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Virology > 6 Herpesviruses > Flashcards

6 Herpesviruses Flashcards

1
Q

where are herpesviruses

A

widely disseminated in nature

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2
Q

how many herpes viruses are there

A

eight human herpesviruses have been isolated

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3
Q

what are the herpesviruses

A
  • herpes simplex virus 1 and 2
  • varicella zoster virus
  • human cytomegalovirus
  • Epstein-Barr virus
  • human herpesviruses 6-8
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4
Q

herpesviruses genome

A

contain a linear, ds DNA genome

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5
Q

what encloses the capsid

A

capsid enclosed in viral tegument, lipid and glycoprotein envelope

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6
Q

Herpes simplex virus 1 (HIV-1) components

A
  1. core
  2. icosahedral capsid
  3. tegument
  4. envelope
    Linear, dsDNA genome
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7
Q

Herpesvirus DNA - genome difference

A
  • herpesvirus genomes vary greatly in size, base composition and structure
  • genomes vary in length from 120kb to 230kb and contain different arrangements of unique and repeat sequences
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8
Q

what are HSV-1 genomes like

A 
Segmented linear genomes
Unique long (UL) and Unique short (US) covalently attached molecules
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9
Q

genes in unique long segment in HSV-1

A

> 62

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10
Q

genes in unique short segment in HSV-1

A

> 12

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11
Q

HSV-1 genomes UL and US segments

A

Both segments can be inverted

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12
Q

what effect does the inversion of UL and US segments cause

A

resulting in 4 different genome rearrangement possibilities

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13
Q

what are the 4 genome rearrangement possibilities

A

P, IL, IS or ILS

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14
Q

what are the sub divided herpesviruses

A

three sub-families on basis of differences in:

  • host range and tissue tropism in vivo
  • host cell range and growth characteristics in vitro
  • site of latent infection
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15
Q

Herpesviridae classification

A

Beta, gamma and alpha

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16
Q

what do all herpesvirus encode

A

all encode many enzymes involved in metabolism (encode virtually all the genes that they need)

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17
Q

what occurs in nucleus

A

viral DNA synthesis and capsid assembly

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18
Q

what destroys the infected cell

A

release of progeny virus

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19
Q

what happens in cell entry

A

Herpes simplex expresses a range of surface proteins
Virus first has to be stabilised on the surface
Herpes virus glycoproteins interact with cell receptors
Will start a fusion with cell membrane and herpes will enter the cell

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20
Q

Endocytosed

A

low pH-dependent fusion

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21
Q

Micropinocytosis

A

pH-independent fusion

22
Q

Expression of viral genes

A

Occurs in regulated cascade:

  • immediate early genes: essential for co-ordinate regulation of other viral genes
  • delayed early genes: encode proteins essential for viral DNA replication
  • late genes: encode structural proteins
23
Q

HSV-1 genome genes encode

A

Some genes encode early transcription factors ( genes)

24
Q

Enhancer region

A

increase expression

25
Q

where is the TAATGARAT sequence

A

upstream

26
Q

in viral replication what is need

A

Enters as linear DNA
Organised into nucleosomes – tight and DNA condensed
Simplex genome enters – will be shut off unless HCF-1 opens it
HCF-1 host cell factor 1 open chromatin

27
Q

what happens when virus first expressed

A

innate immune response acts quickly

28
Q

how are cells killed

A

interaction between nucleofector that turns on all genes e.g. interferon, innate
lead to cell being killed

29
Q

how is HSV-2 transmitted

A

sexual contact

30
Q

how many adults are seropositive for HSV-2

A

10-30%

31
Q

what is latency

A

establish latent infection infection in dorsal root ganglia of sensory nerves (stay at stable number in dorsal root ganglia – only one region of virus expressed – latent)

32
Q

how can HSV-1 infect

A

Can enter through crack in e.g. nail

33
Q

HSV-1 in eye effect

A

replicate in cornea (denrditic ulcer, then infect anterior chamber)

34
Q

how can HSV-2 infect

A

Sexual organs

Mother giving birth with herpes simplex – high mortality rate for baby

35
Q

which HSV causes brain bleeding

A

HSV-2

36
Q

what is Alphaherpesvirus

A

VZV is endemic in most populations - chicken pox

Primary infection

37
Q

how does Alphaherpesviruses infect

A

occur via the respiratory route

38
Q

how many are infected by Alphaherpesviruses

A

At least 10% of population remain uninfected

39
Q

what is HCMV

A

human cytomegalovirus

40
Q

what are the herpesvirus 6 and 7

A

Betaherpesviruses

41
Q

how prevalent is HCMV

A

Prevalence of HCMV in adult populations is 70%

42
Q

what is HCMV a result of

A
  • intrauterine infection
  • perinatal infection
  • intimate or sexual contact
  • transfusion of whole blood, cellular products or solid organs
43
Q

what is the seroprevalence of EBV

A

80-90%

44
Q

where does EBV replicate

A

in epithelial cells of oro-pharynx

45
Q

where does EBV establish latency

A

EBV establishes latent infection in dividing populations of B cells

46
Q

what can primary infection with EBV cause

A

‘glandular fever’ syndrome

47
Q

what is chronic infection associated with

A

associated with three important diseases:

  • Burkitt’s lymphoma
  • nasopharyngeal carcinoma
  • other lymphomas
48
Q

where is Burkitt’s lymphoma problematic

A

Burkitt’s lymphoma is endemic in the malaria belt of equatorial Africa

49
Q

what is Burkitt’s lymphoma associated with

A

100% of endemic BL is associated with EBV infection

50
Q

what causes Burkitt’s lymphoma

A

arises in B cells expressing type 1 latency

51
Q

how does Nasopharyngeal carcinoma arise

A

Arises from epithelial cells expressing ‘type II’ EBV latency genes

52
Q

what does Nasopharyngeal carcinoma require

A

additional environmental and genetic co-factors

Virology (15 decks)

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