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TextLyme Disease
Lyme disease,
first identified in 1975 in Lyme, Connecticut, is a bacterial illness
transmitted by a tick bite. Although the disease is found more frequently
in the North and the upper Midwest, cases have been reported in Virginia
since 1982.
- Learn more about Lyme disease prevention.
- Learn more about Lyme disease from the Centers for Disease Control and Prevention (CDC).
The Pathogen
The causative agent of Lyme disease in the United States is a spirochete bacterium called Borrelia burgdorferi. Other Borrelia bacteria cause diseases similar to Lyme disease in Europe and in Asia.
Evidence is accumulating that these closely-related, but different, spirochetes are associated with different disease expressions. Arthritis appears to occur more frequently following infection with the type that is found in the U.S. Neurological manifestations and cutaneous manifestations are more common in infections with the types found in Europe and Asia.
The Tick
The black-legged tick (Ixodes scapularis), also known as the deer tick, is responsible for transmitting the causative agent of Lyme disease to humans in the northeastern and north-central United States. In the western part of the United States, the Lyme disease vector is 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 taking in blood. Both deer and rodent hosts must be abundant to maintain the enzootic cycle of B. burgdorferi. Ixodes ticks are most likely to transmit Lyme disease to humans after feeding for two or more days.
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Symptoms
The
first sign of infection is usually a circular rash called erythema
migrans or EM. This rash occurs in approximately 70-80 percent of
infected persons and begins at the site of a tick bite after a delay of
3-30 days. A distinctive feature of the rash is that it gradually expands
over a period of several days, reaching up to 12 inches (30 cm) across.
The center of the rash may clear as it enlarges, resulting in a
bull's-eye appearance. It may be warm but is not usually painful. Some
patients develop additional EM lesions in other areas of the body after
several days.
Patients also experience symptoms of fatigue, chills, fever, headache, and muscle and joint aches, and swollen lymph nodes. In some cases, these may be the only symptoms of infection.
If left untreated, the infection may spread to other parts of the body after several weeks. This can produce a number of other symptoms that may appear separately, including loss of muscle tone on one or both sides of the face, severe headaches and neck stiffness, shooting pains, heart palpitations, dizziness and pain that moves from joint to joint.
After several months, about 60 percent of untreated cases begin to have intermittent bouts of arthritis with severe joint pain and swelling. Up to five percent of untreated cases may develop neurological complaints.
Since the black-legged tick is so small in its nymphal stage, many people are not aware of its presence or bite. If you experience any of these symptoms, contact your physician. State that you may have been bitten by a tick. This is extremely important because the diagnosis of Lyme disease is usually based on symptoms and history of tick exposure.
Transmission Cycle
Knowing the complex life cycle of Ixodes ticks is
important in understanding the risk of acquiring Lyme disease and in
finding ways to reduce this risk. The life cycle of the deer tick
requires 2 years to complete. Adult female ticks lay eggs on the ground
in early spring. By summer, eggs hatch into larvae. Larvae feed on mice,
other small mammals, deer, and birds in the late summer and early fall,
molt into nymphs, and then are dormant (inactive) until the next spring.
Nymphs feed on rodents, small mammals, birds and humans in the late
spring and summer and molt into adults in the fall. In the fall and early
spring, adult ticks feed and mate on large mammals (especially deer) and
bite humans. The adult female ticks then drop off these animals and lay
eggs in spring, completing a 2-year life cycle.
Knowing the complex life cycle of Ixodes ticks is important in understanding the risk of acquiring Lyme disease and finding ways to reduce this risk.
The life cycle of the black-legged tick requires two years to complete. Adult female ticks lay eggs on the ground in early spring. By summer, larvae hatch from the eggs. Larvae feed on mice, other small mammals, deer, and birds in the late summer and early fall. They molt into nymphs, and are dormant (inactive) until the next spring. Nymphs feed on rodents, small mammals, birds and humans in the late spring and summer and molt into adults in the fall. In the fall and early spring, adult ticks feed and mate on large mammals (especially deer) and humans. The adult female ticks then drop off these animals and lay eggs in the spring, completing the 2-year life cycle.
Ticks, small rodents and other non-human vertebrate animals all serve as natural reservoirs for B. burgdorferi. This means that the Lyme disease bacteria can live and grow within these hosts without causing them to die. Larval and nymphal ticks become infected with the Lyme disease spirochete, B. burgdorferi, when they feed on small animals that carry the bacteria. The bacteria remain in a tick as it changes from larva to nymph or from nymph to adult. Infected nymphs transmit B. burgdorferi bacteria to other small rodents, mammals and humans, all in the course of their normal feeding behavior.
Although adult ticks often feed on deer, these animals do not become infected. Deer are nevertheless important in transporting ticks and maintaining tick populations.
The Risk
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. The majority of cases reported to the Centers for Disease Control (CDC) are from northeastern states.
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 are also at risk of getting Lyme disease.
Treatment
If a tick is attached to your skin for less than 24 hours, your chance of getting Lyme disease is small. For this reason, daily checks for ticks and promptly removing the attached tick will help prevent infection. Individuals who are bitten by a black-legged tick should remove the tick and may wish to consult their health care provider. Persons should promptly seek medical attention if they develop any signs and symptoms of Lyme disease.
When detected early, Lyme disease can be mild and is easily treated with oral antibiotics such as doxycycline, amoxicillin or penicillin. Even in the late stages, Lyme disease can be treated successfully with antibiotics, but the treatment lasts longer and is more involved.
A Lyme disease vaccine was available in the past. However, as of February 25, 2002 the manufacturer announced that the LYMErix™ Lyme disease vaccine is no longer commercially available.
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