Page 260 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com 6 CHAPTER 31 Classification of Medically Important Viruses 249 mebooksfree.com
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TABLE 31–2 Classification of RNA Viruses
RNA MW
Envelope
Particle
Capsid
1
Size (nm)
Medically Important Viruses
Present
Virus Family
(×10 )
Symmetry
RNA Structure
Picornavirus
28
SS linear, nonsegmented, positive
Icosahedral
2.5
No
Poliovirus, rhinovirus,
polarity
hepatitis A virus
Hepevirus
polarity
2.7
No
Icosahedral
Calicivirus No Icosahedral 30 2.5 SS, linear, nonsegmented, positive Hepatitis E virus
38
Norovirus
SS linear, nonsegmented, positive
polarity
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polarity mebooksfree.com
15
Reovirus
No
75
Rotavirus
Icosahedral
DS linear, 10 or 11 segments
45
Icosahedral
Flavivirus
Yes
SS linear, nonsegmented, positive
Yellow fever virus, dengue
4
polarity
virus, West Nile virus,
hepatitis C virus
Togavirus
Icosahedral
60
Yes
4
polarity
2
100
HIV, human T-cell leukemia
7
Retrovirus
SS linear, 2 identical strands
Yes
Icosahedral
(diploid), positive polarity
virus
80–120
Orthomyxovirus
Helical
4
Yes
SS linear, 8 segments, negative
Influenza virus
polarity
Yes
Helical
6
Paramyxovirus
Measles virus, mumps virus,
SS linear, nonsegmented, negative
150
respiratory syncytial virus
4
75 × 180
Rhabdovirus
Yes
Helical
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polarity
3
Ebola virus, Marburg virus
Filovirus
SS linear, nonsegmented, negative
4
Yes
80
Helical
polarity
SS linear, nonsegmented, positive
Coronavirus
100
10
Yes
Helical
Coronavirus
polarity
80–130
5
Arenavirus
Yes
Helical
SS circular, 2 segments with
Lassa fever virus, lymphocytic
choriomeningitis virus
cohesive ends, negative polarity
Yes
Helical
Bunyavirus
100
5
California encephalitis virus,
SS circular, 3 segments with
hantavirus
cohesive ends, negative polarity
Deltavirus
Uncertain
Yes
polarity
2 1 3 4 SS = single-stranded; DS = double-stranded. 4 37 0.5 SS circular, closed circle, negative Hepatitis delta virus
6
Retrovirus genome RNA contains two identical molecules, each with a molecular weight (MW) of 3.5 × 10 .
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Particles are 80 nm wide but can be thousands of nanometers long.
The nucleocapsid appears spherical but its symmetry is unknown.
organisms of medical importance. Only the virus families
are listed; subfamilies are described in the chapter on the
largest viruses, the poxviruses, have a complex internal
specific virus. Figures 31–1 and 31–2 show a classification
symmetry.
outline for DNA viruses and RNA viruses, respectively,
Parvoviruses
based on the type of genome, the nature of the nucleocap-
sid, and whether an envelope is present.
dral viruses with single-stranded linear DNA. There are
two types of parvoviruses: defective and nondefective. The
DNA VIRUSES These are very small (22 nm in diameter), naked icosahe-
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defective parvoviruses (e.g., adeno-associated virus)
The families of DNA viruses are described in Table 31–1.
require a helper virus for replication. The DNA of defec-
The four naked (i.e., nonenveloped) icosahedral virus
tive parvoviruses is unusual because plus-strand DNA and
families—the parvoviruses, polyomaviruses, papillomavi-
nondefective parvoviruses are best illustrated by Parvovirus
ruses, and adenoviruses—are presented in order of increas-
B19 virus which has a minus-strand DNA genome. This
ing particle size, as are the three enveloped families. The
hepadnavirus family, which includes hepatitis B virus, and
virus causes hydrops fetalis, aplastic anemia in sickle cell
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