Friday, September 24, 2010

What is Lyme disease?

What is Lyme disease? Lyme disease is caused by Gram-negative spirochetal bacteria from the genus Borrelia. At least 11 Borrelia species have been discovered, 3 of which are known to be Lyme-related. The Borrelia species that cause Lyme disease are collectively known as Borrelia burgdorferi sensu lato, and show a great deal of genetic diversity.

Lyme disease can affect multiple body systems and produce a range of symptoms. Not all patients with Lyme disease will have all symptoms, and many of the symptoms are not specific to Lyme disease but can occur with other diseases as well. The incubation period from infection to the onset of symptoms is usually one to two weeks, but can be much shorter (days), or much longer (months to years). Symptoms most often occur from May through September, because the nymphal stage of the tick is responsible for most cases. Asymptomatic infection exists, but occurs in less than 7% of infected individuals in the United States. Asymptomatic infection may be much more common among those infected in Europe.

Antibiotics are the primary treatment for Lyme disease; the most appropriate antibiotic treatment depends upon the patient and the stage of the disease. The antibiotics of choice are doxycycline (in adults), amoxicillin (in children), erythromycin (for pregnant women) and ceftriaxone, with treatment lasting 14 to 28 days. Alternative choices are cefuroxime and cefotaxime. Treatment of pregnant women is similar, but tetracycline should not be used.
A double blind, randomized, placebo-controlled multicenter clinical study indicated that 3 weeks of treatment with intravenous ceftriaxone, followed by 100 days of treatment with oral amoxicillin did not improve symptoms any more than just 3 weeks of treatment with ceftriaxone. The researchers noted that the outcome should not be evaluated after the initial antibiotic treatment but rather 6–12 months afterwards. In patients with chronic post-treatment symptoms, persistent positive levels of antibodies did not seem to provide any useful information for further care of the patient.
In later stages, the bacteria disseminate throughout the body and may cross the blood-brain barrier, making the infection more difficult to treat. Late diagnosed Lyme is treated with oral or IV antibiotics, frequently ceftriaxone for a minimum of four weeks. Minocycline is also indicated for neuroborreliosis for its ability to cross the blood-brain barrier.


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