A 36-year-old man presents at his physician’s office complaining of
fever and headache. On examination, he had leukopenia and increased
liver enzymes, and inclusion bodies were seen in his monocytes.
Historyrevealed that he was an outdoorsman and remembered removing a
tick from his leg. Which of the following diseases is most likely
causing the symptoms described?
A. Lyme disease
B. Ehrlichiosis
C. Rocky Mountain spotted fever
D. Q fever
A. Lyme disease
B. Ehrlichiosis
C. Rocky Mountain spotted fever
D. Q fever
Ans. B.
All the listed diseases except Q fever
are tick-borne. The rickettsia C. burnetii causes Q fever, and humans are
usually infected by aerosol of a sporelike form shed in milk, urine, feces, or placenta
of infected sheep, cattle, or goats. Lyme disease is caused by a spirochete,
Borreliaburgdorferi, and produces the characteristic lesion erythema
chronicummigrans (ECM). The etiologic agent of Rocky Mountain spotted fever is
R. rickettsia. It usually produces a rash that begins in the extremities and
then involves the trunk. Two human forms of ehrlichiosis can occur: human
monocyticehrlichiosis (HME), caused by E. chaffeensis; and human granulocytic
ehrlichiosis. (HGE), caused by an as yet unnamed Ehrlichia.Ehrlichiosis was
previously recognized only as a veterinary pathogen. HME infection is
transmitted by the brown dog tick and A. americanum. HGE infection is
transmitted by I. scapularis, the same tick that transmits Lyme disease. Both
infections cause fever and leukopenia. A rash rarely occurs. E. chaffeensis
infects monocytes, and HGE infects granulocytes; both organisms produce
inclusion bodies called morulae.
