Page 319 - Review of Medical Microbiology and Immunology ( PDFDrive )

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PART IV Clinical Virology
308
applying acetic acid to the tissue. HPV-16 is also implicated
capsid has icosahedral symmetry. There is one serotype.
as the cause of oral cancers.
Summary of Replicative Cycle
Laboratory Diagnosis
After adsorption to host cell receptors, the virion pene-
Infections are usually diagnosed clinically. The presence of
koilocytes in the lesions indicates HPV infection. A poly-
The single-stranded genome DNA has “hairpin” loops at
merase chain reaction (PCR)–based test can be used to
both of its ends that provide double-stranded areas for the
detect the presence of the DNA of 14 high-risk genotypes, trates and moves to the nucleus, where replication occurs.
cellular DNA polymerase to initiate the synthesis of the
including HPV-16 and HPV-18.
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progeny genomes. The viral mRNA is synthesized by cel-
Diagnostic tests based on detection of antibodies in a
lular RNA polymerase from the double-stranded DNA
patient’s serum or on isolation of the virus from a patient’s
tissue are not used.
nucleus. B19 virus replicates only when a cell is in S phase,
which explains why the virus replicates in red cell precur-
Treatment & Prevention
sors but not in mature red cells.
The usual treatment for genital warts is podophyllin; alpha
Transmission & Epidemiology
interferon is also effective and is better at preventing recur-
rences than are non-antiviral treatments. Liquid nitrogen is
B19 virus is transmitted primarily by the respiratory route;
commonly used for skin warts. Plantar warts can be
removed surgically or treated with salicylic acid topically.
transfusions also can transmit the virus. B19 virus infection
Cidofovir may be useful in the treatment of severe HPV
occurs worldwide, and about half the people in the United
infections. transplacental transmission also occurs. Blood donated for
States older than 18 years of age have antibodies to the
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The HPV vaccines are very effective in preventing carci-
virus. Humans are the natural reservoir; animals are not a
noma of the cervix, anal carcinoma, and genital warts. Note
source of human infection.
that HPV vaccines have no effect on existing papillomas.
There are three vaccines against HPV. Gardasil 9, a
recombinant vaccine against nine types of HPV, contains
B19 virus infects primarily two types of cells: red blood cell
the capsid proteins of types 6 and 11, which cause genital
precursors (erythroblasts) in the bone marrow, which
warts, and types 16 and 18, which are the two most com-
accounts for the aplastic anemia, and endothelial cells in
mon causes of cervical, penile, and anal carcinoma. It also
the blood vessels, which accounts, in part, for the rash asso-
contains the proteins of five more types (31, 33, 45, 52, and
58) that are less common causes of these cancers. A quad-
composed of virus and IgM or IgG also contribute to the
rivalent version of Gardasil containing the proteins of types
pathogenesis of the rash and to the arthritis that is seen in
6, 11, 16, and 18 is also available.
some adults infected with B19 virus. Infection provides
The third vaccine, Cervarix, is also a recombinant vaccine ciated with erythema infectiosum. Immune complexes
lifelong immunity against reinfection.
but contains the proteins only of types 16 and 18. Cervarix
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Hydrops fetalis manifests as massive edema of the fetus.
contains an adjuvant called AS04 that stimulates Toll-like
This is secondary to congestive heart failure precipitated
receptors and thereby enhances antibody production.
The role of cesarean section in preventing transmis-
B19–infected erythroblasts in the fetus.
sion of HPV from a mother with genital warts to her
newborn is uncertain. Circumcision reduces the risk of
Clinical Findings
infection by HPV.
There are five important clinical presentations.
PARVOVIRUSES
Erythema Infectiosum (Slapped Cheek Syndrome,
Diseases
This is a mild disease, primarily of childhood, character-
Parvovirus B19 causes erythema infectiosum (slapped
ized by a bright red rash that is most prominent on the
cheek syndrome, fifth disease), aplastic anemia (especially Fifth Disease)
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cheeks (Figure 38–5), accompanied by low-grade fever,
in patients with sickle cell anemia), and fetal infections,
runny nose (coryza), and sore throat. A “lacy,” less intense,
including hydrops fetalis.
erythematous rash appears on the body. The symptoms
Important Properties
The disease in children is also called fifth disease. The
four other macular or maculopapular rash diseases of
Parvovirus B19 is a very small (22 nm) nonenveloped virus
childhood are measles, rubella, scarlet fever, and roseola.
with a single-stranded DNA genome. The genome is
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