Vector control

Vector borne diseases

Human diseases caused by parasites, viruses and bacteria that are transmitted by vectors

Parasite vectors

• Hematophagous Arthropods that ensure the active biological or mechanical transmission of parasites between humans or from other vertebrates to humans

• Ingest parasites during a blood meal from an infected host (human or animal) → transmission to a new host, after parasite replication

Parasitic diseases transmitted by vectors

• Malaria

• Chagas disease

• Leishmaniasis

• Human African trypanosomiasis

• Lymphatic filariasis

• Onchocerciasis

• Dengue

• Chikungunya fever

• Zika virus fever

• Yellow fever

• West Nile fever

• Japanese encephalitis

• Tick-borne encephalitis

Control the vectors

• Limit the proliferation of arthropod populations

• Reduce contacts between arthropod populations and human populations

Trapping systems to capture the vectors

Identifying risks and monitoring vector populations to determine if they cross theoretical transmission density thresholds.

• Light traps (mosquitoes and sandflies)

• CO2 traps (mosquitoes)

• Dragging/flagging method (ticks)

• Tsetse fly traps (non-return device)

Physical methods to control vectors

Aim to reduce human-vector contacts

• Insecticide-treated bed net

• Light UV traps

Insecticide-treated clothes

• Bed net: impregnated with pyrethroids (insecticides like deltamethrin or permethrin) → repel or kill host

• Treated textiles and uniforms

• Anti-insect grids in windows and doors

Light traps (UV) and Electric grids

Use ultraviolet light to attract insects. They can also be enhanced by releasing octenol, a chemical that mimics animal breath and sweat

Ecological methods to control vectors

Aim is to create adverse environmental conditions for vector/intermediate host development

• Drain swampy areas (against mosquitoes and molluscs)

• Clear river banks (against black flies)

• Dry irrigated areas (against mosquitoes)

• Maintenance of canal irrigation (against molluscs)

• Pasture rotation (against ticks)

• Remove aquatic plants (against fluke)

• Improve housing (against Reduviid bugs)

• Ensure efficient waste pickup, limiting rat populations (leptospirosis), small rodents (leishmaniases)

Chemical methods to control vectors

Use of natural or synthetic substances having insecticide activity

DDT (dichloro-diphenyl-trichloethane)

• Opening sodium channels in insect neurons → spams → dead

• Toxicity for birds, fishes, accumulation in the food chain

HCH (hexachlorocyclohexane) or lindane

• Inhibition of GABA receptor

• Non-biodegradable, toxic

Pyrethroids

• Deltamethrin, cypermethrin, permethrin

• Low toxicity for warm-blooded animals by contact or ingestion

• Highly toxic for bees and fishes

• Highly biodegradable

• Opening sodium channels in insect neurons → spams → dead

Benzoyl urea derivatives

Chitin-synthetase inhibitors → impair cuticle formation → insect death during its next shedding cycle

Bio-rationale method

Based on the insect physiological knowledge and on the respect of the environment

Juvenile hormone (JH)

• Allows larva growth but inhibits differentiation into adult through maintaining the larval stage

• In the adult stage, it regulates reproduction (vitellogenesis, oogenesis)

• Not stable enough to use ad commercial insecticide

Methoprene

• Mimics JH → inhibition of adults emergence

• Growth regulator

• Not toxic to mammals

• Inactive in the adult stage

Finopril

Block BABA-gated chloride channels and glutamate-gated chloride (GluCl) channels → disrupts insect nervous system → hyperexcitation of nerves and muscles → paralysis → death

Amitraz

Act as agonist of octopaminergic G protein-coupled receptors (GPCRs) → massive sensory overload → hyperactive, leg shaking, and detachment

Insecticide resistance

Massive agricultural use of insecticides has created intense selective pressure, leading to resistant vector populations

Biological methods to control vectors

Aim is to reduce vector through the use of living organisms or their products

Entomopathogens

Fungi that can infect and seriously disable or kill insects. Act directly or through toxins they generate

Bacillus sphaericus

• Gram positive, aerobe, spore forming, rod shaped

• Synthesize and excrete protein crystals toxic for some insects (B-t. toxins) → destruction of midgut cells of the insect larvae → later consumed by bacteria

B.t. toxins

• The spectrum of activity depends on the strains and toxin molecular weights

• Against lepidoptera, diptera, coleoptera

• Resistance: alteration of the receptor affinity site → reduction of the toxin binding to intestinal cells

• Safe for human and pets

Bacillus thuringiensis

• VectoBac

• Against all kinds of mosquitoes (adult and larvae)

• Acts very quickly

• Dispersable granules

Bacillus sphaericus

• VectoLex

• Against all mosquitoes

• Corn-based granules

• Larvae ingest bacteria → toxins released in the midgut → paralysis → death at the air-water interface → toxins released → ingested again

Entomophage fishes

• High larvae consumption capacity

• Easy breeding transport

• Own population regulation

• Gambusia (mosquitofish), cynaolebias bellorti

Autocidal methods

Introduction of sterile males: breeding of males → sterilized using irradiation → released in wild → females lay eggs but they do not hatch in larvae

Transgenesis control

Use of transgenic males exhibiting specific genotype leading to: sterility, death progeny, sex-ratio in favour of males, annihilated vectorial capacity