5. Basic properties of virus

Basic properties of Virus

1. 5. SOME BASIC PROPERTIES OF THE VIRUS Faculty: Aftab H. Abbasi RN, DCHN, BSN, MA, LL.B Lecturer Nursing Qadri College of Health Sciences Karachi QADRI COLLEGE OF HEALTH SCIENCES, KARACHI

2. BASIC PROPERTIES OF THE VIRUS Definition of Virus: A  virus  is a submicroscopic infectious agent that replicates ( repeat of something) only inside the living cells of an organism, is a small parasite that cannot reproduce by itself.   Viruses  infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea .

3. BASIC PROPERTIES OF THE VIRUS -OR- A  virus  is an infectious agent of small size and  simple composition that can multiply only in living cells of animals, plants, or bacteria.

4. BASIC PROPERTIES OF THE VIRUS Virology: Is the scientific study of viruses – submicroscopic (too small to be seen by an ordinary light microscope) , parasitic particles of genetic material contained in a protein coat – and virus-like agents. Virology  is a subfield of  microbiology .

5. BASIC PROPERTIES OF THE VIRUS - Viruses are inert (lacking the ability or strength to move) (nucleoprotein ) filterable Agents. -Viruses are obligate (restricted to a particular function or mode of life) intracellular parasites. -Viruses cannot make energy or proteins independent of a host cell. -Viral genome (complete set of genetic information in an organism) are RNA or DNA but not both -Viruses lack the enzymes necessary for protein and nucleic acid synthesis. -Viruses do not have the genetic capability to multiply by division. -Viruses occupy the twilight (conceptual area/mysterious) zone that separates the ‘living’ from the ‘nonliving’.

6. Medical importance of viruses -Viral diseases range from minor ailments such as the common cold to terrifying diseases such as rabies or AIDS. -They may be sporadic (occurring at irregular intervals or only in a few places) like mumps, endemic (regularly found among particular people or in a certain area) like infectious hepatitis, epidemic (that affects a large number of people within a community, population, or region) like dengue fever or pandemic like influenza, COVID-19. -They may be localized to circumscribed (within limits) areas (as some arbovirus (viruses which are transmitted by mosquitoes, ticks) diseases) or worldwide (as Herpes simplex). -Viruses can cause cancer in animals and birds, as well as in humans.

7. BASIC PROPERTIES OF THE VIRUS Size of Viruses : A small virus has a diameter of about 20 nm (nanometer) . Example: Parvovirus A large virus have a diameter of up to 400 nm. Example:Poxvirus

8. BASIC PROPERTIES OF THE VIRUS Structure and shape: 1-Virion: The complete infectious unit of virus particle. 2-Capsid : The protein shell, or coat, that encloses the nucleic acid genome. Functions : a . Protect the viral nucleic acid. b . Participate in the viral infection. c . Antigenic and specific for each virus type. d . Provides structural symmetry to the virus particle. 3-Nucleocapsid: The capsid (protein shell of a virus) with the enclosed nucleic acid.

9. BASIC PROPERTIES OF THE VIRUS

10. BASIC PROPERTIES OF THE VIRUS Replication of viruses: The viral multiplication cycle can be divided into six sequential phases, though the phases may sometimes be overlapping. Adsorption or attachment Penetration Uncoating Biosynthesis Maturation Release

11. BASIC PROPERTIES OF THE VIRUS 1- Adsorption: ( the adhesion) Virions may come into contact with cells by random collision but adsorption takes place only if there is an affinity between the two. Differences in susceptibility to viral infection are to a large extent based on the presence or absence of receptors on cells. 2- Penetration : Virus particles may be engulfed by a mechanism resembling phagocytosis , a process known as ‘ viropexis ’ In the case of enveloped viruses, the viral envelope may fuse (join or blend) with the plasma membrane of the host cell and release the nucleocapsid into the cytoplasm.

12. BASIC PROPERTIES OF THE VIRUS 3- Uncoating : Process of stripping (physical separation process) the the virus of its outer layers and capsid so that the nucleic acid is released into the cell. With most viruses, uncoating is effected by the action of lysosomal enzymes of the host cell. 4- Biosynthesis: During this phase, viral nucleic acid, capsid protein, enzymes necessary in the various stages of viral synthesis, assembly and release will be synthesised . Certain ‘regulatory proteins’ which serve to shut down the normal cellular metabolism and direct the sequential production of viral components are also synthesised . The site of viral synthesis depends on the type of virus.

13. BASIC PROPERTIES OF THE VIRUS 5- Maturation: (process  of reaching a stage of full or advanced development) Assembly of daughter virions follows the synthesis of nucleic acid & proteins. Virion assembly may take place in the host cell nucleus. Naked viruses are present intracellularly as fully developed virions but in the case of enveloped viruses, only the nucleocapsid is complete. 6- Release: Progeny (offspring of animals or plants) of bacterial viruses release by the lysis (breaking down)   of the infected bacterium. In the case of animal viruses, release usually occurs without cell lysis . Myxoviruses are released by budding from the cell membrane over a period of time. In the case of some viruses ( varicella ), transmission occurs directly from cell to cell and poliovirus causes profound damage to the host cell and may be released by cell lysis .

14. BASIC PROPERTIES OF THE VIRUS Classification and nomenclature of viruses: Viruses are classified on the basis of biological, physical and chemical properties. - Viruses are broadly classified into DNA and RNA viruses and then further divided into families, subfamilies, genera and species.

15. BASIC PROPERTIES OF THE VIRUS

16. BASIC PROPERTIES OF THE VIRUS DNA viruses: Poxviridae Herpesviridae Adenoviridae Papovaviridae Parvoviridae Hepadnaviridae

17. BASIC PROPERTIES OF THE VIRUS RNA viruses: Picornaviridae Orthomyxoviridae Paramyxoviridae Togaviridae Flaviviridae Bunyaviridae Arenaviridae Rhabdoviridae Reoviridae Coronaviridae Retroviridae Caliciviridae Filoviridae

18. BASIC PROPERTIES OF THE VIRUS Viroids : (small infectious pathogens) Viroids are single-stranded circular RNA molecules that lacks a protein coat and they are mainly plant pathogens. Prions : (are misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals) Prions are infectious proteins without any detectable nucleic acid. They are highly resistant to physical and chemical agents. They produce slow infections with very long incubation period.

19. BASIC PROPERTIES OF THE VIRUS Diseases caused by prions in animals include, scrapie (a disease of sheep involving the central nervous system) of sheep and goats , mink encephalopathy, bovine spongiform encephalopathy. Responsible for Kuru ( Kuru  is a very rare disease. It is caused by an infectious protein ( prion ) found in contaminated human brain tissue.  Kuru  is found among people from New Guinea who practiced a form of cannibalism in which they ate the brains of dead people as part of a funeral ritual) , Creutzfeldt-Jakob disease (( CJD ), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is a fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes, poor coordination, and visual disturbances) and some other chronic neurological degenerative diseases of humans.

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21. BASIC PROPERTIES OF THE VIRUS