Variación del recuento total de células nucleadas (RTCN)

3.13.1

3.13.1 AnophelesAnophelesAnophelesAnophelesAnopheles spp. spp. spp. spp. spp.

Some species of Anopheles that are anthropophilic, i.e. which prefer to bite humans, are important vectors of malaria and, in some areas, of lymphatic filariasis as well. In areas where the vectors are strongly endophilic, i.e. where they tend to rest indoors, interior residual house spraying can effectively control transmission. Use of insecticide-treated mosquito nets is highly recommended to prevent bites by the important Anopheles malaria vector species, which feed indoors at the time such nets are used, even if they do not stay there after feeding. Vectors that are mainly exophilic but feed or rest indoors briefly can also be controlled effectively by indoor residual spraying, especially with insecticides that have a strong fumigant effect (see Tsee Tsee Tsee Tsee Table 1able 1able 1able 1able 1). In refugee camps, spraying the insides of tents with residual insecticides can reduce malaria transmission. In areas where the vectors are strongly exophilic or exophagic, i.e. which rest and bite outdoors, personal protection and other methods, such as space spraying or larval control, should be considered.

Many vector species have developed resistance to organochlorine compounds, and some are also resistant to organophosphate, carbamate and pyrethroid insecticides. An insecticide should be selected on the basis of an assessment of the susceptibility of the target vector. For long-term use, regular monitoring of resistance should be instituted (see section 1.6).

3.1.1

3.1.13.1.1

3.1.13.1.1 Indoor residual sprayingIndoor residual sprayingIndoor residual sprayingIndoor residual sprayingIndoor residual spraying

In view of the general applicability of this method and the relatively well-established standardization of the application techniques and equipment, indoor residual spraying continues to be the most widely used method for malaria vector control. Indoor residual spraying increases the risks for a mosquito each time it enters a house for a blood meal, which it typically does every 2–3 days, so that few will survive the approximately 12 days that are required for malaria parasites to complete part of their life cycle in the vector

23 23 23 23 23

MosquitoesMosquitoesMosquitoesMosquitoesMosquitoes

mosquito. In practice, the effectiveness of house spraying for malaria control depends on adherence to the criteria specified for the insecticide and the application procedure, public acceptance of spraying, the availability of well-maintained equipment, adequately trained spraying personnel, efficient supervision and strong financial support. The size of the operational area depends on local circumstances and is influenced by the distribution of malaria and malaria vectors, the distance from important breeding sites, the flight range of the vectors and demographic features.

(a) Target area

Generally, all the interior walls and ceilings of a house are treated. Not only permanent dwellings but also field huts in which people sleep during the planting or harvesting season and animal shelters might have to be sprayed, depending on local vector behaviour. Where, as is the case with A. culicifacies, the vector bites and rests both in human dwellings and in cattle sheds, both types of structure should be sprayed. On the basis of knowledge of the resting behaviour of the target species, treatment might be confined to the ceiling or the lower or upper half of the walls. In other cases, the undersides of furniture, outside eaves and porches might need to be treated. It should be noted that the residual effect of insecticides can be much shorter on some surfaces, such as porous mud walls, walls covered by cement or alkaline whitewash and surfaces exposed to sunlight.

T T T T

Table 1.able 1.able 1.able 1.able 1. WHO-recommended insecticides for indoor residual treatment againstWHO-recommended insecticides for indoor residual treatment againstWHO-recommended insecticides for indoor residual treatment againstWHO-recommended insecticides for indoor residual treatment againstWHO-recommended insecticides for indoor residual treatment against mosquito vectors

mosquito vectorsmosquito vectors mosquito vectors mosquito vectors

Insecticide Chemical type Dosage of ai Duration Insecticide WHO hazard

(g/m2_{) of effective action classification}

action (months) of aia

Bendiocarb Carbamate 0.100–0.400 2–6 Contact & II

airborne

Propoxur Carbamate 1–2 3–6 Contact & II

airborne

DDT Organochlorine 1–2 > 6 Contact II

Fenitrothion Organophosphate 2 3–6 Contact & II

airborne

Malathion Organophosphate 2 2–3 Contact III

Pirimiphos-methyl Organophosphate 1–2 2–3 Contact & II

airborne

á-Cypermethrin Pyrethroid 0.020–0.030 4–6 Contact II

Bifenthrin Pyrethroid 0.025–0.050 3–6 Contact II

Cyfluthrin Pyrethroid 0.020–0.050 3–6 Contact II

Deltamethrin Pyrethroid 0.020–0.025 3–6 Contact II

Etofenprox Pyrethroid 0.100–0.300 3–6 Contact U

λ-Cyhalothrin Pyrethroid 0.020–0.030 3–6 Contact II

ai, active ingredient

(b) Insecticides

The factors that must be considered in selecting an insecticide for indoor spraying include availability, cost, residual effectiveness, safety, vector susceptibility and excito-repellency17

(see section 1.3). Insecticides suitable for interior residual treatment are listed in Table 1. The use of DDT is discussed in section 1.1.

(c) Application procedures

Hand-operated compression sprayers fitted with a flat fan nozzle are widely used to apply insecticide and water mixtures evenly to walls and ceilings18_{. Water-dispersible}

powders are generally used, because they are cheaper and their residual effect is longer, particularly on porous surfaces. The advantages of other formulations, such as capsule suspensions, suspension concentrates and water-dispersible granules, are listed in chapter 1. Emulsifiable concentrate formulations are not recommended for indoor residual spraying because of their short persistence, especially on porous surfaces.

(d) Treatment cycle

The frequency of treatment depends on the duration of the residual effect of the insecticide at the dosage used, the type of surface sprayed, vector bionomics, the malaria transmission season and climatic conditions. Houses should be sprayed just before periods of high malaria transmission. The average duration of effectiveness of the various insecticides is given in Table 1. Early re-treatment is required, however, if insecticide deposits are removed from surfaces by re-plastering, whitewashing, re-roofing or smoke deposits.

(e) Precautions

Care must be taken to protect sprayers, the public and domestic animals from unnecessary or prolonged exposure to or accidental ingestion of insecticides. Safety guidelines for protecting, monitoring and treating sprayers are discussed in chapter 2. Proper, regular maintenance of spraying equipment also contributes to protecting sprayers from unnecessary contamination (see section 1.5).