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limit of detection
Lyme disease(līm) [ Lyme, CT, where a cluster of cases was reported in 1975],
The infected tick injects its spirochete-laden saliva into the bloodstream, where they incubate for 3 to 32 days and then migrate to the skin, causing the characteristic erythema migrans (EM) rash.
The disease is best diagnosed by the presence of EM, which begins as a red macule or papule at the site of the tick bite and expands in a red ring, leaving a clear center like a target or bull’s eye. The lesion usually feels hot and itchy and may grow to over 20 in (50.8 cm) as more lesions erupt. The lesion is later replaced by red blotches or diffuse urticaria. Conjunctivitis, malaise, fatigue, and flulike symptoms and lymphadenopathy may occur. Antibody tests for Borrelia burgdorferi with an enzyme-linked immunosorbent assay (ELISA) test are also used for diagnosis in patients with a history of exposure and signs and symptoms of Lyme disease but with no evidence of rash. The antibodies are developed against flagellar and outer surface proteins on the spirochete. See: illustration
The course of Lyme disease is divided into three stages. 1 localized infection: begins with the tick bite and proceeds as above.2 disseminated infection: begins weeks to months later. The spirochetes spread to the rest of the body through the blood, in some cases causing arthritis (esp. of the knee joints), muscle pain, cardiac dysrhythmias, pericarditis, lymphadenopathy, or meningoencephalitis. Nonprotective antibodies develop during this stage.3 chronic infection: begins weeks to years after the initial bite. Patients develop mild to severe arthritis, encephalitis, or both, which rarely are fatal.
Oral doxycycline or ampicillin (14–21 or –28 day course) effectively eradicates early uncomplicated Lyme disease. Erythromycin or cefuroxime axetil may be administered to patients allergic to penicillin. Patients with cardiac and neurological involvement may need to be treated with intravenous cephalosporins.
When the disease is treated early, results are good. If treated late, convalescence is prolonged, but complete recovery is the usual outcome in most patients.
The Centers for Disease Control recommends that people should discuss with their health care providers the possibility of getting a Lyme disease vaccination if they are between 15 and 70 years old; live, work, or vacation in endemic areas; or frequently go into wooded or grassy areas. The vaccine is not recommended for children, pregnant women, and those who do not live in or visit endemic areas.
When planning to spend time in places where ticks may be located, people should wear clothing impregnated with insect repellents, hats, long sleeves, pants tucked into socks, heavy shoes, and a tick repellent containing DEET (N, N-diethyltoluamide). Tick repellent should not be directly applied to an infant or toddler’s skin because of the danger of neurotoxicity. If possible, people should stay on paths and away from high grass or brush. They should check clothing carefully for ticks when leaving those areas although tick nymphs, which are smaller than 1 mm in length, may not be easily seen. Once home, people should remove and wash clothing and check their entire body, esp. the hairline and ankles, for ticks or nymphs. If a tick or nymph is found, it should be carefully removed with tweezers, esp. the head and mouth parts, but the body of the tick or nymph must not be squeezed. The site may then be cleansed with an antiseptic, but should be observed for signs of infection (redness, swelling, pain, rash), and the primary health care provider contacted if infection is suspected. Some people make the mistake of trying to remove ticks or nymphs with alcohol, a lighted match, or petroleum jelly. These measures are ineffective and may increase the risk of transmission of tick-borne diseases. Prophylactic antibiotics generally should not be requested (or given). Although pet dogs may receive Lyme vaccine, they should still be checked to prevent them from bringing ticks into the house.
The patient is checked for any drug allergies. Prescribed pharmacologic therapy is explained to the patient, including dosing schedule, the importance of completing the course of therapy even if he feels better, and adverse effects. Patients being treated for Lyme disease often require antibiotics for a prolonged period, esp. in advanced stages, which increases their risk for developing adverse effects (e.g., diarrhea). Methods for dealing with these problems are explained. Patients with chronic Lyme disease often require assistance to deal with changes in lifestyle, family interactions, and ability to perform daily activities. Available local and national support groups can assist with such problems. Patients should be made aware that one occurrence of Lyme disease does not prevent recurrences. The U.S. Department of Health and Human Services has made Lyme disease prevention a priority under its program “Healthy People 2010.” Patients can be referred to the Lyme Disease Foundation (860-870-0070; http://www.lyme.org) or the American Lyme Disease Foundation (http://www.aldf.com) for information and support.
LDSee LACTATE DEHYDROGENASE.
n See time, median lethal.