Pathogenesis

Question 1

Mechanisms by which viruses cause infection in the host

Answer 1

Cytolysis: viral replication results in the destruction of the host cell - release of virus eg.,
Transfer for genetic material: bacteriophages may transfer virulence factors eg., exotoxins

Question 2

Acute infection

Answer 2

Rapid onset of viral production
Production of a large amount of virus
Short and sometimes severe course of disease
With a relatively short duration with rapid recovery – immune clearance ~ 2 weeks
Most viruses that infect humans
respiratory infections (e.g., cold viruses, influenza viruses)
gastrointestinal infections (e.g., Rotaviruses, Noroviruses)

Question 3

Persistent infection

Answer 3

Persistent infectionoccurs when a virus is not completely cleared from the system of the host but stays in certain tissues or organs of the infected person. There is no single mechanism for establishing persistent infection
Key feature is the reduction of host defences and the ability of the virus to kill cells

Question 4

Mechanisms of persistent infection may

Answer 4

involve the regulation of the viral infection
host gene expressions alteration of the host immune response

Question 5

Latent infection

Answer 5

The virus remains in equilibrium with the host for long periods before symptoms again appear, but the actual viruses cannot be detected until reactivation of the disease occurs.
HSV-1 = fever blisters
HSV-2 = genital herpes
VZV = chickenpox-shingles

Question 6

Slow infection

Answer 6

Slow virus period of year separates the initial acute infection and fatal outcomes
Production of virions may continue
HepB

Question 7

Chronic infection

Answer 7

characterised by the continued presence of infectious viruses following the primary infection

Question 8

General properties of persistent infection

Answer 8

Begin when innate immune defenses are modulated or bypassed
Not cleared effectively by the adaptive immune response
Virus particles continue to be produced for long periods
Viruses may be produced at low levels for months or years
Some infections can involve periods of latency infection followed by bouts of reactivation
Infections persist for the lifetime of the host

Question 9

Genomes of latent/persistent infection

Answer 9

Non-replicating genome in a non-dividing cell
Herpes simplex virus, Varicella zoster virus – chickenpox reactivates as shingles
Autonomously replicating genome in a replicating cell
Human papillomavirus, Epstein Bar virus
Proteins on the genome are not fully expressed
The genome integrated into the host chromosome replicates with the host
HIV, parvovirus HHV6
Viral genome replicates as host genome replicate

Question 10

Viral induce transformation

Answer 10

Viral transformation is a change in growth, phenotype, or indefinite reproduction of cells caused by the introduction of inheritable material
The virus causes harmful transformations of an in vivo or cell culture
It can occur naturally or medically
Naturally, transformation can include viral cancers
eg human papillomaviruses (HPV) and T-cell leukemia virus type 1
Hep B and C

Question 11

Viral Oncogenesis through transformation can occur via 2 mechanisms:

Answer 11

The tumor virus can introduce and express a “transforming” gene either through the integration of DNA or RNA into the host genome.
The tumor virus can alter the expression of preexisting genes of the host.
One or both of these mechanisms can occur in the same host cell.