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Lyme Disease
Other Names: Borreliosis
Image Notes: Nymphal and adult deer ticks can be carriers of Lyme disease. Nymphs are about the size of a poppy seed.
Lyme disease, or borreliosis, is an emerging infectious disease caused by bacteria from the genus Borrelia. The vector of infection is typically the bite of an infected black-legged or deer tick, but other carriers (including other ticks in the genus Ixodes) have been implicated. Borrelia burgdorferi is the predominant cause of Lyme disease in the U.S. and Borrelia afzelii and Borrelia garinii are in Europe.
The disease presentation varies widely, and may include a rash and flu-like symptoms in its initial stage, then musculoskeletal, arthritic, neurologic, psychiatric and cardiac manifestations. In a majority of cases, symptoms can be eliminated with antibiotics, especially if treatment begins early in the course of illness. Late or inadequate treatment often leads to "late stage" Lyme disease that is disabling and difficult to treat. Controversy over diagnosis, testing and treatment has led to two different standards of care.
Symptoms
The acute phase of Lyme disease infection is a characteristic reddish "bulls-eye" rash, with accompanying fever, malaise, and musculoskeletal pain (arthralgia or myalgia). The characteristic reddish "bull's-eye" rash (known as erythema chronicum migrans) may be seen in up to 80% of early stage Lyme disease patients, appearing anywhere from one day to a month after a tick bite. The rash does not represent an allergic reaction to the bite, but a skin infection cause by the Lyme bacteria, Borrelia burgdorferi sensu lato.
The incubation period from infection to the onset of symptoms is usually 1–2 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 is uncommon.
Other, less common findings in acute Lyme disease include cardiac manifestations (up to 10% of patients may have cardiac manifestations including heart block and palpitations), neurologic symptoms (neuroborreliosis may occur in up to 18%), as well as simple altered mental status as the sole presenting symptom has been reported in early neuroborreliosis.
Chronic symptoms
Untreated or persistent cases may progress to a chronic form most commonly characterized by meningoencephalitis, cardiac inflammation (myocarditis), and frank arthritis. It should be noted, however, that chronic Lyme disease can have a multitude of symptoms affecting numerous physiological systems: the symptoms appear heterogeneous in the affected population, which may be due to innate immunity or variations in Borrelia bacteria. Late symptoms of Lyme disease can appear months or years after initial infection and often progress in cumulative fashion over time. Neuropsychiatric symptoms often develop much later in the disease progression, much like tertiary neurosyphilis.
In addition to the acute symptoms, chronic Lyme disease can be manifested by a wide-range of neurological disorders, either central or peripheral, including encephalitis or encephalomyelitis, muscle twitching, polyneuropathy or paresthesia, and vestibular symptoms or other otolaryngologic symptoms, among others. Neuropsychiatric disturbances can occur (possibly from a low-level encephalitis), which may lead to symptoms of memory loss, sleep disturbances, or changes in mood or affect.
Cause
Borrelia bacteria, the causative agent of Lyme disease. Magnified 400 times.Lyme disease is caused by Gram-negative spirochetal bacteria from the genus Borrelia. At least 37 Borrelia species have been described, 12 of which are Lyme related. The Borrelia species known to cause Lyme disease are collectively known as Borrelia burgdorferi sensu lato, and have been found to have greater strain diversity than previously estimated.
Until recently it was thought that only three genospecies caused Lyme disease: B. burgdorferi sensu stricto (predominant in North America, but also in Europe), B. afzelii, and B. garinii (both predominant in Eurasia). However, newly discovered genospecies have also been found to cause disease in humans.[citation needed] "There are over 300 strains of Borrelia world wide". It is presently unknown how many of these cause lyme, but many of them may.
Transmission
Ixodes scapularis, the primary vector of Lyme disease in eastern North America.Hard-bodied ticks of the genus Ixodes are the primary vectors of Lyme disease. The majority of infections are caused by ticks in the nymph stage, as adult ticks do not become infected through feeding.
In Europe, the commonly known sheep tick, castor bean tick, or European castor bean tick (Ixodes ricinus) is the transmitter.
In North America, the black-legged tick or deer tick (Ixodes scapularis) has been identified as the key to the disease's spread on the east coast. Unfortunately, only about 20% of persons infected with Lyme disease by the deer tick are aware of having had any tick bite, making early detection difficult in the absence of a rash. Tick bites usually go unnoticed due to the small size of the tick in its nymphal stage, as well as tick secretions that prevent the host from feeling any itch or pain from the bite. The lone star tick (Amblyomma americanum), which is found throughout the southeastern U.S. as far west as Texas, has been ruled out as a vector of the Lyme disease spirochete Borrelia burgdorferi, though it may be implicated with a clinical syndrome southern tick associated rash illness (STARI), which resembles the skin lesions of Lyme disease.
On the west coast, the primary vector is the western black-legged tick (Ixodes pacificus). It was once thought to be a vector, although recent studies demonstrate that this tick species is not a competent vector of Borrelia burgdorferi sensu lato.
While Lyme spirochetes have been found in insects other than ticks, reports of actual infectious transmission appear to be rare. Sexual transmission has been anecdotally reported; Lyme spirochetes have been found in semen[23] and breast milk, however transmission of the spirochete by these routes is not known to occur.
Congenital transmission of Lyme disease can occur from an infected mother to fetus through the placenta during pregnancy, however prompt antibiotic treatment appears to prevent fetal harm.
Text and images are licensed under the GNU Free Documentation License. Material is used from the Wikipedia article "Lyme disease".
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