MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 4 OF 4 — INTERFERON MECH
--- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 4 OF 4 --- INTERFERON MECHANISM Section B essay question in 2021/2022 — must know. What interferons are Glycoproteins produced by virus-infected cells Part of innate immune response Act on neighboring cells to prevent viral spread How interferons help virus-infected cells fight infection Virus infects a cell and triggers that cell to produce interferons alpha and beta Interferons are released and bind to receptors on neighboring uninfected cells This binding activates JAK-STAT signalling pathway in neighboring cells Neighboring cells produce antiviral proteins — including protein kinase R and RNase L Protein kinase R: inhibits protein synthesis in infected cells, preventing viral replication RNase L: degrades viral RNA Neighboring cells also upregulate MHC class I molecules — enhancing recognition by cytotoxic T cells NK cells are also activated by interferons to kill infected cells Net effect: limits viral spread to surrounding cells Types of interferons Interferon alpha and beta: produced by virus-infected cells, act on neighboring cells Interferon gamma: produced by T cells and NK cells, activates macrophages --- ATTENUATED VACCINES — HOW THEY PROTECT Section B essay question — child born in Muranga vaccinated with attenuated vaccine. What an attenuated vaccine is Contains live but weakened form of the pathogen Weakened by repeated passage in laboratory conditions Cannot cause full disease in healthy individual How it protects Attenuated organism enters body and replicates at low level Replication stimulates both humoral immunity — antibody production And cell-mediated immunity — T cell activation B cells produce specific antibodies against the pathogen Memory B cells and memory T cells are formed On exposure to real pathogen, memory cells mount rapid and strong immune response Pathogen is eliminated before disease develops Advantages over inactivated vaccines Stronger and longer lasting immunity Often single dose sufficient Stimulates both arms of immune system Disadvantage Risk of reversion to virulent form — especially OPV --- TRUE PATHOGENIC FUNGI VS OPPORTUNISTIC FUNGI Section B essay question in 2021/2022. True pathogenic fungi Cause disease in both healthy and immunocompromised individuals Have specific virulence mechanisms Geographically restricted — endemic mycoses Examples: Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis Infection acquired by inhalation of spores from environment Primary infection in lungs even in healthy persons Opportunistic fungi Cause disease ONLY or mainly in immunocompromised individuals Part of normal flora or ubiquitous in environment Have low inherent virulence Examples: Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, Mucor species Take advantage of defective host defenses General consequences to human host Superficial infections: cosmetic only, no systemic effect Cutaneous infections: discomfort, disfigurement, secondary bacterial infection Subcutaneous infections: chronic granulomatous disease, tissue destruction, lymphatic spread Systemic infections: life threatening, multi-organ involvement, high mortality in immunocompromised --- MYCETOMA — PATHOGENESIS AND LABORATORY DIAGNOSIS Essay question in 2017/2018 — high priority. Causative agents Eumycetoma: caused by true fungi — Madurella mycetomatis, Pseudallescheria boydii Actinomycetoma: caused by bacteria — Nocardia species, Actinomadura species Pathogenesis Traumatic inoculation of organism into skin — thorn prick, splinter, walking barefoot Organism establishes in subcutaneous tissue Slowly progressive granulomatous inflammation Formation of grains/granules — aggregates of organism Sinus tracts form and open to skin surface, discharging grains Spreads to involve deeper tissues, muscle, bone Bone destruction in advanced disease Does NOT spread via lymphatics or bloodstream — remains local Clinical features Painless swelling of affected area — usually foot Draining sinus tracts Discharge containing grains — color depends on organism Deformity of affected part Laboratory diagnosis Macroscopic: examine grains from discharge — color, size, texture Microscopy: KOH preparation of grains, Gram stain Culture: Sabouraud agar — identify organism Histopathology: tissue biopsy shows granuloma with grains Imaging: X-ray to assess bone involvement Eumycetoma vs Actinomycetoma comparison Eumycetoma: fungal, wide grains, does not respond to antibiotics, responds to antifungals and surgery Actinomycetoma: bacterial, thin filaments in grains, responds to antibiotics — sulfonamides, streptomycin --- DERMATOPHYTOSIS — FIVE TYPES Essay question in mycology CAT — discuss five types. Tinea pedis — Athlete's foot Site: toe webs, soles of feet Features: itchy, white flaky patches, inflammation, skin fissures, stinging Causes: wearing tigh