how do viruses cause disease in humans? Flashcards
what is the basic reproductive number?
- how many new infections one person will generate during their infectious period
what is the name of the system for viral classification?
- baltimore system
- based on viral genetic material
what are the problems a virus must solve?
- what cells to enter and how
- how to replicate inside cell
- how to move from one infected cell to another
- mechanisms to evade host defences
what are entry points for a virus?
skin
alimentary tract
urogenital tract
eye
what is an example of a virus that remains apical even when it spreads?
flu
what is an example of a virus that is basolateral?
- rabies
- is on the basolateral side
- has access to underlying tissue and can spread systematically
how can viruses spread haematogenously?
- direct through capillaries
- replicating in endothelial cells
- through vector bite
- through lymphatic capillaries
what is viraemia?
- presense f virus in the blood
what is a neurotropic virus?
one that infects neural cells
what is a neuroinvasive virus?
- can enter CNS following infection of peripheral site
what is neurovirulence?
can cause disease of neural tissue
which viruses are neurovirulent?
HSV
rabies
which viruses are neuroinvasive?
mumps
describe how mumps can affect CNS
- it is neuroinvasive so can get into CNS
- but not neurovirulent- so won’t cause much damage when in CNS
what 3 things determine viral tropism?
- cell receptors
- cellular proteins that regulate transcription
- cell proteases
describe the effect of HSV on CNS
- not neuroinvasive- o won’t get into CNS
- but very neurovirulent, so if it gets n will cause a lot of trouble
what are the 2 mechanisms by which influenza evades host immunity?
- antigenic shift
- antigenic drift
what is antigenic shift?
the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype
what is antigenic drift?
genetic variation in viruses, arising by the accumulation of mutations in the virus genes that code for virus-surface proteins that host antibodies recognize.
how can viruses be cytolytic?
- inhibition of host protein synthesis leading to loss of membrane integrity
- syncytium formation
- induction of apoptosis
what are non cytocylic ways a virus can injure cells?
- CD8 mediated
- CD4 mediated
- B cell mediated
what are 3 mechanisms by which viruses damage cells?
- cytolytic
- non cytolytic
- cell injury due to free radicals
routes of viral transmission
resp tract skin and mucous membrane faecooral blood borne sexual vertical
