Lecture 8: Virulence of Viruses

Question 1

Pathogenicity

Answer 1

the ability of a virus to cause disease in the host

Question 2

Pathogen

Answer 2

The virus which causes disease

Question 3

Pathogenesis

Answer 3

the manner/mechanism of development of a disease

Question 4

Virulence

Answer 4

quantitative or relative measure of the degree of pathogenicity of the infecting virus

Question 5

Avirulent

Answer 5

not harmful to the host

Question 6

Virulence factors related to the virus

Answer 6

• Genetic variation of virus
• Route of entry of virus in host organs
• Affinity of virus to host organs
• Dose of infection
• Immuno evasion

Question 7

Virulence factors related to the host

Answer 7

• Host species
• Host immunity
• Host physiological factors (nutrition, age, hormones, stages of cell differentiation)
• Fever

Question 8

Lethal dose 50 (LD50)

Answer 8

The dose of the virus required to cause death in 50% of animals

Question 9

Three routes of entry of viruses into host-skin

Answer 9

1. Bite of arthropods
2. Bite of infected animal
3. Contaminated objects

Question 10

Three routes of entry of viruses into host-mucous membrane

Answer 10

1. Conjunctiva
2. Oropharynx
3. Genitourinary tract/rectum

Question 11

Two defenses of mucous membranes

Answer 11

IgA (antibodies)

Virucidal proteins

Question 12

Local spread of viruses on epithelial surfaces

Answer 12

• Causes localized infection

- May or may not proceed to subepithelial/underlying tissues

Question 13

Subepithelial invasion

Answer 13

• Viruses get access to lymphatics, phagocytic cells, and tissue fluids
• Help carry virus to blood stream

Question 14

Viremia

Answer 14

Presence of virus in blood stream

Question 15

Primary viremia

Answer 15

Initial entry of virus into the blood

Question 16

Two ways primary viremia may occur

Answer 16

• Spread of virus to bloof from subepithelial tissue/lymphatics
• Direct injection into blood stream

Question 17

Secondary viremia

Answer 17

Virus has replicated in major organs and has once more entered circulation

Question 18

Disseminated infection

Answer 18

Spreads beyond primary site of infection

Question 19

Systemic infection

Answer 19

A number of organs or tissues are infected

Question 20

Neurotropic virus

Answer 20

Viruses that can infect neural cells. Infection may occur by neural or hematogenous spread

Question 21

Neuroinvasive virus

Answer 21

Viruses enter the CNS after injection at a peripheral site

Question 22

Neurovirulent virus

Answer 22

Cause disease of nervous tissue, manifested by neurological symptoms and often death

Question 23

How do viruses cross the blood-brain barrier

Answer 23

they hide in monocytes

Question 24

Tropism

Answer 24

The specificity/affinity of a virus for a particular host tissue

Question 25

Pantropic

Answer 25

can replicate in more than one host tissue/organ

Question 26

Cell lysis allows

Answer 26

release of new viruses | occurs after viral replication

Question 27

Apoptosis

Answer 27

Programmed cell death | Host will activate as last resort to eliminate viral factories before new virus production is complete

Question 28

Oncoviruses

Answer 28

Cause cancer

Question 29

Persistant infection

Answer 29

Remain dormant | Can cause chronic stimulation of host immune system, resulting in immunopathology

Question 30

Infectious bursal disease

Answer 30

Viral replication causes atrophy of bursa and severe deficiency of B lymphocytes, resulting in immunosuppression, causing host to become susceptible to other pathogens

Question 31

Acute infection

Answer 31

intensive shedding over a short period of time

Question 32

Persistent infection

Answer 32

Shed at lower titers for months-years

Question 33

Skin infection

Answer 33

Localized (papilloma) or disseminated (lumpy skin disease)

Question 34

Warts

Answer 34

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

Question 35

Erythema

Answer 35

Reddening of ski

Question 36

Neuronophagia

Answer 36

killing of neuronal cells by phagocytic cells

Question 37

Perivascular cuffing

Answer 37

inflammatory cells around blood vessels in CNS

Question 38

Disseminated intravascular coagulation

Answer 38

- Widespread activation of clotting mechanism that results in the formation of blood clots in small blood vessels throughout the body - Triggered by viral infection - Over time, clotting proteins in blood are used up and severe bleeding can occur

Question 39

Vasculitis

Answer 39

inflammation and damage to blood vessels

Question 40

Vasculitis can be regulated by

Answer 40

immune-complex formation

Question 41

Teratogenic viruses

Answer 41

cause developmental defects o embryo or fetus after in-utero infection

Question 42

7 viral immune-evasion strategies

Answer 42

- Negative cytokine regulation - Alterations in antigen processing pathways - Evasion of natural killer cells - Alterations in the B cell system - Viral evasion through latency - Inhibition of apoptosis