Subviral Agents

Subviral agents - viroids, prions, and satellites- resemble viruses but lack viral components.

Viroids consist of a single-stranded RNA, lack a capsid, and only infect plants.

They rely on the host's RNA polymerase to replicate and self-cleave to release RNA units.

These RNAs do not encode proteins but form stable secondary structures, acting as small interfering RNAs that silence plant genes.

Prions are infectious agents composed entirely of proteins and lacking nucleic acids.

PrPC is a normal protein in animals. When infectious PrPSc enters the cells, it misfolds PrPC into PrPSc, forming harmful amyloid aggregates that damage the neurons.

This leads to transmissible spongiform encephalopathies, marked by brain degeneration and vacuole formation.

Prion diseases can be inherited or acquired through infected meat or surgical instruments.

Examples include scrapie in sheep, mad cow disease in cattle, and Creutzfeldt–Jakob disease in humans.

Satellites are DNA or RNA enclosed in a capsid. They rely on helper viruses for replication.