Related Subjects:
|Streptococcus Pneumoniae (Pneumococcus)
|Rickettsia (General Principles)
|Rickettsia africae (Tick Bite Fever)
|Rickettsia akari (Rickettsial pox)
|Rickettsia conorii (Mediterranean Spotted Fever)
|Rickettsia prowazekii (Epidemi/Louse-borne Typhus)
|Rickettsia rickettsii (Rocky Mountain spotted fever)
|Rickettsia tsutsugamushi (Scrub typhus)
|Rickettsia typhi (Murine/Endemic typhus)
📖 About
- Scrub Typhus → infectious disease caused by Orientia tsutsugamushi, transmitted to humans by larval mites (chiggers).
- Belongs to the Rickettsiaceae family (related to rickettsiae but distinct).
🔬 Characteristics
- Gram-negative, though poorly visualised on Gram stain due to tiny size & intracellular nature.
- Obligate intracellular parasite → requires host cell ATP & nutrients.
- Grows only in tissue culture → reflects strict intracellular dependence.
🏠 Source
- Reservoir: Wild rodents (e.g. rats) & small mammals 🐀.
- Transmission: Bite of larval mites (chiggers) found in scrubland, forests & grassy areas of rural Asia-Pacific.
🌍 Epidemiology
- Endemic in the “tsutsugamushi triangle”: SE Asia, China, Japan, Northern Australia.
- Peak during wet seasons when mite populations rise.
⚠️ Pathogenicity & Clinical Presentation
- Incubation: 6–21 days post-bite.
- 🧑⚕️ Symptoms: fever, chills, headache, myalgia.
- 🕳️ Eschar: necrotic scab at bite site, surrounded by erythema → classic diagnostic clue.
- Other: lymphadenopathy, GI upset, cough.
- Severe: pneumonitis, myocarditis, meningoencephalitis, multi-organ failure (if untreated).
🧪 Virulence Factors
- Invades vascular endothelial cells → widespread vasculitis.
- Triggers cytokine release → immune-mediated tissue damage.
🔎 Investigations
- 🧪 Weil–Felix test: historic, poor sensitivity/specificity.
- 🧪 Immunofluorescence: rash/biopsy specimens.
- 🧪 Serology: IgM/IgG against Orientia tsutsugamushi (mainstay).
- 🧪 PCR: sensitive, detects early infection in blood/tissue.
💊 Management
- First-line: Doxycycline → shortens illness dramatically (continue for 5–7 days or until 3 days post-fever).
- Alternative: Azithromycin (safe in pregnancy/children).
- Supportive: fluids, oxygen, monitor for complications (respiratory/cardiac/CNS).
- Mortality: <5% with treatment; up to 30% if untreated.
📊 Prognosis
- Excellent recovery with early antibiotics (symptoms often resolve within 48 h).
- Severe/untreated → multi-organ failure & death.
🛡️ Prevention
- Avoid mite-infested scrubland/grassland in endemic areas.
- Use insect repellent (DEET) + protective clothing.
- Community: rodent & mite control; improved sanitation.
⚠️ Exam pearl: Scrub typhus = fever + eschar + lymphadenopathy in Asia-Pacific traveller → treat with doxycycline.
Differentiate from murine typhus (R. typhi, flea-borne) & epidemic typhus (R. prowazekii, louse-borne).
