Rickettsial diseases have affected humanity since the dawn of civilization. Despite the advent of effective antibiotic therapy, humans continue to be afflicted by rickettsial diseases, which still often go undiagnosed because of their protean clinical manifestations.

During the past decade, several major developments have occurred in rickettsiology. With the advent of the newly emerging infections caused by a number of rickettsias, the re-emerging of old pathogenic species of rickettsias that cause both old and new syndromes has helped redefine the level of rickettsial pathogenicity. The intracellular nature of most rickettsias remains a mystery although their genome size is close to that of the free-living neisserias.

Advances in molecular techniques have also helped redefine and reclassify rickettsias by maintaining some in the order Rickettsiales and placing others in other bacterial orders. The latter are still included in rickettsial reviews because of historical precedence. These molecular advances also help us to refine our knowledge of rickettsial pathogenesis.

This volume is the first of two volumes to result from the 4th International Conference on Rickettsiae and Rickettsial Diseases, in which an effort is made to address and clarify issues from clinical, diagnostic, epidemiologic, and molecular perspectives that have remained unsolved in the past. In this volume, several subdisciplines of rickettsiology are included: genomics and proteomics, a protocol for naming newly isolated rickettsiae; bioterrorism; the pathobiology of reckettsial infections including Q (query) fever, antibiotic resistance, and vaccines; the discovery of new ricketsiae; and the pathobiology of Ehrlichia and Anaplasma infections. This volume. along with Century of Rickettsiology, which will be published in 2006 as an Annals volume, will provide a complete picture of the world-wide range of work that is currently being carried out in the field of rickettsiology.

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