IM26.18-20 | Zoonotic Rickettsial and Filamentous Bacterial Infections — Summary & Reflection

KEY TAKEAWAYS

Leptospirosis: spirochaete from waterlogged soil (rats, cattle urine); conjunctival suffusion + jaundice + AKI = Weil's disease; diagnosis: LEPTO IgM ELISA (day 5–7) / MAT; treat: doxycycline (mild) or IV penicillin G / ceftriaxone (severe); ICU for AKI and LPHH.

Brucellosis: Brucella spp. from cattle/goats/sheep; undulating fever + night sweats + sacroiliitis/spondylodiscitis; diagnosis: blood culture + SAT/ELISA; treat: doxycycline × 6 weeks + gentamicin × 7 days (or rifampicin × 6 weeks); NEVER monotherapy.

Plague: Yersinia pestis, rat flea vector; bubonic (bubo) or pneumonic (droplets, airborne precautions); treat: gentamicin or streptomycin × 10 days.

Anthrax: B. anthracis; cutaneous = painless black eschar with gelatinous oedema; inhalation = mediastinal widening; treat: ciprofloxacin × 7 days (cutaneous) or 60 days (inhalation).

Actinomycosis: A. israelii (oral flora, endogenous); cervicofacial — sulphur granules, Gram-positive non-acid-fast filaments; treat: penicillin IV → oral amoxicillin, 6–12 months.

Nocardiosis: N. asteroides (soil, exogenous); opportunistic in immunocompromised; pulmonary ± CNS; weakly acid-fast filaments; treat: TMP-SMX for 6–12 months (triple therapy for CNS).

Scrub typhus: Orientia tsutsugamushi, chigger bite; eschar (concealed skin folds) + fever + rash; diagnose: IgM ELISA; treat: doxycycline × 7 days — fever resolves in 24–48 hours.

Epidemic/endemic typhus: R. prowazekii (louse) / R. typhi (rat flea); macular rash trunk → periphery (sparing face/palms/soles); treat: doxycycline × 7 days.

REFLECT

Return to the three patients in the opening hook. The rice-field worker with leptospirosis, the veterinarian with brucellosis, the forest guard with scrub typhus — all had fever and systemic features, all would likely receive a non-specific 'fever workup' in a setting that doesn't account for their exposure history. How would you systematically elicit the exposure history in a brief outpatient or emergency consultation? What three questions would you ask every febrile patient that are not yet part of the standard 'history of presenting illness' in most Indian medical teaching — animal contact, occupation, and travel — that would unlock these diagnoses? Reflect on the systemic change needed in clinical practice: integrating the 'infection-focused epidemiological history' as a routine component of every fever assessment, not an afterthought triggered only when the standard workup is negative. How does this change — from reactive to proactive exposure history — reduce the time to correct diagnosis and the time to life-saving treatment in the patients you will see in your career?