Viruses

Question 1

What is a bacteriophage?

Answer 1

A bacterium that has been infected with a virus.

Question 2

Describe the features of a viron

Answer 2

Lipid envelope
Cpasid
Nucleic acid- DNA/RNA? ss or ds? positive/negative/ambisense?

Question 3

Describe the processes involved in viral pathogenesis.

Answer 3

1. Implantation at portal entry (e.g. eyes, mouth, skin, UT)
2. Local replication
3. Spread to target organs
4. Multiplication in the target organs
5. Spread to the sites for viral shedding into atmosphere (e.g. milk, saliva, respiratory tract, semen, germ cells)

Question 4

How do viruses cause disease?

Answer 4

1. Infecting cells to produce dysfunction
2. Toxic products of viral replication/ cell necrosis
3. Inflammation
4. Immunosuppression

Question 5

Describe the difference between acute and chronic/persistent infection by viruses.

Answer 5

Acute - virus infects hosts
Chronic/persistent- continues infection beyond time when immune system should’ve cleared it. There is equilibrium set up between host and virus. This can either be by

continuous replication/latency or

by restricted viral gene expression/no viral proteins; immunologically silent.

Question 6

What is latent infection?

Answer 6

Occurs in retroviruses and DNA viruses

During the S phase, the viral genome is replicated alongside the host genome.

It can result in transformation of the host genome which leads to cancer

Question 7

What is the difference between exogenous and endogenous viruses? E.g.?

Answer 7

Endogenous viruses- endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. Most viruses can become endogenous.

Exogenous viruses- These are infectious RNA-containing viruses which are transmitted from human to human. e.g. HIV

Question 8

Define virulence

Answer 8

Relative capacity of an organism to cause disease

Question 9

Define tropism

Answer 9

Specific cells and tissues of a host that support growth of particular pathogen. They determine disease.

Question 10

Describe 5 methods by which we can detect the presence of a virus.

Answer 10

1. Microscopy
2. Use PCR on viral nucleic acid. ADV: within 24hrs, can quantify virus. D.AVV: costly
3. Viral proteins- D.ADV gives you the group of viruses not necessarily the specific one.
4. Antibody mounted against viral antigens
5. Culture- D.ADV: not all viruses will grow in culture, require multiple cell lines and its slow.

Question 11

Suggest 6 methods of prevention/treatment.

Answer 11

1. Vaccines
2. Chemoprophylaxis
3. Supportive measures
4. Antipyretics (reduce fever)
5. Immunoprophylaxis
6. HAART for HIV (keeps viral load low)

Question 12

How can CD8+ t-lymphocytes detect that a cell is infected by a virus?

Answer 12

Viral peptide in MHC1 on cell surface.

Question 13

What condition can cause superinfection by HSV?

Answer 13

Eczema

Question 14

How do virally infected cells control the spread of virus within the body?

Answer 14

They secrete interferon which has a paracrine effect on neighbouring cells causing them to slow down protein synthesis.

Question 15

How could antibodies prevent viruses entering cells?

Answer 15

They could bind to virus-specific-specific receptors thus blocking virus from binding.

Question 16

Describe the role how CD8 positive cells are involved in the immune response against viruses.

Answer 16

1. Virally infected cells produce viral proteins.
2. A sample of this passes through a proteasome and degraded into viral peptides.
3. These are transported back into the ER by TAP and then loaded into a MHC1 molecule in the cell surface.
4. CD8+ T cell specific to this antigen will recognise antigen causes destruction of cell.