Introduction to Virology

Question 1

What are virus particles composed of?

Answer 1

• Nucleic acid genome
• Protein capsid
• Sometimes a lipid envelope associated with virus protein

Question 2

What is Adenovirus, Papillomavirus and Rotavirus?

Answer 2

• Adenovirus affects respiratory & GI
• Papillomavirus affects your genitals, mouth, or throat (passed through skin-skin contact
• Rotavirus - mainly children, stomach bug - very contagious

Question 3

What are Viral Components?

Answer 3

Virus genome:

Genomes of different viruses extremely varied:

• Chemistry - DNA or RNA
• Structure - double stranded, single stranded, linear, circular .

Protein capsid:

• Protects the genome from the environment
• Delivers genome to the cell

Virus envelope:

• In some viruses capsid is enveloped.
• The envelope consists of a lipid bilayer (derived from the host cell) containing viral proteins.

Question 4

What are the steps of gene expression?

Answer 4

1. Genome
2. Transcription (cell and/or virus)
3. mRNA
4. Translation (cell)
5. proteing
6. modification
7. mature protein

Question 5

What are common ways for virus to enter host?

Answer 5

Respiratory tract

• Inhalation & touch
• Sexual (upper respiratory)

Gastro-intestinal tract

• Ingestion and inhalation

Urogenitary tract

• Sexual transmission

Blood

• Vertical (child birth), needles, products, insect vector

Question 6

What is the viral spread withing the host?

Answer 6

Localised (discrete infection)

• Some viruses remain at the site of infection
• rhinovirus, molluscum

Mechanisms of spread:

• Neural spread i.e. Herpes Simplex Virus (HSV)
• Hematogenous spread i.e. in blood (HIV)

Question 7

What are the 2 different factors that the virus can cause damage to the host?

Answer 7

Viral factors:

• Cell lysis
• Cell-cell fusion (e.g. syncitia formation)
• Inhibition of host cell transcription, translation
• Alteration of host cell cycle, proliferation

Host factors:

• Apoptosis (cell ‘suicide’)
• Lysis of infected cells by immune cells
• Inflammation

Question 8

What are Immune responses to infection?

Answer 8

Neutralising Antibodies

• IgG & IgM

Cytotoxic T Cell Response

• Promote destruction of infected cell

Question 9

What are Problems posed by Viral infections?

Answer 9

Latency

• Herpes, Varicella-zoster

Chronic/Persistent infections

• HIV & Hepatitis C

Transformation of host cells

Evolution

• Numbers of replication cycles, RNA

Question 10

Viruses that are important in Dentistry?

Answer 10

BBV

• HIV
• Hepatitis

Respiratory and Mucosal

• Coronavirus
• Herpes
• Influenza
• HPV

Question 11

What is AIDs?

Answer 11

• Retrovirus
• Genome is RNA but changes to DNA
• This is contrary to normal DNA-RNA-Protein
• Reverse Transcriptase
• RT error prone so mutation rate very high
• Evolves 106 times faster than humans

Question 12

What is the key replicative cycle stages for AIDS?

Answer 12

1. HIV releases contents into target cell
2. Reverse transcriptase copies viral RNA into DNA
3. Vrial DNA is insterted into cellular DNA
4. Many copies of Viral RNA and proteins are made
5. New viral particles assemble and bud from cell, potentially killing it.

Question 13

What are key stages in time course of HIV disease?

Answer 13

1. Acute infection
2. Chronic lymphadenopathy
3. Sybclinical immune dysfunction
4. Skin and mucous membrane defects
5. Systemic immune deficiency

Question 14

How can yoou prevent HIV?

Answer 14

• Blood/ tissue - needle stick injuries
• Sex - use condom
• Mother/child