Page 315 - Review of Medical Microbiology and Immunology ( PDFDrive )

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38
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DNA Nonenveloped Viruses

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CHAPTER C ONTENT S

Adenoviruses
Summaries of Organisms
Papillomaviruses
Parvoviruses
Practice Questions: USMLE & Course Examinations
Polyomaviruses

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mebooksfree.com mebooksfree.com mebooksfree.com the main type-specific antigen. All adenoviruses have a com- mebooksfree.com
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ADENOVIRUSES
There are 41 known antigenic types; the fiber protein is
Diseases
mon group-specific antigen located on the hexon protein.
Certain serotypes of human adenoviruses (especially 12,
Adenoviruses cause a variety of upper and lower respira-
18, and 31) cause sarcomas at the site of injection in labora-
tory tract diseases such as pharyngitis, conjunctivitis (“pink
tory rodents such as newborn hamsters. There is no evi-
eye”), the common cold, and pneumonia. Keratoconjuncti-
dence that adenoviruses cause tumors in humans.
vitis, hemorrhagic cystitis, and gastroenteritis also occur.
Some adenoviruses cause sarcomas in rodents. Table 38–1
describes some of the important clinical features of adeno-
viruses and compares them with features of the other two
After attachment to the cell surface via its fiber, the virus
medically important viruses in this chapter, human papil-
penetrates and uncoats, and the viral DNA moves to the
lomavirus (HPV) and parvovirus B19. Summary of Replicative Cycle
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nucleus. Host cell DNA-dependent RNA polymerase tran-
scribes the early genes, and splicing enzymes remove the
Important Properties
RNA representing the introns, resulting in functional
Adenoviruses are nonenveloped viruses with double-
in eukaryotic DNA, were first described for adenovirus
stranded linear DNA and an icosahedral nucleocapsid.
DNA.) Early mRNA is translated into nonstructural pro-
They are the only viruses with a fiber protruding from each
teins in the cytoplasm. After viral DNA replication in the
of the 12 vertices of the capsid. The fiber is the organ of
nucleus, late mRNA is transcribed and then translated into
attachment and is a hemagglutinin. When purified free of
virions, the fiber is toxic to human cells.
structural virion proteins. Viral assembly occurs in the
TABLE 38–1 Clinical Features of DNA Nonenveloped Viruses Certain Types Cause Cancer Vaccine Available
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mebooksfree.com mebooksfree.com Respiratory; fecal–oral Yes mebooksfree.com Yes, but used only in mebooksfree.com
Types Cause
Mode of Transmission
Virus
Different Diseases
Adenovirus
Yes, in animals but not humans
military
Human papillomavirus
Yes
Yes
Yes, in humans
Sexual; skin contact
No
No
No
Respiratory; transplacental
Parvovirus B19
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