Virus classification involves naming and placing viruses into a taxonomic
system. Like the relatively consistent classification systems seen for cellular
organisms, virus classification is the subject of ongoing debate and
proposals. This is largely due to the pseudo-living nature of viruses, which
are not yet definitively living or non-living. As such, they do not fit neatly
into the established biological classification system in place for cellular
organisms, such as eukaryotes and prokaryotes.
Virus classification is based mainly on phenotypic characteristics, including
morphology, nucleic acid type, mode of replication, host organisms, and the
type of disease they cause. A combination of two main schemes is currently
in widespread use for the classification of viruses. David Baltimore, a Nobel
Prize-winning biologist, devised the Baltimore classification system, which
places viruses into one of seven groups. These groups are designated by
Roman numerals and separate viruses based on their mode of replication,
and genome type. Accompanying this broad method of classification are
specific naming conventions and further classification guidelines set out by
the International Committee on Taxonomy of Viruses.
ICTV classification
The International Committee on Taxonomy of Viruses began to devise and
implement rules for the naming and classification of viruses early in the
1990s, an effort that continues to the present day. The ICTV is the only body
charged by the International Union of Microbiological Societies (IUMS)
with the task of developing, refining, and maintaining a universal virus
taxonomy. The system shares many features with the classification system
of cellular organisms, such as taxon structure. Viral classification starts at
the level of order and follows as thus, with the taxon suffixes given in
italics:
Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species
, So far, five orders have been established by the ICTV: the Caudovirales,
Herpesvirales, Mononegavirales, Nidovirales, and Picornavirales. These
orders span viruses with varying host ranges. Caudovirales are tailed
dsDNA (group I) bacteriophages, Herpesvirales contains large eukaryotic
dsDNA viruses, Mononegavirales includes non-segmented (-) strand ssRNA
(Group V) plant and animal viruses, Nidovirales is composed of (+) strand
ssRNA (Group IV) viruses with vertebrate hosts, and Picornavirales
contains small (+) strand ssRNA viruses that infect a variety of plant, insect,
and animal hosts. Other variations occur between the orders, for example,
Nidovirales are isolated for their differentiation in expressing structural and
non-structural proteins separately. However, this system of nomenclature
differs from other taxonomic codes on several points. A minor point is that
names of orders and families are italicized, as in the ICBN.[1] Most notably,
species names generally take the form of [Disease] virus. The establishment
of an order is based on the inference that the virus families contained within
a single order have most likely evolved from a common ancestor. The
majority of virus families remain unplaced. Currently (2008) 82 families and
2,083 species of virus have been defined[2].
Baltimore classification
: Baltimore classification
The Baltimore Classification of viruses is based on the method of viral
mRNA synthesis
Baltimore classification (first defined in 1971) is a classification system that
places viruses into one of seven groups depending on a combination of their
system. Like the relatively consistent classification systems seen for cellular
organisms, virus classification is the subject of ongoing debate and
proposals. This is largely due to the pseudo-living nature of viruses, which
are not yet definitively living or non-living. As such, they do not fit neatly
into the established biological classification system in place for cellular
organisms, such as eukaryotes and prokaryotes.
Virus classification is based mainly on phenotypic characteristics, including
morphology, nucleic acid type, mode of replication, host organisms, and the
type of disease they cause. A combination of two main schemes is currently
in widespread use for the classification of viruses. David Baltimore, a Nobel
Prize-winning biologist, devised the Baltimore classification system, which
places viruses into one of seven groups. These groups are designated by
Roman numerals and separate viruses based on their mode of replication,
and genome type. Accompanying this broad method of classification are
specific naming conventions and further classification guidelines set out by
the International Committee on Taxonomy of Viruses.
ICTV classification
The International Committee on Taxonomy of Viruses began to devise and
implement rules for the naming and classification of viruses early in the
1990s, an effort that continues to the present day. The ICTV is the only body
charged by the International Union of Microbiological Societies (IUMS)
with the task of developing, refining, and maintaining a universal virus
taxonomy. The system shares many features with the classification system
of cellular organisms, such as taxon structure. Viral classification starts at
the level of order and follows as thus, with the taxon suffixes given in
italics:
Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species
, So far, five orders have been established by the ICTV: the Caudovirales,
Herpesvirales, Mononegavirales, Nidovirales, and Picornavirales. These
orders span viruses with varying host ranges. Caudovirales are tailed
dsDNA (group I) bacteriophages, Herpesvirales contains large eukaryotic
dsDNA viruses, Mononegavirales includes non-segmented (-) strand ssRNA
(Group V) plant and animal viruses, Nidovirales is composed of (+) strand
ssRNA (Group IV) viruses with vertebrate hosts, and Picornavirales
contains small (+) strand ssRNA viruses that infect a variety of plant, insect,
and animal hosts. Other variations occur between the orders, for example,
Nidovirales are isolated for their differentiation in expressing structural and
non-structural proteins separately. However, this system of nomenclature
differs from other taxonomic codes on several points. A minor point is that
names of orders and families are italicized, as in the ICBN.[1] Most notably,
species names generally take the form of [Disease] virus. The establishment
of an order is based on the inference that the virus families contained within
a single order have most likely evolved from a common ancestor. The
majority of virus families remain unplaced. Currently (2008) 82 families and
2,083 species of virus have been defined[2].
Baltimore classification
: Baltimore classification
The Baltimore Classification of viruses is based on the method of viral
mRNA synthesis
Baltimore classification (first defined in 1971) is a classification system that
places viruses into one of seven groups depending on a combination of their
