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Lyme disease is an infection caused by Borrelia burgdorferi which belongs to the spirochete family of bacteria. This bacterium lives inside certain ticks (the deer tick in the Northeast and Upper Midwest) and can be spread to humans by the bite of an infected tick.

In its early localized stage, Lyme disease consists of a skin rash, called erythema migrans, that appears at the tick bite site from three days to several weeks later. This rash, starts as a small red mark and, over subsequent days, gradually enlarges in diameter to at least two inches and sometimes as large as 10 or more inches.

If the rash goes unnoticed and untreated, or does not occur (as is the case approximately 10-25 percent of the time), the bacterium may spread through the bloodstream to the rest of the body initiating an early disseminated stage of infection which occurs in the weeks following the tick bite. At this point, the infected person may develop an array of signs and symptoms including multiple skin rashes, fever, joint pain, muscle pain, and headaches. Infection in about five percent of individuals will involve the heart, causing a temporary blockage of the normal heart rhythm. In approximately 20 percent of cases, the infection will affect the nervous system resulting in severe headache and stiff neck, paralysis of the muscles of the face or painful inflammation of nerves. Still other individuals will have no symptoms at all.

If Lyme disease goes unrecognized or untreated with the appropriate antibiotic course, late stage infection may occur months to even years after the onset of infection, and can affect the joints or nervous system.

Lyme arthritis (late stage) causes swelling of one or both knees and, less often, can affect other, predominantly large, joints of the body. Late infection of the nervous system may also occur, however, the clinical manifestations and treatment have been less well defined and agreed upon. Peripheral nerves may be affected, leading to numbness or tingling or less often weakness. Infection of the brain may lead to difficulty with sleep pattern, memory and concentration.

What causes lyme disease

Lyme disease is caused by the transmission of Borrelia burgdorferi bacteria living inside of infected ticks. These ticks can be so small (the size of a poppy seed) as to go unnoticed, feeding at the site of attachment to the skin for several days before dislodging. The Lyme bacteria, which resides in the tick gut, travels to the mouthpart and is injected into the skin.

In the United States, Lyme disease is endemic in most of the Northeast, the upper Midwest and, to a lesser degree, in California and the Pacific Northwest region. The illness is named after the town of Old Lyme, Connecticut where the first cases of Lyme disease were recognized in 1975.

Other tick-borne infections may resemble a “rashless” Lyme disease, and may even occur together with lyme disease (coinfection). These also require prompt medical attention for proper diagnosis and treatment.

Who gets Lyme disease

People most at risk for Lyme disease are those who live or spend leisure time in areas with a high density of infected ticks. In the Northeast and Upper Midwest regions, there is a sharp peak of infection in the late spring and early summer months when the tiny nymphal form of the tick is feeding. A second smaller peak of Lyme disease occurs in the fall when the adult tick feeds. In comparison, the risk of tick bites are lower during the late summer after the nymphal ticks have all become inactive and molted, and in the winter when cold and snowfall render the adult ticks temporarily dormant.

How Lyme disease is treated

In the majority of cases, early stage Lyme disease is treated successfully with two-three week courses of oral antibiotics. Early infection involving the nervous system or heart may require intravenous antibiotics.

Even when the infection is detected after significant delay or at its later stages, antibiotic treatment is still successful in most patients. However, some patients will have lingering symptoms following treatment. General measures of good health such as exercise, good nutrition, and recognition and treatment of any emotional problems that may coexist or develop as a result of prolonged illness also are important adjuncts to treatment.