Virulence and Pathogenicity- Virology

Question 1

Define pathogenicity.

Answer 1

The ability of a virus to cause disease in host

Question 2

Define pathogen

Answer 2

A virus that causes disease

Question 3

Define pathogenesis

Answer 3

The manner/mechanism of development of a disease

Question 4

Define virulence

Answer 4

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

Question 5

Define avirulent

Answer 5

No virulent (not harmful to the host)

Question 6

What factors related to the host effect the virulence of a virus?

Answer 6

Species
Immunity
Physiological factors (age, nutrition status, hormones, stage of cell differentiation)
Fever

Question 7

What factors related to the virus effect its virulence?

Answer 7

Genetic variation of the virus
Route of entry into the host
Affinity of the virus to host organs
Dose of infection
Immuno evasion

Question 8

What factors effect the virulence of a virus unrelated to the host or the virus itself?

Answer 8

Environment

Duel infections

Question 9

What is used to measure virulence?

Answer 9

Lethal dose 50 (LD50) - the dose of the virus that is required to kill 50% of animals, such as mice

Question 10

A more virulent virus would have a higher or lower LD50?

Answer 10

Lower - less is needed

Question 11

What are the routes of entry for a virus?

Answer 11

Skin
Mucous membranes
GI Tract
Respiratory Tract

Question 12

How does a virus penetrate the skin?

Answer 12

Cut or breach
Transcutaneous injections (bite of arthropods)
Bite of infected animal
Contaminated objects (needles, etc)

Question 13

How does a virus penetrate the mucous membrane?

Answer 13

Conjunctiva
Oropharynx
Genitourinary Tract and Rectum

Question 14

How does a virus penetrate the GI Tract?

Answer 14

Contaminated food or water

Question 15

How do viruses spread in a host?

Answer 15

epithelium –> subepithelial layer/ underlying tissues, lymphatics –> blood streams –> nerves

Question 16

How is a virus spread in the epithelium?

Answer 16

Local spread, causes localized infection, may or may not proceed to subepithelium

Question 17

How does a virus spread from the epithelium to the subepithelium?

Answer 17

Overcome local host defense

Question 18

How does a virus spread from the subepithelium to the blood stream?

Answer 18

The virus get access to lymphatics, phagocytic cells, and tissue fluids in the subepithelium which help carry the virus to the bloodstream.

Question 19

Define viremia.

Answer 19

Presence of virus in the blood

Question 20

What is primary viremia?

Answer 20

initial entry of virus into the blood

Question 21

How does primary viremia happen?

Answer 21

Spread of viral infection to blood from subepithelial tissue/ lymphatics

OR

Direct injection in blood, through bite of mosquitoes or syringes

Question 22

What is secondary viremia?

Answer 22

When a virus has replicated/multiplied in major organs and once more entered circulation

Question 23

What is disseminated infection?

Answer 23

Infection spreads beyond the primary site of infection

Question 24

Whats is systemic infection?

Answer 24

If a number of organs or tissues are infected

Question 25

How do viruses spread to the nerves?

Answer 25

Through the peripheral nerves Through receptor neurons in the nasal olfactory epithelium Viruses can cross blood-brain barrier and infect CNS

Question 26

Define neurotropic virus

Answer 26

Viruses that can infect neural cells, infection can occue by neural or hematogenous spread

Question 27

Define neuroinvasive virus

Answer 27

Viruses that enter the central nervous system (spinal cord and brain) after infection of peripheral site

Question 28

Define neurovirulent virus

Answer 28

Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death

Question 29

Define tropism

Answer 29

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

Question 30

Define pantropic viruses

Answer 30

can replicate in more than one host organ/tissue

Question 31

What is the mechanism of viral injury and disease?

Answer 31

Virus-cell interactions

Question 32

What are the outcomes of viral injury?

Answer 32

``` Cell lysis following virus replication Apoptosis Oncoviruses Persistent Infection - viruses remain latent or dormant in host cell for long periods, escaping detection Immunosupression ```

Question 33

What are oncoviruses?

Answer 33

Oncogenic viruses; viruses that cause cancer

Question 34

Define virus shedding

Answer 34

Shedding of infectious virions is crucial to the maintenance of infection in populations

Question 35

Define acute infection in terms of shedding

Answer 35

Usually intensive shedding over short period of time

Question 36

Define persistent infections in terms of shedding

Answer 36

Can be shed at lower titers for months to years

Question 37

Describe viral injuries that effect the skin.

Answer 37

Can be localized or dissminated. Ulcer Nodule Wart Erythema

Question 38

What is a vesicle on the skin?

Answer 38

fluid filled sac

Question 39

Define ulcer

Answer 39

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

Question 40

Define nodule

Answer 40

Solid tumorous mass

Question 41

Define warts

Answer 41

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

Question 42

Define erythema

Answer 42

reddening of the skin

Question 43

How do viruses get into the GI tract?

Answer 43

Ingestion or from the blood, systemic infection

Question 44

What happens once a virus enters the GI tract? What are the physical symptoms?

Answer 44

Intestinal enterocytes are destroyed resulting in malaabsorption and diarrhea resulting in dehydration, acidosis, and hemoconcentration

Question 45

How do viruses effect the respiratory tract?

Answer 45

inflammation obstruction of air passages hypoxia and respiratory distress

Question 46

What is necrosis?

Answer 46

Death of body tissue

Question 47

What is perivascular cuffing?

Answer 47

Inflammatory cells around blood vessels in CNS

Question 48

How do viruses effect the hemopoietic system?

Answer 48

damage to epithelium- blood clots form throughout body followed by hemorrhages viral infection of the fetus- teratogenic viruses

Question 49

Define teratongenic viruses

Answer 49

Cause developmental defects of embryo or fetus after in-utero infection