This document discusses the classification of viruses and viruses important to veterinary medicine. It begins by explaining different systems used to classify viruses, including the International Committee on Taxonomy of Viruses system and the Baltimore classification system, which categorizes viruses based on their genome and replication strategy. The document then discusses important viral families and genera that affect animals, such as rhabdoviruses, pestiviruses, arteriviruses, coronaviruses, influenza viruses, bluetongue virus, and circoviruses. It concludes by noting that viral diseases cannot be treated with antibiotics and vaccines are often the best prevention, though symptoms can be treated with over-the-counter medicines.

2. VIRUS
CLASSIFICATION OF
VIRUSES
VIRUSES OF VET IMP.
Pressented To . DR. Khalil SB.
VIROLOGY DEPART.
Riphah college of veterniary sciences lahore
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3. Content
1. 1.Naming of viruses
2. 2.Classification of virus – ICTV
3. 3.LHT System of Virus Classification
4. 4.Baltimore Classification – 7 classes
5. 5.Holmes classification
6. SUB VIRAL PARTICLE
1. 7. VIRUSES OF VET IMP.
2.
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4. Reasons beyond classification
 Classification of virus been determined by
the structural and chemical composition of
virus
 Are apply to all plant viruses, animal viruses
and bacterial viruses
 Virus is acellular cell – cannot be
categorised using taxonomic classification
 It used International Committee on
Taxonomy of Viruses (ICTV) to classify the
viruses 4

5. What are viruses ?
Nucleic acid contained
within a protective
protein coat
Infect bacteria, plants,
animals (inc humans)
Differences from bacteria
• viruses CANNOT
replicate outwith a
cellular environment
• viruses ARE NOT
affected by antibiotics
Submicroscopic
particles

6. 6
1. genome
± 3. envelope
2. capsid
Virion (virus particle) structure
nucleocapsid
• A virion is the
extracellular form of a
virus and contains either
an RNA or a DNA
genome The virus
genome is introduced into
a new host cell by
infection. The virus
redirects the host
metabolism to support
virus replication.

7. Classification
 Viruses are not classified as members of the kingdoms
 Do not obey the biological taxonomy
 Generally based on:
1. Classical - eg. animal, plant, bacterial virus
system - eg. naked or enveloped virus
2. Genomic - Baltimore classification
3. Serology - classification based on Diagnostic virology
- eg. Infectious bronchitis virus (IBV) of chickens
(a coronavirus) – 3 different types present, these types have
significant antigenic differences, but perhaps very little genetic or
biological difference between these viruses.

8. Size of Viruses
 Ranges of sizes
 20 nm to 500 nm (spherical)
 12 nm to 300-2000 nm (rod like)
 Easily observed with electron microscope
 Ex.1 Mimivirus is 500 nm
 Infects algae
 Ex.2 Parvovirus is 20 nm in diameter
 Infects algae
 Viral genomes range in size 2,000 bp to 1,200,000 bp

9. How are viruses named?
 Based on:
- the disease they cause
poliovirus, rabies virus
- the type of disease
murine leukemia virus
- geographic locations
Sendai virus, Coxsackie virus
- their discovers
Epstein-Barr virus
- how they were originally thought to be contracted
dengue virus (“evil spirit”), influenza virus (the “influence” of bad air)
- combinations of the above
Rous Sarcoma virus

10. The ICTV
International Committee on
Taxonomy of Viruses 1970s,
Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species
The majority of virus families remain unplaced. Currently
(2012), seven orders, 96 families, 22
subfamilies, 420 genera, and 2,618
species of viruses have been defined by
the ICTV

11. •LHT System of Virus Classification
•The LHT System of Virus Classification is based
•on chemical and physical characters like nucleic acid (DNA
or RNA),
•Symmetry (Helical or Icosahedral or Complex),
•presence of envelope, Non enveloped (“naked”)
diameter of capsid, number of capsomers
PNVC) of the International Association of Microbiological
Societies (1962)

13. The Baltimore classification system
David Baltimore, groups viruses into families, depending on
their type of genome (DNA, RNA, single-stranded (ss), double-
stranded (ds), etc.) and of replication.
Group I: Double-stranded DNA viruses
Group II: Single-stranded DNA viruses
Group III: Double-stranded RNA viruses
Group IV & V: Single-stranded RNA viruses
1 Group IV: Single-stranded RNA viruses - Positive-sense
.2 Group V: Single-stranded RNA viruses - Negative-sense
Group VI: Positive-sense single-stranded RNA viruses that replicat
Group VII: Double-stranded DNA viruses that replicate through a single-strande

14. Class Description of genome and replication
strategy
Example of animal virus
I Double stranded DNA genome Herpesvirus, poxvirus
II Single stranded DNA genome Chicken anemia virus
III Double stranded RNA genome Reovirus
IV Single stranded RNA genome plus sense Poliovirus
V Single stranded RNA genome minus sense Influenza virus,Rabies virus
VI Single stranded RNA genome that
replicated with DNA intermediate
Retrovirus
VII Double stranded DNA genome that
replicates with RNA intermediate
Hepatitis B virus
7 class of Baltimore classification

15. Group I: 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.
 Examples
Herpesviridae, Adenoviridae, and Papovaviridae.

16. Group II: 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 –

17. Group III: Double-stranded RNA viruses
As with most RNA viruses, this class replicates in the
in cytoplasm,
not use the host replication polymerases to as DNA
viruses.
This family is not well-studied as rest
includes 2 major families, the Reoviridae and
Birnaviridae.
Replication is monocistronic
meaning that each of the genes codes for only one
protein, unlike other viruses that exhibit more
complex translation.

18. Group IV & V: Single-stranded RNA
viruses
The ssRNA viruses belong to Class IV or V
of the negative sense
 positive sense
according to the sense of polarity of RNA.
The single stranded RNA is the common feature of these
viruses.
The replication of viruses happens in the cytoplasm.
Class IV and V ssRNA viruses do not depend as heavily as
DNA viruses on the cell

19. Group IV: 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,

20. Group V: 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.
 Ex/ Orthomyxoviridaeand Rhabdoviridae

21. Group VI: Positive-sense single-stranded RNA
viruses that replicate through a DNA
intermediate
 viruses include the retroviruses.
 One defining feature is the use of
reverse transcriptase to convert the
positive-sense RNA into DNA. Instead of
using the RNA they use DNA to create the
templates,. Replication can with the help
of the host cell's polymerases.
 ex HIV.

22. Group VII: Double-stranded DNA
viruses that replicate through a
single-stranded RNA
intermediate
 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 .

23. Reverse transcribing viruses
 The process of making a double stranded DNA molecule
from a single stranded RNA template through the
enzyme, reverse transcriptase
Holmes classification
 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)

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DNA Viruses

25. RNA Viruses
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26. Typical infectious cycle
1. Attachment
2. Penetration
3. Uncoating
4. Transcription and/or
translation
5. Replication
6. Assembly
7. Release

27. SUB VIRAL PARTICLE
Prions, "proteinaceous and infectious
particles“
Satellites depend on co-infection of a
host cell with a helper virus for productive
multiplication
Viroids smallest infectious pathogens
known, circular, single-stranded RNA
without protein coats. They are plant
pathogens

28. • Viruses cause disease in animals of economic
and/or welfare importance
• Diagnose viral disease (clinical/lab tests)
• Advise clients control (risk to other animals)
• Animal viruses may pose risk to human health
(zoonosis)
•
Why are viruses important to vets?

29. VIRUSES OF VET IMP.
Rhabdoviruses
 family of -ssRNA viruses that infect hosts, from plants and insects, to
fish and mammals.
 The Rhaboviridae family consists vesiculovirus, infect mammals The
family includes pathogens such as rabies virus,
vesicular stomatitis virus
Foot-and-mouth disease virus
 (FMDV) is a member of the in the Picornaviridae family and is the
cause of foot-and-mouth disease in pigs, cattle, sheep and goats. It is
a non-enveloped, positive strand, RNA virus. FMDV is a highly
contagious virus. It enters the body through inhalation

30. Pestiviruses
+ssRNA genomes. They cause Classical swine fever (CSF) and
Bovine viral diarrhea(BVD
Arteriviruses
are small, enveloped, animal viruses +ssRNA. The family includes
equine arteritis virus (EAV), porcine reproductive and respiratory syndrome virus
(PRRSV), and simian haemorrhagic fever virus (SHFV).
Coronaviruses
are enveloped +ssRNA They infect the URT and GIT of mammals and birds. They
cause wide range of diseases in cats, dog, pigs, rodents, cattle and humans.
Transmission is by F.O.R
Torovirus
family Coronaviridae, subfamily Torovirinae that primarily
infect vertebrates and include Berne virus of horses and Breda virus of cattle.
They cause gastroenteritis in mammals, Influenza
is caused by RNA viruses of the family Orthomyxoviridae and affects birds and
mammals

31. Bluetongue virus
(BTV), a member Reoviridae family .causes serious disease in
livestock (sheep, goat, cattle
Circoviruses
small dsDNA viruses. There are 2 genera: gyrovirus, with one
species called chicken anemia virus; and circovirus, which
includes porcine circovirus
Avian influenza
Wild aquatic birds of influenza A viruses. cause devastating
outbreaks in domestic poultry or give rise to human
influenza pandemics.

32. Viral diseases cannot be treated
with antibiotics.
Vaccines are often the best
protection against most
diseases.
Most vaccines work only if used
before an infection begins.
Symptoms may be treated with
over-the-counter medicines.

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