C hair of Medical Biology, M icrobiology, V irology, and I mmunology

1. Chair of Medical Biology, Microbiology, Virology, and Immunology STRUCTURE,CLASSIFICATION AND PHYSIOLOGY OF VIRUSES RNA-VIRUSES

2. Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat. Viruses are unable to generate energy. As obligate intracellular parasites, during replication, they fully depend on the complicated biochemical machinery of eukaryotic or prokaryotic cells.

3. A complete virus particle is called a virion. The main purpose of a virus is to deliver its genome into the host cell to allow its expression (transcription and translation) by the host cell.

4. Classification DNA-Containing Viruses Hepadnaviridae Parvoviridae Papovaviridae Adenoviridae Herpesviridae Poxviridae Iridovoridae

5. Classification RNA-Containing Viruses Picornaviridae Paramyxoviruses Caliciviridae Orthomyxoviruses Togaviruses Bunyaviridae Arenaviridae Flaviviridae Coronaviridae Reoviridae Rhabdoviridae Birnaviridae Filoviridae Retroviridae

6. Some Useful Definitions in Virology Capsid: The symmetric protein shell that encloses the nucleic acid genome. Often, empty capsids are by-products of the viral replicative cycle. Nucleocapsid: The capsid together with the enclosed nucleic acid. Structural units: The basic protein building blocks of the capsid. Capsomeres: Morphologic units seen in the electron microscope on the surface of virus particles. Capsomeres represent clusters of polypeptides, which when completely assembled form the capsid.

7. Structure of viruses A – naked, not containing an envelope aroud capsid B – enveloped, containing an envelope around the capsid

8. The helical structure of the rigid tobacco mosaic virus rod In the replication of viruses with helical symmetry, identical protein subunits (protomers) self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Such nucleocapsids form rigid, highly elongated rods or flexible filaments;

9. Icosahedral Symmetry An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Lines through opposite vertices define axes of fivefold rotational symmetry: all structural features of the polyhedron repeat five times within each 360° of rotation about any of the fivefold axes.

10. Combined symmetry

11. Replication of poliovirus, which containing an RNA genome

12. Cultivation of Viruses A. Chick Embryos: Virus growth in an embryonated chick egg may result in the death of the embryo (eg, encephalitis virus), the production of pocks or plaques on the chorioallantoic membrane (eg, herpes, smallpox, vaccinia), the development of hemagglutinins in the embryonic fluids or tissues (eg, influenza), or the development of infective virus (eg, polio virus type 2).

13. Cultivation of Viruses • B. Tissue Cultures: • Primary cultures are made by dispersing cells (usually with trypsin) from host tissues. In general, they are unable to grow for more than a few passages in culture, as secondary cultures. • Diploid cell strains are secondary cultures which have undergone a change that allows their limited culture (up to 50 passages) but which retain their normal chromosome pattern. • Continuous cell lines are cultures capable of more prolonged (perhaps indefinite) culture which have been derived from cell strains or from malignant tissues They invariably have altered and irregular numbers of chromosomes.

14. Cell Cultures HeLA, Hep-2, Detroit-6, KB, Vero, Fibroblasts of human embryou, Kidney of rhesus monkey, WI-38, RD, Primary cultures of chiken fibroblasts

15. Morphologic and Structural Effects 1 The cytopathic effect, or necrosis of cells in the tissue culture (polio-, herpes-, measles-, adenovirus, cytomegalovirus, etc). 2 The inhibition of cellular metabolism, or failure of virus-infected cells to produce acid (eg, enteroviruses). 3 The appearance of a hemagglutinin (eg, mumps, influenza) or complement-fixing antigen (eg, poliomyelitis, varicella, measles). 4 The adsorption of erythrocytes to infected cells, called hemadsorption (paramfluenza, influenza). This reaction becomes positive before cytopathic changes are visible, and in some cases it is the only means of detecting the presence of the virus 5 Interference by a noncytopathogenic virus (eg, rubella) with replication and cytopathic effect of a second, indicator virus (eg, echovirus).

16. Morphologic and Structural Effects 6 Morphologic transformation by an oncogenic virus (eg, SV40, Rous sarcoma virus), usually accompanied by the loss of contact inhibition and the piling up of cells into discrete foci Such alterations are a heritable property of the transformed cells. 7 Formation of syncytia, or polykaryocytes, which are large cytoplasmic masses that contain many nuclei (poly, many; karyon, nucleus). 8 Alteration of cytoskeleton organization by virus infection. 9 Genotoxic Effects(Chromosome damage may be caused directly by the virus particle or indirectly by events occurring during synthesis of new viral macromolecules (RNA, DNA, protein). 10 Inclusion Body Formation(They may be situated in the nucleus (herpesvirus), in the cytoplasm (pox virus), or in both (measles virus)

20. Orthomyxovirus Family The name myxovirus was originally applied to influenza viruses. It meant virus with an affinity for mucins.

21. A model of the influenza virion

22. Types:A, B, C Influenza A: In Birds • 16 H variants • 9 N variants In Humans • 3 H variants (H1, H2, and H3) • 2 N variants (N1 and N2) Subtypes:H1N1, H2N2,H2N3

23. Swine New Reassorted virus Influenza Viruses:Antigenic Shift Human virus Avian virus Avian Reservoir Other mammals?

24. Influenza Viruses:Antigenic Drift • Gradual accumulation of mutations that allow the hemagglutinin to escape neutralizing antibodies (Point mutation in HA gene) • Epidemic strains thought to have changes in three or more antigenic sites

26. Influenza Vaccines • Whole virus vaccine: inactivated virus vaccine grown in embryonated eggs; 70-90% effective in healthy persons <65 years of age, 30-70% in persons ≥65 years • Split virus vaccine: previously associated with fewer systemic reactions among the elderly and children <12 years • Subunit vaccine: composed of H and N • Live, attenutated influenza virus vaccines under development

27. FamilyParamyxoviridae Genes: Morbillivirus– measles virus, Respirovirus– parainfluenza virus(serotypes1 and 3) Rubulavirus - mumps virus,parainfluenza virus(serotypes 2, 4а, 4b), Pneumovirus – RS-virus

28. PARAMYXOVIRUSES pleomorphic HN/H/G glycoprotein SPIKES F glycoprotein SPIKES helical nucleocapsid (RNA minus NP protein) lipid bilayer membrane polymerase complex M protein

29. STRUCTURE-PARAMYXOVIRUSES

30. Cell fusion. In the course of infection, paramyxo-viruses cause cell fusion, long recognized as giant cell formation.

31. MUMPS (Epidemic Parotitis) Mumps is an acute contagious disease characterized by a nonsuppurative enlargement of one or both of the parotid glands, although other organs may also be involved. Properties of the Virus:The mumps virus particle has the typical paramyxovirus morphology. Typical also are the biologic properties of hemagglutination, neuraminidase, and hemolysin.

32. Epidemiology The disease reaches its highest incidence in children age 5-15 years, but epidemics occur in army camps. Humans are the only known reservoir of virus. The virus is transmitted by direct contact, airborne droplets, or fomites contaminated with saliva and, perhaps, urine. The period of communicability is from about 4 days before to about a week after the onset of symptoms.

33. Pathogenesis and Pathology The virus travels from the mouth to the parotid gland, where it undergoes primary multiplication. This is followed by a generalized viremia and localization in testes. ovaries, pancreas, thyroid, or brain. The ducts of the parotid glands show desquamation of the epithelium, and polymorphonuclear cells are present in the lumens. There are interstitial edema and lymphocytic infiltration.

35. Orchitis

36. PARAINFLUENZA VIRUS The parainfluenza viruses are paramyxoviruses with morphologic and biologic properties typical of the genus. They grow welt in primary monkey or human epithelial cell culture but poorly or not at all in the embryonated egg. They produce a minimal cytopathic effect in cell culture but are recognized by the hemadsorption method. Laboratory diagnosis may be made by the HI, CF, and Nt tests.

37. PIV STRUCTURE

38. MEASLES (Rubeola) Measles is an acute, highly infectious disease characterized by a maculopapular rash, fever, and respiratory symptoms. Properties of the Virus: Measles virus is a typical paramyxovirus. It lacks neuraminidase activity.

39. Measles virus

40. Koplik's spots

43. RESPIRATORY SYNCYTIAL (RS) VIRUS This labile paramyxovirus produces a characteristic syncytial effect, the fusion of cells in human cell culture. It is the single most serious cause of bronchiolitis and pneumonitis in infants. Properties of the Virus:RS virus does not hemagglutinate.

44. RSV- Structure immunofluoresent stain

45. RSV- syncytium formation

46. Pathogenesis and Pathology This disease is transmitted by coughing, sneezing, sharing wash cloths towels and other things with someone with RSV. This disease is extremely serious when it comes to children and infants under the age of 3 and elders. This disease can result in death.

47. Symptoms for this disease are: sneezing, runny nose, sore throat, low fever, common cold symptoms just more severe. Treatment: Supportive Fluids, oxygen, respiratory support, bronchodilators Antiviral Agents Ribavirin (Virazole), a synthetic guanosine analogue, given as an aerosol RSV Bronchiolitis- clinical features

48. Prophylaxis • Combination live virus vaccines (measles-mumps-rubella) • Live attenuated measles virus vaccine effectively prevents measles.

49. Genera of Picornaviruses