ABSTRACT
This chapter provides an overview of some recognized genera to illustrate variety and intimate nature of the associations of organisms with ticks, insects, and other invertebrates as a necessary framework for considering origin(s) of the arthropod-transmitted rickettsial pathogens of vertebrates. Members of the genus Wolbachia are small, Gram-negative coccoid or rod forms associated with arthropods. They are not typically pathogenic for their hosts and are seldom found in mycetomes. Three species currently recognized in the genus are Wolbachia pipientis, Wolbachia melophagi, and Wolbachia persica, which Brooks describes as consisting of rickettsia-like, pleomorphic organisms that chiefly reside intracellularly in the mycetomes of bedbugs. The genus Symbiotes contains only one species, S. lectularius, which Brooks describes as consisting of Gram-positive, intracellular, straight or slightly curved rods occurring singly or in pairs. The genus Blattabacterium contains a single species, B. cuenoti. The genus Rickettsiella, as defined by Weiss, consists of minute, Gram-negative rod-shaped pathogens of invertebrates.
