9. Lecture Flashcards
what is a virus environment
- another virus
- host cell
- host organism
when does interaction btw viruses occur
Only during multiplication (vegetative virus)
Simultaneous infection of the same cell
virus interaction can occur btw. which types of viruses
― usually related viruses, but not always
types of virus interaction
- Advantageous
- Disadvantageous (interference)
- Neutral (virusexaltation)
Advantageous interaction
on nucleic acid level (recombination)
on protein level (complementation, phenotype mixing)
• Disadvantageous interaction
interference
One virus inhibits the multiplication of the other
recombination
•Exchange of genetic information
→ new virus generation – inherited new properties
At least 20-40 nucleotide homology between the viruses is needed
Intramolecular recombination occurance:
- derailing of the polymerase during replication
- Aujeszky’s disease virus: even 70% transfer
- sometimes between non-related viruses (Polyoma – Adenovirus)
- also with RNA viruses (i.e. FMDV)
•Genetic reassortment definition
• Viruses with segmented genome (ie. Orthomyxoviridae)
• Exchange of segments during viral assembly
• Sudden, major antigenic changes
→ antigenic shift
Reactivation types
Cross-reactivation
Multiple reactivation
latent cell -> lytic stage (replication)
→ Do not use different live vaccines within a short time interval!
•Cross-reactivation
- btw who, example
- how
- Attenuated vaccine strain + related virus
- Repair of the defected virulence-genes
- i.e. herpesviruses
•Multiple reactivation
- btw who, example
- how
- Between two attenuated virus-strains
- Different defected genomic regions
- Mutual completion
Complementation
• Between defective and competent (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
Phenotype mixing
- Exchange of structural proteins
- Leukosis + sarcoma virus: acquiring envelope proteins
- Transcapsidation (Polio- + Coxsackievirus)
NON-HERITABLE!
Adsorption interference
Competition for the same cell-surface receptor
• related viruses, or
• after phenotype mixing, or
• 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 (DI)
• large amounts of incomplete progeny viruses
→ self-limiting infections (Paramyxo-, Rhabdoviridae)
•Heterologous interference
- non-related viruses
- viral suppressor protein production
- ie.: herpes, adenovirus – inhibits pox
Virusexaltation - neutral virus interaction
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
• Cytopathic effect appears
lytogenic cycle of viruses
after the multiplication of viruses, cell death occur
lysogenic cycle of viruses
cells incorporate the viruses NA into its own for exchange of survival
