Table 13-1.

Different Classes of Viruses Grouped According to Replication Strategy (Baltimore Classification)

Class	Genome Type	Replication Strategy	Examples of Genus Infecting Human Cells
I	dsDNA	Semiconservative method using bidirectional replication forks from a single origin	Poxvirus Herpesvirus Adenovirus Papovavirus
II	ssDNA	Formation of a replicative from double-stranded DNA intermediate	Parvovirus
III	dsRNA replicating via (+) RNA	Conservative mechanism in which input RNA is transcribed to mRNA	Reovirus
IV	ssRNA (+) sense genomes	Synthesis of (–) sense RNA on a (+) sense template	Coronavirus Flavivirus Astrovirus Picornavirus
V	ssRNA (–) sense genomes	Begins with transcription by virion-associated RNA-dependent RNA polymerase	Arenavirus Orthomyxovirus Paramyxovirus Rhabdovirus
VI	Diploid ssRNA	Uses a dsDNA, longer than genome length intermediate (provirus), which is integrated covalently into host cell chromosomal DNA	Retrovirus
VII	dsDNA	Uses gapped or nicked circular dsDNA genomes to replicate via longer than genome length messenger-sense ssRNA intermediates	Hepadnavirus

(+), Sense strand; (–), antisense strand.