Chapter 7

Question 1

Define pathogenic.

Answer 1

able to cause disease

Question 2

Define virulence.

Answer 2

relative measure of the harm done to the host

Question 3

What are some of the factors that interact to determine the outcome of infection?

Answer 3

genetic features of the virus, the route and dose of inoculum, and a variety of host factors

Question 4

What host factors can determine the outcome of infection?

Answer 4

age, gender, immune status, concomitant infections, nutritional background, and genetic background

Question 5

When does an acute infection occur?

Answer 5

when a virus firstinfects a susceptible host

Question 6

What is the duration of an acute infection?

Answer 6

it is generally of short duration

Question 7

What is the nature of an acute infection?

Answer 7

the infection may be self-limiting, or controlled by innate or adaptive immune responses

Question 8

What is a persistent infection?

Answer 8

the continuation of infection beyond the time when the immune system might be reasonable expected to clear the infection; the adaptive immune system has not cleared the virus effectively

Question 9

What happens with virus particles or viral gene products during a persistent infection?

Answer 9

they continue to be produced for long periods of time; either continuous replication or establishment of latency

Question 10

What happens to the viral genome during latency?

Answer 10

the viral genome is maintained but there is no productive replication

Question 11

What kind of damage occurs in a persistent infection?

Answer 11

minimal tissue damage either because replication is restricted or replication causes minimal damage to the host cell

Question 12

What is a persisent latent infection?

Answer 12

A reversible, non-productive infection in which only a few, if any, viral genes are expressed. Periodically, productive replication is reactivated

Question 13

What is a persistent progressive infection?

Answer 13

Levels of virus replication, and clinical signs increase over time; also called a slow infection

Question 14

What is a persistent chronic inifection?

Answer 14

Continual virus replication, often at a set level, with or without clinical signs of disease

Question 15

What are the three main portals of entry for viruses?

Answer 15

mucosal surfaces, skin, and vertical transmission

Question 16

What mucosal surfaces can viruses enter?

Answer 16

respiratory, digestive, urogenital, and conjunctival mucosal surfaces

Question 17

What is vertical transmission?

Answer 17

transmission of viruses without passage through the environment

Question 18

What are the three ways of verticle transmission mentioned in class?

Answer 18

in the germ line of fertilized eggs, across the placenta, and during passage through the birth canal

Question 19

How do viruses enter skin?

Answer 19

they must enter through abrasions and penetrations

Question 20

What are some consequences of vertical transmission?

Answer 20

abortion, congenital disease, and persistent infection

Question 21

What is a localized infection?

Answer 21

Viruses replicate only at or near the body surface through which they entered.

Question 22

Where does viral entry, replication, lesion formation, and shedding occur in localized infections?

Answer 22

all in the same organ

Question 23

How does the spread of localized infection in epithelial cells occur?

Answer 23

by sequential infection of neighboring cells

Question 24

Usually, what is the incubation time of viruses that cause localized infections?

Answer 24

it is usually short

Question 25

What are some examples of diarrhea causing localized infections?

Answer 25

coronaviruses and rotavirus

Question 26

What are some localized infections that infect the upper and lower respiratory tract?

Answer 26

influenza and parainfluenza viruses

Question 27

What are the steps (pathogenesis) of a localized infection with influenza?

Answer 27

Day 0 - initial infection Day 1- cell-to-cell spread in mucus layer of epithelium (no signs yet) Day 2- beginning of earliest prodromal signs Day 3- Time of maximal shedding Day 4 - Mild feverm dry cough, minimal inflammation Day 5 - Viral replication begins to wane Day 6 and 7 - fever and other signs at max, inflammation peaks, productive cough, active immune response, viral replication minimal, beginning of recovery

Question 28

What is a systemic virus?

Answer 28

Viruses that spread from entry site following lymphatic and hematogenous dissemination to cause generalized infections in specific organs

Question 29

True or False: In systemic viral infections, site of entry, the target organ, and shedding all occur in the same place.

Answer 29

FALSE

Question 30

What are some viruses that cause systemic infections?

Answer 30

paramyxoviruses, rotaviruses, papillomaviruses

Question 31

What happens at 1?

Answer 31

Following entry at one of the body surfaces, the virus is able to penetrate into the underlying tissues.

Question 32

What happens at 2?

Answer 32

The virus arrives at a regional site and undergoes primary amplification - typically a regional lymph node.

Question 33

What happens at number 3?

Answer 33

The progeny virus produced at this regional site enters the bloodstream, giving rise to the first viremic period, called the primary viremia. This is transient and subclinical

Question 34

What happens at number 4?

Answer 34

The primary viermia serves to seed the central organs of replication, which are typically the liver, spleen, bone marrow, and the vascular endothelium

Question 35

What happens at number 5?

Answer 35

Replication in these central depots liberates large amounts of virus into the blood stream. This is the secondary viremia. About the time the viremia peaks and begins to decline, fever appears.

Question 36

What happens at number 6?

Answer 36

The secondary viremia seeds the sites of shedding, and the sites in which the primary lesions of the disease are found, which may or may not be the same

Question 37

What happens at number 7?

Answer 37

Replication in susceptible cells at these sites produces the characteristic signs and lesions of the disease, and results in liberation of the virus into the environment.

Question 38

What are the four determinants of whether a viral infection remains localized or spreads systemically?

Answer 38

Availability of susceptible cells in deeper tissues, macrophage susceptibility (yes or no), directional release, and temperature range of the virus

Question 39

What are the four possible outcomes of a virus-macrophage interaction?

Answer 39

1. Virus is ingested and degraded by macrophage 2. In the presence of virus-specific antibody, the virus is opsonized and degraded 3. Macropage is susceptible to virus, and results in lytic or persistent infection 4. Macrophage is susceptible to virus, and in the presence of some virus-specific antibodies, replication of macrophages are enhanced

Question 40

What plays an important role in determining the disease pattern of a virus?

Answer 40

the cell surface

Question 41

What does virus release form apical surfaces of respiratory or intestinal epithelium result in?

Answer 41

luminal release, back where the infection started

Question 42

As a general rule, where are enteric viruses that produce localized infections released?

Answer 42

from the apical (luminal) surface, so that their progeny end up in the feces

Question 43

Generally, where are viruses that cause systemic infections released?

Answer 43

from the basolateral surface of mucosal cells in order to facilitate a more systemic spread and avoid antibody in the mucus layer

Question 44

Why is depletion of susceptible cell popylations more important in localized infections?

Answer 44

because the population of host cells in these areas is more limited than in systemic infections

Question 45

What host immunity process seems to be more important in mediating recovery from most active viral infections?

Answer 45

T lymphocyte-mediated cytotoxicity response

Question 46

In localized infections, what is the primary role of the immune response?

Answer 46

to prevent reinfection

Question 47

When does peak shedding occur in systemic infections?

Answer 47

during secondary viremia

Question 48

When should you take diagnostic samples if a viral infection is suspected?

Answer 48

early

Question 49

In both systemic and localized infections, virus _____ has largely ceased by the time fever, disease signs, and lesions are prominent.

Answer 49

shedding

Question 50

When should you take 'post-infection' samples?

Answer 50

a week or more after clinical signs have declined

Question 51

What two virus families use restricted gene expression as a mechanism of persistence?

Answer 51

lentiviruses/retroviruses

Question 52

In high virulence viruses, what are the numbers of LD50 like?

Answer 52

low (5)

Question 53

In medium virulence viruses, what is the number of LD50 like?

Answer 53

medium (5,000)

Question 54

In low virulence viruses, what is the number of LD50 like?

Answer 54

very high (1,000,000)

Question 55

What can replication of latent viruses be induced by?

Answer 55

hormonal changes, pregnancy, stress, steroids, and decline in immune function

Question 56

What are four ways that persistent virus infections can damage the host?

Answer 56

Cytopathic effects of the virus on the cell immunopathologic tissue damage interference with growth or with specialized functions of the cell oncogenic transformation

Question 57

What are some survival strategies in which persistent viruses avoid being eliminated by the host?

Answer 57

Immunological tolerance escape from competent adaptive immune response infection of tissues with reduced immunosurveillance infection of the immune system restricted viral gene expression