|Description:||This photograph depicts a dorsal view of a female cayenne tick, Amblyomma cajennense. This tick specie is a known North, Central and South American vector of Rickettsia rickettsii, which is the etiologic agent of Rocky Mountain spotted fever (RMSF). Note the small scutum, or “shield”, which unlike its male counterpart, covers only a small region of this specimen’s dorsal abdomen, just caudad to it head, and elongated mouthparts. See PHIL 10872 for an image depicting a dorsal view of a male A. cajennense tick.|
Rickettsia rickettsii usually infects members of the tick family Ixodidae (hard ticks), although a closely related rickettsia has been found in the soft bat tick, Carios kelleyi. These ticks have four stages in their life cycle: egg, larva, nymph, and adult. After the eggs hatch, each stage must feed once to develop into the next stage. Both male and female ticks will bite.
Rickettsiae are transmitted to a vertebrate host through saliva while a tick is feeding. It usually takes several hours of attachment and feeding, before the rickettsiae are transmitted to the host. The risk of exposure to a tick carrying R. rickettsii is low. In general, about 1%-3% of the tick population carries R. rickettsii, even in areas where the majority of human cases are reported.