development of antibiotics to treat infectious illnesses in people. In all the excitement over germs, however, his second observation got overlooked: la flacherie was passed from parent to offspring. Almost 150 years later, the idea that susceptibility to infectious disease can be inherited is finally coming of age. A meeting held last week at the Pasteur Institute in Paris heard how the next generation of drugs will target not the microbial agents of infectious illness but their human hosts.

To this end, researchers are studying how different versions of certain genes could cause some people to succumb to infection whereas others are left relatively unscathed. They thus hope to explain not only why some people can be infested with virulent microbes without contracting a disease (whereas others become ill even though they are less infected) but also why such patterns run in families and in ethnic groups.