Lecture 19 - Viruses And Immune Evasion Flashcards
What is a virus?
A package of genetic information protected by a protein shell for delivery into a hostel cell to be expressed and replicated
How old is Virology?
Approx 100 years old
I’m Ancient Greece, what does ios mean?
A poisonous substance
In Latin, what is Virus?
A poisonous malodorous substance
What dates before 1,000 B.C.E?
Mesopotamian laws concerning rabid dogs
Where was Small pox endemic in?
Ganges river basin by the 5th century B.C.E
Who was the first to attempt to rationalise plagues?
Hippocrates
What did Hippocrates conclude about plagues?
caused by small animals in the air too small for human vision
What is the order of Viral Replication?
- Virus Entry
- Uncoating
- Genome replication
- Protein synthesis
- Virus-assembly and maturation
- Virus release
What is Primary Replication ?
The place of primary replication is where the virus replicates after gaining initial entry into the host
This determines whether the infection will be localised at site of entry or spread to become a systematic infection
What is systemic spread?
Apart from direct cell-to-cell contact, the virus may spread via blood stream and the the CNS
Where does secondary reviews location take place?
Susceptible organs/tissues following systemic spread
What is disease mechanisms for Rabies virus?
Transmitted by saliva
Bite of rabid animal
Aerosois in caves populated by infected bats
Where does Rabies Virus replicate?
Muscle at bite site
How long is the incubation period and what does it depend on (Rabies Virus)?
Weeks to months
Depend on: inoculum and distance of bite from CNS
What does Rabies Virus infect?
Peripheral nerves and travels to brain
(Rabies Varies) what does Replication in Brain cause?
Hydrophobia seizures Hallucinations Paralysis Coma Death
Where does Rabies Virus spread to?
Salivary gland from where it is transmitted
What can prevent disease due to long incubation period (Rabies Virus)?
Post exposure immunisation
Rabies Virus
Virus Inoculated
Viral replication in muscle
Virion enters peripheral nervous system
Replication in dorsal ganglion
Rapid ascent in spinal cord
Infection of spinal cord, brain stem, cerebellum and other brain structures
Descending infection via nervous system to eyes, salivary gland, skin, and other organs
What is co-evolution with Host?
Host and parasite exert reciprocal selective pressure on each other
Rapid reciprocal adaptation
What is advantage of co-evolution with Host?
Prosperous host = prosperous Virus
What is disadvantage of co-evolution?
Virus shares same fate as host
Genetic bottleneck events can be fatal
Typically used by DNA viruses
What is adavantage of multiple host species?
If one host species is compromised, Virus can replicate in another
What is disadvantage in infection of multiple host species?
Cannot optimise for any one situation
What uses infection of multiple host species?
RNA viruses
Define viral evolution
The constant change of viral population In the face of selection pressures
What happens if population can’t change or adapt?
It disappears
What does viral population display?
Spectacular diversity
What are sources of diversity?
Mutation
Recombination
What are mechanisms of viral evolution?
Mutation (adaptation)
Recombination
Ressortment
Selection
What does mechanisms of viral evolution depend on?
Large population size
Progeny
What are the features of DNA viruses?
Narrow host range Persistent infection common Not as much Replication Genome replication not as error prone Proof reading Generate less diversity Evolve slower
Features of RNA viruses
Masters of error prone replication
RNA polymerase cannot correct errors
What is the average error frequency of RNA viruses ?
1 in 10^4 or 10^5 nucleotides polymerised
In 10kb RNA Virus genome, what is mutation frequency of RNA virus?
1 in 10^4
What is quasispecies?
Virus population exist as dynamic distribution of non-identical but related replicons
What is an example of small RNA virus?
Human influenza virus
What are features of small RNA virus ?
Interference with innate immunity (type I interferon)
Blockade of host gene transcription
Antigenic hypervariability
What is small RNA virus also known as?
Hit and run
What does small RNA virus cause?
Elimination of virus
What is an example of large DNA virus?
CMV
What are features of large DNA virus ?
Interference with adaptive immunity
Replication at immunoprivileged sites
Molecular latency
What can large DNA virus cause ?
Persistent infection
What is large DNA virus also known as?
hit and hide
What are the viral immune evasion strategies?
Viral evasion of MHC class-I mediated Antigen presentation
Viral evasion of MHC class-II mediated Antigen presentation
Viral evasion of natural killer cell activation
Viral evasion of antibody responses and complement attack
