Rickettsial Diseases Flashcards

1
Q

Morphology / characteristics of Rickettsia

Stain

A

Fastidious, obligate intracellular coccobacillus.

Stain w/ Gimenez or Giemsa. Gram stain does not work.

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2
Q

Reservoir of Rickettsial diseases

A

Dogs, mice rats, flying squirrels.

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3
Q

2 rickettsial diseases that can be acquired via inhalation

A
Q fever (Coxiella burnetii)
Epidemic typhus (Rickttsia prowazekii)
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4
Q

3 main rickettsial disease groups
Which is most virulent
Which is endemic to the US?

A

3 main: Spotted fever group, Typhus group, Q fever group
RMSF is the most virulent
Murine typhus is endemic to US

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5
Q

Which AB’s are used for all rickettsial diseases?

A

Doxycycline (DOC) or tetracycline

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6
Q
RMSF
Bacterial strain
Vector
Season / location
Classic triad
Type of rash
Other sxs (6)
Yes / no eschar?
Diagnosis
Treatment
A
  • Caused by Rickettsia rickettsii.
  • Vector is a tick.
  • Typically occurs in spring / summer in southeast US (especially North Carolina).
  • Classic triad – fever, headache, and rash w/ appropriate exposure / travel history.
  • Rash generally appears by day 5, moving from extremities to trunk (centripetal rash). Rash is present in 90% of cases. Non-blanching petechiae. 10% of pxs do not develop rash, called “spotless RMSF”.
  • Other sxs: myalgia, abdominal pain, nausea, vomiting, edema around eyes / hands / feet, conjunctival suffusion (pink, swollen conjunctivae).
  • No eschar.
  • Diagnosis – clinical presentation and immunofluorescent Ab (IFA)
  • Start tx w/ doxycycline before diagnosis is confirmed.
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7
Q

Diff Dx for rash on palms / soles

A

RMSF, secondary syphilis, E multiforme, strep

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8
Q
Epidemic Typhus
Strain
Vector
Pathogenesis
Location
Sxs (5)
Treatment
Prevention
A
  • Caused by Rickettsia prowazekii.
  • Vector is the human body louse.
  • Lice get infected by feeding on bacteremic people, then organism replicates in gut, cells burst and are released in feces. Introduced into new people by itching, scratching, mucosa, and inhalation.
  • Major killer in WWII concentration camps due to inability to bathe / wash clothes. Also occurs in current war, natural disasters, and regions of great poverty.
  • Outbreaks seen in southwest US where flying squirrels aerosolize the organism; humans breathe it in.
  • Sxs – fever, severe headache, myalgia, central rash, mental status changes (supor / coma)
  • Tx w/ doxycycline.
  • Prevention – control lice population via washing clothes and delousing.
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9
Q

Brill-Zinsser disease

A

Mild, recrudescent form of epidemic typhus seen months/years after initial acute infection

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10
Q
Q Fever
Cause
Vector
Pxs at risk / pathogenesis
Sxs (5)
Diagnosis
A
  • Caused by direct inhalation of Coxiella burnetii.
  • No vector.
  • Occurs in vets, ranchers, and animal researchers who are in contact w/ infected urine, feces, milk, or placenta of sheep, cattle, or goats.
  • Airborne – possible to acquire by just driving through a farm.
  • Sxs – fever and headache are most common. 50% of pxs develop pneumonia after inhalation. Hepatitis and endocarditis may occur.
  • Diagnose w/ serology and histology (shows donut-shaped, noncaseating granulomas)
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11
Q
Mediterranean Spotted Fever
Cause
Vector
Location
Sxs (4)
A
  • Caused by Rickettsia conorii.
  • Vector is dog tick (contact w/ dogs is risk factor).
  • Found in Europe, Africa, and Asia, including France / Spain.
  • Sxs – usually mild illness w/ fever, constitutional sxs, generalized flat rash, eschar at site of tick bite.
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12
Q
African Tick Bite Fever
Cause
Vector
How common?
Location
Sxs (6)
Yes / no eschar?
Diagnosis
Treatment
A
  • Caused by Rickettsia africae.
  • Vector is cow tick. Often picked up by travelers while walking in the bush (safaris / hikes). Locals may acquire tick when working in the fields.
  • Most common rickettsiosis in travel medicine
  • Found in Sub-Saharan Africa, especially South Africa
  • Sxs – headache, myalgia, disseminated rash, regional lymphadenopathy, mouth blisters.
  • 95% of pxs have eschars at site of bite. Over half have multiple eschars (disseminated).
  • Overall this is a mild, self-limited illness.
  • Diagnose w/ IgG to R africae
  • Tx w/ doxycycline
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13
Q

Weil-Felix Reaction

More sensitive / specific tests currently used

A
  • Weil-Felix Reaction - Historical lab test that measures presence of proteus OX:2/19 or K Abs. These Abs cross-react w/ antigens on Rickettsia spp. Not used clinically due to non specificity.
  • Better tests: indirect immunofluorescent Ab (IFA), indirect hemagglutination Ab (IHA), complement fixation (CF)
  • Takes several weeks for Ab titers to be detectable
  • 4-fold rise in titer or single high titer may be confirmatory
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