Introduction to viruses

Presentation comprises of introductory information on virus, related terminology, its composition and structure, classification, nomenclature and taxonomy for under graduate students.

1. INTRODUCTION TO VIRUSES Dr. Vinod Kumar Singh Department of Vet. Microbiology DUVASU, Mathura

2. 4/14/2021 2 Terminology Virus ( latin : slimy liquid or poison ) is a broad general term for any aspect of the infectious agent and includes: the infectious or inactivated virus particle viral nucleic acid and protein in the infected cell Virion is the physical particle in the extra-cellular phase which is able to spread to new host cells; complete intact virus particle

3. 4/14/2021 3 Sub-viral agents Satellites Contain nucleic acid Depend on co-infection with a helper virus May be encapsidated ( satellite virus ) Mostly in plants, can be human e.g. hepatitis delta virus If nucleic acid only = virusoid Viroids Unencapsidated , small circular ssRNA molecules that replicate autonomously Only in plants, e.g. potato spindle tuber viroid Depend on host cell polII for replication, no protein or mRNA Prions No nucleic acid Infectious protein e.g. BSE

4. 4/14/2021 4 Bacteriophage Bacteriophage is any one of viruses that infect bacteria They do this by injecting genetic material, which they carry enclosed in an outer protein capsid. The genetic material can be ssRNA , dsRNA , ssDNA , or dsDNA along with either circular or linear arrangement

5. 4/14/2021 5 Bacteriophage T4 20 Sided polyhedron Double-stranded Locate bacterium Anchor to bacterium Needle which injects DNA into bacteria

6. 4/14/2021 6 Limits of resolution Electron Microscope 0.003 m Light Microscope 0.2 m Unaided Human eye 40 m Microscopic protozoa & fungi 4 - 40 m Classes of organisms Bacteria 0.1 - 10 m Viruses 0.03 - 0.3 m 0.001 0.01 0.1 1 10 100 Size ( m) Relative size of Microorganisms

7. 4/14/2021 7 Relative size of Microorganisms

8. China 1000 B. C. Prevention without knowledge of the agent, based on recognition that survivors of smallpox were subsequently protected against disease Variolation: Inoculation of healthy individuals with dry material from smallpox pustules Roman Empire was weakened by viral epidemics of measles and smallpox between 160 A.D. through 266 A.D Smallpox helped destroy the Aztec Empire during the conquest of Mexico by Spain 4/14/2021 8 History

9. 1718 - Lady Marry Wortley Montagu dicovered the Ottoman Empire concept of variolation and brought the idea to Britain 1796 - E. Jenner performed his vaccination studies showing smallpox infection could be stopped by prior infection with cowpox 1885 - L. Pasteur experimented with rabies vaccination, using the term virus to describe the agent Although Pasteur did not discriminate between viruses and other infectious agents, he originated the terms virus and vaccination in honor of Jenner 4/14/2021 9 History

10. 1879 - Adolf Mayer named tobacco mosaic disease based on the dark and light spots on infected leaves Experiment on transmission of disease by inoculating extracted juice from infected leaves Unable to culture the agent 1892 – Dimitri Ivanowski repeated Mayer’s observation additionally filter the sap of leaves using Chamberland filter 1898 - Martinus Beijerinck Showed that sap of infected tobacco plant retain its infectivity after filteration by chamberland porcelin filter Extented these studies by showing that filtered sap diluted regain its strength after replication in living growing tissue of plant Called this filterable agent as “ Contagium vivum fluidum ” -contagious living liquid 4/14/2021 10 History

11. 4/14/2021 11 1898 - Freidrich Loeffler and Paul Frosch : applied filteration criteria to a disease transmission in cattle which later k/a Foot-and-mouth disease 1900 -Walter Reed demonstrated that yellow fever is spread by mosquitoes 1908 - Karl Landsteiner and Erwin Popper proved that poliomyelitis is caused by a virus. Landsteiner and Popper were the first to prove that viruses could infect humans as well as animals 1911 - Francis Peyton Rous: discovered 1 st tumor causing virus History

12. 4/14/2021 12 1915 - Frederick Twort : detected existance of filterable agents that could kill bacteria 1917 - Felix d’ Herelle : also noted killing of bacteria by agent he called Bacteriophage defined Plaque Assay for quantification of bacteriphage 1931 - Woodruff and Goodpasture used ECE for virus culture 1935 - Wendell Stanley established the chemical nature of viruses when he crystallized TMV and found it to be mostly protein History

13. 4/14/2021 13 1939 - Emory Ellis and Max Delbruck : one step growth curve of bacteriophage ` 1957 - Isaacs and Lindemann discover Interferon (INF) 1979 - WHO declared smallpox globally eradicated History

14. 4/14/2021 14 Virus Properties Ultramicroscopic Filterable agents Obligate intracellular parasite: cannot be grown on artificial media (but not all obligate intracellular agents are virus eg . Anaplasma , Ehrlichia , Rickettsia ) Do not possess cellular organelles viz. mitochondria, golgi , ER associated ribosome's) Multiplication not by binary fission but resembles an assembly line in which different parts of virus come together from different sites in host cell to form new virus particle Genome either DNA or RNA

15. 4/14/2021 15 Property Bacteria Mycoplasma Rickettsia / Chlamydiae Viruses Fungi Size (> 300 nm diameter) + + + < 300 nm + Culture on Artificial media + + _ _ + Obligate intracellular _ _ + + _ DNA and RNA + + + DNA or RNA + Functional ribosomes + + + _ + Characteristics of Infectious Agents

16. 4/14/2021 16 Composition varies in individual virus family Simplest virus consist of a core of nucleic acid surrounded by a protein coat (Capsid) and +/- Envelope Components of virus particle include: Nucleic acid - DNA or RNA single stranded / double stranded Segmented / non segmented linear / circular Composition of Virus

17. 4/14/2021 17 Proteins Structural - capsid made of capsomeres serve as antigens which elicit an immune response Enzymes differ from host cell targets of antiviral therapy Envelope lipoprotein envelope containing viral and host cell components Composition of Virus

18. 4/14/2021 18 Structure of Virus

19. 4/14/2021 19 Viruses varies in shape, size and symmetry Shape: Spherical, Rod, Elongated/Filamentous, Bullet, Brick, cone, etc. Size: usually ranges from 20 nm to 300 nm Symmetry: refers to the way capsomere are arranged in the virus capsid Virus particles exhibit 3 types of capsid symmetry Icosahedral : isometric or cubic Helical: tubular Complex Structure of Virus

20. 4/14/2021 20 Icosahedral capsids 1 2 6 7 9 5 4 3 11 12 8 10 12 vertex 20 faces 60 sides 3 axis of rotation

21. 4/14/2021 21 Icosahedral : Axis of symmetry 2-FOLD 5-FOLD 3-FOLD

22. 4/14/2021 22 Icosahedral : Axis of symmetry

23. 4/14/2021 23 Helical Symmetry Tobacco mosaic virus Amplitute : daimeter Pitch: distance covered by each complete turn

24. Virus Classification I - the Baltimore classification genetic content and replication strategy Virus classification II - the Classical system based on three principles classifying virus itself not host nature of nucleic acid shared physical properties of the infectious agent ( e.g capsid symmetry, dimensions, lipid envelope) Virus classification III - the genomic system based on DNA/RNA sequence By the year 2014 there were 3180 viruses of plants, animals and bacteria - in 7 order , 104 families , 23 subfamilies and 505 genera 4/14/2021 24 Classification of virus

25. 4/14/2021 25 Baltimore classification of virus David Baltimore (Nobel prize 1975) proposed a classification based on combination of type of viral genome (genetic content) information about genome synthesis (replication strategy) focus on synthesis of mRNA (+) strand can be directly translated (-) strand cannot be translated Seven distinct virus groups

26. 4/14/2021 26 Baltimore Classification of Virus Baltimore classification: seven classes of viruses : ds DNA viruses (herpes, papova, adeno, pox) ss DNA viruses ( parvo ) ds RNA viruses (reo, rota ) (+) sense ss RNA viruses ( (picorna, toga, flavi, corona ) (-) sense ss RNA viruses (arena, bunya) RNA reverse transcribing viruses (retro, lenti ) DNA reverse transcribing viruses ( hepedna )

27. 4/14/2021 27 Initially grouped based on disease and symptoms viz. Hepatitis virus: viruses causing liver pathology Mosaic viruses: viruses causing mottling in plants 1966 – International Committee on Nomenclature of Viruses (ICNV) International Committee on Taxonomy of Viruses (ICTV) Virus Taxonomy and Nomenclature

28. 4/14/2021 28 Virus Classification: polythetic system Order: highest taxa Family: practical used highest taxa Subfamily Genus Species Viruses with similar structural, genomic and replication properties are grouped into families (suffix: viridae ) e.g. Herpesviridae Families subdivided into genera (suffix: virus) e.g. Herpes simplex virus, Cytomegalovirus, Varicella zoster virus Subtypes based on nucleotide sequence and antigenic reactivities e.g. Herpes simplex virus type 1, Herpes simplex virus type 2 Virus Taxonomy

29. 4/14/2021 29 Order: suffix: virales Family: suffix: viridae Subfamily: suffix: virinae Genus: suffix: virus Species : can contain more than one word have no specific ending for species having more than one word , 1 st word plus any proper nouns are capitalised Virus Nomenclature must be single word written in continuation without any space 1 st alphabet should be capitalized letter should be italics

30. 4/14/2021 30 Eg . Newcastle disease virus Order: Mononegavirales Family: Paramyxoviridae Subfamily: Paramyxovirinae Genus: Avulavirus Virus Nomenclature