Medical Vectors: Ticks, Trypanosomiasis, OmpathStudy

--- VECTOR TERMINOLOGY Zoophilic — prefers animal blood Anthropophilic — prefers human blood Endophagic — feeds indoors Exophagic — feeds outdoors Endophilic — rests indoors Exophilic — rests outdoors IRS/bed nets only work on endophagic + endophilic vectors — vectors that feed/rest outdoors avoid both Anautogenous — needs a blood meal before laying eggs Autogenous — lays eggs without a blood meal Monophagous — feeds on one host species only; classic example = louse (humans only) Parthenogenesis — asexual reproduction, offspring from unfertilized eggs Fomite — non-living object that transmits a pathogen Refractory vector — biologically incapable of transmitting a given pathogen even after biting an infected host --- TICKS — ARGASID (soft ticks) No scutum Multiple hosts across life cycle Multiple nymphal stages Feed briefly, repeatedly Example: Ornithodoros — vector of relapsing fever TICKS — IXODID (hard ticks) Has a scutum Classic 3-host life cycle Only ONE nymphal stage Boophilus = exception (one-host tick) Examples: Rhipicephalus, Amblyomma, Hyalomma Life cycle of a 3-host tick (15–20 marks — draw and label) Egg hatches in environment → Larva (6 legs) Larva attaches to Host 1, feeds, drops off Larva molts to Nymph (8 legs) in the environment — only nymphal stage in the whole cycle Nymph attaches to Host 2, feeds, drops off, molts to Adult in environment Adult attaches to Host 3, feeds, mates Engorged female drops off, lays eggs in environment — cycle repeats Medical importance of Ixodid ticks (20 marks) Blood loss/anemia from heavy infestation Tick paralysis — neurotoxin in saliva, ascending flaccid paralysis, resolves on tick removal Local dermatitis/skin irritation at bite site Secondary bacterial infection of bite wound Allergic reactions to saliva, occasionally severe Granuloma formation if mouthparts left in skin Vector of Lyme disease Vector of Rocky Mountain spotted fever and other rickettsial diseases Vector of Babesiosis (malaria-like protozoal disease) Vector of Anaplasmosis/Ehrlichiosis Vector of tick-borne encephalitis (viral, some regions) Vector of East Coast Fever ( Theileria parva , via Rhipicephalus appendiculatus ) — Kenya-relevant Long feeding duration (days) → higher transmission risk than soft ticks Transstadial transmission — pathogen persists through larva→nymph→adult molt Transovarial transmission — infected female passes pathogen into her eggs Wide host range across life stages → cross-species pathogen transfer Major livestock pest — reduces productivity independent of disease Drives need for acaricides, pasture management, protective clothing, tick checks Acaricides Kill ticks/mites Among malaria/leishmaniasis/amoebiasis/Q-fever/sleeping sickness options — Q-fever is best controlled by acaricides --- TRYPANOSOMIASIS — African (Old World) sleeping sickness Vector: Glossina (tsetse fly) T. b. gambiense → West African sleeping sickness → Palpalis group T. b. rhodesiense → East African sleeping sickness → Morsitans group Fusca group is NOT significant for T. b. rhodesiense transmission Arabuko Sokoke (forested area) = specific risk zone for sleeping sickness Treatment: melarsoprol, pentamidine, eflornithine, suramin TRYPANOSOMIASIS — American (New World) Chagas disease Caused by Trypanosoma cruzi Vector: triatomine bugs = kissing bugs = reduviid bugs (same insect) Found in Central/South America — NOT Glossina (Africa-only) Transmission: bug defecates near bite site while feeding; scratching rubs contaminated faeces into wound — it's the faeces, not the bite, that transmits the parasite Triatomine bugs in a home → predisposes household specifically to Chagas disease Treatment: nifurtimox --- LEISHMANIASIS Vector: sandflies — Phlebotomus (Old World) / Lutzomyia (New World) Sandflies are larviparous Stage injected into human by vector: promastigote Converts to amastigote once inside human macrophages — this is the multiplying form Treatment: sodium stibogluconate (pentavalent antimonial) Pathologies transmitted by Phlebotominae (12 marks): Cutaneous leishmaniasis — skin ulcers/nodules at the bite site, parasite stays localized in skin macrophages Mucocutaneous leishmaniasis — spreads from skin to mucosal tissue (nose, mouth), causing tissue destruction Visceral leishmaniasis (kala-azar) — spreads to liver, spleen, bone marrow; fever, weight loss, organ enlargement; most severe form Sandfly fever — separate viral disease carried by Phlebotomus , acute febrile illness Bartonellosis (Oroya fever/Carrion's disease) — bacterial disease via Lutzomyia in South America, fever and hemolytic anemia in acute phase --- FILARIASIS Wuchereria bancrofti → vector Culex → elephantiasis/lymphatic filariasis Onchocerca volvulus → vector Simulium → river blindness (onchocerciasis) Loa loa → vector Chrysops → Calabar swellings, eye migration, "pink eye disease" Larval stage in thoracic/chest muscles of vector = L3 (infective stage) Microfilariae = the circulating blood stage seen on a blood smear (distinct