Virus Structure & Classification

1. Virus Structure & Classification developed by Hugh B. Fackrell

2. Lecture Outline • Scope of virology • Nomenclature • Virion • Virus genome • Virus symmetry • Virion structure

3. Scope of Virology • In developed countries viral infections are the most common cause of acute disease that does not require hospitalization • In developing countries viral infections are a common cause of mortality and disability especially among infants and children

4. Viruses as a health hazard Now antibiotics effectively control most bacterial infections Viruses pose a relatively greater and less controlled threat to human health

5. Virus • obligate intracellular parasite • delivers its genome into host cell • genome is either DNA or RNA • genome transcribed and translated by host synethetic machinary Viruses are NOT cellular

6. Virus • submicroscopic particles • smallpox a large virus is at the limit of resolution of the light microscope • most require use of electrom microscope

7. Viruses Infect All Life Forms • Bacteria>> bacteriophage • Plants • Fungi • Insects • Fish • Reptiles • Bird • Mammals

8. Viral Nomenclature • viruse families end with -viridae • eg poxviridae retroviridae • Virus subfamilies -virinae • alphaherpesvirinae herpes simplex • gammaherpesvirinae- epstein Barr virus • Virus genera -virus • enterovirus- polio virus • lyssavirus -rabies virus

9. Siglum • An abbreviation derived from a few or intial letters • (plural sigla)

10. Virus Sigla • Respiratory Enteric and Orphan Viruses • Papilloma, Polyoma & Vacuolating agent Viruses • Hepatocytes & RNA genome

11. Sigla (cont) • Parvovirus -small • Adenovirus - gland eg adenoid tissue • Herpes- creeping- nature of lesions • Toga virus - cloaked with envelope • Arena virus - sand like lesion • Corona virus- crown like peplomers • Bunya virus - Bunyamwera Africa • Calcivirus - cup like

12. Herpes zoster

13. Virion • A fully assembled infectious virus • At least two components • Genome • DNA or RNA • Single stranded or double stranded • Sense or antisense • Capsid • Protective protein coat

14. DNA Viruses • Parvovirus ssDNA, sense or antisense, linear • HepadnaAvirus dsDNA,linear • Papovavirus dsDNA,circular • Adenovirus dsDNA,linear • Herpes virus dsDNA,linear • Pox virus dsDNA, linear

15. RNA Viruses • ssRNA, Sense strand -picornavirus, calicivirus, togavirus, coronavirus • ssRNA, antisense strand -bunyavirus, orthomyxovirus, arenavirus, filovirus, rhabdovirus,paramyxovirus • Retrovirus ssRNA 2 copies • Reovirus dsRNA, 10-12 segments

16. Capsid • Protein coat that protects the genome • protection against nucleases • few structural proteins Capsids Self Assemble

17. Virion Symmetry • Cubical Symmetry • Adenovirus • picorrnavirus • Helical Symmetry • Filovirus • Rhadovirus • Complex Symmetry • poxvirus • T4 bacteriophage

18. Helical Symmetry • Helical rigid • Rhabdovirus,-rabies • Helical pleomorphic • Paramxyovirus -parainfluenza • ,measles & respiratory syncytical virus • Orthomxyovirus -influenza

19. Helical Symmetry

20. Rhabdovirus

21. Cubic Symmetry • Icosahedral Symmetry • 20 equilateral triangles • 12 vertices • 532 symmetry

22. Icoshedral Structure

23. Complex Symmetry • Very rigid, defined structures • may or may not have envelope

24. Complex Symmetry

26. Polio Virus

27. Peplomer • Glycoprotein spikes • on viral envelope • coded by viral genome • coronavirus,orthomyxovirus, arenavirus,Rhabdovirus,paramyxovirus Determine viral host range

28. Viral Envelope • Some viruses are surrounded by an additional covering - viral envelope • derived from host cell membranes • contact virus proteins internally • glycosylated proteins externally 50% of animal viruses have an envelope