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Introduction
Early in the
20th century, European physicians observed patients with a red,
slowly expanding rash (called erythema migrans or EM), associated
this rash with the bite of ticks, and postulated that it was caused
by a tick-borne bacterium. Then in the 1940s, similar tick-borne
illness was described that often began with EM and developed into
multi-system illness. Later that decade, spirochete-like structures
were observed in skin specimens leading to the use of penicillin for
treatment.
Aware of
these findings, a physician in Wisconsin diagnosed a patient with EM
and successfully treated it with penicillin in 1969. In the
mid-1970s, physicians observed clusters of children with arthritis
in and around Lyme, Connecticut. Other clinical symptoms and
environmental conditions suggested that this was a distinct illness
probably transmitted by an arthropod. Researchers linked the
presence of EM rash lesions to preceding tick bites and determined
that early treatment with penicillin not only shortened the duration
of EM but also reduced the risk of subsequent arthritis.
Further
investigation revealed that Lyme disease is caused by the bacterium,
Borrelia burgdorferi. These bacteria are transmitted to
humans by the bite of infected deer ticks and caused more than
23,000 infections in the United States in 2002.
Carrier
Ticks
Black-legged
ticks (Ixodes
scapularis) are responsible for transmitting Lyme disease
bacteria to humans in the northeastern and north-central United
States. On the Pacific Coast, the bacteria are transmitted to humans
by the western black-legged tick (Ixodes pacificus).
Ixodes ticks are much smaller than common dog and cattle
ticks. In their larval and nymphal stages, they are no bigger than a
pinhead. Ticks feed by inserting their mouths into the skin of a
host and slowly take in blood.
Ixodes ticks are most likely to transmit infection after
feeding for two or more days.
Lyme
Disease Risk Factors
In the United
States, Lyme disease is mostly localized to states in the
northeastern, mid-Atlantic, and upper north-central regions, and to
several counties in northwestern California. In 2002, 23,763 cases
of Lyme disease were reported to the Centers for Disease Control and
Prevention (CDC). Ninety-five percent of these cases were from the
states of Connecticut, Delaware, Rhode Island, Maine, Maryland,
Massachusetts, Minnesota, New Jersey, New Hampshire, New York,
Pennsylvania, and Wisconsin.
Individuals
who live or work in residential areas surrounded by tick-infested
woods or overgrown brush are at risk of getting Lyme disease.
Persons who work or play in their yard, participate in recreational
activities away from home such as hiking, camping, fishing and
hunting, or engage in outdoor occupations, such as landscaping,
brush clearing, forestry, and wildlife and parks management in
endemic areas may also be at risk of getting Lyme disease.
Prevention
and Treatment:
Prevention measures can be effective in reducing your exposure to
infected ticks, and most people can be successfully treated with
antibiotic therapy when diagnosed in the early stages of Lyme
disease.
Additional Lyme
Disease Information
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