The document discusses virus classification and taxonomy. It notes that recent classification systems have emphasized the viral genome as the primary determinant of taxonomy. Genomic sequencing and comparison to other known viral sequences is also used. Viruses are classified based on properties like their genome, capsid structure, host, and more. A taxonomy system of orders, families, subfamilies, genera and species is outlined. Different classification schemes like the Baltimore scheme are also summarized.
2. More recent classification systems adopted by the International
Committee on Viral Taxonomy (ICTV) have really emphasized the viral
genome as the primary determinant for viral taxonomy.
Furthermore, there is a drift towards the use of genomics for virus
classification – that is sequence analysis of the viral genome, and
comparison to other known viral sequences.
The naming system for viruses that has been adopted by the ICTV is
very useful for animal viruses, and is widely used.
Latinized virus family names start with capital letters and end with the
suffix –viridae (e.g., Herpesviridae). These formal names are often used
interchangably with the common names for viruses (e.g., herpesviruses).
3. Taxonomic level Suffix Example
Order -virales (a group
of related families)
Mononegavirales
Family -viridae Paramyxoviridae
Subfamily -virinae Paramyxovirinae
Genus -virus Morbillivirus
Species (an individual
virus)
Measles virus
4.
5. Basis of virus classification
Presence of Envelope
Capsid Structure
Genome properties
Shapes of the Viruses
Baltimore Classification of Viruses
Replication Properties and Site of Replication
Type of Host
Symptomatology
Mode of Transmission
6. The envelope is a lipid-containing membrane that
surrounds some virus. Virus encoded glycoproteins are
exposed on the surface of the envelope. These
projections are called peplomers. particles.
Enveloped Virus:
DNA viruses: Herpesviruses, Poxviruses,
Hepadnaviruses
RNA viruses: Flavivirus, Toga virus, Coronavirus,
HDV, Orthomyxovirus, Paramyxovirus,
Rhabdovirus, Bunyavirus, Filovirus Retroviruses
Non-Enveloped Virus:
DNA viruses- parvovirus, adenovirus and
papovavirus.
RNA viruses- Picornavirus, HAV and HEV
7.
8. Capsid Classification Examples
Naked icosahedral Hepatitis A virus, polioviruses
Enveloped icosahedral
Epstein-Barr virus, herpes simplex
virus, rubella virus, yellow fever virus,
HIV-1
Enveloped helical
Influenza viruses, mumps virus,
measles virus, rabies virus
Naked helical Tobacco mosaic virus
Complex with many proteins; some
have combinations of icosahedral and
helical capsid structures
Herpesviruses, smallpox virus,
hepatitis B virus, T4 bacteriophage
11. DNA viruses
Enveloped DNA Viruses
Herpesviridae; Herpes Simplex Viruses 1 Herpes Simplex Viruses 2 Varicella-Zoster Virus
(Human Herpesvirus-3) Epstein Barr Virus (Human Herpesvirus-4) Cytomegalovirus (Human
Herpesvirus-5) Human Herpesvirus-6 Kaposi Sarcoma (Human Herpesvirus-8)
Poxviridae; Poxvirus Molluscum Contagiosum Virus, Monkeypox virus
Hepednaviridae; Hepatitis B Virus
Non-enveloped DNA Viruses
Adenoviruses
Papovaviridae; Human Papillomavirus
Polyomaviridae; Polyomaviruses
Parvoviridae; Parvoviruses
12. Non-enveloped RNA viruses
Picornaviridae; Polioviruses, Coxsackie A Virus, Coxsackie B Virus, Echo Viruses, Hepatitis A
Viruses
Reoviridae; Rotaviruses
Enveloped RNA viruses
Orthomyxoviridae; Influenza Virus A, B and C
Coronaviridae; Coronavirus
Paramyxoviridae; Mumps Virus, Measles Virus, Parainfluenza V virus, Respiratory Syncitial
Virus
Togaviridae; Rubella Virus
Caliciviridae; Norwalk Virus, Hepatitis E Virus
Rhabdoviridae; Rabies
Retroviridae Human T-Lymphotrophic Virus 1, Human Immunodeficiency Virus
Flaviviridae; Yellow fever virus dengue, Japanese Encephalitis, Hepatitis C virus
Togaviridae; Venezuelan Equine Encephalitis Virus (VEE), Eastern Equine Encephalitis (EEE),
Western Equine Encephalitis (WEE)
Bunyaviridae; California Encephalitis Virus, Hantavirus, Sandfly Fever, Rift Valley Fever, Crimean-
Congo Haemorrhagic Fever
Filoviridae; Marburg Virus Ebola Virus
Arenaviridae; Lassa Virus, Lymphocytic choriomeningitis Virus
13. Virus family
Examples (common
names)
Virion
naked/enveloped
Capsid
symmetry
Nucleic acid
type
Group
1. Adenoviridae
Adenovirus, infectious
canine hepatitis virus
Naked Icosahedral ds I
2. Papovaviridae
Papillomavirus,
polyomaviridae,
simian vacuolating
virus
Naked Icosahedral ds circular I
3. Parvoviridae
Parvovirus B19, canine
parvovirus
Naked Icosahedral ss II
4. Herpesviridae
Herpes simplex virus,
varicella-zoster virus,
cytomegalovirus,
Epstein–Barr virus
Enveloped Icosahedral ds I
5. Poxviridae
Smallpox virus, cow
pox virus, sheep pox
virus, orf virus,
monkey pox virus,
vaccinia virus
Complex coats Complex ds I
6. Hepadnaviridae Hepatitis B virus Enveloped Icosahedral
circular,
partially ds
VII
7. Anelloviridae Torque teno virus Naked Icosahedral ss circular II
14. Virus Family Examples (common names)
Capsid
naked/enveloped
Capsid
Symmetry
Nucleic acid type Group
1. Reoviridae Reovirus, rotavirus Naked Icosahedral ds III
2. Picornaviridae
Enterovirus, rhinovirus,
hepatovirus, cardiovirus,
aphthovirus, poliovirus,
parechovirus, erbovirus,
kobuvirus, teschovirus,
coxsackie
Naked Icosahedral ss IV
3. Caliciviridae Norwalk virus Naked Icosahedral ss IV
4. Togaviridae Rubella virus, alphavirus Enveloped Icosahedral ss IV
5. Arenaviridae
Lymphocytic
choriomeningitis virus
Enveloped Complex ss(-) V
6. Flaviviridae
Dengue virus, hepatitis C
virus, yellow fever virus,
Zika virus
Enveloped Icosahedral ss IV
7. Orthomyxoviridae
Influenzavirus A,
influenzavirus B,
influenzavirus C, isavirus,
thogotovirus
Enveloped Helical ss(-) V
15. 8. Paramyxoviridae
Measles virus, mumps
virus, respiratory
syncytial virus,
Rinderpest virus, canine
distemper virus
Enveloped Helical ss(-) V
9. Bunyaviridae
California encephalitis
virus, hantavirus
Enveloped Helical ss(-) V
10. Rhabdoviridae Rabies virus Enveloped Helical ss(-) V
11. Filoviridae
Ebola virus, Marburg
virus
Enveloped Helical ss(-) V
12. Coronaviridae Corona virus Enveloped Helical ss IV
13. Astroviridae Astrovirus Naked Icosahedral ss IV
14. Bornaviridae Borna disease virus Enveloped Helical ss(-) V
15. Arteriviridae
Arterivirus, equine
arteritis virus
Enveloped Icosahedral ss IV
16. Hepeviridae Hepatitis E virus Naked Icosahedral ss IV
17. Retroviridae HIV Enveloped VI
16. Baltimore Classification
Group Characteristics Mode of mRNA Production Example
I Double-stranded DNA
mRNA is transcribed directly
from the DNA template
Herpes simplex (herpesvirus)
II Single-stranded DNA
DNA is converted to double-
stranded form before RNA is
transcribed
Canine parvovirus
(parvovirus)
III Double-stranded RNA
mRNA is transcribed from the
RNA genome
Childhood gastroenteritis
(rotavirus)
IV Single stranded RNA (+) Genome functions as mRNA Common cold (picornavirus)
V Single stranded RNA (-)
mRNA is transcribed from the
RNA genome
Rabies (rhabdovirus)
VI
Single stranded RNA viruses
with reverse transcriptase
Reverse transcriptase makes
DNA from the RNA genome;
DNA is then incorporated in
the host genome; mRNA is
transcribed from the
incorporated DNA
Human immunodeficiency
virus (HIV)
VII
Double stranded DNA viruses
with reverse transcriptase
The viral genome is double-
stranded DNA, but viral DNA
is replicated through an RNA
intermediate; the RNA may
serve directly as mRNA or as a
template to make mRNA
Hepatitis B virus
(hepadnavirus)
18. Most of the animal viruses are roughly spherical
with some exceptions.
Rabies virus: Bullet shaped
Ebola virus: Filamentous shaped
Poxvirus: Brick shaped
Adenovirus: Space vehicle shaped
19. Animal viruses: viruses which infect animal cell
including man e.g.; influenza virus, rabies virus, mumps
virus, poliovirus etc.
Plant viruses: viruses that infect plants. Their genetic
material is RNA. E.g.; tobacco mosaic virus, potato virus,
beet yellow virus and turnip yellow virus
Bacteriophage: Viruses which infect bacterial cells.
Their genetic material is DNA. There are many varieties
of and each kind of will attack only one species or only
one strain of bacteria.
20. Classification by Symptomatology
A. Generalized Diseases: Diseases in which virus is spread throughout
the body via the bloodstream and in which multiple organs are
affected. Skin rashes may occur. These include smallpox, vaccinia,
measles, rubella, chickenpox, yellow fever, dengue, enteroviruses,
B. Diseases Primarily Affecting Specific Organs: The virus may
spread to the organ through the bloodstream, along the peripheral
nerves, or by other routes.
1. Diseases of the nervous system – Poliomyelitis, aseptic meningitis
(polio-, coxsackie-, and echoviruses), rabies, arthropod-borne
encephalitides, lymphocytic choriomeningitis herpes simplex,
meningoencephalitis of mumps, measles,, and "slow" virus
infections.
2. Diseases of the respiratory tract – Influenza, parainfluenza, respiratory
syncytial virus; pneumonia and bronchiolitis, adenovirus pharyngitis,
common cold (caused by many viruses).
21. Classification by Symptomatology
3. Localized diseases of the skin or mucous membranes – Herpes simplex
type 1 (usually oral) and type 2 (usually genital), molluscum
contagiosum, warts, herpangina, herpes zoster, and others.
4. Diseases of the eye – Adenovirus conjunctivitis, Newcastle virus
conjunctivitis, herpes kerato-conjunctivitis, and epidemic hemorrhagic
conjunctivitis (enterovirus-70).
5. Diseases of the liver-Hepatitis type A (infectious hepatitis) and type B
(serum hepatitis), yellow fever, and, in the neonate, entero-viruses,
herpes viruses, and rubella virus.
6. Diseases of the salivary glands – Mumps and cytomegalovirus.
7. Diseases of the gastrointestinal tract – Rotavirus, Norwalk type virus.
22.
23. Micro-organisms have been classified into 4 hazard groups by the ACDP (Advisory Committee
on Dangerous Pathogens) on the basis of pathogenicity to humans, risk to laboratory workers,
transmissibility to the community, and whether effective prophylaxis is available.
Group 1. - An organism that is most unlikely to cause human disease
Group 2. - An organism that may cause human disease and which may be a hazard to laboratory
workers but is unlikely to spread to the community. Laboratory exposure rarely produces
infection and effective prophylaxis or treatment is usually available. Examples include
herpesvirses, ortho and paramyxoviruses, picornaviruses, adenoviruses, unconventional slow
viruses.
Group 3 - An organism that may cause severe human disease and presents a serious hazard to
laboratory workers. It may present a risk of spread to the community but there is usually
effective prophylaxis or treatment available. Examples include HIV, HBV, Hantaviruses,
Japanese B encephalitis, Rift Valley fever, Yellow Fever, rabies.
25. 1. Heat and cold Viral infectivity is generally destroyed by
heating at 50-600 C for 30 mins except hepatitis virus, adeno
associated virus and scrapie virus. Viruses may be also be
destroyed hours at 200 C, days at 40 C. Viruses can be
preserved at -200c,-700c, -900 C in deep freezers or -1960 C
(liquid nitrogens) except for the polio virus.
2. PH ; Viruses can be preserved at physiological PH (7.3-.4).
They are stable at PH 5-9
26. 3. Ether susceptibility; Ether susceptibility can be used to distinguish
viruses that possess an envelope from those that do not. Arboviruses,
myxoviruses and herpes viruses are destroyed by ether whereas
enterovirus, reovirus and adenovirus are resistant to the action of ether
4. Detergents; Non-ionic detergents solubilize lipid
constituents of viral membranes. The viral proteins in the
envelope are released. Anionic detergents also solubilize viral
envelopes; in addition, they disrupt capsids into separated
polypeptides.
5. Salts; Many viruses can be stabilized by salt in
concentrations of 1 mol/L so that they are not inactivated by
heating at 500c for 1 hour. e.g. MgCl2, MgSO4, Na2SO4.
27. 6. Radiation; UV light, X rays and high-energy particles/heavy
particles inactivate viruses, the UV rays dimerizes the
pyrimidine bases with nucleic acid strand and gamma rays
cause lethal break in the genome
7. Disinfectants; Lysol, Dettol are ineffective agents against
viruses. Higher concentrations of chlorine, iodine may kill
viruses. Dilute formaldehyde and Beta propiolactone,
hydrochloric acid, KMnO4 destroys viral infectivity by
reacting with nucleic acid.
8. Antibiotics; Antibacterial antibiotics have no effect on
viruses.
