The virus and the virion

The illustration at left depicts a virion – the infectious particle that is designed for transmission of the nucleic acid genome among hosts or host cells. A virion is not the same as a virus. I define virus as a distinct biological entity with five different characteristics. Others believe that the virus is actually the infected host cell.

The idea that virus and virion are distinct was first proposed by Bandea in 1983. He suggested that a virus is an organism without a cohesive morphological structure, with subsystems that are not in structural continuity:

Viruses are presented as organisms which pass in their ontogenetic cycle through two distinctive phenotypic phases: (1) the vegetative phase and (2) the phase of viral particle or nucleic acid. In the vegetative phase, considered herein to be the ontogenetically mature phase of viruses, their component molecules are dispersed within the host cell. In this phase the virus shows the major physiological properties of other organisms: metabolism, growth, and reproduction.

According to Bandea’s hypothesis, the infected cell is the virus, while the virus particles are ‘spores’ or reproductive forms. His theory was largely ignored until the discovery of the giant mimivirus, which replicates its DNA genome and produces new virions in the cytoplasm within complex viral ‘factories’. Claverie suggested that the viral factory corresponds to the organism, whereas the virion is used to spread from cell to cell. He wrote that “to confuse the virion with the virus would be the same as to confuse a sperm cell with a human being”.

If we accept that the virus is the infected cell, then it becomes clear that most virologists have confused the virion and the virus. This is probably a consequence of the fact that modern virology is rooted in the study of bacteriophages that began in the 1940s. These viruses do not induce cellular factories, and disappear (the eclipse phase) early after cell entry. Contemporary examples of such confusion include the production by structural virologists of virus crystals, and the observation that viruses are the most abundant entities in the seas. In both cases it is the virion that is being studied. But virologists are not the only ones at fault – the media writes about the AIDS virus while showing an illustration of the virion.

Those who consider the virus to be the infected cell also believe that viruses are alive.

…one can conclude that infected eukaryotic cells in which viral factories have taken control of the cellular machinery became viruses themselves, the viral factory being in that case the equivalent of the nucleus. By adopting this viewpoint, one should finally consider viruses as cellular organisms. They are of course a particular form of cellular organism, since they do not encode their own ribosomes and cell membranes, but borrow those from the cells in which they live.

This argument leads to the assumption that viruses are living, according to the classical definition of living organisms as cellular organisms. Raoult and Forterre have therefore proposed that the living world should be divided into two major groups of organisms, those that encode ribosomes (archaea, bacteria and eukarya), and capsid-encoding organisms (the viruses).

BANDEA, C. (1983). A new theory on the origin and the nature of viruses Journal of Theoretical Biology, 105 (4), 591-602 DOI: 10.1016/0022-5193(83)90221-7

Forterre, P. (2010). Defining Life: The Virus Viewpoint Origins of Life and Evolution of Biospheres, 40 (2), 151-160 DOI: 10.1007/s11084-010-9194-1

33 thoughts on “The virus and the virion”

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  2. I like this way of looking at viruses. What would a “correct” illustration of the HIV virus look like? Just a cell showing provirus integration and perhaps some viral mRNA's being transcribed?

  3. doctor i want to know how to detect the quantity of H1N1 virus when it influenze and proliferate in the cells,and is it a right method to use FCM for detection? or is antibodies Immunofluorescence technique a better choice?

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  6. Very succinctly put. This dispelled a long standing confusion of mine, thank you.

  7. Marvin Phonera

    am stunned, the text eplains well the basics of a virus and gives an introduction to virology with ease.

  8. I like this idea of thinking of the virus as having 2 distinct phases “virion” and “infectious cell”. This is going to be very helpful in creating the visual for my science for non-scientist classes.

  9. This actually makes it more complicated, turns a simple classification into ontological “what is life debate”, a huge digression from moving into useful work. A virus is an infectious obligate parasite, but as you’ll lean later, a virus isn’t infectious. this definition is more of a how than a what. How about a virus is : the genetic material, and a virion is the vehicle that transports it, a cell with virus particles is simply a cell infected with a virus.

  10. The thing is, science and academics are not supposed to be easy, they are just what they are. If it’s complicated, so be it, try harder to understand

  11. I use this:
    “Viruses are acellular organisms whose genomes consist of nucleic acid, and which obligately replicate inside host cells using host metabolic machinery and ribosomes to form a pool of components which assemble into particles called VIRIONS, which serve to protect the genome and to transfer it to other cells.”

    And lately, this:
    “A virus is an infectious acellular entity composed of compatible genomic components derived from a pool of genetic elements.”

    So Claverie’s comment crystallises very nicely something I have been teaching for years: virions are like spores or seeds; you can freeze ’em, freeze-dry them, store them in the absence of any metabolic activity for centuries, it seems – and then reconstitute a virus by simply introducing it to the correct environment, in the shape of a host cell.

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    yhnxx for the information but l guess virion is the active form of the virus l want to say that when the virus want to enter the cell we call it virion
    what do u think !!!!

  14. So, the virus is the taxonomic category of these biological entities, and the virion is the individual entity?

  15. Of course an insightful comment is immediately met with conspiratorial nonsense. Of course.

  16. The extracellular virion is anything but active; it’s more of a dormant virus, much as a pinecone can be considered a dormant tree. The contents of the virion only come to live upon entry into a host cell.

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  24. Gabriella Jade Roberts

    Are virions basically vesicles that are used as transporters for viruses? Once they have attached to the host cell they become a virus.

    Is it safe to think of viruses as the active form and virions as the inactive (dormant) form which is used mainly for transportation but no other activity?

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