Only one genus - "Spirillum" has been described in this family. Members of the genus "Spirillum" are large, elongate, spiral shaped, rigid cells. Rat bite fever is caused by either "Streptobacillus moniliformis" or "Spirillum minor". Spirillum volutans is a gram-negative, bacterium from the genus of Spirillum which occurs in freshwater. It is caused by the Gram-negative rod "Spirillum minus" (also known as "Spirillium minor"). The cause of tick-borne relapsing fever across central Africa was named "Spirillum duttoni".