Concepts in microbiology - viruses and prions Flashcards
1
Q
Genetic material found in viruses
A
DNA or RNA
2
Q
Which infectious agent has no nucleic acid?
A
Prions
3
Q
What is meant by viruses being ‘metabolically inert’?
A
They do not possess ribosomes so cannot undergo protein synthesis. Some have enzymes
4
Q
How are the swaps used to sample viruses different to microbiological samples?
A
Swabs need to be placed in a viral transport medium
5
Q
How are viruses grown?
A
Using cells (unlike bacteria which can grow on agar plates)
6
Q
Place in size order: bacteria, virus, eukaryotic cell
A
eukaryotic > bacterium > virus
7
Q
Term used to describe a complete virus particle
A
Virion
8
Q
Components making up a virion
A
envelope, capsid, nucleic acid genome
9
Q
What makes up the envelope of some viruses?
A
Lipid membrane
10
Q
Function of envelope in some viruses
A
protect the capsid
11
Q
What is the capsid in viruses?
A
A protein shell around the nucleic acid genome (RNA or DNA) made of capsomers
12
Q
Name of the protein units that make up the capsid in viruses
A
Capsomers
13
Q
6 key stages of viral replication
A
Attachment, penetration, uncoating, synthesis of viral components, assembly, release
14
Q
Possible effects of viruses on cells
A
Cell death, transformation, latent infection
15
Q
Term used to describe the change in cell morphology caused by an infecting virus
A
cytopathic effects
16
Q
Example of a virus that causes cell death
A
Herpes simplex virus spreads rapidly between epithelial cells causing them to lyse. Forms an ulcer
17
Q
What is the transformation effect of a virus on a host cell?
A
The cell is not killed but changed to a cancerous cell
18
Q
Example of a virus that causes transformation of cells
A
Human papilloma virus can cause oral cancer and oropharyngeal cancer
19
Q
What is the latent infection effect of viruses on cells?
A
The remnants of virus and nucleic acids remain in the cell with no obvious effect on cell function
20
Q
Example of a virus that causes latent infection of host cells
A
Herpes simplex virus causes recurrent Herpes labialis
21
Q
Why do viruses infect specific cells?
A
antigen is only specific to particular glycoprotein receptors on cells
22
Q
How may replicated virus particles be protected from the host’s immune system?
A
As the viral particles emerge from the host cell, the plasma membrane may form an envelope around the virus (now has self-antigens)
23
Q
Name of drugs that prevent replication of virus
A
anti-viral drugs
24
Q
Modes of viral transmission
A
inhalation via respiratory tract, ingestion via GIT, inoculation, congenital (mother to foetus), sexual transmission
25
Example of a virus passed on by inhalation via respiratory tract
coronavirus, rubella
26
Example of a virus transmitted by ingestion via GIT
Norovirus (spreads through contaminated food, water, surfaces)
27
How can viruses be passed on by inoculation?
Through skin abrasions, mucous membranes, transfusions, transplants, injections, bites (introduces infectious material into body)
28
Example of virus passed on by inoculation
Hepatitis B
29
Example of virus passed on congenitally
Rubella - infected pregnant mother has 90% chance of passing on Rubella which may lead to child having Congenital Rubella Syndrome. Also transmitted by inhalation.
30
Example of virus transmitted sexually
HIV
31
Example of virus affecting the nervous system
Rabies
32
Example of viruses affecting the respiratory tract
Adenovirus, influenza
33
Examples of viruses that cause localised diseases of skin and mucous membranes
Herpes simplex virus
34
Example of virus that affects the eyes
adenovirus (conjunctivitis)
35
Example of virus that affects liver
hepatitis C
36
Example of virus that affects the salivary glands
Mumps (parotid gland swelling)
37
Example of virus that affects the gastrointestinal tract
norovirus
38
Reasons for using viral diagnositics
Stop antibiotics, find most effective treatment, evaluate anti-viral drug susceptibility, public health and IP&C reasons (knowing stage of infection in individual and community for intervention), epidemiology / surveillance.
39
What is epidemiology?
the study of the distribution of disease in populations and the factors which determine this distribution
40
How to begin diagnosing a viral infection
Review the clinical history, examine patient, use a systems based approach for differential diagnosis (e.g. surgical sieve), make a provisional diagnosis, plan special investigations
41
What is the surgical sieve?
Method for coming up with multiple diagnoses for patient using mnemonic (MEDIC HAT PIN: metabolic, endocrine, degenerative, infective, congenital...causes)
42
What specimens are used for nucleic acid detection e.g. HSV?
swabs, faeces, aspirates, plasma, CSF, vesicle fluids, urine
43
Which specimen is monitored by PCR e.g. to count the HIV load?
plasma (from blood culture)
44
Which specimen is used in serology e.g. counting Hep B antibodies titres?
Serum (from blood culture)
45
Techniques used in viral diagnostics
nucleic acid detection / sequencing, antigen detection e.g. hep B surface antigen in blood serum
46
How does nucleic acid detection / sequencing work?
Based on PCR principle - small amount of nucleic acid is amplified so there is enough for detection.
47
When sequencing a virus containing RNA, what step must occur before PCR?
Reverse transcription to convert RNA to DNA. Primer added to RNA and a complementary DNA strand is produced. Primer added to complementary DNA...
48
What is the first class of antibody produced during acute infection phase?
IgM
49
Which antibody indicates more time has passed / a later stage of infection?
IgG (change in antibody class from IgM -> IgG
50
What is the genetic material in influenza viruses?
RNA
51
How is influenza transmitted?
Airborne droplets enter the respiratory tract
52
How does a virus (e.g. influenza) enter the host cell?
Antigens attach to receptors on host cell triggering receptor mediated endocytosis. Virus is internalised in a membrane bound capture vesicle
53
What are kinesins?
The host proteins that transport the virus (within capture vesicle) along microtubules.
54
What does the uncoating process involve in viral replication? Influenza example
Matrix proteins detach from proteins covering RNA genome due to influx of H+ from fusion with lysosome. Hemagglutinin inserts itself into vesicle membrane causing it to fuse with the viral membrane allowing the release of RNA.
55
How are viral components synthesised?
RNA enters the nucleus via nuclear pores. The RNA is transcribed to mRNA by RNA polymerase. mRNA is translated into viral proteins by ribosomes.
56
How are progeny viruses released from the host cell?
By budding
57
How are virions assembled within the host cell?
Viral proteins and viral RNA exit the nucleus and travel to the plasma membrane where they are packaged into viral envelope proteins when they bud from the host cell.
58
Examples of viruses that vaccines are ineffective against
common cold, HIV
59
Name of 2 glycoproteins found on the capsid of influenza virus
Haemagglutinin (HA) and neuraminidase (NA)
60
Function of haemagglutinin?
Bind to sialic acid on host cell surface receptors
61
How many types of hemagglutinin spikes are there in influenza?
14 H types
62
Function of neuraminidase
Neuraminidase cleaves the sialic acid molecule on the host receptors which the hemagglutinin is bound to, allowing the virion to be released from the host cell.
63
How many types of neuraminidase are there in influenza?
9 N types
64
2 ways that the antigens on influenza virus (HA and NA) can change
Antigenic drift, antigenic shift
65
What is antigenic drift and how is it caused?
Minor, gradual changes in the antigens due to point mutations in the genome of the virus each time it is replicated.
66
Why can antigenic drift render flu vaccines ineffective?
Changes in antigens accumulate over time so that antibodies are no longer complementary to the antigen (antigens not recognised by immune system)
67
Which change in antigen structure can cause an epidemic (regional outbreak)?
Antigenic drift
68
Which types of influenza are affected by antigenic drift?
A, B, C all drift (all 3 types)
69
What is antigenic shift?
A major change in antigenic structure of a virus caused by recombination
70
How can recombination occur in antigenic shift?
Pig cells have both human and bird virus receptors. The human and bird virus genes can randomly combine within the pig cell to generate a new flu virus.
71
Which change in antigenic structure can result in a pandemic (international outbreak)?
Antigenic shift
72
Which influenza type can undergo antigenic shift?
Only type A
73
How are influenza viruses classified?
Using the type of hemagglutinin and neuraminidase receptors found on the capsid e.g. H2N2 influenza virus has HA type 2, NA type 2
74
What is the chain of infection?
1. infectious agent
2. reservoir
3. portal of exit
4. mode of transmission
5. portal of entry
6. susceptible host
75
What are prion diseases referred to as?
Transmissible Spongiform Encephalopathies
76
What does Transmissible spongiform encephalopathies mean?
The prion disease can be passed on and mainly affects the brain causing a spongy appearance
77
What are prion diseases / transmissible spongiform encephalopathies?
Fatal neurological diseases caused by the accumulation of prion protein (a cell membrane protein) within the CNS.
78
Who discovered prions?
Prusiner - won 1982 Nobel prize
79
Where is the name prion derived from?
Proteinaceous Infectious particle
80
What is a prion?
Abnormal form of a protein found in the brain responsible for causing transmissible spongiform encephalopathies
81
Name of transmissible spongiform encephalopathy that affects sheep (studied by Prusiner)
Scrapie
82
Name of CJD-like disease in Papua New Guinea tribe in 1950s/60s
Kuru
83
What feature of prions may account for its resistance to sterilisation and disinfectants?
No nucleic acid
84
3 forms of prion disease
Infectious (transmitted via contaminated blood/instruments), genetic (families), sporadic (random 1 in 1 million develops sCJD)
85
Cause of prion disease
Accumulation of an abnormal form of a natural protein in the brain
86
Feature of normal prion proteins
Contain alpha helices that are pliable and no the protein is more readily broken down by the body
87
Feature of abnormal prion proteins
Contain beta-pleated sheets which are more rigid so prion is more difficult to be broken down
88
Where do normal prion proteins exist?
On the exterior surface of cell membranes (intercellular communication function)
89
Which infectious agent does not trigger an immune response?
Prions
90
What characteristic of prions determines where the pathology occurs in the brain and hence the symptoms?
Shape of prions e.g. structure, carbohydrate side chains.
91
What is PrPc?
Prion protein cellular - normal form of prion protein
92
What is PrPSc
Prion protein scrapie - abnormal form of prion protein
93
How are normal prions (PrPc) produced?
Prion protein gene is transcribed into mRNA which is translated at ribosomes in PrPc.
94
How do abnormal prion proteins (PrPSc) reproduce?
An abnormal prion (PrPSc) transforms a normal prion (PrPc) into a PrPSc by a chain reaction.
95
At which stage does the speed of abnormal prion protein (PrPSc) production increase?
Once the initial conversion of one PrPc to PrPSc is achieved, there is a more rapid aggregation of abnormal PrPSc.
96
Types of human CJD
Sporadic (sCJD)
Familial (fCJD)
Iatrogenic (iCJD)
Variant (vCJD)
97
How may familial CJD be transmitted?
Inherited mutations in prion gene
98
What is iatrogenic CJD?
The infectious form of CJD
99
How may iatrogenic CJD be transmitted?
Surgical instruments, contaminated hormones/dura mater graphs, Kuru (cannibalistic rituals)
100
Cause of variant CJD?
Consumption of food contaminated with bovine spongiform encephalopathy
101
Difference in age of onset between sporadic and variant CJD
sCJD approximately age 60-70 whereas vCJD has a much younger onset
102
Why were people more concerned about vCJD compared to sCJD?
vCJD has a much higher infectious dose and spreads outside the NS to peripheral tissues (appendix, tonsils, spleen)
103
Since the peak of vCJD cases in 2000, how was the epidemic overcome?
Interventions to restrict spread of disease e.g. food precautions, control of blood transfusion
104
Which staining technique was used to detect abnormal prions (vCJD) in the trigeminal ganglion?
Immunohistochemistry
105
Which technique was used to detect prions in vCJD in dental tissues (alveolar nerve and tongue)?
Immunocytochemistry
106
What are the concerning features of CJD?
Abnormal prions are difficult to clean from instruments, can survive steam sterilisation, decades long incubation period, asymptomatic / pre-symptomatic carriage of iatrogenic CJD
107
Example of action taken by health department to reduce risk of vCJD transmission
Single use of matrix bands and endodontic files (tested positive for residual blood contamination after sterilisation)
108
What infection prevention measure can be used when treating a patient with / increased risk of CJD?
Reprocess instruments according to best practice and return to use
