rickettsial infections

Question 0

rickettsial infections

Answer 0

• replicates by binary fission (contract with chlamydia)
• humans are accidental hosts, get from insect bites
• targets bv endothelial cells (kill–> necrotizing vasculitis)

Question 1

3 rickettsial infection groups?

Answer 1

1. spotted fever group
2. typhus group
3. Q fever

Question 2

spotted fever group

Answer 2

ROCKY MOUNTAIN SPOTTED FEVER caused by Rickettsia rickettsii that’s transferred by tick bites and targets ENDOTHELIAL CELLS –> spreads to vascular smooth mm and endothelium of larger vessels…EXUDATION, DIC –> fluid loss–> SHOCK (20-50% DIE UNTX)
-PUL EDEMA, ACUT ALV INJURY
Histology: IC rods arranged in parallel rows (“flotilla at anchor facing the wind”)
-SX: constitutional sx, maculopapular eruptions –> PETECHIAE, CUTANEOUS LESIONS ON SOLES OF FEET AND PALMS

Question 3

typhus group

Answer 3

1. epidemic (louse borne) typhus
2. endemic (murine) typhus
3. scrub typhus

Question 4

epidemic (louse-borne) typhus

Answer 4

• rickettsia prowazekii, penetrate abrasion/inhaled, man-louse FECES-man life cycle thats assoc with cold climates/poor sanitation/crowding (organism remains infectious for 3months)
• targets CAPILLARY ENDOTHELIA ->systemic vasculitis
• can est latent inf –> cause Brill-Zinsser dz later, splenomegaly, necrotic areas, typhus nodules (mast, lymphocytes, plasma, macrophages- around vessels.
• dying pts: encephalitis, myocarditis, pna, interstitial nephritis, shock
• SX: fever,headache, myalgias, then RASH (macular lesions). severe: rash becomes confluent and purpuric.
• TX: large scale de-lousing

Question 5

endemic (murine) typhus

Answer 5

• rickettsia typhi causes milder sx than epidemic typhus.
• get this from infected flea feces (humans disrupt the rat-flea-rat cycle), assoc with areas with lots of RATS.
• TYPHUS NODULES (mononuclear infiltrates). can be INHALED/wound. inhaled–> pul infections

Question 6

scrub typhus

Answer 6

• Tsutsugamushi fever: caused by Rickettsia tsutsugamushi in rodents –> mites (chiggers) –> larvae attaches to passerbys.
• multiloculated vesicle at inoculation site that ULCERATES, ESCHAR –> HEALS: then headache, PNA, RASH, LYMPHADENOPATHY, HEPATOSPLENOMEGAL.
• complications: myocarditis, MENINGOENCEPHALITIS, SHOCK
• UNTX: 30% die

Question 7

Q fever

Answer 7

• coxiella burnetii (gram-, pleomorphic coccobacillus) thats common in ppl who are exposed to infected animals. INHALED
• FOCAL PNA (DRY COUGH, present as atypical pna)-(CONSOLIDATION) that disseminates and affects mostly MONOCYTES and macrophages, RESOLVES/PERSISTS as CHRONIC INFECTION.
• in LIVER ==> granulomas w/ “fibrin ring”.
• MILD FEBRILE DZ THAT RESOLVES ITSELF (fever, headache, myalgia, NOOOOOOO RASH)