1 / 9

NAJRAN UNIVERSITY College of Medicine

NAJRAN UNIVERSITY College of Medicine. Microbiology &Immunology Course Lecture No. 19. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. Virus-cell interactions Replication Viruses multiply only in living cells The replication cycle consists of the following steps:

osric
Download Presentation

NAJRAN UNIVERSITY College of Medicine

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 19 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. Virus-cell interactions • Replication • Viruses multiply only in living cells • The replication cycle consists of the following steps: • 1- Attachment (adsorption) • Viral replication starts with interaction of the virus with specific receptors on the cell surface • Receptor molecules differ for different viruses (viral tropism) • Antiviral antibodies can inhibit this process

  3. 2- Penetration (Engulfment) • Non-enveloped viruses penetrate the host cell by a process of phagocytosis forming a cytoplasmic vacuole that will dissolve releasing the nucleocapsid into the cytoplasm • Enveloped viruses penetrate the cell by fusion of the viral envelope with the cell membrane releasing the nucleocapsid into the cytoplasm

  4. 3- Uncoating • It is the physical separation of viral nucleic acid from its capsid • 4- Eclipse phase • During this period (some hours), several enzymes are produced by the host cells under control of viral genome • The cell metabolism is now directed to the synthesis of new viral particles • This phase ends with the formation of the infectious virus

  5. 5- Assembly • Viral nucleic acid becomes surrounded by its capsid to form the mature virion (nucleocapsid) • 6- Release • Release of viruses to extracellular environment either by cell lysis or by budding through cell membrane leaving the host cell intact • Enveloped viruses mature by a budding process

  6. Inclusion bodies: • They are virus specific structures produced in the course of viral replication. (Areas of viral assembly) • Inclusion bodies may be: • Intranuclear: e.g. herpes viruses • Intracytoplasmic: e.g. pox viruses • In both: e.g. measles virus • Their presence in the cells is diagnostic of: • Negri bodies in Rabies • Guarnieri bodies in small pox • Torr’s bodies in yellow fever

  7. Pathogenesis of viral infections: • The outcome of virus-cell interaction may be: • Cell death or lysis • Abortive infection: No synthesis of new viral particles. Viral replication is blocked • Latent infection: The viral genome persist inside the host cell for a period. There will be flare-up of clinical disease • Transformation: The host cell will acquire new characters leading to rapid growth and malignancy

  8. Viral infections may be: • Superficial: short incubation period – No invasion. E.g. Influenza viruses, Rota virus • Systemic: After viral entry, it will spread to local lymphoid tissues followed by viraemia and spread to target organs. • Examples: • Skin & M.M. in measles and chicken pox • Liver in hepatitis viruses • Meninges in enterovirus meningitis

  9. Persistent: The virus will persist for a long period. Three types of persistent viral infections: • 1- Chronic infection: leading to chronic diseases as in HBV and HCV • 2- Latent infection: The virus persists silent for a period of time with intermittent flare-up. E.g., measles • 3- Slow virus infection: A very long incubation period, gradual onset and progressive course. E.g., AIDS

More Related