What is the difference between a virus and a prion?
Question
The other day in our virology class, someone asked what’s the actual difference between a virus and a prion. I remembered reading that viruses carry genetic material, while prions are just misfolded proteins without any DNA or RNA. This answer breaks down the difference in structure, replication, immune response, and more—it really helped me understand how unique prions are.
Answer ( 1 )
Biochemical Composition
Viruses contain genetic material (either DNA or RNA) enclosed in a protein coat called a capsid, sometimes with an additional lipid envelope. Prions, on the other hand, consist entirely of protein with no nucleic acid. They are misfolded forms of normal host proteins, and the term “prion” stands for “proteinaceous infectious particle.”
Structural Organization
Viruses have diverse structures, often 20–400 nm in size, and are organized with icosahedral, helical, or complex symmetries. Prions are abnormally folded proteins that form stable, beta-sheet-rich aggregates or fibrils. The normal prion protein (PrPC) is rich in alpha-helices, while the disease form (PrPSc) is rich in beta-sheets.
Replication Mechanisms
Viruses replicate through a complex cycle involving host cell machinery and their own genetic instructions. Prions replicate without genetic material, using the misfolded PrPSc to induce normal PrPC to misfold—a process called “seeded conversion” or “templated folding.”
Resistance to Decontamination
Viruses are generally inactivated by standard disinfection methods such as heat, UV radiation, and chemicals. Prions are extremely resistant and survive autoclaving, formaldehyde, UV, and many chemical disinfectants due to their stable beta-sheet structure.
Host Range and Tissue Tropism
Viruses can infect all life forms, from bacteria to humans, and often target specific tissues based on receptor compatibility. Prions primarily affect mammals and target the central nervous system, leading to spongiform changes and other neurodegenerative effects.
Pathogenicity Mechanisms
Viruses damage host cells through direct lysis, apoptosis, immune responses, or by transforming cells. Prions cause disease by forming toxic aggregates that disrupt cell function and eventually lead to cell death.
Immune Response
Viruses typically trigger strong immune responses—both innate and adaptive. Prions, being misfolded versions of self-proteins, generally evade immune detection, contributing to the fatal nature of prion diseases.
Treatment Approaches
Antiviral drugs and vaccines are available for viruses. No effective treatments currently exist for prion diseases, though research is ongoing into compounds that stabilize normal protein structures or disrupt aggregates.
Source: Prion Biology and Diseases (book); Nature Reviews Microbiology