is through contamination of fleabite wounds or other skin abrasions with infective flea
feces. The incubation period is from 6 to 14 days, with 12 the usual.
Immunity conferred after attack is not always permanent.
d. Treatment. Specific therapy is the same as for epidemic typhus. Due to the
efficacy of specific treatment and vector control, need for development of a vaccine is
not considered critical. Use of the measures for the control of and protection from
rodents and fleas markedly reduces the incidence of murine typhus in man.
Section IX. TICK-BORNE DISEASES
5-37. LYME DISEASE
a. General. Since it was first identified in 1982, Lyme disease
has become the most commonly reported tick-borne disease in the
United States. It occurs throughout the U.S. Most cases, however, are
reported from three main foci. These are along the eastern seaboard from
Massachusetts to Georgia; upper Midwest, mainly Wisconsin and Minnesota; and along
the Pacific in Oregon and northern California. It also occurs in parts of Europe and
(1) Transmission. The causative agent is spirochete bacteria Borrelia
burgdorferi. It is transmitted to humans through the bite of infected ticks.
(2) Vectors. Various species of ticks in the genus Ixodes are the primary
vectors for Lyme disease. The role other tick genera play is not clearly understood.
In the U.S., the black legged tick, Ix. scapularis is the primary vector
in all but the Pacific Northwest.
In California and Oregon, Ix. paciflcus is the primary vector.
Other Ixodes spp. serve as vectors elsewhere in the world.
(3) Reservoirs. The reservoirs for Lyme disease appear to be wild rodents
and ungulates (hoofed mammals), especially deer.
b. Etiology. There appear to be three environmental requirements for Lyme
disease to occur in an area. These are the presence of small rodents, large ungulate
reservoirs, and Ixodes ticks. Rodents serve as hosts for tick larvae (newly hatched) and
nymphs, and infect them with the Lyme spirochete. Adult ticks feed primarily on deer,
but may feed on other large animals including humans.