<unk>  (abbreviated as<unk>  is a unicellular, Gram-negative coccobacillus (plural coccobacilli) that  is native to the New World. It belongs to the spotted fever group (SFG) of<unk>  and is most commonly known as the causative agent of Rocky Mountain spotted fever (RMSF). By nature,<unk>  is an obligate intracellular parasite that survive by an endosymbiotic relationship with other cells. <unk>  is a non-motile, non-spore forming aerobic organism. Cells are typically 0.3–0.5 × 0.8–2.0 μm in size. They lack a distinct nucleus and membrane bound organelles. Their outer membrane is composed mostly of lipopolysaccharides.
Rocky Mountain spotted fever (RMSF) is transmitted by the bite of an infected tick while feeding on warm-blooded animals, including humans. Humans are considered to be accidental hosts in the<unk> –tick life cycle and are not required to maintain the<unk> e in nature.
Rickettsia rickettsii
Borrelia mayonii
Bartonella quintana
Yersinia pestis
Borrelia afzelii
Rickettsia typhi
Borrelia recurrentis
Borrelia burgdorferi