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Introduction
Spirochaetes are bacteria belonging to the family of
Spirochaetacea. They are long, motile and twisted spirally
round a long axis. They are found in water, soil and
decaying organic matter. They divide by transverse fission
and there is no definite nucleus. Many of them are
saprophytes and commensals. Genera of Spirochaetes of
medical importance are:
Treponema
Borrelia
Leptospira
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GENUS TREPONEMA
Characteristics: Treponemes are small, slender, flexible
cork-screw shaped anaerobic organisms, measuring 5-
15um x 0.2um with 6-12 evenly sized coils. They have a
slow bending and rotating motility. They cannot be
stained by Gram’s stain but can be demonstrated by silver
and T. cunicola. But T. pallidum is now classified as T.
pallidum subspecies pallidum and T. pertenue as T.
pallidum subspecies pertenue impregnation method. They
are not culturable.
Type species: T. pallidum. Other important members of
the genus are T. pertenue, T. carateum.
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Pathogenicity: T. pallidum subsp. pallidum causes syphilis
which is acquired sexually and congenitally.
Sexually transmitted syphilis: This STD occurs in 3
stages:
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1.Primary syphilis:
Onset: 2 – 4 weeks after infection
Presentation: Ulcer on the genitalia. Ulcer known as hard
chanre – firm, clean and circumscribed. Chancre fluid is
rich in treponemes. Ulcer heals up spontaneously in 10 –
40 days.
2. Secondary syphilis:
Onset: 2 – 8 weeks after primary syphilis.
Presentation: Skin eruptions, red rashes with papules.
Widespread multiplication and dissemination in blood.
Patient highly infectious. Other symptoms include fever,
malaise and general lymphadenapathy. May last from 10
days to 1 year.
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3. Tertiary syphilis (early and late latent stages):
Early latent stage: This is inactive stage following
secondary syphilis. Patient is non-infectious, though
feotus of an infected mother can be infected.
Late latent stage: Onset is approximately 3 years after
secondary stage.
Presentation: Inflammatory lesions in any organ or tissue
but CNS and cardiovascular systems are mostly involved.
Complications may include gummas or granuloma of skin
or bone, liver damage, eye impairment and ear
dysfunction. Patient is non-infectious except to the foetus
of an infected mother
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Congenital syphilis:
Infected mother transplacentally transmits the disease to
the foetus. Congenital syphilis may result in still birth in
about 40% of cases and abortion is also frequent.
Onset: Signs appear about one year after birth – skin
rashes, jaundice, painful limbs, anaemia and saddle-nose.
Non-venereal syphilis:
This is usually acquired as occupational hazard by
doctors, nurses and laboratory workers; or through blood
transfusion. The organism gains entry into the body
through abraded skin.
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Other treponemal infections:
T. pallidum subsp. pertenue causes yaws – an endemic
disease of tropical countries which is pathologically
similar to syphilis but differs in its contagious and non-
venereal nature. it produces ulcerating papules on the
skin.
T. carateum causes pinta – an endemic disease in Mexico,
South America and Phillippines.
T. cunicola causes rabbit syphilis and morphologically
resembles T. pallidum.
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Laboratory diagnosis:
Specimen: Serous fluid from lesion
DG microscopy: Three consecutive specimens must be
examined before reporting negative.
Culture: This is not done though Reiter’s strain is
cultivable. Nichol’s strain is maintained in an adult rabbit
testis by serial passaging.
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Serology: Syphilis is diagnosed serologically using non-
specific screening tests such as RPR and VDRL tests and
specific confirmatory tests such as FTA and TPHA tests.
The screening tests detect reagin antibody using
cardiolipin antigens. The specific tests detect treponemal
antibody using treponemal antigens. The routine
serological tests are therefore divided into non-
treponemal and treponemal tests:
Non-treponemal tests: ( non-specific tests): These tests
detect reagin antibody, a non specific antibody that is
present in syphilitic serum. It appears in a patient’s serum
in 10-14 days after exposure. The antigen is cardiolipin
antigen which contains alcoholic extract of ox heat muscle
to which cholesterol and lecithin are added .These tests are
used to :
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•Screen for active syphilis
•As tests of cure
•As an aid in diagnosing congenital syphilis.
Non- treponemal tests include the Rapid plasma regain
(RPR) test, Venereal diseases reference laboratory (VDRL)
test, Unheated serum regain (USR) test etc. They all use
the same antigen and easy to perform but RPR and VDRL
are the most commonly used.
RPR test is performed on a card and the antigen is coated
with charcoal: 50ul of the plasma ( serum or blood ) and a
drop of the antigen are mixed on the test card, shaken at
100 rpm for 8 minutes. Agglutination is visible to the
naked eye.
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VDRL test is performed on a perspex slide and viewed
under the microscope. The antigen is not coated and the
serum is inactivated at 560C for 30 minutes before the test
is done. It is recommended for use with CSF in
neurosyphilis.
False positive result is fairly common. This may be due to:
•Technical error
•Cross reaction with other treponemal species
• Biological false positives (BFP): These are due not to
technical error but as a result of certain infectious and non
infectious conditions such as malaria, mumps, hepatitis,
rheumatoid arthritis, tissue damage etc.
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Treponeaml test(aka Specific tests): These are tests
that detect antibody to T. pallidum subsp. pallidum and
other species. These tests are:
Treponema pallidum immobilization (TPI) test: The
test uses live treponemes which when mixed with the
patient’s serum, the antibody in the serum immobilizes
the organisms when examined under the darkground
microscope.. The treponemes are Nicholl’s strains
recovered from the testis of rabbit. The disadvantage is
that there is always the risk of infection to the worker,
and the method is cumbersome and expensive.
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Flourescent treponemal antibody-sorbent (FTA-ABS) test:
The test uses Nicholl’s strain as antigen fixed on a slide.
Diluted patient’s serum is added on to the antigen, excess
washed off and the smear treated with anti human
immunoglobulin conjugate. After incubating and washing,
the slide is examined under the fluorescent microscope.
The test is most specific and sensitive though expensive. It
is positive for life.
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•Treponema pallidum haemagglutination (TPHA): This
test is similar to the FTA in sensitivity. Antigen is
Nicholl’s strain coated with tanned turkey or chicken
or sheep red blood cells ( sensitised cells). A non
sensitized cell suspension is used as control. In the
presence of treponemal antibody, the treponemes
adhere to the sensitized red cells and settle at the
bottom of the micro titre plate well as orange to red
layer. It is easy to perform, fast and cheap. It is positive
for life.
FTA-ABS and TPHA tests are also positive for T.
pertenue and T carateum.
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DNA probes e.g. (PCR): These are new diagnostic tools
that are highly specific and sensitive. As of now, they are
very expensive and are not be used routinely.
