The Genus Leptospira
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The Genus Leptospira BEN ADLER AND SOLLY FAINE
Introduction Members of the genus Leptospira are helicoidal bacteria that may exist as free-living saprophytes or in association with a diverse range of animal hosts. They either are the cause of acute leptospirosis or are associated with particular host tissues (especially the renal proximal tubules) on a long-term basis (possibly for the life of the animal). Two additional species, L. parva and L. illini, which were previously included in the genus, have been reclassified as the separate genera Turneria and Leptonema, respectively (Hovind-Hougen, 1979; Hookey et al., 1993; Ellis, 1995), although the former has not been officially published. These three genera comprise the family Leptospiraceae within the order Spirochaetales, which also contains the families Spirochaetaceae and Serpulinaceae. Human leptospirosis has clearly existed since the earliest times, but it is impossible to ascribe with any certainty various records of febrile jaundice to leptospirosis or to other causes. Many of the early descriptions are reviewed in Faine et al. (1999). It was in 1860 that Adolph Weil, professor of medicine at the University of Heidelberg, published his description of an “. . . infectious disease accompanied by splenomegaly, jaundice and nephritis” (Weil, 1886), the most severe form of which now bears his name as Weils disease. Leptospires were first isolated in pure culture by Japanese workers in 1914 (Inada et al., 1916) only a short time before a similar isolation in Europe (Uhlenhuth and Fromme, 1915), although it is clear that the first visual observations of Leptospira were made by Stimson a few years earlier in silver stained sections of human kidney from a patient thought to be suffering from yellow fever (Stimson, 1907; Stimson, 1909).
Taxonomy The taxonomy of Leptospira has been both complicated and controversial; at various times over the past 60 years, the genus has contained only
two species or almost 200 species. It is only with the relatively recent application of accepted molecular methods that the taxonomic status of members of the genus has been unequivocally determined. The genus is defined as Leptospira Noguchi (1917), type species Leptospira interrogans (Stimson, 1907), type strain serovar Icterohaemorrhagiae, Ictero No. I (ATCC 43782). Following the first isolation of Leptospira, the next three decades saw the isolation of scores of strains that were clearly different with respect to epidemiology, disease pattern and a very limited range of phenotypic characteristics. Because of the limited phenotypic differences available, antigenic differences in agglutinating (lipopolysaccharide; LPS) antigens were used as the basis for identification and classification. The serovar became the basic taxon, with each serovar accorded species status, e.g., L. pomona, L. icterohaemorrhagiae, L. hardjo, etc. Antigenically related serovars were placed together in serogroups, which per se have no taxonomic status. From a taxonomic viewpoint,
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