Medical Microbiology III Exam: Viruses, OmpathStudy

UNIT CODE: BMM1301 MEDICAL MICROBIOLOGY III Mount Kenya University — School of Medicine Main Exam Date: Mon 15th April, 2019 Time: 2 Hours Instructions: Answer ALL questions in Section A and ONE question in Section B --- SECTION A (40 MARKS) Q1. State three criteria for virus classification (6 marks) Biological properties (host range, transmission) Physical/chemical properties (nucleic acid type, capsid shape) Pathological properties (tissue tropism, pathogenicity) --- Q2. With examples, define emerging and re-emerging viral diseases (6 marks) Emerging: New viruses appearing in a population for the first time — e.g. HIV, Ebola, Zika Re-emerging: Previously controlled diseases resurfacing — e.g. Polio, Cholera, Dengue Often linked to ecological disruption, travel, immunosuppression, or mutation --- Q3. State unique symptom and transmission vector for each: (6 marks) (a) Zika virus disease Unique symptom: Microcephaly in newborns (congenital) Vector: Aedes mosquito (b) Ebola Unique symptom: Hemorrhagic fever with massive bleeding Vector: Direct contact with infected blood/body fluids; fruit bats (reservoir) (c) Dengue fever Unique symptom: "Breakbone fever" — severe myalgia/arthralgia + thrombocytopenia Vector: Aedes aegypti mosquito --- Q4. Differentiate black piedra and white piedra (6 marks) Feature Black Piedra White Piedra --- --- --- Causative agent Piedraia hortae Trichosporon spp Colour of nodules Black/dark brown White/cream Location Scalp hair Beard, moustache, pubic hair Consistency Hard nodules Soft nodules --- Q5. Briefly describe the classification of dermatophytes (6 marks) Trichophyton — infects hair, skin, and nails Microsporum — infects hair and skin only Epidermophyton — infects skin and nails only Classified further by ecology: Anthropophilic (human), Zoophilic (animal), Geophilic (soil) --- Q6. Compare and contrast Madura foot and Chromoblastomycosis (6 marks) Feature Madura Foot (Mycetoma) Chromoblastomycosis --- --- --- Causative agents Fungi or bacteria (eumycetoma/actinomycetoma) Pigmented fungi e.g. Fonsecaea , Phialophora Location Foot mainly Extremities (legs, arms) Morphology Swelling, sinuses, grains Warty, cauliflower-like lesions Cells in tissue Grains/granules Sclerotic (Muriform) bodies Treatment Antifungals/antibacterials Itraconazole, surgery --- Q7. State the significance of dyes/stains in fungal disease diagnosis (6 marks) KOH (Potassium Hydroxide): Dissolves keratin, reveals fungal hyphae/spores — used for skin scrapings PAS (Periodic Acid-Schiff): Stains fungal cell wall red/pink — used in histology India Ink: Reveals Cryptococcus capsule as a clear halo in CSF Calcofluor White: Fluorescent stain — highlights chitin in fungal cell walls Gram stain: Useful for some fungi e.g. Candida (Gram-positive yeast) GMS (Gomori Methenamine Silver): Stains fungi black — used in tissue sections --- SECTION B — Answer ONE question (20 marks each)--- Q1. Discuss the causative agent, clinical manifestation and treatment of Histoplasmosis (20 marks) Causative Agent: Histoplasma capsulatum Dimorphic fungus — mould at 25°C, yeast at 37°C Found in soil enriched with bird/bat droppings Endemic in Ohio and Mississippi River valleys Infection via inhalation of microconidia Pathogenesis: Microconidia inhaled → convert to yeast in lungs Yeast multiply within macrophages → spread via lymphatics/bloodstream Immunocompetent: usually self-limiting Immunocompromised: disseminated disease Clinical Manifestations: Acute pulmonary: Mild fever, headache, cough, chest pain — resembles flu Chronic pulmonary: Resembles TB — productive cough, weight loss, night sweats Disseminated: Hepatosplenomegaly, lymphadenopathy, skin/mucosal lesions, adrenal involvement Asymptomatic in most immunocompetent individuals Treatment: Mild/moderate: Itraconazole (oral) Severe/disseminated: Amphotericin B (IV) followed by Itraconazole Immunocompromised: Long-term suppressive therapy with Itraconazole --- Q2. Discuss the causative agent, clinical manifestation and treatment of Cryptococcosis (20 marks) (if chosen) Causative Agent: Cryptococcus neoformans Basidiomycete yeast Has a large polysaccharide capsule — main virulence factor Found in pigeon droppings and soil Infects via inhalation Primarily affects immunocompromised (HIV/AIDS, transplant patients) Pathogenesis: Inhaled → lungs (primary site) Crosses blood-brain barrier → meningitis Capsule resists phagocytosis Produces melanin — protects against oxidative killing Antigen titre in CSF/serum useful for diagnosis Clinical Manifestations: Pulmonary: Cough, fever, chest pain — can be asymptomatic CNS (Cryptococcal meningitis): Headache, fever, neck stiffness, photophobia, altered consciousness Cutaneous: Papules, nodules, ulcers Ocular: Visual disturbances Diagnosis: India Ink stain of CSF — capsule seen as clear halo Latex agglutination — detects capsular antigen Culture on Sabouraud agar — brown colonies on Niger seed agar (melanin) Treatment: Induction: Amphotericin B +