Viruses and prion


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Viruses and prion

  1. 1. <ul><li>Viruses and Prions </li></ul>
  2. 2. Objectives: <ul><li>1. Discuss the key differences between prokaryotic and eukaryotic cellular components </li></ul><ul><li>2. Describe the basic structure of bacteria. </li></ul><ul><li>3. Discuss the taxonomy of bacteria. </li></ul><ul><li>4. Explain how do organisms get their names. </li></ul>
  3. 3. VIRUSES * One of the smallest forms of microorganisms and infects other forms of live: Animal --- Plants --- Bacteria * They can cause oral and orofacial disease - - produces oral signs of systemic infection and transmitted to patients and dental staff
  4. 4. Main Features: * Small size (10-100nm). * Genome: either DNA or RNA but never both- ss (single strand) or ds (double strand), linear or circular. * Metabolic activity: Obligate intracellular parasites.
  5. 5. Structure <ul><li>* Viruses consist of a nucleic acid core containing the viral genome, surrounded by a protein shell called a capsid. </li></ul><ul><li>* The capsid consist of repeating units of one or more protein molecules called capsomeres. </li></ul><ul><li>* Nucleic acid + Capsid + Capsomere = Nucleocapsid </li></ul><ul><li>* Nucleocapsid may be naked or enveloped within </li></ul><ul><li>a lipoprotein sheath. </li></ul><ul><li>* In enveloped viruses the protein units called capsomeres. </li></ul>
  6. 6. Viral Nucleic acid <ul><li>DNA or RNA never both. </li></ul><ul><li>The RNA, in turn, may be ss or ds and the genome may consist of one or several molecules of nucleic acid. </li></ul><ul><li>If the genomes composed of a single molecules , this may linear or have a circular configuration. </li></ul>
  7. 7. Viral Protein <ul><li>Made up of 2 or 3 different polypeptide chains (some only 1 polypeptide). </li></ul><ul><li>Virion surface proteins may have a special affinity for receptors on the surface of host cells. </li></ul>
  8. 8. <ul><li>Viral lipid and Carbohydrate: The lipids and carbohydrates of viruses are found in the envelopes and mostly derived from the host cells. </li></ul><ul><li>Virus symmetry: arranging of nucleocapsids: </li></ul><ul><li>1- Icosahedral symmetry: ex. Herpesviruses. </li></ul><ul><li>2- Helical symmerty: Most mammalian RNA viruses. </li></ul><ul><li>3- Complex symmetry: ex. Poxviruses. </li></ul>
  9. 9. Taxonomy <ul><li>The attributes used in classification: </li></ul><ul><li>Symmetry </li></ul><ul><li>Presence or absence of an envelope </li></ul><ul><li>Nucleic acid composition (DNA or RNA). </li></ul><ul><li>The number of nucleic acid strands </li></ul><ul><li>polarityde </li></ul>
  10. 10. DNA viruses <ul><li>Papovaviruses: </li></ul><ul><li>Small, icosahedral DNA viruses with capacity to produce tumours in vivo and to transform cultured cell lines. </li></ul><ul><li>Papilomavirus: </li></ul><ul><li>This genus contain human serotypes which cause benign skin tumours or warts and both oral and skin papilomas (e.g. hand and plantar warts)- it is now known that the papilomaviruses may be involved in genital and oral cancers. </li></ul>
  11. 11. DNA viruses <ul><li>Adenoviruses: </li></ul><ul><li>Icosahedral DNA viruses, commonly associated with respiratory and eye infections in humans. </li></ul><ul><li>Syndromes associated with adenoviruses include: </li></ul><ul><li>* acute febrile pharyngitis (primarily in infants </li></ul><ul><li>and children). </li></ul><ul><li>* acute adult respiratory disease, ranging from </li></ul><ul><li>phryngitis to pneumonia. </li></ul><ul><li>* ocular infections. </li></ul>
  12. 12. DNA viruses <ul><li>Herpesviruses: </li></ul><ul><li>Predominant viral cause of oral infections in humans, often the infections are recurrent, and latent. </li></ul>
  13. 13. Structure of Herpesviruses <ul><li>Enveloped, linear, double-stranded DNA molecule. </li></ul><ul><li>Has over 100 members </li></ul><ul><li>Spread among vertebrates and invertebrates </li></ul><ul><li>Unstable at room temperature </li></ul><ul><li>Rapidly inactivated by lipid solvents ex: alcohol. </li></ul>
  14. 14. <ul><li>During Reproduction: </li></ul><ul><li>Typical and highly intracellular inclusions are found in cells that have undergo active virus replication. </li></ul><ul><li>|* Polykaryotes or giant cells readily appear in tissue lesions. </li></ul>
  15. 16. <ul><li>Different herpesviruses cause a variety of infections diseases, some localized and some generalized, often with vesicular rash. </li></ul><ul><li>Herpesviruses establish latent infection, which can be readily reactivated by immunosuppression. </li></ul><ul><li>The herpesviruses that commonly infect humans can be distinguished by their antigenic and genomic profiles. </li></ul><ul><li>They cannot be differentiated by electron microscopy owing to identical capsid morphology. </li></ul>
  16. 17. Type of herpesviruses that can cause infection in oral and perioral tissues: <ul><li>Herpes simplex virus </li></ul><ul><li>Herpes zoster virus </li></ul><ul><li>Epstein-Bar virus </li></ul><ul><li>Human cytomegalovirus </li></ul><ul><li>Herpesviruses 6 and 8 </li></ul>
  17. 18. DNA Viruses <ul><li>Poxviruses: </li></ul><ul><li>Largest viruses to infect humans or animals. </li></ul><ul><li>Cause: Molluscum contagiosum in human </li></ul><ul><li>Human occasionally acquire infection by animal poxviruses, e.g. cowpox. </li></ul>
  18. 19. DNA Viruses <ul><li>Parvoviruses: </li></ul><ul><li>Icosahedral viruses </li></ul><ul><li>ss DNA </li></ul><ul><li>The B19 virus is responsible for a febrile illness. particularly in children, manifesting as a maculopapular rash. </li></ul>
  19. 20. DNA Viruses <ul><li>Hepdnaviruses: </li></ul><ul><li>small, spherical DNA viruses causing hepatitis. </li></ul><ul><li>Chronic liver infections and possibly liver cancer. </li></ul><ul><li>They are of particular interest in dentistry because of their mode of transmission via blood and saliva. </li></ul>
  20. 21. RNA Viruses <ul><li>Picornaviruses: </li></ul><ul><li>Smallest family of RNA viruses </li></ul><ul><li>Include the genus: Enteroviruses </li></ul><ul><li>Respiratory infections and pharyngitis caused by human enteroviruses (coxsackie A). </li></ul><ul><li>Coxsackie B cause more serious disease: carditis, which may be lethal in the newborn. </li></ul>
  21. 22. RNA Viruses <ul><li>Orthomyxoviruses: </li></ul><ul><li>Have tubular nucleocapsid and lipoprotein envelope. </li></ul><ul><li>Influenza A viruses of birds, mammals and human are in this category. </li></ul>
  22. 23. RNA Viruses <ul><li>Paramyxoviruses: </li></ul><ul><li>Large, pleomorphic envelopd RNA viruses. </li></ul><ul><li>This family contains four common and important pathogens: </li></ul><ul><li>Measles, mumps, parainfluenza and respiratory syncytial viruses. </li></ul>
  23. 24. RNA Viruses <ul><li>Retroviruses: </li></ul><ul><li>Large, spherical enveloped </li></ul><ul><li>RNA tumour viruses characterized by </li></ul><ul><li>Unique genome, a unique enzyme and a unique mode of replication. </li></ul>
  24. 25. Retroviruses: <ul><li>Viral genome: </li></ul><ul><li>The viral genome RNA is first transcribed into DNA by a virus-specific enzyme, reverse transcriptase. </li></ul><ul><li>This DNA can serve as a templet for mRNA synthesis. </li></ul>
  25. 26. Medically important viruses in this family <ul><li>HIV TYPES 1 and 2. </li></ul><ul><li>HTLV-I (Human T-cell leukaemia virus) cause tumours. </li></ul><ul><li>ATLL (adult T-cell leukaemia-lymphoma </li></ul><ul><li>HTLV-II associated with hairy cell leukaemia. </li></ul>
  26. 27. Viral Replication <ul><li>1- Adsorption or attachment of the virus particle to the specific receptors of the host cell plasma membrane. </li></ul><ul><li>2- Penetration or uptake: the process by which the virus or its genome enters the host cell cytoplasm by three mechanisms: </li></ul><ul><li>Endocytosis, fusion and translocation. </li></ul>
  27. 28. <ul><li>3- Uncoating and eclipse: The eclipse phase= begins with uncoating of the lipid membrane and protein capsid surrounding the nucleic acid viral core. </li></ul><ul><li>4- Transcription: synthesis of viral mRNA then transcription and synthesis of viral proteins. </li></ul><ul><li>5- Synthesis of viral components. </li></ul><ul><li>6- Assembly </li></ul><ul><li>7- Release </li></ul>
  28. 29. Prion and prion-induced disease <ul><li>Proteinaceus infectious particles </li></ul><ul><li>Major features: </li></ul><ul><li>1- They are neither viruses nor viroids. </li></ul><ul><li>2- do not have either DNA or RNA </li></ul><ul><li>3- have ability to self replicate </li></ul><ul><li>4- very long incubation period </li></ul><ul><li>5- highly resistant to heat, chemical agents and irradiation </li></ul><ul><li>6- Iatrogenic transmission of prion disease by neurological instruments has been reported. </li></ul>
  29. 30. pathogenesis <ul><li>Prions appear to replicate incessantly, first in lymphoid tissue, then brain cells </li></ul><ul><li>The vacuoles in brain cells give rise to the sponge-like appearance of the brain. </li></ul>