Inturuduction ot viruses Flashcards
1
Q
why are viruses important?
A
Important role in cancer (e.g. lymphoma) and immunosuppression (e.g. HIV)
2
Q
what is a virus?
A
A virus is an obligate intracellular parasite, meaning that it can only survive within a host cell and depends on it for replication and metabolic processes, e.g., protein synthesis. Viruses can be classified based on their genome (DNA or RNA) or other structural components, such as the capsid, the envelope, and the viral receptor proteins (spikes). The viral replication cycle occurs within the host cell and involves attachment to and penetration of the host cell, uncoating of the nucleic acid, replication of the nucleic acid, synthesis of virus proteins, assembly of the components, and release of new viruses via budding or cell lysis. The process of nucleic acid replication differs between DNA and RNA viruses.
3
Q
viruses can contain both DNA and RNA. True/False
A
False.
It contains either DNA or RNA (vs bacteria)
4
Q
viruses can replicate outside the cells. True/False
A
False.
Are totally dependent on a host cell for replication.
rely on the cellular processes of their hosts to reproduce themselves
vs bacteria which can survive and replicate both intracellularly and extracellularly
5
Q
what is the approximate size difference between viruses and bacteria
A
10-300nm vs 1000nm
6
Q
which microscope is used to study viruses?
A
electron microscopes (vs bacteria: light microscopes)
7
Q
what is the difference of genome between bacteria and viruses
A
both DNA and RNA vs either DNA or RNA
8
Q
viruses are classified according to their…
A
- their phenotypic characteristics e.g. morphology
- their nucleic acid
- their mechanism of replication
- the hosts they infect and diseases they cause
9
Q
give examples of DNA vs RNA viruses
A
1) DNA–herpesviruses, poxviruses, hepadnaviruses, adenoviruses, papillomaviruses, polyomaviruses, and parvoviruses.
2) RNA-reoviruses, picornaviruses, hepeviruses, caliciviruses, togaviruses, retroviruses, coronaviruses, orthomyxoviruses, paramyxoviruses, rhabdoviruses, filoviruses, arenaviruses, bunyaviruses, and deltaviruse
10
Q
what is the virion?
A
The infective form of a virus when present outside of cells, which consists of DNA or RNA, a protein capsid, and sometimes an envelope.
11
Q
the viral capsid is composed of?
A
protein coat composed of capsomeres (aggregations of protomer subunits) that encloses the genome
- -Helical capsid structure: in enveloped viruses
- -Icosahedral capsid structure: in nonenveloped viruses and enveloped viruses
12
Q
what is the envelope?
A
–Lipid bilayer around the capsid that contains viral glycoproteins and host cell proteins
–The presence of the lipid bilayer makes nearly all enveloped viruses vulnerable to rapid inactivation by organic solvents (e.g., alcohol), detergents, and dry heat
–Originates from host cell’s plasma membrane
–Some viruses do not possess envelopes. These are referred to as nonenveloped viruses, or sometimes, naked viruses
E.g., Papillomaviridae, Adenoviridae, Parvoviridae, Polyomaviridae, Caliciviridae, Picornaviridae, Reoviridae, and Hepeviridae
–Herpesviridae acquire their envelope from the nuclear membrane
13
Q
the envelope is derived from?
A
host cell plasma membrane
14
Q
herpesviridae acquire their envelope from the host cell plasma membrane. True/False
A
False
From host cell nuclear membrane
15
Q
nonenveloped viruses are environmentally resistant. True/False
A
True.
16
Q
what are the shapes of the capsid?
A
- Helical capsid structure: in enveloped viruses: Protein binds around nucleic acid in a helical fashion e.g., coronavirus
- Icosahedral capsid structure: in nonenveloped viruses and enveloped viruses: Has 20 faces each an equilateral triangle e.g., adenovirus
17
Q
which virus contains a complex capsid?
A
poxvirus
18
Q
describe the capsid of bacteriophage
A
have a capsid head and tail
19
Q
what is the bacteriophage?
A
A DNA/RNA virus that infects bacteria and replicates within the cell, giving the bacteria the ability to produce certain virulence factors (e.g., exotoxins).
20
Q
what is the biological role of the capsid?
A
1) Introduces viral genome into host cells
- -Capsid protein interaction with host cell receptors
2) -Contains antigens
- -Stimulate the host immune system
- -Different viruses = different capsids = different serological characteristics
3) protection
21
Q
is capsid protective?
A
Yes. The capsid is resistant to:
- Drying
- Heat
- Detergents
- Acids
- Proteases
22
Q
capsid allows the viruses to…
A
- Can survive in the gastrointestinal tract
- Retain infectivity on drying
- Survive well on environmental surfaces
- Spread easily via fomites
23
Q
capsid leads to the lysis of the infected cell. True/False.
A
True
- -Must kill host cells for the release of mature virus particles
- -Humoral antibody response may be sufficient to neutralize infection
24
Q
enveloped viruses lyse the host cell to get out. True False.
A
False.
Enveloped viruses: released via budding
(vs nonenveloped viruses which get out via cell lysis)
25
describe the genome of DNA viruses
DNA viral genomes can be
1) Double-stranded DNA genomes (dsDNA): most DNA viruses
2) Single-stranded DNA genomes (ssDNA): e.g., Parvoviridae
3) Linear: most DNA viruses
4) Circular: e.g., Papillomaviridae, Polyomaviridae, Hepadnaviridae
26
describe the genome of RNA viruses
--RNA viral genomes can be
1)Double-stranded RNA genomes (dsRNA): Reoviridae
2)Single-stranded RNA genomes (ssRNA): most RNA viruses
--Positive-sense RNA viruses (+ssRNA): e.g., Retroviridae, Togaviridae, Flaviviridae, Coronaviridae, Hepeviridae, Caliciviridae, Picornaviridae
--Negative-sense RNA viruses (-ssRNA): e.g., Arenaviridae, Bunyaviridae, Paramyxoviridae, Orthomyxoviridae, Filoviridae, Rhabdoviridae
3)Linear: most RNA viruses
4)Circular: e.g., Arenaviridae, Deltaviridae
Segmented (e.g., Bunyaviridae, Arenaviridae)
27
what is positive-sense RNA?
A type of viral RNA that, unlike negative-sense RNA, can be readily translated into proteins. It does not require RNA-dependent RNA polymerase.
28
what is negative-sense RNA?
A type of viral RNA that must be transcribed by RNA-dependent RNA polymerase into positive-sense RNA before it can be translated into proteins.
29
give examples of positive vs negative-sense RNA
+()---Retroviridae, Togaviridae, Flaviviridae, Coronaviridae, Hepeviridae, Caliciviridae, Picornaviridae
(-)--- Arenaviridae, Bunyaviridae, Paramyxoviridae, Orthomyxoviridae, Filoviridae, Rhabdoviridae
30
the envelope is composed of...
phospholipids and glycoprotein
31
The envelope helps the virus to attach the host cell.True/False.
contains viral proteins = attach the virus to receptors on susceptible host cells
32
what is the role of the envelope?
- -Confers a distinctive serological characteristic by which some viruses can be diagnosed
- -Surface polypeptides (e.g. Haemaglutinins of influenza)
- -Bind specific receptor sites on the host cell
- -Viral antigens stimulate host immune responses
- -Some viruses carry a small number of enzymes (e.g. Neuraminidase of influenza)
33
what is neuraminidase?
A viral enzyme that cleaves neuraminic acid residues from glycoprotein, which results in viral release from the host cell. Found in the influenza virus.
34
what is the hemagglutinin?
A glycoprotein on the surface of influenza virions that binds to sialic acid residues on the respiratory epithelium. Following endocytosis, hemagglutinin causes fusion of the viral envelope with the host endosomal membrane. This protein is also the target of neutralizing antibodies against influenza.
35
what is the clinical significance of neuraminidase?
Inhibited by Oseltamivir: A neuraminidase inhibitor used to treat influenza A and B. Inhibits viral budding and prevents the dissemination of the virus into the bloodstream. Treatment is indicated for patients with severe illness or at increased risk (e.g., immunocompromised, elderly). Most drug efficacy is lost if treatment is not initiated with 24 hours of symptom onset.
36
viral envelope confers viruses resistant to environment. T/F
```
False.
An envelope is sensitive to
--Drying
--Heat
--Detergents
--Acid
```
37
what are the consequences of virus having an envelope?
- -Must stay wet during transmission
- -Transmission in large droplets and secretions
- -Can not survive in the gastrointestinal tract
- -Do not need to kill cells in order to spread (budding)
- -May require both a humoral and a cellular immune response
38
Hepatitis A and poliovirus belong to the family of
picornaviridae.
A family of non-enveloped viruses with a positive-sense, single-stranded RNA structure. Includes poliovirus, echovirus, rhinovirus, coxsackievirus (A and B), and hepatitis A virus.
39
Influenza virus belong to the family of...
orthomyxoviridae.
A family of enveloped viruses with a negative-sense, single-stranded, 8-segmented RNA structure. Includes influenza viruses A and B.
40
describe retroviruses
A family of positive-sense, single-stranded RNA viruses that use reverse transcriptase to create a DNA intermediate and integrate with the genome of a host cell. This permits the production of proteins necessary for virus replication. Examples include the human immunodeficiency virus and human T-lymphotropic virus.
41
describe herpesviridae
A family of enveloped viruses with a linear, double-stranded DNA structure. Includes herpes simplex virus, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, and human herpesviruses 6, 7, and 8.
42
what is the vector?
An organism that transmits a pathogen from one organism to another. Invertebrates such as ticks, mites, lice, mosquitoes, and/or flies are important disease vectors.
43
Rabies is transmitted by...
- Spread through the saliva of a rabid animal after a bite injury
- Most common animal reservoir worldwide: dogs
- Most common animal reservoirs in the US: bats, raccoons, skunks, and foxes
44
how dengue is transmitted?
Vector-borne: mosquitoes most commonly from the species Aedes aegypti
45
how influenza is transmitted?
Person-to-person transmission: directly via respiratory droplets (sneezing or coughing) or indirectly through contact with contaminated surfaces
46
give examples of viruses that are transmitted through inflation pathway
influenza and rhinoviruses
47
give examples of viruses that are transmitted fecal-orally
Rotavirus, norovirus, hepatitis A&E
48
give examples of blood-borne transmission
Hepatitis B & C, HIV
49
give examples of congenital transmission of viruses
Rubella, CMV, Hepatitis B & C, HIV
50
what is the tropism?
The ability or the tendency of a pathogen to infect a specific cell or organism. Determined by factors such as cell surface receptors, transcription factors, and other signaling molecules.
51
the tropism is determined by?
- -Cell receptors for the virus.
- -Cell transcription factors that recognize viral promoters and enhancer sequences.
- -Ability of the cell to support virus replication.
- -Physical barriers.
- -Local temperature, pH, and oxygen tension enzymes and non-specific factors in body secretions.
- -Digestive enzymes and bile in the gastrointestinal tract that may inactivate some viruses.
52
what is the most important factor determining tropism?
Cell receptors for the virus.
53
what is the promoter and enhancer?
1) A segment of DNA upstream (toward the 5' end) of a gene that regulates transcription initiation.
2) Short DNA sequences ∼ 20 bp in length that Increase the transcription rate by binding of specific transcription factors (activators)
54
explain the viral life cycle
1) Attachment to the host cell: viruses use host cell surface proteins and receptors for entry
2) Penetration into the host cell
- -Nonenveloped viruses: via endocytosis or transmembrane transport
- -Enveloped viruses: via endocytosis or fusion with host cell's cell membrane
3) Uncoating of the nucleic acid
4) Replication of the nucleic acid and formation of virus proteins by transcription and translation (in retroviruses, RNA is initially transcribed into DNA)
- -Early mRNA is for the synthesis of
* Proteins to shut down host cell defense mechanisms
* Proteins for genome replication (e.g., viral RNA polymerase)
- -Late mRNA is for the synthesis of viral structural proteins
5) Assembly of virus components
6) Viral release
- -Enveloped viruses: released via budding
- -Nonenveloped viruses: released via host cell lysis
55
why do viruses need to infect the cell to replicate?
Do not possess the necessary machinery themselves to replicate, utilize cell’s reproduction system to make copies of itself
56
how viruses are internalized into the host cell?
- -Nonenveloped viruses: via endocytosis or transmembrane transport
- -Enveloped viruses: via endocytosis or fusion with host cell's cell membrane
57
what is the objective of viral uncoating?
to make the genome available, viral nucleic acid into cytoplasm/ nucleus
58
viral proteins are synthesized in?
Protein synthesis always in the cytoplasm
59
the viral nucleic acid is synthesized in?
Nucleic acid can be made in nucleus or cytoplasm
60
list some important receptors on the cell surface that viruses use to penetrate the cell
- CMV: integrins (e.g., heparan sulfate)
- EBV: CD21
- HIV: CD4, CXCR4, CCR5
- Parvovirus B19: P antigen on erythrocytes
- Rhabdovirus: nicotinic acetylcholine receptor
- Rhinovirus: ICAM-1
61
describe the viral pathology
1) Cytolysis: viral replication results in the destruction of host cell → release of the virus
- -Seen with nonenveloped viruses
- -Some enveloped viruses
2) Immunopathological host reactions: cellular immune response to the invading virus is triggered by cytotoxic T cells → destruction of infected cells (e.g., HBV); the virus, however, is not cytopathogenic
3) Transfer of genetic material: bacteriophages may transfer virulence factors (e.g., exotoxins)
62
what are the effects of the virus on cells?
1) cell death-cytopathologic changes
2) transforamtion-cell become malignant (HPV)
3) latent infection--eg herpes virus, may subsequently reactivate
63
list some oncogenic viruses
- -Hepatocellular Cancer - Hepatitis B & C
- -Cervical Cancer- Papillomavirus
- -Lymphoma - HIV & Epstein Barr virus (EBV)
- -Nasopharyngeal Cancer -EBV
- -Kaposi’s Sarcoma - HIV with HHV8
- -T Cell Leukaemia - HTLV-1
64
what are the ways of viral spread?
1)Intracellular (cell to cell)
Intercellular bridges e.g., HSV
2)Extracellular
The virus is released from infected cells and spreads to other cells locally and distally (hematogenous/lymphatic cells) e.g., influenza virus
3)Neural
Peripheral nerves to CNS e.g., rabies, HSV
4)Nuclear
Viral genome incorporated into host genome – passed onto succeeding cell generations e.g., HIV
65
give examples of intracellular viral spread
Intercellular bridges e.g., HSV
66
the influenza virus is spread from cell to cell intracellularly. True/False
False.
Extracellularly
The virus is released from infected cells and spreads to other cells locally and distally (hematogenous/lymphatic cells)
67
examples of viruses that spread through the nerves?
rabies, HSV (neurotropic), use dynein protein which transports the stuff from the axon to the neuron cell body (retrograde)
68
example of the nuclear spread of the virus
Viral genome incorporated into host genome – passed onto succeeding cell generations e.g., HIV
69
what are the outcomes of viral infection?
1)Many viral infections are mild & self-limiting
e.g., coronaviruses causing the common cold
2)May be severe in vulnerable patients
E.g., Cytomegalovirus in transplant patients
3)May be silent
e.g., hepatitis C
4)May reoccur intermittently
e.g., Herpes simplex virus (Cold sores)
5)May be fatal
e.g., rabies
70
what is the course of viral infection?
- -Abortive (no viral replication or cell damage)
- -Acute
- -Chronic
- -Persistent
1) Latent (inactive; no replication): virus remains dormant in infected cells
2) Productive (viral replication occurs, dormant infection with few or no signs of infection)
3) Transforming (virus may or may not replicate): triggers malignant transformation (e.g., EBV, HPV)
71
give an example of latent infection
VZV causes a primary infection (chickenpox). After the disease has resolved, the virus becomes dormant in the dorsal root ganglia of nerves and upon reactivation, begins to replicate, causing reinfection (shingles).
72
what are the classes of antiviral agents/
- -Agents that deactivate the virus directly e.g. U.V., cryotherapy
- -Agents that augment the host response e.g. interferon
- -Agents that inhibit viral replication e.g. Aciclovir
73
what is the herd immunity?
Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune
74
give examples of viral infections that can be prevented by vaccination
- Influenza
- Measles, Mumps & Rubella (MMR)
- Hepatitis B
- Hepatitis A
- Polio
- HPV
75
how viruses are detected or identified?
1) microscopy
2) culture
3) antibody detection (serology
4) antigen detection
5) genome detection (PCR)
76
overview of viral diagnostics
1) Antibody detection
- -Viral hemagglutination inhibition test: used in the diagnosis of viral infections (e.g., influenza, mumps, and measles).
- -ELISA or direct immunofluorescence (e.g., HSV).
2) PCR: quantitative detection of viral load (e.g., HIV, HCV)
3) Virus isolation: a prerequisite for resistance testing (e.g., HIV)
4) Time-consuming and labor-intensive methods
- -Cell culture
- -Electron microscopy
- -Not typically used for clinical diagnostics
77
what is the role of fluorescent microscopy in viral diagnostics?
Rapid detection of viral antigens in a specimen using commercially produced antibodies
78
what is the role of light microscopy in viral diagnostics?
To look for inclusion bodies
Virus-induced masses within the cytoplasm of cells
Can be pathognomonic without need for culture (Negri bodies in hippocampal cells in rabies)
79
describe the viral culture
1) Viruses only replicate within living cells so need LIVING cells to culture viruses
2) Animals/chicken eggs/cell or tissue culture (unlike bacteria which grow on agar plates)
- -Human or animal cells are grown in artificial culture, these cells are living, hence can support viral growth
- -Examine the cells for the effect of viral growth
1) ‘Cytopathic effect’
2) Haemabsorbtion (cells acquire the ability to stick to mammalian red blood cells)
- -Confirm the ID of the virus by immunofluorescence/neutralization / Haemabsorbtion inhibition
80
viruses can be grown on blood agar. True/False.
False.
Viruses only replicate within living cells so need LIVING cells to culture viruses, unlike bacteria which grow on agar plates
81
what is the Vero cell
A lineage of cells used in cell cultures.
Vero cells are used for many purposes, including:
1) screening for the toxin of Escherichia coli, first named "Vero toxin" after this cell line, and later called "Shiga-like toxin" due to its similarity to Shiga toxin isolated from Shigella dysenteriae
2) as host cells for growing viruses;
3) as host cells for eukaryotic parasites, specially of the trypanosomatids
82
what are the disadvantages of cell culture
1) Long period (up to 4 weeks) required for result.
2) Often very poor sensitivity, sensitivity depends to a large extent on the condition of the specimen.
3) Susceptible to bacterial contamination.
4) Susceptible to toxic substances which may be present in the specimen.
5) Many viruses will not grow in cell culture e.g. Hepatitis B, diarrhoeal viruses, parvovirus, papillomavirus.
83
list some viruses that cannot be grown on cell cultures
hepatitis B, diarrheal viruses, parvovirus, papillomavirus
84
what is the serology?
A laboratory study of the serum. Most commonly refers to the detection of specific antibodies and/or antigens in the blood (e.g., ANA, Lyme IgM), HBsAg (hepatitis B surface antigen.
85
how many blood samples are required for viral serology?
Two samples required (paired sera): one at the onset of illness & a second after 7-14 days
A rise in antibodies confirms infection
****no always, a rise of titer typically for IgG/total antibodies, IgM antibodies typically will confirm acute infection
86
what is fluorescent microscopy?
A technique involving antibodies coupled with a fluorescent compound to identify a specific protein or organism by targeting a surface antigen.
87
what are the advantages of molecular diagnostic techniques? (PCR)
1) Fast
2) Increasingly used for
- Rapid diagnosis of viral infection
- Guide treatment e.g., HIV viral load
- Detection of resistance to antiviral drugs
3) Not every virus can be cultured
(e. g., hepatitis C)
