Ticks, including many that bite humans, are hosts to several obligate intracellular bacteria in the spotted fever group (SFG) of the genus Rickettsia

Review from JAMA — Bed Bugs (Cimex lectularius) and Clinical Consequences of Their Bites

Background. Rickettsia parkeri rickettsiosis, a recently identified spotted fever transmitted by the Gulf Coast tick (Amblyomma maculatum), was first

Geographic distribution of Rickettsia parkeri in its US tick vector, Amblyomma maculatum, was evaluated by PCR. R. parkeri was detected in ticks from Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina, which suggests that A. maculatum may be responsible for additional cases of R. parkeri rickettsiosis throughout much of its US range.

Until recently,Amblyomma maculatum(the Gulf Coast tick) had garnered little attention compared to other species of human-biting ticks in the United States.A. maculatumis now recognized as the principal vector ofRickettsia parkeri, a pathogenic spotted fever group rickettsia (SFGR) that causes an eschar-associated illness in humans that resembles Rocky Mountain spotted fever. A novel SFGR, distinct from other recognizedRickettsiaspp., has also been detected recently inA. maculatumspecimens collected in several regions of the southeastern United States. In this study, 198 questing adult Gulf Coast ticks were collected at 4 locations in Florida and Mississippi; 28% of these ticks were infected withR. parkeri, and 2% of these were infected with a novel SFGR. Seventeen isolates ofR. parkerifrom individual specimens ofA. maculatumwere cultivated in Vero E6 cells; however, all attempts to isolate the novel SFGR were unsuccessful. Partial genetic characterization of the novel SFGR revealed identity with several recently described, incompletely characterized, and noncultivated SFGR, including “CandidatusRickettsia andeanae” andRickettsiasp. Argentina detected in several species of Neotropical ticks from Argentina and Peru. These findings suggest that each of these “novel” rickettsiae represent the same species. This study considerably expanded the number of low-passage,A. maculatum-derived isolates ofR. parkeriand characterized a second, sympatricRickettsiasp. found in Gulf Coast ticks.