lecture 2 part 1 Flashcards
which viruses MUST encode or carry RNA dependent RNA polymerase?
RNA viruses
where do RNA viruses replicate?
in the cytoplasm
which have faster mutation rates – DNA viruses or RNA viruses?
RNA viruses
most DNA viruses occupy…
the nucleus
what do virulence factors do?
what happens if a virus loses their virulence factors?
virulence factors enhance the attachment, transmission, replication, and evasion of host reponses
when a virus loses its virulence factors, it is said to be ATTENUATED. it can infect, but loses the ability to replicate.
this is the basis for vaccine development
for each virus, which 4 questions should be considered?
-how does the virus get in?
-where does it go?
-how does it replicate?
-how does the body respond?
what is the incubation period of a virus?
the number of days between infection and when you start to feel symptoms
name the 5 general stages of viral infection
-acquisition — gained access to the body
-initiate primary site infection
-incubation period
-spread to secondary site (in some cases)
-resolution or persistance
the 2nd stage of viral infection (after acquisition) is the initiation of PRIMARY SITE infection.
what is happening during this time?
the innate immune response is activated (phagocytes, IFN response)
-often happens in ORAL or RESPIRATORY tract bc we breathe in most viruses
in the 5 stages of viral infection, when is the adaptive response triggered? what 2 things can result from it?
adaptive response can be triggered when the infection spreads to the secondary site and replication begins in the target tissue
the triggering of the adaptive response can be beneficial in cases when the antibody response occurs, OR it can develop into an immunopathology – immune system’s response to infection ends in bad results. NOT a result of the virus itself (ie: septic shock)
can viruses progress to the secondary site without symptoms?
YES – this is called asymptomatic
what is “prodrome”?
early, non specific syndromes such as fever aches and chills. this is due to the INNATE response to infection – cytokines cause the hypothalamus to raise the temperature
what is convalescence?
the period in which the body recovers from infection – time for the cells to heal.
in this time, the person could experience symptoms from the tissue repair mechanisms. they also develop immunological memory
what is the most common route of entry for viruses?
inhalation
why is it that inhalation is the most common route of entry for viral transmission?
they prefer to infect oral and respiratory mucosa.
epithelial cells express viral receptors
the cells there possess the necessary replication machinery for the virus
what kind of virus would be more likely to be shed in the feces: naked or enveloped?
NAKED
an enveloped virus is less stable. the membrane itself has spike proteins. when the virus goes through the gut, the enzymes destroy the envelope (such a low pH)
a naked virus has attachment proteins in the PROTEIN COAT. more stable – can stand the low pH
how do M cells assist with viral transmission?
M cells are like “gatekeepers” in Peyer’s Patches of the small intestine. they can choose whether or not to let the viruses into the GI tract
can viruses be transmitted via the blood? explain
YES
blood goes into a lymph node through the HEV (high endothelial venule).
once a virus is in the blood or the lymph node, it can go anywhere
can viruses be transmitted transcutaneously?
what about maternally? (mother to neonate)
yes to both
what is viremia?
the presence of viruses in the blood
name the FIVE mechanisms of dissemination (spread) of viruses from the primary site
-diffusion (aka local spread)
-viremia (through the bloodstream)
-within infected leukocytes and lymphocytes (remember: once a virus is in the blood or lymph, it can go anywhere)
-through M cells – small enough viruses can get through
-into the CNS (through peripheral NEURONS. neurons are very long and can go directly to the brain – called the neuron walk) also by viremia to the CNS or meninges, or by macrophage migration
which virus infects the CNS through the “neuron walk”
rabies virus
what is the viral pathology: “abortive”?
a failed infection. nothing happens.
the virus could’ve infected non-permissive cells OR the virus could have a mutation
what is the viral pathology: “inapparent”?
asymptomatic (no consequences)
the virus invades the cell, but nothing really happens. the infection still exists tho
what is the viral pathology: “lytic”?
the infection kills the host cell
what is another name for the viral pathology: “non-lytic”?
persistent
explain what a non-lytic/persistent infection is and the 4 types
a non-lytic/persistent infection is one that exists, but does not result in cell death
4 types:
-chronic – goes into cell and continually blebs off virus
-latent – not productive. nucleic acid is resident there. it’s inactive and capable of making an infection, but it’s not. integrates into host chromosome and is quiescent. virus is making proteins that support its function
-recurrent – on/off production
-transforming – immortalizing. the virus infects the cell. doesnt kill it, but the cell is immortal. continually divides ex: RNA tumor virus (retrovirus)
cells can be permissive, non-permissive, or ____________. explain them
permissive, non-permissive, or semi-permissive
permissive – allow the complete viral replicaiton cycle
semi-permissive – allow slow and inefficient replication
non-permissive – lack the essential machinery or actively block replication or assembly
HSV-1 is ____
herpes virus
HCV is _____
hepatitis C virus
give an example of a virus that is a “slow, chronic infection”
mad cow disease
give an example of a virus that…
is an acute infection followed by latent infection and periodic reactivation
HSV-1 (herpes)
give an example of a virus that….
is an acute infection followed by a chronic infection
HCV (hepatitis C)
give an example of a virus that….
is an acute infection followed by viral clearance by the immune response (no more infection)
the flu
give an example of a virus that…..
is an acute infection followed by persistent infection (not lytic) and virus overproduction
HIV
differentiate between chronic and latent persistent (non-lytic) infections
chronic infection — productive. still producing active viral particles
latent infection – nonproductive. quiescent. virus becomes a part of host chromosome and makes proteins that support its function. can become activated again to make active viral particles
explain what is happening in lytic infections
in a lytiv infection, CPE’s (cytopathic effects) are being produced that induce morphological changes of the host cell
they inflict a lot of damage (and inhibit its repair), inhibit DNA and protein synthesis of the host, degrade host nucleic acid, and disrupt the host cellular functions
Viral CPE (cytopathic effects) induce changes in morphology leading to ______
cell death
in non-lytic infections, the viruses persist intracellularly.
viruses are released through ___ or ____
exocytosis or budding
non-lytic infections occur after what event?
occur after the infection of NON-PERMISSIVE CELLS where the virus cannot replicate
in a non-lytic infection, are the viral DNA/RNA in the host cell?
YES, but they’re not replicating
explain how viral gene products transform the host cells in a non-lytic infection
the viral gene products get incorporated into the host nucleus which disrupts the regulation of growth of the host cell.
this leads to oncogenic transformation – promotion of unregulated growth
______% of cancers are related to VIRAL oncogenes
15%
ex: HPV and cervical cancer
do papillomaviruses yield tumors in the host?
HPV = papillomaviruses
yes, but they’re often benign
do poxviruses yield tumors in the host?
occasionally, usually benign
hepatitis ___ and hepatitis ___ yield tumors in the host
B and C
do herpes viruses yield tumors in the host?
yes
describe some components of the innate immune response to viruses
-they detect viral nucleic acids through TLRs and RLRs
-they release cytokines
-IFN response
-immune cell activation through APCS
briefly describe the adaptive immune repsonse to viruses
-antibody mediated immunity
-T cell mediated immunity
antibody mediated immunity is especially used for which viruses?
cytolytic viruses and and viremia (viruses in the blood)
the ___ response is critical for defense against viruses
INTERFERON
Name 3 effects of the interferon response
-induce the resistance to viral replication in all cells
-increase the expression of ligands for receptors on NK cells
-activate NK cells to kill virus infected cells
which are membrane bound – TLRs or ILRs?
TLRS
TLR___ binds ____RNA and signals via ____ to induce IFN gene expression
TLR7 binds ssRNA and signals via MyD88 to induce IFN gene expression
TLR3 binds dsRNA and signals via TRIF to induce IFN gene expression
TLRs detect both ssRNA and dsRNA in _____
endosomes
RLRs detect RNA ___ (where)
in the cytoplasm
which is made first in the IFN response:
IFN a or IFN b
IFN b binds to another cell receptor = paracrine response
when IFN b or IFNa bind to OWN CELL RECEPTOR, production on IFN a is induced = autocrine response
name the 2 pathways induced by IFN
what do they inhibit?
2’-5’ oligosynthetase
protein kinase
they interfere with viral RNA being translated into protein
explain the 2’-5’ oligosynthetase pathway.
what activates is?
activated by the interferon response
in the presence of viral dsRNA, 2’-5’ oligosynthetase activated ribonuclease which degrades mRNA.
since there’s no RNA, there is no protein synthesis. this means the cell itself dies too.
suicide response
explain the protein kinase pathway
what activates it?
activated by the interferon response
interferon response induces protein kinase. in the presence of dsRNA, protein kinase inhibits a subunit of a protein synthesis initiation factor (called eIF-2)
again – this is a suicide pathway. there is no virus production but also no protein synthesis – cell dies
