This document discusses virus classification. It describes that viruses are not classified under the typical biological taxonomy and are instead generally classified based on factors like their genome, structure, disease caused, and discovery. It then provides details on several classification systems, including the Baltimore classification system which groups viruses into 7 groups based on their genome and replication strategy. The document also provides examples and key characteristics of viruses that fall under each of the 7 Baltimore groups.

1. Vikas Kumar
A0999320037
MSc. First semester

2. Viruses are not classified as a members of the kingdom.
Do not obey the biological taxonomy.
Generally based on:-
1:-Classical system:-e.g., Animal, Plant, bacterial virus.
e.g., Naked or enveloped virus.
2:-Genomic System:- Baltimore classification.
3:-Serology:- Classification based on Diagnostic virology
e.g., Infectious bronchitis virus of chickens

3. Based on
*The disease they cause
e.g., Polio virus, Rabies virus
* The type of disease
e.g., Murine leukemia virus
*Geographic locations
Sendai virus, Coxsackie virus
*Their discoveries
e.g., Epstein –Barr virus
*How they originally thought to be contracted
e.g., Dengue virus(“evil spirit”),influenza virus(the ‘influence’ of bad air)

4. The ICTV International Committee on
Taxonomy of Viruses 1970s,
Order (-Virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species
Most of the virus family remain unplaced. According(2012), seven order,96
families,22 subfamilies,420 genera, and 2618 species of viruses have been
defined by the ICTV.

5. The Baltimore Classification system
David Baltimore, groups viruses into families, depending on
their type of genome(DNA,RNA, single standard(ss),
Double standard(ds), etc.) and of replication.
 Group 1- Double standard DNA viruses
 Group 2- Single Standard DNA viruses
 Group 3- Double Standard RNA viruses
 Group 4- Single standard RNA viruses-Positive sense
 Group 5- Single standard RNA viruses-Negative sense
 Group 6- Single Standard RNA genome that replicated with DNA
intermediate
 Group 7- Double Standard DNA genome that replicated with RNA
intermediate

6. 7 Classes of Baltimore Classification

7. Group 1- Double -
Stranded DNA Viruses
• This type of virus usually must enter the host
nucleus before it is able to replicate.
Furthermore, these viruses require host cell
polymerases to replicate the viral genome.
• Highly dependent on the cell cycle.
• The virus may induce the cell to forcefully
undergo cell division, which may lead to
transformation of the cell and, ultimately,
cancer.
• Icosahedral symmetry
• Size of viruses-120-200nm.
• Host: Mainly mammals and Birds
• Examples-Herpesviridae, Adenoviridae, and
Papovaviridae.

8. Group 2- Single
Stranded DNA Viruses
• Viruses in this category include the
Anelloviridae, Parvoviridae(infect
vertebrates).
• Geminiviridae ,Nanoviridae(infect plants).
• Microviridae (infect prokaryotes).
• Most of them have circular genomes( the
parvoviruses are the only known exception).
• Eukaryote- infecting viruses replicate
mostly within the nucleus.
• Icosahedral symmetry
• 18-26 nm diameter
• Genome size- 4-6kbp
Parvovirus B19:Causative agent of Fifth disease

9. Group-3 Double
strandad RNA viruses
• As with most RNA viruses, this class replicates
in the cytoplasm,
• Not use the host replication polymerases to as
DNA viruses.
• It includes 2 major families, the reoviridae and
Birnaviridae
• Replication is monocistronic.
• Icosahedral Symmetry
• 60-80 nm diameter
• 18-32kbp, 10-12 segments.
• Major Diseases: Gastroenteritis in humans and
animals

10. Group 4- Single
stranded RNA viruses-
Positive sense
• The positive-sense RNA viruses and indeed all
RNA defined as positive-sense can be directly
accessed by host ribosomes to immediately
form proteins reproduce in the cytoplasm.
• Viruses with polycistronic mRNA where the
genome RNA forms the mRNA and is translated
into a polyprotein product that is cleaved to form
the mature proteins
• This means that the gene can produce proteins
from the same strand of RNA,
• Examples of this class include the
families Caliciviridae, Picornaviridae
• Icosahedral Symmetry
• 20-30 nm diameter
• Major Diseases: Common cold, polio, hepatitis
A, foot and mouth disease
Hepatitis B virus

11. Group 5- Single
stranded RNA viruses –
negative sense
• The negative-sense RNA viruses and indeed all
genes defined as negative-sense cannot be directly
accessed by host ribosomes to immediately form
proteins. Instead, they must be transcribed by viral
polymerases into a "readable" form, which is the
positive-sense reciprocal
• Examples: Vesicular stomatitis virus,Rabies
Virus,Potato yellow dwarf virus
• Helical Symmetry
• 20-30 nm diameter
• Genome size : 11-15kbp
• Disease caused: rabies, vesicular
stomatitis, Yellow dwarf of potato. Rabies virus

12. Group 6- Positive sense-
Single stranded RNA viruses
with reverse transcriptase
• Viruses include the retroviruses.
• One defining feature is the use of reverse
transcriptase to convert the positive-sense RNA
into DNA.
• Replication can with the help of the host cell's
polymerases.
• ex HIV.
• Spherical Symmetry
• 80-110 nm diameter
• Major Diseases: Immunodeficiency diseases,
leukemias, solid tumors

13. Group 7- Double Stranded
DNA viruses with reverse
transcriptase
• This small group of viruses, exemplified by
the Hepatitis B virus (which is in
the Hepadnaviridae family), have a double-
stranded,
• The RNA serves as viral reverse transcriptase
for production of the DNA .
• Icosahedral Symmetry
• 40-50 nm diameter
• Size : 3kbp
• Major Diseases: Liver diseases including liver
cancers.

14. Holmes (1948) classify viruses into 3 groups
under one order, Virales
 Group I: Phaginae (attacks bacteria)
 Group II: Phytophaginae (attacks plants)
 Group III: Zoophaginae (attacks animals)