Page 344 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com C H A P T E R mebooksfree.com
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RNA Nonenveloped Viruses 40

mebooksfree.com mebooksfree.com mebooksfree.com REOVIRUSES mebooksfree.com mebooksfree.com
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CHAPTER C ONTENT S

PICORNAVIRUSES
Enteroviruses
Rotavirus
Rhinoviruses
Self-Assessment Questions
Summaries of Organisms
CALICIVIRUSES
Norovirus
Practice Questions: USMLE & Course Examinations
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mebooksfree.com mebooksfree.com mebooksfree.com rhinoviruses grow better at 33°C, in accordance with the mebooksfree.com
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PICORNAVIRUSES

Enteroviruses replicate optimally at 37°C, whereas
Picornaviruses are small (20–30 nm) nonenveloped viruses
composed of an icosahedral nucleocapsid and a single-
lower temperature of the nose. Enteroviruses are stable
stranded RNA genome. The genome RNA has positive
polarity (i.e., on entering the cell, it functions as the viral
under acid conditions (pH 3–5), which enables them to
mRNA). There is no polymerase within the virion. Picor-
acid-labile. This explains why rhinovirus infections are
naviruses replicate in the cytoplasm of cells. They are not
restricted to the nose and throat.
inactivated by lipid solvents, such as ether, because they do
Important features of viruses that commonly infect the
not have an envelope. survive exposure to gastric acid, whereas rhinoviruses are
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intestinal tract are summarized in Table 40–2. These
The picornavirus family includes two groups of medical
include the picornaviruses but also rotavirus and norovirus,
importance: the enteroviruses and the rhinoviruses.
which are described later in this chapter, and adenovirus,
Among the major enteroviruses are poliovirus, Coxsackie
viruses, echoviruses, and hepatitis A virus (which is
described in Chapter 41). Enteroviruses infect primarily
the enteric tract, whereas rhinoviruses are found in the
nose and throat (rhino = nose) (Table 40–1).
TABLE 40–1 Picornaviruses of Medical Importance

Stomach Acid
Virus Initial Site of Infection Inactivated by Optimal Temperature Diseases
for Replication
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Poliovirus
37°C
Poliomyelitis
No
Gastrointestinal (GI) tract
GI tract
Meningitis Myocarditis, hand-foot-
37°C
Coxsackie viruses
No
and-mouth disease, etc.
37°C
Meningitis
No
Echoviruses
No
Hepatitis
37°C
Hepatitis A virus
GI tract
Common cold
Upper respiratory tract
Rhinoviruses
33°C
Yes
333
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