ID

• Viruses


  Cannot replicate without a host and are susceptible to environmental factors such as heat, UV light, and desiccation, though some viruses like those spread via fecal-oral route are more resistant
• Portals of entry for viruses in mammalian hosts


  • Eyes (conjunctiva)
  • Mouth
  • Respiratory tract
  • Alimentary canal
  • Skin (via abrasion/injury, arthropod vectors, animal bites)
  • Urogenital tract
  • Placenta
• Skin as a barrier


  Overcome by vectors that deliver viruses directly into the bloodstream or to subcutaneous tissues
• Viral dissemination within the host


  1. Direct cell-to-cell contact

  2. Bloodstream spread (active or passive viraemia)

  3. Nervous system spread (typically after a viraemia phase)
• Viral tropism


  • Specificity of a virus for certain cell types influenced by factors such as the presence of specific receptors, the host cell's ability to support virus replication, physical barriers, and the host's innate immune defenses
• Mechanisms of viral shedding and transmission


  • Horizontal (direct contact, saliva, blood, semen, and other body fluids)
  • Vector-borne (especially for arboviruses transmitted by insects like mosquitoes and ticks)
  • Vertical (from mother to child during pregnancy, childbirth, or via breast milk)
• Viruses


  Cannot replicate without a host and are susceptible to environmental factors such as heat, UV light, and desiccation, though some viruses like those spread via fecal-oral route are more resistant
• Portals of entry for viruses in mammalian hosts


  • Eyes (conjunctiva)
  • Mouth
  • Respiratory tract
  • Alimentary canal
  • Skin (via abrasion/injury, arthropod vectors, animal bites)
  • Urogenital tract
  • Placenta
• Skin as a barrier


  Overcome by vectors that deliver viruses directly into the bloodstream or to subcutaneous tissues
• Viral dissemination within the host


  1. Direct cell-to-cell contact

  2. Bloodstream spread (active or passive viraemia)

  3. Nervous system spread (typically after a viraemia phase)
• Viral tropism


  • Specificity of a virus for certain cell types influenced by factors such as the presence of specific receptors, the host cell's ability to support virus replication, physical barriers, and the host's innate immune defenses
• Mechanisms of viral shedding and transmission


  • Horizontal (direct contact, saliva, blood, semen, and other body fluids)
  • Vector-borne (especially for arboviruses transmitted by insects like mosquitoes and ticks)
  • Vertical (from mother to child during pregnancy, childbirth, or via breast milk)
• Signs and symptoms of viral infections


  • Fatigue and fever
  • Rashes
  • Diarrhea
  • Neurological signs
• Diagnostic methods for viral infections


  • Virus culture and serology (culturing the virus in specific cell types, serological tests like ELISA)
  • Molecular diagnostics (PCR for DNA viruses, RT-PCR for RNA viruses)
• Antiviral drugs


  Target specific stages of the viral life cycle to inhibit replication, challenges include drug resistance and side effects on host cells
• Development of antivirals


  1. Screening potential compounds

  2. Rational drug design based on viral protein structures

  3. Extensive testing through clinical trials
• Vaccination types


  • Live attenuated and inactivated vaccines
  • Subunit, VLP, and nucleic acid vaccines
• Passive immunization and immunomodulators


  Provide immediate immune protection through the administration of antibodies and substances that modify immune responses, respectively
• Bacteriophages


  Viruses that specifically infect prokaryotes (bacteria and archaea), typically with a high specificity for their host species or strain
• Structural types of bacteriophages


  • Head-tail
  • Helical
  • Icosahedral
• Phage replication cycle


  1. Adsorption

  2. Penetration

  3. Transcription and translation

  4. Replication

  5. Assembly and release
• Phage genome classes in T7


  • Class I (sets up the cell for phage infection)
  • Class II (includes genes required for DNA replication)
  • Class III (codes for structural components and lytic enzymes)
• Lysogenic cycle


  The phage genome integrates into the bacterial chromosome as a prophage, which can remain dormant until triggered by environmental factors
• Lytic cycle


  Characterized by the active replication of phages followed by the lysis of the host cell to release progeny phages
• Medical and research applications of bacteriophages


  • Phage therapy
  • Phage typing
  • Phage display
• Plaque assay


  Used to measure virus concentration in terms of plaque-forming units (PFU) per milliliter
• Quantal assay


  Measure lethal doses (LD50) to determine the dose at which 50% of exposed organisms die, providing information on viral virulence
• Hemagglutination


  Based on the ability of certain viruses to agglutinate red blood cells, used for easy and rapid virus quantification
• Techniques for studying virus structure


  • Electron microscopy and X-ray crystallography
  • Density gradient centrifugation
• Techniques for detecting viruses


  • Serological methods (detect viral proteins using antibodies)
  • Viral nucleic acid detection (qPCR and sequencing)
• Functional studies of viruses


  • Tissue culture and animal studies
  • Rational drug design
• Ellis & Delbrück (1939) demonstrated that virus replication occurs in phases within the infected host
• Luria & Delbrück (1943) showed that bacterial resistance to viruses results from spontaneous mutations rather than being induced by the viruses
• Hershey & Chase (1952) confirmed that DNA, not protein, is the genetic material in phages through experiments using radioactive isotopes
• Fiers et al. (1976) sequenced the genome of bacteriophage MS2, marking the beginning of molecular genetics and genomics
• Virology techniques are fundamental in advancing our understanding of viruses, from basic research to clinical applications, enabling the development of strategies to combat viral diseases effectively
• Poxvirus subfamilies


  • Chordopoxvirinae (infect vertebrates)
  • Entomopoxvirinae (infect invertebrates)
• Poxvirus virion structure


  • Oval or brick-shaped, measuring between 200-400 nm, with a complex and detailed structure that includes over 100 virus-encoded proteins
  • External surface features ridges arranged in parallel rows, sometimes helically
  • Highly resistant to environmental degradation
• Poxvirus genome


  • Linear dsDNA, unusually large for viruses, ranging from 130-375 kilobases, encoding around 200 proteins
  • Inverted terminal repeats (ITRs) at both ends are crucial for replication and stability
• Poxvirus entry mechanism


  Employs a sophisticated Entry-Fusion Complex that includes multiple protein types for attachment and membrane fusion