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Infectious Disease: Unit 2 > Rickettsia/Bartonella > Flashcards

Flashcards in Rickettsia/Bartonella Deck (15):

Major biological characteristics of Rickettsiae and related bacteria

  • Rickettsiae
    • Obligate intracellular bacteria 
    • Gram-negative coccobacillus (but stains poorly)
  • Usually have animal reservoirs and are arthropod-borne (louse/tick)
  • Humans generally incidental-only hosts
    • Except louse-borne typhus
  • Very small genome; uses host metabolites


Intracellular growth cycles of Rickettsiae and related bacteria

  • Replicate in cytoplasm rather slowly
    • 9-12 hours
  • Can't be cultured on artificial media
  • Lose infectivity outside cells


Pathogenesis of Rickettsiae

  • Most species are pathogenic
  • More or less all of them do the same thing: invade endothelial cells and spread through vascular system
  • Cause increased vascular permeability --> edema, hypovolemia, ischemia
  • Presents with: high fever, headache, petechial rash
  • Can have severe consequences if untreated


Rickettsiae: 3 main groups

  • Spotted fever group
    • Transmitted through wood ticks = Rocky Mountain spotted fever
    • Presents with rash on extremities spreading to trunk (centripetal spread)
  • Typhus group
    • Transmitted mainly through lice
    • Epidemic typhus, endemic typhus, Brill-Zinsser
    • Presents with rash on trunk spreading to extremities (centrifugal spread)
  • Scrub typhus group
    • Transmitted through chiggers
    • Doesn't present with rash


Rocky Mountain spotted fever

  • Caused by Rickettsia rickettsia
  • Most common rickettsial infection in US
  • Presents with petechial rash that starts on extremities and moves to trunk
  • Spread by tick bites
  • Reservoir: small rodents
  • Incidence not actually the Rockies but is instead largely Arkansas and Missouri (like tularemia)
  • Usually hits children (60% of patients under 15)


Epidemic typhus

  • Caused by Rickettsia prowazekii
  • Reservoirs: humans, flying squirrels
  • Transmission through human body louse
    • Doesn't bite, but itching smashes louse into skin --> inoculation
  • Nits (lice eggs at hair follicles) are a sign of louse infection
  • Tends to pop up during wars and other natural disasters
  • Presents as petechial rash on trunk (can become necrotic or hemorrhagic), high fever and prostration, renal failure, stupor
  • 20-70% mortality rate if untreated (pneumonia and circulatory collapse)
  • Infection + survival = lifelong immunity
  • Effective live attenuated vaccine (usually for military only)


Brill-Zinsser disease

  • Caused by Rickettsia prowazekii
  • Similar symptoms as endemic typhus, but milder
  • Probably caused by reactivation of endemic typhus


Endemic typhus

  • Caused by Rickettsia typhi (from fleas that have bitten rats) or Rickettsia felis (from fleas that have bitten cats)
  • Milder than epidemic typhus
    • Low-grade fever, mild headache, joint pain


Scrub typhus

  • Caused by Orientia tsusgamushi
  • Transmitted by chiggers who've bitten rats
  • Presents without rash, but eschar develops at site of bite like tularemia or plague
  • Immunity is short-lived


Q fever

  • Caused by Coxiella burnetti
    • Obligate intracellular bacteria that multiply in phagolysosomes (fusogenic)
    • Extremely resistant to dessication (dries up and then just drifts around waiting to get inhaled)
  • Reservoir: ruminants (particularly fetal membranes of cows/sheep)
  • Transmitted by aerosolized membranes/dust
  • Super virulent: just 1 organism can be infectious
  • Causes self-limited influenza-like illness
    • Doesn't present like other rickettsial infections and isn't caused by Rickettsia species


Characteristics of Erlichia spp. & their major infections

  • Ehrlichia:
    • Obligate intracellular bacteria
    • Infect phagocytic cells & multiply inside vacuoles
  • Can see on blood smear - filled vacuoles inside leukocytes (morulas)
  • Ehrlichia more or less = Anaplasma
  • Clinical manifestations:
    • Similar to rickettsial infections - high fever, prostration, aches and pains, but no rash
  • Cause leukopenia & thrombocytopenia, high ALT/AST
  • Transmitted by lone-star tick
  • # of cases increasing in last 10 years - may just be due to better diagnostics


Characteristics of Bartonella spp. & major infections

  • Bartonella
    • Facultative intracellular bacteria
    • 3 pathogenic species - most common in US is Bartonella henselae (cat-scratch disease)
  • Manifestations:
    • Oroya fever (B. bacilliformis)
    • Trench fever (B. quintana)
    • Cat-scratch disease (B. henselae)
  • In immunosuppressed patients, B. henselae or B. quintana can cause bacillary angiomatosis
    • Normally self-limited trench fever or cat-scratch disease runs amok and causes painless, angioproliferative skin lesions (look like Kaposi's sarcoma) and hepatic blood cysts (abdominal pain)


Oroya fever

  • Caused by B. bacilliformis
  • Can pick up through sandfly in South America
  • Invades RBCs, causes anemia & skin lesions


Trench fever

  • Caused by B. quintana
  • Transmitted by louse bite
  • Presents similarly to rickettsia but with relapsing fever every 5 days


Cat-scratch disease

  • Caused by B. henselae
  • Transmitted through cat scratches, bites, or licks
  • Cat is asymptomatic
  • Infects capillary endothelial cells
  • Causes fever, painful lymphadenopathy
  • Usually self-limited