Viral Pathogenesis

Question 1

Common routes of infection and initial sites of replication

Answer 1

• common routes: respiratory, alimentary, or genitourinary tract
• replication: epithelial cells near body surface/barriers

Question 2

Enterotropic virus definition

Answer 2

replicates in the gut

Question 3

Neurotropic virus definition

Answer 3

replicates in the nervous system

Question 4

Factors that determine tropism

Answer 4

• access to desired tissue
• receptors required for virus binding/entry
• expression of host genes required for virus infection and replication
• relative failure of host defenses

Question 5

Tissue tropism affect on viral development

Answer 5

can drive population variant among or within individuals; particularly in viruses w/highly error-prone replication systems

Question 6

Transmission and shedding definition

Answer 6

release of infectious particles from an infected host

Question 7

Site of shedding for local infections

Answer 7

occurs from the site of initial infection

Question 8

Site of shedding for disseminated/systemic infections

Answer 8

-multiple or distant sites possible

Question 9

Fomite definition

Answer 9

virus-associated objects

Question 10

Types of viral transmission

Answer 10

• single susceptible host vs. alternate infection of one host w/another (e.g. insect to human)
• close contact (e.g. enveloped viruses)
• fomites (e.g. hardier, non-enveloped viruses)
• usually horizontal, but may be vertical/germ-line

Question 11

Immune-mediated pathology associated with viruses

Answer 11

• IMP=viral disease as a result of host immune response to infection
• antibody-mediated (immune complexes)
• cell-mediated (rash, fever, malaise)
• autoimmunity (cross-reactivity)
• immune modulation/suppression

Question 12

Acute local viral disease: 1. first site of replication 2. viremia 3. secondary replication 4. site of symptoms 5. incubation period 6. duration of immunity 7. Ab responsible for resistance 8. example

Answer 12

1. epithelium
2. no
3. none
4. entry epithelium
5. 1-3 days
6. often short
7. secretory IgA
8. common cold

Question 13

Persistent chronic viral infection

Answer 13

• viral infection that continue to produce new virus over long period of time
• result of acute primary infection that is not cleared OR
• virus retains ability to transmit to other organisms or host offspring

Question 14

Latent chronic viral infection

Answer 14

• substantial periods in which the host produces no detectable virus
• little or no disease in healthy host
• viral genome is silent
• retain the ability to re-initiate transcription and replication to produce new virus

Question 15

Acute systemic viral disease: 1. first site of replication 2. viremia 3. secondary replication 4. site of symptoms 5. incubation period 6. duration of immunity 7. Ab responsible for resistance 8. example

Answer 15

1. epithelium
2. yes, primary and secondary
3. lymphoid organs, lung, skin
4. systemic
5. 10-21 days
6. usually lifelong
7. serum IgG and secretory IgA
8. measles

Question 16

Slow chronic viral infection

Answer 16

• no symptoms on initial infection
• long incubation period
• may or may not induce immune response
• eventual disease followed by progressive deterioration and death

Question 17

Examples of viral diseases: 1. Acute local 2. Acute systemic 3. Chronic 4. Latent 5. Slow/progressive

Answer 17

1. colds, diarrhea 2. smallpox, measles 3. Rubella in neonate 4. VZV in nerves 5. AIDS, canver

Question 18

General characteristics of chronic viral infection

Answer 18

• ongoing virus infection/replication
• mild or inapparent disease in healthy host
• manifestation of disease often coincides w/immune suppression

Question 19

Host factors in susceptibility to viral disease

Answer 19

• receptors for virus entry, accessibility and permissivity
• age of host
• genetic background
• immune status

Question 20

Types of virulence genes (4)

Answer 20

1. affect ability of virus to replicate
2. modify host defense mechanism
3. facilitate virus spread in and among hosts
4. directly toxic to host cells