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302: Scientific basis of medicine > Viruses > Flashcards

Viruses Flashcards

1
Q

Incubation period

A

Period between start of infection and onset of symptoms

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2
Q

Basic reproduction number (R0)

  • Definition
  • Rates: avian flu, plague, ebola, influenza, SARS, Measles
A

The transmission rate of a disease, from one case.

  • The number of new infections that arise from one person their infective period.
  • Affected by type of infection, mode of transmission and location
Avian flu- 0.7
Plague- 1.3
Ebola=
Influenza= 1-3
SARS- 3
Measles= 16
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3
Q

Size of viruses

A

20-400nm

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4
Q

Structure of virus

A

Genetic material
- Nucleic acid= DNA or RNA

Protein coat

Envelope/ undeveloped

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5
Q

Viral pathogenesis journey

A
  1. Encounter
    - Virus encounters the host
  2. Entry
  3. Mulitplication
  4. Spread
  5. Damage
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6
Q

Viral entry into the body

A

Skin

  • Abrasions
  • Bites
  • Needle punctures

Alimentary tract
- Movement of GIT facilitates entry

Urogenital tract
- Abrasions facilitate entry

Eye

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7
Q

Baltimore system for viral classification 1-7

  • Definition
  • Types
A

Classification of viruses based on the type of genome and method of replication.

1- dsDNA

2- ssDNA

3- dsRNA

4- positive ssRNA

5- negative ssRNA

6- positive RNA with DNA intermediate

7- gapped dsDNA

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8
Q

Type 1 virus examples

A

dsDNA

  • Adenovirus
  • Herpes simplex virus
  • PoxVirus
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9
Q

Type 2 virus examples

A

ssDNA

- Parvovirus

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10
Q

Type 3 virus examples

A

dsRNA

- Reovirus

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11
Q

Type 4 virus examples

A

positive ssRNA

- Poliovirus

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12
Q

Type 5 virus examples

A

negative ssRNA

- Influenza virus (orthomyoxvirus), rhabdoviruses

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13
Q

Type 6 virus examples

A

positive RNA with DNA intermediate

- Retrovirus (HIV)

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14
Q

Type 7 virus examples

A

Gapped dsDNA

- Hep B virus (Hepadnavirus)

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15
Q

Viral spread and release mechanisms

A

Localised replication
- Within epithelium/ system

Dissemination/ systemic infection

  • Haematogenous
  • Neurological

Viral release

  • Apical (i.e flu)
  • Basolateral (i.e rabies), csn invade underlying spread.
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16
Q

Haematogenous spread

- Entry into blood

A

Entry via

  • Capillaries
  • Endothelial replication
  • Vector bite
  • Lymphatic capillaries
17
Q

Viraemia

  • Defintion
  • Passive/ active
  • Primary/ secondary
A

Presence of virus in blood

  • Can be calculated as %
  • Measures viral replication

Passive vs active

  • Passive= introduction of virus into the blood stream
  • Active= replication of virus in blood stream

Primary
- Spread to blood from primary site of infection

Secondary
- Further infection of other tissues from primary site of infection, via bloodstream

18
Q

CNS infection of virus

  • Neurotrophic
  • Neuroinvasive
  • Neurovirulent
A

Neurotropic
- Infection of neural cells

Neuroinvasive
- Viral infection of CNS from peripheral site

Neurovirulent
- Virus that can cause disease of nervous tissue

19
Q

Determinants of viral tissue tropism

A

Presence of cell receptors on hosts/ virus allowing entry
- e.g HIV/ CD4

Cell proteases

Cellular proteins that regulate viral transcription

20
Q

Viral virulence

A

Determined by genes

  • Ability to replicate
  • Modification of host’s defence mechanisms (virokines/ viroceptors)
  • Ability to spread
  • Mechanisms to kill cells
21
Q

Viral mechanism of cell injury

A

Cytolytic
- Inhibit host protein/RNA synthesis= loss of membrane integrity= syncytium= apoptosis

Non cytolytic

  • Lymphocyte mediated (CD4, CD8, B)
  • Free radicals
22
Q

Examples of acute viral infections

A

Acute infection
- Non equilibrium between virus and host response

Rhinovirus

Rotavirus

Influenza virus

23
Q

Examples of persistent viral infections

A

Lymphocytic choriomeningitis virus

24
Q

Examples of latent, reactivating viral infections

A

Herpes simplex

25
Q

Examples of slow viral infections

A

Measles virus SSPE

HIV

26
Q

Latent infections

A

Seen in DNA or retroviruses

Viral genome is replicated along with host cell chromosome in cell growth

Examples

  • HSV: fever, blisters, cold-sores
  • Retrovirus: transformation into cancer
27
Q

Mechanisms of viruses evade the immune system (5)

A

Antigenic variation

  • Influenza: can change its surface antigens (neuraminidase, hemagglutinin)
  • HIV
  • Rhinovirus

Inhibition of antigen processing

  • Block transported associated with antigen processing: HSV
  • Removed MCH-1 from endoplasmic reticulum: CMV

Production of cytokine receptor homologues

  • IL-1, IFN-G: poxvirus
  • Chemokine: CMV

Production of immunosuppressive cytokines
- IL-10: EBV

Infection of immunocompetent cells
- HIV

302: Scientific basis of medicine (28 decks)

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