As we enter the third millennium, we take our capability to cure infectious diseases for granted. We anticipate that when we are afflicted by a sore throat, a wheezing cough or an infected cut, there will be a magic pill that will remove the poisonous substance from our bodies. Certainly we have developed an arsenal of antibiotics which can kill or inhibit many of the bacteria that can cause infection and, for the latter part of the twentieth century, the fear that these infections cause has disappeared. We have been much less successful in developing drugs that work against fungal infections and have only limited success against infections caused by viruses. We are still terrified of that one infectious disease that is poised to eradicate the human race, the one against which we have no defence. An epidemic of plague killed an estimated 100 million people in the Middle East, Europe and Asia during the sixth century. Plague returned during the fourteenth century, when it was known as the Black Death, and it is estimated to have killed up to half the population of Europe, or about 75 million people. In the 1980s, HIV appeared poised to cause an AIDS epidemic and in the 1990s, a prion, the causative agent of BSE, seems ready to cause havoc through the population of the United Kingdom. The AIDS epidemic did not materialise, at least not in the developed world, and we simply do not know enough about prion diseases to know if they are equipped to cause a human epidemic of plague proportions. Ignorance has been our greatest handicap and we are still woefully ignorant of many infectious diseases.

In the distant past, the major causes of premature death were precipitated by some infection or another. These were not necessarily epidemics but the general background of infection was so great that if you happened to catch one of these infections, your life might be threatened. However, this is still our own history; infectious diseases remain the prominent cause of premature death amongst the populations of the developing world. Almost everyone in the developing world has access to antibiotics, so why has the problem of infection not been eradicated there also? The reasons are many and may have less to do with conventional therapy than we might presuppose.

The earliest texts reveal the impact of infectious diseases; leprosy is described frequently both in the Old and New Testaments. We know that