35.6 Population Virology

Question 1

What factors can influence persistence and transmission of a virus?

Answer 1

Availability of hosts. population density, multiple different hosts.

Question 2

What are the different routs of transmission?

Answer 2

*Feco-oral route
*Respiratory droplets or aerosol
*Saliva
*Genito-urinary transmission
*Transfusion, blood products (e.g. drug abuse)

Question 3

Give an example of a virus transmitted through the feco-oral route.

Answer 3

Polio

Question 4

Give an example of viruses transmitted via respiratory droplets or aerosol.

Answer 4

Influenza, SARS-CoV-2

Question 5

Give an example of a virus transmitted via saliva

Answer 5

EBV

Question 6

Give an example of a virus with Genito-urinary transmission.

Answer 6

HIV

Question 7

Give an example of viruses transmitted through transfusion and blood products.

Answer 7

HIV/ HBV

Question 8

How can viral infections be prevented/ treated?

Answer 8

*Vaccination (e..g. smallpox eradication)
*Antiviral drugs

Question 9

Why do viruses have a high mutability of their genome?

Answer 9

*RNA-dependent RNA polymerases and reverse transcriptase are used in replication - they have a very low fidelity rate.
*Especially RNA viruses (Blatimore 3-7)

Question 10

Why do the enzymes involved in virus replication have a low fidelity rate, what is the fidelity rate?

Answer 10

these enzymes have a very low fidelity rate compared to eukaryotic counterparts due to lower affinity threshold + lack of proofreading mechanism.

Question 11

What introduces a selection pressure on the viruses?

Answer 11

Neutralizing Abs and T-cells

Question 12

What is antigenic drift?

Answer 12

Small changes in the antigenic structure due to random mutations within the antigen gene, caused for example by the error-prone RNA polymerase
* Lead to epidemics (i.e. yearly seasonal outbreaks of the flu)

Question 13

Which viruses commonly display antigenic drift?

Answer 13

Influenza/ SARS-CoV-2/ HIV

Question 14

What is antigenic shift?

Answer 14

Large changes in the antigens due to obtaining a new gene for the antigens (haemagglutinin and neuraminidase) from e.g. swine flu
* Lead to pandemics

Question 15

Which virus often displays antigenic shift?

Answer 15

influenza

Question 16

What is antigenic conservatism?

Answer 16

Conservation of a core component needed for normal functioning.
*e.g. VP1/2/3 surface capsid proteins used for engagement of host CD155 and entry all have conserved core in polio virus.

Question 17

Why are there less available treatments for viruses compared to bacteria?

Answer 17

Limited choice of targets, often due to viruses inhabiting host cells. Many antiviral therapies target viral enzymes, however there is still a risk of development of resistance.

Question 18

What are the different anti-viral therapies available for HIV?

Answer 18

*HIV reverse transcriptase inhibitors
*HIV protease inhibitors
*HIV entry inhibitors
*HIV integrase inhibitors

Question 19

What are the 2 different classes of HIV reverse transcriptase inhibitors?

Answer 19

*chain terminators - inhibit the synthesis of new viral DNA molecules in a similar way to sanger sequences.
*Direct RT inhibitors - competitively inhibit RT action on +ssRNA

Question 20

Give an example of a chain terminator (anti-HIV)

Answer 20

Zidovudine

Question 21

Give an example of a direct RT inhibitor (anti-HIV)

Answer 21

Nevirapine

Question 22

Give an example of a HIV protease inhibitor and its mechanism of function

Answer 22

saquinavir
*to prevent the cleavage of gag, pol and env precursors into functional forms

Question 23

Give an example of a HIV integrase inhibitor and its mechanism of function.

Answer 23

Raltegravir
*prevent the effective insertion of viral DNA into the host cell chromosomes

Question 24

Give an example of a HIV entry inhibitor and its mechanism of action.

Answer 24

Maraviroc
*binds to CCR5 on the surface of T-cells preventing HIV env protein gp120 from doing so.

Question 25

What is ART (Anti-retroviral therapy)?

Answer 25

The use of combinations of 2 or 3 anti-retroviral drugs to minimise drug resistance that result from high HIV mutation rate.

Question 26

State the two main types of antineuraminidase drugs (used to treat influenza).

Answer 26

• zanamifir (Relenza)
• oseltamivir (Tamiflu)

Question 27

How can the release of new influenza viruses from host cells be targeted by antiviral drugs?

Answer 27

Neuramidinidase inhibitors are used as antiviral drugs, since neuraminidase is required to cleave sialic acid, releasing new viruses.

Question 28

How can herpes be treated?

Answer 28

• Aciclovir and ganciclovir
• Herpes viruses have thymidine kinase (TK) genes
• These convert the aciclovir and ganciclovir into triphosphates that act as chain terminators in DNA replication
• They can be used against HHV-1, HHV-3 and HHV-5, but they are not effective in latency because TK is not expressed

Question 29

What issues are there with viruses in palliative care?

Answer 29

*Lack of effective drugs
- sometimes anti-viral drugs used to alleviate symptoms + suffering
*Lack of specific diagnosis due to similarity of symptoms
- difficult to make specific diagnosis early enough to give effective treatment.

Question 30

What is the role of anti-inflammatory drugs in palliative care?

Answer 30

They can be used to reduce symptoms of an infection to improve quality of life and alleviate suffering, however they can make it easier for the virus to damage cells and lead to lytic changes.
Therefore, not an ideal treatment option.