Page 213 - Review of Medical Microbiology and Immunology ( PDFDrive )

mebooksfree.com
mebooksfree.com
mebooksfree.com

mebooksfree.com
mebooksfree.com
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com or hemagglutination (TPHA, MHA-TP) assays with specific mebooksfree.com
mebooksfree.com
mebooksfree.com
202
PART II Clinical Bacteriology
3
Microscopy
treponemal antibodies in the patient’s serum.
Spirochetes are demonstrated in the lesions of primary or
These antibodies arise within 2 to 3 weeks of infection;
secondary syphilis, such as chancres or condylomata lata,
therefore, the test results are positive in most patients with
by dark field microscopy or by direct fluorescent antibody
primary syphilis. These tests remain positive for life after
(DFA) test. They are not seen on a Gram-stained smear. In
effective treatment and cannot be used to determine the
biopsy specimens, such as those obtained from the gum-
response to treatment or reinfection. They are more expen-
mas seen in tertiary syphilis, histologic stains such as silver
sive and more difficult to perform than the nonspecific
stain or fluorescent antibody can be used.
tests and therefore are not used as screening procedures.
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com Penicillin G is effective in the treatment of all stages of mebooksfree.com
mebooksfree.com
Nonspecific Serologic Tests
Treatment
These tests involve the use of nontreponemal antigens.
Extracts of normal mammalian tissues (e.g., cardiolipin
from beef heart) react with antibodies in serum samples
syphilis. A single injection of benzathine penicillin G
from patients with syphilis. These antibodies, which are a
(2.4 million units) can eradicate T. pallidum and cure early
mixture of IgG and IgM, are called “reagin” antibodies (see
(primary and secondary) syphilis. Note that benzathine
earlier). Flocculation tests (e.g., Venereal Disease Research
penicillin is used because the penicillin is released very
Laboratory [VDRL] and rapid plasma reagin [RPR] tests)
slowly from this depot preparation. Treponema pallidum
detect the presence of these antibodies. These tests are
grows very slowly, which requires that the penicillin be pres-
positive in most cases of primary syphilis and are almost
always positive in secondary syphilis. The titer of these
allergic to penicillin, doxycycline can be used but must be
nonspecific antibodies decreases with effective treatment,
given for prolonged periods to effect a cure. In neurosyphilis,
in contrast to the specific antibodies, which are positive for ent in bactericidal concentration for weeks. If the patient is
high doses of aqueous penicillin G are administered because
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com promptly with the type of penicillin used for the stage of mebooksfree.com
mebooksfree.com
life (see later).
benzathine penicillin penetrates poorly into the central ner-
False-positive reactions occur in infections such as lep-
vous system. No resistance to penicillin has been observed.
rosy, hepatitis B, and infectious mononucleosis and in vari-
However, strains resistant to azithromycin have emerged.
ous autoimmune diseases. Therefore, positive results have
Pregnant women with syphilis should be treated
to be confirmed by specific tests (see later). Results of
nonspecific tests usually become negative after treatment
their disease. Neonates with a positive serological test
and should be used to determine the response to treatment.
should also be treated. Although it is possible that the posi-
These tests can also be falsely negative as a result of the
tive test is caused by maternal antibody rather than infec-
prozone phenomenon. In the prozone phenomenon, the
tion of the neonate, it is prudent to treat without waiting
titer of antibody is too high (antibody excess), and no floc-
culation will occur. On dilution of the serum, however, the
declines.
test result becomes positive (see Chapter 64). These tests
More than half of patients with secondary syphilis who
are inexpensive and easy to perform and therefore are used several months to determine whether the titer of antibody
are treated with penicillin experience fever, chills, myalgias,
as a method of screening the population for infection. The
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com nemes and the release of endotoxin-like substances. Patients mebooksfree.com
and other influenzalike symptoms a few hours after
mebooksfree.com
nonspecific tests and the specific tests (see later) are
receiving the antibiotic. This response, called the Jarisch-
described in more detail in Chapter 9.
Herxheimer reaction, is attributed to the lysis of the trepo-
The laboratory diagnosis of congenital syphilis is based on
the finding that the infant has a higher titer of antibody in the
should be alerted to this possibility, advised that it may last
VDRL test than has the mother. Furthermore, if a positive
for up to 24 hours, and told that symptomatic relief can be
VDRL test result in the infant is a false-positive one because
obtained with aspirin. The Jarisch-Herxheimer reaction
maternal antibody has crossed the placenta, the titer will
also occurs after treatment of other spirochetal diseases
decline with time. If the infant is truly infected, the titer will
such as Lyme disease, leptospirosis, and relapsing fever.
remain high. However, irrespective of the VDRL test results,
any infant whose mother has syphilis should be treated.
this reaction because passive immunization with antibody
against TNF can prevent its symptoms.
Specific Serologic Tests 2 Tumor necrosis factor (TNF) is an important mediator of
Prevention
These tests involve the use of treponemal antigens and there-
mebooksfree.com
mebooksfree.com mebooksfree.com mebooksfree.com ment, use of condoms, administration of antibiotic after mebooksfree.com
mebooksfree.com
fore are more specific than those described earlier. In these
Prevention depends on early diagnosis and adequate treat-
tests, T. pallidum reacts in immunofluorescence (FTA-ABS)
2
FTA-ABS is the fluorescent treponemal antibody-absorbed test. The
3
TPHA is the T. pallidum hemagglutination assay. MHA-TP is a hemag-
patient’s serum is absorbed with nonpathogenic treponemes to remove
glutination assay done in a microtiter plate.
cross-reacting antibodies prior to reacting with T. pallidum.
mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com