Virus Pathogenesis

Question 1

T/F: Virulence is an absolute property of a virus, regardless of any variables.

Answer 1

FALSE - depends on many things!

Question 2

The dose of virus needed to cause death or infection in 50% of test subjects is known as:

Answer 2

LD50

ID50

Question 3

Will a more virulent virus have a higher or lower LD50 or ID50?

Answer 3

Lower - takes less virions to do the same job

Question 4

Steps in viral infection

Answer 4

Entry and replication
Spread, tropism, infection of target organs
Virus-cell interactions
Tissue and organ injury
Shedding

Question 5

What are the skin’s defenses against infection?

Answer 5

Dense keratin layer
Low pH
Fatty acids
Normal flora
Dryness
Immune cells

Question 6

Transcutaneous routes of pathogen entry

Answer 6

Arthropod bite
Bite of infected animal
Contaminated objects (needles)

Question 7

What are the GI tract’s defenses against infection?

Answer 7

Mucous
Stomach acidity
Intestinal alkalinity
Bile and Pancreatic enzymes
Defensins/ IgA/Macrophages

Question 8

What are the respiratory tract’s defenses against infection?

Answer 8

Mucous
Alveolar macrophages
NALT/BALT
Temperature gradient

Question 9

What type of infection spreads beyond the primary site?

Answer 9

Disseminated

Question 10

What direction of viral shedding from cells facilitates systemic spread?

Answer 10

Basolateral release - gives access to underlying tissues

Question 11

What direction of viral shedding from cells facilitates virus dispersal?

Answer 11

Apical release

Question 12

________ _______ is the initial entry of the virus into the bloodstream following infection.

Answer 12

Primary viremia

Question 13

______ ______ happens after the virus has replicated in major organs and once again entered the bloodstream.

Answer 13

Secondary viremia

Question 14

________ _______ is a direct inoculation of a virus into the blood, such as by arthropod bite or contaminated syringe.

Answer 14

Passive viremia

Question 15

What are neurotropic viruses?

Answer 15

viruses that can infect neural cells

Question 16

What kind of viruses are able to enter the central nervous system after infection at a peripheral site?

Answer 16

Neuroinvasive viruses

Question 17

What kind of viruses cause disease of nervous tissue, manifested as neurological symptoms and often death?

Answer 17

Neurovirulent viruses

Question 18

If a virus always enters the PNS, but rarely the CNS, and causes severe symptoms/death when it does enter the CNS, it is considered to have ___ _______ but ___ _______.

Answer 18

Low neuroinvasiveness and high neurovirulence

Question 19

If a virus almost always enters the CNS, but rarely causes neurological disease it is considered to have _______ and ____ _______.

Answer 19

Neuroinvasiveness and low neurovirulence

Question 20

If a virus readily spreads from the PNS to the CNS and causes death 100% of the time without prompt antiviral medication it is considered to have ____ ______ and ____ ______.

Answer 20

high neuroinvasiveness and high neurovirulence

Question 21

When a virus travels in the opposite direction of neural impulse flow, from axon terminal to dendrite/cell body, it is called __________ spread.

Answer 21

retrograde

Question 22

When a virus travels in the direction of neural impulse flow, from dendrite/cell body to axon terminal, it is called ______ spread.

Answer 22

anterograde

Question 23

What are 2 routes a virus can take to spread to the CNS?

Answer 23

Olfactory

BBB

Question 24

What type of infection features intensive shedding over a short period of time?

Answer 24

Acute

Question 25

In what type of infection does a virus spread at low titers for months or years?

Answer 25

Persistent

Question 26

Definition of pantropic virus

Answer 26

Virus that can replicate in more than one host tissue/organ

Question 27

Fluid filled sacs or elevations in the skin

Answer 27

Vesicles

Question 28

An opening in the skin caused by sloughing of necrotic tissue, extending past the epidermis

Answer 28

Ulcer

Question 29

Palpable, solid, elevated mass. Distinct borders and can be extending deep into the dermis.

Answer 29

Nodule or tumor

Question 30

Benign skin growths that appear when a virus infects the top layer of skin

Answer 30

Warts

Question 31

Solid elevations on the skin without fluid

Answer 31

Papules

Question 32

Reddening of the skin (can be a consequence of systemic viral infection).

Answer 32

Erythema

Question 33

Gastrointestinal infection can happen via which 2 pathways?

Answer 33

Ingestion | Hematogenous spread/systemic infection

Question 34

Effects of viral infection on the intestinal tract

Answer 34

Destruction of enterocytes and hyper secretion, leading to GI disease, malabsorption, and diarrhea, causing dehydrating, acidosis, and hemoconcentration.

Question 35

Effects of viral infection on the respiratory tract

Answer 35

Loss of ciliary activity and integrity of mucus layer ``` Destruction of epithelium Inflammation Exudation Influx of inflam cells Obstruction of airways Hypoxia/distress Secondary infection ```

Question 36

Effects of viral infection on the CNS

Answer 36

``` Encephalitis Encephalomyelitis Neuronal necrosis Neuronophagia Perivascular cuffing Demyelination Neuronal vacuolation ```

Question 37

Effects of viral infection on the hematopoietic system

Answer 37

Damage to endothelium (hemmorrhage) Disseminated Intravascular Coagulation Edema Infarction

Question 38

What happens during DIC?

Answer 38

A bunch of clots form in the small vessels, restricting blood flow and causing multi-organ failure. After that, coagulation factors are all used up which leads to hemorrhage throughout the body.

Question 39

The abnormal development or arrest in development of the embryo or fetus.

Answer 39

Teratogenesis *May lead to death or malformations during the antenatal period.

Question 40

T/F: During the body's immune response against infection, tissue injury to the host can occur.

Answer 40

TRUE - Virus-Induced Immunopathology. *depends on a balance between the protective and destructive effects of the host immune response

Question 41

What are some manifestations of Immunopathology?

Answer 41

Tissue damage d/t hypersensitivity reactions Autoimmune diseases (moon blindness) Inflammation-mediated tissue damage (fibrosis) Immunodeficiency disorders

Question 42

The roll of T cells in virus-induced immunopathology

Answer 42

Cytotoxic T cell mediated lysis of infected host cells Release of cytokines from CD4+ and CD8+, and other cells, that cause inflammation and tissue damage. (Chronic in persistent infections)

Question 43

Role of TLRs in virus-induced immunopathology

Answer 43

Persistent activation of these receptors leads to production of pro-inflammatory cytokines and interferons (^^ inflammation)

Question 44

T/F: Production of ROS to combat viral infections will only harm the pathogens.

Answer 44

FALSE - ROS can also injure nearby host cells

Question 45

How do antibodies contribute to immunopathology?

Answer 45

Binding of Ab to an infected cell activates the complement system and initiates an inflammatory reaction

Question 46

What's an example of virus-induced immunopathology leading to immunosuppression?

Answer 46

Infectious Bursal Dz: viral replication causes atrophy of the Bursa of Fabricius in birds, leading to a deficiency in B lymphocytes.

Question 47

What type of viral infections may not be detected clinically and may lead to spread of the virus?

Answer 47

Inapparent infections

Question 48

In what type of infection is the virus not demonstrable except in cases of immunosuppression or cytokine activation when it is reactivated?

Answer 48

Latent (persistent) infections

Question 49

Foot and Mouth Dz in cattle tends to stay in and shed from infected tissue after acute disease. This is an example of what kind of infection?

Answer 49

Chronic (persistent) infection

Question 50

Prion diseases have a prolonged incubation period that lasts months or years, during which time numbers of infectious particles gradually increase, and eventually cause a progressive lethal disease. This is an example of what kind of infection?

Answer 50

Slow (persistent) infection

Question 51

What kind if infection is cleared rapidly by the host immune system?

Answer 51

Acute infection