IV. Viral Pathogenesis

Viral Pathogenesis is the capacity of a virus to cause disease in a target host. It is a sophisticated study about the relationship between viral replication, host defence and viral evasion of the host defence.

I’ll just organise this topic into different parts for easier explaining.

1. Sites of Viral Entry into the host.
2. Viral spreading in the host body.
3. Modes of Transmission.
4. Virus-induced injury (cellular).
5. Sites of Viral entry into the host.

I shall now start explaining each and every one of these points…

1. Sites of Viral Entry into the host.

There are various places that a virus can enter and start causing disease to the host.

A. Animal host (E.g. Humans, lions, fishes, etc.)

• Skin
• Cuts, abrasions, etc.
• Conjunctiva (eyelids)
• Urogenital tract
• Respiratory tract
• Alimentary tract

B. Plant host

• Any part of the plant as long as there is direct penetration of the cell wall.

2. Virus spreading in the host body.

i. Systemic infection

• Many organs are infected

ii. Haematogenous spread

• Spread through the bloodstream
• Viremia
• Active / Passive
• Primary / Secondary

iii. Neural spread

3. Modes of Transmission.

• Spread through germ cells
• Consumption of infected tissue
• Respiratory Secretions
• Aerosols during speaking, sneezing, coughing, breathing, singing
• Faeces
• Blood

4. Virus-induced injury (cellular) and effects.

The cells that are infected with viruses will display Cytopathic Effects (CPE).

Some of these effects consist of:

• Altered shape
• Detachment from substrate
• Lysis
• Membrane fusion; syncytium
• Membrane permeability
• Inclusion bodies
• Apoptosis

Other effects shown would be the Formation of Syncytium, shutting off of cell functions and Immunopathological lesions.

a. Formation of Syncytium

Below is a diagram describing Syncytium formation.

b. Shutting off of cell functions

• E.g. poliovirus shuts off cellular function in neurons resulting in cell death and hence paralysis

c. Immunopathological lesions

• Impairment of immune response due to infection of immune cells. (E.g. HIV on CD4⁺ & CD8⁺ T lymphocytes)

• Enhancement of immune response causing haemorrhagic fever. (E.g. Dengue haemorrhagic fever, Hantaan, Ebola, etc.)