c. Symptoms. Following the bite of an infected tick, a distinctive skin lesion
called an erythema migrans (EM) develops within 5 to 10 days.
(1) Initial, acute phase. The EM lesion begins as a red macule or papule that
expands in an annular manner, while clearing in the center. Lesions can expand to
more than 30 centimeters; secondary lesions may develop. This initial, acute phase
may be accompanied by general malaise, fever, fatigue, headache, joint stiffness, and
These symptoms may precede EM lesion development and may last several
weeks if left untreated.
(2) Later phase. A variety of neurological symptoms may follow within weeks
to months after the onset of initial symptoms. These may include meningitis,
encephalitis, and facial palsy. EM lesions are generally self-clearing after several
weeks while other symptoms may subside or become chronic.
(3) Cryptic phase. The bacteria typically then goes into a cryptic phase,
followed by latent chronic swelling and arthritis of the large joints a few weeks to several
years after the initial infection.
d. Treatment. Lyme disease generally responds well to antibiotics, especially
tetracycline and doxycycline, in its early acute stage. Lyme disease is extremely
difficult, however, to treat in chronic stages, and may require lengthy intravenous
antibiotic therapy. There are currently vaccine trials underway in the U.S. to prevent
infection. Personal protective measures should be taken to prevent tick bites.
5-38. ROCKY MOUNTAIN SPOTTED FEVER
a. General. This tick-borne disease is seen not only throughout the United
States, where it is currently most prevalent in the Southeastern and Middle Atlantic
seaboard states, but also in other countries of the Western Hemisphere.
(1) Transmission. The causative agent, Rickettsia rickets/i, is ordinarily
transmitted to man by the bite of an infected hard tick, of which a number of genera are
involved. Transmission can also occur through contamination of the host skin with tick
feces or tissue from crushed ticks. Ticks become infected for life by feeding on infected
rodents, dogs, or humans, and they pass on the infection to progeny that hatch from
infected eggs (transovarian transmission).
(2) Symptoms. Symptoms in humans appear about 3 to 10 days after
transmission of the rickettsiae. Rocky Mountain spotted fever (RMSF) is an acute
infection of the innermost wall of the blood vessels, characterized by:
Sudden onset of fever