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Leptospirosis is an emerging infectious disease of global importance, as illustrated by recent large outbreaks in Asia, Central and South America, and the United States. The disease is caused by pathogenic leptospires and is characterized by a broad spectrum of clinical manifestations, varying from inapparent infection to fulminant, fatal disease. In its mild form, leptospirosis may present as an influenza-like illness with headache and myalgias. Severe leptospirosis, characterized by jaundice, renal dysfunction, and hemorrhagic diathesis, is referred to as Weil's syndrome. Etiologic Agents Leptospires are spirochetes belonging to the order Spirochaetales and the family Leptospiraceae. . | Chapter 164. Leptospirosis Leptospirosis is an emerging infectious disease of global importance as illustrated by recent large outbreaks in Asia Central and South America and the United States. The disease is caused by pathogenic leptospires and is characterized by a broad spectrum of clinical manifestations varying from inapparent infection to fulminant fatal disease. In its mild form leptospirosis may present as an influenza-like illness with headache and myalgias. Severe leptospirosis characterized by jaundice renal dysfunction and hemorrhagic diathesis is referred to as Weil s syndrome. Etiologic Agents Leptospires are spirochetes belonging to the order Spirochaetales and the family Leptospiraceae. Traditionally the genus Leptospira comprised two species the pathogenic L. interrogans and the free-living L. biflexa the current designations are L. interrogans sensu lato and L. biflexa sensu lato respectively. Seventeen genomospecies of pathogenic leptospires are now recognized on the basis of their DNA relatedness. The genome sequences of two strains have been published and reporting of the genomes of other strains is in progress. This information will undoubtedly lead to a better understanding of the pathogenesis of leptospirosis. However for clinical and epidemiologic reasons it is still more practical to use a classification system based on serologic differences. The pathogenic leptospires are divided into serovars according to their antigenic composition. More than 250 serovars make up the 26 serogroups. Leptospires are coiled thin highly motile organisms with hooked ends and two periplasmic flagella that permit burrowing into tissue Fig. 164-1 . These organisms are 6-20 pm long and 0.1 pm wide. They stain poorly but can be seen microscopically by dark-field examination and after silver impregnation staining. Leptospires require special media and conditions for growth it may take weeks for cultures to become positive. Figure 164-1 SùurCỀỉ F uCi AS K-Hiipttr .
