Rickettsial Diseases

Question 1

Morphology / characteristics of Rickettsia

Stain

Answer 1

Fastidious, obligate intracellular coccobacillus.

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

Question 2

Reservoir of Rickettsial diseases

Answer 2

Dogs, mice rats, flying squirrels.

Question 3

2 rickettsial diseases that can be acquired via inhalation

Answer 3

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

Question 4

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

Answer 4

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

Question 5

Which AB’s are used for all rickettsial diseases?

Answer 5

Doxycycline (DOC) or tetracycline

Question 6

RMSF
Bacterial strain
Vector
Season / location
Classic triad
Type of rash
Other sxs (6)
Yes / no eschar?
Diagnosis
Treatment

Answer 6

• 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.

Question 7

Diff Dx for rash on palms / soles

Answer 7

RMSF, secondary syphilis, E multiforme, strep

Question 8

Epidemic Typhus
Strain
Vector
Pathogenesis
Location
Sxs (5)
Treatment
Prevention

Answer 8

• 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.

Question 9

Brill-Zinsser disease

Answer 9

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

Question 10

Q Fever
Cause
Vector
Pxs at risk / pathogenesis
Sxs (5)
Diagnosis

Answer 10

• 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)

Question 11

Mediterranean Spotted Fever
Cause
Vector
Location
Sxs (4)

Answer 11

• 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.

Question 12

African Tick Bite Fever
Cause
Vector
How common?
Location
Sxs (6)
Yes / no eschar?
Diagnosis
Treatment

Answer 12

• 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

Question 13

Weil-Felix Reaction

More sensitive / specific tests currently used

Answer 13

• 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