Viral Infections Flashcards
1
Q
What are most viruses inactivated by?
A
Heat
Desiccation
UV light
2
Q
What type of viruses are particularly resistant to Heat, Desiccation or UV light?
A
viruses that infect via the faecal oral route
3
Q
What are the types of transmission?
A
Horizontal (host to host)
Vector-borne (host to vector to host)
Vertical (mother to child)
4
Q
What are the portals of entry into the host for a virus?
A
Eyes (conjunctiva)
Mouth
Skin
Urogenital tract
Anus
5
Q
entry for a virus into the host via the mouth?
A
Respiratory tract
Alimentary canal
6
Q
Entry for a virus into the host via the urogenital tract?
A
Vagina/urethra/penis
Placenta
7
Q
Entry for a virus into the host via the skin?
A
abrasion/injury
arthropod vector
animal bite
8
Q
What portal of entry into a host do Adenovirus (8, 22) and Herpes simplex virus use?
A
Eyes
9
Q
What portal of entry into a host do Japanese encephalitis virus and West Nile virus?
A
Skin via animal bite
10
Q
What portal of entry into a host do Dengue virus and Rabies virus use?
A
Skin via animal bite
11
Q
What portal of entry into a host do Herpes simplex virus (HSV-1), Human papillomavirus, Ebola virus,
and Molluscum contagiosum virus use?
A
Skin via abrasain or injury
12
Q
What portal of entry into a host do Norovirus, and Rotavirus use?
A
Gastrointestinal
13
Q
What portal of entry into a host do Adenovirus (40 & 41),
Hepatitis A virus, and Poliovirus use?
A
Gastro intestinal
14
Q
What portal of entry into a host do Measles Mumps and Rubella use?
A
Respiratory
15
Q
What portal of entry into a host do Influenza virus and Rhinovirus use?
A
Respiratory
16
Q
What portal of entry into a host do Hepatitis B virus, Human papillomavirus, and Rubella virus use?
A
Urogenital
17
Q
What are the types of viral tropism?
A
Cellular
Tissue
Host
18
Q
What is a virus called when it can infect many cell types and tissues?
A
pantropic
19
Q
What are the four factors for a cell to infect a particular cell and tissue type?
A
Presence of entry receptors on host cell (susceptibility)
Production of cellular factors required to complete replication cycle (permissivity)
Physical barriers (accessibility)
Intrinisic and innate immune defences (immunity)
20
Q
What happens during the dissemination mechanism of direct cell to cell contact?
A
Virus moves directly from infected cell to uninfected cell without entering the extracellular space
21
Q
What is an advantage of disseminating via direct cell to cell contact?
A
Avoids host immune effectors
22
Q
What is viraemia?
A
Dissemination mechanism via the blood stream (haematogenous spread)
23
Q
What happens during active viraemia?
A
viruses infect cells/tissue at primary site of infection and then enter the bloodstream e.g. by budding into capillaries or blood vessels
24
Q
What happens during passive viraemia?
A
viruses may get into the bloodstream by direct inoculation e.g. arthropod vectors; blood transfusion; sharing of non-sterilized needles
25
What is an example of a virus that disseminates via active viraemia?
Measles
26
What is an example of a virus that disseminates via passive viraemia?
flavivirus
27
How long is the duration of accute viral infection?
1-2 weeks
28
How long does a chronic viral infection last?
Months to years
29
How long does a latent viral infection last?
Hosts lifetime
30
How does a chronic viral infection spread?
Continuous shedding of viral particles
31
What does the virus do during a latent viral infection?
Episodic reactivations
Viral genome may be integrated into host chromosome or remain as episome
Maintenance of latency usually requires a few viral genes to be expressed to silence rest of viral gene expression
32
What mediums are used for horizontal transmission?
Saliva (*Fomites)
Blood
Semen
Urine
Faeces
Direct contact with skin/ mucosal membranes
Animal bite
33
What medium of infection for horizontal transmission do both HIV and ebola use?
semen
34
What medium of infection for horizontal transmission do both HIV and HBV use?
blood
35
What medium of infection for horizontal transmission does Hantavirus use?
Urine
36
What medium of infection for horizontal transmission do enteroviruses and rotaviruses use?
direct contact with skin/ mucosal membranes
37
Why are many respiratory viruses enveloped?
Damp environment – viruses more stable
38
What is the surface area of a human lung?
30-50m
39
Why is the intestinal epithelium a good place for viruses to reproduce?
constantly replicating so this is a productive environment for viral replication
40
Viruses that replicate here have to be acid stable, resistant to bile salts and proteases
Where?
GI tract
Less common for enveloped viruses to infect here
41
How do the eyes protect themselves from infection?
Basal tears constantly wash surface of eye and remove foreign particles
42
What causes conjunctivitis?
Localised viral infection leads to inflammation of conjunctivae
43
What is the conjunctivae?
Inner surface of eyelid
44
What happens if there is a systemic spread from conjunctivits due to enterovirus 70?
paralytic illness
45
What happens if Herpes virus 1 infects via a micro-abrasion of cornea?
immune destruction of cornea / retina leading to blindness, also spreads systemically to infect neurons in sensory ganglia (latent infection)
46
How does the epidermis act as an effective barrier from viral infection?
Epidermis is
- dead layer of cells do not support viral infection
- devoid of devoid of blood vessels, lymphatics and nerve fibres so viruses that initiate epidermal infections are typically restricted to the site of entry and can only spread within the host if they can cause viraemia
47
What are arboviruses?
Transmitted via arthropods
48
For the arboviruses Japanese encephalitis virus and Dengue virus a human host has different outcomes? What are they
For Japanese encephalitis virus a human host is a dead end but for dengue virus it is apart of the cycle
49
What is a zoonose?
Virus that goes from animal to human
50
Why is the urogenital tract an inhospital environment for viruses?
Vagina low pH 3.4 – 4.5, mucus traps virus particles
flow of urine in urethra
51
What is vertical transmission?
Mother to child transmission
52
What does in utero mean?
virus has ability to cross placenta e.g. varicella-zoster virus; rubella virus, HIV, Zika virus
53
What are the modes of vertical transmission?
in utero
during childbirth
in breastmilk
54
What are the methods of diagnosis for viral infections?
Patient signs and symptoms
Virus culture
Microscopy
Serology
Molecular diagnostics
55
In a Tzanck smear of acetone fixed cells from a skin lesion it reveals a multinucleate giant cell syncitium.
What Virus is causing this?
HSV induced cell fusion
56
Owl eye intranuclear inclusions in lung tissue
| What Virus causes this? (H&E stain)
cytomegalovirus
57
When observing a virus cell culture what should you look for?
Cytopathic effects (CPEs)
Rounding
Inclusion bodies
Giant cells (Syncitia)
58
Why are many virus types difficult to culture perhaps even unculturable?
Some cell types are very difficult to culture
Some viruses require additional components in growth media
59
What is ELVIS?
enzyme linked virus inducible system
| a genetically engineered cell line expressing reporter genes for HSV
60
What does a haemagluttination assay do?
Measures ability of virus in sample to agglutinate RBCs
61
What does the haemagluttination inhibition assay do?
Measures ability of antibody in sample to interfere with virus-induced agglutination of RBCs
62
What does the complement fixation test do?
Measures ability of antiviral antibodies to fix complement and prevent lysis of indicator RBCs
63
What is a chromogenic antibody?
detected by microscopy or automated reader
| produces a coloured product
64
What is luminescent antibody?
detected by film exposure or automated reader
| produces a luminescent product
65
What is a Fluorescent antibody?
detected by UV microscopy or automated reader
| Produces a Flourophore that produces flourescense
66
What is a radiometric antibody?
detected by film exposure or automated reader
| produces radiation
67
What is the ELISA test?
Enzyme Linked immunoabsorbant assay
Use to detect antigen in sample or to detect antibodies specific to virus (seroconversion)
Direct, indirect or “sandwich” capture assays
68
What happens during a direct ELISA?
an antigen or sample is immobilized directly on the plate and a conjugated detection antibody binds to the target protein
69
What happens during an indirect ELISA?
Two step process for detection
primary antibody specific to antigen binds to target
abeled secondary antibody against the host species of the primary antibody binds to the primary antibody for detection
70
What happens during a sandwich ELISA?
```
Two antibodies (matched antibody pairs)
One of the antibodies is coated on the surface of the multi-well plate and used as a capture antibody to facilitate the immobilization of the antigen. The other antibody is conjugated and facilitates the detection of the antigen.
```
71
What are the methods of detection of viral nucleic acids?
Southern / Northern blotting
Restriction fragment length polymorphism (RFLP) of nucleic acid purified from cultured virus
In situ hybridisation to directly label virus in samples or in culture using nucleic acid probes
Nucleic acid amplification
High throughput sequencing
72
For detecting viral nucleic acids via nucleic acid amplification what are some methods of doing this?
PCR for DNA viruses
RT-PCR for RNA viruses
73
For an efficient antiviral what two factors need to be focused on?
Specifity
| Selectivity
74
Why is the selectivity of an antiviral important?
so it targets the virus not the host
75
Why is specifity of an antiviral important?
So it targets one desired target in the virus
76
What is the preferred antiviral?
One that targets virus components
| because less likely to cause side effects
77
What is CC50?
concentration at which cytotoxicity is 50% (half of treated cells die)
78
What is EC50?
concentration which is 50% effective in producing the desired outcome
79
What is the calc for therapeutic index?
Therapeutic index = CC50 / EC50
80
What is better Higher or lower therapeutic index?
Higher TI is better, and TI of 100-1000 is desirable for a drug
81
What do mutations allowing resistance to antivirals often also cause?
A fitness cost
| ie. being worse at survival within the host
82
What is the classical approach to the development of antivirals?
Classical approach: high throughput screening
Chemical libraries screened in multi-well cell culture assays
Lead compound identified
83
What is involved during x-ray crystalography for the development of antivirals?
Structural conformation of viral protein e.g. during target binding
Computer modelling (in silico) used to map potential interactions with extensive number of molecules
If they mimic substrate halfway through enzyme catalysed reaction “transition state mimetics”
Refined by chemical modifications to improve specificity, stability, delivery to target cells and formulation
84
What is the order of the development pathway for antiviral development?
```
Target identification (in silico testing)
Initial screening
In vitro testing
In vivo testing (pre clinical)
Small-scale safety trial in humans
Small-scale efficacy trial in humans
Large-scale human trials
New drug applications
Approval for use
```
85
During antiviral testing how should you look for Reduction in virus titre (in vitro and in vivo)
Plaque assay - count of infectious virions
TCID50 (Tissue culture infectious dose sufficient to infect 50% of cultures)
86
During antiviral testing how should you look for the Reduction of viral biomarkers?
RNA or DNA via quantitative (RT)-PCR, protein via Western blot
87
During antiviral testing how should you look for the Reduction cytopathic effects (CPE)?
Number and size of lesions in target organ
Reduction in tissue markers of infection
88
During antiviral testing how should you look for the reduction in clinical signs of disease?
Symptoms eg. fever or weight loss
89
What is bioavailability?
getting more drug to the infected site
90
What is therapeutic index?
Ratio of benefit versus undesirable side effects
91
How can passive immunity be achieved in antiviral therapy?
Passive immunity provided by injecting anti-virus neutralizing antibodies may help clear viral infection (mAbs, convalescent sera)
92
How can Zmapp be effective in treating ebola?
Zmapp contains three chimeric monoclonal antibodies
Synthesised in tobacco plants by infiltrating Agrobacterium expressing anti-Ebola antibody genes into leaves
Shown to be effective in animal studies but experimental in humans
93
What are immunomodulators?
Immunomodulators affect the immune response to viral infections
Often used in combination therapies
94
What is interferon alpha?
An immunomodulator
A cytokine used in the treatment of genital warts caused by HPV, Kapossarcoma lesions caused by HHV-8, and hepatitis caused by hepatitis B and C viruses
95
What is Imiquimod?
An immunomodulator
| stimulates macrophages to secrete cytokines and is used in the treatment of genital warts caused by HPV
96
What is Inosine pranobex?
An immunomodulator
| an immune stimulant used to treat HSV-1 and HSV-2 infections and also to treat measles complications
97
What is one of the most effective combination therapies?
Highly active antiretroviral therapy (HAART)
98
What does HAART do?
Highly active antiretroviral therapy (HAART) combines at least 3 different antivirals from at least 2 classes
99
Why does combination therapy help fight resistance to antivirals?
helps combat resistance as mutations conferring resistance to one drug can have even higher fitness cost in presence of another drug
100
How can you prevent viral infections?
Good hygiene & sanitation
Passive immunisation
Vaccines
101
What is Palivizumab?
humanized monoclonal antibody (IgG) directed against an epitope in the A antigenic site of the F protein of the Respiratory Syncytial Virus (RSV
Method for passive immunity in prevention of viral infections
102
How does Palivizumab work?
Inhibits RSV (respiratory synical virus) entry into the cell and thereby prevents infection
103
How is Palivizumab administered?
Injection once a month during respiratory synical virus season
104
What does passive immunisation using palivizumab demonstrate?
that humoral antibody plays a major role in protection against disease caused by RSV but currently no vaccine available
105
What is VZIG / VariZIG (Varicella-Zoster immunoglobulins) used for?
used to protect people at risk of severe complications from chicken pox
via passive immunity
106
What are live attenuated vaccines?
Replication competent viruses capable of infection but in which the ability to cause disease is weakened (attenuated) by mutation
107
How are viruses mutated to make them suitable for live attenuated vaccines?
Mutations induced by passaging virus in semi-permissive cells or animals and/or under altered conditions e.g. low temp
108
Who can live attenuated vaccines not be used on?
Cannot be used in immunocompromised (inc. elderly)
109
What sort of host immune responses can live attenuated vaccines activate?
Can be highly immunogenic and activate both serological (via MHC-II) and cell-mediated (via MHC-I) immune response
May generate mucosal immunity (IgA) which can enhance protection against some viruses that infect via mucosal membranes
110
During distribution what conditions do live attenuated vaccines need to be in?
cold chain
| refridgeration
111
What are inactivated vaccines?
Whole inactivated (“killed”) vaccines produced by culturing virus and then chemically inactivating
112
In an inactived virus vaccine what does the virus do and what does this mean for the vaccine?
Do not replicate in host so less immunogenic and require higher doses and booster doses
113
What sort of host immune responses can inactivated viruses stimulate?
Activate serological (via MHC-II) response but unable to stimulate cell-mediated (via MHC-I) immune response
114
What is the best sort of virus to use an inactivated vaccine for?
Best used against viruses where serum neutralising antibody is protective
115
Can inactivated vaccines be used in the immunocompromised?
Cannot cause infection so used in immunocompromised
| but must be sure is 100% inactivated to avoid the Cutter (1955) incidence
116
What was the Cutter (1955) incident?
Cutter incident in 1955 where inactivated Polio vaccine was improperly inactivated and 400 000 doses given to children in US reulting in 200 cases of paralytic poliomyelitis and 10 deaths
117
What is the method of inactivation for viruses for the inactivated vaccine? And what must be preserved?
Method of inactivation (e.g. formaldehyde, β-propiolactine) is critical as must preserve antigens without denaturing or altering them (RSV vaccine failure)
118
What are subunit vaccines?
Purification of immunogenic viral proteins from whole virus
119
What is an example of a subunit vaccine?
influenza trivalent inactivated vaccine contains HA and NA from 2 Influenza A and 1 Influenza B strain
120
What are cheaper to use prokaryotic or eukaryotic expression systems for making a subunit vaccine?
Prokaryotic expression systems are cheaper and easier to use, but may not produce proteins with correct post-translational modifications and may have problems with solubility
121
What is used to make cloned subunit vaccines?
A range of expression systems have been used to express recombinant viral proteins
122
What is a VLP vaccine?
Capsid proteins may be cloned, expressed and assembled to make virus-like particles (VLP)
Contain conformational epitopes not found in purified subunits
Non infectious (lack nucleic acid), no inactivation required
123
What sort of vaccine is the Hepatitis B vaccine?
Hepatitis B vaccine is VLP formed from HBsAg produced in yeast
124
How are VLP vaccines for HPV formed?
HPV vaccines are VLPs formed of L1 made in yeast (Gardasil) and insect cells (Cervarix)
125
What are adjuvants?
additives in vaccine preparation
enhance presentation of antigen and uptake by APCs
directly stimulate the immune response (cytokines or APCs)
localise antigen to site of inoculation (depot effect) & provoke an intense local immune stimulation (not diffuse)
target antigens to a particular immune response pathway
126
What do aluminium salts do as an adjuvant?
Aluminium salts have depot effects and are used in several vaccines
127
What does Squalene oil and surfactant emulsion based adjuvant MF59 do?
used in some influenza vaccines can carry antigens into the cytoplasm and stimulate cytotoxic T-cell response (MHC-I)
128
What is being devloped to happen during nucleic acid based vaccines?
Plasmid DNA carrying genes encoding viral antigens under control of strong eukaryotic promoter
Cannot replicate in host, but once inside nucleus it will be expressed
Can stimulate both arms of the immune response (antibodies and CTL)
129
WHat is the main problem for the devlopment of nucleic acid based vaccines?
Delivery method is the main problem – intramuscular injection; small gold beads from gene gun; mucosal delivery
130
What does a recombinant vector vaccine do?
Attenuated viruses can be used as viral vectors by inserting genes from a pathogenic virus into a replication defective variant – only capable of undergoing one cycle of replication in human but viral proteins are produced
131
What immune responses does a recombinant vector vaccine stimulate?
Can stimulate full range of immune responses
132
What is a negative to recombinant vector vaccines?
Once used in a person, the same vector cannot be used again due to immune response to the vector
