Master Medical Entomology with our Year 2 Parasitology past papers. Ace your exams with essential study resources and practice questions.
DANIEL ROSASI - Comprehensive Study Guide --- SECTION A: LONG ANSWER QUESTIONS (20 Marks Each) Question 1: Life Cycle of a Three-Host Tick (20 Marks) With an illustration, outline the life cycle of a three-host tick Answer: Life Cycle Stages: - Egg Stage (Fall) Adult females drop off the third host after feeding, usually in the fall - Females lay eggs in the environment - Eggs hatch into six-legged larvae - Larvae overwinter in this stage - Larval Stage (Spring - First Host) In spring, larvae seek out and attach to the first host, usually a small rodent - Larvae feed on the first host - Later in summer, engorged larvae leave the first host - Larvae molt into nymphs, usually in fall - Ticks overwinter in the nymphal stage - Nymphal Stage (Following Spring - Second Host) During the following spring, nymphs seek out and attach to the second host - Second host is usually another rodent or lagomorph - Nymphs feed on the second host and drop off later in summer - Nymphs molt into adults off the host in late summer or fall - Adults overwinter in this stage - Adult Stage (Next Spring - Third Host) The next spring, adults seek out and attach to a third host - Third host is usually a larger herbivore (cervids, bovids), carnivore, or human - Adults feed and mate on the third host during summer - Females drop off the host in fall to continue the cycle - Females may reattach and feed multiple times Important Notes: - The three hosts do not necessarily have to be different species or different individuals - Humans may serve as first, second, or third hosts --- Question 2: Myiasis (20 Marks) Discuss myiasis under the following sub-headings A. AETIOLOGY (3 Marks) - Myiasis is the invasion of organs and tissues of humans or other vertebrates by fly larvae - Fly larvae feed on living or dead tissues or, in intestinal myiasis, on the host's ingested food - Flies in several genera may cause myiasis in humans Important Species: - Dermatobia hominis - Primary human bot fly - Cochliomyia hominivorax - Primary screwworm fly (New World) - Chrysomya bezziana - Old World screwworm - Cordylobia anthropophaga - Tumbu fly - Cuterebra, Oestrus, Wohlfahrtia - Animal parasites that occasionally infect humans B. PATHOGENESIS (5 Marks) Types of Myiasis: 1. Accidental Myiasis - Usually involves eating food contaminated by eggs or larvae of non-parasitic flies (e.g., house flies) - Larvae may survive for some time in the intestine - No flies are specially adapted to cause intestinal myiasis in humans - Symptoms: Abdominal pain, diarrhea, blood discharge, vomiting - Living larvae may be passed in excreta or vomit 2. Obligatory Myiasis - Occurs in other mammals, not typically humans - Essential for fly maggots to live on a live host for at least part of their life - Examples: Larvae of Cordylobia anthropophaga , Cochliomyia hominivorax , Chrysomya bezziana , Dermatobia hominis , Wohlfahrtia magnifica - All obligatory parasites of humans and other vertebrates 3. Facultative Myiasis - Larvae are normally free-living, often attacking carcasses - Under certain conditions may infect living hosts - Urogenital myiasis: Occasionally occurs in humans, usually involving larvae of Musca or Fannia species - Ovipositing flies attracted to unhygienic discharges lay eggs near genital orifices - Hatching larvae enter genital orifice and pass up urogenital tract - Considerable pain may be caused during urination - Larvae may obstruct passages, causing discharge of mucus, blood, and eventually larvae Different Terms for Myiasis by Body Part: - Dermal myiasis - Affects different parts of the body - Cutaneous myiasis - Skin infection - Intestinal/enteric/gastrointestinal myiasis - Digestive system - Ophthalmic myiasis - Eyes - Creeping myiasis - When larvae burrow under skin surface producing creeping eruption - Traumatic myiasis - When wounds become infested C. DIAGNOSIS (3 Marks) - Diagnosis made by finding fly larvae in tissue - Identification to genus/species level involves comparing morphological structures:Anterior and posterior spiracles - Mouthparts - Cephalopharyngeal skeleton - Cuticular spines - Travel history can be helpful for genus/species identification D. TREATMENT (4 Marks) - Simple removal: When larvae occur in wounds, sores, dermal or subdermal tissues, removal under aseptic conditions is usually relatively simple - Complex removal: When larvae are deeply embedded in underlying tissues or have penetrated mucous membranes, eyes, frontal sinuses, or cavities, removal is more difficult - Surgery may be needed for deeply embedded larvae E. CONTROL (6 Marks) - Ash/salt on tables/latrines to discourage landing of flies - Curtains to entrances of eateries to prevent fly entry - Screens on windows to prevent fly entry - Use of insecticides to kill flies - Cover food and water during storage to avoid contamination - Washing of fruits and vegetables - Use of electric fly traps (emit purple light to attract and electrocute flies) --- Question 3: Medical Importance of Arthropods (2 Marks Each) 1. ANOPHELES SPECIES - Transmission of malarial parasite ( Plasmodium ) - Allergic reactions to mosquito bites due to saliva (contains anticoagulant) 2. SIMULIUM SPECIES - Transmit Onchocerca volvulus which causes river blindness (blocks/obstructs lymphatics in optical region) - Proboscis can cause tearing and rupturing of skin, leading to bleeding and anemia 3. PHLEBOTOMUS SPECIES - Previously sensitized people may experience severe, almost intolerable irritations from bites (known as "harara") - Transmit Leishmania species (VL, CL, MCL, and PKDL) 4. LUTZOMYIA SPECIES - Causes mucocutaneous leishmaniasis - Transmit L. braziliensis complex and L. mexicana complex 5. AEDES SPECIES - Primary vectors for Arbovirus diseases:Yellow fever - Dengue virus - Chikungunya virus - Japanese encephalitis - Rift Valley fever - Zika virus - O'nyong'nyong virus 6. CULICOIDES SPECIES - Transmit filarial nematodes: Mansonella perstans - M. streptocerca - M. ozzardi 7. CHRYSOPS SPECIES - Vectors in West and Central Africa of filarial worm Loa loa (eye worm) - People can develop severe allergic symptoms 8. GLOSSINA SPECIES - Cause Trypanosomiasis: G. morsitans → T. b. rhodesiense → East African Sleeping Sickness (EASS) - G. palpalis → T. b. gambiense → West African Sleeping Sickness (WASS) 9. MUSCA SPECIES - Vectors of helminths (e.g., E. vermicularis ), bacteria, protozoa, and viruses - Spread diseases through mechanical transmission (dysentery, diarrhea, enteric diseases) 10. CIMEX SPECIES - Feeding (repeated and vigorous) can cause iron deficiencies, especially in infants and elderly people 11. BLATTA SPECIES (Cockroaches) - Mechanical transmission of enteric pathogens: Klebsiella pneumoniae - Mycobacterium leprae - Shigella dysenteriae - Salmonella species (including S. typhi and S. typhimurium ) - Serratia species - Staphylococcus aureus - E. coli - Entamoeba histolytica - Inhaling body parts causes allergies (symptoms include sneezing, skin breakouts) - Recurrent body part infection causes asthma in extreme cases --- Question 4: Genetic-Based Control Methods for Vector-Borne Diseases (20 Marks) Introduction - Insects are responsible for transmission of major infectious diseases - Recent advances in insect genomics and transformation technology provide new strategies for control - Genetic modification offers alternatives to conventional insect-based control strategies Advantages of Genetic Control - Offers several advantages over conventional insecticide-based strategies - Caution required: Great caution needed regarding:Safety after release into environment - Acceptance by target populations Current Control Limitations - Current control measures heavily depend on insecticides - Adverse environmental effects - Prolonged use results in development of insecticide resistance Two Broad Categories of Genetic Approach 1. Genetic Suppression of Vector Competence - Suppress ability of vectors to transmit pathogens - Specific to contr