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302: Scientific Basis of Medicine > Infection 4: How do viruses cause disease in humans? > Flashcards

Infection 4: How do viruses cause disease in humans? Flashcards

1
Q

Incubation period

A

From infection to onset of symptoms in primary case

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2
Q

Infectious period

A

Involves incubation period and symptoms

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3
Q

What is a virus?

A

Particle made of nucleic acid and a protein coat

Small in size (100x smaller than our cells)

Obligate intracellular- only replicates inside living cells

Can infect wide range of organism

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4
Q

Virus particles

A

Nucleic acid

  • DNA or RNA
  • ds or ss
  • +/ve/-ve/ambisense

Protein coat

Enveloped/ unenveloped

Nucelocapsid

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5
Q

Nucleocapsid

A

Nucleic acid and protein coat

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6
Q

Virion

A

Complete intact virus particle

The physical particle in the extra-cellular phase which is able to spread to new host cells

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7
Q

Viruses which cause encephalitis/ meningitis

A

JC virus

Measles

LCM virus

Arbovirus

Rabies

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8
Q

Viruses which cause common cold

A

Rhinovirus

Parainfluenza virus

Respiratory syncytial virus

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9
Q

Viruses which cause pharyngitis

A

Adenovirus

Epstein-Barr virus

Cytomegalovirus

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10
Q

Viruses which cause gingivostomatitis

A

Herpes simples type 1

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11
Q

Viruses which cause cardiovascular infection

A

Coxsackie B virus

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12
Q

Viruses which cause hepatitis

A

Hepatitis A, B, C, D, E

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13
Q

Viruses which cause skin infections

A

Varicella zoster virus

Human herpesvirus 6

Smallpox

Molluscum contagiosum

Human papillomavirus

Parvovirus B19

Rubella

Measles

Coxsackie A virus

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14
Q

Viruses which cause eye infection

A

Herpes simplex virus

Adenovirus

Cytomegalovirus

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15
Q

Viruses which cause parotitis

A

Mumps virus

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16
Q

Viruses which cause pneumonia

A

Influenza virus A and B

Parainfluenza virus

Respiratory syncytial virus

Adenovirus

SARS cornoavirus

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17
Q

Viruses which cause myelitis

A

Poliovirus

HTLC-I

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18
Q

Viruses which cause gastroenteritis

A

Adenovirus

Rotavirus

Norovirus

Astrovirus

Conoavirus

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19
Q

Viruses which cause pancreatitis

A

Coxsackie B virus

20
Q

Problems a virus must solve

A

Must know what cells to enter and how to enter them

How to replicate inside a cell

How to exit and move from one infected cell to a new cell

Develop mechanisms to evade host defences

21
Q

Viral pathogenesis

A

The process by which virus causes disease in a host

Two components of viral disease

  • effects of viral replication on the host
  • effects of host response on virus and the host
22
Q

Pathogenesis journey

A

Encounter

Entry

Multiplication

Spread

Damage

Outcome

23
Q

Encounter

A

Virus meets host

24
Q

Entry

A

Virus enters host

25
Q

Multiplication

A

Virus replicates in the host

26
Q

Spread

A

Virus spreads from the site of entry

27
Q

Damage

A

The virus, host response or both cause tissue damage

28
Q

Outcome

A

The virus or the host wins, or they coexist

29
Q

Skin

A

Abrasions

Insect/ animal bites

Needle punctures

30
Q

Alimentary tract

A

Gastroenteritis viruses

Movement facilitate viral entry

Hostile environment

  • extreme acidity/ alkalinity
  • digestive enzymes
31
Q

Urogenital tract

A

Mucus membranes; low pH

Abrasions facilitate viral entry

  • HPV: local lesions
  • HIV: viral spread
32
Q

Eye

A

Localised infection- conjunctivitis

Viral spread- eye blindness/ CNS

33
Q

Viral spread

A

After replication at site of infection

  • some remain localised within epithelium or within one system
  • some cause disseminated or systemic infection

Viral release

  • apical e.g. flu- facilitate viral dispersal, but virus does no invade underlying tissues
  • basolateral e.g. rabies- provides access to underlying tissues and may facilitate systemic spread
34
Q

Haematogenous spread

A

Ways of viral entry to blood:

  • directly through capillaries
  • by replicating in endothelial cells
  • through vector bite
  • by lymphatic capillaries

Once in the blood, virus has access to almost every tissue

35
Q

Viraemia

A

Presence of infectious virus in the blood

  • passive/ active viraemia
  • primary/ secondary viraemia

Diagnostic value- measuring viral replciation

Practical problem- need to screen blood donors

36
Q

Neural spread

A

Less common than haematogenous spread

Viruses can go either way

  • from peripheral sites to CNS
  • from CNS to peripheral sites
37
Q

Infection of the CNS

A

Neurotropic- virus can infect neural cells

Neuroinvasive- virus can enter CNS following infection of peripheral site

Neurovirulent- virus can cause disease of nervous tissue

38
Q

Tissue tropism

A

Limited or pantropic

Determinants of tropism

  • cell receptors- HIV/CD4+
  • cellular proteins that regulate viral transcription- JC/ viral enhancers in oligodendrocytes
  • cell proteases- flue/ serine proteases
39
Q

Viral genes affecting virulence

A

Those that affect the ability of virus to replicate

Those that modify host’s defense mechanism

Those that enable virus to spread

Those that have intrinsic cell killing effects

40
Q

Cytolytic viruses

A

Inhibition of host protein and RNA synthesis leads to loss of membrane integrity

Syncytium formation

Induction of apoptosis

41
Q

Non-cytolytic viruses

A

CD8+ mediated

CD4+ mediated

B cell mediated

42
Q

Chronic/ persistent infection

A

Continuous replication

Latency- restricted viral gene expression

43
Q

Latent infection

A

DNA viruses or retroviruses

Persistence of viral DNA

During cell growth the viral genome is replicated along with the host cell chromosomes

44
Q

Herpes simplex virus reactivation

A

Fever, blisters or cold sores

45
Q

How influenza viruses evade host defense mechanisms?

A

The virus can change its surface antigens- the immune response no longer able to identify them

Mechanisms of antigenic variation on HA and NA

  • antigenic drift
  • antigenic shift

302: Scientific Basis of Medicine (18 decks)

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