To outline how viruses are classified according to the type of nucleic acid they contain (RNA or DNA) and whether that nucleic acid is single‑stranded (ss) or double‑stranded (ds).
Key Principles
Viruses are obligate intracellular parasites and lack the cellular machinery for independent replication.
The genetic material of a virus determines many of its biological properties, including replication strategy and host range.
For the purpose of this topic, classification is limited to two criteria:
Nature of the nucleic acid (RNA or DNA).
Strand configuration (single‑stranded or double‑stranded).
Within the single‑stranded RNA category, further distinction is made between positive‑sense (+) and negative‑sense (–) genomes, because this influences how the viral RNA can be used directly as mRNA.
Classification Scheme
Nucleic Acid Type
Strand Configuration
Typical Example Families
DNA
Double‑stranded (dsDNA)
Herpesviridae, Adenoviridae, Poxviridae
DNA
Single‑stranded (ssDNA)
Parvoviridae, Circoviridae
RNA
Double‑stranded (dsRNA)
Reoviridae, Totiviridae
RNA
Single‑stranded, positive‑sense (ssRNA⁺)
Picornaviridae, Flaviviridae, Coronaviridae
RNA
Single‑stranded, negative‑sense (ssRNA⁻)
Orthomyxoviridae, Rhabdoviridae, Filoviridae
Suggested diagram: Flowchart showing the decision process from nucleic acid type (DNA/RNA) to strand configuration (ds/ss) and, for ssRNA, to sense (+/–).