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ness (“mad dog” syndrome), progressing to ataxia, seizures and death; dumb or paralytic form: paralysis of
throat or masseter muscles, profuse salivation, inability to swallow, progressing to coma and death.
Rickettsial Infections
ID: Rickettsial Infections
COL Naomi Aronson, MC, USAIntroduction: Rickettsia rickettsia is a tick-borne bacteria that causes Rocky Mountain Spotted Fever
(RMSF) in the New World. Other tick-borne spotted fevers include African and Mediterranean tick fever
(or Boutonneuse fever, Rickettsia conorii), Queensland tick typhus (Rickettsia australis). All these “spotted
fevers” present similarly and are managed the same way. Fulminant RMSF is noted in blacks with G6PD
deficiency. The incubation period is 3-12 days after a tick bite. Rickettsia prowazekii causes the severe
illness typhus, and is transmitted worldwide between humans by the body louse. In the U.S, contact with
flying squirrels has also been associated with transmission. A milder illness may recur years after the first
attack, not associated with re-infection (Brill Zinsser disease). The incubation period is 7-14 days.
Orientia tsutsugamushi infection follows chigger bites in the Asiatic-Pacific area and causes scrub typhus.
The dark punched-out skin ulcer at site of the bite is known as the “tache noire” (also in most spotted fevers),
and is helpful to clinically suggest this infection. The incubation period is 7-21 days.
Murine typhus is caused by Rickettsia typhi, which is transmitted worldwide by flies that feed on rats. The
illness resembles louse borne typhus but is much milder. Murine typhus peaks in the late summer/autumn
and is prevalent in the urban environment. The incubation period is 6-18 days.
Rickettsialpox is caused by Rickettsia akari and is transmitted by rodent mite and chigger bites. The
vesicular rash is similar to chickenpox, and is seen in urban areas of the northeastern US and some other
areas in the world (Africa, Ukraine). The incubation period is 9-14 days.
Subjective: Symptoms
Spotted fevers: Acute (1-3 days): Fever >102°F, headache, myalgias, rash (typical but not in all cases),
tache noire (except RMSF), mental status changes. Sub-acute (4-7 days): Same as acute. Chronic (> 1
week): continued myalgias, rash , and tache noire
Typhus Group: Acute (1-3 days ): Fever (can last up to 14 days), chills, myalgias, headache Sub-acute (4-7
days): rash, ± cough Chronic (> 1 week): cough, rash
Focused History: Have you had a recent tick bite? (exposure) Did you have a flu-like illness and fever
a couple of days before the rash? (c/w typhus group infection) Have you been in the woods or traveled
overseas in the last 2 weeks? (exposure; see above for geographic clues). Do you have a dark scab-like skin
sore with surrounding redness? (the tache noire of scrub typhus and other rickettsial infections)
Objective: Signs
Using Basic Tools: Inspection
All: Fever to 104oF, terminates by day 14 (except Brill Zinsser, which may recur), often ill-appearing,
Sub-acute/Chronic: Rash
Rocky Mountain spotted fever (other spotted fevers too): Sub-acute (4-7 days): maculopapular rash
that starts on extremities includes palms/soles/face, petechiae and hemorrhagic lesions can occur, digital
gangrene is rare Chronic (>1 week): may see late desquamation
Typhus (louse borne): Acute (1-3 days): Conjunctival injection Sub-acute (4-7 days): Small macules in
axilla/trunk that spread over body and can become dark in color (hemorrhagic). Rare digital gangrene
Scrub typhus: Acute (1-3 days): Tache noire (see Color Plates Picture 6) Sub-acute (4-7 days): Spreading
dull red maculopapular rash starts on trunk, spreads to extremities
Murine typhus: Sub-acute (4-7 days): Maculopapular rash that is sparse and discrete mainly trunk and
extremities, can be palm/soles
Rickettsialpox: Acute (1-3 days): Tache noire Sub-acute (4-7 days): Maculopapular rash with vesicles that
crust, spares palms and soles