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classification of virus and basic terms
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.
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classification of virus and basic terms
- 2. VIRUS CLASSIFICATION OF VIRUSES VIRUSES OFVET IMP. Pressented To . DR. Khalil SB. VIROLOGY DEPART. Riphah college of veterniary sciences lahore 2
- 3. Content 1. 1.Naming ofviruses 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. 3
- 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 arenot 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 virusesnamed? 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 Committeeon 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 ofVirus 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 classificationsystem 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 ofgenome 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-strandedDNA 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-strandedDNA 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-strandedRNA 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-strandedRNA 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-strandedRNA 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-sensesingle-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-strandedDNA 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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- 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 causedisease 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 VETIMP. 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. Theycause 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), amember 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 cannotbe 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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