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|
|Retroviruses||HIV, HTLV-I||Yes||Complex||ssRNA||HIV/AIDS, leukemia|
|Orthomyxoviruses||Influenza viruses||Yes||Helical||ssRNA||Influenza (flu)|
|Coronaviruses||Corona virus||Yes||Complex||ssRNA||Common cold, Severe acute respiratory syndrome (SARS)|
|Cystoviruses||Cystovirus||Yes||Icosahedral||dsRNA||Infects Pseudomonas bacteria|
- Viruses can be classified on the basis of capsid shape, presence or absence of an envelope, and type of nucleic acid.
- Describe how viruses are classified.
- What is the difference between viruses in the Herpesvirus family and the Retrovirus family?
- What are the four types of nucleic acid that may be present in a virus?
- Give an example of a disease caused by a member of the Orthomyxoviruses.
- Give an example of a disease caused by a retrovirus.