Page 316 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 38 DNA Nonenveloped Viruses
nucleus, and the virus is released by lysis of the cell, not by
budding.
Three live, nonattenuated vaccines against serotypes 4, 7,
and 21 are available but are used only by the military. Each
Transmission & Epidemiology
of the three vaccines is monovalent (i.e., each contains
only one serotype). The viruses are administered sepa-
Adenoviruses are transmitted by several mechanisms:
aerosol droplet, fecal–oral route, and direct inoculation
together. The vaccines are delivered in an enteric-coated
of conjunctivas by tonometers or fingers. The fecal–oral
capsule, which protects the live virus from inactivation by
route is the most common mode of transmission among
young children and their families. Many species of animals rately because they interfere with each other when given
stomach acid. The virus infects the gastrointestinal tract,
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are infected by strains of adenovirus, but these strains are
where it causes an asymptomatic infection and induces
not pathogenic for humans.
immunity to respiratory disease. This vaccine is not avail-
Adenovirus infections are endemic worldwide, but out-
able for civilian use.
Epidemic keratoconjunctivitis is an iatrogenic disease,
breaks occur among military recruits, apparently as a
result of the close living conditions that facilitate transmis-
sion. Certain serotypes are associated with specific syn-
care personnel who examine eyes.
dromes (e.g., types 3, 4, 7, and 21 cause respiratory disease,
especially in military recruits; types 8 and 19 cause epi-
PAPILLOMAVIRUSES
demic keratoconjunctivitis; types 11 and 21 cause hemor-
rhagic cystitis; and types 40 and 41 cause infantile
gastroenteritis).
Human papillomavirus (HPV) causes papillomas, which
are benign tumors of squamous cells (e.g., warts on the
Pathogenesis & Immunity Diseases
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skin). Some HPV types, especially types 16 and 18, cause
Adenoviruses infect the mucosal epithelium of several
carcinoma of the cervix, penis, and anus.
organs (e.g., the respiratory tract [both upper and lower],
the gastrointestinal tract, and the conjunctivas). Immu-
nity based on neutralizing antibody is type-specific and
lifelong.
Papillomaviruses are nonenveloped viruses with double-
In addition to acute infection leading to death of the
stranded circular DNA and an icosahedral nucleocapsid.
cells, adenoviruses cause a latent infection, particularly in
The HPV genome has seven early genes (E1–E7) and two
the adenoidal and tonsillar tissues of the throat. In fact,
late genes (L1 and L2). The early genes encode proteins
these viruses were named for the adenoids, from which
they were first isolated in 1953.
tion of the progeny DNA genomes, and the late genes
encode the structural proteins of the progeny virions.
Clinical Findings involved in the synthesis of viral mRNA and in the replica-
Two of the early genes, E6 and E7, are implicated in
carcinogenesis. They encode proteins that inactivate pro-
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Laboratory Diagnosis mebooksfree.com
In the upper respiratory tract, adenoviruses cause such
teins encoded by tumor suppressor genes in human cells
infections as pharyngitis, pharyngoconjunctival fever, and
(e.g., the p53 gene and the retinoblastoma [RB] gene,
acute respiratory disease, characterized by fever, sore
throat, coryza (runny nose), and conjunctivitis. In the
important step in the process by which a normal cell
lower respiratory tract, they cause bronchitis and atypical
becomes a cancer cell.
pneumonia. Hematuria and dysuria are prominent in hem-
There are at least 100 types of papillomaviruses, classi-
orrhagic cystitis. Gastroenteritis with nonbloody diarrhea
fied primarily on the basis of DNA restriction fragment
occurs mainly in children younger than 2 years of age. Most
analysis. There is a pronounced predilection of certain
adenovirus infections resolve spontaneously. Approxi-
types to infect certain tissues. For example, skin warts are
mately half of all adenovirus infections are asymptomatic.
tal warts are usually caused by HPV-6 and HPV-11.
Approximately 30 types of HPV infect the genital tract.
The most frequent methods of diagnosis are isolation of the caused primarily by HPV-1 through HPV-4, whereas geni-
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virus in cell culture and detection of a fourfold or greater
Summary of Replicative Cycle
rise in antibody titer. Complement fixation and hemagglu-
After attachment and uncoating, the genome DNA moves
tination inhibition are the most important serologic tests.
RNA polymerase with early viral protein E2 acting as a
Treatment
transcriptional activator. Early viral protein E1 acts as a
There is no antiviral therapy.
helicase that separates the DNA strands of the incoming
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