A
DNA virus is a
virus that has
DNA as its
genetic material and replicates using a DNA-dependent
DNA polymerase. The
nucleic acid is usually double-stranded DNA (dsDNA) but may also be single-stranded DNA (ssDNA). DNA viruses belong to either
Group I or
Group II of the
Baltimore classification system for viruses. Single-stranded DNA is usually expanded to double-stranded in infected cells. Although
Group VII viruses such as
hepatitis B contain a DNA
genome, they are not considered DNA viruses according to the Baltimore classification, but rather
reverse transcribing viruses because they replicate through an RNA intermediate. Notable diseases like
smallpox,
herpes, and
chickenpox are caused by such DNA viruses.