We live in a microbial world populated by millions of species of bacteria, viruses, fungi and protozoa. Peaceful coexistence usually prevails. Occasionally, though, a microbe with the ability to cause a serious infectious disease will evolve, and a life and death struggle ensues.
Every organism on earth has to contend with this eventuality, from the single-celled to the most complex animals; humans are certainly no exception. Infectious organisms have caused catastrophic loss of life from the very beginning of human evolution. Some, such as the protozoa responsible for malaria, have plagued us for millennia. Others have emerged in the modern era, seemingly out of nowhere; HIV, Ebola virus, Bird flu and antibiotic-resistant bacteria, to name but a few.
The survival of all life forms has been contingent on the development of suitable defenses against infectious microbes, through pathways encoded in the DNA of every organism. These range from individual genes found in certain bacteria which produce enzymes that chop up the DNA of invading viruses, to the hundreds of genes found in higher animals that are involved in the workings of sophisticated immune systems. Deploying their own genetic tricks, infectious microbes have adapted by changing their DNA, or acquiring new genes that enable them to cripple immune defenses or render antimicrobial drugs useless. These wily infectious microbes have caused the premature death of billions of people. There is another twist to this DNA point/counterpoint. Mutations have arisen in the human genome that provide a measure of protection against some of the most lethal infectious organisms. Through Darwinian natural selection - survival of the fittest - these mutations, which originated in a handful of individuals at the dawn of civilization, expanded in the population and are now found in hundreds of millions of people throughout the world. Although they protect their possessors against the ravages of malaria, cholera, HIV/AIDS, and other life-threatening infectious diseases, s me adaptive mutations have taken on a new level of significance in the modern era; they also cause the most common inherited disorders in the world. This book is an account of some of the most malignant infectious microbes encountered by humans and the genetic disorders they spawned. It's also a tale of how scientific progress over the past 150 years is giving man the tools to fight back.