Viruses

Question 1

What is a virus?

Answer 1

“An infectious, obligate Intracellular parasite comprising Nucleic acids (DNA or RNA) surrounded by a protective protein coat an/ or a protective envelope derived from a host cell membrane”

Question 2

What are viruses made up of?

Answer 2

All viruses contain:
Protein
Nucleic acid
Some viruses contain:
Glycoproteins
Lipids (membrane)

Question 3

Describe DNA containing viruses

Answer 3

They are very diverse
Range in size from 3600 bases to 2.5 million bases
Can be single or double stranded
Can be linear or circular

Question 4

Describe RNA containing viruses

Answer 4

Also diverse
Range in size from 1700 bases to 32000 bases
Can be single stranded or double stranded
Can be linear, segmented or circular

Question 5

What are the 6 key stages to the viral replication cycle?

Answer 5

1. Attachment
2. Penetration
3. Uncoating
   4a. Transcription of viral genomes b. Translation of early genes
4. Assembly
5. Release

Question 6

Describe attachment

Answer 6

Vast majority of viruses sue specific receptors n cells to gain entry into them
Absorption leads to an attachment of a virion to a host cell

Question 7

Define adsorption

Answer 7

Process of cell coming into contact with virus

Question 8

List the 3 different types of tropism

Answer 8

Cellular
Tissue
Host

Question 9

Describe penetration

Answer 9

Process of membrane fusing with receptor mediated endocytosis
The lipid membrane of viruses fuses to lipid membrane of a host

Question 10

Describe uncoating

Answer 10

The release of Nucleic acid and enzymes

Question 11

Describe the transcription of viral genes

Answer 11

DNA viruses are transcribed via DNA dependent RNA polymerases
RNA viruses are transcribed using viral enzymes encoded by the genome carried in the virion
For retroviruses the RNA gene is copied first to DNA using reverse transcriptase followed by the host enzyme transcribing the viral DNA
+ve sense and ssRNA virus gene acts like mRNA to be transcribed

Question 12

Describe the translation of early genes

Answer 12

Cellular ribosomes translate viral mRNA
Control proteins bind to host DNA
DNA and RNA replication enzymes are used if they’re encoded for

Question 13

Describe translation of late genes

Answer 13

Genes for capsomeres and envelope proteins

Question 14

Describe assembly

Answer 14

Each virus has a unique assembly pathway
If the virus is enveloped it requires both lipid envelope and envelope glycoproteins
When the Golgi apparatus and Endoplasmic reticulum become important

Question 15

Describe the release process

Answer 15

Also known as egress
When the viruses leave the host cell
Some viruses are cytopathic whilst other are non-cytopathic

Question 16

Describe the difference between cytopathic and non-cytopathic viral cells

Answer 16

Cytopathic cells will damage the cell that it replicates in rather than non-cytopathic cells will migrate from host cells through the body

Question 17

Give the two phases that viruses can obtain

Answer 17

Extracellular- dead phase
Intracellular- Alive in a host cell

Question 18

List the different vial transmission routes in humans

Answer 18

1. Respiratory
2. Faecal-oral
3. Sexual contact
4. Blood borne
5. Vertical (mother to child)
6. Human- arthropod- human

Question 19

List the methods of viral transmission in zoonoses

Answer 19

1. Vertebrate- vertebrate
2. Vertebrate reservoir

Question 20

List the basic approaches to developing a vaccine

Answer 20

1. Whole inactivated virus
2. Live attenuated virus
3. Synthetic peptides
4. Recombinant subunit
5. Viral DNA or RNA
6. Recombinant bacterial vectors
7. Recombinant viral vectors

Question 21

List the outcomes of natural viral infection

Answer 21

Asymptomatic- Immune system handles the virus
Acute infection- small symptoms occur but they are resolved quickly
Immunological resolve- life long (chronic) infection
Detrimental immunity
Cancer
Latent infection
Death

Question 22

What is antiviral therapy?

Answer 22

Drugs used to treat viral infections

Question 23

Give the 3 types of antiviral drugs and how they work

Answer 23

Non-specific antivirals- Intefer with viral replication
Direct- acting- Target specific steps in the life cycle of viruses
Indirect-acting- Often target host pathways

Question 24

How are viruses inactivated to be made into a vaccine and why is this helpful?

Answer 24

By adding non-ionic chemical detergents
They inactivate a viruses infectivity but retain their antigenicity

Question 25

How can DNA vaccines be used?

Answer 25

To make cells produce certain antigens

Question 26

What are the 2 types of responses that occur when the immune system detects a virus?

Answer 26

Innate response
Adaptive response

Question 27

List the innate immune cells and their function

Answer 27

Cytokines- Allow cell to communicate with each other
Natural killer cells- Recognises part of the infected cells and go in and kill them
Macrophages- phagocytose and sterilise ‘foreign’ substances

Question 28

List the cells involved in the adaptive immune response and their function

Answer 28

B cells- Produce lots of antibodies
T cells:
Cytotoxic T cells- Recognise viral nested cells
T helper cells- Ensures all other components of immune system are best they can be
Regulatory T cell- Control immune activation ad allow it to be switched off when infection is cleared

Question 29

Give 2 emerging viruses

Answer 29

Nipah Virus
Lassa Fever

Question 30

Give 2 viral diseases and an effect they have on the body

Answer 30

Poliovirus pathogenesis- Virus replication in the cells of the anterior horn of the CNS that leads to tissue damage and eventual muscle paralysis
COV2- Causes cardiac and respiratory impairment,muscle fatigue and loss of taste and smell