Mechanism of viral infection and pathogenesis Flashcards
How are viruses species specific
- They are adapted to non-human hosts
- Surface barriers exclude them
- Innate Immunity prevents them from establishing
- Our adaptive immune response has seen something
similar
List some common viruses of man
- Influenza Smallpox
- Common cold
- Measles
- Mumps
- RSV
- COVID-19
- Chickenpox/Shingles
- Glandular fever
- Hepatitis
- Papillomas (Warts)
- AIDS
- Kaposi’s sarcoma
We may have eliminated these with vaccines:
- Smallpox
- Poliomyelitis
What are the general patterns of different infections
- Acute infection
- Latent, reactivating infection
- Persistent infections
Describe acute infections
Resolved by immunity or not which causes death
- Measles
- Small Pox - 50% mortality
- Ebola - more than 50% mortality
Describe latent, reactivating infections
There is reactivation of the infection many times after the primary infection
What infections are often latent reactivating ones
- Herpes simplex virus
- Chickenpox
- Varicella Zoster Virus
- Shingles
Describe herpes simplex and VZV latency
- There is primary infection where the virus becomes latent in dorsal root ganglions after causing initial symptoms
- Recurrence after stimulus event such as fever or stress
Describe persistent infection in the presence of an active immune response
- Viral levels are constantly controlled by active host immunity
- HIV, HCV and Measles
Describe how normal persistent infections work
Seen in congenital rubella
- if infected in utero, virus is
seen as self, baby is born immunotolerant and virus continues to replicate (and cause damage) in neonatal tissues
Death due to congenital problems
How does virus infection of a host lead to disease
Pathogenesis results from cell and tissue damage caused by the viral infection. On most occasions
the damage is limited by the host’s immune
system
What are Inapparent infections
Asymptomatic infection
- 90% of all poliovirus infections are asymptomatic
(inapparent) - Many infections in the earliest phase of the COVID
pandemic were asymptomatic
Describe the course of infection of Hepatitis C
- Acute infection
- Chronic inflammation
- Fibrosis
- Cancer or Cirrhosis
Describe the immunopathology of HCV
- Chronic hepatitis is a disease of severe liver damage and loss of hepatocytes – caused by persistent HCV infection
- HCV is non-cytopathic
- Associated with extensive liver infiltration of leukocytes
- Pro-inflammatory cytokine levels are high
- Viral clearance and disease are associated with the generation and infiltration of CD8+ cells which attack infected cells and destroy them
Describe the immunopathology of dengue fever
- Severe dengue, which may include dengue shock syndrome
(DSS), and haemorrhage
The greatest risk is a previous infection with a different
serotype - Antibodies formed in response to a dengue infection are
not cross-protective against other subtypes of the virus. - Can cause more severe disease due to antibody-dependant enhancement
What is antibody-dependant enhancement
- Non-neutralizing antibodies coat the virus, forming immune
complexes which get internalised into mononuclear
phagocytes through their Fc receptors - fixation of
complement by circulating immune complexes results
in release of products of the complement cascade
leading to sudden increased vascular permeability,
shock and death
