11 - RNA Viruses

Question 1

Big difference between DNA and RNA viruses

Answer 1

RNA viruses and more likely to evolve/mutate faster than DNA viruses due to absence of proof reading mechanism

Question 2

Influenza virus

Answer 2

• Single strand (-) sense RNA
• RNA is segmented
• Each segment codes for one or two proteins
• Envelope glycoproteins HA
  and NA critical for entry and
  exit of virus into host cell

Question 3

Influenza A

Answer 3

• All IVA are viruses of birds
• 18 HA and 11 NA identified
  to date

Question 4

what does the H and N stand for in H1N1

Answer 4

Hemagglutinin and Neuraminidase

Question 5

Genetic reassortment

Answer 5

• ‘Mixing’ of RNA via coinfection of a host cell by more than one IV
• Can result in formation of IV with genomes which have never been seen by human immune systems
• infection can result in very severe disease and high rates of death

Question 6

Infuenza antigenic changes

Answer 6

Structure of hemagglutinin (H) and neuraminidase (N) periodically change

Question 7

Influenza antigenic changes (shift)

Answer 7

• Major change, new subtype
• Exchange of gene segment (reassortment): resulting virus is immunologically distinct from previous IV
• no existing immunity
• May result in pandemic

Question 8

Influenza antigenic changes (drift)

Answer 8

• Minor change, same subtype
• Point mutations in HA and/or NA genes: pre- existing immune response cannot control replication
• May result in epidemic

Question 9

Coronaviruses

Answer 9

(+) sense, enveloped, non segmented RNA viruses with largest genomes of RNA viruses: ~30 kb

Question 10

Human immunodeficiency virus

Answer 10

• Family Retroviridae
• Icosahedral, enveloped ss(+)RNA
• Infects CD4+ cells by binding of viral gp120
• Quasispecies
• CD4+ T cell count gradually and consistently declines

Question 11

How does HIV replicate

Answer 11

By conversion of viral RNA to complementary DNA (viral reverse transcriptase), which then integrates (viral integrase) into host cell genome (provirus), remains integrated for life of cell

Question 12

Quasispecies

Answer 12

a group of related variant viruses that arise by mutation

Question 13

HIV-1

Answer 13

Cause of almost all human infections. May have come from chimpanzees

Question 14

HIV-2

Answer 14

A less aggressive disease progression. Genetically more closely related to simian immunodeficiency virus (SIV)

Question 15

Group M HIV-1

Answer 15

Dominant form worldwide. Clades A-K within group M

Question 16

Circulating recombinant forms (CRF)

Answer 16

Emerging variants of HIV-1 that are combined clades

Question 17

HIV transmission

Answer 17

• Injecting drug
• Transfusion
• Contaminated equipment
• During delivery
• Breast milk
• Sexual

Question 18

Early phase HIV infection

Answer 18

• Initial viruses are macrophage tropic
• Envelope glycoprotein gp120 is able to bind to CD4 molecules and chemokine receptors called CCR5
• Relatively ‘non virulent’

Question 19

Late phase HIV infection

Answer 19

• Viruses are T cell trophic, having gp120 capable of binding to CD4 and CXCR4 found on T4 lymphocytes
• Highly virulent
• Induces syncytia

Question 20

What is the appearance of T tropic HIV viruses associated with

Answer 20

Rapidly declining CD4 counts and AIDS

Question 21

Diagnosis of AIDS

Answer 21

CD4+ T cells <200 cells/μl

Question 22

Conclusion of the Sydney Blood Bank Cohert (Long Term Non Progressers)

Answer 22

Attenuation of the HIV-1 genome, specifically the nef gene, interferes with viral replication and can influence disease outcome

Question 23

CCR5-delta32

Answer 23

Slow progressers that were homozygous for a 32bp deletion in the CCR5 gene (results in a frame shift and generates non functional receptor for HIV-1)

Question 24

CCR5

Answer 24

Chemokine receptor expressed on T cells, macrophages, dendritic cells and microglia