Medical Parasitology

## 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 *Plas