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, which is also called Lyme borreliosis, is a vector-borne disease. This term means that it is delivered from one host to another. It is also classified as a zoonosis, which means that it is a disease of animals that can be transmitted to humans under natural conditions. 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 directly from one person to another, or from pets to humans.
Controversy clouds the true incidence of Lyme disease because no test is definitively diagnostic for the disease, and many of its symptoms mimic those of so many other diseases. Cases of Lyme disease have been reported in 49 of the 50 states; however, 95% of the more than 25,000 confirmed cases reported to the Centers for Disease Control and Prevention (CDC) in 2013 were from only 14 states (Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin). The disease is also found in Scandinavia, continental Europe, the countries of the former Soviet Union, Japan, and China; in addition, it is possible that it has spread to Australia.
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. The CDC attributes this increase to the growing size of the deer herd and the geographical spread of infected ticks rather than to improved diagnosis. In addition, some epidemiologists believe that the actual incidence of Lyme disease in the United States may be five to ten times greater than that reported by the CDC. The reasons for this difference include the narrowness of the CDC's case definition as well as frequent misdiagnoses of the disease.
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 millimeters), 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 caused by B. burgdorferi. Once B. burgdorferi 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 Lyme disease 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 many people who are 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 Lyme disease) 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 outward. About 75% of patients with Lyme disease develop EM. 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 flulike 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, forgetfulness, confusion, mood swings, irritability, numbness.
Neurologic problems, such as pain (unexplained and not triggered by an injury), Bell's palsy (facial paralysis, usually one-sided but may be on both sides), and a mimicking of the inflammation of brain membranes known as meningitis (fever, severe headache).
Arthritis (short episodes of pain and swelling in joints) and other musculoskeletal complaints. Arthritis eventually develops in about 60% of patients with untreated Lyme disease.
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, multiple sclerosis, 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.
In February 1999 the U.S. Food and Drug Administration (FDA) approved a new blood test for Lyme disease called PreVue. The test, which searches for antigens (substances that stimulate the production of antibodies) produced by B. burgdorferi, gives results within one hour in the doctor's office. A positive result from the PreVue test is confirmed by a second blood test known as the Western blot, which must be done in a laboratory.
Doctors 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; however, overprescribing of antibiotics can lead to serious problems, so the decision to treat must be made with care. Disease organisms can develop resistance to families of medications over time, rendering the drugs useless. Furthermore, testing and treatments can be expensive. 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 benefits of treating early must be weighed against the risks of overtreatment. The longer a patient is ill with Lyme disease before treatment, the longer the course of therapy must be, and the more aggressive the treatment. The development of opportunistic organisms may produce other symptoms. For example, after long-term antibiotic therapy, patients can become more susceptible to yeast infections. Treatment may also be associated with adverse drug reactions.
For most patients, oral antibiotics (doxycycline or amoxicillin) are prescribed for 21 days. When symptoms indicate nervous system involvement or a severe episode of Lyme disease, intravenous antibiotic (ceftriaxone) may be given for 14–30 days. Some physicians consider intravenous ceftriaxone the best therapy for any late manifestation of disease, but treatments for late Lyme disease are still a matter of debate as of 2014. Corticosteroids (oral) may be prescribed if eye abnormalities occur, but they should not be used without first consulting an eye doctor.
The doctor 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 hide from antibiotics. Finally, antibiotics can kill B. burgdorferi only while it is active rather than dormant.
Supportive therapies may minimize symptoms of Lyme disease or improve the immune response. These include vitamin and nutritional supplements, mostly for chronic fatigue and increased susceptibility to infection. For example, yogurt and Lactobacillus acidophilus preparations help fight yeast infections, which are common in people on long-term antibiotic therapy. In addition, botanical medicine and homeopathy can be considered to help bring the body's systems back to a state of health and well-being. A Western herb, spilanthes (Spilanthes spp.), may be effective in treating diseases such as Lyme disease that are caused by spirochetes (spiral-shaped bacteria).
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. Coinfection 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. Most fatalities reported with Lyme disease involved patients coinfected with babesiosis.
A vaccine for Lyme disease known as LYMErix was available from 1998 to 2002, when it was removed from the U.S. market. The decision was influenced by reports that LYMErix may be responsible for neurologic complications in vaccinated patients. Researchers from Cornell–New York Hospital presented a paper at the annual meeting of the American Neurological Association in October 2002 that identified nine patients with neuropathies linked to vaccination with LYMErix. In April 2003, the National Institute of Allergy and Infectious Diseases (NIAID) awarded a federal grant to researchers at Yale University School of Medicine to develop a new vaccine against Lyme disease. As of late 2014, the best prevention strategy is through minimizing risk of exposure to ticks and using personal protection precautions.
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:
Spraying tick repellent on clothing and exposed skin.
Wearing light-colored clothing to maximize ability to see ticks.
Tucking pant legs into socks or boot top.
Checking children and pets frequently for ticks.
In highly tick-populated areas, each individual should be inspected at the end of the day for ticks.
The two most important factors are removing the tick quickly and carefully, and seeking a doctor's evaluation at the first sign of symptoms of Lyme disease. When in an area that may be tick-populated:
Check for ticks, particularly in the area of the groin, underarm, behind ears, and on the scalp.
Stay calm and grasp the tick as near to the skin as possible, using a tweezer.
To minimize the risk of squeezing more bacteria into the bite, pull straight back steadily and slowly.
Do not try to remove the tick by using petroleum jelly, alcohol, or a lit match.
Place the tick in a closed container (for species identification later, should symptoms develop) or dispose of it by flushing.
See a physician for any sort of rash or patchy discoloration that appears 3 to 30 days after a tick bite.
See also Antibiotics; Bacterial infections; Fatigue; Joint integrity and function; Mobility issues; Neurologic examination; Osteoarthritis.
مقالات كريدو ذات الصلة
The term zoonosis (plural, zoonoses) is derived from the Greek roots for animal ( zoon ) and disease ( osis ) and was coined initially to...
Lyme borreliosis is a tick-borne spirochetal disease caused by Borrelia burgdorferi . This systemic illness potentially involves the...
Lyme disease is an infection caused by a bacterium, Borrelia burgdorferi , which is carried around in the adult deer tick, Ixodes dammini . It...