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Members of the family Leptospiraceae are thin, spiral, highly motile bacteria that are best visualized by darkfield microscopy . These characteristics are shared with other members of the Order Spirochaetales, but few additional parallels exist among spirochetes. This chapter describes basal features of Leptospira that are central to survival and, in the case of pathogenic leptospiral species, intimately linked with pathogenesis, including its morphology, characteristic motility , and unusual metabolism. This chapter also describes the general methodology and critical requirements for in vitro cultivation and storage of Leptospira within a laboratory setting.

During the years 1999–2002, a total of 4,898 individuals of 26 species of hematophagous insects (4,149 mosquitoes, 583 black flies, and 166 tabanid flies) was examined for the presence of spirochetes using dark-field microscopy. There was an overall recovery of spirochetes from the midguts of Culicidae and Simuliidae of 23.5% and 11.4%, respectively. Spirochetes were not detected in Tabanidae. Seven spirochetal strains have been successfully recovered from mosquitoes and black flies: BR149 (Culex pipiens), BR151 (Cx. pipiens), BR173 (Cx. pipiens), BR177 (Cx. pipiens), BR193 (Aedes cinereus), BR208 (Cx. pipiens), and BR231 (Simulium noelleri). The strains have been adapted to laboratory conditions (BSK-H Complete medium). Their preliminary determination based on 16S rRNA gene sequencing has shown that they differ from the Lyme disease spirochete Borrelia burgdorferi sensu lato as well as other members of the Order Spirochaetales indicating novel bacterial species in the Family Spirochaetaceae.

The order Spirochaetales consists of helically shaped bacteria with a distinguishing anatomy and locomotion. Although these bacteria are morphologically similar, their physiology and habitats are heterogeneous. The order Spirochaetales contains obligate anaerobes, facultative anaerobes, and obligate aerobes. Substrate requirements range from fatty acids to amino acids. Habitats are extremely diverse, and range from mud to the convoluted tubules of the mammalian kidney.