lecture 2 part 1

Question 1

which viruses MUST encode or carry RNA dependent RNA polymerase?

Answer 1

RNA viruses

Question 2

where do RNA viruses replicate?

Answer 2

in the cytoplasm

Question 3

which have faster mutation rates – DNA viruses or RNA viruses?

Answer 3

RNA viruses

Question 4

most DNA viruses occupy…

Answer 4

the nucleus

Question 5

what do virulence factors do?
what happens if a virus loses their virulence factors?

Answer 5

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

Question 6

for each virus, which 4 questions should be considered?

Answer 6

-how does the virus get in?

-where does it go?

-how does it replicate?

-how does the body respond?

Question 7

what is the incubation period of a virus?

Answer 7

the number of days between infection and when you start to feel symptoms

Question 8

name the 5 general stages of viral infection

Answer 8

-acquisition — gained access to the body

-initiate primary site infection

-incubation period

-spread to secondary site (in some cases)

-resolution or persistance

Question 9

the 2nd stage of viral infection (after acquisition) is the initiation of PRIMARY SITE infection.
what is happening during this time?

Answer 9

the innate immune response is activated (phagocytes, IFN response)

-often happens in ORAL or RESPIRATORY tract bc we breathe in most viruses

Question 10

in the 5 stages of viral infection, when is the adaptive response triggered? what 2 things can result from it?

Answer 10

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)

Question 11

can viruses progress to the secondary site without symptoms?

Answer 11

YES – this is called asymptomatic

Question 12

what is “prodrome”?

Answer 12

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

Question 13

what is convalescence?

Answer 13

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

Question 14

what is the most common route of entry for viruses?

Answer 14

inhalation

Question 15

why is it that inhalation is the most common route of entry for viral transmission?

Answer 15

they prefer to infect oral and respiratory mucosa.
epithelial cells express viral receptors
the cells there possess the necessary replication machinery for the virus

Question 16

what kind of virus would be more likely to be shed in the feces: naked or enveloped?

Answer 16

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

Question 17

how do M cells assist with viral transmission?

Answer 17

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

Question 18

can viruses be transmitted via the blood? explain

Answer 18

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

Question 19

can viruses be transmitted transcutaneously?
what about maternally? (mother to neonate)

Answer 19

yes to both

Question 20

what is viremia?

Answer 20

the presence of viruses in the blood

Question 21

name the FIVE mechanisms of dissemination (spread) of viruses from the primary site

Answer 21

-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

Question 22

which virus infects the CNS through the “neuron walk”

Answer 22

rabies virus

Question 23

what is the viral pathology: “abortive”?

Answer 23

a failed infection. nothing happens.
the virus could’ve infected non-permissive cells OR the virus could have a mutation

Question 24

what is the viral pathology: “inapparent”?

Answer 24

asymptomatic (no consequences)
the virus invades the cell, but nothing really happens. the infection still exists tho

Question 25

what is the viral pathology: “lytic”?

Answer 25

the infection kills the host cell

Question 26

what is another name for the viral pathology: “non-lytic”?

Answer 26

persistent

Question 27

explain what a non-lytic/persistent infection is and the 4 types

Answer 27

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)

Question 28

cells can be permissive, non-permissive, or ____________. explain them

Answer 28

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

Question 29

HSV-1 is ____

Answer 29

herpes virus

Question 30

HCV is _____

Answer 30

hepatitis C virus

Question 31

give an example of a virus that is a “slow, chronic infection”

Answer 31

mad cow disease

Question 32

give an example of a virus that…

is an acute infection followed by latent infection and periodic reactivation

Answer 32

HSV-1 (herpes)

Question 33

give an example of a virus that….

is an acute infection followed by a chronic infection

Answer 33

HCV (hepatitis C)

Question 34

give an example of a virus that….

is an acute infection followed by viral clearance by the immune response (no more infection)

Answer 34

the flu

Question 35

give an example of a virus that…..

is an acute infection followed by persistent infection (not lytic) and virus overproduction

Answer 35

HIV

Question 36

differentiate between chronic and latent persistent (non-lytic) infections

Answer 36

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

Question 37

explain what is happening in lytic infections

Answer 37

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

Question 38

Viral CPE (cytopathic effects) induce changes in morphology leading to ______

Answer 38

cell death

Question 39

in non-lytic infections, the viruses persist intracellularly.
viruses are released through ___ or ____

Answer 39

exocytosis or budding

Question 40

non-lytic infections occur after what event?

Answer 40

occur after the infection of NON-PERMISSIVE CELLS where the virus cannot replicate

Question 41

in a non-lytic infection, are the viral DNA/RNA in the host cell?

Answer 41

YES, but they’re not replicating

Question 42

explain how viral gene products transform the host cells in a non-lytic infection

Answer 42

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

Question 43

______% of cancers are related to VIRAL oncogenes

Answer 43

15%
ex: HPV and cervical cancer

Question 44

do papillomaviruses yield tumors in the host?

Answer 44

HPV = papillomaviruses

yes, but they’re often benign

Question 45

do poxviruses yield tumors in the host?

Answer 45

occasionally, usually benign

Question 46

hepatitis ___ and hepatitis ___ yield tumors in the host

Answer 46

B and C

Question 47

do herpes viruses yield tumors in the host?

Answer 47

yes

Question 48

describe some components of the innate immune response to viruses

Answer 48

-they detect viral nucleic acids through TLRs and RLRs

-they release cytokines

-IFN response

-immune cell activation through APCS

Question 49

briefly describe the adaptive immune repsonse to viruses

Answer 49

-antibody mediated immunity
-T cell mediated immunity

Question 50

antibody mediated immunity is especially used for which viruses?

Answer 50

cytolytic viruses and and viremia (viruses in the blood)

Question 51

the ___ response is critical for defense against viruses

Answer 51

INTERFERON

Question 52

Name 3 effects of the interferon response

Answer 52

-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

Question 53

which are membrane bound – TLRs or ILRs?

Answer 53

TLRS

Question 54

TLR___ binds ____RNA and signals via ____ to induce IFN gene expression

Answer 54

TLR7 binds ssRNA and signals via MyD88 to induce IFN gene expression

TLR3 binds dsRNA and signals via TRIF to induce IFN gene expression

Question 55

TLRs detect both ssRNA and dsRNA in _____

Answer 55

endosomes

Question 56

RLRs detect RNA ___ (where)

Answer 56

in the cytoplasm

Question 57

which is made first in the IFN response:
IFN a or IFN b

Answer 57

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

Question 58

name the 2 pathways induced by IFN
what do they inhibit?

Answer 58

2’-5’ oligosynthetase
protein kinase

they interfere with viral RNA being translated into protein

Question 59

explain the 2’-5’ oligosynthetase pathway.
what activates is?

Answer 59

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

Question 60

explain the protein kinase pathway
what activates it?

Answer 60

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