From Wikipedia, the free encyclopedia.
Lyme disease or Lyme borreliosis is an
infectious tick-borne disease, caused by the Borrelia spirochete, a
gram-negative microorganism.
Lyme disease is so named because it is generally believed to have first
been observed in and around Lyme, Connecticut in 1975. Before 1975,
elements of Borrelia infection were also known as "tick-borne
meningopolyneuritis", Garin-Bujadoux syndrome, Bannwarth syndrome or
sheep tick fever. It is transmitted to humans by the bite of infected
ticks.
History
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 pathogen, its response to penicillin,
the role of the Ixodes tick (wood tick) as its vector, and symptoms that
included not only the rash but additional ones that affected the nervous
system.
Researchers in the US had 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. However, the
full syndrome now known as Lyme disease, 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.
In 1982 a novel spirochete was isolated and cultured from the midgut of
Ixodes ticks, and subsequently from patients with Lyme disease. The
infecting agent was first isolated by Willy Burgdorfer, a scientist at
the National Institutes of Health who specialized in the study of
spirochete microorganisms. The spirochete was named Borrelia burgdorferi
in his honor.
Microbiology
The disease is caused by the parasite Borrelia, which has well over
three hundred known genomic strains but is usually cultured as Borrelia
burgdorferi, Borrelia afzelii and Borellia garinii. Different Borrelia
strains are predominant in Europe and North America.
The disease has been found to be transmitted to humans by the bite of
infected Ixodes ticks. Not all ticks carry or can transmit this
particular disease. It should also be noted that in a few cases the
disease may also be transmitted by other blood-sucking parasitic insects
such as mosquitoes, fleas or blackflies. However other Borrelia strains
(i.e. B. garinii) are probably transmitted this way.
Other tick-borne infections may be transmitted simultaneously with Lyme,
including Bartonella, Babesiosis, Ehrlichiosis, and Rickettsia.
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. Borrellia burgdorpherri has been isolated in skin
specimens of white-footed mice in museum specimens as far back as the
1870s in Massachusetts.
Transmission
Ixodes rinicus, the wood tick (a.k.a. black-legged deer tick) 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 1970s.
The number of cases of the disease have been increasing, as are endemic
regions in the United States. Lyme disease is reported in nearly every
state in the U.S., but 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 for the tick to 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. 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:
"bull's-eye" rash (erythema migrans) - a
circle or ring of inflamed skin surrounding the initial tick bite) or
papular (raised) rash
fever
malaise
fatigue
headache
muscle and joint aches in large joints
sore throat
sinus infection
paralysis - usually associated with Lyme meningitis or Rocky Mountain
spotted fever.
The incubation period from infection to the onset of symptoms is usually
1–2 weeks, but can be much shorter (a couple of days), or even 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:
meningitis
neuropathy - numbness, tingling, burning, itching, oversensitivity
muscle and joint aches
tremor, twitches
Bell's palsy
pain
immune suppression
myalgia
fatigue
hallucinations
short-term memory loss
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. Fatality can occur when the spirochete enters brain
fluids and causes meningitis, or due to conductivity defects in the
heart. Chronic cases have been known to linger for years before a
definitive diagnosis.
Lyme disease is often misdiagnosed as
chronic fatigue syndrome, multiple sclerosis, fibromyalgia, rheumatoid
arthritis, and many other autoimmune and neurological diseases, which
leaves the infection untreated and allows it to further penetrate the
organism. If the neurologic form of borreliosis is left untreated for
years, it may lead to severe debility of the patient. Spirochetes have
been noted in deaths in observed autopsy reports.
Diagnosis
The most reliable method of diagnosing Lyme disease is a clinical exam
by an experienced practitioner. Supportive data by laboratory tests is
never well-advised due to the known non-validity of the CDC's current
testing criteria. 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 "bull's eye" rash only occurs in a
small percent of all infections. The rash is not always seen as bullseye
and sometimes can be a papule the size of small coin. Sometimes the tick
bite can leave no rash at all.
The serological 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. It is
estimated that about a quarter of all infections don't register on any
antibody test, and hence empirical treatment is occasionally warranted
if the clinical suspicion remains high despite negative serology.
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
rarely susceptible to false-positive results but can often show
false-negative results.
In cases of chronic Lyme disease, diagnosis is often clinical and must
take all factors into account (tick bite exposure, symptom history,
etc.). 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 disease can cause
severe and possibly lifelong disability and morbidity.
Prevention
Avoiding areas in which ticks are found can reduce the probability of
contracting Lyme disease. 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.
A vaccine against the North American strain of the virus was available
between 1998 and 2002. When taking it off the market, the manufacturer
cited poor sales, though some people believe that the actual reason was
that the vaccine was not safe or effective at all.
Treatment
Traditional treatment of acute Lyme disease usually consists of a
minimum two-week to one-month course of antibiotics, preferably
doxycycline (two 200 mg capsules a day).
With the chronic late-stage form of the disease, it may be necessary to
continue antibiotic treatment for months or even years. In some cases,
immunomodulating drugs are necessary. Not all chronic or tertiary cases
are resolved.
The most effective antibiotic treatment in the chronic stage appears to
be ceftriaxone (Rocephin®), given intravenously (as oral antibiotics are
often ineffective at completely eradicating the disease in any but the
initial/early stage). This may, however, cause problems for sensitive
patients, as ceftriaxone can cause gallbladder problems. Since there are
a maze of different borrelia strains - which can not be identified in
vivo - it is often the treating physician's educated guess as to which
antibiotic will best treat the given strain a patient has.
