Viruses

Question 1

Introduction to viruses - characteristics of viruses:

Answer 1

• Acellular infection agent with DNA or RNA
• Neither grow nor respond to environment
• Cannot carry out any metabolic pathway
• Cannot reproduce independently
• Recruits cell’s metabolic pathways to increase their numbers
• No cytoplasmic membrane, cytosol, organelles

Question 2

Introduction to viruses - genetic material:
May be…
What does the genetic material look like?

Answer 2

1. Genetic material may be DNA or RNA but not both
2. Linear and segmented or single and circular

Question 3

Introduction to viruses - capsid morphology:
What does the capsid provide?
Composed of?

Answer 3

1. Provide protection for nucleic acids
2. Proteinaceous subunits called capsomeres

Question 4

Introduction to viruses - viral shapes:

Answer 4

Helical, polyhedral and complex

Question 5

Introduction to viruses - viral envelope:
How are they equired?
Composed of?
What are some proteins coded as?

Answer 5

1. Acquired from host cell during viral replication/release
2. Composed of phospholipid bilayer and proteins
3. Some proteins are virally coded glycoproteins (spikes)

Question 6

Introduction to viruses - classification:
Morphology
Serology
Genetic material
Form of genetic material

Answer 6

1. By electron microscopy
2. Antibody cross reactivity
3. Sequence homology
4. Baltimore Classification System

Question 7

Viruses have 4 possible types of nucleic acid genomes:

Answer 7

• Double stranded DNA (+ and - sense)
• Single stranded DNA (+ sense) and single stranded DNA (- sense)
• Double stranded RNA (+ and - sense)
• Single stranded RNA (+ sense) and single stranded RNA (- sense)

Question 8

During virus replication, what 2 things are produced?

Answer 8

• Produce copies of the viral genome
• Produce mRNA which is able to be translated into viral proteins

Question 9

5 steps of viral replication

Answer 9

1. Attachment
2. Entry
3. Uncoating
4. Replication
5. Assembly and release

Question 10

What is lytic replication?
What is lysogeny?
What are the temperate phages of lysogeny?
What happens with lysogenic conversion?

Answer 10

1. Replication cycle usually results in death and lysis of host cell
2. Modified replication cycle
   Infected host cells grow + reproduce normally for generations before they lyse
3. Prophages - inactive phages
4. Results when phages carry genes that alter phenotype of bacterium

Question 11

What are the differences between bacteriophage and animal virus replication?

Answer 11

• Presence of envelope around some viruses
• Eukaryotic nature of animal cells
• Lack of cell wall in animal cells

Question 12

Viruses causes what percentage of human cancers?
What do some carry?
What do some interfere with?

Answer 12

1. 20-25%
2. Some carry oncogenes or some promote oncogenes already in host
3. Some interfere with tumour repression

Question 13

Viral diseases and treatment - viral conjunctivitis:
Signs and symptoms
Pathogen
Epidemiology

Answer 13

1. Itchy eyes, tearing, redness, discharge, light sensitivity
2. • Most caused by adenovirus but can be others
     - Most problematic is Herpes Simplex virus
3. Self limiting disease, highly contagious

Question 14

Viral diseases and treatment - viral conjunctivitis:
Treatment
Diagnosis
Prevention

Answer 14

1. No treatment unless HSV then topical antivirals like Idoxuridine, vidarabine, trifluridine
2. Symptoms used but further investigation in severe cases
3. Avoid touching eyes, use different towels and linen, stay at home

Question 15

Viral diseases and treatment - viral otitis media:
Signs and symptoms
Pathogens
Epidemiology

Answer 15

1. Severe pain in ears
2. Adenoviruses
3. Viruses in pharynx spread to sinuses via throat

Question 16

Viral diseases and treatment - diagnosis/treatment:

Answer 16

Symptoms often diagnostic and no effective treatment, no known prevention

Question 17

Viral diseases and treatment - viral meningitis:
Signs and symptoms
Pathogen
Pathogenesis

Answer 17

1. Similar to bacterial meningitis, usually milder
2. 90% cases caused by genus Enterovirus
3. Damage to cells in the meninges triggers it

Question 18

Viral diseases and treatment - viral meningitis:
Epidemiology
Diagnosis/treatment

Answer 18

1. • More common than bacterial/fungal
     - Spread via respiratory droplets and faeces
2. • Diagnosed by characteristics signs/symptoms in the absence of bacteria in CSF
     - No specific treatment

Question 19

Viral diseases and treatment - cold sores (herpes):
Signs and symptoms
Pathogen
Pathogenesis

Answer 19

1. • Slow spreading skin lesions
     - Recurrent lesions common
2. Caused by human herpes viruses 1 and 2
3. • Painful lesions caused by inflammation and cell death
     - Cause fusion of cells to form syncytia

Question 20

Viral diseases and treatment - cold sores (herpes):
Epidemiology
Diagnosis/treatment

Answer 20

1. • Spread between mucous membranes of mouth and genitals
     - Herpes in adults not life threatening
2. • Diagnosis from lesion presence
     - Immunoassay reveals presence of viral antigens
     - Chemotherapeutic drugs help control disease but not cure

Question 21

Viral diseases and treatment - hand foot and mouth disease:
Signs and symptoms
Pathogen
Epidemiology

Answer 21

1. • Cold-like symptoms, loss of appetite, mild fever, 38-39C
     - Non itchy red rash with bumps/fluid filled sac found around hands and feet
     - Painful mouth ulcers
2. • Coxsackievirus A16, A6, A10
     - Enterovirus 71 (more complications)
3. • Spread by oral-oral or faecal-oral route
     - Not life threatening but can cause encephalitis

Question 22

Viral diseases and treatment - hand foot and mouth disease:
Diagnosis/treatment

Answer 22

• Diagnosed by symptoms
• No treatment as usually self limiting
• No vaccine, prevention by good hygiene

Question 23

Viral diseases and treatment - respiratory syncytial virus:
Signs and symptoms
Pathogen
Pathogenesis

Answer 23

1. • Fever, runny nose and coughing in babies or immunocompromised people
     - Mild cold-like symptoms in older children or adults
2. Respiratory syncytial virus (RSV)
3. • Virus causes syncytia to form in lungs
     - Immune response to RSV further damages lungs

Question 24

Viral diseases and treatment - respiratory syncytial virus:
Epidemiology
Diagnosis/treatment

Answer 24

1. Transmission via close contact
2. • Diagnosis by immunoassay
     - Supportive treatment for children
     - Prevention includes aseptic technique of healthcare and day care employees

Question 25

Anti-virals - mechanism of action:

Answer 25

- Key is selective toxicity - Antibacterial drugs constitute largest number and diversity of antimicrobial agents - Fewer drugs to treat eukaryotic infections - Even fewer antiviral drugs

Question 26

Anti-viral - inhibition of metabolic pathways: Antiviral agents can target unique aspects of viral metabolism (examples) Protease inhibitors interfere with an enzyme HIV needs in its replication cycle (examples

Answer 26

- Amantadine, rimantadine and weak organic bases prevent viral uncoating - Boceprevir, darunavir, fosamprenavir and telaprevir

Question 27

Anti-viral - inhibition of nucleic acid synthesis: Nucleotide or nucleoside analogs - how they work? effective against? Reverse transcriptase inhibitors - act against?

Answer 27

1. - Interfere with function of nucleic acids - Distort shapes of nucleic acid molecules and prevent further translation, transcription or replication - Most often used against viruses - Effective against rapidly dividing cancer cells 2. - Act against enzyme HIV uses in its replication cycle - Do not harm people as humans lack reverse transcriptase

Question 28

Prevention of virus attachment: What occurs? Why is there not much info?

Answer 28

- Attachment antagonists block viral attachment/receptor proteins - New area of antimicrobial drug development