Page 322 - Review of Medical Microbiology and Immunology ( PDFDrive )

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RNA Enveloped Viruses mebooksfree.com
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39

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CHAPTER C ONTENT S

ORTHOMYXOVIRUSES
RHABDOVIRUSES
Influenza Viruses
PARAMYXOVIRUSES
Rabies Virus
RETROVIRUSES
Measles Virus
Mumps Virus
FILOVIRUSES
Respiratory Syncytial Virus
Ebola Virus
Parainfluenza Viruses
CORONAVIRUSES Human T-Cell Lymphotropic Virus
Marburg Virus
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Self-Assessment Questions
Coronavirus
TOGAVIRUSES
Summaries of Organisms
Rubella Virus
Practice Questions: USMLE & Course Examinations

ORTHOMYXOVIRUSES

INFLUENZA VIRUSES
clinical features of the other medically important viruses in
Influenza viruses are important human pathogens because
this chapter.
they cause both outbreaks of influenza that sicken and kill features of influenza virus and compares them with the
In 1997, an outbreak of human influenza (avian influ-
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mebooksfree.com mebooksfree.com mebooksfree.com 1 human influenza caused by H1N1 influenza A virus of mebooksfree.com
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thousands of people each year as well as infrequent but
enza, bird flu) caused by an H5N1 strain of influenza A
devastating worldwide epidemics (pandemics).
virus began. This outbreak and subsequent outbreaks are
Influenza viruses are the only members of the ortho-
described on page 317. In 2009, there was an outbreak of
myxovirus family. The orthomyxoviruses differ from the
paramyxoviruses primarily in that the former have a
swine origin (swine-origin influenza virus, S-OIV). This
segmented RNA genome (usually eight pieces), whereas
outbreak and the subsequent pandemic are described on
the RNA genome of the latter consists of a single piece.
page 317. In 2013, an outbreak of influenza caused by an
The term myxo refers to the observation that these
H7N9 strain of influenza virus occurred.
viruses interact with mucins (glycoproteins on the sur-
face of cells).
In addition, the orthomyxoviruses are smaller (110 nm
Disease
in diameter) than the paramyxoviruses (150 nm in diame-
ter). See Table 39–1 for additional differences. 1. Human Influenza Virus
Influenza A virus causes worldwide epidemics (pandemics)
Table 39–2 shows a comparison of influenza A virus
mebooksfree.com mebooksfree.com mebooksfree.com Pandemics occur when a variant of influenza A virus that 311 mebooksfree.com
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of influenza, influenza B virus causes major outbreaks of
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with several other viruses that infect the respiratory tract.
influenza, and influenza C virus causes mild respiratory
Table 39–3 describes some of the important clinical
tract infections but does not cause outbreaks of influenza.
contains a new hemagglutinin against which people do not
1
The total molecular weight of influenza virus RNA is approximately
have preexisting antibodies is introduced into the human
6
(2–4) × 10 , whereas the molecular weight of paramyxovirus RNA is
population.
6
higher, approximately (5–8) × 10 .
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