Medical Entomology Past Paper MCQs — Past OmpathStudy

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 mosqu