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CLOSE THIS BOOKPublic Health Technician (MSF, 1994, 192 p.)
III - Vector control
VIEW THE DOCUMENT(introduction...)
VIEW THE DOCUMENTA. Introduction
VIEW THE DOCUMENTB. The principal vectors: biology and control methods
VIEW THE DOCUMENTC. Precautions for use and storage of insecticides
VIEW THE DOCUMENTD. Spraying equipment
VIEW THE DOCUMENTE. Technical briefs

Public Health Technician (MSF, 1994, 192 p.)

III - Vector control

This chapter is an introduction to vector control. It presents some methods of chemical control of the principle disease vectors. It should always be born in mind that a large-scale control programme necessarily demands specialist skills.

A. Introduction

Since the introduction of DDT forty years ago, numerous chemical products have been invented for the destruction of disease vectors and agricultural insect pests.

Two major problems have appeared:

- Many insects vectors have developed a resistance to these products.
- Their human toxicity has, at times, caused serious public health problems.

In the context of the work of Medecins Sans Frontieres we are confronted by these problems in several ways:

- in the course of medical treatment after poisoning,
- as users during a specific vector control programme,
- as trainers in public health.

This chapter should, within the limited context of our actions, allow us to choose and to use suitably some selected insecticides, to know the precautions for their use and finally to be able to take emergency medical action in the case of poisoning.But it is also intended as a warning against the apparent ease of use and effectiveness of these products.

The use of pesticides is costly, is never without risk and is not always effective. In the context of a medical programme it may be conceived:

- either in an emergency phase (an epidemic due to a vector),
- or when the control of vector breeding sites is a problem (difficult to locate, far away, etc.).

Chemical control should always be planned alongside a programme of improvement of the site and/or of general living conditions and hygiene (the removal of stagnant water and refuse, scrub clearance, reduction of living density, water and sanitation services, etc.).

If no action is taken in this direction even the most active and powerful insecticide would have little impact in the long term.

The pesticides are frequently used in agriculture often, however, the users are not informed of the precautions to take during the transport and use of these products. The health problems which result may go unnoticed because the poisoning is chronic.

Here again, the remedy is prevention: information and education.

B. The principal vectors: biology and control methods

Mosquitoes
Lice
Flies
Fleas
Rodents

General introduction

Knowledge, however small, of the biology of each vector is a sine quae non of effective control measures.

It is useless to try to combat body lice by treating the hair, or to try to control Culex larvae by treating clean standing water. It is vital to know how, where and when to act.

Nevertheless, it is possible to identify some principles common to all vector control programmes:

- The aim should be to make the local environment unfavourable for the development and survival of the vector (environmental hygiene).
- Combat is generally more effective if * is focused on immature forms of the vector.
- Complete eradication is frequently unattainable; the objective should be to keep the vector population below a level at which it poses a too great risk of an epidemic.

Mosquitoes

Mosquitoes form the largest group of vectors of medical importance, with more than 3,000 species. Their life cycle is closely linked with water.

Life cycle

There are four stages of development. The first three are aquatic (egg, larva, nymph), and generally last for two weeks.

The adult (or imago) feeds on plant sap. Its lifespan varies from one to several months. The maturation of eggs in the female needs a blood meal (except for the first laying in Culex species).

Larvae may thrive in any water body except for deep water such as large river, lake or sea.

Certain genera (Aedes) use sites where the water level is variable (dependent on rainfall), such as tree trunks or leaves. Others are more specific to stagnant and heavily polluted water (Culex).

The activity of the adult varies with species: the sphere of action, hours and places of activity, type and specificity of food, etc.

Thus, in order to carry out effective control it is important to find out what species is concerned and what are its specific features.

Control methods

ENVIRONMENTAL HYGIENE

The main aim is to alter the environment so as to make it unfavourable for the reproduction of the species concerned.

-Aedes aegypti

This species is often associated with human dwellings where it breeds in any open container of water. Control measures aim at getting rid of these types of sites, or at protecting them (with a cover, or mosquito netting with mesh <0.7 mm).

Large water containers should be frequently emptied (at least once per week).

- Culex

Control measures aim to eliminate bodies of stagnant water loaded with organic matter (e.g. in latrines), or if not, then to eliminate surface vegetation in stagnant water and ensure that these water bodies are at least 1.2 m deep.

- Anopheles

Control measures are identical to those for Culex, although Anopheles have a wider distribution. Land drainage and filling also has an impact but this is rarely possible.

However, it may be necessary to couple these environmental hygiene and improvement measures with chemical control of larvae and adults.

In this case the relevant government department should be called in, as the misuse of insecticides, particularly in the aquatic environment may cause irreparable ecological disturbance and favour the development of resistance, etc.

In the case of a viral epidemic (encephalitis, yellow fever, etc.), individual protection should be done by using:

- mosquito nets (mesh diameter less than 0 - 7 mm) on openings of houses and over beds;
- repellent creams and lotions

CHEMICAL CONTROL

- Larvicides

· fuel oil: spread over the whole water surface (little used).
· paraffin: 30 l/ha, 1 glass/latrine/week.
· malathion: 224 to 692 g active product/ha.
· temephos: 56 to 112 g active product/ha.
· deltamethrin: 2.5 to 10 g active product/ha.

Chemicals formulated in granules or in emulsifiable concentrate.

- Adulticides

· Persistent treatment

- deltamethrin:0.05 g active product/m2
- malathion: 1 to 2 g active product/m2
- permethrin: 0.5 g active product/m2
- propoxur: 1 to 2 g active product/m,
- pirimiphos-methyl: 1 to 2 g active product/m2

· Aerial application

Confined to specialists.

Lice

Only the body louse is a potential vector. It is found almost exclusively between the skin and clothes. Transmission of possible pathogens through the louse's excretions (e.g. typhus) or by the louse being crushed (e.g. recurrent fever).

The louse population may grow when personal hygiene is poor (lack of water, soap or clothes), where there is overcrowding and when it is cold. A situation of a risk of epidemic may be reached, demanding emergency measures, including the use of an insecticide.

Before any action is taken, a study of the resistance of the lice to insecticides should be done by a competent laboratory or by an experienced person in the field. In the absence of resistance (which is rare), DDT or malathion may be used. If in doubt, propoxur (or permethrin) is almost always a good choice.

Powder is used, as treatment of the body. The concentration depends on the product, but 30 g of powder per person is the standard dose. Powder is applied to the fully clothed subject at the neck, half at the front and half at the back, then spread by rubbing. Pay special attention to belts and socks if these are worn. Bedding, blankets and clothes may also be treated, in a plastic bag for example.

Every bout of fever or large drop in temperature (e.g. on death) promotes the movement of lice to a new host. Patients should therefore be disinfected before being admitted to a hospital structure.

Control measures include:

- Improvement of hygiene and reduction of overcrowding.
- Preventive treatment of clothes, blankets etc distributed (by immersion, spraying or powdering).
- Active treatment of every body by powdering (treatments, 1 week apart).
- Treatment of clothes by damp heat (1 hour at 70) and by dry heat (ironing).

Only this method ensures the elimination of lice, ticks, and bacteria (but it uses a lot of energy).

It must not be forgotten when treating that dust from clothing etc. is contaminating (excrete of lice).

- If possible, inform people of the danger of crushing lice between finger nails or teeth (risk of spread of borrelia).

Equipment

- Powder blower (hand or knapsack)
- Soupspoon: still the cheapest and most practical (1 soupspoon = 15 g: use one at the front and one at the back).
- Powdering tin or pierced bag.
- Bath, tub or simple knapsack sprayer for liquid application.

Informing the population and training operators are two essential parts of a control programme.

Precautions:

- Powders: dust masks and gloves for teams of operators doing treatment.
- Liquids: see Precautions for use.

When treating head lice, malathion is, the usual choice of insecticide (except if there is resistance). Prepare an aqueous solution of 4% active product, add a gentle detergent if possible (e.g. fabric detergent or shampoo, to aid the penetration into ticks) and apply about 15 ml to the head of each person. Leave to act for 24 hours before rinsing. Do not use on children of less than three years.

Deltamethrin may also be used, as a solution of 0.03% active product (2.5 ml of concentrated solution/litre or one sachet of 33 g/litre of water), or a 0.05% solution of permethrin. This treatment should be avoided if at all possible.

Flies

General points

This order is composed of a wide range of species which differ in their ecology, their behaviour and their medical importance.

The domestic fly has a life cycle of 10 to 30 days, depending on temperature.

The larvae develop in mammal and bird excrete, in waste waters, and in decomposing organic matter (medical and domestic refuse). The adult which lives for 2 to 8 weeks has a radius of activity of about three kilometres. It feeds on moist or liquid substances rich in sugars and proteins.

This species is closely linked to the human environment and frequently moves between contaminated areas (excrete, medical wastes, etc.), food and drink, thus playing a disease-carrying role.

Other species are of particular medical importance due to their specific biology: those attracted by lacrymal or nasal secretions, open wounds, domestic refuse, dead bodies, etc. They are important in the spread of conjunctivitis, plan (yaws), trachoma, dysentery, etc.

Glossinia (Tsetse fly, vector of trypanosomiasis) and glossinnia (black fly, vector of onchocerciasis) demand the implementation of a specific programme because of their medical importance and their biology; the complexity of such a programme is beyond the scope of this guide.

Control methods

Larval sites, i.e. the places where eggs are laid and where the larvae develop, are very often a product of human activity.

The basic principle of all control measures should be to reduce or remove these sites,or to prevent access by flies. Without these environmental hygiene measures, all control efforts are in vain.

In practical terms, these measures focus on:

- Animal excreta: cleaning of stockraising areas.
- Refuse: organize collection and ensure disposal by burning or burial under at least 30 cm of soil. Make covered refuse containers available (in particular in kitchens, laboratories and health centres).
- Spilled food: make smooth floors in feeding centres (smoothed cement or plastic sheeting) to aid cleaning.
- Wastewater: ensure good removal and disposal, particularly at washing areas for clothes and cooking ustensils.

Recourse to chemical products should be avoided as much as possible, because of the rapidity of appearance of resistant strains which render this option costly and ineffective.

In practice:

- In the case of massive infestation by larvae of a defecation trench or latrines, used engine oil, diesel or kerosene is used to spread an impermeable layer which asphyxiates the larvae (but take care of the risks of polluting the water table). Ashes or earth may be added to latrines pits (after each defecation, or at least every morning and night), to reduce the contact between flies and excreta.

- In the case of an epidemic, when the presence of flies creates a risk of increased spread of the pathogen, and when an operating theatre or treatment room must be protected, the use of larvicides and alduticides may be considered, but always in tandem with environmental hygiene measures.

· Destruction of larvae

Spraying of larval sites with an emulsion or a suspension until the surface is completely wetted.

· Destruction of adults

Treatment with a residual effect should be done on the surfaces where flies land at night, as it is here that there is the longest contact time. These places may differ according to the species and the climate. In general they are external surfaces of building (in hot countries), trees, fences, dustbins, animal shelters, etc.

The insecticide is applied in an emulsion or a suspension.

Malathion (5% solution, 1 to of active or deltamethrin (see technical brief) are the most suitable.

To give a permanent protection to certain places (e.g. operating theatre, dispensary, kitchen), strips of gauze or cotton impregnated with insecticide may be used (1 m length/m2 of ground surface area). Renew the impregnation every two months. Where there is a concentration of flies in a limited area (e.g. in a feeding centre), poisoned baits may be used (though there is a risk of poisoning of children and poultry). These baits should always be placed outside (on the windowsill, door, etc). They may be:

- Dried food mixed with a toxic product (1 to 2%). The bait is then spread at a rate of 6g/ 10 m2. or
- A 10% aqueous sugar solution mixed with the toxic product (0.1 to 0.2%), which is spread with a watering can or sprayer.
- Fly traps.

Fleas

Fleas are blood-feeding (haematophagic) insects with a close relationship with their host. Their developmental stages all occur on land.

The flea is usually a specific parasite but it is capable of changing its host (wild or domestic rodent, man, etc.) in certain circumstances.

Biology

The development cycle lasts about one month. The eggs are laid in dusty places in houses or in rodents nests.

The larvae are found in dark places (negative photo-trohism).

In the adult stages both sexes are blood feeders.

Contamination of the host may take place through a bite (plague) or excrete (typhus), so dust may be highly contaminating.

Control methods

Control is essentially by chemical methods, even if cleaning dwellings and burning dust gets rid of eggs and larvae.

It is essential to determine the sensitivity to any given insecticide because of the many problems of resistance.

Bedding and clothes are treated with an insecticide powder.

Disinfectant products (chlorine solution, 4% cresyl, etc.) are effective against eggs and larvae.

In the case of a risk of epidemic (plague) it is essential to destroy the population of fleas without harming the host species (e.g. rat) because of the risk of human infestation would be increased.

Control is done by putting insecticide powder on the rodent's trails or in their nests. Permethrin (0.5%), propoxur (1%) or any other effective insecticide is used. (Organochlorines are generally ineffective.). The powder is laid down in lines 50 cm long and 3 mm wide near to a non-poisonous bait, to attract the maximum number of rodents.

Rodents

General points

Rodents make up about half the mammal population and thus play an important role as reservoirs of pathogens in the transmission of diseases to other mammals.

Domestic rodents (and those of medical importance) are composed essentially of three species of the muride family: the black rat, the brown rat and the mouse.

Methods of transmission

Pathogenic agents are transmitted by:

- an ectoparasite of the rodent which thus plays only a secondary role (e.g. plague);
- rodent excrete (e.g. salmonella, leptospirosis);
- a bite.

Biology

- The black rat

The adult measures about 40 cm from head to tail and weighs 250 g.

The muzzle is pointed, the ears round and protruding from the fur, and the eyes protuberant. The animal may be dark grey or brown.

The nest is built generally on the ground, in vegetation or in trees (and exceptionally in a burrow or sewer).

In houses the nests are generally built under the roof and the territory is more "aerial" than terrestrial with a radius of about sixty meters.

Its diet is very varied (vegetable and animals). Sexual maturity is reached at two months (5 litters of 7 to 8 rats per month).

- The brown rat (or sewer rat)

The colour is generally brown. It is bigger than the black rat and may exceed 400 g. Its muzzle is rounded and the eyes and ears are smaller than those of the black rat.

This species is not well adapted to hot countries. Nests are built in burrows (entrance diameter: about 8 cm).

The diet is less varied than that of the black rat. The brown rat prefers refuse and human wastes. Its biology is identical to that of the black rat.

- The domestic mouse

This is a well known universal species. Its biology is similar to that of the rats. It can survive with the water enclosed in food (flour, etc.) whereas the rat needs "free" water (e.g. infusion liquids).

Its maximum weight is 20 g, and its length 20 cm. For two animals of the same size, the head and feet are larger in the young rat.

Nests are built in any place where there is an accumulation of material for making the small shelter which the mouse needs, making control difficult, specially as the adult's sphere of activity is never more than a few meters.

Control methods

ENVIRONMENTAL HYGIENE

As for any other vectors, this means making the environment unsuitable for rodents, working on two fronts:

- Food

· packaging of stored food
· disposal of refuse

- Reproduction: eliminatation of likely sites (refuse tips, waste packaging scrub).

PROTECTION AGAINST RODENTS

The aim is to prevent access by rodents to important or vulnerable areas (food stores, infusion liquids, etc.).

- Block or protect all openings greater than 6mm with cement or metal netting
(1 mm wire, mesh less than 6 mm dia).
- Fit discs on cables joining roofs.
- Paint a smooth band on walls at 1m from the ground to prevent passage on rough vertical surfaces.
- Fix galvanized sheet (1mm) at the bottom of doors and on the skirtings.

Stores are always places where people come in and out and where doors are often left open. It is therefore useful, in addition to the above mentioned measures, to organise stores according to the following points:

- Repair all broken packages;
- Leave a passage (1m) between walls or pillars and stacks, to allow inspection;
- Stack bags with care, leaving a sufficient space between the top of the stack and the roof;
- Clean the store daily and never let a stack remain intact for more than a month.
- Inspect the store at least once per week, looking for:

· insects,
· signs of damage on the bags (water, mould, fermentation, etc.),
· the presence of rodents,
· empty bags and refuse not thrown away.

TRAPPING

This method never achieves complete eradication by itself. It may be used to get rid of the last few survivors of a chemical control campaign or individuals of an isolated and small infestation.

Spring traps are the only efficient models. The key points to follow are:

- Many traps should be used.
- The traps should be placed perpendicular to the rodents' trails.
- Rat traps should be left unset for several days so that the rats become used to them (except for mouse traps). A well placed trap does not need bait.

POISONING (POISONED BAIT)

Two classes of product are used:

- Single dose poisons

These are only effective if the animal ingests a lethal dose at the first feed, otherwise it will not go back to the bait.

These substances are extremely toxic and in addition they need special skills and experience in rodent control if their use is to be at all effective. For information, they are:

· Zinc phosphate (1 to 5%),
· fluorocetamide (2%),
· sodium fluoroacetate (0.25%),
· certain anticoagulants.

- Multiple-dose poisons

These are anticoagulants with a cumulative effect used at low doses, which have two advantages:

· The slowness of their effect allows the animal to absorb a lethal dose before the first effects are felt.
· Their mode of action makes them less dangerous to man and other domestic animals, and there is an effective antidote.

Products in use

See the table on the following page.

The bait is bought ready to use, or made with broken cereal grains which are soaked over night to moisten them to make a thick paste. Sugar may be added (5%) to make it more attractive, as it is important to persuade the animal away from its usual food and get it to stick to this new diet.

The poison is then mixed in, and the bait is laid on the rodents' trails in piles of 25g (mice) or 200g or more (rats).

These baits should be out of reach of other animals. They can be laid in particular ways (e.g. a slightly open plastic bag, a short piece of pipe, a small wooden box, etc.).

Effects should be seen in 3 weeks for the brown rat, 4 to 5 weeks for the black rat and the mouse.

The baits are always renewed, and left in excess. The dead bodies should be disposed of quickly and well: pick them up twice per day and put them in a plastic bag (with their fleas).

Chemical control will only be effective if it is complemented by environmental hygiene and if both efforts cover the whole area concerned.

Periodic inspection should allow renewed control measures before being faced with a new massive infestation.


Figure

C. Precautions for use and storage of insecticides

Precautions to be taken by the operator

Before use, the operator must be sure of the nature of the product and familiar with the manufacturer's specifications. In case of any doubt about the origin of this product, its storage conditions, or if the label is missing, a concentrated insecticide should never be used.

Check the spraying equipment. Pressured equipment should always be operated first with water to trace any leaks (often a cause of poisoning).

For engine-driven sprayers, protect the insecticide feed pipe from the exhaust pipe.

The preparation stage (dilution, filling the tank) is the most dangerous, as concentrated products are handled.

During preparation and treatment the following rules should be respected and enforced:

- Do not smoke, drink or eat.
- Do not keep cigarettes on you.
- Do not put anything to your mouth (to unscrew, blow, unblock, etc.).
- Wear protective equipment corresponding to the toxicity of the product being used:

· Powder: dust-mask and gloves.
· Liquid: canvas overalls, wide-brimmed hat, boots and gloves resistant to hydrocarbons, side protection glasses and mask. For the mask, the cartridge should correspond to the product being used and should be changed regularly (every 60 hours, in the open air). Check that it is airtight before starting work (take care of beards, hair, etc.).

- Make sure that these safety precautions are feasible (heat, etc.).
- Do not spray if it is windy.
- Establish a rotation of the team to avoid too long exposure for each individual.
- Empty and clean the equipment at the place of treatment. Do not throw remaining products in ditches, ponds, water courses or any place which may involve pollution of the aquatic environment.
- Ensure that the staff are well trained in taking the above measures.
- Ensure that the medical services have been warned and that they have the means to take the necessary action in case of poisoning.
-Always have a shower system available (bucket of water and soap).

Criteria for selecting staff

Avoid people with the following risk conditions when selecting staff to make up a treatment team:

- Pregnancy,
- Alcoholism, chronic or otherwise,
- History of liver or nerve disorders,
- Heavy smoking,
- Allergies or skin diseases.

More subjective criteria are also important:

- professional integrity,
- meticulous work,
- neatness and tidiness.

Before starting to make up and train a team, find out if suitable people are already available in the region (although a mosquito control team is not trained to manage a programme to control lice, or do aerial spraying).

Precautions to take during transport and storage

TRANSPORT

One of the most frequent risks of poisoning by insecticides is from leakages of concentrated toxic products during transport. International legislation forbids the transport of concentrated products with foodstuffs. Serious accidents have already occurred through not respecting this basic rule.

For land transport, always repack drums with leaks or with worn corners at the base. Put straw (or other absorbent material) in the bottom of the vehicle.

This should be burned on arrival. Load with care, pack the drums closely together and tie them down to avoid them jumping up and down.

The packaging of certain powdered products needs special protection against rain (craft paper bags).

Direct contact between the driver and the load should be avoided (separate cab), specially for powdered and granulated products.

STORAGE

Insecticides should be stored under lock and key. They should be out of reach of children, animals and thieves. The store should be separate and at a distance from food stores. The building should be cool, well ventilated and dry. Ideally, the store should not be deep, so that drums of concentrated products may be handled without having to go right into the store. Raise the containers off the ground if there is any risk of flooding.

Long-term storage should be in metal drums coated on the inside with a flexible varnish. Use anti-rust paint if there is any trace of oxidisation. The drums should be stored on their sides with the plugs (of the drain holes) towards the bottom, and recovered with liquid, in order to avoid the entry of air and humidity which would oxidise and denature the product.

Never store more insecticides than necessary, as disposal of the excess requires very special techniques.

Empty containers

There are several important precautions which must be taken when reusing metal containers:

- Empty the container well.
- Rinse several times with a detergent solution.
- Rinse a final time with a mixture of water, detergent + 10% sodium bicarbonate.
Leave in the container for several hours, stirring from time to time, then rinse with clear water.

All the water used in this process should be disposed in a hole in the ground.

It is preferable to avoid reusing? the drums for food or water. If, for a good reason, this rule cannot be respected, make sure that the above measures have been taken.

D. Spraying equipment

The type of equipment depends on the product being used and on the type of treatment (surface, spatial, etc.).

Powders

- Soup spoon: treatment of individuals.
- Powder blower (hand or knapsack): treatment of the ground, bedding, people.
- Pierced tin, or jute sack: treatment of floors, of vegetation.

Liquids

-Aerial application

Just for information.

-Atomisers

This equipment gives an immediate and temporary treatment by creating a fog (condensation of the solvent in the air into very fine droplets).It is an engine-driven machine portable or mounted on a vehicle.

- Sprayers

This equipment gives a persistent treatment by spreading the insecticide in visible drops on walls, floors, stretches of water, etc.

Four techniques are used:

· The liquid is pumped in a tank.
· The liquid is expulsed in a watertight receptacle by the compression of its surface air.
· The liquid is carried away by a gaseous current.
· The liquid is expulsed by centrifugation.

E. Technical briefs

Classification of insecticides
Chemical methods for insect control
Formulations
Propoxur
Permethrin
Deltamethrin
Malathion
Pyrimiphos-methyl
Temephos
Repellents
Impregnation of mosquito nets

Classification of insecticides

A classification enables the grouping of chemically related compounds, to deduce their toxicity and precautions for use.

MINERAL COMPOUNDS

- Mineral oils: spreading on the water surface asphyxiates and poisons larvae which are there. (mosquitoes, etc.).

ORGANOCHLORINE COMPOUNDS (NEUROTROPIC POISON)

- DDT (Dichloro-diphenyl-trichloroethane): a compound of low toxicity to vertebrates. Effective against mosquitoes, ectoparasites (lice, fleas, etc.).

Contact insecticide. Large problems of resistance and big-accumulation, not very biodegradable.

- Methoxychlorine: same as for DDT. Partially biodegradable.
- HCH (Hexachloroocyclohexane) ("Lindane", "Gamurexane"): more toxic, less persistent than DDT, but less resistance and more biodegradable.
- Chlordane: used only for controlling cockroaches and grasshoppers.
- Dieldrin: very toxic, problems of resistance. To be avoided.

ORGANOPHOSPHOROUS COMPOUNDS (ACETYLCHOLINESTERASE INHIBITOR)

- Malathion: low toxicity, used against ectoparasites and mosquitoes.
- Fenitrothion: low toxicity, used against mosquitoes (eggs and larvae).
- Fenthion: used against mosquito larvae in urban areas and in stock raising areas.
- Temephos: almost no toxicity, used against larvae in drinking water. Problems of resistance.
- Chlopyripos: urban larvicide.
- Dichlorvos: against domestic arthropods (high toxicity and vapour pressure).
- Chlophoxim: mosquito larvicide.
- Pyrimiphos-methyl: skin contact dangerous, used by spraying (aqueous dilution), widely used in public health work

CARBAMATES (ANTICHOLINESTERASICS)

- Propoxur: domestic insecticide, low toxicity.
- Carbaryl: problems of resistance.

PYRETHRIN-PYRETHRINOIDS

- Decamethrin (Deltamethrin) ("K-Othrine"): low toxicity, irritant to mucosa.
Effective alduticide, almost universally used but expensive.
- Permethrin: ditto.


Figure

Formulations

- Technical product

Active ingredient in its purest commercial form. Used almost exclusively for ultra low volume (ULV) application.

- Powder and granules

Active ingredient (0.5 to 10%) with inert carrier (talc, gypsum, etc.). Powder is used for the control of lice and fleas. Granules allow better penetration of dense vegetation.

- Wettable powder

Active ingredient (20 to 80%) + wetting agent + inert carrier. Used for preparation of aqueous solutions.

- Concentrated suspension

Active ingredient in a fine powder (10 to 50%) + wetting agent + water. Used for preparing aqueous suspensions.

- Solution

Active ingredient dissolved in a solvent. As most insecticides are insoluble in water, the solvent is most commonly gas oil, kerosene or even acetone or xylene.

- Emulsifiable concentrate

Active ingredient (25% or more) + solvent + emulsifying agent (oil). This formulation allows dilution in water later.

- Emulsion

Emulsifiable concentrate + water.

- Slow-release formulations

Slow-dissolving capsules, granules, briquettes, etc., which allow continuous release of larvicide in water.

The concentration may be expressed as weight per volume (for liquid formulations) as weight per weight (dry formulations).

INTERNATIONAL CODE OF DIFFERENT FORMULATIONS (EXTRACT)

AB: bait as a grain
AE: aerosol generator
AL: other liquids to be used without dilution
BB: bait as a block
BR: briquette
CB: concentrate for preparation of bait
CG: granulated in capsules
CS: capsules suspended in a liquid, to be diluted in water before use
DP: dusting powder
EC: liquid concentrate, to be diluted in water before use
EO: emulsion with oil, ready to use
EW: emulsion with water, ready to use
FG: fine granules (0.3 to 2.5 mm)
GB: granulated bait
GG: large granules (2 to 6 mm)
GR: granules ready for use
LA: Lacquer
MG: micro-granules (0.1 to 0.6 mm)
OF: concentrated suspension to be diluted in oil
OL: liquid to be diluted in oil
PB: bait in bars
RB: bait, ready for use
SL: liquid formulation to dilute in water
SP: powder to dilute in water
SU: suspension, ready to use for ULV treatment
TC: product in its most concentrated commercial form
UL: liquid, ready to use for ULV treatment
WP: wettable powder, for dispersion in water

Propoxur (Carbamate)

Commercial names

- Baygon
- Blattanex
- Unden

Toxicity (per os for rats)

- LD50 = 95 mg/kg

Mode of action

- Contact or ingestion

Formulation

- Powder to dilute: 1%, 2%
- Wettable powder: 50 %, 70%

Method of use

- Dusting powder

Ready to use at the rate of 1 to 2g of active ingredient (100 or 200g of powder per m2)

- Wettable powder

Dilute in water for a final concentration of 0.5 to 1% of active ingredient (powder at 50% > 20 g/litre, - powder at 70% > 1kg/litre), spray at a rate of 100 ml/m2

For use against

- Body lice
- (mosquitoes, cockroaches, bugs, fleas).

Cost

- Powder: about $3 US/kg (25kg metal drum).

Quantity to allow

- For treating 1,000 people for body lice: 40kg + losses.

Precautions

- Avoid inhaling (dust masks for treatment team).

Permethrin (Pyrethrinoid)

Commercial names

- Ambush
- Coopex
- Stomoxin

Toxicity (rats)

- LD50 = 430mg/kg

Mode of action

- Contact, ingestion

Formulation

- Dusting powder: 0.5 and 1%
- Concentrated solution: 25% and 10%

Method of use

- Dusting powder

Ready to use

- Concentrated solution

Depending on vector

For use against

- Lice
- Impregnation of mosquito nets

Cost

- Powder: about $2 US/kg (25kg bag)
- Concentrated solution: about 16 US $/litre

Quantity to allow

- For treating 1,000 people for body lice: 40kg + losses.

Precautions

- Avoid contact with mucosa (dust mask, goggles).
- Possible skin allergies.
- Do not rinse with hot water.

Deltamethrin (Pyrethrinoid)

Commercial names

- K-Othrine
- Decamethrin
- NRDC 161
- Cistin
- Decis

Toxicity (rats)

- LD50 = 135 mg/kg

Mode of action

- Contact and ingestion

Formulation

- Wettable powder: 2.5%
- Concentrated liquid: 25g/litre

Method of use

- Wettable powder

One sachet of 33g/6litres of water

- Concentrated liquid

1 litre/200 litres of water

- Spray at the rate of 1 litre/10 m2

For use against

- Flies, cockroaches (bait)
- (fleas, ants, mosquitoes, etc.).

Cost

- Wettable powder: about $3 US per 33g sachet

Quantity to allow

-1 sachet per 60 m2

Precautions

- No specific precautions

Malathion (organophosphate)

Commercial name

- Malathion

Toxicity (rats)

- LD50 = 2.100 mg/kg

Mode of action

- Contact

Formulation

- Concentrated liquid; concentration varies with manufacturer.

Method of use

- Prepare a 1% Malathion shampoo with a detergent solution. Apply 15 to 20 ml per person. Do not rinse for 24 hours.

For use against

- Headlice

Cost

- About $6 US/litre

Quantity to allow

- Depends on concentration of initial solution

Precautions

- Use a deodorised product.

Pyrimiphos-methyl (organophosphate)

Commercial name

- Actellic

Toxicity (rats)

- LD50 = 2.018 mg/kg

Mode of action

- Contact

Formulation

- Emulsifiable concentrate
- Wettable powder
- Dusting powder

Method of use

- Flies

· Actellic 50 EC: 1 litre in 40 litres of water
· Actellic 25 PM: 1kg in 20 litres of water
· Powder at 2%: ready for use

- Bait

1 g/m2 of powder at 2%, mixed with sugar half and half)

For use against

- Adulticide with immediate or residual effect on flies, mosquitoes, lice, fleas, etc.

Cost

- Concentrate at 50%: about $14 US/litre
- Powder, 1%: about $4 US/kg; powder, 2%: about $5 US/kg

Quantity to allow

- Depends on formulation used

Precautions

Temephos (organophosphate)

Commercial name

- Abate

Toxicity (rats)

- LD50 = 8.600mg/kg

Mode of action

- Contact

Formulation

- 2% solution
- Emulsifiable concentrate
- Granules
- Briquettes

Method of use

- Reservoir of drinking water: 56 to 112g of active ingredient/hectare for 2 to 4 weeks
- River: 1g/m3 of flowing water for 10 minutes

For use against

- Mosquito larvae in drinking water
- Simulium (blackfly) larvae

Cost

- 2 % solution: about $7 US/kg

Quantity to allow

- Depends on the formulation and the area to be treated.

Example: 2% solution: 3 ml/3 m3 of drinking water.

Precautions

- No specific precautions

Repellents

Repellents are chemical products used on cloth or on the skin for protection against insects.

Products used

- DEET or diethyltoluamide
- Dibutyl phtalate
- Dimethyl phtalate

Formulations

- Lotion

The active ingredient is dissolved in an organic solvent. This formulation may be used on the skin or on cloth. Only natural fibres or nylon have no risk of reaction with the solvent.

- Cream

The active ingredient is incorporated in a cream.

An attractive effect has sometimes been noted during the first minutes. For this reason, creams are not effective until after 30 minutes.

Dose

The normal dose is:

- 20g of active ingredient per m2 (cloth, mosquito net, etc.).
- 7g of active ingredient per person.

Effectiveness

This varies according to the species concerned. It may be assumed that 100% protection lasts not more than two hours, whatever the product, and that it is about 80% after 5 hours.

Precautions

- These products conform to the standards of the cosmetics industry and do not pose any particular risks for the skin.
- Only benzyl benzoate and dibutyl phtalate have a repellent action in a very humid atmosphere.
Other repellents should be applied on a dry surface; this application should be renewed if the surface has got wet (rain, excessive sweating, etc.).

Impregnation of mosquito nets

The use of mosquito nets impregnated with insecticide gives individual protection against nocturnal insects in houses (carriers of malaria), which is much more effective than using an untreated net.

Choice of insecticide
Deltamethrin 2.5% EC or WP
Or, if not, permethrin, 20 or 10% EC

Dose

-Deltamethrin: 25 mg of active ingredient per m2 of cloth (minimum 15 mg/m2)
- Permethrin: 200 to 500 mg/m2

Impregnation method

1. Determine the total area of the cloth

2. Determine the volume of water absorbable by the cloth: dip several identical mosquito nets in a known volume of water, then wring lightly; measure the reduction in the volume of water and divide this volume by the number of mosquito nets (the average is about 15 ml per m2).

3. Dilution

Determine the quantity of active ingredient per mosquito net: multiply the dosage of active ingredient per m2 by the area of the net; then determine the corresponding volume of concentrated solution and thus the factor of dilution (volume of water + volume of concentrated solution).

Example:

- area: 18.7 m2
- dose of active ingredient: 25 mg/m2
- product: deltamethrin 2.5 mg/m2
- volume of concentrated solution: 467.5 x 100 / 2500 = 18.7 ml
- volume for impregnation of mosquito net: 280 ml
- dilution = 280. 18.7, or 1/15

4. Impregnation

- One net:

Put the mosquito net in a water-tight plastic bag. Add the predetermined volumes of water and insecticide for that mosquito net.

Close the bag and knead well to ensure good impregnation, then take out the mosquito net and leave it to dry, preferably flat, to avoid dripping and the movement of the insecticide to the bottom of the cloth.

Replace the mosquito net in the bag for storage and distribution.

- Several nets:

After having determined the dilution factor, prepare a volume of insecticide solution sufficient for the number of mosquito nets to be treated. Dip the nets, then wring lightly and proceed as above.

These operations should be performed by staff trained in the use of insecticides.

Take care when disposing of excess solution to avoid damaging aquatic life and affecting water quality.

Choose a coloured cloth which dirties less easily and which is therefore washed less often.

Persistence depends on the product and the climate but mostly on washing; a persistence of six months is realistic in most cases if the net is not washed.

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