Retroviruses

Question 1

What do normal RNA viruses contain?

Answer 1

• double stranded RNA positive

- single strand RNA negative

Question 2

What distinguishes retroviruses?

Answer 2

• diploid positive sense RNA

- contain reverse transcriptase which generates DNA which is integrated into host genome

Question 3

Main example of a retrovirus

Answer 3

HIV

Question 4

What is the life cycle of a retrovirus?

Answer 4

• virus binds to specific receptor on cell surface
• double strand RNA enters cell
• changes to DNA by reverse transcriptase
• DNA in nucleus integrates into host DNA
• millions of copies of virus can be made, proteins made
• proteins assemble at cell surface
• virus efflux picking up coat of bilayer

Question 5

What is the receptor which HIB binds to?

Answer 5

CD4

Question 6

Features of the retrovirus structure

Answer 6

• surface envelope (binding to target cell surface)
• matrix (holds virus shape)
• capsid inside matrix containing RNA to make copies of itself
• lipid envelope
• protease
• reverse transcriptase

Question 7

What do accessory proteins do?

Answer 7

Interact with host innate immune response to viral infections counteracting it

Question 8

What is the key enzyme!!! What does it do???

Answer 8

Reverse transcriptase - transcription of viral RNA to DNA

Question 9

What does integrase do?

Answer 9

Integration of ds DNA into host genome to form provirus

Question 10

What does protease do?

Answer 10

After new virion release, cleaves certain proteins for viral maturation and infectivity

Question 11

What are the 2 groups of retroviruses?

Answer 11

Oncovirinae - induce oncogenesis causing tumours

Lentivirinae

Question 12

What are some examples of oncovirinae?

Answer 12

RSV (rous sarcoma virus)
HTLV-1 (human T cell lymphotropic virus, first to be discovered)
HTLV -2

Question 13

What does the genome of retroviruses consist of?

Answer 13

Gag, Pol, Env (structural genes)
Plus accessory proteins
Regulatory genes

Question 14

How widespread is HTLV?

Answer 14

Southern Japan (via Portuguese explorers who had been in Africa)
Central America (slave trade reached)
South America (slave trade)
Africa where it originated in ancient times
Caribbean
15-20 million people

Question 15

How is HTLV is transmitted?

Answer 15

• prolonged breast feeding mother to child
• sexual contact
• blood transfusion

Question 16

How common are the different types of HTLV?

Answer 16

1 is most common, 4 is least

Question 17

What does HTLV1 cause?

Answer 17

Adult T cell leukaemia
HTLV1 associated myelopathy
Tropical Spastic Paraparesis

Question 18

What is the latency period of HTLV1?

Answer 18

20-30 years

Long

Question 19

What is TSP? How does it present?

Answer 19

Tropic Spastic Paraparesis

• chronic
• progressive
• nervous system disease
• weakness, stiff muscles, muscle spasms, sensory disturbances, sphincter dysfunction
• affects adults in equatorial regions

Question 20

How is TSP treated?

Answer 20

• high dose of IV methylprednisolone and daily prednisolone

Question 21

What is adult T cell leukaemia?

Answer 21

Clonal aggressive malignancy of CD4+ T lymphocytes

- skin can be involved

Question 22

How is adults T cell leukaemia treated?

Answer 22

• chemotherapy often ineffective

- ongoing trials (IFNalpha)

Question 23

What does HTLV2 cause?

Answer 23

• HAM/TSP

- hairy cell leukaemia

Question 24

What is the long latency of HTLV2?

Answer 24

Longer than HTLV1

20-30 years

Question 25

What is hairy cell leukaemia?

Answer 25

• leukaemia cells collect in spleen
• spleen swells
• few normal WBCs as leukaemia invades bone marrow
  = reduced infection resistance

Question 26

How is HTLV transmission different from HIV transmission?

Answer 26

• requires cell to cell contact

Question 27

What are some examples of lentivirinae?

Answer 27

HIV-1

HIV-2

Question 28

How widespread is HIV?

Answer 28

• over 70 million people infected
• main epidemic is HIV1 in West Africa
• from chimpanzees to human

Question 29

How is HIV transmitted?

Answer 29

• unprotected sexual intercourse with infected partner
• vertical transmission mother to child (in utero, during delivery or via breastmilk)
• injection drug use

Question 30

What does HIV require to infect cells?

Answer 30

• both CD4 and chemokine receptor (CXCR4 or CCR5)

to be expressed by cells

Question 31

What is the course of HIV infection?

Answer 31

• first 3 weeks virus multiplies lots and CD4 cell target cell decline
• immune system takes control and increases CD4 and reduces viral load (clinical latency where individual is unaware of infection)
• CD4 declines further and viral load increases (opportunistic infections)

Question 32

What are the opportunistic infections of HIV?

Answer 32

• oral candidiasis

- interstitial pneumonia

Question 33

What is a clade?

Answer 33

• related virus from a common ancestor (shows how diverse the virus is)
• HIV has many clades so is very diverse vs. measles for example
• Clade B in North and South America and Western Europe and Australia
• Clade C, A and AG are most common

Question 34

What is a recombinant?

Answer 34

When clades combine and make a new virus

Question 35

What is the treatment of HIV?

Answer 35

• HAART (immediately)

Question 36

Role of gag

Answer 36

Codes for proteins which make up matrix, capsid and nucleoprotein structures

Question 37

Role of pol

Answer 37

Codes for reverse transcriptase and integrase and protease enzymes

Question 38

Role of env

Answer 38

Codes for surface and transmembrane components of viral envelope protein