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Lyme disease

From Academic Kids

Adult deer ticks can be carriers of Lyme disease.
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Adult deer ticks can be carriers of Lyme disease.

Lyme disease is an infectious tick-borne disease, caused by the Borrelia spirochete, a gram-negative microorganism. It is transmitted to humans by the bite of infected ticks.

Contents

History

Lyme Disease is so named because it is generally believed to have first been observed in and around Lyme, Connecticut in 1975. Before 1975 the Borrelia infection was also called tick-borne meningopolyneuritis, Garin-Bujadoux, Bannwarth Syndrome or sheep tick fever.

The disease was first documented as a skin rash in Europe in 1883. Over the years, researchers there identified additional features of the disease, including an unidentified bacterium that was treatable with penicillin, the role of the Ixodes, or wood, tick as its carrier, and symptoms that included not only the rash but additional ones that affected the nervous system.

Researchers in the US have been aware of tick infections since the early 1900s. For example, an infection called tick relapsing fever was reported in 1905, and the wood tick, which carries an agent that causes Rocky Mountain spotted fever, was identified soon after.

The full syndrome now known as Lyme disease, however, was not identified until a cluster of cases thought to be juvenile rheumatoid arthritis occurred in three towns in southeastern Connecticut, in the United States. Two of these towns, Lyme and Old Lyme, gave the disease its popular name.

Microbiology

In 1982 a novel spirochete was isolated and cultured from the mid-gut of Ixodes ticks, and subsequently from patients with Lyme disease. The infecting agent was first isolated by Willy Burgdorfer, a scientist at the National Institute of Health who specialized in the study of spirochete microorganisms. This gave this spirochete its name, Borrelia burgdorferi.

Borrelia burgdorferi resembles other spirochetes in that it is a highly specialized, motile, two-membrane, spiral-shaped bacterium which lives primarily as an extracellular pathogen. One of the most striking features of Borrelia burgdorferi as compared with other eubacteria is its unusual genome, which includes a linear chromosome approximately one megabase in size and numerous linear and circular plasmids.

Long-term culture of Borrelia burgdorferi results in a loss of some plasmids and changes in expressed protein profiles. Associated with the loss of plasmids is a loss in the ability of the organism to infect laboratory animals, suggesting that the plasmids encode key genes involved in virulence.

Borrelia burgdorferi may persist in humans and animals for months or years following initial infection, despite a robust humoral immune response.

Borrelia burgdorferi is susceptible to antibiotics in vitro, however, there are contradictory reports as to the efficacy of antibiotics in vivo in regard to complete eradication of the bacterium from the host.

Borrelia burgdoferi have been found in skin specimens of white footed mice in museum specimens as far back as the 1870's in Massachusetts, USA.

Consequent to the apparent long term infection, considerable attention has focused on the development of a vaccine for Lyme disease.

Current evidence suggests humoral immunity plays an important role in prevention of infection and resolution of disease; however, one of the difficulties in developing a meaningful strategy for immunization is that it is not understood what aspects of humoral and cell-mediated immunity are required to counter established infection.

Cause

It is caused by the bacterium Borrelia, which has well over a hundred known genomic strains but is usually cultured as Borrelia burgdorferi, Borrelia afzelii and Borellia garinii.

The disease has been found to be transmitted to humans by the bite of infected ticks. Not all ticks carry or can transmit the disease.

Lyme disease also incorporates the transmissions of tick borne co-infections including Bartonella, Babesiosis, Ehrlichiosis, and Rickettsia.

Transmission

Borrelia is found in mammal blood upon infection and is transmitted by the tick "spitome" or saliva. The spirochete is transferred when the tick feeds on a desirable host. Roughly 17,000 infections are reported in the United States each year. The illness often goes unreported and the real numbers may be ten-fold higher.

The wood or black-legged deer tick (Ixodes rinicus) has been identified as the key to the disease's spread. This condition had been described in medical literature dating back to the early twentieth century but little to no research had been done until Lyme Disease was reintroduced to the medical field in the late 1970's.

The number of cases, as well as endemic regions in the United States, have been increasing. Lyme disease is reported in nearly every state in the U.S. There are concentrated areas in the northeast, mid-Atlantic states, Wisconsin, Minnesota, and northern California. Lyme disease is endemic to Europe and Asia.

Lyme disease has been proven to be congenitally passed from an infected mother to fetus through the placenta during pregnancy. There is some anecdotal, largely unconfirmed evidence of sexual transmission.

It is not necessary that the tick be attached for 24 hours or longer in order for disease transmission to occur; however, the longer the duration of tick attachment, the greater the risk of disease transmission. However, even short term attachment can result in transmission of the disease. Also improper tick removal can result in early disease transmission so it is very important to remove a tick properly.

Symptoms

Lyme Disease has many symptoms, but skin symptoms, arthritis and various neurological symptoms are usually present. Conventional therapy is with antibiotics.

Acute (early) symptoms

The incubation period from infection to the onset of symptoms is usually 1-2 weeks, but can be as long as one month. However, it is possible for an infected person to display no symptoms, or display only one or two symptoms, which can make diagnosis difficult.

Chronic (late) symptoms

The late symptoms of Lyme disease can appear months to years from infection. Left untreated, Lyme disease can cause chronic disability, but is rarely fatal. Chronic cases have been known to linger for years before a definitive diagnosis. This is mainly due to the protean manifestations and the many diseases with very similar symptoms, such as chronic fatigue syndrome, multiple sclerosis, rheumatoid arthritis and many other autoimmune and neurological diseases.

Diagnosis

The most reliable method of diagnosing Lyme disease is a clinical exam supported by laboratory tests. In cases where the "bull's eye" rash is present in conjunction with a fever or the patient saw the tick, treatment can begin without any further tests.

The laboratory tests available are the Western blot and ELISA, but neither is a reliable indicator: test results vary between labs and within the same lab, sero-negative results are frequent.

Polymerase chain reaction (PCR) tests for Lyme disease may also be available to the patient. A PCR test attempts to detect the genetic material (DNA) of the Lyme disease spirochete, where as the Western blot and ELISA tests look for antibodies to the organism. PCR tests are also susceptible to false-positive results.

In cases of chronic Lyme disease, diagnosis is often clinical and must take all factors into account (tick bite exposure, symptom history, etcetera). Positive diagnosis will continue to be problematic until a more reliable test is developed.

Prognosis

The severity and treatment of Lyme disease can be complicated by simultaneous infection with other tick-borne diseases, also known as coinfections, bacterial load and immune suppression in the patient.

The disease is rarely fatal in and of itself. Chronic Lyme can cause severe disability and morbidity.

Prevention

The probability of contracting Lyme disease can be reduced by avoiding areas in which ticks are found. If such places cannot be avoided, exposure to Lyme disease can be reduced by:

  • applying insect repellent to exposed skin, especially those containing DEET. Permethrin can also be applied to clothing,
  • wearing light-coloured clothing so that ticks can be located easily and removed,
  • wearing long sleeves and pants and tucking pant bottoms into the tops of socks.

In addition, tick removal immediately when found may prevent infection. It is an excellent idea to preserve the tick and have it tested for Lyme disease if the bite occurred in an endemic area.

Carefully remove the tick with a pair of tweezers. Take extra care to preserve as much of the tick as you can for identification and laboratory testing.

Treatment

Treatment of acute Lyme disease usually consists of a minimum one month course of antibiotics, preferably doxycycline.

Patients with coinfections may need prolonged treatment to recover or go into remission.

With the chronic late-stage form of the disease, it may be necessary to continue antibiotic treatment for months or years. In some cases immunomodulating drugs are necessary.

External links

da:Borreliose de:Borreliose es:Enfermedad de Lyme fr:Borréliose nl:Lyme-ziekte sv:Borrelia wa:Mĺ d' Lyme

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