Virus/ Host Interaction

Question 1

What is viral persistence?

Answer 1

Viral persistence: the inability of the immune system to clear an acute viral infection

Question 2

What are the causes of viral persistence?

Answer 2

• Causes of viral persistence
-Immunodeficiency due to HIV infection -Transplant -Chemotherapy -Genetic conditions -Congenital infections (BVDV)

Question 3

What are the outcomes to persistent viral infections?

Answer 3

• Outcomes of the persistent viral infections
- No apparent effects (Polyomavirus, Herpesvirus) -Chronic or progressive infections (measles, chronic hepatitis) -Cancer -Clinical reactivation (Genital herpesvirus infection)

Question 4

What is the significance of persistent viral infections?

Answer 4

• Significance of persistent infections
- Maintenance of virus in animal population

Question 5

What are the mechanisms of viral persistence?

Answer 5

• Viral evasion to the host innate immune response
• Modulation of the adaptive immune system
• Induction of latency
• Infection of tissues not readily accessible to the immune system such as keratinocytes
• Immune response escape mutants: HBCV, HIV
• Prolonged survival of the infected cell (oncogene)

Question 6

What is the routes of viral infection?

Answer 6

Respiratory
Skin
Conjunctiva
Genital Tract
Placenta
Alimentary Tract

Question 7

What are the respiratory tract defenses?

Answer 7

1. The mucous blanket
2. The beating of the ciliated epithelium

Question 8

How many droplets need to be inhaled to cause respiratory infection? What size droplets penetrates the bronchioles?

Answer 8

Inhalation of droplet nuclei (1-10) cause infection
1-3 um droplets penetrate bronchioles.

Question 9

What are the protective mechanisms of skin?

Answer 9

• Intact skin is barrier against viruses -> but can be penetrated by
• insect bites, animal bites, contaminated instruments ( iatrogenic)

Question 10

What is important to remember about viruses of the genital tract in animals ? What are some examples?

Answer 10

Venereal infection rare in animals.
BHV-1 venereal transmission
EHV-3 coital exanthema in horses

Question 11

What are the sophisticated immune defenses of the respiratory tract? What are some example of viruses that affect the respiratory tract.

Answer 11

Respiratory tract: the respiratory tract and all other mucosal surfaces possess sophisticated immune defense mechanisms, as well as non-specific inhibitory mechanisms (ciliated epithelium, mucus secretion, lower temperature) which viruses must overcome

• Influenza
• IBRV (Infectious bovine rhinotracheitis)
• Common Cold (Rhino, Adeno, Corona) viruses
• Parainfluenza Virus
• Respiratory syncytial virus (RSV)

Question 12

How can viruses affect the placenta in animals and what is the outcome? What are the results of this?

Answer 12

• Viremia in pregnant female the virus may cross the placenta and infect fetus.
  Killed fetus results in: infertility, mummified fetus, abortion, still birth, and if fetus survives it may have congenital anomalies.

Question 13

How do you get an infection of the alimentary tract? What are the defenses of the alimentary tract that helps remove viruses?

Answer 13

• Virus ingested with food and water
  Defenses: Low ph of stomach and high ph of intestines inactivates some viruses, Digestive tract has protective layer of mucus. Peristaltic action helps remove viruses.

Question 14

What is an example of a virus that uses the conjunctival route of viral infection?

Answer 14

IBRV conjunctival form.

Question 15

What are the major modes of transmission of respiratory viruses in short/ long range transmission?

Answer 15

• Droplet infection: an infection transmitted
  from one individual to another by droplets
  of moisture expelled from the upper
  respiratory tract through sneezing or
  coughing
  • Aerosol: Aerosol Transmissible Diseases
  Aerosol transmissible diseases (ATDs), such
  as measles, are transmitted by infectious
  particles or droplets through inhalation or
  direct contact with mucous membranes in
  the respiratory tract or eyes
  • Fomite: or environmental surfaces • (1) Clinical contact surfaces such as dental
  units, x-ray machines, equipment knobs, etc • (2) Housekeeping surfaces

Question 16

What is primary viremia?

Answer 16

The initial entrance of virus into blood ( which spreads to the replication sites)

Question 17

What is secondary viremia?

Answer 17

This is the point when the virus enters back into systemic circulation from one of its replication sites, and travels to its preferred target site.

Question 18

What do most viruses that enter through the skin need ?

Answer 18

Skin: most viruses which infect via the skin require a breach in the physical integrity of this effective barrier, e.g. cuts or abrasions Keratin

Question 19

What are methods of entry of CPD in sheep and cowpox?

Answer 19

Trauma of milking/ suckling

Question 20

What are examples of transmission of BTV, AHSV,LSDV?

Answer 20

Arthropod bites.

Question 21

What are methods of entry of EIAV?

Answer 21

Infected needles.

Question 22

What are methods of entry for Rabies virus?

Answer 22

Animal bites.

Question 23

What is shingles? Where is the route of infection?

Answer 23

Shingles: viral disease characterized by a painful skin rash with blisters in a localized area
• Infection through the conjunctiva and upper respiratory tract

Question 24

Where does shingles primary viremia replication occur?

Answer 24

• Replication in the primary lymph nodes
• Primary viremia

Question 25

Where does shingles primary viremia replication occur?

Answer 25

• Replication in liver, spleen, and other organs
• Secondary viremia

Question 26

What signs can be seen with shingles ? What is the cause of the latent infection?

Answer 26

• Infection of the skin and appearance of skin rashes
• Infection of sensory ganglia and establishment of latent infection