Rickettsiia diseases

The genus Rickettsia includes lethal pathogens such as R. rickettsii, the etiologic agent of Rocky Mountain spotted fever, and R. prowazekii, the etiologic agent of epidemic typhus. All the members of this genus are obligately intracellular bacteria, and those that are pathogenic to humans preferentially target the vascular endothelium and are transmitted by arthropod vectors. The diseases they cause are systemic and difficult to diagnose because of initial nonspecific signs and symptoms, and the lack of appropriate diagnostic tests. These small bacteria have a gram-negative wall structure and have lost many genes that became unnecessary once they evolved to an intracellular lifestyle. Much remains to be learned about these fascinating intracellular parasites. Factors that have limited their investigation include the required biosafety level 3 to work with most of the pathogenic rickettsiae, the lack of tools for genetic manipulation, and their intracellular nature, which adds a layer of complexity for experimental work.