Medical Entomology Exam 2018/2019

# 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):**