Bacteriology & Medical Entomology Main Exam OmpathStudy

Paper Two — Main Exam Mount Kenya University — School of Medicine — Department of Medical Microbiology Bachelor of Medicine and Bachelor of Surgery (MBChB) — Paper One Unit Code: MBMM3300 — Unit Title: Bacteriology and Entomology Date: Tue 9th July, 2024, 8:00 AM — Main Exam — Time: 3 Hours Section A (35 Marks) 1. Insecticides colored BLUE have a lethal dose (LD50, mg/kg) of? A. 1-50 B. 501-5000 C. 51-500 D. 5000 E. ≥5000 Answer: B Explanation: This follows the WHO Hazard Classification color-coding system for pesticides. Blue band = Class III (slightly hazardous) = oral LD50 501-5000 mg/kg. --- 2. Insecticides colored YELLOW have a lethal dose (LD50, mg/kg) of? A. 1-50 B. 501-5000 C. 51-500 D. 5000 E. ≥5000 Answer: C Explanation: Yellow band = WHO Class II (moderately hazardous) = oral LD50 51-500 mg/kg. --- 3. Insecticides colored GREEN have a lethal dose (LD50, mg/kg) of? A. 1-50 B. 501-5000 C. 51-500 D. 5000 E. ≥5000 Answer: D Explanation: Green band = WHO Class U (unlikely to present acute hazard) = oral LD50 5000 mg/kg. Must-know area: memorize the full WHO color-hazard table (Red=Ia/Ib extremely/highly hazardous, Yellow=II moderate, Blue=III slight, Green=U unlikely) — this table is clearly a recurring MCQ source. --- 4. Which of the following insecticides inhibits electron transport chain? A. Rotenone B. Sabadilla C. Pyrethrum D. Nicotine E. Ryanodine Answer: A Explanation: Rotenone is a classic Complex I (NADH-ubiquinone oxidoreductase) inhibitor of the mitochondrial electron transport chain, halting ATP production in insect cells. --- 5. Which of the following insecticides inhibits conversion of ADP to ATP? A. Rotenone B. Sabadilla C. Pyrethrum D. Nicotine E. Ryanodine Answer: A Explanation: By blocking the electron transport chain, Rotenone indirectly prevents the proton gradient needed for ATP synthase to convert ADP to ATP — this is often taught as a linked consequence of Complex I inhibition. --- 6. Which of the following insecticides inhibits closure of sodium channels? A. Rotenone B. Sabadilla C. Pyrethrum D. Ryanodine E. All of the above Answer: C (Pyrethrum) — Sabadilla (B) may also be accepted depending on your lecture notes Explanation: Pyrethrum/pyrethroids act as sodium channel modulators, keeping voltage-gated sodium channels open longer than normal, causing repetitive nerve firing and paralysis. Sabadilla (veratridine alkaloids) works similarly on sodium channels. Ryanodine instead targets calcium release channels, so E is incorrect. Verify this specific answer against your lecture slides, since B and C both act on sodium channels via slightly different alkaloid mechanisms. --- 7. Which of the following insecticides target the GABA-A site? A. Aldrin B. DDT C. Bendiocarb D. Malathion E. Permethrin Answer: A Explanation: Aldrin (an organochlorine, cyclodiene class) blocks GABA-gated chloride channels, causing continuous neuronal excitation and insect death. --- 8. Which of the following insecticides target the acetylcholine esterase? A. Aldrin B. DDT C. Bendiocarb D. Deltamethrin E. Permethrin Answer: C Explanation: Bendiocarb is a carbamate insecticide; carbamates (like organophosphates) inhibit acetylcholinesterase, causing acetylcholine accumulation at synapses and continuous nerve stimulation. --- 9. Which of the following insecticides mimic octopamine? A. Aldrin B. Amitraz C. Bendiocarb D. Malathion E. Permethrin Answer: B Explanation: Amitraz (a formamidine) acts as an octopamine receptor agonist — octopamine is an invertebrate neurotransmitter, and its overstimulation disrupts normal nerve signaling. --- 10. Which one of the following is a one-host tick? A. Boophilus B. Ornithodoros C. Hyalomma D. Rhipicephalus E. Haemaphysalis Answer: A Explanation: Boophilus (now classified under Rhipicephalus microplus) completes its entire life cycle (larva, nymph, adult) on a single host animal — the classic one-host tick example. --- 11. Which one of the following is a two-host tick? A. Boophilus B. Ornithodoros C. Hyalomma D. Rhipicephalus E. Haemaphysalis Answer: C Explanation: Hyalomma ticks typically feed as larvae and nymphs on one host, then drop off, molt, and re-attach to a second (often different) host as adults — the classic two-host tick pattern. --- 12. Which one of the following is transmitted by ixodes ticks? A. Francisella tularensis B. Orientia tsutsugamuchi C. Mansonella ozzardi D. Oropouche virus E. Borrelia duttoni Answer: A Explanation: Ixodes (hard) ticks transmit Francisella tularensis (tularemia) along with Borrelia burgdorferi (Lyme disease, not listed here). Orientia tsutsugamuchi is chigger-mite transmitted; Mansonella ozzardi and Oropouche virus are Culicoides-transmitted; Borrelia duttoni is soft-tick (Ornithodoros) transmitted. --- 13. Which one of the following is transmitted by argasid ticks? A. Borrelia duttoni B. Francisella tularensis C. Orientia tsutsugamuchi D. Mansonella ozzardi E. Oropouche virus Answer: A Explanation: Argasid (soft) ticks, genus Ornit