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Microbiology > Infectious disease and pathogenicity 2- Viruses > Flashcards

Infectious disease and pathogenicity 2- Viruses Flashcards

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1
Q

Structure of a virus

A 
Nucleic acid- can be DNA/RNA
single/double stranded
Surrounding protein coat- capsid
Icosahedral (20 sides)
Helical 
Nucleocapsid
Matrix
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2
Q

What is a retrovirus?

A

Store their genetic info as RNA instead of DNA
So when they enter human RNA must be converted to DNA to replicate
e.g HIV

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3
Q

What’s a nucleocapsid?

A

Viral capsid protein enclosing a nucleic acid
Found in the cytoplasm
Involved in viral replication

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4
Q

What is gp120?

A

Docking glycoprotein in membrane of virus

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5
Q

What is gp41

A

Transmembrane glycoprotein in virus membrane

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6
Q

What are glycoproteins in virus’ membranes role?

A

Attach virus to Host cell= fusion between membranes

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7
Q

Examples of non-enveloped DNA viruses

A

Parvovirus
Papovavirus
Adenovirus

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8
Q

What DNA does parvovirus have?

A

ss DNA

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9
Q

What DNA does papovavirus have?

A

ds DNA

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10
Q

Examples of enveloped DNA viruses?

A

Poxvirus

Herpesvirus

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11
Q

What kind of DNA does poxvirus have?

A

ds DNA

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12
Q

What kind of DNA does herpesvirus have?

A

ds DNA

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13
Q

Examples of enveloped RNA viruses

A

Togavirus
Coronavirus
Retrovirus
(all ss RNA)

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14
Q

Examples of non enveloped RNA viruses

A

Picornavirus (ss RNA)

Reovirus (ds RNA)

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15
Q

What is a bacteriophage?

A

DNA virus that infects bacteria

Have a role in bacterial virulence- spread pathogenicity to infect next bacterium

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16
Q

What is phage therapy?

A

When bacteriophages are used to kill bacteria
Used to study viral replications
But means more bacteriophage production= transmit genes to bacteria (e.g resistant)

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17
Q

What is viral pathogenesis?

A

Process where a viral infection causes disease
Outcome of infection depends on host’s response
Most infections are subclinical- don’t show symptoms

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18
Q

What is an acute infection?

A

Full recovery of infection but causes long term problems e.g acute viral encephalitis (brain swelling) leading to neurological sequelae
Can lead to chronic infection

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19
Q

What is a chronic infection?

A

Silent subclinical infection for life
A long silent period before disease appears
Can be reactivation of acute disease
Causes chronic relapse and exacerbations

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20
Q

Examples of viruses that have a long silent period?

A

HIV

SSPE

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21
Q

Examples of viral infections with relapses and exacerbations

A

HBV

HCV

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22
Q

What are the factors of viral pathogenesis?

A

Effects of viral infection on cells (intracellular pathogenesis)
Entry into host
Courses of infection (primary rep, systemic spread, secondary rep)
Cell/tissue tropism
Cell/tissue damage
Host immune response
Virus clearance/persistence

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23
Q

What is cell/tissue tropism?

A

cells and tissue of host supporting growth of a virus/bacteria

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24
Q

What are the 3 ways that cells can respond to infection?

A
  1. No change
  2. Death
  3. Transformation
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25
How does virus cause direct cell damage/death?
1. Division of cell's energy= apoptosis 2. Inhibiting macromolecular synthesis 3. Ribosomes in cell competing for viral mRNA 4. Competition for viral promoters and transcriptional enhancers e.g for RNA polymerases 5. Inhibit interferon defence mechanisms
26
How does a virus cause indirect cell damage?
Viral genome is integrated Mutations in host genome Inflammation Host immune response
27
What routes can virus' take to enter body?
``` Skin- cutsabrasions, virus can employ vectors to breach skin barrier Conjunctiva and mucous membranes GI tract Respiratory tract Urogenital tract ```
28
Process of viral replication?
1. Virus penetrates host cell 2. DNA/RNA released from virus (uncoating) 3. Viral DNA is integrated by integrase 4. RNA converted to DNA (if needed) 5. Viral subunits are synthesised- protease acts on polypeptides 6. Virus is assembled 7. Lysis of cell= virus spreads and infects nearby cells
29
What is primary replication?
Place where virus replicates after initial entry into host cell determines if infection will stay localised or spread= systemic infection
30
What is systemic spread?
Virus can spread via bloodstream/CNS
31
What is secondary replication?
Result of systemic spread | New area that is infected
32
Cell tropism- what is the viral affinity for body tissues determined by?
Cell receptors for virus Cell's TF's that recognise viral promoters and enhancer sequences Cell's ability to support viral replication Physical barriers Temperature, pH, oxygen Digestive enzymes and bile in GI tract that may kill viruses
33
What is different about retroviruses?
Tend not to kill cells released from cell by budding rather than lysis Cause persistent infections
34
What does picornavirus cause?
Cause lysis and death of host cell | leading to fever and increased mucus
35
What has the greatest impact on outcome of infection?
Immune response
36
Role of cellular and humoral immunity in clearing the virus
Cellular immunity- clears virus | Humoral immunity- protects against reinfection
37
What is the result when a virus stays and isn't cleared from the body?
(Chronic) persistent infections
38
What are the 2 types of persistent infections?
A chronic infection is a type of persistent infection- is eventually cleared, while latent or slow infections last the life of the host True latency - latent viral infection- When a virus is present in the body but exists in a resting (latent) state without producing more virus. A latent viral infection usually does not cause any noticeable symptoms and can last a long period of time before becoming active and causing symptoms
39
What is true latency?
Virus remains in cell for a long time | Genome still integrated in host's genome or exist as episomes (DNA replicates independent of host)
40
Example of a true latent virus
HSV (herpes simplex virus) | VZV (varicella-zoster virus)
41
What is persistence?
Virus not completely removed | replicates at a very low level- interferons control low levels
42
Examples of a virus that persists?
HIV | HBV
43
Mechanisms of viral persistence?
Antigenic variation- strains of virus change so new antibodies needed Downregulation of MHC I expression- lack of immune cells recognising virally infected cells Down-regulation of accessory molecules in immune response e.g LFA and ICAM Infection of immunoprivileged sites in body e.g HSV in sensory ganglia of CNS Direct infection of cells in immune system= immunosuppression
44
What viruses directly infect cells of the immune system?
Herpes virus | HIV
45
Clinical features of hepatitis B
Long incubation period Replicates at low levels before clinical problem arrives Result of damage to liver= jaundice
46
Spectrum of hepatitis diseases
chronic persistent hepatitis- asymptomatic chronic active hepatitis- symptomatic exacerbations of hepatitis Cirrhosis of liver Hepatocellular carcinoma (liver cancer)
47
Treatment of hepatitis B
Cure- pegylated interferon with a nucleotide analogue | reduces viral replication- targets viral RNA polymerase
48
Problem with treatment for hepatitis
Treatment is expensive- lifetime regime | virus can be resistant
49
What are orthomyxoviruses (influenza)
``` Enveloped ss RNA (10 genes encoded on 8 separate RNA segments) 3 types of influenza- A,B,C ```
50
Which type of influenza causes the most infection?
A
51
What is the tropism that influenza uses?
Respiratory tract
52
What is in the lipid bilayer of orthomyxoviruses (influenza)?
Haemagglutinin and neuraminidase glycoproteins | Hemagglutinin spikes on viral membrane attach to respiratory tract= agglutination of RBCs
53
Orthomyxovirus life cycle
1. Virus' hemagglutinin spikes attach to respiratory epithelial cell and fuses with membrane 2. Virus is endocytosed- in a vesicle 3. Virus is uncoated= nucleocapsid segments released into cytoplasm 4. Nucleocapsid segments transported to nucleus 5. - sense RNA strand converted to + sense strand 6. +sense RNA strand used in transcription and translation to make viral proteins- capsid, glycoprotein spikes in virus membrane 8. + sense RNA strand makes new - RNA strands- assembled into nucleocapsids and released from nucleus to cell membrane 9. Mature virus is released an budded off with an envelope and spikes
54
What is the latency period?
The time between being infected and becoming infectious
55
What is the incubation period?
Time from being infected to showing symptoms (infectiousness)
56
Differences between a cold and flu
Fever: cold= rare, flu= prominent Headache- cold= rare, flu= prominent Extreme exhaustion- cold= never, flu= prominent Sore throat- cold= common, sometimes
57
What are hemagglutinin glycoprotein spikes found on influenza?
15 different subtypes most important virulence factor attaches to host cells
58
What's neuraminidase found in membrane of influenza?
9 different subtypes | assists in viral budding and release
59
What do the glycoproteins- neuraminidase and hemagglutinin frequently undergo?
Genetic changes (mutations) = reduce effectiveness of host immune response
60
What is antigenic drift?
``` Constant mutation (year on year) simple point mutation ```
61
What is antigenic shift?
1 of genes/RNA strands swapped with gene/strand from another influenza virus from a different animal host Results in new HA and/or new HA and NA proteins in influenza viruses that infect humans
62
Characteristics of influenza A
Acute, highly contagious respiratory illness Respiratory transmission Binds to ciliated cells of respiratory mucosa Causes shedding of cells in respiratory epithelium= severe inflammation
63
Symptoms of being infected by influenza A
``` Fever headache myalgia pharyngeal pain shortness of breath coughing ```
64
What is a secondary infection that can result from influenza A?
Pneumonia
65
Diagnosis of influenza A?
Rapid immunofluorescence tests- detect antigens from pharyngeal specimen serological testing- blood test that looks for antibodies in blood
66
Treatment for influenza A
Oseltamivir Zanamivir Amantadine Rimantadine
67
Prevention of influenza A
Vaccine
68
Acyclovir MOA etc
Anti-viral Interaction: viral DNA polymerase MOA: Inhibits viral DNA polymerase - Converted into acyclovir triphosphate- higher affinity for viral DNA polymerase than cellular NDA polymerase Competing w DNA polymerase so strongly preventing other bases associating with the enzyme Preventing DNA replication

Microbiology (5 decks)

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