Viral Pathogenesis

Question 1

modes of transmission

Answer 1

direct contact, injection, transplantation, fecal oral (+/- envelope important)

Question 2

how often are we exposed to pathogen

Answer 2

constantly; they are everywhere though they vary based on living conditions

Question 3

reasons viruses continue to persist in population

Answer 3

health, nutrition, genetic makeup, age, immune status

Question 4

what is an outbreak

Answer 4

introduction of a virus into a new location which originates from a common source

Question 5

how is the identification of the source of an outbreak so important

Answer 5

to stop the outbreak

Question 6

what is an epidemic

Answer 6

introduction of a new strain of virus to an immunological naive population which occurs over a LARGER geographical area

Question 7

what is a pandemic

Answer 7

worldwide epidemic

Question 8

are a majority of viral disease symptomatic

Answer 8

no but those that target essential tissues/organs –> serious disease

Question 9

symptoms and severity of viral diseases depend on what

Answer 9

• Patient’s ability to prevent/resolve infection
• Virulence and target tissue
• Ability to repair damage

Question 10

what are some mechanisms of viral pathogenesis

Answer 10

• Circumvent protective barriers
• Evade immune control
• Kill cells or trigger destructive immune and inflammatory response (control infection)
• Possibly transform cells

Question 11

what are some inherent barriers for host defenses

Answer 11

– Skin
– Mucous
– Ciliated epithelium
– Low pH

Question 12

what are some induced barriers for host defenses

Answer 12

– Fever
– Low pH
– Humoral and cellular components

Question 13

what are some non specific host defenses

Answer 13

– Interferon
– Complement
– Other cytokines

Question 14

what are some specific host defenses

Answer 14

– Antibody production

– Specific immune system

Question 15

when does transcription of interferons occur?

Answer 15

transcription only occurs after exposure to an inducer – viral infection, dsRNA – RNA viruses best

Question 16

what do viruses do to our immune responses

Answer 16

it suppresses them

Question 17

what can immune response to viral infection cause

Answer 17

tissue injury

Question 18

example of immune response to viral infection causing tissue injury: what can circulating immune complexes lead to?

Answer 18

deposits —> arthritis

aka CMV

Question 19

in dengue, what is the mechanism in which tissue injury happens?

Answer 19

hemorhagic shock syndrome: fixation of complement by circulating immune complexes 􏰁–> release of products via complement cascade 􏰁–> sudden increase in vascular permeability, shock, death

Question 20

basic steps of viral disease

Answer 20

• Acquisition
• Initiation of infection at the primary site
• Incubation period (amplification, spread to secondary site maybe)
• Replication in target tissues
• Immune responses (limit AND contribute)
• Transmission
• Resolution or persistent infection

Question 21

can viruses cause more than one disease

Answer 21

yeah

Question 22

what is it called for viruses to lose their virulence

Answer 22

attenuation

Question 23

result of viruses encoding their virulence factors

Answer 23

– Promoting replication, transmission
– Access and binding to target tissue
– Escape of immune system

Question 24

outcomes of viral infection

Answer 24

1) Abortive - Failed “attempts”: no virus multiplication
2) Lytic - Cell death
3) Persisting - Infection without cell death, selection of ideal target cell subsets (Chronic – nonlytic, productive)
4) Latent-recurrent infection - Presence of virus without virus production but with potential for reactivation

Question 25

difference between replication of virus during acute infection and during chronic infection via continuous productive infection

Answer 25

both of them after virus infects host cell --> entry and uncoating --> gene expression --> assembly and release (they have antigens for B and T cell recognition) but in chronic a variant strand of the virus (one that was not killed) will begin the process all over again and produce variant antigens for B and T cell recognition

Question 26

how is latency established

Answer 26

- modulation of viral gene expressions - viral subversion of cellular apoptotic pathway - avoidance of clearance by the immune system - selection of cell subsets ideal for long-term maintenance of the viral genome

Question 27

when does persistence occur in viral infections

Answer 27

when the cell is not killed - could be chronic, latent, recurrent, immortalizing, transforming

Question 28

what are determinants on if a virus will be lytic or persistent

Answer 28

- access to target tissue - stability - ability to cross barriers, establish viremia, and spread

Question 29

viruses apply a lot of avoidance strategies to persist. what are some of these strategies?

Answer 29

* viruses can alter / interfere with the processing of viral peptides by professional APCs * can downregulate co-stimulatory and/or MHC molecules (required for T cell signaling, expansion) * inhibit the differentiation of AP conventional dendritic cells, infect effector T and B cells directly all of these are just ways in which the infected host's innate or adoptive immune system is suppressed

Question 30

what does the susceptibility of host cell to virus depend on?

Answer 30

presence of receptor for virus attachment

Question 31

during what basic steps of viral disease does one see the prodrome phase?

Answer 31

- It could just be during acquisition | - Or it could be in acquisition, primary and/or secondary site replication

Question 32

during what basic steps of viral disease does one see the symptoms of disease

Answer 32

at the sites of replication or at the target tissue

Question 33

outcome and severity of viral infection can be due to what factors?

Answer 33

- virus strain, inoculum size | - health of host host response system (immune response helps determines severity, duration)

Question 34

what does the target tissue of a virus determine

Answer 34

the predominant disease

Question 35

most common site of viral infections and disease

Answer 35

oral and respiratory tract (upper and lower) with primary infections spreading to other sites

Question 36

how do oral and respiratory tract viral infections spread

Answer 36

respiratory droplets, contact, food, water, saliva

Question 37

example of a respiratory tract viral infection

Answer 37

influenza

Question 38

mechanism in which influenza occurs

Answer 38

aerosol inoculation of virus --> replication in respiratory tract --> desquamation of mucus secreting and ciliated cells --> influenza syndrome

Question 39

desquamation of mucus secreting and ciliated cells can lead to what?

Answer 39

secondary bacterial infection (pneumonia), primary viral pneumonia, CNS muscle involvement

Question 40

what other things add to the desquamation of mucus secreting and ciliated cells that lead to influenza

Answer 40

antibody, interferon induction, T cell responses though antibody and T cell responses do lead to future protection

Question 41

what are consequences of GI tract viral infection

Answer 41

no symptoms --> gastroenteritis, vomiting, diarrhea | Generally self limiting

Question 42

what promotes GI tract viral infections

Answer 42

poor hygiene

Question 43

GI tract viral infections has more significant effect in what population

Answer 43

infants

Question 44

example of a GI tract viral infection

Answer 44

rotavirus

Question 45

transmission of rotavirus

Answer 45

fecal matter especially in day care settings (respiratory possible)

Question 46

who is at a risk for GI tract viral infections

Answer 46

Infants

Question 47

how do you control rotavirus

Answer 47

hand washing and isolation | live vaccines

Question 48

effects of rotavirus

Answer 48

from asymptomatic --> viral disease

Question 49

what is rotavirus resistant to

Answer 49

environmental and gastrointestinal conditions

Question 50

virus induced skin diseases

Answer 50

exanthems and hemorrhagic fevers

Question 51

major classifications of viral rashes

Answer 51

* macules (flat colored spots) * papules (slightly raised areas from immune response) * nodules (larger raised areas of the skin) * vesicular lesions (blisters likely to contain virus)

Question 52

what do hemorrhagic fevers infect

Answer 52

endothelial cell lining of the of the vasculature, possibly compromising the structure of the blood vessel