Viruses and Virology (Lecture 15-22) Flashcards
1
Q
What is the structure of a virus?
A
- Nucleic acid (surrounded and protected by capsid (protein coat))
- DNA / RNA
- Protein coat (capsid)
- Protection and entry
- Viral envelope
- Derived from host cell
2
Q
Give examples of enveloped viruses
A
SARS COV2 and HIV
3
Q
Give examples of enveloped viruses
A
SARS COV2 and HIV
4
Q
What are VAPs for?
A
Help the virus recognize and enter the host cell
5
Q
Why are spike proteins called “spike” proteins?
A
The virus’ VAP is located within the envelope and looks like a spike
6
Q
Describe how poliovirus infects their neuronal cells
A
Causes paralysis
7
Q
Describe how HIV infects their immune cells
A
Causes immune deficiency syndrome or AIDS
8
Q
How do viruses recognize and bind to their specific host cells in the first place?
A
Interaction b/w VAPs from the viral end and specific components found on the surface of the cell end called cellular receptors.
9
Q
Describe how COVID-19 recognizes its host cell
A
- Spike protein of COVID recognizes ACE2 receptors
- ACE2 receptors: possess receptor that is susceptible to viral infection (incl lung cells)
10
Q
What is the difference between a nucleocapsid in an enveloped virus n a naked virus?
A
The NC of an enveloped virus doesn’t have the VAPs bc they’re located within the viral envelope
11
Q
What information is encoded in the viral genome?
A
Nucleic acid: DNA/RNA → carries genetic information
12
Q
What proteins can viral NA encode?
A
- Structural proteins (e.g. capsid proteins, VAPs)
- Non-structural (NS) proteins
- No role in viral structure but hv different roles in viral replication
- Pathogenesis
- Transformation
- Modulation (escape) of host defenses
13
Q
What is NOT encoded in viral genomes?
A
- Complete protein synthesis machinery (eIFs, tRNAs)
- Proteins involved in cell wall production or membrane biosynthesis
- Centromeres/telomeres found in standard host chromosomes
14
Q
Describe a capsid and its function
A
- Protein shell that surrounds viral genome
- Protect NA and facilitate its delivery into host cells
15
Q
Describe a capsid’s structure
A
Composed of 1 or more different types of proteins that repeat over and over again to create the entire capsid
16
Q
Describe a capsomere’s structure
A
Strong but slightly flexible capsid
Difficult to break open
17
Q
How is a virus’ stable structure achieved?
A
- Symmetrical arrangement of many identical viral protein subunits → provide maximal contact
- Each subunit has identical bonding contacts w its neighbours n this repeated interaction at the subunit interfaces
18
Q
How is a virus’ unstable structure achieved?
A
- Contact is not covalent
- Can be dissociated or taken apart once the virus attaches to the host cell to release the genome
19
Q
Why do viruses use an icosahedral structure?
A
- Permits the greatest number of capsomeres to be packed in a regular stable figure
- Easiest and most efficient way of making regular stable structure, which is important for a virus
20
Q
How are capsomeres organized in helical viruses?
A
- Around and along the NA in a spiral helical pattern
- Helix is flexible
- Virus length is determined by length of NA
- Virus width is determined by the size and packaging of protein subunits
21
Q
Examples of viruses w complex structures
A
Poxviruses
22
Q
How does the virus obtain a viral envelope?
A
After infecting the host cell thus the viral envelope is bilayer phospholipid (similar to the host cell’s membrane
When the virus exits the infected cell, it pushes itself through the cellular membrane acquiring the envelope, outer membrane, ER membrane and the nuclear membrane
23
Q
How is the viral envelope affected by environmental conditions?
A
The viral envelope, due to its lipid content, is sensitive to heat, drying, detergents, lipid solvents (such as alcohol), and stomach acidity.
24
Q
What happens if the viral envelope is lost?
A
Loss of the viral envelope leads to the loss of VAPs and renders the virus non-infectious and harmless.
25
Why is hand washing with soap important in preventing the transmission of enveloped viruses like influenza and coronaviruses?
Enveloped viruses are easily inactivated by washing with soap due to the sensitivity of their lipid envelopes to detergents.
26
Are all viruses enveloped?
No, viruses transmitted through the fecal-oral route (e.g., rotaviruses) are non-enveloped (naked) to survive the acidic environment of the stomach.
27
What is the general stability of enveloped viruses compared to non-enveloped viruses?
Enveloped viruses are less stable and more sensitive to heat, drying, detergents, and lipid solvents than non-enveloped viruses.
28
How long can a naked virus-like rhinovirus survive in the environment?
Rhinovirus, being non-enveloped, can survive in the environment for significant periods.
29
Based on the organization of the capsid, what are the main 3 types of virus structure?
- Icosahedral
- Helical
- Complex
30
Why are capsids made of 1 or a few proteins that repeat over and over?
- Allows for efficient production and assembly of the virus
- Provide structural stability, forming a strong framework that protects the viral genetic material
- Ability to self-assemble, simplifying the virus's life cycle and ensuring accurate and efficient capsid formation.
31
HIV and SARS-COV2 are both enveloped viruses while rotaviruses and polioviruses are non-enveloped. Which viruses are considered more stable and why?
- Non-enveloped viruses
- Their capsid is more stable than the enveloped viruses’ outer lipid envelope, which is fragile and sensitive to environmental conditions
32
How can viruses be classified based on their components?
Viruses can be classified based on their main components, such as the type of nucleic acid (DNA or RNA), capsid symmetry (icosahedral, helical, or complex), and the presence of an envelope (enveloped or non-enveloped/naked).
33
What are the classification characteristics based on nucleic acid?
Whether the nucleic acid is single-stranded or double-stranded, linear or circular, and whether it exists as one molecule or multiple segments.
34
How are enveloped icosahedral RNA viruses classified?
Enveloped icosahedral RNA viruses, such as SARS-CoV-2 and coronaviruses, are classified as enveloped viruses due to the presence of a viral envelope. They are also classified as icosahedral based on the symmetry of their capsid.
35
What are the limitations of classifying viruses based on morphology?
- Morphology alone does not provide information about the biology, pathology, or molecular biology of viruses.
- Similarities in morphology can exist among viruses with different fundamental characteristics, leading to inaccurate classifications.
- Molecular understanding is crucial for accurate virus classification.
36
What are the disadvantages of classification based on diseases?
- Focuses on some viruses and ignores others
- Single viruses may cause more than 1 disease
- Viruses infect more than 1 host (may affect different hosts differently)
37
What are the main criteria for the classification of viruses?
- Nucleic acid
- Type of nucleic acid DNA or RNA
- Single/double stranded
- Linear, circular, single molecule or segmented
- If single-stranded: negative or positive (polarity)
- Capsid symmetry
- Icosahedral, helical or complex
- Presence or absence of lipid envelope
38
What is meant by positive sense RNA?
RNA strand whose nucleotide sequence is identical to that of the mRNA.
It can act directly as mRNA for translation into a specific protein.
39
What is meant by negative sense RNA?
RNA strand whose sequence is complementary to the mRNA.
It cannot act directly as mRNA for protein translation.
It must first be replicated by RNA polymerases to produce the complementary +RNA strand.
40
What is meant by negative sense RNA?
RNA strand whose sequence is complementary to the mRNA.
It cannot act directly as mRNA for protein translation.
It must first be replicated by RNA polymerases to produce the complementary +RNA strand.
41
Can a complementary -RNA strand be translated into the same protein as the +RNA strand?
No, a complementary -RNA strand cannot be translated into the same protein as the +RNA strand because its nucleotide sequence has changed. It may not be translated at all or result in a different protein. The +RNA strand is required for accurate protein translation.
42
How can -RNA be converted into +RNA for protein translation?
In order for -RNA to act as mRNA, it must first be replicated by RNA polymerases to generate the complementary +RNA strand. The +RNA strand can then function as mRNA and be translated into a specific protein.
43
What is the relationship between replication and the conversion of +RNA to -RNA and vice versa?
Replication of +RNA can generate -RNA, and replication of -RNA can produce +RNA. These conversions are necessary for the RNA to act as mRNA and ensure accurate protein translation.
44
What is the basis of Baltimore system in classifying viruses?
How different viruses produce their mRNA and how they replicate their genomes
45
What are the main characteristics of viroid?
- Single circular ssRNA molecule
- No protein component
- Range in size from 220 to 400nt
- Rod-shaped or dumb bell shaped molecules
46
What are the main characteristics of prions?
- Abnormal forms of normal cellular proteins that can induce changes in the shape of their normal counterparts
- Leads to spongiform encephalopathies (progressive neurological degeneration and fatal diseases)
47
What are some examples of diseases caused by prions?
- Scrapie in sheep
- Bovine spongiform encephalopathy (BSE or "mad cow" disease) in cattle
- Kuru and variant Creutzfeldt-Jakob disease in humans
48
What is the impact of prions on cellular proteins?
- Induce changes in the shape of normal cellular proteins, leading to a cascade of detrimental effects.
- The altered protein structure caused by prions has catastrophic consequences for the host, resulting in progressive neurological degeneration and the characteristic spongy appearance of the brain observed post-mortem.
49
Describe the first step of viral replication: Recognition
Viruses can recognize specific structures on the host cell called cellular receptors through their VAPs
50
Describe the second step of viral replication: attachment
- The binding or attachment of the virus to the target cells through and interaction between these VAPs and specific cellular receptors
- Very specific and determines the host cell and the species range
51
Describe the third step of viral replication: entry
Virus enters / penetrates the cell into the cytoplasm
52
How do some enveloped virus enter host cell?
Some enveloped viruses fuse directly with the plasma membrane of the host cell.
53
What happens when enveloped viruses fuse with the plasma membrane?
Internal components of the virion (NA+ capsid) are immediately delivered to the cytoplasm of the cell
54
What happens when enveloped viruses can’t fuse directly w the plasma membrane?
Require an acid pH for fusion to occur
Taken up by the invagination of the membrane into endosomes
55
What happens after enveloped viruses are taken up by endosomes?
As the pH inside the endosomes drops, the viral envelope fuses with the endosomal membrane, resulting in the delivery of the internal components of the virus to the cytoplasm of the host cell.
56
What happens after enveloped viruses are taken up by endosomes?
As the pH inside the endosomes drops, the viral envelope fuses with the endosomal membrane, resulting in the delivery of the internal components of the virus to the cytoplasm of the host cell.
57
What is the role of acidic pH in the entry of these enveloped viruses?
The acidic pH inside endosomes triggers fusion between the viral envelope and the endosomal membrane. This fusion event allows for the release of viral components into the cytoplasm of the host cell.
58
How does the requirement for acidic pH impact the entry process of these enveloped viruses?
The need for an acidic environment and fusion with endosomes slows down the entry process compared to direct fusion with the plasma membrane. This additional step allows for a regulated and controlled release of viral components.
59
How are non-enveloped viruses taken up into endosomes?
Endocytosis then cross/destroy the endosomal membrane
60
Describe uncoating
Capsid destabilized inside cytoplasm → releases and delivers NA into cytoplasm or nucleus
61
What remains of the virus after uncoating?
Viral nucleic acid (NA) and any other enzymes present in the virus
62
How does the virus utilize the host cell machinery for protein synthesis and NA replication?
The virus hijacks the host cell's protein synthesis machinery to produce its own proteins and utilizes other cellular machinery for replication of its own nucleic acid.
63
Where is viral mRNA produced?
Viral mRNA is produced in the nucleus of the host cell, or sometimes the viral genomic RNA may act directly as mRNA.
64
How are new viruses assembled?
Once enough viral nucleic acid and viral proteins accumulate in the host cell, each copy of the nucleic acid is packaged into viral capsid proteins, resulting in the production of thousands of new viruses.
Typically occurs in the cytoplasm of the host cell
65
How do complex capsids assemble?
Assemble into empty capsid structure (procapsid) w the aid of scaffolding proteins
Scaffolding proteins are removed from procapsid before packaging viral NA
66
How do helical and icosahedral capsids assemble?
Assemble around viral NA
67
Describe characteristics of class 1 viruses. Give examples
- dsDNA genome
- Adenovirus
- Herpesvirus
68
Describe how class I viruses replicate
- Transcribed by RNA polymerase to produce viral mRNA
- Viral mRNA is read and translated by host ribosome to produce viral proteins
- Viral genome is copied/replicated by DNA polymerase to produce many dsDNA copies
- Each dsDNA is packaged w viral proteins to produce many new viral virions
69
How are dsDNA viruses grouped based on genome replication?
Those whose genome is copied by viral DNA polymerase and those whose genome is copied by host DNA polymerase.
70
What distinguishes larger dsDNA viruses from smaller ones in terms of replication?
Larger dsDNA viruses have a larger genome that encodes for a viral DNA polymerase, which the viruses use to replicate their genome.
In contrast, smaller dsDNA viruses have a smaller genome that does not have enough space to encode for a DNA polymerase, so they rely on the host DNA polymerase for replication.
71
Describe characteristics of class 2 viruses. Give examples
- ssDNA
- B19 → causes childhood febrile disease similar to rubella
72
How does ssDNA virus replication differ from dsDNA virus replication?
- In ssDNA viruses, the viral ssDNA cannot be transcribed by the host RNA polymerase directly. It must first be replicated by the host DNA polymerase to produce dsDNA
- The dsDNA can then be recognized and transcribed by the host RNA polymerase to generate viral mRNA.
73
How are viral proteins produced in ssDNA viruses?
- Transcribed dsDNA produces viral mRNA
- This is read and translated by host ribosome to produce viral proteins
74
How is the viral DNA replicated in ssDNA viruses?
- Viral ssDNA genome is replicated by host DNA polymerase
- Host DNA polymerase produces multiple copies of ssDNA
- These copies are packaged into viral proteins to create new viral particles
75
Describe characteristics of class 7 viruses. Give examples
- dsDNA but one of the DNA strands is complete but other is not
- Also has an RNA piece and a protein that is attached to it
76
How is the incomplete dsDNA genome of class VII viruses replicated?
- Incomplete dsDNA genome of class VII viruses cannot be recognized and copied by the host DNA polymerase
- So it first undergoes repair by cellular DNA repair polymerase → removes RNA piece and protein and fills the gap w DNA
- Result: complete dsDNA genome that can be recognized by host RNA polymerase for transcription
77
What is the role of reverse transcriptase (RT) in class 7 virus replication?
- RT: enzyme present in class VII
- Uses viral mRNA as a template to produce complementary -DNA strand
- -DNA strand is used to generate +DNA strand
- +DNA strand is incomplete n contains RNA piece n protein (RT)
78
How are new copies of the dsDNA genome assembled in class VII viruses?
The new copies of the dsDNA genome, produced through the action of reverse transcriptase, can be assembled along with viral proteins to create many new viral particles.
79
Why is the presence of RNA-dependent RNA polymerase (RdRp) important for RNA viruses?
RNA viruses need to encode the RdRp enzyme in their genomes because host cells do not possess this enzyme.
80
What is the role of RNA-dependent RNA polymerase (RdRp) in RNA virus replication?
Responsible for both producing viral mRNA for protein synthesis and synthesizing new RNA genomes for the production of viral particles.
81
How do RNA viruses ensure the production of both mRNA and RNA genomes?
- RNA viruses utilize RdRp to transcribe viral genome, generating viral mRNA that can be translated into viral proteins
- RdRp enzyme aids in replicating RNA genome → generating new copies of the viral genome for the production of viral particles
82
Describe how RNA viruses w +ssRNA replicate
- +ssRNA can act as mRNA → allows for direct translation of the genome by ribosome to produce viral proteins
- RNA replicase (viral protein) is required [host cells do not hv]
- RNA replicase replicates the viral genome, generating multiple copies of +ssRNA that can serve as viral genome
- These copies along w viral proteins assemble to produce new viruses
83
Describe how RNA viruses w -ssRNA replicate
- -ssRNA is replicated by RNA replicase → generates +ssRNA that can be used as mRNA
- RNA replicase replicates the viral genome, generating multiple copies of +ssRNA that can serve as viral genome
- These copies along w viral proteins assemble to produce new viruses
84
Describe how RNA viruses w -ssRNA replicate
- -ssRNA is replicated by RNA replicase → generates +ssRNA that can be used as mRNA
- RNA replicase replicates the viral genome, generating multiple copies of +ssRNA that can serve as viral genome
- These copies along w viral proteins assemble to produce new viruses
85
Give an example of a human virus family that has a dsRNA genome
- Reovirus
- Common member of this family is rotavirus
- Causes diarrhea and vomiting (esp in kids)
86
What is the replication process of dsRNA viruses?
- dsRNA viruses hv a segmented genome
- Viral dsRNA is used as a template by RdRp to produce +RNA
- +RNA acts as mRNA for translation of viral proteins
- RdRp is involved in replicating viral genome, generating multiple copies of dsRNA segments
- These copies, along w viral proteins, assemble to produce new viruses
87
How does a retrovirus replicate and integrate its genome into the host chromosome?
- Retroviruses use RT to convert their +RNA genome to dsDNA w RT
- Using RT, viral RNA produces complementary ssDNA
- ssDNA is used as a template by RT to produce another DNA strand (this is a dsDNA copy of the virus)
- dsDNA is delivered into nucleus and integrated into host chromosome using integrase
- Provirus (integrated viral DNA) is transcribed along w host DNA using cell replication
- Viral mRNA produced is translated by ribosome to produce viral proteins
- Some of the viral mRNA can also serve as the viral genome, which is packaged with viral proteins to produce new viral particles.
88
What are the different strategies that viruses used to enter the host cell?
- Fusing directly w the plasma cell
- Endocytosis
- Acid pH fusion
89
In viral infections, what determines the host and cell range? Give examples
The host and cell range in viral infections is determined by the ability of the virus to enter and replicate within specific host cells.
90
What are the main steps of viral replication?
- Recognition
- Attachment
- Entry
- Uncoating
91
Describe how a primary cell culture is prepared from animal organs or tissues
- A primary cell culture is freshly prepared from animal organs or tissues
- The cells are first extracted from tissues to break up tissue and release single cells.
- They must be suspended in a liquid culture medium in a Petri dish or tissue-culture flask
- Cells stop dividing due to contact inhibition.
- Cells must be transferred to another vessel with fresh growth medium.
- Primary cells are Diploid cells and have a limited life span as they undergo a finite number of divisions, from around 10 to 100,and can not be passaged for many times.
92
What are continuous cell lines?
Cell cultures that originate from naturally occurring tumors.
93
How are continuous cell lines different from primary cells?
- Continuous cell lines are immortal and can divide indefinitely, whereas primary cells have a limited lifespan.
- Continuous cell lines are also heteroploid, meaning they have an abnormal number of chromosomes, while primary cells typically have a normal diploid chromosome count.
94
What is contact inhibition, and how does it relate to continuous cell lines?
Contact inhibition is a phenomenon where cells stop dividing when they come into contact with neighboring cells. Continuous cell lines may have lost their contact inhibition, allowing them to grow in piles or lumps, unlike primary cell cultures.
95
How can continuous cell lines be maintained and propagated?
Passaging: transferring a small number of cells from an existing culture into a new culture vessel, allowing them to continue growing and dividing
96
Why are continuous cell lines called "immortal"?
Continuous cell lines have the ability to divide indefinitely without entering senescence or undergoing programmed cell death (apoptosis) [genetic alterations acquired during their transformation from normal cells to tumor cells]
97
TERM: Cyto pathic effects (CPE)
Distinct observable cell abnormalities/changes in the cells due to viral infection
98
TERM: hemadsorption
Cells infected w certain viruses acquire the ability to bind to n absorb RBC
99
How is hemadsorption related to virus detection?
- Some viruses (e.g. influenza, parainfluenza, measles, mumps) hv haemagglutinins (HA) (surface glycoproteins)
- HA molecules recognize n bind to susceptible host cells
- By adding RBC of appropriate species to cell culture, if viruses are present n actively replicating, RBC will adhere to infected cells → results in hemadsorption
100
Caveats of cell culture
- Relatively slow
- Low sensitivity
- Successful culture depends on the viability of the virus in the specimen
- Cell cultures are v susceptible to the bacterial contamination
- Cell culture is not applicable to a number of viruses
- Hepatitis B, parovirus
101
Which viruses can produce CPE within one day of inoculation in cell culture?
Herpes simplex viruses
Occasionally enteroviruses
102
What is a common problem with virus culture in terms of sensitivity?
The sensitivity of virus culture is often low, meaning that some viruses may not be readily detected using this method.
103
Why is proper collection and transportation of the specimen important for successful virus culture?
The viability of the virus in the specimen is crucial for successful virus culture. Therefore, the sample must be collected and transported correctly to ensure its good quality.
104
What are the challenges related to bacterial contamination in cell culture for virus detection?
Cell cultures are highly susceptible to bacterial contamination, requiring the addition of antibiotics to prevent such contamination. Additionally, experienced personnel are needed to perform cell culture techniques effectively.
105
What are the main methods of quantifying viruses?
- Measuring the number of viral particles → EM
- Measuring the number of infectious viral particles → ELISA and IMF
106
Characteristics of electron microscopy
- Timing consuming
- Expensive
- Requires skilled personnel
107
What is the principle behind the enzyme-linked immunosorbent assay technique?
- Sample (serum) is added to a plate coated w a capture antibody that binds to target antigen
- If antigen present → binds to antibody
- Secondary antibody is added, which recognizes n binds to different region of the antigen or to Fc region of primary antibody
- Secondary antibody is conjugated w an enzyme (e.g. HRP)
- Substrate is added to system
- Conjugated enzyme (HRP) cleaves substratem resulting in colour change
- Intensity of colour change = amt of antigen/antibody present in the sample
108
What is the principle of the plaque assay for virus quantification?
- Monolayer of susceptible host cells is prepared in an agar plate.
- The sample containing an unknown concentration of the virus is added to the cells, allowing the virus to attach and infect the cells.
- A semi-solid overlay of agar is then added to prevent diffusion. During incubation, the viruses infect cells and produce new viruses → formation of multiple holes or plaques (zones of cell lysis).
- Each plaque represents the lysis caused by a single viral particle. The number of plaques in the plate is counted, and the concentration of the virus is calculated as plaque-forming units per milliliter (PFU/ml), where PFU represents the number of plaques or viral particles in 1 ml of the original sample
109
What is the plaque assay used for in virus quantification?
Allows for the determination of the concentration of infectious viral particles in a sample.
110
What types of viruses can be quantified using the plaque assay?
Viruses that cause cell lysis
111
Why is serial dilution necessary in the plaque assay?
To reduce the concentration of viruses in each solution. This is done to ensure that the number of plaques formed is within a countable range (between 30-300 plaques) to obtain an accurate viral titer measurement.
112
What dye is commonly used in the plaque assay to visualize plaques?
Crystal violet [stains only live cells, helps visualize cleared areas or plaques on agar plates]
113
How is the AID50 (Animal Infectious Dose 50) determined?
- Performing 10 fold serial dilutions of sample containing the virus
- Each dilution is used to infect 4 animals
- After incubation, the number of infected animals is counted
- Dilution causes infection in 2/4 animals is considered to hv 1 AID50 unit
114
What is the purpose of the direct hemagglutination assay (HA) in virus detection?
Detect the presence of viruses, such as influenza, in samples. It relies on the ability of certain viruses to bind to and agglutinate red blood cells (RBCs), causing hemagglutination.
115
How is the direct hemagglutination assay (HA) performed?
- Sample containing the virus is mixed with a fixed standardized amount of RBCs.
- The assay is carried out in a microtiter plate with V- or round-bottomed wells.
- If agglutinating viruses are present in the sample, the RBC and virus clump together, producing a diffuse mat over the bottom of the well (agglutination).
- In the absence of the virus, the red blood cells roll or sediment to the bottom of the well and form a dense pellet. Flat-bottomed wells cannot be used in this assay.
116
What is the main difference between the HA assay and other virus quantification methods like the plaque assay or TCID50?
Unlike other methods of virus quantification (such as the plaque assay or TCID50), the HA assay does not provide estimates of viral infectivity, as virus replication is not required for this assay.
The HA assay specifically detects the presence of agglutinating viruses and is not a measure of viral replication or infectious viral particles.
117
Describe the lag phase
No increase in the number of living bacterial cells
118
Describe log phase
Exponential increase in number of living bacterial cells
119
Describe stationary phase
Plateau in number of living bacterial cells
Rate of cell division and death roughly equal
120
Describe death phase
Exponential decrease in number of living bacterial cells
121
Describe inoculation (virus single step growth cycle)
Inoculum of virus binds to cells
122
Describe eclipse (virus single step growth cycle)
Virions penetrate the cell
123
Describe burst (virus single step growth cycle)
Host cells release many viral particles
124
Describe burst size (virus single step growth cycle)
Number of virions released per bacterium
125
What aspect of the life cycle of a virus leads to the sudden increase in the growth curve?
Typically attributed to the exponential replication of the virus within a host.
During the early stages of infection, the virus enters host cells and starts to replicate. As the virus multiplies, the number of infected cells and the amount of viral genetic material increase rapidly. This leads to a sudden surge in viral load, resulting in a steep rise in the growth curve.
126
CPE examples
Cell rounding: Infected cells lose their normal flat appearance and become rounded.
Cell detachment: Infected cells detach from the surface and float freely.
Syncytium formation: Infected cells fuse together, forming multinucleated giant cells.
Cell lysis: Infected cells burst open, releasing newly produced viruses.
These effects can be observed under a microscope and are indicative of viral infection and replication within the host cells.
127
How would you detect non-CPE-producing viruses?
Non-CPE-producing viruses are viruses that do not cause obvious visible changes or damage to the infected host cells. Detecting such viruses may require alternative methods that do not rely on the observation of CPE. Some techniques that can be used to detect non-CPE-producing viruses include:
- Molecular methods: Polymerase chain reaction (PCR), reverse transcription PCR (RT-PCR), and other nucleic acid amplification techniques can directly detect viral genetic material.
- Serological assays: These tests detect the presence of specific antibodies produced by the host in response to viral infection.
- Electron microscopy: Viruses can be visualized using electron microscopy, which allows for their direct observation without relying on CPE.
128
What are the main advantages of cell culture
- Viral isolation and propagation: Cell culture provides a controlled environment for the growth and replication of viruses. It allows researchers to isolate and propagate viruses in the laboratory, facilitating their study and characterization.
- Virus quantification: Cell culture techniques enable the quantification of viral particles or viral replication within host cells, providing valuable information about viral growth kinetics and the effectiveness of antiviral treatments.
- Vaccine development and testing: Cell culture systems can be used to produce viruses for vaccine development. They also serve as a platform for testing the efficacy and safety of vaccines.
- Mechanism of viral infection: Cell culture allows researchers to investigate the mechanisms by which viruses enter cells, replicate, and cause disease. It provides insights into host-virus interactions and the development of antiviral therapies.
129
How can you use hemadsorption to identify viruses?
Hemadsorption is a technique used to identify viruses that possess the ability to bind red blood cells (erythrocytes). In this method, host cells infected with hemadsorbing viruses are mixed with red blood cells. If the virus has the capability to bind to the red blood cells, the infected cells will show clumping or adherence of red blood cells to their surface
130
Susceptible cell
Expresses the specific receptors that are recognised by a specific virus through specific VAPs
131
Permissive cell
Contains proteins n molecules within the cell that are necessary for replication to occur
132
Resistant cell
Has no receptor
May or may not be able to support viral replication
133
Non-permissive cell
Does not support viral replication
May or may not be susceptible
134
What are the 5 portals of virus entry?
- Skin
- Respiratory tract
- GI tract
- Genital tract
- Conjunctiva (eye)
135
How do viruses enter the respiratory tract?
Enter mainly via respiratory droplets
136
Explain why the size of the droplets are important
- Large droplets rapidly fall to the ground
- Small droplets dry very quickly
- Middle-sized droplets are inhaled n transmit infections most efficiently
137
What are the conditions of GI tract?
- Stomach acidity
- Low pH
- Digestive enzyme
- Bile in intestines
138
Why do enveloped viruses rarely cause infections in the GI tract?
Inactivated due to harsh conditions [susceptibility of their envelopes]
139
How do viruses enter the skin?
- Trauma / inoculation
- Medical procedures
- Sharing needles
- HBC
- HBV
140
Vertical transmission
Transfer of virus from the mother
141
Examples of intrauterine viral infection
Rubella virus and CMV
142
Examples of perinatal transmission
Neonatal HSV
143
Localized infections
- Viruses infect and replicate only within cells at the initial site of infection.
- Example: Rhinovirus infects epithelial cells of the upper respiratory tract, causing diseases restricted to the upper respiratory tract.
144
Systemic infections
- Viruses infect the initial site of entry, replicate locally, and then spread to other sites within the body.
- Example: Measles virus enters through the respiratory tract but causes infections in other locations.
145
Measles virus
- Enters the body through the respiratory tract.
- Causes systemic infections, spreading to various locations in the body.
146
Poliovirus
- Enters the body through the gastrointestinal (GI) tract.
- Rarely causes GI infection.
- Spreads to neurons, leading to paralysis.
147
Examples of localized infections
- Rhinovirus: Infects upper respiratory tract epithelial cells, causing upper respiratory tract diseases.
- Papillomavirus: Infects skin epithelial cells, causing skin warts on hands, feet, and other areas.
148
Localized infections
- Viruses are shed from the primary site of infection.
- HPV strains that infect the skin are spread through skin-to-skin contact.
- Respiratory viruses like rhinovirus and coronaviruses are shed within respiratory secretions.
- Examples: HPV, rhinovirus, coronaviruses.
149
Gastrointestinal infections
- Gastrointestinal viruses like poliovirus and rotavirus are shed in feces.
- Contaminated food or water can transmit these viruses to a new host.
- Example: Poliovirus, rotavirus.
150
Genital infections
- Viruses like HIV and herpesviruses replicate within genital compartments.
- Shed in semen or vaginal secretions.
- Can be transmitted through sexual contact.
- Example: HIV, herpesviruses.
151
Conjunctivitis
- Adenovirus is shed in tears and eye discharge.
- Can be transmitted to others through contact with infected secretions.
- Example: Adenovirus conjunctivitis.
152
Viremia
- Some viruses can be found in the blood and can be transmitted through blood.
- Presence of virus in the blood
- Common occurrence of infection with several viruses including HIV and hepatitis.
153
Uraemia
- The presence of virus within the urine
- Occurs within several systemic viral infections
154
Uraemia
- The presence of virus within the urine
- Occurs within several systemic viral infections
155
What characteristics must a gastrointestinal virus possess in order to effectively infect through this route?
Stability in the gastrointestinal environment.
Resistance to bile salts.
Efficient replication in intestinal cells.
Fecal-oral transmission.
Efficient viral shedding in feces.
Resistance to the host immune response.
156
Pathogenesis
The ability/capacity of the virus to cause disease
157
Virulence
Quantitative or relative measure of the pathogenesis of the infecting virus
158
What are the 4 mechanisms of viral injury and disease?
- Direct cytotoxicity of the virus
- Virus-induced immunopathogenesis
- Virus-induced immune suppression
- Virus-induced transformation
159
How does poliovirus cause damage to the host?
Poliovirus kills neurons, leading to paralysis of muscles innervated by those neurons.
160
What is the effect of Ebola virus on host cells?
Ebola virus damages vascular endothelial cells, resulting in hemorrhage.
161
Describe virus-induced immunopathogenesis
Tissue injury may reflect host defense mechanisms that include apoptosis or immune responses that target virus-infected cells
162
Describe HBV in terms of virus-induced immunopathogenesis
Viral antigens on infected hepatocytes recognized by cytotoxic T cells
163
Describe HCV in terms of virus-induced immunopathogenesis
Ag-Ab complexes deposit within small blood vessels and leading to the development of inflammation
164
Describe virus-induced immune suppression
- Some viruses can specifically target and infect cells of the immune system
- Causes immunodeficiency
165
What are some examples of viral infections that can directly promote tumor development?
- Human papillomaviruses (HPV)
- HPV can cause several types of cancer, including cervical cancer, by encoding proteins such as E6 and E7 that interfere with cell cycle progression checkpoints and promote cellular transformation.
166
Do all infections with oncogenic viruses lead to the development of cancer?
Multiple additional factors, such as the individual's immune system and other environmental and hormonal factors, determine the risk of developing disease.
167
What is the role of the immune response in reducing the risk of developing Epstein-Barr virus (EBV)-associated cancers?
The viral proteins of EBV are recognized by the host immune response. Individuals with healthy immune systems are at a much lower risk of developing EBV-associated cancers due to the immune system's ability to control viral infection.
168
Which high-risk genotypes of human papillomavirus (HPV) are associated with a greater risk of developing cervical carcinoma?
- HPV 16 or 18 are associated with a much greater risk of developing HPV-associated cervical carcinoma.
- The specific HPV genotype plays a role in determining the risk of cancer development.
169
Describe how HIV replication occurs
- Interaction between the viral attachment proteins which is known as gp120 and the cellular receptor CD4
- Entry of the virus into the host cells
- The viral nucleic acid is released from the capsid
- Synthesis of viral proteins
- Replication of nucleic acid
- Assembly
170
What are the 3 phases of the clinical course of HIV infection?
- Acute
- Chronic
- AIDS
171
What is the AIDS phase characterized by?
Increased susceptibility to opportunity infections
172
Describe what occurs during the acute phase of HIV infection
Infection of activated CD4+ T cells in mucosal lymphoid tissues n the death of many infected cells
173
Do CD4+ T cell counts return to normal in individuals with HIV infection?
- Yes, in many cases, the number of blood CD4+ T cells can return to normal levels.
- This is because the individual may continue to produce new CD4+ T cells, which allows for the replacement of these cells almost as quickly as they are destroyed.
174
Describe what occurs during the chronic phase of HIV infection
- Virus spreads throughout the body to infect helper T cells, macrophages and dendritic cells in peripheral lymphoid tissues
- Virus is contained within lymphoid tissues n the loss of CD4+ T Cells is replenished from progenitors
175
Describe what occurs during the AIDS phase of HIV infection
- Lymph nodes n the spleen are sites of continuous HIV replication n cell destruction
- Number of circulating blood CD4+ T cells steadily declines
- Continuous cycle of virus infection, T cell death n new infection leads to loss of CD4+ cells
176
Why do AIDS patients become susceptible to many different types of infections?
- CD4+ helper T cells are essential for both cell-mediated n humoral immune response to various microbes
- Thus, the loss of these lymphocytes lead to high susceptibility of different types of infections
177
What are the consequences of viral protein production and budding during HIV infection?
- Increase in plasma membrane permeability, which can result in:
- Influx of lethal amounts of calcium, leading to apoptosis (programmed cell death).
- Osmotic lysis of the cell caused by the influx of water
- Interference with cellular protein synthesis, potentially leading to cell death.
- All these contributes to the overall damage n destruction of infected cells during HIV infection
178
How are virus-infected CD4 cells targeted and killed during HIV infection?
- Virus-infected CD4 cells can be recognized by specific CD8 T cells.
- These CD8 T cells directly target and kill the infected CD4 cells through the induction of perforins and granzymes.
179
What are the effects of HIV infection on T cell responses to antigens and humoral immune responses?
HIV infection leads to a decrease in T cell responses to antigens and weak humoral immune responses.
180
How does HIV infection leads to a decrease in T cell responses to antigens and weak humoral immune responses?
- In infected CD4 T cells, CD4 receptors are bound to gp120 (viral protein) → makes them unavailable to interact w major histocompatibility complex class II (MHC II) molecules on APCs
- Interaction b/w APCs n CD4 T cells is important for the activation of other T cells n activation of B cells to induce antibody prodcution
- Thus, the impairment of this interaction due to binding of gp120 to CD4 receptors hinders proper functioning of immune response → reduced T cell responses n weakened humoral immune responses in HIV-infected individuals
181
What is the role of NSP4, the nonstructural glycoprotein of rotavirus?
- NSP4 acts as a viral enterotoxin that inhibits a co-transporter involved in fluid balance
- Inhibition leads to fluid leakage out of cells → causes diarrhea
- NSP4 also stimulates intracellular calcium release → further promoting fluid removal
