Snapshot A 24-year-old man presents to his primary care physician for a rash. He had been hiking in Tennessee during a retreat at his new job last week. He reports that he pulled a tick off of himself, though he did not think much of it at the time. Since then, he has had fevers and headaches daily. A few days after the onset of fever, he developed a rash that started on his wrists and ankles and now has spread to his chest. On physical exam, there are small blanching erythematous macules on his chest and petechiae on his extremities. His palms and soles are spared. He is started on empiric antibiotics. (Rocky Mountain spotted fever) Introduction Classification Rickettsia spotted fever group (tick-borne) Rickettsia rickettsii (Rocky Mountain spotted fever) most common Rickettsia conorii (Mediterranean spotted fever) Rickettsia akari (Rickettsialpox) Rickettsia africae (African tick bite fever) typhus group Rickettsia prowazekii (louse-borne epidemic typhus) Rickettsia typhi (flea-borne murine typhus) Orientia scrub typhus group Orientia tsutsugumushi (mite-borne) formerly Rickettsia tsutsugamushi obligate intracellular gram-negative bacteria transmission via blood-feeding arthropod vectors ticks, lice, and flea Epidemiology incidence depends on geographic distribution of the vector North America (R. rickettsii and R. akari) Europe (R. conorii) Asia (R. conorii and O. tsutsugamushi) Africa (R. africae and R. conorii) South America (R. prowazekii) worldwide (R. typhi) Pathogenesis the bacteria is transmitted into the human body via arthropod saliva when bitten vascular endothelial cells are targeted by the bacteria replication can cause local hemorrhage Prognosis most resolve with treatment epidemic typhus (R. prowazekii) may recur (Brill-Zinsser disease) Rocky Mountain spotted fever (R. rickettsii) has highest mortality Presentation Symptoms fever rash headache Physical exam Clinical Manifestations of Rickettsial Diseases Disease Vector Rash Eschar Regional Lymphadenopathy Rocky Mountain spotted fever (R. rickettsii) Tick Macular Petechial Purpuric Spreads centripetally (extremities to trunk) No No Mediterranean spotted fever (R. conorii) Tick Macular Papular Purpuric Yes No Rickettsialpox (R. akari) Mite Vascular Papular On trunk and extremities Yes Yes African tick bite fever (R. africae) Tick Vesicular Maculopapular Yes, multiple Yes Epidemic tyhpus (R. prowazekii) Louse Macular Papular Petechial Spreads centrifugally (trunk to extremities) No No Murine typhus (R. typhi) Flea Macular Papular Petechial Spreads centrifugally No No Scrub typhus (O. tsutsugamushi) Mite Macular Pale Yes Yes Studies Labs detection of immunoglobulin G (IgG) is confirmatory Weil-Felix test serum cross-reacts with proteus antigens may have thrombocytopenia and elevated liver function tests Skin biopsy visualization of infecting organism on tissue Making the diagnosis most cases are clinically diagnosed and confirmed with laboratory evaluation Differential Q fever distinguishing factors also an intracellular gram-negative bacteria manifests as fever and pneumonia or endocarditis does not manifest with rash Treatment Management approach empiric treatment is started as soon as possible Medical doxycycline indication first-line therapy chloramphenicol indication contraindications to doxycycline Complications Neurologic sequelae Peripheral gangrene Reactive arthritis