9. Lecture

Question 1

what is a virus environment

Answer 1

• another virus
• host cell
• host organism

Question 2

when does interaction btw viruses occur

Answer 2

Only during multiplication (vegetative virus)

Simultaneous infection of the same cell

Question 3

virus interaction can occur btw. which types of viruses

Answer 3

― usually related viruses, but not always

Question 4

types of virus interaction

Answer 4

• Advantageous
• Disadvantageous (interference)
• Neutral (virusexaltation)

Question 5

Advantageous interaction

Answer 5

on nucleic acid level (recombination)

on protein level (complementation, phenotype mixing)

Question 6

• Disadvantageous interaction

Answer 6

interference

One virus inhibits the multiplication of the other

Question 7

recombination

Answer 7

•Exchange of genetic information
→ new virus generation – inherited new properties
At least 20-40 nucleotide homology between the viruses is needed

Question 8

Intramolecular recombination occurance:

Answer 8

• 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)

Question 9

•Genetic reassortment definition

Answer 9

• Viruses with segmented genome (ie. Orthomyxoviridae)
• Exchange of segments during viral assembly
• Sudden, major antigenic changes
→ antigenic shift

Question 10

Reactivation types

Answer 10

Cross-reactivation
Multiple reactivation

latent cell -> lytic stage (replication)

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

Question 11

•Cross-reactivation

• btw who, example
• how

Answer 11

• Attenuated vaccine strain + related virus
• Repair of the defected virulence-genes
• i.e. herpesviruses

Question 12

•Multiple reactivation

• btw who, example
• how

Answer 12

• Between two attenuated virus-strains
• Different defected genomic regions
• Mutual completion

Question 13

Complementation

Answer 13

• 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

Question 14

Phenotype mixing

Answer 14

• Exchange of structural proteins
• Leukosis + sarcoma virus: acquiring envelope proteins
• Transcapsidation (Polio- + Coxsackievirus)

NON-HERITABLE!

Question 15

Adsorption interference

Answer 15

Competition for the same cell-surface receptor
• related viruses, or
• after phenotype mixing, or
• different viruses, but the same receptor (ie. CAR)

Question 16

Autointerference

Answer 16

• 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)

Question 17

•Heterologous interference

Answer 17

• non-related viruses
• viral suppressor protein production
• ie.: herpes, adenovirus – inhibits pox

Question 18

Virusexaltation - neutral virus interaction

Answer 18

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

Question 19

lytogenic cycle of viruses

Answer 19

after the multiplication of viruses, cell death occur

Question 20

lysogenic cycle of viruses

Answer 20

cells incorporate the viruses NA into its own for exchange of survival