Virion

Virion (from Latin virus — poison and Greek suffix -ion, denoting particle) is a complete, structurally finished infectious unit of a virus. It represents a phase of the virus life cycle, existing outside the host cell, serving solely to transport the viral genome to new susceptible tissues.

Etiology and pathophysiology

Virions are not living microorganisms (they lack cellular structure, cannot supply themselves with energy, and cannot produce proteins to build their particles).

The structure of the virion may include the following components:

• Nucleocapsid — consists of a capsid (protein coat) and the enclosed nucleic acid (one or more genome molecules of single or double-stranded RNA or DNA);
• Peplomers (protein spikes) — may protrude from the capsid in some viruses (e.g., coronaviruses) and are used to establish contact with the host cell.
• Viral envelope (supercapsid) — an external membrane present in many viruses (e.g., influenza viruses, coronaviruses, HIV), which includes a lipid bilayer and surface proteins necessary for envelope formation upon exiting the cell. This structure aids in attachment to the cell and evasion from the immune system while the virion searches for a cell to infect.

Clinical significance

Understanding the structural organization of a virion is important for epidemiology and pharmacology. Virions with an external lipid envelope are vulnerable to surface-active substances.

This is why thorough handwashing with soap or treatment with alcohol-based antiseptic physically dissolves the lipid layer, irreversibly destroying the virion.