16 - General features of viral infection

Question 1

What is an successful viral infection?

Answer 1

Survival of viruses

Question 2

Extent of virus propagation in the host organism

Answer 2

• Localized infection (Papillomatosis, rabies)
• General infection (viraemia)

Question 3

Infection routs

List the different infection routes

Answer 3

1. Transcutaneous
2. Airborne
3. Oral
4. Venereal
5. Transplacental or intrauterine
6. Germinative
7. Latrogenic

Question 4

​Infection routs

1. Transcutaneous infection

Answer 4

• Via the skin
• Keratinized cells on the surface → no virus infection
• Injuries:
  
  • Papilloma
  • Rabies (bite)
• Arthropod vector - arthropod-borne: arbovirus
  
  • From mosquito, tick, fly, louse
  • Mecanical vector - biological vector
  • Viruses:
    
    • Orbiviruses
    • Togaviruses
    • Flaviviruses
    • Bunyaviruses
• ​Special: conjuctiva (herpes)

Question 5

​Infection routs

2. Airbourne

Answer 5

• Via the respiratory tract
• Drop infection
• Aerosol particles
• UV ligth, drying out
• Defense systems:
  
  • Mucosal immunity (IgA, lymphoid cells, alveolar macropage)
  • Temperature: 33°C – polymerase activity low
  • Microvilli
• Respiratory diseases (paramyxovirus, rhinovirus)

Question 6

​Infection routs

3. Oral infection

Answer 6

• Via the enteric system

Defense:

• Oral cavity:
  
  • Lysozyme
• Stomach:
  
  • Acidic pH
  • Protective enzymes
• Small intestines:
  
  • Digestive enzymes
  • Bile (detergent)

Infection:

• Resistant viruses, mainly non-enveloped
• Viruses:
  
  • Adenoviruses
  • Reoviruses
  • Picornaviruses
  • Caliciviruses
  • Astroviruses
  • Coronaviruses
  • Orthomyxoviruses
• Protolytic enzymes sometimes acitvate virus receptors

Question 7

​Infection routs

4. Venereal infection

Answer 7

• Via the urogenital tract
• Causes of infection: Sexual intercourses
• Sensitive viruses
• Cell-associated transmission
• Viruses:
  
  • Herpesviruses
  • Papillomaviruses
  • Hepadnaviruses
  • Arteriviruses
  • Retroviruses

Question 8

Infection routs

4. Transplacental- or intrauterine infection

Answer 8

• Via the placenta
• Different placental structures acts as barriers
• Viruses control age/development of the embryo
• Conseqeunce of infection:
  
  • Resorption
  • Tolerance
  • Abortion
  • Mummification
• Viruses:
  
  • Herpesviruses
  • Parvoviruses
  • Flaviviruses

Question 9

Infection routs

5. Germinative infection

Answer 9

• Via the egg (birds)
• Cause of infection:
  
  • On the surface of the egg - at hatching (ie. herpes)
  • Inside the egg
    
    • Circoviruses
    • Adenoviruses
    • Picornaviruses
    • Retroviruses
• The yolk is immune

Question 10

Infection routs

6. Latrogenic infection

Answer 10

• By veterinarians
• Cause of infection:
  • Non-sterile equipment
    
    • Papillomaviruses
    • Flaviviruses
  • Needle, syringe:
    
    • Flaviviruses
    • Arteriviruses
    • Retroviruses

Question 11

Infection routs

Give an example of a mixed infection

Answer 11

Oronoasal infection from influenza

Question 12

Give the facotrs influencing the result of infection

Answer 12

• Susceptibility
  
  • Abortive infection – non pathogenic, not suitable route → host spectrum
    
    • Stenoxen
    • Euryxen
• Infectivity
  
  • Viral receptors, nucleic acid
• Amount of viruses
  
  • Chances of successful infection
  • Capacity of the immune system
• Pathogenicity
  
  • Overt disease ↔ adaptation
• Virulence
  
  • Degree of expression (pathogenicity)