Lecture 4 Flashcards
How have viruses evolved
By different independent routes
What do RNA viruses proceed
DNA viruses
Why do errors accumulate rapidly with RNA
Not subject to proof reading
What are known especially in influenza viruses (2)
- Antigenic drift
2. Antoigenic shift
What is the reason for spontaneous mutations
Error rate of enzymes - in RNA dependent polymerase is much higher than that for DNA dependant polymerase
What are Quasispecies
Different isolates of the same species/serotype
What is FMDV known for
Mutations and quasispeices
The productions of quasi species may assist with?
the virus to persist in the individual host
What is antigenic drift?
Viruses will slowly accumulate point mutations
What can spontaneous point mutations lead to
Serologically detectable differences - response of the immune system
What is antigenic shift?
The dramatic changes which accompany reassortment of viruses with segmented genomes
What are viral mutations
Reassortment/antigenic shift
What do pigs have receptors for
Both Human and avian viruses
Where is gene reassortment important
Segmented viruses
What is recombination
A physical interaction of viral genomes in co-infected cells
When does recombination occur
When a host cell in infected with two parent viruses
When do conditional lethal mutants replicate
Under norma physiological environmental conditions, but not under others
When do temperature sensitive mutants replicate
Under normal physiological temperature but stop with Tm changes
What does attenuated mutants mean
Lost ability to cause disease in humans/animals
Where are attenuation and attenuated mutants used
In vaccines
What is a defective virus
A virus will not produce the formation of live, active progeny. This type of infection is called an abortive infection and the reason for this
- The host cell is defective
- The virus itself that is defective and cannot replicate
What do defective viruses do
Block adsorption receptors of cells for infective viruses
What is pathogenesis
Mechanism of disease development - the process by which a viral infection leads to disease
What is pathogenicity
The ability of microorganisms to produce disease in a host
What is virulence
the degree of pathogenicity
What are the 6 prerequisites for pathogenicity
- Gain entry to host
- Colonize
- Enter the tissues
- Multiply
- Resist or interfere with the host’s defence mechanisms
- Cause damage
What is essential for viruses to enter a cell
Receptor attachment
How can a virus enter (6)
- Respiratory system
- Conjunctiva and other mucous membranes
- Digestive system
- Urogenital system
- Mechanical - skin injury
- Transpacental
What are cell receptors for viruses
Attachment sites
What are cell transcription factors
Recognise viral promoters and enhancer sequences
How is a virus released from host cell (4)
- Skin
- Respiratory tract
- Digestive tract
- Genital tract, urinary tract, saliva, milk and blood
Why do viruses try to evade the host’s immune response
To enable them to persistently infect their host
What does restricted gene expression mean
Replication only takes place in a limited population of cells
What does viral-induced immunosuppression mean
Viruses destroy immunocompetent cells such as machrophages, neutrophils and lymphocytes
What is immunological tolerance
In prenatal infections, the infected host may not recognise the foreign virus and therefore, antiviral antibodies are not produced
List 5 mechanisms of viral persistence
- Restricted gene expression
- Viral-induced immunosupression
- Immunological toerange
- Non-immunogenicity
- Stimulation of the production of non-neutralising antibodies or defective cell mediated immunity
What are 4 consequences of persistence
- Chronic viral infection
- Slow viral infections
- Oncogenic viral infections
- Latent viral infections
What is a quasispecies
different isolates of the same species/serotype
How does a live virus work
They grow the virus in a different host so it is a weaker strength.
Where do most viruses go
Lymph nodes
When will viruses leave the blood stream
When they reach a target organ where they do the most damage
What is a latent infection
May persist in a specialised group of cells
What is immunological tolerance
When the virus crosses the placenta, the virus is seen as self to the immune system so it doesn’t pick it up.
