Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms. Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. Currently, two main schemes are used for the classification of viruses: the International Committee on Taxonomy of Viruses (ICTV) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV.

1. VIROLOGY-2

2. https://www.slideshare.net/FarzinAsghari
Dr. Farzin Asghari Sana

3. ICOSAHEDRAL SYMMETRY
Dr. Farzin Asghari Sana

4. ICOSAHEDRAL SYMMETRY
Dr. Farzin Asghari Sana

5. ICOSAHEDRAL SYMMETRY
Dr. Farzin Asghari Sana

6. ICOSAHEDRAL SYMMETRY
Dr. Farzin Asghari Sana

7. Dr. Farzin Asghari Sana

8. Morphology and relative size of viruses. Herpesvirus, adenovirus, poxvirus, retroviruses, and
rhabdoviruses have characteristic shapes, whereas other viruses are distinguished by size,
presence of an envelope, or an icosa(delta)hedral capsid.
Dr. Farzin Asghari Sana

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10. RNA or DNA
• segmented or non-segmented
• linear or circular
• single-stranded or double-stranded
• if single-stranded RNA
• is genome mRNA (+) sense or complementary to mRNA
(-) sense
CLASSIFICATION
NUCLEIC ACID
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14. Genome
•The genome of a virus can be either DNA or RNA
•DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
•RNA- ss: segmented or non-segmented
ss: polarity+(sense) or polarity–(non-sense)
ds: linear (only reovirus family)
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Dr. Farzin Asghari Sana

15. Viral genome strategies
•dsDNA (herpes, papova, adeno, pox)
•ssDNA (parvo)
•dsRNA (reo, rota)
•ssRNA (+) (picorna, toga, flavi, corona)
•ssRNA (-) (rhabdo, paramyxo, orthomyxo, bunya, filo)
•ssRNA (+/-) (arena, bunya)
•ssRNA (+RTase) (retro, lenti)

16. HERPESVIRIDAE
HEPADNAVIRIDAE
ENVELOPED
PAPILLOMAVIRIDAE
POLYOMAVIRIDAE
(formerly grouped together as the PAPOVAVIRIDAE)
CIRCULAR
ADENOVIRIDAE
LINEAR
NON-ENVELOPED
DOUBLE STRANDED
PARVOVIRIDAE
CIRCOVIRIDAE
SINGLE STRANDED
NON-ENVELOPED
POXVIRIDAE
COMPLEX
ENVELOPED
DNA VIRUSES
All families shown are
icosahedral except for
poxviruses
Dr. Farzin Asghari Sana

18. Hepadnaviridae
TEM micrograph showing hepatitis Bvirions
Virus classification
Group: Group VII (dsDNA-RT)
Order: Unassigned
Family: Hepadnaviridae
Genera
•Orthohepadnavirus
•Avihepadnavirus
Dr. Farzin Asghari Sana

19. Hepatitis b virus a major cause of hepatitis
DNA virus – hepadnavirus 3200 bp
Compact - uses overlapping genes
Complicated replication – has a ssDNA
component to RNA to DNA
Difficult to grow
Liver damage may be due to host immunity Dr. Farzin Asghari Sana

20. Structure of hepatitis b virus
Dr. Farzin Asghari Sana

21. HBV Structure & Antigens
Dane particle
HBsAg = surface (coat) protein ( 4 phenotypes : adw, adr, ayw and ayr)
HBcAg = inner core protein (a single serotype)
HBeAg = secreted protein; function unknown

22. Parvoviridae
Parvovirinae
Parvovirus Erythrovirus
H.Parvovirus
B19
Dependovirus Bocavirus Amdovirus
Densovirinae
Include 4
genera
Dr. Farzin Asghari Sana

23. Parvovirus replication
• Unlike the double-stranded DNA viruses !!
• ssDNA parviruses can replicate only in dividing cells.
• Parvoviruses replicate in the nucleus:
• Transcription and replication of the genome
• Accumulation of nonstructural proteins
• Assembly of virions
Dr. Farzin Asghari Sana

24. Dr. Farzin Asghari Sana

25. POLYOMAVIRUSES
These include SV40, BK, JC and polyoma viruses.
All have a similar strategy for DNA replication.
They are small (~40nm diameter), icosahedral, non-enveloped viruses that replicate
in the nucleus. Depending on the host cell, they can either transform the cell or
replicate the virus and lyze the cell.
Dr. Farzin Asghari Sana

26. Adenoviruses
got their name from the adenoidal tissues (tonsils) in which they were
first identified (in 1953 W.Rowe and collaborators).
Size – 70-90 nm
Shape - icosahedral. Their morphogenesis occurs in the cell nucleus,
where they also aggregate to form large crystals
Their genome is a linear, ds DNA
Type of symmetry - cubic
Naked.
Capsid consist of 252 capsomers
Dr. Farzin Asghari Sana

27. Adenovirus
Dr. Farzin Asghari Sana

28. HERPESVIRIDAE
The Herpesviridae are a large family of DNA viruses that cause diseases in animals,
including humans The family name is derived from the Greek word herpein ("to
creep"), referring to the latent, re-occurring infections typical of this group of
viruses. Herpesviridae can cause latent or lytic infections.
• Alphaherpesvirinae
– Herpes simplex virus type 1 HSV-1
– Herpes simplex virus type 2 HSV-2
– Varicella-zoster virus VZV
• Betaherpesvirinae
– cytomegalovirus CMV
– Human herpesvirus type 6 HHV-6
– Human herpesvirus type 7 HHV-7
• Gammaherpesvirinae
– Epstein-Barr virus EBV Dr. Farzin Asghari Sana

29. Dr. Farzin Asghari Sana

30. Iridoviridae
Virus classification
Group: Group I (dsDNA)
Family: Iridoviridae
Genera
•Megalocytivirus
•Ranavirus
•Iridovirus
•Chloriridovirus
•Lymphocystivirus
Dr. Farzin Asghari Sana

31. Genus Host Details
Tissue
Tropism
Entry Details
Release
Details
Replication
Site
Assembly
Site
Transmissio
n
Lymphocystivirus Fish None
Cell receptor
endocytosis
Lysis;
budding
Nucleus Cytoplasm Unknown
Megalocytivirus Fish None
Cell receptor
endocytosis
Lysis;
budding
Nucleus Cytoplasm Unknown
Ranavirus
Frogs;
snakes
None
Cell receptor
endocytosis
Lysis;
budding
Nucleus Cytoplasm Contact
Iridovirus Insects None
Cell receptor
endocytosis
Lysis;
budding
Nucleus Cytoplasm Contact
Chloriridovirus
Diptera with
aquatic
larval stage,
mainly
mosquitoes
None
Cell receptor
endocytosis
Budding Nucleus Cytoplasm Unknown

32. Virus classification
Group: Group I (dsDNA)
Order: Unassigned
Family: Poxviridae
Genera
Subfamily Chordopoxvirinae
Avipoxvirus
Capripoxvirus
Cervidpoxvirus
Crocodylipoxvirus
Leporipoxvirus
Molluscipoxvirus
Orthopoxvirus
Parapoxvirus
Suipoxvirus
Yatapoxvirus
Subfamily Entomopoxvirinae
Alphaentomopoxvirus
Betaentomopoxvirus
Gammaentomopoxvirus
Dr. Farzin Asghari Sana

33. Taxonomy
•Subfamily Chordopoxvirinae
•Human pathogenic genera
• Genus Orthopoxvirus;
• diseases: cowpox, vaccinia, smallpox ,monkeypox
• Genus Parapoxvirus; type species: Orf virus
• Genus Molluscipoxvirus; type species: Molluscum contagiosum virus
• Genus Yatapoxvirus; type species: Yaba monkey tumor virus
• Nonpathogenic genera
• Genus Avipoxvirus; type species: Fowlpox virus
• Genus Capripoxvirus; type species: Sheeppox virus
• Genus Leporipoxvirus; type species: Myxoma virus
•Genus Suipoxvirus; type species: Swinepox virus
•Subfamily Entomopoxvirinae
• Genus Entomopoxvirus A
• Genus Entomopoxvirus B
• Genus Entomopoxvirus C Dr. Farzin Asghari Sana

34. FLAVIVIRIDAE
TOGAVIRIDAE
RETROVIRIDAE
ICOSAHEDRAL
CORONAVIRIDAE
HELICAL
ENVELOPED
ICOSAHEDRAL
PICORNAVIRIDAE
CALICIVIRIDAE
ASTROVIRIDAE
NONENVELOPED
SINGLE STRANDED
positive sense
BUNYAVIRIDAE
ARENAVIRIDAE
ORTHOMYXOVIRIDAE
PARAMYXOVIRIDAE
RHABDOVIRIDAE
FILOVIRIDAE
SINGLE STRANDED
negative sense
REOVIRIDAE
DOUBLE STRANDED
RNA VIRUSES
ENVELOPED
HELICAL ICOSAHEDRAL
NONENVELOPED
Dr. Farzin Asghari Sana

35. RNA viruses
Dr. Farzin Asghari Sana

36. Dr. Farzin Asghari Sana

37. VIROLOGY