Virion

Definition

The complete, infectious, extracellular form of a virus, consisting of a nucleic acid genome enclosed within a protein capsid and, in many viruses, an outer lipid envelope. The virion is metabolically inert and exists primarily to protect the viral genome during transmission between hosts and to mediate attachment and entry into susceptible cells. Upon cellular invasion, the virion uncoats, releasing the genome to hijack host machinery for replication.

Etymology

From Latin *virus* (poison, slimy liquid) + diminutive suffix *-ion*, modeled on terms like *bacterion*.

Example

In mosquito-borne flaviviruses such as dengue virus, the mature virion acquires an envelope from host cell membranes during budding; this envelope bears glycoproteins essential for binding to receptors on midgut epithelial cells, enabling vector infection.

Synonyms

• virus particle
• viral particle

Related Terms

• Capsid
• envelope
• vector competence
• Horizontal transmission
• Vertical transmission
• Arbovirus
• baculovirus
• nucleopolyhedrovirus
• occlusion body
• Transovarial transmission
• cytopathic effect

Usage Notes

Distinguish carefully from 'virus,' which may refer to the entire replication cycle or taxonomic entity; 'virion' specifies only the particle stage outside cells. In arthropod pathology, 'occlusion-derived virion' and 'budded virion' describe distinct morphotypes in baculovirus infections of insects. Plural 'virions' is standard; avoid 'viria.'