Page 216 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 24 Spirochetes
The rash may sometimes be accompanied by nonspe-
24 to 48 hours to transmit an infective dose.
cific “flulike” symptoms such as fever, chills, fatigue, and
headache. Secondary skin lesions frequently occur. Arthral-
Should prophylactic antibiotics be given to people who
have been bitten by a tick? The decision depends on two
gias, but not arthritis, are another common finding in this
early stage. In approximately 25% of cases of Lyme disease,
main factors: the percentage of infected ticks in the area
no rash is seen.
In stage 2 (early disseminated stage), which occurs
percentage of infected ticks is high and the length of time is
weeks to months later, cardiac and neurologic involvement
more than 48 hours, it may be cost-effective to prescribe
doxycycline prophylactically. Any person bitten by a tick
predominates. Myocarditis, accompanied by various forms and the length of time the tick has fed on the person. If the
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of heart block, occurs. Acute (aseptic) meningitis and cra-
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should be advised to watch carefully for a rash or flulike
nial neuropathies, such as facial nerve palsy (Bell’s palsy),
symptoms for the next 3 weeks.
are prominent during this stage. Bilateral facial nerve palsy
A vaccine containing a recombinant outer surface pro-
is highly suggestive of Lyme disease. Peripheral neuropa-
thies also occur.
able but has been withdrawn.
A latent phase lasting weeks to months typically ensues.
In stage 3 (late disseminated stage), arthritis, usually of the
2. Borrelia recurrentis & Borrelia
large joints (e.g., knees), is a characteristic finding. Lyme
hermsii
arthritis is thought to be autoimmune in origin. Encepha-
lopathy also occurs in stage 3.
reliae cause relapsing fever. During infection, the antigens
Some patients treated for Lyme infection continue to have
of these organisms undergo variation. As antibodies
prolonged subjective symptoms of fatigue, joint pains, or
develop against one antigen, variants emerge and produce
mental status changes after objective findings have disap- Borrelia recurrentis, Borrelia hermsii, and several other bor-
relapses of the illness. This can be repeated 3 to 10 times.
peared. No confirmed microbiologic evidence for B. burgdor-
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Borrelia recurrentis is transmitted from person to person
feri infection has been detected in those patients, and
by the human body louse. Humans are the only hosts. Bor-
prolonged antibiotic therapy has not relieved the symptoms.
ted to humans by soft ticks (Ornithodoros). Rodents and
Laboratory Diagnosis
other small animals are the main reservoirs. These species
Although the organism can be grown in the laboratory,
of Borrelia are passed transovarially in the ticks, a phenom-
cultures are rarely positive and hence are usually not per-
enon that plays an important role in maintaining the
formed. The diagnosis is typically made serologically by
organism in nature.
detecting either IgM antibody or a rising titer of IgG anti-
During infection, the arthropod bite introduces spiro-
body with an enzyme-linked immunosorbent assay
(ELISA) or an indirect immunofluorescence test. IgM is
fever, chills, headaches, and multiple-organ dysfunction.
typically detectable 2 weeks after infection and peaks at 3 to
Each attack is terminated as antibodies arise.
6 weeks. Serologic tests done before 2 weeks are likely to chetes, which then multiply in many tissues, producing
Diagnosis is usually made by seeing the large spiro-
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yield negative results. Thirty days after infection, tests for
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chetes in stained smears of peripheral blood. They can be
IgG are more reliable.
cultured in special media. Serologic tests are rarely useful.
Unfortunately, there are problems with the specificity
and sensitivity of these tests because of the presence of
prevent relapses. Avoidance of arthropod vectors is the best
cross-reacting antibodies against spirochetes in the normal
means of prevention.
flora. A positive test result should be confirmed with a
Western blot (immunoblot) analysis. In addition, patients
3. Borrelia miyamotoi
treated early in the disease may not develop detectable
antibodies. A polymerase chain reaction (PCR) test that
Borrelia miyamotoi causes a relapsing feverlike syndrome.
detects the organism’s DNA is also available.
wide, including the United States. It is transmitted by
Treatment & Prevention
Ixodes ticks. Clinically, the disease begins with an influ-
The treatment of choice for stage 1 disease or other mild It was discovered in 1995 in Japan but causes disease world-
enzalike syndrome (fever, headache, and myalgia) accom-
manifestations is either doxycycline or amoxicillin. Amoxi-
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panied by hepatitis and thrombocytopenia. Relapsing
cillin should be used in pregnant women and young chil-
episodes occur. The manifestations can resemble anaplas-
mosis (see Chapter 26) that is also transmitted by Ixodes
dren, as doxycycline is contraindicated. For more severe
forms or late-stage disease, ceftriaxone is recommended.
The diagnosis is typically made serologically by detecting
There is no significant antibiotic resistance.
Prevention involves wearing protective clothing and
IgM antibody or by PCR assay testing for the gene encoding
using insect repellents. Examining the skin carefully for
the Glp Q protein that is specific for B. miyamotoi.
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