Since the dawn of civilisation, and with it the creation of towns and cities where large numbers of people lived in close proximity, infectious diseases have been a primary cause of premature death. Over recent decades, however, mass vaccination campaigns, new antibiotic drugs and improvements in water supply and sewage treatment have largely eradicated many of the illnesses that were part of everyday life a century or more ago - tuberculosis, cholera, diphtheria, syphilis to name but a few.
The World Health Organisation predicts that by the year 2000 polio, a crippling viral infection, will be the next disease to be vanquished. There are grounds for optimism given that the last polio case in the western hemisphere occurred in Peru in 1991, thanks largely to an extensive vaccination effort in South America.
Such optimism has become strangely out of place, however, in the post- Aids world. The sudden appearance of HIV, and its rapid spread around the planet, has become one of the most alarming developments in the history of 20th-century medicine. The emergence of other new diseases, such as Ebola virus in Zaire, morbillivirus (a relative of measles) in Australia and hantavirus in the US, have increased concern about the deadly infectious grenades that nature can still lob in our general direction.
On top of this, bacterial diseases that were once easy to treat with anti-biotics have become widely resistant to our arsenal of drugs - resistant strains of TB are now prevalent in New York City and hospitals in Britain live in fear of super-resistant strains of Staphylococcus, which can cause a range of life-threatening illnesses. As if this was not bad enough, a breakdown in health care and sanitation elsewhere in the world has created a climate that has fostered the return of ancient diseases.
Laurie Garrett, a respected American journalist, has produced an exhaustive account of the threat we face in her book The Coming Plague (published by Virago on 14 September at pounds 20). It was the power of her writing that spurred the White House to launch an investigation last December by 20 US Government agencies. They recently confirmed that the past optimism with regard to infectious disease has now all but faded.
''Our understandable euphoria was premature," the official report of the investigation says. ''It did not take into account the extraordinary resilience of infectious microbes. These have a remarkable ability to evolve, adapt, and develop resistance to drugs in an unpredictable and dynamic fashion. It also did not take into account the accelerating spread of human populations into tropical forests and overcrowded mega-cities where people are exposed to a variety of emerging infectious agents.''
The ''globalisation'' of human societies has now created the conditions where a little local difficulty can suddenly become a world pandemic. As Jonathan Mann, the former head of the Aids programme of the WHO, says in a preface to The Coming Plague, the explosive growth of jet travel has almost eradicated the notion of geographical isolation. ''Few habitats on the globe remain truly isolated or untouched, as tourists and other travellers penetrate into the most remote and previously inaccessible areas.''
In the first of our two extracts from her book, Laurie Garrett tracks the emergence and identification of a new deadly virus in America's heartland just two years ago. The story of the 1993 outbreak in the south-western states of hantavirus - an infection carried by the age-old vector, rodents, and known in other forms in other countries since the 1950s - epitomises the battle between mankind and the microbes. Steve ConnorReuse content