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Planning for the introduction of ITMNs must be based on adequate knowledge of malaria transmission patterns and relevant vector characteristics. This must include the collection and analysis of the following information:
· Malaria morbidity and mortality data categorized by age, sex, occupation, and ethnic groups. Based on these, plans for the ITMN activities may be made in relation to the specific target, or priority groups. Capacity for the collection, analysis and use of such information must be developed· Seasonal patterns that will be used to develop a schedule for the distribution, treatment and re-treatment of the nets. In most cases treatment or re-treatment should take place just prior to the peak period(s) of transmission.
· Vector habits play a major part in determining how effective ITMNs will be. In areas where the major vector(s) bite(s) primarily indoors or late at night, the nets can be expected to be more effective than in areas where the vectors feed outdoors before people go to sleep or after they get up.
· Levels of nuisance insects, including all species of mosquitos, bed bugs, lice, and other biting insects. Elimination of these nuisance insects may be a major factor in determining how well the nets are accepted and used.
The first step is to define the size of the population to be covered by ITMNs. This requires the collection of basic demographic data on the population in the operational area. This should be the population:
· In the general (major) administrative areas within which activities are envisaged;· In the specified areas where ITMN operationalization is ongoing/planned;
· Involved in each type of high/special risk groups i.e. children under 5 years, pregnant women, and displaced persons/refugees;
· In different types of high or special risk areas, e.g. with exceptional drug resistance problem.
Based on the epidemiological data, and taking into consideration the available resources, the target groups to receive ITMNs can be defined. These are usually one or more of those above and in particular the priority group.
The acceptance and use of ITMNs depends on a range of social and cultural factors, some of which are:
Sleeping patterns: What time do people go to sleep?, where do they sleep?, and which members of the family sleep together?, and do they get up before dawn when Anopheles gambiae is still biting;Current usage of nets: Do people already use nets?, what kind of nets do they use?, where do they get them from?, and how much they cost ? etc.;
Cultural attitudes towards nets: In some cultures nets are a form of privacy, define individual space or define relationships within a family;
Colours: In some cultures white or black may have significance; so the choice of the colour of nets may be of major importance. Some may prefer specific colours, and
Sizes: Proportion of each size of net to fit the available beds and sleeping mats; typically four sizes of nets will be required;
Once the target population is defined, the planners must get an idea of these characteristics. These may be accessed from available data, and/or through sample surveys. An estimate should also be made on the existing net usage, and the expected acceptance of ITMNs. These will determine the amount and type of health promotional needs to achieve high levels of acceptance and usage. Subsequent development/delivery of IEC messages should accommodate the socio-cultural backgrounds and practices of the target populations. Programme adjustments must aim to counter any negating influences.
Short- and medium-term plans of action must be developed and integrated within those of the NMCPs. These should cover activities/events leading to the end-use of ITMNs (Annex 1). For each activity area and level of implementation, the roles/responsibilities must be specified in terms of primary, support, participatory and collaborative functions. The mechanisms or processes to be followed, and the support needs and conditions to be met must be clarified.
The plans should indicate how the resources (human, logistic and financial) are to be mobilized, the arrangements for procurement, storage and distribution, the potential sources, and the estimated timings of activities. Wherever possible, the activities must be linked with other aspects of malaria control as would be relevant for example in training and information management. Plans must include arrangements to ensure effective partnerships/collaboration and linked to the institutional/administrative framework for malaria control. Some of the basic concepts to be considered, including the objectives and ITMN targets, are discussed above.
The needs assessments to operationalize plans of action must be made for the country, as well as for the target populations and areas, and for each major activity area. Estimates must be made on human resources, logistics and finances including costs of imports, communications and transport, distribution systems including stock management, storage, net treatment sites, and training and operational research. The needs must be assessed according to what is already available and the projected needs. Allowances must be made for inflation and population increases, in long-term planning.
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Examples of issues to be considered in needs assessment for a target population are: ¨ Number of people targeted for protection (based on recent census); ¨ Number of mosquito nets to be introduced and treated, according to size of the target population; ¨ Number, types and sizes of nets estimated to be already available and treated; ¨ Number of nets to be treated, yearly for a period of 5 years; ¨ Number of personnel needed for each activity based on experiences/estimates on work outputs, e.g. average number of nets to be treated per worker/day in collective dipping; ¨ Number of people from each participating body, and at each managerial level involved in ITMN programme to be trained and the specific training needs for each category in the immediate, and medium-term; ¨ Amount of insecticides needed for 6-months, one year or more, according to types of insecticide and formulations, transmission season, and net washing practices. An assumption may be made for a specified coverage achievement of the operational targets e.g. 80%; ¨ Number and locations of storage sites and insecticide-treatment centres, and the number of mobile teams needed for net-treatments; ¨ Transport requirements; when, how often, from where to what points of use; ¨ Funding needs for each activity, their potential sources (if known or earmarked); |
Annex 2 provides an example of estimating the number of mosquito nets needed for an ITMN programme covering a 5 year period and where net targeting is focused on high risk groups (children 0-4 years, pregnant women). Some of the assumptions made here are:
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¨ The overall population in the country is 12 million, with 66.7% assumed to be in areas of stable transmission; ¨ Coverage achievement expected not more than 50%; ¨ Net use: Two children aged 2 years per net; each pregnant women one net; ¨ Total fertility rates, 6.0 per woman; ¨ Rate of increase in population 3%; ¨ Mosquito nets have a useful life of at least 5 years; this however may apply more to polyethylene nets as experience has shown even the 100 denier polyester nets do not last that long. |
Annex 3 provides an example of estimating the number of mosquito nets needed for the same population but with nets distributed to the entire household irrespective of the epidemiological stratification (not in malaria free areas). Here the assumptions are:
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¨ All age groups are at
risk; |
When budgeting in both instances, some of the considerations may be that, the price of a family size net is US$ 5 (including freight and insurance); the cost of treating a net is approximately US$ 0.5 per year (i.e. US$ 2.5 for 5 years); thus the total cost for one treated net is US$ 7.5 for 5 years, and the insecticide cost is already included in the cost of net treatments.
Budgeting needs to take into account the capital costs involved in e.g. supplies for net treatments, vehicles, and office equipment and furniture; and the recurrent costs such as for personnel (salaries, per diem and overtime), other supplies, and transport (fuel, etc.).
The needs assessment for these may take into account whether the ITMN programmes are being newly established, or are incorporated or linked with other components of malaria control activities, or with other services. Many of the resources and costs may be shared, and often equipment loaned temporarily.
Thus the needs estimations will depend on the objectives, and resource status at national and local levels.
Many types of materials are being used for making nets. The most common are: cotton, nylon, polyester, | polyethylene, polypropylene, and synthetic/cotton mixtures. These are either knitted or woven to create the netting material which is made into different shapes and sizes of nets.
In insecticide-treatment of nets, the amount of diluted insecticide emulsion absorbed depends on the type of material, i.e. weight, fabric weave, and size/surface area of net. The fabric-insecticide interaction depends on the type of material, the formulation and dosage of insecticide. These and the effects of washing influence the effectiveness of treated nets. Better understanding is needed on these interactions. In general, cotton absorbs more emulsion while insecticides such as permethrin, lambdacyhalothrin, and alphamethrin are less insecticidal on cotton than on the synthetics. This allows a single dilution strength of these insecticides to be used on cotton and the synthetics. No difference is reported between cotton and nylon with deltamethrin.
Nylon and polyester nets being light and flexible can be wrung well after dipping with little emulsion wasted from dripping while drying. With cotton, the insecticide solution drips even after thorough wringing leading to some waste of insecticide. Polyethylene and polypropylene nets with thick rather stiff fibres are difficult to wring.
In general, multi-filament synthetic materials (polyester, nylon) are preferred because:
· they are generally cheaper than cotton materials; although cheap cotton nets are also made e.g. in China and India;· they are easier to impregnate;
· they absorb less insecticide;
· a given dose of pyrethroids is more effective on them, and less insecticide is lost during washing and drying;
· they are more durable; and
· they allow more aeration to the net users.
When selecting nets for a programme the other important factors to be considered are:
Mesh - the number of holes per square inch. For example, 156 mesh has 12x13 holes per sq. inch, and 196 mesh with 14x14 holes per sq. inch. The wide mesh allows better ventilation. The 156 mesh is considered a standard for bednets.
Denier - the strength of the thread expressed as the weight of 9 000 meters of thread in grams. Three options, 40, 75, 100 deniers are available at present. Of these, the 40 and 75 denier nets are too fragile. The 100 denier 156 mesh is the strongest providing more durability against wear, tear and use. The extra cost for this compared to the lower denier ones is considered worthwhile.
Shape - the more commonly used designs are the rectangular (fig. 1), and conical (fig. 2). The rectangular nets can be hung from strings or frames to beds and are more spacious. This reduces the chances of arms and legs touching nets and risks of mosquito bites. Rectangular nets (without a door) are preferred over other styles because they allow a larger area of coverage inside the net. Elimination of the door slit reduces the cost while ensuring full protection to the occupants. The conical nets are generally easier to hang and fold and are especially useful in smaller rooms where the beds may also be used for sitting etc. in the daytime. Some nets are designed for travelers, e.g. conical ones with trade names Spider, (fig. 3), Klamboe, or Louisiane; the pyramid shaped Tracker (fig. 4); and wedge shaped Solo (fig. 5), or Rallye. Each type has its specifications in terms of weight, fabric, mesh, denier, suspension system, packaging and costs.
Shapes of nets commonly used
Fig. 1 Rectangular
shape
Fig. 2 Conical shape
Example of shapes of nets designed mainly for travelers
Fig. 3 Conical shape
Spider
Fig. 4 Pyramid shape
Tracker
Fig. 5 Wedge shaped
Solo
Size - four sizes of rectangular nets are commercially available and have become the de facto standards:
|
|
width |
length |
height |
|
Single |
70 |
180 |
150 |
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Double |
100 |
180 |
150 |
|
Family |
130 |
180 |
150 |
|
X-Family |
190 |
180 |
150 |
The conical nets in use are approximately 8.76 m2 for the single nets, 10.20 m2 for the double nets, 11.64 m2 for the family size, and 14.52 m2 for X-family size.
Colour - green, blue or pink nets are preferred because they avoid cultural problems often associated with white. In some areas however white nets may be preferred even though they show the dirt more than coloured nets. Coloured nets usually cost slightly more than the white nets. The prices may be negotiated especially when making bulk purchases.
Coding - logos, numbers or lettering can be imprinted on the nets by the manufacturer. Alternatively, blank tags can be sewn into one of the seams for writing numbers or other identifying marks. This may be useful to identify nets at family/household, individual, or donor levels, and by net sizes, or otherwise to identify the nets for re-treatments, and in monitoring, including checks on net washing.
Skirting - a solid fabric skirt can be sewn around the bottom of each net to avoid sagging and tearing of nets, or to reinforce the weight bearing apex of conical bednets. They can protect sleepers from insects and dirt falling when used at the top. The heavier materials however absorb large amounts of insecticide mixture, a waste and a problem in calculating insecticide requirements. Some suggestions being made to limit insecticide absorbency are to:
· use detachable borders,
· make narrow borders with non-absorbent material such as synthetics, and
· bind the borders with plastic and string during dipping as with tie and dyeing.
Reinforcement - special reinforcement of the corners or other seams can be requested. Although adding to the cost, reinforced corners may increase the effective life of a net. Selection of shapes, sizes and colours depend on the beds and sleeping arrangements, and people's beliefs, perceptions and preferences for colours. These must be taken into consideration in planning to improve compliance when introducing ITMNs.
Local production of nets - nets may be sewn locally, using netting rolls often available from the same companies that produced the finished nets. Rolls are generally 100 or 200 yards long, 78 inch wide, 75,156,196 denier (holes per square inch); and come in various colours. The prices vary with the material, mesh and denier.
Local community organizations, village committees, women's groups, cottage industries, and commercial sectors may be involved. Experience in the Western Pacific has shown that the quality of locally sewn nets can be as good or better than those produced commercially. Special sizes and shapes adapted to local needs can be made this way, including special nets for traditional infant carriers, hammocks or other special sleeping arrangements. It is important to set standards for materials, and train those sewing how to handle, cut the netting fabric, and stitch it. They must be monitored and guided periodically.
Often the final cost of locally sewn nets exceeds that from commercial sources. This must be balanced against a number of other considerations:
¨ Locally made nets identified as local products may be more readily accepted;
¨ Income accrues to those making the nets;
¨ Ability to produce specialized shapes and sizes.
¨ However in the long-term, local production must be directed to ensure adequate and ready availability of nets at affordable prices.
The choice of insecticide may depend on the vector susceptibility, established or anticipated efficacy, availability, cost and affordability. The insecticides selected must have been evaluated through the WHO, Division of Control of Tropical Diseases (CTD) where the specifications and conditions for use etc. are also stipulated. The insecticides should also be registered in the country, or in a neighbouring country where the appropriate pesticide registration procedures and requirements are being followed. Updated information on these must be maintained at procurement levels and through the management information system.
So far only the synthetic pyrethroids, and the “near pyrethroid” etofenprox are suitable for bednet treatments. They are excito-repellent, quick-acting, and effective in small quantities that can be made to adhere to fabrics. Those available at present are:
|
Insecticide |
Formulation |
Dose (mg/m2) |
Toxicity: oral LD50 of a.i. for rats (mg/kg of body weight) |
|
Alphacypermethrin |
SC |
20-40 |
79 |
|
Bifenthrin |
SC |
25 |
55 |
|
Cyfluthrin |
EW |
30-50 |
250 |
|
Deltamethrin |
SC |
15-25 |
135 |
|
Etofenprox |
EC |
200 |
> 10 000 |
|
Lambdacyhalothrin |
CS |
10-20 |
56 |
|
Permethrin |
EC |
200-500 |
500 |
SC= suspension concentrate; EW= oil-in-water emulsion;
CS= capsule suspension; EC= emulsifiable concentrate
There may also be other suitable formulations.
Permethrin
Permethrin the first pyrethroid to be used is the most widely used in net-treatment outside China. It exists in two isomers, the cis and trans. The cis form is more insecticidal and toxic to mammals. Formulations are available with cis:trans isomer ratios of 40:60, and 25:75.
Permethrin can be used in dosages of 200-500 mg a.i./m2. However, because of possible underdosing and reduced efficacy with washing and handling the recommended and most used dosage is 500 mg a.i/m2. The efficacy of unwashed treated-nets may last about 6 months, allowing 6-monthly re-treatments where year round protection is expected. Washing can remove about half the permethrin and more than half the insecticidal activity. Higher dosages (e.g. 1000 mg/m2) have been effective in curtains.
Deltamethrin, lambdacyhalothrin
These belong to the sub-group of pyrethroids with an alpha-cyano group in the molecular structure. They can be used in small quantities in a net allowing better adherence to the substrate and longer residual activity. Their use may be cheaper per individual net treatment. However they tend to be more toxic (than permethrin) to mammals and insects. Dermal exposure can cause sensory side effects which are reported to be temporary, toxicologically harmless but may be disturbing. Splashes on skin can cause a tingling or burning sensation lasting hours. Sleeping under a freshly treated net can cause a running nose and sneezing for a few days. So far these effects are reported more for lambdacyhalothrin.
Deltamethrin and lambdacyhalothrin may be used at dosages of 15-25 mg a.i./m2
Other alpha-cyano compounds
With the other alpha-cyano compounds, e.g. cyfluthrin and alphacypermethrin, the preliminary observations suggest that these are no different to the other alpha-cyano pyrethroids.
Etofenprox
The pyrethroid-like (pseudopyrethroid) etofenprox is structurally different, but functionally similar to the conventional pyrethroids. Its efficacy and dosage requirements are similar to permethrin. The mammalian toxicity is remarkably low, much lower than even permethrin.
The formulations considered for fabrics so far are the emulsifiable concentrates (EC), the suspension concentrates (SC), emulsion oil-in-water (EW), and microencapsules (CS). Wettable powders are unsuitable except deltamethrin. Formulations for agriculture which may contain offensive solvents are not recommended and should be avoided.
Emulsifiable concentrates (EC)
The most common pyrethroid formulations in use for net-treatment are the emulsifiable concentrates (EC). These are distinctive in that the clear often yellowish liquid concentrate turns milky when mixed with water. The ECs contain solvents often more toxic to mammals than the insecticide itself and which help the pyrethroids to penetrate the skin. Solvents often give freshly treated nets a characteristic smell which could influence communities' perceptions on safety and discourage the use of ITMNs. Most experience acquired relates to EC formulations of permethrin, deltamethrin and lambdacyhalothrin. EC formulations for public health are expected to be different from those for agriculture, and the latter may contain more hazardous solvents. The formulations used for ITMNs must meet the specifications for public health use.
Wettable powders (WP)
The WP formulations are generally not suitable for net treatment as the powder falls off easily with rapid loss of insecticidal activity. An exception so far is deltamethrin WP which is reported better on cotton but worse on synthetics than SC.
Suspension or Flowable concentrates (SCs)
These are aqueous formulations, the use of which can avoid side effects which may occur sometimes to the dippers working long-hours above dipping baths.
Emulsion oil-in-water (EW)
Except for permethrin, water-based formulations are available for the other pyrethroids used in the treatment of nets. Their efficacy is comparable to the relevant EC formulations. The water-based formulations have the solvent and the insecticide suspended as an emulsion in a water medium. Skin penetration and oral toxicity are expected to be reduced. It is not yet clear if they reduce paraesthesia.
Microcapsules (CS)
Lambdacyhalothrin is available in a formulation consisting of a viscous suspension of minute plastic capsules from which the insecticide slowly diffuses.
Currently, insecticides can be obtained in 0.5 to 2 litre bottles, 20, 25 and 50 litre metallic drums, and in individual sachets for treatment of individual nets. Bulk purchases in bigger containers are generally cheaper. The bulk procurement in drums may be repacked at national or programme level, according to the local needs. This may however cause insecticide losses from spillage/leakage during repackaging, leverage for dilution, misuse, and pilferage. Arrangements are needed to avoid such losses. WHO recommended safety precautions must be adhered to during handling and repackaging. Quality control, and stringent measures along with supervision and monitoring are therefore needed. Where people can afford sachets/doses for individual treatments, they may be delivered through commercial outlets. The package labels should provide adequate information to the users on the composition, procedures for use, and safety precautions.
Improvements are needed in developing packaging systems which accommodate the insecticide requirements for different types of net materials and sizes, insecticides and formulations, and for individual and bulk uses. These must be at prices affordable to the potential users.
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