MYCOVIRO

• Virus


  A submicroscopic, strict obligate intracellular parasite, capable of infecting any animal, plant, or bacterial cell
• Viruses are found in every ecosystem
• Viral tropism


  Virus types are very specific, and each has a limited number of hosts it can infect

  
• Capsid


  The protein shell, or coat, that encloses the nucleic acid genome
• Capsomeres


  Morphologic units seen in the electron microscope on the surface of icosahedral virus particles, representing clusters of polypeptides

  
• Defective virus


  A virus particle that is functionally deficient in some aspect of replication
• Envelope


  A lipid-containing membrane that surrounds some virus particles, acquired during viral maturation. Virus-encoded glycoproteins are exposed on the surface as projections called peplomers

  
• Nucleocapsid


  The protein-nucleic acid complex representing the packaged form of the viral genome

  
• Structural units


  The basic protein building blocks of the coat, often referred to as a protomer
• Subunit


  A single folded viral polypeptide chain
• Virion


  The complete virus particle, which in some instances is identical with the nucleocapsid, and in more complex virions includes the nucleocapsid plus a surrounding envelope

  
• Virus particles, referred to as virions, consist of an inner nucleic acid core (RNA or DNA), a protein coat (capsid), and in some larger viruses, a lipid-containing envelope

  
• DNA virus


  Viruses which contain DNA as genetic material

  
• RNA virus


  Viruses containing RNA as genetic material

  
• Unlike other living cells where ds DNA is always a genetic material, a viral genome may consist of linear or circular ds DNA, single stranded DNA, ss linear RNA or ds linear RNA

  
• Capsid


  The outer layer, also known as coat or shell, that serves as an impenetrable shell around the nucleic acid core and helps introduce the viral genome into the host cell during infection
• Capsomeres


  The protein coat or capsid is made up of a number of morphologically similar subunits called capsomeres, each further composed of protomers, arranged precisely and tightly together in a repetitive pattern to form complete capsids
• The number of capsomeres in a capsid varies from virus to virus
• Virus nucleocapsid


  The complete complex of nucleic acid and protein coat of a virus particle

  
• Naked virus


  A virus without an envelope
• Envelope


  A bilayer of lipoprotein and glycoprotein, acquired by the progeny virus from the host cell during virus release by budding process. Some viruses have glycoprotein spikes called peplomers, involved in binding to host cells
• Enzymes


  Some viruses contain enzymes that play a central role during the infection process, e.g. lysozyme in bacteriophages, and reverse transcriptase in retroviruses
• Symmetry of viruses


  • Helical (spiral)
  • Icosahedral (cubical)
  • Complex
  • Binal

  
• Helical (spiral) symmetry


  The capsomere and nucleic acid are wound together to form helical or spiral tube-like structures
• Icosahedral (cubical) symmetry


  An icosahedron is a polygon with 12 vertices, 20 facets, and 30 edges, with each facet being an equilateral triangle. Icosahedral capsids are the most stable and found in many human pathogenic viruses
• Complex symmetry


  Some viruses are more complex, being composed of several separate capsomeres with separate shape and symmetry, not having either icosahedral or helical symmetry

  
• Binal symmetry


  A type of complex symmetry, where viruses like T-phages have an icosahedral head and helical tail

  
• Steps of virus infection

  1. Attachment

  2. Entry

  3. Replication and assembly

  4. Release/egress
• Attachment


  A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope
• Entry


  The nucleic acid of bacteriophages enters the host cell naked, leaving the capsid outside. Plant and animal viruses can enter through endocytosis or direct fusion of the viral envelope with the cell membrane. Once inside, the viral capsid is degraded and the viral nucleic acid is released
• Replication and assembly


  The replication mechanism depends on the viral genome. DNA viruses usually use host cell proteins and enzymes, while RNA viruses usually use the RNA core as a template. Exceptions include retroviruses that reverse transcribe their RNA genome into DNA

  
• Release/egress


  The last stage of viral replication, where the new virions produced in the host are released to infect adjacent cells and repeat the replication cycle
• Baltimore classification


  A classification system that places viruses into one of seven groups depending on their nucleic acid (DNA or RNA), strandedness, sense, and method of replication

  
• Viruses are obligate intracellular parasites and cannot grow on inanimate media, requiring living cells for replication, which can be provided by inoculation in live animals
• The laboratory animals used for viral culture include monkeys, rabbits, guinea pigs, rats, hamsters, and mice, with the choice depending on the type of virus
• Systemic mycoses


  Infections that affect the internal organs/deep tissues in the body, primarily involving the respiratory system, caused by dimorphic fungi that can infect healthy and immunocompetent individuals
• Blastomyces dermatitidis


  • Causes suppurative and granular infection, with primary infection exhibiting flu-like symptoms. Virulence factors include a weak antigen, small thick-walled spores easily carried by air, and easy adherence to host tissues
• Laboratory diagnosis of blastomycosis

  Examination of tissue or purulent material may reveal large, spherical, refractile yeast cells. Culture at 22°C produces white, tan, or brown colonies, while at 37°C it produces characteristic broad-based budding yeast cells

  
• Blastomycosis


  Caused by Blastomyces dermatitidis
• Laboratory diagnosis of blastomycosis

  1. Examination of tissue or purulent material

  2. Use of KOH (10%) or calcofluor white

  3. Examination of mould phase