INTRODUCTION TO VIROLOGY Flashcards
1
Q
containing genetic material (DNA or RNA) surrounded by a protective protein coat and depend on their host for all aspects of their reproduction.
A
Obligate intracellular parasites
2
Q
Spreads from cell to cell via infectious unit
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Virion
3
Q
initiated upon entry, dissociation in a host cell and directs synthesis of viral components by cellular system
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Host replication
4
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de novo self-assembly from the newly synthesized components
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Formation of progeny virus particles
5
Q
Viruses are not solely pathogenic nuisances; they can be .
A
beneficial
6
Q
Not all pathogenic viruses fulfill the
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Koch’s postulates.
7
Q
Viruses can cross
A
species boundaries.
8
Q
All viruses must produce (?) that can be translated by cellular ribosomes.
A
mRNA
9
Q
Strandedness, is either
A
single single stranded (ss) or double stranded (ds)
10
Q
Groups include
A
ssRNA, dsRNA, ssDNA, and dsDNA.
11
Q
Polarity include (?), immediate translations for protein synthesis; (?), no immediate translations for the protein.
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positive sense (+)
negative sense (-)
12
Q
Shape of nucleic acid is either
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linear or circular
13
Q
for both (+) and (-) senses.
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Ambisense
14
Q
Protein shell(coat) that protects the NA genome.
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Capsid
15
Q
Basic unit of a capsid.
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Capsomere
16
Q
Individual protein subunits that assembles into types of capsids (eg., icosahedral, helical, complex)
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Capsomere
17
Q
Required for entry of the infectious virion particle
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Spike glycoprotein (S)
18
Q
Most abundant protein (Eg., SARS-CoV-2)
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Membrane protein (M)
19
Q
Smallest among the major Structural protein
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Envelope glycoprotein (E)
20
Q
single-stranded positive sense RNA genome
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Nucleocapsid (N)
21
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is based on comparing and contrasting set of characters that can be used to define the properties of any particular taxon.
A
Taxonomic classification
22
Q
• Four (4) Characteristics used in the Taxonomic Classification:
A
- Nature of the nucleic acid (NA) in the virus particles (DNA or RNA)1
- Symmetry of the protein (capsid)
- Presence or absence of a lipid membrane (envelope)
- Dimensions of the virion and capsid
23
Q
Presence of Nucleic acid
RNA
A
Arenaviridae Flaviviridae
Astroviridae Orthomyxoviridae
Bunyaviridae Paramyxoviridae
Caliciviridae Picornaviridae
Coronaviridae Rhabdoviridae Filoviridae Reo-, Togaviridae
24
Q
Presence of Nucleic acid
DNA
A
Adenoviridae Parvoviridae
Hepadnaviridae Polyomaviridae
Herpresviridae Poxviridae
Papilomaviridae
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- ALL RNA viruses are “ss” except
Reoviridae
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- ALL DNA viruses are “ds” except
Parvoviridae
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- ALL RNA viruses have helical capsid symmetry except
Calici-, Flavi-, Picorna-, Reo-, and Togaviridae
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- (?), either helical or icosahedral symmetry
Retroviridae
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- ALL DNA viruses have icosahedral symmetry except (?) that has a complex symmetry
Poxviridae
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Withstand harsh environment conditions
Naked
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Cannot be dried out
Enveloped
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Resistant to drying, aicids, & detergents
Naked
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Not stable to acid
Enveloped
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Many are transmitted fecal-oral route
Naked
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General must remain in body fluids
Enveloped
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Types of Capsid
Naked
Enveloped
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Francis Crick, conceptualized the central dogma for flow of information form DNA genome in all living cells:
o DNA → mRNA → protein
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The translational machinery for protein synthesis depends on the .
host’s cell
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But viral genomes comprise both (?) in a variety of conformations.
DNA and RNA
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allows relationships among viruses with RNA or DNA genomes to be determined on the pathway required for mRNA production.
The Baltimore System
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The Baltimore System was inspired by
David Baltimore, 1971
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Assigns viruses to seven (I to VII) distinct classes on the bases of the (!) of their genomes.
nature and polarity
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Since all viruses must produce (!) that can be translated by cellular ribosomes, knowledge of the composition of the viral genome provides insight into the pathways required to produce mRNA, indicated by arrows
mRNA
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INITATION
Attachment Penetration Uncoating
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BIOSYNTHESIS
Genome Replication Assemble and Release
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Interaction of a virion with specific receptor site on the surface of a host cell.
Attachment
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Receptor binding reflects fortuitous configurational homilies and play an important role in cell tropism and viral pathogenesis.
Attachment
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Initiates irreversible structural changes in the virion.
Attachment
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Penetration
Accomplish in various ways:
1. Receptor-mediated endocytosis 2. Clathrin- mediated endocytosis 3. Direct penetration 4. Fusion
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Interaction of viral protein to host cell is facilitated with a second cellular receptor (coreceptor)
Penetration
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Occurs concomitantly with or shortly after penetration.
Uncoating
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This is the separation of viral nucleic acid from the virion and genome may be released as free nucleic acid or nucleocapsid.
Uncoating
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GOAL: specific mRNA must be transcribe for the viral nucleic acid for successful expression and duplication of genetic information
Genome Replication
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Once accomplished, translation of mRNA begins
Genome Replication
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NOTE: different viruses use different pathways to synthesize mRNA depending on the structure of NA (eg., Rhabdoviridae carry RNA Pol to synthesize mRNAs.
Genome Replication
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RULE: [(-)] sense viruses must supply their own RNA Pol.
Genome Replication
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Newly synthesize viral genomes and capsid polypeptides assemble together to form progeny viruses.
Assemble and Release
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Assemble and Release
Effects to the host cell:
1. Cell death 2. Mutation due to chronic persistent infection 3. Viral-induced apoptosis 4. Cytopathic effects
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Viral Growth Curve
Inoculation Eclipse Maturation
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Host cell is inoculated with the virus that consequently undergoes attachment.
Inoculation
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Sometimes the amount of the virus decreases because the visions attached to host cells are not yet considered viruses.
Inoculation ñ
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Viruses are not being manufactured within host cells. Viral contents enter the cell during the penetration step of the viral life cycle.
Eclipse
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After genetic material is uncoated, genetic material is copied and viral components are formed during biosynthesis.
Eclipse
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After synthesis of capsids, enzymes and other materials, new virus particles are formed during the assemble stage.
Maturation
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Total virus count increases before extracellular virus count increases: there is a lag while visions are being created, but not enough have been created for release to occur.
Maturation
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Non-enveloped viruses accumulate in cells until cell lysis.
Maturation
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Enveloped viruses assemble near cell membranes and “bud” off via exocytosis
Maturation
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The process by which viruses cause disease— a collateral outcome of the parasitic nature of viruses.
Viral Pathogenesis
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Individual differences among prospective hosts, group dynamics and behaviors, geography, and climate all influence how efficiently a virus can establish infection within a population.
Viral Pathogenesis
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(?) in the appearances of some viruses may be due to variations in viral particle stability at various temperatures or humidity, changes in the integrity of host barriers (eg., skin or mucosa), or seasonal changes in the life cycles of viral vectors, such as mosquitoes.
Seasonal differences
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does not necessarily signify susceptibility to disease.
Susceptibility to infection
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helped to identify the causal relationships between a microbe and the disease it causes in the host; but, these postulates may not be fulfilled when associating some viruses with a particular disease
Koch’s postulates
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Steps in Viral Pathogenesis
Entry and Primary
Viral spread and tropism
Cell injury and Manifestation
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Attachment of the virus to the host cell with the subsequent replication of the virus a the site of entry.
Entry and primary replication
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Viruses spread to other body parts of the body within the host.
Viral spread and tropism
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The spread of other viruses is tissue specific which is affected by gene enhancers and activating enzymes.
Viral spread and tropism
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Destruction of virus-infected cell and physiologic alteration seen in host cell
Cell injury and Manifestation
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Types of infection:
1. Acute viral infection
2. Chronic infection
3. Latent infection
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characterized by rapid onset of disease and relatively brief period of symptoms, eventually resolved within days
1. Acute viral infection
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viruses are continually detected even at low levels
2. Chronic infection
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viruses in an occult or in a cryptic form most of the time
3. Latent infection
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• Sites of latency include
for VZV and HSV
neurons in the dorsal rectal ganglia (shingles)
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for CMV
T-cells, macrophages
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for EBV
B-cells
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for HBV
Hepatocytes
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for HPV
Epithelium
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Non-persistent pattern, rapid onset soon after contraction.
Patterns of viral diseases
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Persistent pattern, acute plus complications
Patterns of viral diseases
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Abortive, acute manifestations plus death of the virus due to
1. Non-permissive cells 2. Environmental 3. Defective
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include morphologic changes on host cells.
Cytopathic effects
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Effects of viruses on cells
1. Morphological alterations
2. Inclusion bodies
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• Nuclear shrinking (pyknosis) for
Picornaviruses
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• Proliferation of nuclear membrane for
alpha viruses and herpesviruses
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• Vacuoles in cytoplasm for
Polyomaviruses, papillomaviruses
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• Syncytium formation (cell fusion) for
Paramyxoviruses and coronaviruses
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• Margination and breaking of chromosomes for
Herpesviruses
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• Virion in nucleus for
Adenoviruses
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• Virion in cytoplasm (Negri bodies) for
Rabies virus aviruses
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• Factories in cytoplasm (Guarnieri bodies) for
Poxviruses
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• Clumps of ribosomes for
Aren
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Morphological alterations
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Inclusion bodies
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1. Have (?) ready
all PPEs and materials
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2. Check VTM for clarity and turbidity (VTM should be (?) in color. Tap the tube and mix contents)
clear and salmon pink
105
3. Check integrity of the swab and tongue depressor (use only (?)). DO NOT use calcium alginate or swabs with wooden sticks.
sterile Dacron or rayon swabs with plastic shafts
106
4. Check (?) of kits. DO NOT use beyond expiry
expiration date
107
5. DO NOT use (?) which may have been opened
swabs or tongue depressors
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6. Correctly (?) the patient and (?) the tube prior to collection
identify
label
109
7. Take out the VTM (?)
(2-30oC)
110
8. Label the VTM with the (?). Information should be legible and label should remain attached under all conditions of storage and transport.
patient’s full name, date and time of collection
111
1. Specimens should be collected (?) from onset of infection since it is the time when the virus is in high concentration. DO NOT collect beyond seven (7) days.
within seven (7) days
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2. Only (?) should perform the procedure
qualified and trained staff
113
3. Remove possible (?) (eg., loose hair)
visual obstruction
114
4. Use a (?) for each individual patient
single kit
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5. Strictly follow (?) prior to each procedure (eg., biosafety protocols)
infection control guidelines
116
Viral Culture Technique
Plaque Assay
Embryonated eggs
Viral cell culture
117
Easy to grow. Reliable determination of the titers of viruses
Plaque Assay
118
Plaque Assay
1. Virus, bacteria and agar are (?). Monolayers of cultured cells are (?) with a preparation of virus to allow adsorption to cells.
2. After removal of the inoculum, the cells are covered with nutrient medium containing a supplement (most commonly (?)— which forms a gel)
3. When the original infected cells release (?), the gel restricts the spread of viruses to neighboring infected cells.
4. After replication, the virus lyses the bacteria, forming (?) (circular zone of infected cells)
mixed, incubated
agar
new progeny particles
plaques
119
• Each plaque is assumed to come from a
single viral particle
120
• Reported in plaque forming units
(PFU/mL)
121
[A] Single plaque formed by (?) virus in Giorgia bovine kidney cells stained with chromogenic substrate.
[B] Plaques formed by (?) on human HeLa cells stained with crystal violet.
[C] Illustration of the (?) from an initial infected cells to neighboring cell, resulting in a plaque
pseudorabies
poliovirus
viral spread
122
• Convenient and inexpensive
Embryonated eggs
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Embryonated eggs
• Hole drilled in Chicken egg shell ((?)after fertilization) and virus is injected into the site appropriate for its replication.
5 to 14 days
124
• This method of virus propagation is now routine only for influenza virus.
Embryonated eggs
125
• Credited to John Enders, Thomas Weller, and Frederick Robbins (1949) who made the discovery that poliovirus could multiply in cultured cells.
Viral cell culture
126
• To prepare a cell culture, tissues are dissociated into a single-cell suspension by mechanical disruption followed by treatment with proteolytic enzymes.
Viral cell culture
127
• Cells are suspended in culture medium and place in plastic flasks or covered plates.
Viral cell culture
128
• As the cells divide, they cover the plastic surface. Epithelial and fibroblastic cells attached to the plastic and form a monolayer, whereas blood cells such as lymphocytes settle, but do not adhere.
Viral cell culture
129
• The cells are grown in a chemically defined and buffered medium optimal for their growth
Viral cell culture
130
Viral cell culture
• Commonly used cell lines double in number in (?) in such media
24 to 48h
131
Kinds of cell culture
1. Primary cell cultures
2. Secondary cell cultures
3. Continuous cell lines
132
, prepared from animal tissues with limited life span usually no more than 5 to 20 cell divisions
1. Primary cell cultures
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, most common from embryos.
2. Secondary cell cultures
134
, consists of a single cell type that can be propagated indefinitely in culture
3. Continuous cell lines
135
Commonly used primary cultures are derived from monkey kidneys, human embryonic amnion and kidneys, human foreskin and respiratory epithelium, and chicken or mouse embryos
1. Primary cell cultures
136
— primarily used for vaccine production.
chicken or mouse embryos
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Immortal lines that usually derived from tumor strain with a mutagenic chemical or tumor virus (eg., HeLa [Henrietta Lacks] and L and 3T3 cells)
Continuous cell lines
