13 - Viral interactions

Question 1

What is defined as viral environment?

Answer 1

• Another virus
• Host cell
• Host organism

Question 2

When does viral interaction occur?

Answer 2

• Only during multiplication (vegetative virus)
• Simultaneous infection of the same cell
• Only between certain viruses (usually related viruses, but not always)

Question 3

Types of viral interactions

Answer 3

• Advantagous
  
  • ​On nucleic acid level (recombination)
  • On protein level (complementation, phenotype mixing)
• Disadvantageous (interference)
• Neutral (virusexaltation)

Question 4

Advantagous interaction

Recombination

Answer 4

• On nucleic acid level
• Excange of genetic information → new virus generation - inherited new properties
• At least 20-40 nucleotide homology between the viruses is needed
• Intramolecular recombination:​
  
  • Derailing of the polymerase during replication
  • Aujeszky’s disease virus: even 70% transfer
  • Sometimes between non-related viruses (Polyomavirus ⟷ adenovirus)
  • Also with RNA virus (i.e. FMDV)
• Genetic reassortment:
  
  • ​Viruses with segmented genome (ie. orthomyxoviridae)
  • Excange of segments during viral assembly
  • Sudden, major antigenic cahnges → antigenic shift
• Reactivation;
  
  • ​Cross-reactivation:
    
    • Attenuated vaccine strain + related virus
    • Repair of the defected virulence-genes
    • i.e herpesviruses
  • Multiple reactivation:
    
    • Between two attenuated virus-strains
    • Different defected genome regions
    • Mutual completion

→ Do not use different live vaccines within a short time interval!

Figure: intramolecular recombination

Question 5

Advantagous interaction

Complementation

Answer 5

• On protein level
• Between defective and cometent (helper) viruses
• Exchange of enzymes (mainly polymerase) → multiplication of the defected virus
  
  • Heat sensitive mutant + wild type virus
  • Avirulent virus + inactivated virulent virus (pox)
  • Dependovirus + adenovirus

Question 6

Advantagous interaction

Phenotype mixing

Answer 6

• On protein level
• Exchange of structural proteins
• Leukosis virus + sarcoma virus: acquiring envelope proteins
• Transcapsidation if a similar capsid (poliovirus + coxsackievirus)
• Non-heritable!

Question 7

Disadvantageous interaction

Interference

Answer 7

• One virus inhibits the multiplication of the other
• Adsorption interference:
  
  • Competition for the same cell-surface receptor, either:
    
    • Related viruses
    • After phenotype mixing
    • Different viruses, but the same receptor (ie. CAR)
• Autointerference:
  
  • _​_Complete and incomplete forms of the same virus
  • Also at adsorption
  • Incomplete virion: shorter nucleic acid → higher mobility, polymerase affinity
  • Competition for enzymes, ribosomes → defective interfering particles
  • Large amounts of incomplete progeny viruses → self-limiting infections (paramyxoviridae, rhabdoviridae)
• Heterologous interference:
  
  • _​_Non-related viruses
  • Viral suppressor protein production
  • Ie.: herpesvirus, adenovirus, inhibits pox

Question 8

Neutral interaction

Virusexaltation

Answer 8

• The viruses are able to multiplicate independently
• The simultaneous infection does not effect the multiplication

But….

• Changes the viral influence on the host cell or organism:
  
  • Increased pathogenicity (Poliovirus + Coxsackievirus in monkey)
  • Cytopathic effect appears (Classical swine fever virus, BVDV + Newcastle disease virus)