Viral Classification

Overview

Viruses can be classified in a number of different ways in order to highlight the nature of their genome, the geometry of their capsid, whether they possess an lipid envelope, or their tropism for a particular tissue type.

Genome Classification

Viral genomes are first categorized by their chemical composition as either DNA or RNA genomes. The headings of the sections below are interlinks which will list viruses within that category.

dsDNA Viruses: dsDNA genomes possess two anti-parallel strands in a double-helix structure
ssDNA Viruses: ssDNA genomes possess only a single strand and do not form a double-helix structure

dsRNA Viruses: dsRNA genomes possess two anti-parallel strands much like DNA in a double-helix-like structure
ssRNA Viruses: ssRNA genomes possess only a single strands which can be organized in different orientations
Positive ssRNA Viruses: Orientation of genes in the RNA genome is such that they can be directly translated to proteins much like a host cell's mRNA
Negative ssRNA Viruses: Orientation of genes in the RNA genome is reversed such that they must be first replicated to the positive RNA strand prior to protein translation
Retroviruses: These are RNA viruses whose genome must first be "Reverse-transcribed" to DNA and only then transcribed and translated.

Capsid Geometry Classification

As discussed in Viral Structure, viral capsids are highly ordered protein shells which possess specific geometries that can be used for classification
Icosahedral Viruses: Capsid is an Icosahedron which possesses twenty faces of equilateral triangles
Helical Viruses: Capsid is arranged as a long helix
Complex Viruses: Capsid has a complex shape that does not fall into the above categories

Possession of an Envelope

Tissue Tropism

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