Virology Flashcards
(141 cards)
1
Q
What are viruses?
A
Acellular organisms that are submicroscopic and obligate intracellular parasites.
2
Q
What are virions?
A
Virus particles that are produced from the assembly of pre-formed components. They do not undergo growth or division.
3
Q
What is variolation?
A
The inhalation of dried crusts or inoculation of pus from lesions - effective but risky.
4
Q
What is vaccination?
A
The inoculation of a virus from a material that was safe to those who came in contact with it (e.g. animal disease) and it cannot be contracted by others who it would be a danger to, unlike variolation.
5
Q
Physical ways to determine virus structure
A
Filtration through membranes of various pore sizes
Sedimentation properties
Spectroscopy: UV light determines nucleic acid, visible light determines light scattering properties
X-ray diffraction determines atomic structure
6
Q
Chemical ways to determine virus structure
A
Resistance to pH changes
Resistance to protein denaturaing agents
7
Q
Determining virus structure by EM
A
Transmission and scanning electron microscopes, resolution improved by dropping temperature
8
Q
Name the three main functions of a virus particle
A
To protect genetic material
To recognise and interact with a host cell
Genome/protein delivery to host cell
9
Q
Capsid
A
Protective protein coat
10
Q
Envelope
A
Outer lipoprotein bilayer membrane possessed by many viruses
11
Q
Genome
A
Nucleic acid comprising genetic material of organism
12
Q
Helix
A
Cylindrical solid formed by staking repeated subunits
13
Q
Icosahedron
A
Solid shape with 20 triangular faces around a sphere
14
Q
Nucleocaspid
A
Ordered complex of proteins and genome
15
Q
Virion
A
Morphologically complete, mature infectious particle
16
Q
What are the three major forms seen in viral capsids?
A
Helical, Icosahedral and Enveloped
17
Q
What is the structure of a helical capsid?
A
Multiple identical protein subunits arranged with rotational symmetry around edge of circle to form a disk. Multiple disks are stacked to form a cylinder. The genome is coated by the protein shell or kept in the hollow part of the cylinder.
18
Q
What are some examples of viruses with helical capsids?
A
Influenza, mumps, measles, rabies.
19
Q
What is the structure of an icosahedral capsid?
A
Protein subunits are arranged in a hollow quasi-spherical structure with the genome inside. The simplest ones are built of 3 identical subunits forming one triangular face.
20
Q
What are some examples of viruses with icosahedral capsids?
A
Picornaviruses, including polio, foot-and-mouth and rhinoviruses.
21
Q
What are naked virus particles?
A
Viruses without an envelope, leaving the capsid proteins vulnerable to the environment.
22
Q
How do naked virus particles infect a host cell?
A
They escape at the end of the replication cycle leaving genetic material behind. The cell dies, degrades and lyses which releases virions.
23
Q
What is the main problem with a naked virus particle mechanism?
A
The host cell dies quickly and prematurely so latent and persistent infections cannot arise.
24
Q
How does a virus particle exit the host cell without killing it?
A
By extrusion, also known as budding. The particle is coated in a lipid envelope derived from the host cells own membrane, allowing it to slip through the membrane and bud off.
25
What are the three virus-derived envelope proteins?
Matrix proteins, glycoproteins and transmembrane proteins.
26
Virus Matrix proteins
Internal virion proteins that link nucleocapsid assembly to envelope.
27
Virus Glycoproteins
Often antigens anchored to membrane that provide external environment contact.
28
Virus Transmembrane proteins
Form channels through envelope giving virus control over membrane permeability.
29
How do viruses assemble themelves?
A large negative nucleis acid molecule is packaged into a small capsid by using positive molecules, virus or host histone proteins or packaging signals in the viruses own genome.
30
How many strands does viral RNA have?
Can be single stranded or double stranded.
31
How many strands does viral DNA have?
Can be single, double or partially double stranded.
32
What different structures can a virus genome have?
Linear, circular or segmented.
33
What are the 3 different polarities that single stranded genomes can have?
Postive-sense, Negative-sense or ambisense.
34
Positive-Sense
Same polarity or nucleotide sequence as mRNA
35
Negative-Sense
Not the same polarity or nucleotide sequence as mRNA
36
Ambisense
Mixture of positive and negative-sense.
37
Name 6 areas of a virus genome that have been studied.
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Composition
Segment size and number
Nucleotide sequence
Terminal structures
Open Reading Frames
Regulatory signals
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38
What is a virus infection unit?
The smallest unit that can cause a detectable effect when added to a susceptible host.
39
What are the two ways virions can be counted?
Directly by electron microscope or indirectly by measuring effects on host.
40
What is a virus plaque assay?
An indirect method of virus quantification using an agar overlay technique.
41
What are the steps in a virus plaque assay?
Dilution of suspension with virus material is mixed with melted agar and host bacteria.
Mixture is poured onto nutrient agar plate.
Host cells grow, viral particles cause cell lysis which spreads to other cells.
Virus replication causes plaques.
42
What are the three phases of viral replication?
Initiation of infection
Replication and expression of virus genome
Release of mature virions from infected cell
43
Viral replication in the nucleus
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Attachment penetration of cell
Genome uncoating
Migration to nucleus
Exiting from nucleus
Assembly maturation
Release from cell
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44
Virus replication in cytoplasm
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Attachment penetration of cell
Genome uncoating
Expression
Proteins
Replication
Assembly maturation
Release from cell
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45
What is virus attachment?
The specific binding of virus attachment protein to cellular receptor molecule which reside on host cell surfaces.
46
What is virus tropism and how is it regulated?
Virus tropism is the cell type a virus will normally infect and it is regulated by the cellular receptor molecules that bind specific virus attachment proteins.
47
Which process out of attachment and penetration requires energy?
Penetration
48
What are the three possible mechanisms of viral penetration?
Entire virus translocation across membrane of cell
Endocytosis of virus into intracellular vacuoles
Fusion of virus envelope with cell membrane (only for enveloped viruses)
49
Describe uncoating
After virus penetration the virus capsid is removed and the genome is exposed in the form of a nucleoprotein complex.
50
How does viral translocation penetration work?
Viral particle binds cellular receptor molecule
Particle translocation across membrane by receptor
Particle released into cytoplasm
Receptor recycled by cell
51
How does viral endocytosis penetration work?
Viral particle invades clathrin coated pit in membrane
Pit closes and starts to bud off membrane - adherence
Pit joins ends to form a clathrin coated vesicle with viral particles enclosed - joining
52
How does virus envelope fusion penetration work?
Extra cellular virus goes through endocytosis
Acidification of vesicle
Membrane fusion
Genome released
53
What are the two major tasks a virus must complete when inside a cell?
It must make virus proteins by making appropriate mRNA that can interact with host ribosomes to direct protein synthesis
Virus needs to replicate genome
54
How many classes of viruses are there?
Seven
55
Describe class 1 viruses
Double stranded DNA genome e.g. Herpes virus, pox virus
Mechanism of mRNA production and genome replication is the same as the host cell
Can be host factor nucleus replicators or virus factor cytoplasm replicators.
56
Describe class 2 viruses
Single stranded DNA genome e.g. Chicken anaemia virus
Second DNA strand synthesised in nucleus to produce mRNA
dsDNA intermediate formed during replication and used for transcription
One strand becomes viral genome and the other is discarded
57
Describe class 3 viruses
Double stranded RNA genome e.g. Reoviruses
Segmented genomes
Virus transcribes negative sense RNA to make positive sense mRNA which requires RNA dependent RNA polymerase which is part of the virion
58
Describe class 4 viruses
Single stranded RNA genome of plus configuration e.g. Poliovirus
Infecting RNA is used directly by the cell as mRNA to easily make virus proteins
Requires virus specific RNA dependent RNA polymerase to make complementary minus strands of RNA then plus strands are made from this
Extra plus strands can be translated as mRNA or packaged as genome into new virions
59
Describe class 5 viruses
Single stranded RNA genome of minus configuration e.g. Influenza virus
mRNA synthesised first by virion carried RNA polymerase
Complementary positive sense strand of RNA synthesised by polymerase and used as mRNA
Positive strand used to make more negative strand genomes
60
Describe class 6 viruses
Single stranded RNA genome that replicates with DNA intermediate e.g. Retroviruses
Reverse transcriptase carried in virions for later use
Virion ssRNA converted to dsDNA by hybrid RNA DNA intermediate. dsDNA integrated into host genome as template for mRNA synthesis
61
Describe class 7 viruses
Double stranded DNA genome that replicates with RNA intermediate e.g. Hepatitis b virus
Virion carried DNA polymerase completes DNA replication
Transcription by host RNA polymerase in nucleus
Viral reverse transcriptase copies to DNA to be packaged into new virions
62
What is the seven class virus classification system called?
The Baltimore system
63
When does the virus become infectious?
At the maturation stage
64
How are mature viruses released?
Non enveloped viruses are released by lysis of the host cell
| Enveloped viruses bud from the cell
65
Why can some viruses spread via cell to cell contact?
They can avoid release into the external environment offering more protection.
66
Why is he rate of spontaneous mutation in some viruses e.g. HIV?
Because there are high error rates in RNA dependant RNA polymerases.
67
What is a quasispecies?
A mixture of molecular variants due to high spontaneous mutation rates.
68
Name 4 types of viral mutations
Biochemical markers, deletions, plaque morphology, revertant
69
What is a biochemical marker mutation?
A change in the chemistry of the virus e.g. Drug resistance mutation or altered virulence
70
What is a deletion mutation?
One or more virus genes removed which can only revert to wild type via recombination.
71
What is a plaque morphology mutation?
When the plaque is larger than normal the virus replicates quicker than wild type, when smaller it replicates more slowly
72
What is revertant mutation?
Involves reverse mutation by correction of original mutation or second site compensatory mutations which involve a separate gene from the original.
73
What is the most significant response to virus infection in animals?
The activation of the immune system.
74
What is the humoral immune response?
Production of antibodies
| Clears virus and stops it spreading to uninflected cells
75
Name all the main virus entering sites to the human body
Eyes, mouth, respiratory tract, skin abrasions, anus, urogenital tract, alimentary canal
76
Name 3 things that can infect a viral infection course
Biology of virus
Response to infection by host
Site at which virus enters body
77
Why can't viruses infect the skin without injury?
Because the outer layer is made of dead cells which cannot be infected.
78
Describe 3 ways viruses can breach the skin by injection and give examples.
Biting Arthropods by taking blood meals e.g. Arboviruses
Biting animals e.g. Rabies
Contaminated needles or blood to blood contact e.g. Hepatitis and HIV
79
Why are STIs and eye infections common?
Because the methods of infection are through mucosal membranes which are easier to penetrate than other barriers e.g. The skin
80
Name 3 types of viruses that infect through the genitourinary tract.
Herpesviruses, papillomaviruses, retroviruses
81
Name 2 types of viruses that infect through the conjunctiva.
Adenoviruses, Picornaviruses
82
What are 3 reasons the GI tract is a favourable site of infection?
Intestinal epithelium has fast replication rate
Lots of lymphoid tissue
Constant stream of food and fluids make it easy for viruses to travel
83
Name 3 ways the body can counteract viruses infecting the GI tract via the oral route.
Low pH in stomach
Many digestive enzymes
Specific defense mechanisms
84
Name a virus that infects the mouth or oropharynx via the GI tract
Herpesvirus
85
Name 5 viruses that infect the intestinal tract.
Adenoviruses, Coronaviruses, Reoviruses, Picornaviruses (enteroviruses) and Caliciviruses
86
Why is the respiratory tract a favourable site of viral infection?
Constant contact with the external environment by respiration makes it easy for viruses to travel directly to the site.
87
How are respiratory viruses normally transmitted to a new host?
Via the respiratory tracts of other hosts i.e. breathing in close proximity.
88
Name 2 defenses that the body has to protect the respiratory tract from viruses.
Filtering and cells/antibodies from the immune system.
89
Name 4 viruses that locally infect the upper respiratory tract.
Orthomyxoviruses, Picornaviruses, Adenoviruses, Coronaviruses
90
Name 2 viruses that locally infect the lower respiratory tract.
Parainfluenza, Respiratory syncytial viruses (both paramyxoviruses)
91
Name 4 viruses that systemically infect the body via the respiratory tract.
Herpesviruses, Paramyxoviruses, Poxviruses, Togaviruses
92
What does herpes virus cause when systemic infection via the respiratory system occurs?
Varicella-Zoster (chicken pox)
93
What does paramyxovirus cause when systemic infection via the respiratory system occurs?
Mumps and Measles
94
What does poxvirus cause when systemic infection via the respiratory system occurs?
Smallpox
95
What does togavirus cause when systemic infection via the respiratory system occurs?
Rubella
96
What is Horizontal transmission?
Direct host to host transmission of the virus.
97
What is vertical transmission?
Transmission of a virus from one generation of hosts to the next, could be via the fetus, breastfeeding after birth or the germline itself.
98
Name 3 ways a virus can spread through a host system.
Direct cell to cell contact
Via the bloodstream
Via the nervous system
99
Describe polio dissemination.
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Virus ingested
Gut associated lymphoid tissues
Regional lymph nodes
Blood
Blood brain barrier
Spinal cord
Gut
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100
Describe rabies dissemination
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Virus entry
Striated muscle
Peripheral Nerves
Central Nervous System
Peripheral Nerves
Salivary gland
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101
What is local spread?
The infection of contiguous cells resulting in lesions or sores.
102
What is viremia?
The dissemination of a virus through the hosts bloodstream. The virus may be free in the plasma of the blood or be cell associated.
103
What is the difference between primary and secondary viremia?
Primary viremia is when the virus enters the blood after local replication whereas secondary viremia is when the virus enters the blood from widely dispersed sites of replication.
104
What is an acute infection and give examples.
An infection that is quickly cleared by the immune system and immunity is required. May be local (rhinovirus) or disseminated (measles).
105
What is a persistent infection and name the 3 categories.
The virus can stay in the host for a long time so that new susceptible individuals can enter into the population. Can be slow, latent or chronic.
106
What is a slow infection and give an example
The infection progresses slowly and inevitably towards death and the virus can be taken from all stages of infection e.g. HIV.
107
What is a chronic infection and give and example
An infection that has constantly high rates of replication and viremia. Can be absent, late to develop or chronic but doesn't always lead to death e.g. Hepatitis B.
108
What is a latent infection and give an example
An infection that has an acute stage with symptoms, the immune system attacks and the virus will go into asymptomatic latency. The genome of the virus remains in the host cell and sometimes can be reactivated e.g. herpes.
109
Name 4 types of viral immune evasion
Counteraction of host cytokines
Inhibition of antigen presentation
Evasion of complement mediated defence
Antibody avoidance
110
How do viruses counter host cytokines?
Encode soluble homologues of cytokine receptors as decoys
Encode cytokine homologues as antagonists
Block activities of cytokine induced effectors
Produce neutralizing cytokine binding proteins
Directly inhibit cytokine induced gene expression
111
How do viruses inhibit antigen presentation?
Down-regulation of gene expression of MHC class 1 receptors on molecules of infected cells e.g. HIV
112
How do viruses evade complement mediated defence?
Incorporation of host cells into envelope especially host derived proteins that protect healthy host cells from complement immune attacks and by secreting proteins that accelerate C4 breakdown.
113
How do viruses avoid antibodies?
Antigenic variation e.g. spontaneous mutation
Inherently poor antigens e.g. in HIV
Replication in immunopriviledged sites e.g. CNS
Establishing a latent infection so viral proteins not expressed
114
Name 5 types of vaccines
Recombinant, DNA, live-attenuated, subunit and inactivated
115
What is a DNA vaccine?
Fragments of a harmful virus's genome encoding immunogenic proteins are inserted into the host so that it will be translated and become immunized.
116
What is a recombinant vaccine?
A harmless or attenuated virus gets part of a harmful virus's genome incorporated into it and then carries it to the host which recombines in the host cell to produce an immunogenic protein.
117
What is a live attenuated vaccine?
A virus with a reduced pathogenicity is introduced to the host to elicit an immune response. This can be dangerous - may be biochemically or genetically unstable.
118
What is a subunit vaccine?
A specific virus protein (often coat protein) is brought into the host in a high dosage which elicits a rapid and high level of immunity.
119
What is an inactivated vaccine?
The virus is exposed to a denaturing agent to lose infectivity and keep antigenicity
120
Name 4 chemotherapy methods used in virology.
Nucleoside analogues, fusion inhibitors, protease inhibitors, influenza antiviral agents
121
Describe nucleoside analogues
Azidothymidine (AZT) inhibits retroviruses by inhibiting reverse transcription and production of virally encoded DNA intermediate
122
Describe fusion inhibitors
Enfuvirtide binds gp41 membrane protein of HIV which stops conformational changes that lead to HIV and T lymphocytes fusing
123
Describe protease inhibitors
Prevent viral replication by binding active site of HIV protease which stops large viral proteins being processed into individual components
124
Describe influenza antiviral agents
Adamantanes interfere with influenza A ion transport proteins which inhibits virus uncoating.
Neuraminidase inhibitors block active site of neuraminidase in influenza A and B.
125
What is the incubation period for hand, foot and mouth disease?
3 - 5 days
126
What are the symptoms of hand, foot and mouth disease?
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Fever
Sore throat
Swollen lymph nodes
Diarrhoea
Rash
Blisters
Ulcerations
Dehydration
Aseptic meningitis and encephalitis
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127
How is hand, foot and mouth disease transmitted?
Contact with saliva, blister fluids and faeces
Aerosol
Fomites
128
Virology of hand, foot and mouth disease
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Caused by enterovirus of picornavirus family
ssRNA positive sense
Small capsid virus
Moderate divergence
Rencombination
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129
Diagnosis of hand, foot and mouth disease
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Swab and vesicle in VTM
Cell culture (cytopathic effect)
Neutralisation tests
Molecular testing
Co-incidental detection
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130
What are the symptoms of Norovirus?
Nausea
Vomiting
Diarrhoea
Abdominal Pain
131
How is Norovirus transmistted?
Faecal-oral route
Aerosol transmission of vomitus
Contamination of water
132
Norovirus Virology
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Caused by enterovirus (picornavirus)
ssRNA positive sense
Small capsid virus
Unculturable
5 genogroups
Low infectious dose
High shedding rate
Short term immunity
Immune against alcohol disinfectants
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133
Norovirus Diagnosis
Not able to be cultured
| RT-PCR
134
Norovirus Epidemiology
Main cause of acute non-bacterial gastroenteritis
Seasonal
Animal reservoirs (shellfish)
135
Molluscum Contagiousum Symptoms
Common skin and mucosal disease
Small white/pink lesions
Waxy core
Itchy but painless
136
MCV Transmission
Direct and fomites
137
MCV Epidemiology
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Worldwide (122m)
Common in humid and crowded areas
Common in children
Adult STI
Immunocompromised people
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138
MCV Clinical Management
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Cryotherapy
Laser
Salicylic acid
Imiquimod
Anti-retroviral drugs
Personal Hygiene
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139
Describe Roche Sequencing Platform
Longer reads up to 1000bp
Scalable
Capable of sequencing 1/4 of human genome in one run
140
Describe Illumina Sequencing Platform
Shorter reads up to 250bp
Scalable
Caable of sequencing 150 genomes in one run
141
Describe Ion torrent Sequencing platform
Shorter reads up to 200bp
Fast
Can sequence 1/4 genome in one run
