BIOMED SCIE Lecture 14 Fungi and Viral Pathogens

• Pathogenic Fungi


  Eukaryotes with chitin cell walls that use organic chemicals for energy, consisting of masses of mycelia (networks of branched hyphae)
• Fungal Diseases (Mycoses)


  • Superficial mycoses: Localized, e.g., hair shafts
  • Cutaneous mycoses: Affect hair, skin, and nails
  • Subcutaneous mycoses: Beneath the skin
  • Systemic mycoses: Deep within body
• Fungi as parasites


  • Toxic metabolic products from fungal growth in host
  • Allergic response- fungal growth in homes
  • Trichothecene toxins inhibit protein synthesis
  • Proteases
  • Capsule prevents phagocytosis
• Pathogenic Fungi


  • Fusarium
  • Candida albicans (skin)
  • Trichophyton
  • Cryptococcus neoformans - meningitis
• Ergot toxin


  Claviceps purpurea - ergotamine, killed 40,000 in France in 944, the Great Fear, characterized by gangrene, nervous spasms, burning sensations, hallucinations, and temporary insanity
• Aflatoxin


  Aspergillus - can be carcinogenic
• Mycotoxins


  Neurotoxins: Phalloidin, amanitin - Amanita phalloides, also known as deathcap
• Algae


  • Contain chlorophyll and carry out oxygenic photosynthesis
  • Most are microscopic but some can be macroscopic such as seaweeds
  • Large and diverse group
• Pathogenic Algae - Red Tide

  • Dinoflagellates Gonyaulax - neurotoxin kills fish and humans but harmless to shellfish
  • Pfeisteria - neurotoxin causing lesions, has been known to kill billions of fish
• Viruses


  • Acellular infectious particles consisting of DNA or RNA core surrounded by a protein coat, which may be enclosed in a lipid envelope
  • Replicated only when in a living cell
• Phages


  • Bacteriophages are the most common biological entities on earth
  • Have incredible specificity leading to emergence of phage therapy
  • Have lytic or lysogenic life cycles
• Viruses


  • Obligate intracellular parasites that can replicate only within a host cell
  • Each virus has a host range, a limited number of host cells that it can infect
• Viruses


  1. Penetrate and grow inside host

  2. Attach onto host cell and then enter

  3. Effect host cell plasma membrane

  4. Inhibit host DNA/RNA, protein synthesis

  5. Can cause a Cytopathic effect (CPE)
• Influenza Virus


  Respiratory infection, H - Haemagglutinin, N - Neuraminidase
• Prions


  • Slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals
  • Propagate by converting normal proteins into the prion version
• Prion diseases


  • Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans
• Prion disease agent


  • Agent insensitive to UV irradiation
  • Distinct from conventional virus
  • Devoid of DNA or RNA
  • Composed primarily, even uniquely of a protein called Prion
• Prion conversion


  Normal protein -> Original prion -> New prion -> Aggregates of prions
• Coronaviruses


  • Diverse family of enveloped positive-sense single-stranded RNA viruses that infect humans, other mammals and avian species
  • COVID-19 caused by SARS-Cov2, related to SARS-Cov and MERS-Cov
• Biology and pathogenesis of SARS-Cov2 similar to SARS and MERS
• Vaccine candidates and studies completed for SARS and MERS prior to pandemic
• Vaccine Targets


  • Spike protein already known from studies on SARS-Cov and MERS-Cov
  • 4 different proteins
  • Data from studies in animal models administered certain vaccine constructs against other coronaviruses (SARS-CoV and MERS-CoV) raised concerns of a theoretical risk for COVID-19 vaccine-associated enhanced respiratory disease (ERD)
  • Poor immunogenicity from M + E proteins
  • N protein vaccination led to ERD
• Most fungi are non pathogenic but many pathogenic fungi exist
• Viruses are obligate parasites which are fast evolving with specific targets
• Prions are proteins which can convert others to a pathogenic form
• The Covid-19 Pandemic highlights the ever increasing importance of infection biology