VIRUSCLASSIFICATION OF

VIRUSESVIRUSES OF VET IMP.

Pressented To . DR. Khalil SB.

VIROLOGY DEPART.

Riphah college of veterniary sciences lahore2

Content

1. 1.Naming of viruses2. 2.Classification of virus – ICTV3. 3.LHT System of Virus Classification4. 4.Baltimore Classification – 7 classes 5. 5.Holmes classification

6. SUB VIRAL PARTICLE1. 7. VIRUSES OF VET IMP. 2.

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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

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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

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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.

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 virussystem - 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.

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

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

The ICTV International Committee on Taxonomy of Viruses  1970s,

Order (-virales)Family (-viridae)Subfamily (-virinae)Genus (-virus)SpeciesThe 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

•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)

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.

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

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

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.

ExamplesHerpesviridae, Adenoviridae, and Papovaviridae.

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 –

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.

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

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, 

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

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.

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 .

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

RNA Viruses

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Typical infectious cycle

1. Attachment

2. Penetration

3. Uncoating

4. Transcription and/or translation

5. Replication

6. Assembly

7. Release

SUB VIRAL PARTICLEPrions, "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

• 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)

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Why are viruses important to vets?

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

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

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 influenzaWild aquatic birds of influenza A viruses. cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics. 

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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