Blood Bourne Viruses

Question 0

What are capsids?

Answer 0

Protein coating of viral nucleic acids made up of only repeating units

Question 1

What is a virus?

Answer 1

A small infectious agent that replicates only inside the living cells of other organisms

Question 2

What are the two symmetries of capsids?

Answer 2

Icosahedral - form an almost spherical structure

Helical - found in RNA viruses that have capsids bound around helical nucleic acid

Question 3

What is an enveloped virus?

Answer 3

When the nucleic acids and capsid proteins are surrounded by a lipid envelope derived from the host cell or nuclear membranes

Question 4

What are lipid viruses sensitive to?

Answer 4

Substances that dissolve the lipid membrane

Question 5

What can be viruses be classified by?

Answer 5

Genetic material
Mode of replication
Structure and symmetry of structural proteins (capsids)
Presence/absence of an envelope

Question 6

What are the two classifications of DNA viruses?

Answer 6

Double stranded (dd)
Single stranded (ss)

Question 7

Name some dd viruses

Answer 7

Pox virus
Herpes
Adenovirus

Question 8

How do DNA viruses normally replicate?

Answer 8

In the nucleus of the host cell
Produce a polymerase which reproduces viral DNA
(Viral DNA not normally incorporated into host DNA)

Question 9

Two classifications of RNA viruses?

Answer 9

Sense (positive)

Antisense (negative)

Question 10

How do RNA sense (positive) replicate?

Answer 10

RNA may serve directly as mRNA

Translated into structural protein and an RNA-dependent RNA polymerase

Question 11

How can antisense (negative) viruses replicate?

Answer 11

Contain an RNA-dependent RNA polymerase that transcribes the viral genome into mRNA.
Alternatively, transcribed RNA can act as a template for further viral antisense RNA

Question 12

What are retroviruses?

Answer 12

Viruses which possess ss+ RNA that cannot act as mRNA
Transcribe into DNA by reverse transcriptase and incorporated into host DNA
Subsequent transcription to make mRNA and viral genomic RNA is under control of host transcriptase enzymes

Question 13

Classify HIV

Answer 13

Spherical enveloped RNA retrovirus

Question 14

How does HIV replicate?

Answer 14

Uses reverse transcriptase to produce DNA copy from viral RNA
This is incorporated into the host nucleus to become a template for further viral RNA

Question 15

What are the two types of HIV and which is most common?

Answer 15

HIV-1 most common

HIV-2 found mainly in west Africa

Question 16

Which type of HIV is less virulent?

Answer 16

HIV-2

Question 17

How is HIV transmitted?

Answer 17

Parenterally

Sexually

Question 18

How is HIV spread in developing countries?

Answer 18

Heterogenous sex
Unscreened transfusions
Contaminated medical equipment

Question 19

Which cells does HIV infect?

Answer 19

Those with a CD4 receptor

So T cells and macrophages

Question 20

Pathogenesis of HIV?

Answer 20

Binds to host cells
Virus and cell fuse
This releases enzymes for reverse transcription and integration into host genome (using integrase)
T cell itself is activated by fighting an infection
Causes cellular transcription factors to be present which allows HIV to be actively produced
Mature in bud at host cell plasma membrane (long chains of proteins come together)
Buds off to infect another cell
Protein chains in new viral particle cut by protease into individual proteins which combine to make a working virus

Question 21

Why is it difficult to design treatments for HIV?

Answer 21

Reverse transcription of HIV viral RNA to DNA is error prone so has a high mutation rate

Question 22

What are the aims of management of HIV?

Answer 22

Minimise replication
Prevent emergence of resistant virus
Reconstitute immune response

Question 23

What types of drugs are used in the management of HIV?

Answer 23

Non-nucleoside reverse transcriptase inhibitors (NNRTIs)
Nucleoside RTIs (NRTIs)
Protease inhibitors
Fusion inhibitors
Integrase inhibitors
Co-receptor/enthusiasm inhibitors

Question 24

How can transmission from mother to child be prevented?

Answer 24

Administration of HAART
C-section
Avoid breastfeeding

Question 25

Principles of infection prevention of HIV?

Answer 25

Avoid high risk partners
Avoid unprotected sex
Blood products should be screened
Free needle exchange programmes
Anti-retrovirus prophylaxis for needle-stick injuries

Question 26

Classify hep B

Answer 26

Hepadnavirus
Small
Enveloped
dd DNA

Question 27

What does the DNA in HBV code for?

Answer 27

HBsAg, HBcAg, HBcAg - 3 surface antigens
Large active polymerase protein
Transactivator protein

Question 28

What percentage of the world’s population have been infected with HBV? Proportion who are chronic carriers?

Answer 28

Third of the population has been infecte

5% are chronic carriers

Question 29

What percentage of those who carry HBV will go on to develop liver disease?

Answer 29

25%

Question 30

Mechanisms of infection of HBV?

Answer 30

Parenteral
Sexual
Congenital

Question 31

Incubation period of HBV before development of acute hepatitis?

Answer 31

Up to 6 months

Question 32

Complications of chronic hepatitis?

Answer 32

Cirrhosis

Hepatocellular carcinoma

Question 33

Symptoms of HBV?

Answer 33

Fever
Malaise
Jaundice
Raised ALTs

Question 34

Main treatment of HBV?

Answer 34

Peglycated interferon (IFN) is the best for sustained suppression without drug resistance
Can also use a nucleoside inhibitor to reduce viral load but resistance can emerge

Question 35

What can antiviral suppression of HBV for 2-5 years result in?

Answer 35

Ever say of hepatic fibrosis and prevents cirrhosis

If cirrhosis is established, can improve liver function and reduce cancer risk

Question 36

Prevention of HBV?

Answer 36

Immunisation
Vaccine and immunoglobulin to neonates of infected mothers
Needle exchange programmes
Sexual health education