GUIDELINES FOR MALARIA VECTOR CONTROL IN ETHIOPIA

Transcription

1 GUIDELINES FOR MALARIA VECTOR CONTROL IN ETHIOPIA Malaria and Other Vector-borne Diseases Control Unit Epidemiology and AIDS Control Department MINISTRY OF HEALTH March 2002 ADDIS ABABA

2 1 GUIDELINE FOR MALARIA VECTOR CONTROL IN ETHIOPIA 1. Introduction Malaria remains one of the major determinants of ill health in many countries of Africa, Asia and Latin America. In Africa south of Sahara, malaria is the leading health problem, with almost the entire population being at risk. More than 74% of the population live in highly endemic areas while about 18% lives in epidemic prone areas and only 7% lives in low or malaria free areas. The annual clinical cases are in the magnitude of 350 to 500 million with more than one million deaths, most of them among children under five years of age. The situation is worsening with the evolution of resistance to cheap and easily available drugs and insecticides, changes in environmental conditions leading to increasing epidemics, civil unrest coupled with population movements and economic development programmes in risk areas such of wetlands, desert fringes, and highlands. Indeed malaria has spread into areas, which previously had low or no transmission. Malaria affects the poor of the society exacerbating inequity in health and impeding development. The economic consequences of malaria related diseases are high. It contributes to more than 10% of DALYs in the region. It is estimated that direct and indirect cost of malaria amounted to more than $ 2 billion in Malaria control in Africa decreased tremendously with the end of the eradication era. What little was gained during that time in vector control declined quickly to practically nothing by the early 70s and only a few countries in southern and northern Africa continued with vector control activities. Increased interest in tackling the malaria problem started again towards the end of the 80s, with the call for the African countries to evaluate their malaria control situation and reallocate adequate resources towards malaria control efforts. The global ministerial conference held in Amsterdam in 1992, adopted a global strategy for malaria control, and later by the world assembly in 1993, with the following basic elements: 1. To provide early diagnosis and prompt treatment 2. To plan and implement selective and sustainable preventive measures including vector control 3. To detect early, contain or prevent malaria epidemics 4. To strengthen local capacity in basic and applied research, in particular the ecological, social and economic determinants of disease. The African region has renewed their efforts towards malaria control largely through support from the Director General of the World Health Organisation. The Director General made available $ 9 million to the African region for accelerated implementation of malaria control programmes in 1996 which lead to intensified provision of technical support to countries with 38 countries developing their action plans and benefiting from these funds for the last 2-3 years. Research on malaria has been strengthened and partners sensitised to participate in malaria control efforts in Africa. The Roll Back Malaria movement will further efforts towards collaboration of all stakeholders for better planning and implementation of malaria control.

3 2 2. Purpose of the Guidelines and the potential users 2.1 Purpose of Guidelines The guideline gives a brief description of global strategies available for vector control and situations suitable and cost effective for each strategy. It is intended to provide guidance and to serve as a basis for the planning of country specific vector control strategies. 2.2 Potential users The guideline is intended for use by those responsible for malaria control. These include national malaria control programme personnel; regional malaria control programme, health facilities, government sectors other than the health sector, NGOs, and relevant international and bilateral agencies and other donors in support of malaria vector control. 3. MALARIA VECTOR CONTROL 3.1 Objective of vector control The objective of vector control in malaria control programme is to reduce levels of transmission, thus reducing malaria morbidity and mortality. 3.2 Planning of Vector Control Interventions Malaria control is a big challenge due to many factors: There is the complexity of disease control process; the complexity of the vectors; expensiveness of the control program. There is a variation of disease patterns and transmission dynamics from place to place, by season and according to climate and environmental circumstances. Since malaria varies from season to season and from place to place within a country, approaches will also differ in the planning and implementation of vector control. Each region's circumstances will influence the organisation of practical programmes to identify local problems and priorities, and the design and implementation of appropriate interventions. Therefore, selection of suitable, sustainable and costeffective interventions must be based on local analysis. The following major problems underline malaria control programmes in Ethiopia: 1. Existing health services in most areas are inadequate for good quality and coverage of disease management. 2. Most regions lack both financial and technical resources for implementing malaria control programmes. 3. Use of selective, cost effective strategies in vector control has not been advocated in adequate manners. This, therefore, calls for careful consideration and appropriate decisions on what control measures to be applied, for a maximum cost-effectiveness. A number of control measures are available which differ in their levels of effectiveness. Thus selection of a method should consider the magnitude of the malaria problem, the major vectors involved, levels of transmission and risks groups, available resources, technical and operational realities. Sustainability of selected interventions must be

4 3 assured. In most cases these measures should be used in an integrated manner to maximise effectiveness. 4. AVAILABLE TECHNICAL INTERVENTIONS The available interventions may be divided into two categories. One, those that are simple and require individual or household efforts and provide individual protection, and two, large scale interventions requiring more concerted community efforts and aimed at reducing mosquito population, thus providing community protection. 4.1 Personal protective measures Personal protective measures include those giving individual protection to reduce mosquito bites, for example: use of repellents, protective clothing and use of mosquito nets. Providing protection to a whole household such as insect proofing of house use of insecticide sprays, coils or local herbs and prevention of breeding in and around houses. These measures are simple and easy to apply, require no particular expertise and can be applied by individuals or household for their own protection Repellents - Repellents are normally applied directly to skin or clothing/ other fabrics e.g arm and ankle bands, or mosquito screens. The most commonly used insecticide is Deet (Diethyl-toluamide). Repellents are recommended for people staying outdoors at night for work or leisure and those working in plantations and may be at risk during daytime. - Repellents are available in various forms (cream, lotion, soap, jelly) and modes of application - They are easy to apply - Repellents prevent human-mosquito contact by acting as an irritant to the mosquitoes - Repellents evaporate quickly and so are short lived (few hours), requiring regular applications. - Repellents do not knock down or kill mosquitoes - Overall cost may be high - Effectiveness to control malaria is limited, has to be used in addition to other measures Protective Clothing Long garments are won to reduce areas exposed to mosquito bites. These are convenient in cooler areas and in the evening for outdoor activities. However, in hot climate they are uncomfortable and inconvenient to wear while working. There is little or no protection when the material used is light and mosquitoes can bite through them.

5 Use of mosquito nets Mosquito nets have been used for a long time as a protection against bloodsucking insects and other nuisance creatures. A net must be lowered and tucked under a mattress or sleeping mat to prevent entry by mosquitoes. Otherwise, the net should be lowered to the floor round the sleeping place. They should have a border of strong material to prevent the net from being torn. - Nets can be made locally from different materials and can be made in different shapes - Nets are flexible and can be used indoors or outdoors, and moved from place to place. - Nets are less protective when are not used properly or are torn - In hot climates nets may be uncomfortable to use due to poor ventilation - Contact with the net during sleeping allows mosquitoes to feed on individuals sleeping under it. Effectiveness to control malaria is limited. Treating a net with insecticides improves its effectiveness (see below) Aerosols - Aerosols are packed in pressurised cans for easy spraying or can be applied with a spray pump. Aerosols are normally sprayed indoors in the evening with doors and windows closed to allow the insecticide to knock down and kill any mosquitoes, which could be resting inside. Some aerosols are also repellent and will prevent further mosquito entry for a day or so. But in most cases effects of aerosols are very short lived. - Aerosols are widely available and in many varieties - They are easy to apply - Have rapid knock-down effect on insects including mosquitoes - Very short residual effect (few hours to one day) and are rapidly degraded by light - Effectiveness to control malaria is limited, has to be used in addition to other measures - Use of aerosols is expensive for long term application Coils, vaporisers and anti-mosquito plants - Coils contain pyrethrum or other insecticides in a vaporiser base, which when heated release the insecticide in form of vapour or smoke. Burning of local herbs known to have repellent effects e.g. Citronella and other aromatic trees fall into this category. Usually these are burned indoors or outdoors and the smoke repels and sometimes knocks down mosquitoes.

6 5 - They have rapid knock-down effect on mosquitoes - Widely available even in rural areas - Some preparations are relatively cheap - Have very short residual effect thus need daily application - May have unpleasant side effects due to irritant smoke e.g. coughing - Effectiveness to control malaria is limited, has to be used in addition to other measures House screening/proofing - This involves screening of doors, windows and other openings to prevent insects from entering the house. Netting materials are best as they allow good ventilation. - They are long lived once applied. - Screens may be treated with an insecticide to make them more effective - Less effective where people stay outdoors during mosquito active times. - May be relatively expensive in poor rural communities Prevention of breeding in and around dwellings Prevention of breeding around dwelling involve the removal of possible breeding sites near homes by filling ditches, borrow pits and holes where water collects, burying empty tins and other containers where water may be collected and act as breeding sites. Individuals or communities in rural or urban areas may apply this measure to reduce mosquito populations. - Easy to apply and cost almost nothing - Help to keep home environment clean - Have little effect on malaria transmission except when widely applied. 4.2 DISEASE CONTROL / TRANSMISSION CONTROL Disease control in the community on the other hand requires more concerted efforts and need to be applied on a larger scale. Measures applied to reduce transmission aims at reducing breeding and survival of the mosquito vectors. Some of these measures require particular expertise and specialised equipment to apply and almost all measures requires good knowledge of local vectors, especially their breeding and resting behaviours. These interventions include: Environmental management/sanitation Use of biological agents (biological control)

7 6 Use of chemical insecticide e.g. indoor house spraying/ larviciding/fogging, Use of Insecticide Treated Materials Environmental management Environmental management involves the modification of the environment to make it unfavourable for the vectors to breed. These include draining or filling up of ponds and borrow pits, intermittent draining of irrigated areas and maintenance of irrigation channels. Construction of drainage channels. Environmental management can effectively be used in urban settings to control mosquito breeding. - Can be applied anywhere, where breeding sites are well defined, limited in number and accessible - Environmental management applies a multi-sectoral approach, involving all concerned partners e.g. health, agriculture, etc - Generally easy to apply and can be done by the communities themselves - Need to cover a relatively high proportion of breeding sites to be effective, thus proving ineffective on its own in most rural setting in sub Saharan Africa - Cost effective when permanently than repetitively applied. - More effective where breeding is seasonal - Some instances may require high capital costs, for example in the construction of drains in urban settings Use of Chemical insecticides Chemical insecticides can be used against the immature as well as the adult stages of mosquitoes Larviciding Larviciding involves the killing of immature stages of mosquitoes by application of various forms of chemicals to the breeding sites. The most common chemicals are insecticides of various groups, insect growth regulators or bacterial larvicides. - Larviciding is effective in localised well accessible breeding sites - May be applied in conjunction with other methods - Not effective in most rural areas of the African region where breeding sites are ubiquitous. - Have short-lived activity therefore require frequent applications. - Some larvicides are harmful to other non-target organisms including natural predators of mosquito larvae and may result in environmental pollution if insecticides to be used are not well selected. - Larvicides are expensive

8 Space Spraying Space spray employs the same principles as the small aerosols but applied in a larger scale. However, ultra low volume (ULV) sprays or fogs are used. Space spraying is usually applied in and around houses and outdoor resting-places. Space spraying requires special equipment such as thermal foggier and motorised knap-sacks. Sometimes large pumps mounted on vehicles are used for the purpose. They are fast acting and therefore highly recommended in outbreak situations. - Relevant in urban areas and in areas where people congregate outdoors during vector active periods - Suitable for control of outbreaks because of its immediate effect on adult mosquito populations - Less labour intensive and large areas can be sprayed in a short time - It kills indoors and outdoor resting mosquitoes - Needs timely application to coincide with vector activity times - Have short residual effect, thus requiring frequent applications and high recurrent costs - Highly technical in application with high operational costs - Effective where vector is highly exophilic/ exophagic. - May cause pollution and contamination of the environment and other nontarget organisms e.g. bees Indoor Residual House Spraying Indoor spraying is one of the most valuable tools in malaria vector control. It was the strategy used in the most successful eradication programmes of the 50's and 60's. Indoor house spraying involves the spraying of inside walls with a long lasting (residual) insecticide. A variety of insecticides are available for indoor spraying, and selection of which insecticide to use will depend on the local situations (eg. susceptibility of local vectors, vector behaviour, areas to be sprayed) and resources available (cost of the insecticide and human power). The commonly used insecticide during the 50's and 60's was DDT. DDT is still used in some African countries for the control of epidemics, for example South Africa and Ethiopia although its use is now very much restricted. Other groups of insecticides such as organophosphates, carbamates and pyrethroids are available for indoor spraying. Indoor house spraying is considered appropriate and cost effective where the following conditions are met: - A high percentage of structures in an operational area have adequate sprayable surfaces and can be well sprayed. - The majority of vector population rest indoors - The vector is susceptible to the insecticide in use. Before any residual house spraying is implemented, it is imperative that detailed studies are undertaken on disease transmission, the behaviour of local vectors and their susceptibility to insecticides to be used, the extent and nature

9 8 of localities targeted for indoor residual spraying and resources available for the exercise. - Indoor house spraying reduces vector life span and vector population, thus interrupting transmission. - Have a long lasting residual effect, thus requiring less application. - Is the method of choice in epidemic control because of its fast effect on adult mosquitoes. - Need to be applied in areas with sprayable structures - Where vectors feed and rest outdoors, indoor spraying is ineffective - Its application is highly technical and with high operational costs - Highly labour intensive and requires specially trained manpower and specialised equipment. - Communities may object to spraying of their houses, due to various reasons - Re-plastering for any purpose reduce the potency of the insecticide Insecticide Treated Materials (ITMs) Insecticide Treated materials (ITMs) is one of the most up coming malaria control strategy, which combines a physical barrier with an insecticide against adult vectors. Insecticide treated materials are important in malaria control because when used widely in the community, ITMs has been shown to reduce transmission of the disease. The evidence from several studies show that use of insecticide treated materials reduced severe malaria cases in children by about 45% and all cause mortality by about 20% compared to those not protected by any net. (C. Lengeler Insecticide treated bed-nets and curtains for malaria control. The Cochrane Library, Issue 4) Materials and Insecticides for ITMs. A wide range of materials can be treated with insecticides e.g. window/door curtains, wall mats, cloth etc. In selecting materials for ITMs multi-filament synthetic materials are preferred because they are relatively cheaper than cotton, durable, easier to treat and takes in less insecticide. Currently, the pyrethroids group of insecticides is the only group recommended for the treatment of materials. These insecticides are relatively safe to humans, have a rapid insecticidal effect and persist on fabrics for a long time. A number of these insecticides are available and selection of which one to use will depend on the local conditions such as frequency of washing of materials and available resources (cost of insecticide). WHO recommended insecticides for treatment of materials, their formulation and dosage per square meter of material is shown in Table 1 below. - Treatment of materials with insecticide is simple and can be accommodated in the PHC system and carried out by communities.

10 9 - ITMs are portable and suitable in most situations for example travelling or in nomadic populations - Use of insecticide treated materials reduces other biting insects such as bedbugs, lice, flies and cockroaches. - Initial cost of materials especially nets precludes wide use in many rural poor communities. - In hot climates nets may be uncomfortable to use due to poor ventilation - Frequent washing of the fabric reduces the effectiveness of the treated material. - In some cultures use of ITMs especially mosquito nets may need some kind of adaptation. Table 1. WHO recommended insecticides for treatment of materials for malaria vector control. Insecticide Formulation 1 Dosage 2 Alpa-cypermethrin SC 10% Cyfluthrin EW 5% 50 Deltamethrin SC 1% and WT 25% Etofenprox EW 10% 200 Permethrin WC 10% SC= suspension concentrate; EW= emulsion, oil in water; WT= water dispersible tablet; EC= emulsifiable concentrate. 2 milligrams of active ingredient per square meter of material Adapted from WHO/CDS/CPE/WHOPES/ Biological Control Biological control of mosquito vectors involves the introduction of natural enemies into mosquito breeding sites. These could be in form of parasites or predatory animals e.g. fish, insects, fungi, nematodes or plants. Use of biological control agents require a good understanding of the agents and the mosquitoes to be controlled as well as their local environment. The most widely employed biological control agent is the larvivorous fish and to some extent the bacteria Bacillus thuringiensis Use of Larvivorous Fish Most fish fries are potential predators of mosquito larvae. However fish with potential for mosquito control (larvivorous fish) are those which show preference for mosquito larvae over other types of food, are small in size, have high reproductive rate in small bodies of water and are locally available. The most promising species are the Gambusia affinis and Poecilia reticulata - In suitable environment larvivorous fish may provide a self perpetuating larval control method

11 10 - Fish are environmentally acceptable - Need no special equipment for introduction and maintenance - Takes time for the fish to establish themselves, so not suitable in outbreak situations - Do not provide total control therefore has to be applied in combination with other methods Use of bactericides Bactericides are biological larvicides, which can be applied into mosquito breeding sites to kill mosquito larvae. Bactericides are used in the same manner as chemical larvicides. - Better than chemical larvicides because of their reduced effects on environment - They are short lived so require regular application - They are more expensive than chemical insecticides 5. SELECTION OF THE MOST APPROPRIATE CONTROL MEASURE For selection of the most appropriate control measure, a good knowledge of the local transmission dynamics is necessary. The methods available target the developmental stages (larval stages) and for the adults, take the advantage of the feeding and resting behaviour of adult females. Thus, a good knowledge of the breeding, resting and feeding behaviour of the local vectors must be well documented before selecting an intervention. Baseline information should be collected before initiation of intervention for proper monitoring and evaluation. Depending on the dynamics and the endemicity of malaria in an area, some interventions may prove very expensive and low costeffective. To reduce unnecessary costs, countries should first stratify its malaria transmission according to the major eco-epidemiological types, before deciding on which intervention measures to be applied where. 5.1 Stratification of areas for intervention 1. Areas with perennial or long periods of transmission, endemic stable malaria with An. gambiae & An. funestus as the main vectors - termed STRATA A 2. Areas with seasonal endemic transmission, and An. gambiae are main vectors - termed STRATA B 3. Areas with unstable, epidemic prone malaria with An. gambiae the main vectors - termed STRATA C 4. Areas with no malaria transmission - termed STRATA D 5.2 Application of different strategies for different STRATA 1. Repellents

12 11 - Recommended for STRATA A, B & C for personal protection 2. Insecticide Treated Materials STRATA A: - Recommended; Reduction of transmission, reduction of severe and complicated cases STRATA B: - Recommended; Reduction/interruption of transmission, reduction of incidence 3. Indoor House spray STRATA A: - Not recommended; high operational costs STRATA B: - Recommended; Interruption of transmission, reduction of incidence STRATA C: - Recommended; Interruption of transmission, reduction of incidence 4. Anti-larval measures STRATA A: - Recommended in localised breeding sites; Reduction of STRATA B: transmission; to be applied with other methods - Recommended if breeding sites are localised; reduction of transmission, reduction of incidence; STRATA C: - Recommended if breeding site are localised, to be applied with other methods 5. Environmental management: STRATA A: Recommended if breeding sites are localised, to supplement other strategies. STRATA B: Recommended if breeding site very localised References 1. WHO Technical report series No. 839: Implementation of the global Malaria control strategy 2. Document: WHO/SDC/CPE/WHOPES/99.5: Safety of Pyrethroid-treated mosquito nets 3. J. A. Rozendaal 1997.Vector Control: Methods for use by individuals and Communities in the Community.