microbiology- how viruses cause disease Flashcards
describe viruses
simple micro-organisms
not capable of independent existence
require host cell
describe the basic viral structure
dna/rna located in the capsid protein
lipoprotein envelope which protein molecules attached
how are viruses classified
- type of nucleic acid
2. presence/absence of an envelope
what are the steps of the virus life cycle
1.attachment 2 entry 3. replication 4 assembly 5 release
describe how the virus attaches
it enters the body by inhalation, ingestion or injection and then collides with the host cell
define viral tropism
this is what determines if the virus can enter and attach by binding to a specific receptor
how does the cell life cycle continues
cells be permissive
what does permissive mean
contain the whole range of components required by the virus for replication to be completed
what are the three types of tropism
cellular
tissue
host
describe entry
immediately follows attachment
how do enveloped viruses enter
enter by membrane fusion or endocytosis
how do non enveloped viruses enter
entry by endocytosis or penetration( direct injection)
describe the stages of entry
membrane fusion
- occurs by receptor binding
- the virus fuses with the host membrane
- release of virion content into the host cytoplasm
how does replication occur
once inside the cell the virus removes its capsid and exposes its genome- the uncoating is specific to the virus
what types of uncoating do we have
nuclear or cytoplasmic
what are the stages of replication
viruses hijack the replication process in cells by creating and injecting their own viral MRNA
using host cell machinery to make viral proteins instead of host proteins
new virons are constructed from viral proteins
describe assembly
All viruses components are transported to a site of assembly and put together
• influenza virus proteins and new RNA are assembled at
the cell membrane, which then forms a “bud”
describe release
by
lysis:
cell splits apart and dies
exocytosis: host cell transports the visions and release at surface
budding: visions enclose themselves in a host membrane
what are the major mechanisms by how viruses cause disease
route of infection mucosal contact injection respiratory droplet faecal oral direct contact
to establish effective entry what does their need to be
enough virus
host cells which are accessible susceptible permissive
also the host immune system needs to be inadequate or absent
what do localised infections look like
typically shorter incubation period
virus remains at the site of entry
may form focal lesions
may affect large areas of the same mucous membrane
what do generalised/disseminated infections look like
longer inc time initial replication phase NEAR site of entry then general spread to lymph nodes via nerves etc
target organs which viruses can affect
skin rashes
respiratory tract
liver
central nervous system
describe chronic illness duration
▪ Infection persists for a long period of time
▪ Host immune system is unable to fully control virus
▪ Ongoing viral replication alongside immune response progressively damages host cells over time
describe illness duration in the latency phase
WHERE THE VIRUS INFECTS cells but does not replicate
where does the herpes simplex virus and varicella zoster discover latency
in the dorsal root ganglion of the trigeminal nerve
what does it mean when a virus transforms
Some viruses have the potential to induce malignant change by disruption the normal expression of the host cell genes
what can epstein barr virus be associated with
Burkitts lymphoma
what are the clinical stages of virus infection
incubation period
prodromal period
specific illness period
recovery period
describe incubation period
the virus is attaching and undergoing the non productive stage of life cycle
describe prodromal period
Non specific manifestations such as general body ache, malaise, fever
Early host immune response
describe specific illness period
Specific effects of virus on the target cells
Host immune systems immunologic attack
how can we reduce the effect of viruses
by using antivirals that attack and effect different cycles of the viruses life cycle
usually by targeting more than one stage
which medications can block viral attachment and entry
enfuvirtide
maraviroc
give examples of medications that block uncoating
amatadine
rimantadine
give examples of medications that block nucleic acid synthesis
NRTIS
acyclovir
give examples of medications that block late protein synthesis and processing
blocked by protease inhibitors
the importance of viruses in dentistry
respiratory transmission COVID 19 percutaneous injuries and blood splashes HBV skin to mouth herpetic whitlow
give examples of medications that block penetration
interferon alfa
give examples of medications that block viral release
neuraminidase inhibitors
