j dawson VIROLOGY Viral Basics V iruses are infectious particles consisting of RNA or DNA covered by a protein coat infect cells and use host metabolic machinery to replicate ID: 1039816
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1. VIROLOGY and MYCOLOGYDr. j. dawson
2. VIROLOGY
3. Viral Basics• Viruses are infectious particles consisting of RNA or DNA covered by a protein coat infect cells and use host metabolic machinery to replicate nucleic acid can be double stranded (ds) or single stranded (ss) can be enveloped or naked• Virions are mature virus particles that can be released into the extracellular environment• Host susceptibility is governed by the host cell and virus surface proteins (viral tropism) and cellular immunity
4. Viral Disease Patterns1. acute infections (e.g. adenovirus) host cells are lysed in the process of virion release some produce acute infections with late sequelae (e.g. measles virus induced subacute sclerosing panencephalitis)2. chronic infections (>6 mo): (e.g. HBV, HIV) host cell machinery is used to produce and chronically release virions
5. 3. latent infections viral genome remains latent in host cell nucleus can reactivate (e.g. HSV, VZV)
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10. CLASS 1To replicate the viral genome, DNA-dependent DNA polymerase enzymes (sometimes provided by the cell) copy both the (+) and (-) DNA strands producing dsDNA viral genomes. To produce viral mRNA molecules, host cell-DNA-dependent RNA polymerase enzymes copy the (-) DNA strand into (+) viral mRNA. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes.
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12. CLASS 2To replicate the viral genome, DNA-dependent DNA polymerase enzymes (usually provided by the cell) copy the (+) DNA strand of the genome producing a dsDNA intermediate. DNA-dependent DNA polymerase enzymes (again, usually provided by the cell) then copy the (-) DNA strand into ss (+) DNA genomes. To produce viral mRNA molecules, host cell-DNA-dependent RNA polymerase enzymes copy the (-) DNA strand into (+) viral mRNA. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes.
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14. CLASS 3To replicate the viral genome, viral RNA-dependent RNA polymerase enzymes (replicase) copy both the (+) RNA and (-) RNA strands of the genome producing a dsRNA genomes. To produce viral mRNA molecules, viral RNA-dependent RNA polymerase enzymes (transcriptase) copy the (-) RNA strand into (+) viral mRNA. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes.
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16. CLASS 4To replicate the viral genome, viral RNA-dependent RNA polymerase enzymes (replicase) copy the (+) RNA genome producing ss (-) RNA. Viral RNA-dependent RNA polymerase enzymes (replicase) then copy the (-) RNA strands producing ss (+) RNA viral genome. Translation can occur immediately due to the (+) RNA (mRNA). To produce more viral mRNA molecules, RNA-dependent RNA polymerase enzymes copy the (-) RNA strand into (+) viral mRNA. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes.
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18. CLASS 5To replicate the viral genome, viral RNA-dependent RNA polymerase enzymes (transcriptase) copy the (-) RNA genome producing ss (+) RNA. Transcriptase must be carried into the cell with the virion. Viral RNA-dependent RNA polymerase enzymes (replicase) then copy the (+) RNA strands producing ss (-) RNA viral genome. The (+) mRNA strands also function as viral mRNA and can then be translated into viral proteins by host cell ribosomes.
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20. CLASS 6To replicate the viral genome, viral reverse transcriptase enzymes (RNA-dependent DNA polymerases) copy the (+) RNA genome producing ss (-) DNA strands. Viral reverse transcriptase can also function as a DNA-dependent DNA polymerase enzymes and will copy the (-) DNA strands to produce a dsDNA intermediate. Reverse transcriptase must be carried into the cell with the viron. The viral DNA will move to the nucleus where it integrates into the cell’s DNA using the viral enzyme integrase which also must be carried into the host cell with the virion. Once in the host cell’s DNA, host cell DNA-dependent RNA polymerase enzymes then copy the ds (-) DNA strands to produce ss (+) RNA genomes. To produce viral mRNA molecules, host cell DNA-dependent RNA polymerase enzymes copy the ds (-) DNA strand into (+) viral mRNA. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes.
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22. CLASS 7To produce viral mRNA molecules, host cell-DNA-dependent DNA polymerase completes the missing DNA gaps. Viral mRNA can then be produced by host DNA-dependent RNA polymerase. The (+) viral mRNA can then be translated into viral proteins by host cell ribosomes. To replicate the viral genome, RNA-dependent DNA polymerase enzymes copy the (+) RNA strands producing (-) ssDNA, then the RNA-dependent DNA polymerase makes a (+) DNA complement.
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32. BREAK ANYONE OR PRESS ON?
33. MYCOLOGY
34. Fungal BasicsFungi are eukaryotic organisms, they can have the following morphologies1. yeast (unicellular)2. moulds, i.e. lamentous fungi (multicellular with hyphae)3. dimorphic fungi (found as mould at room temperature (25) but grow as yeast-like forms at body temperature(37))
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36. Mechanisms of Fungal Disease• Primary fungal infection by: overgrowth of normal oral (e.g. Candida species) inhalation of fungal spores traumatic inoculation into skin• Toxins produced by fungi (e.g. ingestion aflatoxins)• Allergic reactions to fungi (e.g. bronchopulmonary aspergillosis)
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41. Hypha (ae): Filaments originating from a germinating fungal spore or branching from other filaments with apical growth, lateral branching. Mycelium: A mat of hyphae, characteristic of the cultureRhizoid: Rootlike, branched hypha extending into the mediumSpherule: Large round, thick-walled structure containing spores
42. Dematiaceous: Having structures that are brown to black (due to melanotic pigment in the cell wall)Dimorphic: two distinct morphological forms. A mould phase at 25-300C and yeast phase when cultured at 35-370CGerm tube: Tubelike outgrowth from a conidium or spore; beginning of a hyphaHyaline: Clear, transparent, colourlessPhaeo prefix meaning dark (brownish or blackish)Phialide A cell that produces and extrudes conidia. Shaped like a flask or vase
43. SPORES Spores may be sexual or asexual. Spores germinate to produce new colonies. - Propagule that develops by sexual reproduction ( ascospore, basidiospore, or zygospore) or by asexual means within a sporangium (sporangiospore)A. SEXUAL SPORES: Develop from specialized cells in the mycelium as a result of nuclear fusion.
44. Basidiospores: - Sexual spores which develop exogenously on a club-shaped structure (basidium) found in Basidiomycetes Zygospores: Sexual spores produced by fusion of two identical cells as in Zygomycetes Oospores: Sexual spores produced by fusion of two unlike cells found in Phycomycetes also
45. ASEXUAL SPORESSpores which develop without nuclear fusion. 1. Thallospores: These derive directly from, or as part of the original hyphae (without nuclear fusion). The following are types of thallospores:BlastosporesChlamydosporesConidiospores (conidia)MacroconidiaMicroconidiaArthrosprores (arthroconidia)
46. SPORANGIOSPORES - Spores which develop endogenously within a swollen structure - Sporangium on the end of a hypha. Occurs in Phycomycetes . (obselete term for non-sepated fungi) Conidium: An asexual propagule that forms on the side or the end of the hypha or conidiophore Chlamydoconidium: An enlarged rounded conidium that is thick walled due to concentration of protoplasm. May be located at the end of the hypha (terminal) or along the hypha (intercalary), singly or in chains.
47. YeastBudding: A process of asexual reproduction in which the new cell develops as a similar outgrowth from the older parent cell (yeast or yeast-like fungi) a.k.a. BLASTOSPORES
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49. Superficial Mycoses1) Pityriasis versicolor (Liver spots) - Aetiology – Malassezia furfur2) Tinea Nigra - skin of the palm or sole with persistent slowly growing brown or black patches. They are slightly scaly and do not itch or sting, mostly common in tropical regions and often infects those with a tendency to excessive sweating (hyperhidrosis).
50. Dermatophyes (Ringworm fungi)- Affect skin, nail and hair - structures with an abundance of keratin. These fungi are: Trichophyton - skin, nail and hair Epidermophyton – skin and nail Microsporum – skin and hair
51. Tinea capitis - ringworm of scalpTinea barbae - chronic folliculitis of beard, neck or faceTinea corporis - infection of glabrous skinTinea manus - involves interdigital spaces and palmer surfaces of handTinea unguium - infection of nails Tinea cruris - infection of groin ( commonly called jock itch)Tinea pedis - infection of feet (commonly called athlete’s foot)
52. Candidiasis Pathogenic Yeast-like fungi, Endogenous infection - Include skin infections, nail infection, thrush, oesophagitis, enteritis, pneumonia, septicemia
53. Subcutaneous MycosisSporotrichosis – Sporothrix schenckii - Maduromycosis (madura foot) – caused by a variety of fungi - Chromoblastomycosis (granulomatous infection of skin) - cause by dematiaceous fungi
54. MYCETOMASubcutaneous swelling following minor trauma. Later, sinuses that discharge purulent and seropurulent exudates containing grains which are fungal colonies are formed. Destruction of deeper tissues, and deformity and loss of function in the affected limbs may occur in late stages.CHROMOBLASTOMYCOSES:minor trauma to the skin, usually from vegetative material such as thorns or splinters; this trauma implants fungi in the subcutaneous tissue. In many cases, the patient will not notice or remember the initial trauma, as symptoms often do not appear for years
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56. 1) Superficial - Skin scrapings ( Wood’s lamp-Tinea versicolor/Liver spots) - Epilated hair ( use sterile forceps, black piedra – demateacious fungus) 2) Cutaneous - Skin scrapings (Active periphery, tops of vesicles) - Epilated hairs (Wood’s lamp) - Nail clippings (subungual detritus, avulsed nail).
57. Wood’s LampBright green to yellow-green fluorescence of hairs infected by M. canis, M. audouinii, M. rivalieri, and M. ferrugineum Dull green or blue-white color of hairs infected by T. schoenleinii.Short stubby and brittle hairs without fluorescence should still be removed for fungal culture and identification.Malassezia furfur emits a yellowish-white or copper-orange fluorescence. Wood's lamp can detect sub-clinical infection and the extent of infection.
58. 3) Subcutaneous Dematiaceous fungi (Some dematiaceous) Aspirates, scrapings, surgical tissues/biopsy Eumycotic & actinomycotic mycetoma Pus, exudates, biopsy material 4) Systemic - sputum, bronchoalveolar lavage, transtracheal aspirate, lung biopsy, Pus or exudates, mucocutaneous lesions, biopsy, whole blood (H. capsulatum)
59. 5) OpportunisticBiopsy material, transtracheal aspirate, sputum(early morning) Infected nails, eg (Aspergillus, C. albicans)Blood culture (Pseudallescheria boydii or Fusarium sp)CSF (C. neoformans)Purulent exudates/bronchial washes/body fluids etc (Actinomyces isrealii)
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