This book combines mathematical models with extensive use of epidemiological and other data, to achieve a better understanding of the overall dynamics of populations of pathogens or parasites and their human hosts. The authors thus provide an analytical framework for evaluating public health strategies aimed at controlling or eradicating particular infections. With rising concern for programmes of primary health care against such diseases as measles, malaria, river blindness, sleeping sickness, and schistosomiasis in developing countries, and the advent of HIV/AIDS and other `emerging viruses', such a framework is increasingly important. Throughout, the mathematics is used as a tool for thinking clearly about fundamental and applied problems relating to infectious diseases. The book is divided into two major parts, one dealing with microparasites (viruses, bacteria, and protozoans) and the other with macroparasites (helminths and parasitic arthropods). Each part begins with simple models, developed in a biologically intuitive way, and then goes on to develop more complicated and realistic models as tools for public health planning. A major contribution by two of the leaders in the field, this book synthesizes previous work in this rapidly growing area with much new material, combining work scattered between the ecological and medical literature.