Lyme Disease

Lyme disease is an infection transmitted by the bite of ticks carrying the spiral-shaped bacterium Borrelia burgdorferi. The disease was named for Lyme, Connecticut, the town where it was first diagnosed in 1975, after a puzzling outbreak of arthritis. The organism was named for its discoverer, Willy Burgdorfer. The effects of this disease can be long-term and disabling unless it is recognized and treated properly with antibiotics.

Lyme disease is a vector-borne disease, which means it is delivered from one host to another. In this case, a tick bearing the B. burgdorferi organism literally inserts it into a host's bloodstream when it bites the host to feed on its blood. It is important to note that neither B. burgdorferi nor Lyme disease can be transmitted from one person to another.

In the United States, Lyme disease accounts for more than 90% of all reported vector-borne illnesses. It is a significant public health problem and continues to be diagnosed in increasing numbers. More than 99,000 cases were reported between 1982 and 1996. When the numbers for 1996 Lyme disease cases reported were tallied, there were 16,455 new cases, a record high following a drop in reported cases from 1994 (13,043 cases) to 1995 (11,700 cases). Controversy clouds the true incidence of Lyme disease because no test is definitively diagnostic for the disease, and the broad spectrum of Lyme disease's symptoms mimic those of so many other diseases. Originally, public health specialists thought Lyme disease was limited geographically in the United States to the East Coast. Now it is known that it occurs in most states, with the highest number of cases in the eastern third of the country.

The risk for acquiring Lyme disease varies, depending on what stage in its life cycle a tick has reached. A tick passes through three stages of development—larva, nymph, and adult—each of which is dependent on a live host for food. In the United States, B. burgdorferi is borne by ticks of several species in the genus Ixodes, which usually feed on the white-footed mouse and deer (and are often called deer ticks). In the summer, the larval ticks hatch from eggs laid in the ground and feed by attaching themselves to small animals and birds. At this stage, they are not a problem for humans. It is the next stage, the nymph, that causes most cases of Lyme disease. Nymphs are very active from spring through early summer, at the height of outdoor activity for most people. Because they are still quite small (less than 2 mm), they are difficult to spot, giving them ample opportunity to transmit B. burgdorferi while feeding. Although far more adult ticks than nymphs carry B. burgdorferi, the adult ticks are much larger, more easily noticed, and more likely to be removed before the 24 hours or more of continuous feeding needed to transmit B. burgdorferi.

Lyme disease is a collection of effects caused by B. burgdorferi. Once the organism gains entry to the body through a tick bite, it can move through the bloodstream quickly. Only 12 hours after entering the bloodstream, B. burgdorferi can be found in cerebrospinal fluid (which means it can affect the nervous system). Treating Lyme disease early and thoroughly is important because B. burgdorferi can hide for long periods within the body in a clinically latent state. That ability explains why symptoms can recur in cycles and can flare up after months or years, even over decades. It is important to note, however, that not everyone exposed to B. burgdorferi develops the disease.

Lyme disease is usually described in terms of length of infection (time since the person was bitten by a tick infected with B. burgdorferi) and whether B. burgdorferi is localized or disseminated (spread through the body by fluids and cells carrying B. burgdorferi). Furthermore, when and how symptoms of Lyme disease appear can vary widely from patient to patient. People who experience recurrent bouts of symptoms over time are said to have chronic Lyme disease.

The most recognizable indicator of Lyme disease is a rash around the site of the tick bite. Often, the tick exposure has not been recognized. The eruption might be warm or itch. The rash, erythema migrans (EM), generally develops within 3–30 days and usually begins as a round, red patch that expands. Clearing may take place from the center out, leaving a bull's-eye effect; in some cases, the center gets redder instead of clearing. The rash may look like a bruise on people with dark skin. Of those who develop Lyme disease, about 50% notice the rash; about 50% notice flu-like symptoms, including fatigue, headache, chills and fever, muscle and joint pain, and lymph node swelling. However, a rash at the site can also be an allergic reaction to the tick saliva rather than an indicator of Lyme disease, particularly if the rash appears in less than three days and disappears only days later.

Weeks, months, or even years after an untreated tick bite, symptoms can appear in several forms, including fatigue, neurological problems, such as pain (unexplained and not triggered by an injury), Bell's palsy (facial paralysis, usually onesided but may be on both sides), mimicking of the inflammation of brain membranes known as meningitis (fever, severe headache, stiff neck), and arthritis (short episodes of pain and swelling in joints). Less common effects of Lyme disease are heart abnormalities (such as irregular rhythm or cardiac block) and eye abnormalities (such as swelling of the cornea, tissue, or eye muscles and nerves).

A clear diagnosis of Lyme disease can be difficult, and relies on information the patient provides and the doctor's clinical judgment, particularly through elimination of other possible causes of the symptoms. Lyme disease may mimic other conditions, including chronic fatigue syndrome (CFS), multiple sclerosis (MS), and other diseases with many symptoms involving multiple body systems. Differential diagnosis (distinguishing Lyme disease from other diseases) is based on clinical evaluation with laboratory tests used for clarification, when necessary. A two-test approach is common to confirm the results. Because of the potential for misleading results (false-positive and false-negative), laboratory tests alone cannot establish the diagnosis.

Physicians generally know which disease-causing organisms are common in their geographic area. The most helpful piece of information is whether a tick bite or rash was noticed and whether it happened locally or while traveling. Doctors may not consider Lyme disease if it is rare locally, but will take it into account if a patient mentions vacationing in an area where the disease is commonly found.

The treatment for Lyme disease is antibiotic therapy. If a patient has strong indications of Lyme disease (symptoms and medical history), the doctor will probably begin treatment on the presumption of this disease. The American College of Physicians recommends treatment for a patient with a rash resembling EM or who has arthritis, a history of an EM-type rash, and a previous tick bite.

The physician may have to adjust the treatment regimen or change medications based on the patient's response. Treatment can be difficult because B. burgdorferi comes in several strains (some may react to different antibiotics than others) and may even have the ability to switch forms during the course of infection. Also, B. burgdorferi can shut itself up in cell niches, allowing it to elude antibiotic actions. Finally, antibiotics can kill B. burgdorferi only while it is active rather than dormant. If aggressive antibiotic therapy is given early, and the patient cooperates fully and sticks to the medication schedule, recovery should be complete. Only a small percentage of Lyme disease patients fail to respond or relapse (have recurring episodes). Most long-term effects of the disease result when diagnosis and treatment is delayed or missed. Co-infection with other infectious organisms spread by ticks in the same areas as B. burgdorferi (babesiosis and ehrlichiosis, for instance) may be responsible for treatment failures or more severe symptoms. Lyme disease has been responsible for deaths, but that is rare.

An genetically engineered vaccine for Lyme disease was made available in the United States in 1999. Immunity requires three injections, the first two given a month apart; a third injection given a year later. Clinical trials conducted in 1997 from a large study of 10,000 adults in many locations showed strong promise of the vaccine's safety and efficacy. The Centers for Disease Control recommends the vaccine for those who live and work in Lyme disease endemic areas, and who have repeated and prolonged exposure to tick-infested areas (e.g., park rangers, landscape workers). The Lyme disease vaccine will not prevent other diseases spread by ticks, however, so protective measures against tick bites should still be observed. The vaccine is not recommended for travelers who will have little exposure when visiting areas where Lyme disease has occurred.

Precautions to avoid contact with ticks include moving leaves and brush away from living quarters. Most important are personal protection techniques when outdoors, such as using repellents containing DEET, wearing light-colored clothing to maximize ability to see ticks, tucking pant legs into socks or boot top, and checking children frequently for ticks.