186.1 🎓 醫孞生版

186.1.0.1 📌 䞀頁重點

  • 菌: Obligate intracellular gram - coccobacilli (vasculature endothelium)
  • 3 䞻芁 groups:
Group Disease Vector Reservoir Geography
Spotted Fever Group (SFG) RMSF (R. rickettsii), Mediterranean Spotted Fever (R. conorii), Rickettsialpox (R. akari), African tick bite fever (R. africae) Tick (mostly) Tick/mammal Americas, Mediterranean, Africa, world
Typhus Group Epidemic typhus (R. prowazekii), Endemic/murine typhus (R. typhi), Recrudescent typhus (Brill-Zinsser) Louse (epidemic), flea (murine) 人 (epidemic, latent), rat (murine) Africa, S. America (epidemic); USA + Asia (murine)
Scrub Typhus Group Orientia tsutsugamushi Chigger mite Rodents Asia-Pacific (Taiwan, China, Japan, SE Asia, India), expanding
  • 臚床 (general): 急 fever + 頭痛 + 玅疹 + ± eschar (tâche noire / scrub typhus eschar) at bite site + LAP + multi-organ dysfunction in severe
  • RMSF specifics: rash starts wrists/ankles → palms/soles → trunk (centripetal!); petechial; 30% have NO rash early
  • Treatment:
    • Doxycycline 100 mg PO/IV bid × 5-7d (or until afebrile 3d) — empirical for all suspected rickettsial illness regardless of age/pregnancy if life-threatening
    • Alt: chloramphenicol (rare now, historical pregnancy), azithromycin (scrub typhus mostly)
  • Doxycycline in children: Safe for short courses < 21 days (revised 2018 — no tooth staining concern for short Tx)

186.1.0.2 1⃣ 现菌孞

  • Obligate intracellular (cannot culture standard)
  • Endothelium-tropic — small vessel vasculitis → systemic petechiae, organ damage
  • Gram - but stains poorly; Giemsa or Gimenez stain better
  • Some lab capability (BSL-3) for culture
  • 16S rRNA / specific PCR — emerging
186.1.0.2.1 Tribe Family
  • Rickettsiaceae family includes 3 genera:
    • Rickettsia (SFG + Typhus group)
    • Orientia (scrub typhus)
    • Ehrlichia / Anaplasma (separate, Ch 187)

186.1.0.3 2⃣ Spotted Fever Group (SFG)

186.1.0.3.1 A. Rocky Mountain Spotted Fever (RMSF) — R. rickettsii
186.1.0.3.1.1 流行病孞
  • USA most lethal tickborne disease; ironically more common SE USA (NC, OK, AR, TN) than Rocky Mountain region
  • Vector: Dermacentor variabilis (dog tick) + D. andersoni (wood tick) + Rhipicephalus sanguineus (brown dog tick, SW USA, Mexico)
  • 4-14 d post-bite
186.1.0.3.1.2 臚床
  • Triad: fever + headache + rash (only ~ 60% have all 3)
  • Rash: starts wrists/ankles → palms/soles → trunk (centripetal spread)
  • Initial maculopapular → petechial → purpura (severe)
  • 30% have NO rash in first 3 days — fatal “spotless RMSF” delays diagnosis
  • Multi-organ: hepatitis, AKI, ARDS, encephalopathy, myocarditis, DIC, gangrene of digits
  • Mortality 20-30% untreated; < 5% with timely treatment
186.1.0.3.1.3 Dx
  • Clinical suspicion in endemic area + fever + rash + history → treat empirically
  • Serology paired (acute + convalescent IFA)
  • PCR of blood / tissue
  • Skin biopsy immunohistochemistry
186.1.0.3.1.4 Tx
  • Doxycycline ASAP — don’t wait for confirmation
  • All ages including children — IDSA + AAP 2018 confirm safety for short Tx
  • Pregnancy: doxy if life-threatening (preferred over chloramphenicol — IDSA 2024)
186.1.0.3.2 B. Mediterranean Spotted Fever — R. conorii
  • “Boutonneuse fever”
  • Rhipicephalus sanguineus tick (dog)
  • Mediterranean basin
  • Tâche noire (black eschar) at bite site
  • Similar to RMSF; doxycycline 7d
186.1.0.3.3 C. Rickettsialpox — R. akari
  • Mite-borne (Liponyssoides sanguineus) — house mouse host
  • Urban USA (NYC)
  • Eschar + papular-vesicular rash
  • Mild, self-limited
  • Doxycycline
186.1.0.3.4 D. African Tick-Bite Fever — R. africae
  • Sub-Saharan Africa
  • Amblyomma tick
  • Multiple eschars common
  • Doxycycline
186.1.0.3.5 E. Other SFG
  • R. parkeri (USA Gulf coast)
  • R. helvetica
  • R. honei (Asia, Taiwan)
  • R. felis (cat flea, global)

186.1.0.4 3⃣ Typhus Group

186.1.0.4.1 A. Epidemic Typhus — R. prowazekii
  • Body louse (Pediculus humanus humanus) — same vector as LBRF
  • 人 reservoir (asymptomatic carrier → recrudescence Brill-Zinsser)
  • War, famine, refugee, crowding
  • 高 mortality 20%+ untreated
  • Maculopapular rash starts trunk → extremities (CENTRIFUGAL — opposite RMSF)
  • Severe CNS sx
  • Doxycycline + delouse
186.1.0.4.2 B. Brill-Zinsser Disease (Recrudescent Typhus)
  • Years-decades after primary R. prowazekii infection
  • Stress / immunosuppression triggers
  • Mild — but person can transmit if reinfested with louse → outbreak
186.1.0.4.3 C. Endemic / Murine Typhus — R. typhi
  • Flea (Xenopsylla cheopis) — rat fleas (also opossum fleas, cat fleas)
  • Rat reservoir
  • USA Gulf Coast (TX, CA, HI), Asia, S America, Mediterranean
  • Milder than epidemic
  • Fever, headache, rash (later), often mistaken for FUO
  • Doxycycline 7d

186.1.0.5 4⃣ Scrub Typhus — Orientia tsutsugamushi

186.1.0.5.1 Vector
  • Chigger mite (Leptotrombidium) — only larval stage bites human
  • Rodent reservoir
  • Grass / scrub / military training fields
186.1.0.5.2 流行病孞
  • Asia-Pacific endemic: Taiwan, China, Japan, Korea, India, SE Asia, Pacific Islands, N Australia
  • Now expanding to S America, Mid East (rare)
  • Taiwan: ~ 500 cases/yr (notifiable)
186.1.0.5.3 臚床
  • 5-20 d post-bite
  • Eschar at bite site (60-70% cases — pathognomonic, often hidden in groin / axilla / scalp — search carefully)
  • 急 fever + headache + myalgia + LAP (regional + generalized)
  • Maculopapular rash (trunk → extremities, less prominent than RMSF)
  • Multi-organ in severe: meningoencephalitis, pneumonitis, ARDS, AKI, hepatitis, DIC, myocarditis
  • Mortality untreated 5-30%
186.1.0.5.4 Dx
  • Eschar pathognomonic — search thoroughly
  • Weil-Felix (OXK 倧 titer) — historical, low sens
  • IFA paired serology — gold standard
  • PCR of blood / eschar tissue
  • ELISA / rapid antigen test
186.1.0.5.5 Treatment
  • Doxycycline 100 mg PO/IV bid × 7d (preferred)
  • Azithromycin 500 mg PO qd × 3d alt (pregnancy, pediatric, doxy-failure)
  • Chloramphenicol historical
  • Rapid response — afebrile within 24-48 hr (diagnostic if responds)
  • 嚎重: IV doxy + ICU

186.1.0.6 5⃣ 蚺斷 General Principles

186.1.0.6.1 When to Suspect
  • Acute fever + headache + ± rash + outdoor / tick / mite / flea / louse exposure + endemic geography
  • ALWAYS look for eschar (groin, axilla, scalp, skin folds)
186.1.0.6.2 Lab
  • Treat empirically based on suspicion — don’t wait
  • WBC normal / low
  • Thrombocytopenia common
  • Mildly ↑ LFT (AST/ALT)
  • Hyponatremia (clue)
  • Atypical lymphocytes possible
  • CSF (if encephalitis): mononuclear pleocytosis
186.1.0.6.3 Confirmation
  • Serology (IFA paired; acute + convalescent 2-3 wk apart)
  • PCR of blood, eschar tissue
  • Specialized labs (CDC, university)

186.1.0.7 6⃣ Treatment Summary

Disease Tx Duration
RMSF + SFG Doxycycline 100 bid 5-7d (or until afebrile 3d)
Epidemic typhus Doxycycline 100 bid 7d
Murine / Endemic typhus Doxycycline 100 bid 7d
Scrub typhus Doxycycline 100 bid 7d (or azithro 3d alt)
Severe / CNS Doxycycline IV 100 q12h 7-14d
Pregnancy Doxycycline if life-threatening (or chloramphenicol — limited use) Same
Pediatric Doxycycline (safe < 21d short course per 2018 IDSA / AAP) 7d