[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) › Rickettsia rickettsii / Rickettsia typhi [Microbiology](https://durgical.com/en/microbiology/) · [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) # Rickettsia rickettsii / Rickettsia typhi - Bacterium - Gram-negative - Exam priority: medium Bacteria that live inside blood vessels; spread by ticks or fleas, they cause fever with spots that can be fatal. Updated 2026-11-01 Also called: spotted fever, Tobia fever, murine typhus ## Key points - Fever + headache + rash moving from wrists and ankles to the trunk, including palms and soles - Doxycycline at any age, without waiting for confirmation - Endothelial damage: oedema, hypotension, low platelets - Murine typhus: fleas; centrifugal rash that spares palms and soles ## At a glance **Gram** Gram-negative **Shape** Small coccobacilli **Oxygen** Obligate intracellular (endothelium) **Family** Rickettsiaceae **Stain** Stain poorly with Gram; Giemsa or Giménez in tissue ## Morphology - Live free in the cytoplasm of endothelial cells - R. rickettsii moves cell to cell with actin tails ## Transmission - R. rickettsii: bite of hard ticks (Amblyomma, Rhipicephalus, Dermacentor) - R. typhi: rat or cat flea faeces rubbed into scratched skin - No person-to-person spread **Reservoir:** Ticks (transovarial transmission), rodents, dogs and other mammals; R. typhi: rats and opossums **Vector:** Hard ticks (spotted fever); rat and cat fleas (murine typhus) ### Isolation precautions What the care team adds to standard precautions. - Standard ## Virulence factors - Infect endothelium and cause widespread vasculitis - Increased vascular permeability: oedema, hypotension, multi-organ failure - Damage to small vessels of skin, brain, lung and kidney ## Diseases it causes - R. rickettsii spotted fever (Rocky Mountain spotted fever, Tobia fever) - Murine (endemic) typhus from R. typhi ## Clinical picture - High fever, severe headache and myalgia after a tick bite - Rash after a few days: starts at wrists and ankles, moves to the trunk and involves palms and soles; may turn petechial - Murine typhus: milder illness, rash spreading outward from the trunk - Low platelets, low sodium and raised transaminases ## Diagnosis - Clinical-epidemiological diagnosis: treatment does not wait for the lab - Indirect immunofluorescence (IFA) with paired samples: fourfold titre rise - PCR or immunohistochemistry on skin biopsy - Weil-Felix: historical test, poorly sensitive ## Treatment Doxycycline at any age, started on clinical suspicion, because delay raises mortality; chloramphenicol is an alternative in special situations such as pregnancy. Sulfonamides can worsen the illness. Drug class only; doses and regimens are set by the clinician from the current guideline. In Pharmacology: - [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/) - [Chloramphenicol](https://durgical.com/en/pharmacology/chloramphenicol/) ## Prevention - Long clothing, repellents and body checks after time in rural areas - Tick control on dogs and horses; rodent and flea control - Remove ticks with tweezers without crushing them ## In Colombia Spotted fever was described in Colombia as «Tobia fever» (Cundinamarca) and has caused outbreaks with high fatality in Villeta (Cundinamarca), Los Córdobas (Córdoba) and Necoclí and Turbo (Antioquia). It is suspected with fever and rash in rural areas and is often mistaken for dengue or leptospirosis. ## Memory aid Spotted fever «comes in at the ankles and climbs»: like a tick crawling up from the feet, the rash starts at wrists and ankles and moves to the centre. ## Test yourself Think of the answer, then tap the question to see it. ## Which antibiotic is used for spotted fever, even in young children? Doxycycline, started on clinical suspicion without waiting for lab results. ## How does the R. rickettsii spotted fever rash spread? It starts at wrists and ankles, spreads to the trunk and includes palms and soles. ## Which cell does Rickettsia infect, and with what result? The endothelial cell; it causes vasculitis, capillary leak, oedema and hypotension. ## Which vector transmits R. typhi? Rat and cat fleas; their faeces enter through scratched skin. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/rickettsia-rickettsii-rickettsia-typhi/) ## Related - [Orientia tsutsugamushi](https://durgical.com/en/microbiology/orientia-tsutsugamushi/) - [Ehrlichia / Anaplasma](https://durgical.com/en/microbiology/ehrlichia-anaplasma/) - [Coxiella burnetii](https://durgical.com/en/microbiology/coxiella-burnetii/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. [← Back to the group: Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [About Rocky Mountain Spotted Fever | Rocky Mountain Spotted Fever (RMSF) | CDC](https://www.cdc.gov/rocky-mountain-spotted-fever/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024); [Rocky Mountain spotted fever: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000654.htm) (MedlinePlus (U.S. National Library of Medicine), 2024); [Typhus Fevers Basics | Typhus Fevers | CDC](https://www.cdc.gov/typhus/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/rickettsia-rickettsii-rickettsia-typhi/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/rickettsia-rickettsii-rickettsia-typhi/