Virulence mechanisms of viruses and prions

Virulence Mechanisms of Viruses

General Definition

A virus is a type of microorganism that is incapable of reproducing on its own. Instead, viruses invade host cells and use the host’s biological machinery to multiply.
The virulence of a virus is its capacity to infect and harm a host.

Viral Entry and Replication

Viruses enter host organisms and cells through processes such as endocytosis, direct penetration, or fusion with the host cell membrane.
Once inside a host cell, the virus’s DNA or RNA takes over the cell’s machinery to replicate and produce new virus particles. This process often damages or kills the host cell.

Evasion of the Immune System

Viruses evade the host immune system in a variety of ways. Some modify the host cell surface to avoid recognition or silence alarm signals the cell would normally send out.
Others hide inside host cells, where they can replicate without being detected by the immune system.
Some viruses use antigenic variation, regularly changing their surface proteins to avoid the hosts’ immune responses.

Induction of Host Cell Death

Viruses can cause host cell death through various methods, including apoptosis (programmed cell death), necrosis (premature death due to damage), or pyroptosis (a type of cell death involving inflammation).

Virulence Mechanisms of Prions

General Definition

Prions are infectious proteins that can cause disease in a host.
Prions work by changing the shape of normal proteins found in the host’s cells, causing them to function improperly and leading to disease.

Prion Replication and Spread

Prions replicate by converting normal proteins into the misfolded prion form.
This leads to an increase in the number of misfolded proteins, which aggregate and cause damage to the cell.
The spread of prions within a host organism can cause extensive tissue damage and can be fatal.

Evasion of the Immune System

As prions are misfolded proteins rather than foreign objects, they can evade the host’s immune system.
This allows prions to persist and accumulate in host tissues without being detected or destroyed by the immune response.

Induction of Neurodegenerative Disease

Prion diseases are a type of neurodegenerative disease, meaning they cause the death of neurons, or nerve cells.
This damage results in diseases such as Creutzfeldt-Jakob disease in humans, Bovine Spongiform Encephalopathy (BSE or ‘mad cow disease’) in cattle, and scrapie in sheep.
These diseases are characterised by rapidly progressive dementia, motor dysfunction and ultimately death.

Understanding these virulence mechanisms is crucial for developing treatments and vaccines for viral and prion diseases. It also underscores the importance of ongoing surveillance and control measures to prevent their spread.