Rickettsial Diseases PDF

Preface

In the last 20 years, the rickettsial field has undergone significant evolution at the epidemiological, microbiological, and molecular levels. Between 1984 and 2004 alone, at least nine additional rickettsial species or subspecies were identified as causes of tick-borne rickettsioses around the world. Of these agents, six were initially isolated from ticks, often years or decades before a definitive association with human disease was established. Also, outbreaks of the louse-borne epidemic typhus re-emerged in Africa, with the most recent outbreak (and the largest since World War II) observed in Burundi in the 1990s, during their civil war. Fleas, which have been historically associated with the transmission of murine typhus, have been involved in the cycle of Rickettsia felis, an emerging pathogen belonging to the spotted-fever group of Rickettsia. Furthermore, about one million cases of scrub typhus due to Orientia tsutsugamushi have been estimated to occur each year around the world and as many as one billion people may be exposed, particularly in rural locations.

Recent developments in molecular taxonomic methods have resulted in the reclassification of the rickettsiae. For example, the Rochalimaea, united within the genus Bartonella, and Coxiella were removed from the order Rickettsiales and the classification of this order continues to be modified as new data becomes available. Because Q fever caused by Coxiella burnetii is still considered as a "rickettsiosis" and remains in the field of rickettsiologists, it will be largely described in this book.

The rickettsial field has recently entered the genome area. In 2001, the first genome of a tick-transmitted rickettsia (R. conorii strain Seven) was fully sequenced and revealed several unique characteristics among bacterial genomes, including long palindromic repeat fragments irregularly distributed throughout the genome. Further, comparison of the R. conorii genome with that of R. prowazekii (the agent of epidemic typhus and included in the typhus group of the genus Rickettsia), provided additional data on the evolution of rickettsial genomes, the latter appearing to be a subset of the first. Recently, the genomes of R. sibirica, R. rickettsii, R. akari, R. felis, and R. typhi have been reported. Those of R. belli, R. massiliae, R. africae, and R. slovaca are currently being sequenced. These data will certainly provide insights into the mechanism of rickettsial pathogenicity and will provide new molecular diagnostic targets and new tools for phylogenetic and taxonomic studies as well as new treatment measures.

We anticipate that this book will appeal to physicians specializing in infectious diseases, dermatology, or even travel medicine, as well as clinical laboratory personnel and epidemiologists. Not only physicians and scientists in Europe and the United States will find this book useful, but also those from tropical regions in Africa, Asia, Australia, and the Americas, where numerous emerging diseases have been described in recent years and where rickettsial diseases constitute a differential diagnosis in febrile patients.