Medical Entomology Exam 2018/2019 MCQs — MCQ OmpathStudy

Medical Entomology Exam 2018/2019 --- SECTION A (Answer ALL Questions) Question 1 (6 marks) Differentiate the following terminologies as used in medical entomology: i) Propagative ii) Cyclodevelopmental iii) Cyclopropagative Answer: i) Propagative Transmission (2 marks): The pathogen multiplies within the vector but undergoes no developmental changes The organism increases in number but remains essentially the same morphologically Example: Yersinia pestis in fleas during plague transmission Vector acts as a biological incubator for pathogen reproduction ii) Cyclodevelopmental Transmission (2 marks): The pathogen undergoes developmental changes within the vector but does not multiply Essential morphological and physiological changes occur in the vector Example: Malaria parasites ( Plasmodium spp.) in Anopheles mosquitoes Sporozoites develop in mosquito salivary glands iii) Cyclopropagative Transmission (2 marks): Combination of both propagative and cyclodevelopmental transmission The pathogen both multiplies AND undergoes developmental changes within the vector Example: Trypanosoma cruzi in triatomine bugs (Chagas disease) Organism transforms through different morphological forms while multiplying --- Question 2 (6 marks) Describe six methods of controlling molluscs in the environment. Answer: 1. Chemical Control (1 mark): Use of molluscicides such as metaldehyde and methiocarb Copper sulfate and niclosamide for aquatic snails 2. Biological Control (1 mark): Introduction of predators such as chickens, ducks, and fish Use of competitor snail species 3. Physical Barriers (1 mark): Use of barrier plants around water sources Physical screening of water intake points 4. Environmental Modification (1 mark): Drainage of stagnant water bodies Removal of aquatic vegetation that harbors snails 5. Chemical Repellents (1 mark): Use of repellents such as salt spreading around areas Lime application to alter pH 6. Sanitation and Hygiene (1 mark): Proper sewage disposal to prevent contamination Community education on avoiding contact with infested water --- Question 3 (6 marks) With examples, give three classes of insecticides for controlling mosquitoes. Answer: 1. Organochlorines (2 marks): Mechanism: Bind to GABA receptors, causing formation of GABA-A-chloride ionophore complex Examples: DDT (dichlorodiphenyltrichloroethane), endosulfate Effect: Disruption of nervous system causing paralysis 2. Organophosphates (2 marks): Mechanism: Inhibit acetylcholinesterase, making acetylcholine unavailable Examples: Malathion, temephos, fenitrothion Effect: Continuous nerve stimulation leading to death 3. Pyrethroids (2 marks): Mechanism: Target sodium channels in nerve membranes Examples: Permethrin, deltamethrin, cypermethrin Effect: Disruption of nerve impulse transmission causing knockdown and death --- Question 4 (6 marks) Fill in the following blank spaces (only one answer): i) Culex species are major vectors of: Filariasis ii) Onchocerca volvulus is transmitted by: Black flies/Simulium species iii) Leishmania tropica is transmitted by: Phlebotomus species/Sandflies iv) Fresh water snails are major vectors for: Schistosoma haematobium causing Schistosomiasis Answer Explanations: Culex mosquitoes transmit Wuchereria bancrofti causing lymphatic filariasis Simulium species transmit Onchocerca volvulus causing river blindness Phlebotomus sandflies transmit Leishmania species causing leishmaniasis Freshwater snails ( Bulinus spp.) are intermediate hosts for Schistosoma haematobium --- Question 5 (6 marks) Outline the development of filarial nematodes in their vectors. Answer: Stage 1 - Ingestion (1 mark): Microfilariae are ingested by vector during blood meal from infected host Microfilariae present in peripheral blood of infected individual Stage 2 - Migration to Flight Muscles (2 marks): Microfilariae penetrate gut wall and migrate to thoracic flight muscles Development occurs in the muscle tissue of the vector Stage 3 - First Molt (L1 to L2) (1 mark): First larval stage (L1) molts to second larval stage (L2) Occurs approximately 7-14 days post-infection Stage 4 - Second Molt (L2 to L3) (1 mark): Second larval stage molts to third larval stage (L3) L3 is the infective stage for humans Stage 5 - Migration to Proboscis (1 mark): Infective L3 larvae migrate from flight muscles to proboscis/mouthparts Ready for transmission during next blood meal (14-21 days total development) --- Question 6 (6 marks) Outline the control of leishmaniasis in the environment. Answer: 1. Vector Control (2 marks): Spraying insecticides in sandfly breeding sites Use of residual spraying in houses and animal shelters 2. Environmental Modification (1 mark): Cleaning termite mounds and organic debris where sandflies breed Removal of vegetation close to human habitations 3. Personal Protection (1 mark): Use of repellents and protective clothing Sleeping under fine-mesh bed nets 4. Reservoir Control (1 mark): Treatment and control of infected domestic animals