Virus Flashcards
(78 cards)
1
Q
What is viral latency?
A
Virus lies dormant (latent) within a cell
2
Q
What are the 7 stages of viral replication?
A
- Attachment
- Penetration (endocytosis)
- Uncoating ( viral contents released)
- Transcription/ mRNA production
- Synthesis of virus components
- Virion assembly
- Release (liberation stage)
- Absorption
3
Q
What are the four types of viruses?
A
- Icosahedral
- Helical
- Helical and icosahedral (bacteriophage)
- Enveloped (Virion, Extracellular)
4
Q
Viruses can be categorised dependent on their shape or sizes. What are the 4 groups?
A
- filamentous
- isometric (or icosahedral)
- enveloped
- head and tail (icosahedral and helical)
5
Q
- dsDNA and ssDNA
- genome must be transcribed into mRNA prior to viral replication
A
DNA viruses
6
Q
What are the (7) Baltimore groups?
A
- DNA viruses
- RNA viruses
- Retroviruses
7
Q
This is defined as processes by which viral infection results in a disease
A
Viral pathogenesis
8
Q
What are the three requirements for successful infection?
A
- Sufficient virus
- Cells accessible, susceptible, permissive
- Local antiviral defence absent or overcome
9
Q
What are the 6 ways of transmission
A
- Horizontal
- Zoonotic
- Latrogenic
- Nosocomial
- Vertical
- Germ Line
10
Q
transmission between members of the same species
A
Horizontal transmission
11
Q
transmission between members of different species (animals to humans)
A
zoonotic transmission
12
Q
Transmission by which an individual is infected while in hospital or health care facility
A
Nosocomial Transmission
13
Q
Activity of healthcare workers leads to infection of the patient (transmission)
A
Latrogenic Transmission
14
Q
Transmission by which transfer of infection between parent and offspring
A
Vertical Transmission
15
Q
agent transmitted as part of the genome
A
Germ line Transmission
16
Q
- Most common route of viral entry
- Viruses enter by aerosolized droplets from cough or sneeze, or contact with saliva
- Large droplets lodge in nose; smaller in airways or alveoli
- Absorptive area of lung: 140 m2; –Ventilation rate 6 L/min (0.5 L per breath)q
A
Infiltration by Respiratory Tract
17
Q
What are the barriers of infection in the respiratory tract?
A
- swallowing
- ciliary action from lower tract
- macrophages in alveoli
18
Q
Why there is good chance of viral/cell interaction in the alimentary tract?
A
The alimentary tract is designed to mix, digest, absorb food, so contents are always in motion – great for viral/cell interactions
19
Q
What are the barriers of infection in the alimentary tract? What makes it a hostile environment?
A
Hostile environment: stomach is acidic, intestine is alkaline; presence of digestive enzymes, bile detergents, mucus, antibodies, phagocytic cells
20
Q
- Protected by mucus, low pH
- Minute abrasions from sexual activity may allow viruses to enter
- Some viruses produce local lesions (e.g. HPV)
- Some viruses spread from urogenital tract (e.g. HIV)
A
Urogenital Tract
21
Q
How virus can enter the eye?
A
By the sclera and conjunctiva route
22
Q
Hoe does infection in the ye usually occur?
A
Infection usually occurs after injury and/or ophthalmologic procedures.
23
Q
What are disseminated infections in the eye?
A
enterovirus 70 spread to CNS
24
Q
Virus HSV-1, target, result?
A
HSV-1 can infect cornea, blindness may result, virus spread to sensory ganglia
25
How does virally entry usually occur in the skin?
Viral entry usually occurs by breaks or punctures in the skin or skin abrasions; insect or animal bites; needle punctures.
26
Why does infection occur in the skin?
Outer layer of dead cells cannot support infection
| Epidermis is devoid of blood or lymphatics - so local replication only.
27
Hoe does viral infection in the skin spread?
Dermis and sub-dermal tissues are highly vascularized - infection may spread
28
Some viruses spread beyond the primary site
Disseminated viral spread
29
many organs are infected by virus
Systemic viral spread
30
How the integrity of the basement membrane can be compromised?
Below the epithelium is the basement membrane; integrity can be compromised by epithelial inflammation and destruction
Below basement membrane are subepithelial tissues, where virus encounters tissue fluids
Role of directional release of virus from polarized cells e.g. epithelial cells, neurons etc.
31
- Viruses that produce disseminated infection often do so by entering the blood
- Virus in extracellular fluids are taken up by lymphatic capillaries
- Once in blood, virus has access to almost every tissue
- Other viruses spread freely in the blood (viremia)
Hematogenous spread
32
How can viruses enter blood directly through capillaries?
by replicating in endothelial cells, or through vector bite
33
How can the virus easily spread to the blood?
Virus enters lymphatic system, as it is more permeable that circulatory capillaries. Viruses can replicate in immune cells (in lymph nodes) and spread infection to distant tissues.
34
Presence of infectious virus in the blood
Viremia
35
This results from virus replication (measles)
Active viremia
36
This results from virus introduced into the blood without replication (Dengue Virus)
Passive Viremia
37
An antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically.
Neutralizing antibody (NAb)
38
How does an NAb recognise viruses?
NAb recognize proteins or glycoproteins on the virion surface of enveloped viruses or non-enveloped viruses- so blocking these proteins which enable the entry of the virus into the cell
39
- Viral entry to local nerve endings
- Definitive characteristic of pathogenesis
- For other viruses invasion of the CNS is an infrequent diversion from normal replication
Neural Spread
40
Examples of viruses that infect neural tissue
rabies, alpha herpesviruses
41
Examples of non-primary CNS replication
Poliovirus, reovirus
42
What are the three ways viruses can spread to the CNS?
1. Neural
2. Olfactory
3. Hematogenous
43
Poliovirus, yellow fever virus, mouse hepatitis virus, Venezuelan encephalitis virus, rabies virus, reovirus (type 3 only; type 1 spread by viremia), herpes simplex virus types 1 and 2, pseudorabies virus
(Poliovirus, rabies virus)
Neural virus spreading to CNS
44
Poliovirus, herpes simplex virus, coronavirus
| Coronavirus
Olfactory virus spreading to the CNS
45
Poliovirus, coxsackievirus, arenavirus, mumps virus, measles virus, herpes simplex virus, cytomegalovirus
(Measles virus)
Hematogenous virus spreading to the CNS
46
(Infections of the CNS)
A ______ virus can infect neural cells (infection may occur by neural or hematogenous spread from a peripheral site)
Neurotropic
47
(Infections of the CNS)
A _______ virus can enter the CNS after infection of a peripheral site
Neuroinvasive
48
(Infections of the CNS)
A _________ virus can cause disease of nervous tissue
Neurovirulent
49
(Infections of the CNS)
HSV: ___ neuroinvasiveness, ____neurovirulence
HSV: low neuroinvasiveness, high neurovirulence
50
(Infections of the CNS)
Mumps: ____ neuroinvasiveness, _____ neurovirulence
Mumps: high neuroinvasiveness, low neurovirulence
51
(Infections of the CNS)
Rabies: _____ neuroinvasiveness, _______ neurovirulence
Rabies: high neuroinvasiveness, high neurovirulence
52
The spectrum of tissues infected by a virus.
An enteric virus replicates in the gut and not in the lung; a neurotropic virus replicates in cells of the nervous system and not in hematopoietic cells
Tissue Tropism
53
The tropism of some viruses is limited while other viruses are ________ (can replicate in many organs- e.g. Ebola)
Pantropic
54
What are the 3 determinants of viral tropism?
1. Cell receptors for viruses
2. Cellular proteins that regulate viral transcription
3. Cellular proteases involved in the maturation of virions
55
The capacity of a virus to cause disease in an infected host. How badly virus can affect
Viral virulence
| - A virulent virus causes significant disease, while an avirulent or attenuated virus causes reduced or no disease
56
How is virulence quantitated?
–LD50 (Lethal Dose 50%; amount of virus needed to kill 50% of infected hosts)
–the mean time to death
–the mean time to appearance of symptoms
–measurement of fever, or weight loss
–measurement of pathological lesions (poliovirus); reduction in blood CD4+ lymphocytes (HIV-1)
57
What makes viruses virulent?
Virulence genes are usually identified by mutation: deletion or disruption of one of these genes results in a virus that causes reduced or no disease in a specified system
58
Viral genes affecting virulence fall into four classes. What are the four classes?
–Those that affect the ability of the virus to replicate
–Those that modify the host’s defense mechanisms
–Those that enable the virus to spread in the host
–Those which have intrinsic cell killing effects
59
What are some genes that modify the host's defence mechanisms?
Virokines and viroceptors
60
Mimic normal cellular molecules critical to host defense
– sabotage the body’s innate and adaptive defenses
– not required for growth in cell culture
Virokines and viroceptors
61
Examples of virokines and viroceptors
– soluble cytokine receptor - bind cytokines, block action
– proteins that bind key proteins in complement cascade
– proteins that affect MHC-1 antigen presentation
62
Give an example of a toxic viral protein
NSP4
63
-Nonstructural glycoprotein of rotaviruses: a viral enterotoxin
When expressed in cells, causes increase in intracellular calcium.
- When fed to young mice, causes diarrhea by potentiating chloride secretion.
- Triggers a signal transduction pathway in intestinal mucosa
NSP4
64
How the virus is shed (virus shedding)
1. Respiratory secretions (aerosols produced by coughing, sneezing, speaking
2. Nasal secretions contaminating hands, tissues
3. Mucosal shedding
4. Urine
5. Semen
6. Faeces
65
How have host cells evolved to eradicate intruding viruses?
- developed intricate signaling networks to detect, control
- E.g. Interferons are signaling proteins released by host cells in response to viruses (to increase anti-viral response)
66
A disease caused by bacteria, viruses or parasites, that can spread from animals to humans.
-Examples – Ebola, Bird Flu, SARS-CoV2
Zoonosis
| Zoonotic viruses are often RNA based – which accounts for their adaptability.
67
What types of specimens are collected to diagnose ?
1. Respiratory tract: Nasal and bronchial washings, throat and nasal swabs, sputum
2. Eye: throat and eye swab/scraping
3. Gastrointestinal tract: stool and rectal swabs
4. Vesicular rash: vesicle fluid, skin scrapings
5. Maculopapular rash: throat, stool, and rectal swabs
6. CNS: stool, tissue, saliva, brain biopsy, cerebrospinal fluid
7. Genital: vesicle fluid or swab
8. Urinary tract: urine
9. Blood borne: blood
68
How are viruses tested?
- Detection of antibody mounted against the virus
- Detection of viral protein (antigen)
- Detection of viral nucleic acid
69
How is viral antigen detected?
- Immunofluorescence
- sputum sample
- quick test, but needs manufacturing of specific monoclonal antibodies
- need expert personnel and fluorescent microscope set up
70
How is viral antibody detected?
- Commonest test used is the enzyme-linked immunosorbent assay (ELISA
- The coupled enzyme is usually HRP that causes a chemical reaction in the presence of dye – allowing visualization of the result.
71
How does ELISA work?
1. Substrate changes colour when cleaved by the enzyme attached to the second antibody
2. Anti-human immunoglobulin (2nd antibody) coupled to an enzyme
3. Patient serum contains antibodies
4. Purified antigens pre-coated onto an ELISA plate
72
Automation and random access analyser
Can run multiple serological tests for different viruses simultaneously
73
What's the Commonest test used is polymerase chain reaction (PCR)?
Viral nucleic acid detection
| -quantify virus/viral load
74
What viruses is the Viral nucleic acid detection for?
- All viruses especially non-cultivable viruses
| - Viruses in low copy numbers
75
What is the SARS-CoV2 PCR testing method?
Viral nucleic acid detection
76
General Methods by which virus infections or spread can be limited
- Medical mask
- Gloves
- Overalls
- goggles
- surgical cap
- apron
77
What are some long-term and short term specific measures for viral prevention?
vaccines, chemoprophylaxis, immunoprophylaxis
78
Give some examples of Germ Line Transmission
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