Snapshot A 30-year-old woman presents to the emergency room for a rash. She had been traveling and hiking in southern Europe. She does not recall having any tick bites but admits that it may be possible as she had many bug bites on her legs, though she attributed these to mosquitoes. She started having fevers 2 days ago along with a severe headache and developed a rash today. On physical exam, she has a maculopapular rash on her trunk as well as multiple eschars surrounding a bug bite on her left calf. She is started on doxycycline. (Mediterranean 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) ETIOLOGY 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 Presentation Symptoms fever rash headache Physical exam Rickettsial DiseasesClinical Manifestations of Rickettsial DiseasesDiseaseVectorRashEscharRegional LymphadenopathyRocky Mountain spotted fever (R. rickettsii)TickMacularPetechialPurpuricSpreads centripetally (extremities to trunk)NoNoMediterranean spotted fever (R. conorii)TickMacularPapularPurpuricYesNoRickettsialpox (R. akari)MiteVascularPapularOn trunk and extremitiesYesYesAfrican tick bite fever (R. africae)TickVesicularMaculopapularYes, multipleYesEpidemic tyhpus (R. prowazekii)LouseMacularPapularPetechialSpreads centrifugally (trunk to extremities)NoNoMurine typhus (R. typhi)FleaMacularPapularPetechialSpreads centrifugallyNoNoScrub typhus (O. tsutsugamushi)MiteMacularPaleYesYes 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 Differential Q fever distinguishing factors also an intracellular gram-negative bacteria manifests as fever and pneumonia or endocarditis does not manifest with rash DIAGNOSIS Making the diagnosis most cases are clinically diagnosed and confirmed with laboratory evaluation 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 Prognosis Most resolve with treatment Epidemic typhus (R. prowazekii) may recur (Brill-Zinsser disease) Rocky Mountain spotted fever (R. rickettsii) has the highest mortality