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Classification, Morphology and Methods for the detection of Viruses
This document discusses viruses, including their definition, properties, morphology, classification, and methods for detection. Some key points: - Viruses are the smallest known infectious agents, containing either DNA or RNA but not both. They lack cellular organization and rely on host cell machinery to replicate. - Viruses have a protein capsid that surrounds and protects their nucleic acid. They can have helical, icosahedral, or complex symmetry. Some are enveloped and others are non-enveloped. - Viruses are classified based on their nucleic acid type, number of strands, genome structure, and other properties. This includes DNA and RNA virus families such as Adenoviridae, Herpes
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Classification, Morphology and Methods for the detection of Viruses
- 1. Classification, Morphology andMethods for the detection of Viruses Dr. Rakesh Prasad Sah Assistant Professor, Microbiology
- 2. Definition • are thesmallest known infective agents containing only one type of nucleic acid (DNA or RNA) as their genome. • Do not possess cellular organization and they have no metabolic activity.
- 3. Properties of Viruses •Do not have cellular organization. • Contain only one type of nucleic acid; either DNA or RNA but never both. • Obligate intracellular parasites. • Lack enzymes necessary for protein and nucleic acid synthesis and are dependent for replicaton on the machinery of host cells. • Multiply by a complex process and not by binary fission. • Unaffected by antibacterial antibiotics.
- 4. Differences between Virusand Bacteria Properties Bacteria Viruses Cell wall + _ Ribosome's & enzymes + _ DND & RNA Both present Only one Binary fission + _ Growth in Inanimate media + _ Sensitivity to antibiotics + _ Sensitivity to interferon _ +
- 5. Morphology of Viruses •Viriods: ssRNA that lacks protein coat. • Prions: infectious proteins without any detectable N.A.
- 6. Morphology of Viruses •Extracellular infectious viral particle is called ‘Virion’. • Viruses are much smaller than bacteria. For a time, they were known as ‘filterable agents’ as they can pass through filters that can hold back bacteria. • They can not be seen under light microscope hence called as ‘ultramicroscopic’. • Size range: 20-300 nm • Parvovirus: 20 nm (smallest virus) • Pox virus: 300 nm (biggest virus and can be seen under light
- 8.
- 9. Viral Capsid • Virusesconsists of nucleic acid core surrounded by a protein called capsid. • Capsid is composed of large number of capsomer which is made up of polypeptide molecules. • The capsid with theenclosed nucleic acid is known as nucleocapsid.
- 10. Functions of Capsid •It protects viral genome from physical destruction & enzymatic inactivation by nucleases in biological material. • It provides binding site which enable the virus to attach to specific site on the host cell. • It facilitates assembly and packaging of viral genetic information. • It serves as a vehicle of transmission from host to another. • It is antigenic and specific for each viruses • It provides the structural symmetry to the virus particle.
- 11. Viral Symmetry 1. IcosahedralSymmetry • An icosahedral (icosa, meaning 20 in greek) is a polgon with 12 vertices or corners and 20 facets or sides. • Each facet is in the shape of an equilateral triangle. • Eg. Adeno viruses Adenovirus
- 12. 2. Helical Symmetry •The nucleic acid and capsomers are wound together in the form of helix or spiral. • Eg. Influenza virus, parainfluenz virus, rabies virus. 3. Complex Symmetry • Viruses which don not show either icoshedral or helical symmetry due to complexity of their structure are referred to have complex symmetry. • Eg. Pox viruses
- 14. Viral Envelope • Virionsmay be enveloped and nonenveloped (naked). 1. Enveloped Virus • The envelop or outer covering of virus containing lipid is derived from the plasma membrane of the host cell during the release by budding from the cell surface. • Enveloped viruses are susceptible to the action of lipid solvent such as ether, chloroform and detergent. • Eg. Herpes virus, Hepatitis B virus, HIV virus
- 15. 2. Non envelopedvirus • Viruses which does not have outer covering. • Naked viruses are more likely to be resistant to lipid solvents like ether, chloroform and detergent. Peplomers • In mature virus particle, the glycoproteins often appear as projecting spikes on the outer surface of the envelop which are known as peplomers. • A virus may have more than one type of peplomers. E.g the influenza virus carries two types of peplomers, the hemagglutinin and neuraminidase
- 16. Functions of Peplomers •It helps for attachment of virus to the host cell receptors to initiate the entrance of the virion into the cell. • It attach to receptors on red blood cells, causing these cell to agglutinate. • It has enzymatic activity like neuraminidase which cleave neuraminic acid from host cell glycoproteins. • It has antigenic properties.
- 18. Viral Nucleic Acids •Viruses contain a single kind of nucleic acid either DNA or RNA which encodes the genetic information necessary for replication of the virus. • The genome may be single stranded or double stranded, circular or linear, segmented or non segmented. • According to nucleic acid present, viruses can be classified in to DNA viruses and RNA viruses.
- 20. Classification of viruses •Type of nucleic acid • Number of strands of nucleic acid • Polarity of viral genome • Symmetry of nucleic acid • Presence / absence of a lipid envelope
- 21. Classification of viruses DNAViruses Family Species Parvoviridae Adeno associated virus, Parvovirus , Densovirus Herpesviridae HSV 1 & 2, VZV, CMV, HHV type 6,7,8, E.B. virus Hepadenaviridae Hepatitis B virus Papovaviridae Wart viruses, Polyoma viruses, S V 40 Adeno viriadae Adenovirus Poxviridae Variola , Vaccinia, Cowpox, Monkey pox, Molluscum contagiosum,
- 22. Classification of viruses RNAViruses Family Species Orthomyxoviridae Influenza viruses A,B,C Picornaviridae Enteroviruses :Polio, Echo, Coxsackie, Parechovirus, Rhinovirus Hepatovirus : Hepatitis A Paramyxoviridae Paramyxovirus: Human parainfluenza viruses, mumps, Newcasle disease virus Morbillivirus: measles Pneumovirus : RSV & related viruses Bunyaviridae Arboviruses, Hanta virus, Nairo virus, Phlebovirus, UKUvirus
- 23. Classification of viruses •RNA Viruses Family Species Arenaviridae LCM, Lassa viruses Rhabdoviridae Vesiculovirus : Vesicular stomatitis virus, Chandi[ura virus Lyassa virus : Rabies virus Togaviridae Alpha viruse :Gr A arboviruses Rubiviruses : Rubella Pesivirus : Hog cholera virus Coronaviridae Coronavirus , SARS Retroviridae HTLV-1, HTLV-2, HIV 1 & 2, Human foamy virus, Hepatitis D virus Visna and maedi viruses of Sheep
- 24. Classification of viruses` •RNA Viruses Family Species Flaviviridae yellow fever, dengue, JE, Hepatitis C Calciviridae Calcivirus Hepatitis E virus Filoviridae Marburg, Ebola virus Reoviridae Reovirus , Rotavirus Kemerovo virus, Colarado tick fever
- 25. Laboratory Diagnosis ofViral Infections • For the proper management of certain diseases – Rubella first trimester abortion is recommended. – Baby born HbsAg positive mother immunization at birth (mandatory) • Diagnosis – E.g. Herpes viruses antiviral chemotherapy is available. • Screening of blood donors (for HIV & Hep-B & others) • Early detection of epidemics – E.g. influenza, encephalitis, poliomyelitis etc control measures to prevent spread of inf. • PEP (Post-exp prophylaxis) – HIV, Hep-B
- 26. Lab Diagnosis ofViral Infection Direct demonstration of Virus or it’s components Isolation of Virus Detection of specific Antibodies
- 27. Direct Demonstration ofVirus and It’s components • Electron Microscopy • Immunoelectron Microscopy – Sensitivity of electron microscopy can be increased by adding specific antibody to the specimen to aggregates can be observed under electron microscopy. Specimen Viruses Faeces Rotavirus, Hepatitis A virus, adenovirus, Norwalk virus, astrovirus Vesicular Fluid Herpes simplex, Varicella-zoster CSF Enterovirus, Varicella-zoster Urine Cytomegaloviurs (CMV)
- 28. • Fluorescent Microscopy •Light Microscopy
- 29. • Viral Antigens •Nucleic Acid Probes
- 30. • PCR (PolymeraseChain Reaction)
- 31. • Isolation ofthe Virus – Animal inoculation – Egg inoculation – Cell cultures
- 32. • Detection ofSpecific Antibodies – Neutralization test
- 33.
- 34. – Complement fixationtest Positive Test All the available complement is fixed by the Ag-Ab rxn: no hemolysis occurs, so the test is positive for the presence of Abs. Negative Test No Ag-Ab rxn occurs. The complement remains and the RBCs are lysed in the indicator stage. So the test is negative.
- 35. – ELISA – ICT(Immunochromatographic tests)