Viral classification and Types of Replication in virus
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The document provides an overview of viral classification and types of replication, explaining that viruses multiply only in living cells and detailing the steps involved in the viral replication cycle. It covers various mechanisms of entry, uncoating, multiplication, and release of new virions, as well as specific characteristics of different types of RNA and DNA viruses. Additionally, it lists common viral diseases affecting bovines.
Viral classification and Types of Replication in virus
- 1. Viral Classification & Types of replication in virus Submitted by: Rakshith K MVHK1742 Submitted to: Dr Suguna Rao Professor Dept. of Veterinary Pathlogy Veterinary college, Bangalore
- 4. Multiplication of virus • Virus multiply only in living cells. • Host cell must provide the energy and synthetic machinery, and the precursors for the synthesis of viral proteins and nucleic acids. • Many of the pathological effects of viral infections is by process of viral multiplication. • Until a virus enters a cell, it is more dead than alive.
- 5. Entry • Direct inoculation into the bloodstream. (Arthropod borne) E.g.: Togaviridae • Penetrating the skin, or mucosal barrier of the respiratory or gastrointestinal tract. • Reach the target organ. • Some virus do primary multiplication in the cells at the portal of entry & spread to target organ (for disease production) – E.g.: Herpes. • Some direct spread to target organ – E.g.: Reovirus.
- 6. Spread: 1. Lymphatic or bloodstream (e.g., With reoviruses) 2. Infected lymphocytes (e.g., With cytomegaloviruses) 3. Neuronal axons (e.g., With rhabdoviruses) 4. Cross the placenta to the foetus (e.g., With cytomegalovirus)
- 7. General steps in a virus replication cycle include: 1) Attachment: • Interaction of a virus particle (virion) with a specific receptor site on the surface of a cell. • Specific binding of virus to the cell surface receptors
- 8. 2) Penetration • The virus particle is taken up inside the cell. • Penetration, engulfment, or viropexis. • Enveloped viruses: Virion envelope fuses with the plasma membrane allowing entry of the nucleocapsid. • Non-enveloped viruses: Receptor-mediated endocytosis (pinocytosis) OR translocation (change of location)
- 9. 3) Uncoating • After penetration, the virion is uncoated. • The RNA or DNA of the virus particle is exposed by removal of the capsid (protein coat). • The infectivity of the virus is lost at this point. • Uncoating is followed by the "eclipse phase", when no virions are seen.
- 10. • Infection of a cell, does not necessarily lead to viral multiplication and cell damage. • Cell must be permissive for productive infection means appropriate receptors and be capable of supporting replication. • Non-productive infection – infection by Defective cells. (defect in some aspect of replication) • Such persistent infections may, under appropriate circumstances, get activated to productive infection, or lead to cell transformation.
- 12. • Transcription varies with type of nucleic acid, enzymes carried by virion & intracellular location of virus. • DNA virus- nucleus, use host RNA polymerase. • Single-stranded positive sense RNA viruses- mRNA. • Negative-sense viruses (orthomyxo-, paramyxo- and rhabdoviruses) - carry RNA polymerases.
- 13. Virus Replication Cycle 1. Interaction of a target cell 2. Attach to the target cell membrane via ligand receptor interactions. 3. Enter the target cell via endocytosis/membrane fusion and spread genomic and protein components via “uncoating” within the cell. 4. (a) RNA viruses most commonly replicate in the cytoplasm. (b) DNA viruses most commonly replicate in the nucleus. 5. Reassemble of virus 6. Release of progeny from the target cell by budding or cell lysis
- 14. Multiplication of Single-Stranded RNA (ss RNA) Viruses - I • Positive (+) strand viruses: Togaviruses and picornaviruses. • Viral RNA can serve directly as mRNA. • Viral RNA links to ribosome & nucleotide sequences of RNA are directly translated to proteins. • Viral (+) strand RNA 1. directly translated to proteins 2. Synthesise complementary negative (-) strand RNA. • Complementary (-) strand RNA serves as a template for synthesis of additional (+) strands. • Repeat the process and ultimately form viral progeny. • Since replication doesn’t depend on any enzyme carried by the virion, RNA extracted from (+) strand RNA viruses is infectious.
- 15. Multiplication of Single-Stranded RNA (ss RNA) Viruses - II • Negative (-) strand viruses: Arenaviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and rhabdoviruses. • Viral RNA be transcribed into a (+) strand mRNA. • Transcriptase carried within the virion. • RNA extracted from (-) strand RNA viruses is not infectious, since replication depends on virion transcriptase.
- 16. Multiplication of Single-Stranded RNA (ss RNA) Viruses - III • Retro virus: • These viruses have a DNA step in replication. • Viral RNA serves as a template for the synthesis of viral DNA. • This depends on the enzyme reverse transcriptase (RNA- dependent DNA-polymerase) carried by virion. • cDNA is made out of viral RNA. • This cDNA is integrated in to cellular DNA. • Viral multiplication is by transcription and translation of integrated viral DNA, which codes for necessary proteins. • Viral RNA and proteins pakaged to for viral progeny.
- 17. Multiplication of Double-Stranded RNA (ds RNA) Viruses • Reoviruses • their RNA is transcribed by virion polymerase • (-) strand (+) mRNA viral proteins & enzymes. • Same (+) mRNA complimentary to (-) strand RNA, yielding double stranded RNA for assembly of virions.
- 18. DNA viruses Multiplication of Single-Stranded DNA (ss DNA) Viruses • Single-stranded (DNA) parvoviruses replicate in the nucleus. • They depend on host cell enzymes for synthesis of complementary DNA to form double-stranded DNA. • This dsDNA transcribed into mRNA & genomic DNA.
- 19. Multiplication of Double-Stranded DNA (ds DNA) Viruses • Papovavirus, Adenovirus, and Herpesvirus. • dsDNA is transported to nucleus, cellular enzymes are used for production of mRNA. • Replication of DNA uses 1. host cell polymerases – Papavo 2. Virally coded polymerase – Herpes and Adeno • Poxvirus multiplication occurs in the cytoplasm. • virion is uncoated by both cellular enzymes and enzyme products of an early transcribed mRNA. • Cytoplasmic DNA replication by enzymes carried within the virion and translation products of early and late mRNA.
- 20. 5) Release of new virions • Non enveloped virus mature in host cell in nucleus or cytoplasm. Cell lysis cause their release. • Enveloped virus obtain envelop by budding. Release by budding will not cause cell lysis. (All (-) strand RNA virus) • Retro, Arena virus – Non-cytolytic. • Togaviruses, Paramyxo, and Rhabdoviruses – Cytolytic.
- 21. EXCEPTIONS: • Pox virus is released by both mechanism (BUDDING) • acquire envelop by golgi complex intracellularly. • acquire 2nd envelop by plasma membrane while budding. • Pox virus: without envelop • Released without envelop by disruption of cell. • Both are infectious • Both intracellular and intranuclear multiplication
- 22. • Herpes virus: (enveloped) • Acquire envelop by inner lamella of nuclear membrane. • These enveloped virions pass with in cisternae without contact with cytoplasm and released. • No cell disruption. • But productive forms of herpes cause cell damage.
- 23. Common viral diseases of Bovines • Vesicular Stomatitis • Bovine viral diarrhoea-mucosal disease • Foot-and-mouth Disease (Aphthous Fever) • Cowpox • Rabies • Bovine Ephemeral Fever • Bovine cutaneous papillomatosis • Rinderpest • Calf neonatal diarrhoea • Lumpy Skin Disease • Bovine Respiratory Syncytial Virus (BRSV) • Bovine leukaemia virus • Bovine immunodeficiency virus • Bovine Parvovirus Infection • Buffalopox • Akabane Disease (of Cattle): Also known as "congenital arthrogryposis hydranencephaly syndrome", Akabane disease caused by a bunyavirus.