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7.9: Virus Classification

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    f-d:03e3a4ab461b5574643d1b384dbec94a1fff9ff010c565326452ff46 IMAGE_TINY IMAGE_TINY.1

    How are viruses classified?

    In part by their shape. This picture represents a bacteriophage, a virus that infects bacteria. Notice the distinctive shape. This virus has a complex shape.

    Classification of Viruses

    Like the classification systems for cellular organisms, virus classification is the subject of ongoing debate. This is largely due to the nature of viruses, which are not living organisms by the classic definition, but neither are they necessarily non-living. Therefore, viruses do not fit neatly into the biological classification system of cellular organisms, as plants and animals do.

    Virus classification is based mainly on characteristics of the viral particles, including the capsid shape, the type of nucleic acid (DNA or RNA, double stranded (ds) or single stranded (ss)) within the capsid, the process of replication, their host organisms, or the type of disease they cause. The Table below lists characteristics such as capsid shape, presence of an envelope, and the diseases the viruses can cause.


    Virus Family Virus Envelope Capsid shape Nucleic Acid Disease
    Adenoviruses Adenovirus No Icosahedral dsDNA upper respiratory infections
    Parvoviruses Parvovirus No Icosahedral ssDNA fifth disease, Canine parvovirus
    Herpesviruses Herpes simplex virus, Varicella zoster virus, Epstein Barr virus Yes Icosahedral dsDNA Herpes, chicken pox, shingles, infectious mononucleosis
    Hepadnaviruses Hepatitis B virus Yes Icosahedral dsDNA Hepatitis B
    Reoviruses Rotavirus No Icosahedral dsRNA gastroenteritis
    Retroviruses HIV, HTLV-I Yes Complex ssRNA HIV/AIDS, leukemia
    Orthomyxoviruses Influenza viruses Yes Helical ssRNA Influenza (flu)
    Rhabdoviruses Rabies virus Yes Helical ssRNA Rabies
    Coronaviruses Corona virus Yes Complex ssRNA Common cold, Severe acute respiratory syndrome (SARS)
    Cystoviruses Cystovirus Yes Icosahedral dsRNA InfectsPseudomonasbacteria


    • Viruses can be classified on the basis of capsid shape, presence or absence of an envelope, and type of nucleic acid.


    1. Describe how viruses are classified.
    2. What is the difference between viruses in the Herpesvirus family and the Retrovirus family?
    3. What are the four types of nucleic acid that may be present in a virus?
    4. Give an example of a disease caused by a member of the Orthomyxoviruses.
    5. Give an example of a disease caused by a retrovirus.

    This page titled 7.9: Virus Classification is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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