Master medical parasitology for Year 2. Explore common parasitic infections, diagnosis, treatment, and prevention. Essential guide for students.
MEDICAL ENTOMOLOGY Vector Control Methods 1. Physical/Mechanical Control - Screened windows and doors - Mosquito nets on walls - Draining pools of water - Removing long grass - Emptying containers 2. Biological Control - Using living organisms to control vectors - Toxorhynchites mosquito species - larvae feed on larvae of Anopheles, Culex, and Aedes - Gambusia affinis (fish) - feeds on mosquito larvae - Bacillus thuringiensis (Bt bacteria) - bacterial form - Bacillus sphaericus - Other predators 3. Genetic Engineering - Sterile male technique - Refractory vectors - modifying genes of vectors so that pathogens cannot develop - Result: change in target site 4. Chemical Control - Insecticides Classification Based on Toxicity (LD50): - LD50 1-50 : Extremely toxic/dangerous - LD50 50-500 : Moderately toxic - LD50 5000 : Safe Types of Insecticides: A) Chlorinated Hydrocarbons - Relatively stable - Act as nerve poisons - Lipid/fat soluble - Disrupt Na+ channels - Most are banned (e.g., DDT) due to long persistence and bioaccumulation in fatty tissues - Examples: DDT, Dieldrin, Endrin B) Organophosphates (OP) - Less persistent, don't accumulate in fatty tissues - Block cholinesterase (acetylcholine won't be broken down) - Examples: Malathion, Chlorpyrifos, Parathion, Diazinon, Dimethoate C) Carbamates - MOA similar to organophosphates - Bind to acetylcholinesterase - Better biodegradability, availability, and solubility - Examples: Carbaryl, Propoxur, Bendiocarb - Lower mammalian/human toxicity - Advantage over OP : Chronic exposure to carbamates is less likely to cause illness than organophosphates; inhibiting action is reversible D) Pyrethroids - Synthetic/semi-natural compounds - Examples: Permethrin (used in ITNs, LLINs), Deltamethrin - They bind to voltage gated sodium channels and delay their inactivation. increasing permeability - Results in excitation, lack of coordination, and paralysis - Relatively safe for outdoor use - Effect is rapid (knockdown effect) E) Insect Growth Regulators (IGRs) - Block insect sugar/chitin biosynthesis pathway - Example: Pyriproxyfen, Diflubenzuron F) Formamidines - Mimic activity of octopamine (neurotransmitter/neurohormone/neuromodulator) - They bind to octopamine receptors in insects, leading to disordered neuronal excitation and death - MOA is different, useful in resistant insects - Example: Amitraz - Effective against mites and ticks - Examples: Chlordimeform, Amitraz G) Avermectins - Cause paralysis and death by inhibiting transmission of nerve impulses - Narrow spectrum, active only against specific invertebrates - Can also be used against parasitic nematodes - Example: Abamectin H) Neonicotinoids - Both systemic and contact activity against sucking insects - Mimic nicotine - Example: Imidacloprid I) Miticides - Effective against mites - Examples: Bromopropylate, Cyhexatin, Tetradifon Types of Insecticides by Application: - Contact poison - Fumigant - Systemic - Stomach poison - Respiratory poison --- MOSQUITO-BORNE DISEASES Family: CULICIDAE Genus: ANOPHELES Key Species: - Anopheles gambiae complex (supervector) - An. funestus - An. arabiensis - zoophilic - An. melas - An. stephensi - supervector, transmits malaria mostly in Asia; recently reported in Africa (unlike other African species, can withstand high temperatures and arid conditions) Behavior: - Anthropophilic - Endophagic (feeds indoors) - Endophilic (rests indoors) Life Cycle: - Complete metamorphosis (holometabolous) - Duration depends on temperature (optimal 25°C) and humidity (78%) Breeding: - Stagnant water with vegetation and algae - Eggs laid singly and laid one at a time - Float on water surface Larval Stage: - 4 instars (L1-L4) - Larva lies parallel to water surface (breathes through spiracles on body side) - Feeding stage Pupal Stage: - Resting stage - Comma-shaped - Emerges after 2-3 days Adult Stage: - Emerges and mates post-emergence - Females : Feed on sugar solutions AND blood (require blood meal for egg development - anautogenous) - Males : Only feed on sugar solutions - Parthenogenesis possible (egg development without fertilization) Identification: - Resting position : 45° angle to surface - Antennae : Males - bushy/plumose; Females - smooth/pilose - Feeding : Only females take blood meals - Both sexes feed on sugar solutions Geographic Distribution: - Determined by location of parasite Medical Importance: - Primary : Transmission of malaria (genus Plasmodium ) Control Measures: - Chemical : Larvicides, breeding site treatment - Biological : Toxorhynchites species (T. rutilus) prey on mosquito larvae - Genetic : Refractory index - use of endosymbionts/bacteria that kill mosquito, preventing Plasmodium survival - Physical/Mechanical :Draining/removal of containers - Mosquito nets - IRS (Indoor Residual Spraying) - Trans-ovarian light traps - Screening windows - Cutting tall grass/weeds - Mesh on walls --- Genus: CULEX Key Species: - Culex quinquefasciatus Behavior: - Exophagic (feeds outdoors) - Exophilic (rests outdoors) - Feeding time: 3pm-6pm, nocturnal - Diurnal feeding: 10am Breeding: - Contaminated water (sewage, drains) Life Cycle: - Complete metamorphosis - Eggs, larvae, pupae, adult stages - Eggs : Laid simultaneously, attached to each other forming a raft; float on water as a raft - Larvae : Breathe via siphon; feed on particles and algae; hang at 45° angle to surface (unlike Anopheles ) Host Detection: - Eyes and olfactory cues Medical Importance: - Transmission of filarial nematodes ( Wuchereria bancrofti ) - Transmission of arboviruses (Rift Valley fever, West Nile virus) - Can transmit virus from female to eggs (transovarial transmission), so adults emerge with virus Control: - Breeding site management : Improving sanitation, installing proper sewage systems - Chemical : Insecticides on larval habitats (spray over 7-10 days; oils/films less effective in presence of organic matter) - Genetic engineering : Light traps - Physical : Wire mesh screens --- Genus: AEDES Key Species: - Aedes aegypti - Aedes albopictus Appearance: - Black color with white spots - Painful biters Behavior: - "Container breeders" - prefer breeding in clean containers - Biting time: Early morning and late evening - Bimodal biting behavior Breeding: - Clean containers, tires, flower vases - Both males and females take blood meals during oviposition Life Cycle: - Similar to Culex - Complete metamorphosis Medical Importance: Both species transmit: - Dengue fever - Chikungunya - Zika virus - Yellow fever - O'nyong-nyong - Japanese encephalitis - Arboviruses transmitted vertically (transovarial) - Rift Valley fever (mechanical transmission) Control: - Physical : Remove vegetation, predators, drain containers; straighten rivers and remove obstructing material to increase water velocity - Chemical :Insecticides on water surfaces (15-30 min duration) - Use of Bt (Bacillus thuringiensis) - Biological : Light traps, mosquito-eating fish --- Family: PSYCHODIDAE (Sandflies) Subfamily: PHLEBOTOMINAE Distribution: - Worldwide - Old World: Mediterranean, Indian subcontinent, Sub-Saharan Africa, Asia - New World: Central and South America Genera: - Phlebotomus (Old World) - 4 subgenera - Lutzomyia (New World) - Lutzomyia umbratilis (Brazil) - Sergentomyia (zoophilic) Bionomics: - Oviposition in small cracks, holes in ground, base of termite mounds - Can breed in chicken coops, poultry houses, animal burrows, rubbish heaps - Prefer high humidity areas; cannot withstand desiccation - Complete life cycle Behavior: - Females require blood meal - Some species are autogenous - Anthropophilic - Weak fliers - Short mouthparts - Bite exposed body parts - Bimodal biting pattern: feeding times in early morning and early evening Medical Importance: - Transmission of leishmaniasis (3 forms): Leishmania donovani - visceral leishmaniasis - Leishmania tropica - cutaneous leishmaniasis (Old World) - Leishmania braziliensis complex - mucocutaneous leishmaniasis - Transmission of Carri