Rickettsial Diseases Flashcards
Morphology / characteristics of Rickettsia
Stain
Fastidious, obligate intracellular coccobacillus.
Stain w/ Gimenez or Giemsa. Gram stain does not work.
Reservoir of Rickettsial diseases
Dogs, mice rats, flying squirrels.
2 rickettsial diseases that can be acquired via inhalation
Q fever (Coxiella burnetii) Epidemic typhus (Rickttsia prowazekii)
3 main rickettsial disease groups
Which is most virulent
Which is endemic to the US?
3 main: Spotted fever group, Typhus group, Q fever group
RMSF is the most virulent
Murine typhus is endemic to US
Which AB’s are used for all rickettsial diseases?
Doxycycline (DOC) or tetracycline
RMSF Bacterial strain Vector Season / location Classic triad Type of rash Other sxs (6) Yes / no eschar? Diagnosis Treatment
- 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.
Diff Dx for rash on palms / soles
RMSF, secondary syphilis, E multiforme, strep
Epidemic Typhus Strain Vector Pathogenesis Location Sxs (5) Treatment Prevention
- 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.
Brill-Zinsser disease
Mild, recrudescent form of epidemic typhus seen months/years after initial acute infection
Q Fever Cause Vector Pxs at risk / pathogenesis Sxs (5) Diagnosis
- 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)
Mediterranean Spotted Fever Cause Vector Location Sxs (4)
- 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.
African Tick Bite Fever Cause Vector How common? Location Sxs (6) Yes / no eschar? Diagnosis Treatment
- 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
Weil-Felix Reaction
More sensitive / specific tests currently used
- 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