,
. 27 October 1975
ICP/MPD/006
ENGLISH ONLY WORKSHOP ON ANTI-MOSQUITO MEASURES DIRECTED AGAINST MALARIA Sponsored by the
WORLD HEALTH ORGANIZATION REGIONAL OFFICE FOR THE WESTERN PACIFIC
Kuala Lumpur, Malaysia 4-16 August 1975
FINAL REPORT
NOT FOR SALE PRINTED AND DISTRIBUTED by the
REGIONAL OFFICE FOR THE WESTERN PACIFIC of the World Health Organization Manila, Philippines
The views expressed of the advisers and workshop and do not policy of the World
in this report are those participants at the necessarily reflect the Health Organization.
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CONl'ENTS
1. 2.
I HrR.ODUCTI ON ................................................................................ . EIUEF REVIEW OF MOSQUITO-BORNE DISEASES OTHER THAN MALARIA AND THEIR CONTROL IN THE WES'IERN PACIFIC REGION ..................................................................................................
1
2 2
2.1 2.2
2.3
Filariasis ................................................................................ Dengue fever/dengue haemorrhagic fever ••••••••••••••• Japanese encephalitis ••••••••••••••••••••••••••.•••••
2
3
ENVIRONMENTAL MANAGEMENT .•.••....••.•••••.•..••...•••••••••
4.
CHEMICAL CONTROL
............................................................................. 4-
4.1
Recent development in pesticides and their field evaluation ..............................................................................
4.2 4.3 4.4 4.5 4.6 5.
Recent development in spraying operation and equipment (including ULV application) .............................................. Ia.rvlcides .................................................................................... ..
Herbicides ...................................................................................... Aircraft disinsect10n •••••••••••••••••••••••••••••••• Safe use of pesticides
..................................
5 6 7 7 7
BI 0100-rCAL CONmOL ••••••••••••••••••••••••••••••.••••••••••
8 8 9 9 10
5.1 5.2 5.3
Larvivorous fish •••••••••••..•.••••••••••.••••••••••• Predacious plants and insects •••••••.••..•.•••••••••. Pathogens and paraSites
...............................
6.
GENETIC CONTROL
6.1 6.2 6.3 6.4
Sterile-male technique Cytoplasmic incompatibil1ty •••••••••••.••.•••.••••••• Hybrid sterility •.•••••••...•..•.••..•••••••••••••••• Chromosome translocations
................................
............................
10 10 10 10 11
7. 8. 9.
PLANNIl«J AND ORGANIZATION OF ANTI-LARVAL OPERATION ••••••••• EPIDEMIOLOGICAL, ENTCIttOLOGICAL AND OPERATIONAL EVAWATION
..
12
CRITICAL REVIEW OF THE DIFFERENT CONI'ROL METHODS •••••••••••
14 14 14 15
9.1 9.2 9.3
Environmental management .............................. . Chemical control Biological and genetic control •••••••••••••••••••••••
...............................................
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10.
INTEGRATED CONTROL AND COMPREHENSIVE APPROACH IN PLANNING VECTOR CONTROL PROGRAMMES •••••••••••••••••••••••••••••• CO~WSIONS
16
11.
•••••••••••••••••••••••••••••••••••••••••••••••••••••
17 18
ACKNOWIm>CiEME:N'I' •••••••••••••••••••••••••••••••••••••••••••••••••
ANNEX I
LIST OF PARTICIPANTS. OBSERVERS AND SECRETARIAT •••••••••••••••••••••••••••••••• "........ - PROORAMME •••••••••••••••••••••••••••••••••••••••••••
19
ANNEX II
23 25/26
ANNEX III - LIST OF DOCUMENTS DISTRIBUTED •••••••••••••••••••••••
1.
INTRODUCTION
A workshop on anti-mosquito measures directed against malaria was convened in Kuala Lumpur, Malaysia, from 4 to 16 August 1975. At the opening ceremony, Dr Jones Varughese, Director of the Public Health Institute. expressed his appreciation that the workshop was being held in the Institute. and welcomed the participants. A message sent by Dr Francisco J. Dy. Director of the WHO Regional Office for the Western Pacific. was read by the acting WHO Representative. Dr Dy thanked the Government of Malaysia for its generosity in acting as host and for providing the necessary facilities. He was particularly grateful to the Honourable Minister of Health, Tan Sri Lee Siok Yew, for consenting to open the workshop in person. The Honourable Minister of Health, on behalf of his Government, thanked WHO for holding the workshop in Kuala Lumpur as he considered the discussions to be held would greatly benefit the malaria eradication programme in Malaysia. In the message sent by Dr Dy, mention was made of the fact that DDT indoor residual spraying was still being used in anti-malaria work and that it had proved very successful in controlling the mosquito vectors. In some areas, however. it had not yielded satisfactory results either because of the resting and feeding habits of the local vector species or because the vector had developed resistance to certain insecticides. In these cases supplementary control measures might be necessary. The objective of the workshop was to update the participants' knowledge of modern methods of mosquito control, including anti-larval measures, and to provide them with information on the latest developments in pesticides, spraying equipment and techniques, including that of ultra-low-volume (ULV) application. Recent studies on alternative methods. such as biological and genetic control, would also be reviewed. These methods could be used to control not only malaria but also other mosquito-borne diseases. The workshop was attended by a number of key national and WHO malaria staff (see Annex I). The programme and list of documents distributed are given in Annexes II and III respectively. Field demonstrations of different insecticidal dispersing equipment. such as Fontan, Leco (H-D and Mini types), Micro-Gen, Microsol, Swingfog (portable and vehicle-mounted types) and Tifa were given in Kuala Lumpur. The group also visited Penang to observe tidal gates, automatic Siphons, sluice gates, stone-packed drains, bamboo-pipe subsoil drains, fascine drains (coconut husk packing and coconut leaf shading), agitation wells, the spraying equipment and nozzles used for larviciding, the packing and transportation of larvivorous fish, as well as mist spraying, using a Solo knapsack mist blower, and ULV application using H-D Leco with malathion and fenitrothion.
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2.
BRIEF REVIEW OF MOSQUITO-BORNE DISEASES OTHER THAN MALARIA AND THEIR CONTROL IN THE WESTERN PACIFIC REGION
Since all the participants are at present working with antimalaria programmes it was considered that a review of other mosquitoborne diseases and their control would be useful for their future work, particularly during an outbreak of, for example. dengue fever/dengue haemorrhagic fever. The diseases transmitted by mosquitoes other than malaria in the Western Pacific Region are filariasis. dengue fever/ dengue haemorrhagic fever and Japanese encephalitis. 2.1 Filariasis
Filariasis occurs in many countries and territories and is an important public health problem, particularly in the South Pacific area. Periodic Wuchereria bancrofti has a wide distribution, and the important vectors are Culex pipiens fatigans (in most localities). anopheline species (in some localities) and Aedes poicilius (in the Philippines). The subperiodic form occurs only in the eastern zone of the South Pacific and its important vector is !!. polynesiensis. The periodic form of Brugia malayi has been found in China. in a small area of Japan. in Kalaysia. and in the Republic of Korea. The vectors are Mansonia mosquitoes. anophelines and Ae. togoi. The subperiodic form is known so far only in Brunei, Malaysia and the Philippines, with Mansonia species as the vectors. Diethylcarbamazine has mainly been used to control filariasis. Studies are being undertaken to evaluate the influence of DDT indoor residual spraying, as an anti-malaria measure, on filariasis in New Hebrides and Papua New Guinea. Field trials on vector control by source reduction and space spraying are planned to be undertaken in the South Pacific. The use of herbicides for the control of the host plants of Mansonia mosquitoes has not been tried in the Region, but it has produced excellent results in Sri Lanka where !. malayi has now a~st disappeared. 2.2 Dengue fever/dengue haemorrhagic fever Outbreaks have occurred recently in many countries and areas.
A!' aegYpti is the primary vector. Systematic surveys of this mosquito have been undertaken. and the results indicated that the Breteau index (number of positive water containers with~. aegYpti larvae per 100 houses) of 858 obtained in Go-Cong, Viet-Nam, is so far probably the highest in the world, and an index of 500 in Davao, the Philippines, is the fourth highest. The actual application of the Breteau index and premise index (percentage of premises positive for Ae. aegYpti larvae) for the transmission of dengue fever/dengue haemorrhagic fever has not yet been worked out. but those applied to the transmission of urban yellow fever may be cited for reference. Areas in which the Breteau indices are less than S and house indices less than 4 are considered unlikely
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to promote the urban ~ransmission of yellow fever by ~. aegypti. Areas where the Breteau ind~ces exceed 50 and house indices 35. as well as where the human biting collection exceeds 2 female mosquitoes per manhour. are considered as involving a high risk of transmission. For long-term control of Ae. aegypti. Abate 1% sand granules at 1 ppm is used as a supplement to source reduction. ULV application of insecticides from the air or on the ground, as well as thermal fogging, was employed to stop outbreaks in Fiji, Malaysia, Singapore and Tonga.
2.3
Japanese encephalitis
Japanese encephalitis is an important public health problem in the Republic of Korea. Cases have been found also in Brunei, China, Hong Kong, Japan, Laos, Malaysia, Singapore and Viet-Nam. The most important vector is Culex tritaeniorhynchus wherever it occurs. Other species, such as £. gelidus and £. annulus, also play an important role in transmission. Swine are an important amplifying host. It was reported that in Sarawak, MalaYSia. Japanese encephalitis is transmitted by £. gelidus from pigs to pigs, and then to man by £. tritaeniorhynchus. The Japanese encephalitis Vector Research Unit was established by the Government of the Republic of Korea and WHO in early 1969 in Seoul to study the ecology and control of the vector mosquitoes. Its work was terminated at the end of 1974. It was reported that larcicides. such as Abate, fenitrothion and chlorpyrifos, can be applied to ricefields and more ideally to suburban swamps, but the costs are too high for a large scale programme. Spraying of animal shelters with OP compounds seems efficient, but it is hardly practicable over large areas. To combat widespread epidemics in highly populated areas, large scale aerial ULV application with melathion, fenitrothion or naled, has shown good results in the Republic of Korea. Ground ULV application has also proved successful in controlling mosquito adult popUlations in an urban area. Japanese encephalitis vaccines have been used in Japan and the Republic of Korea as prophylaxis for children and for the control of the virus amplifier, pigs. 3•
ENVIRONMENTAL MANAGEMENT
Environmental management for mosquito control means physically altering the environment to prevent, limit. reduce or eliminate mosquito production. It may be as simple as shutting off the flow of irrigation water promptly when a crop has been irrigated to avoid the application of excess water. or as complex as reviewing detailed plans of a major engineering project for a large water resource development. In public health, most projects of this sort may involve only minor ditching. filling, stream improvement, etc. Mosquito control projects are usually Simple, requiring only simple engineering work or surveys within the capability of the project staff, but major projects may require specialized professional engineering guidance. An adequate survey of the area and breeding sites involved is an essential prerequisite to the execution of environmental management.
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The measures most frequently employed include drainage. impoundment. contour designs, bank improvement, re-use of waste water, removal of organic solids, regulation of flow rates in channels or levels and depths of water, and flushings. Also involved are land preparation for other primary uses by filling, grading and drainage, crop management in agricultural areas, pumping for flooding or dewatering, and the management of tidal marshes or lagoons. Field personnel should be constantly alert to detect situations where a little source reduction may eliminate mosquito production. Equipment of various kinds for environmental management may be necessary, depending upon the project's undertaking. Major heavy equipment, including draglines, back hoes, cablewat excavators, ditching machines, dredges, bulldozers. etc., may often be obtained locally on rental or contract. During a field visit in Kuala Lumpur, it was noted that a number of highly successful "source elimination" projects had been carried out by the City of Kuala Lumpur in cooperation with the Malaysian malaria eradication personnel. These were mainly ditch lining projects, but a major reclamation project, where a polluted swampy mosquito producing pond was converted to a mosqUito-free clean water recreational lake and park, had also been undertaken. 4. CHEMICAL CONTROL
Chemicals remain one of the most important components of mosquitoborne disease control programmes. DDT is still the insecticide of choice for the control of malaria vectors, none of which has as yet developed resistance to it in the Western Pacific Region. As mentioned earlier, certain supplementary measures may be required in some areas. Recently developed insecticides, spraying equipment and techniques have been applied for the control of dengue fever/dengue haemorrhagic fever vector mosquitoes in the Region, and are gradually being app lied also for the contro 1 of malaria vectors in special situations. 4.1 Recent development in pesticides and their field evaluation
The number of new, effective, safe and low priced pesticides are not becoming available as rapidly as desired. It was noted that in 1971 there were only 38 new compounds submitted to the WHO programme for evaluating and testing new insecticides, as compared to 50-60 annually during 1967-70 and 150-200 annually during 1962-1966. Recently, the extended use of malathion for the control of malaria, Japanese encephalitis and dengue fever/dengue haemorrhagic fever has been noted. The WHO Expert Committee on Insecticides, which met in 1972. recommended the use of propoxur and fenitrothion operationally when the need for alternatives to DDT makes this necessary. provided that precautionary
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measures are taken. Some new insecticides, such as Landrin and Mobam (of the carbamate compounds), and phenthoate and jodfenphos (of the organo-phosphorus group) are recommended for extended field trials. Abate has been used extensively for ~. aegypti control in the In the Philippines, it was tried out for the control of larvae of Anopheles minimus flavirostris which breeds in slow-moving waters. Fenthion and chlorpyrifos as emulsifiable sprays are effective against £.~. fatigans larvae in polluted water. . Reg~on.
Insect-growth regulators (juvenile hormones, such as Altosid) were tested as larvicides in ricefields in the Republic of Korea. These are not yet in operational. use. New compounds submitted to the WHO programme for evaluating and testing new insecticides have to be tested for seven stages: Stage I: screening test - entomology. laboratory and simulated field test entomology and toxicology.
Stages II and Ill: Stage IV: Stage V: Stage VI: Stage VII:
experimental hut test - entomology and chemical formu lations. village trial - entomology, toxicology and chemical formulations. operational field trial - entomology, toxicology and operational experience. large-scale trial - epidemiology and operational assessment. o eration and e ui ment (includin
4.2
Recent ULV application
New operational policies, which would correspond more exactly to local requirements and conditions and enable maximum benefit to be attained from control operations, were proposed. In anti-malaria programmes, newer pesticides and equipment, as well as better application techniques, are being tested in order to increase efficiency or to resolve technical and operational problems. Hand-operated compression sprayers may be used for indoor residual spraying or for larviciding. Mist blowers, provided with proper nozzles and formulations, are chosen for adulticiding or larviciding, as are thermal and cold foggers for outdoor or indoor space adulticides. Vehiclemounted units have a greater capacity and can be used to apply windcarried swaths 50-150 metres wide, if motorable roads exist in the area. In most situations ULV application is reported to be more economical than thermal fogging. Various types of ULV equipment have been tested, and further trials have been organized in certain areas. One cold aerosol generator is being used in the Solomon Islands for the control
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of outdoor resting Anopheles farauti. Mist blowers are used in Penang as a supplementary measure to control the adult mosquitoes of Anopheles maculatus and~. campestris. All of the fogging techniques require favourable weather conditions or air movement for the optimum distribution of pesticides. Usually a wind speed of 3-6 km/h with low turbulence is most suitable. Mist blowers can be used in still air to produce a swath 20-30 metres wide. ULV aerial application is very effective for adulticiding and larviciding over large. open field areas. Penetration by aerial application into and inside houses is considerably less than by ground application of fogs and mist. The Hudson compression sprayer is being continuously tested in anti-malaria programmes and new parts and accessories. including nozzle tips with improved performance and a longer life of service. are being used. The group considered that the sprayer had considerably improved by the introduction of the new pressure gauge, a plastic screen in the cut-off valve and in the dip-tube, and two carrying straps instead of one for use in larviclding operations. It is important to evaluate the performance of nozzle tips in order to establish an economical replacement schedule, based on the cost of the tips in relation to the cost of the insecticide wastage. Collapsible or telescopic lances and swivel nozzles have been developed and are available for use in control operations. 4.3 Larvicides
Oils applied usually by the knapsack compression sprayer have been in use for many years. Because of the increasing cost of Oil. newer compounds are now being used and these have proved to be cheaper and more effective. The hand compression sprayer, when equipped with proper nozzles, provides efficient equipment for the application of liqUid formulation. Solid formulations, such as granules, applied by hand or by horn seeder, are recommended for mosquito breeding habitats with dense vegetation. or for use in confined breeding places where a residual effect may be desired, e.g., Abate 11. sand granules applied to wells and artificial water containers. The techniques of application can vary from direct application, with the larvicider walking at a normal speed (3-5 km/h) along a stream or a ditch, to the swinging lance technique, when he walks inside large collections of water. The walking speed of the larvicider, the swath width, and the discharge rate of nozzles are the factors which determine the rate of application and the strength of the spray liquid which regulates the dosage of larvicide. Power sprayers may be used in situations where large areas are to be treated and there are motorable roads.
I
I
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4.4
Herbicides
The main purposes of weed control are to improve crop production, to increase efficiency in irrigation and the water supply system, to facilitate vector control, and to promote water quality. Weeds may be controlled by chemical, mechanical or biological means. The chemical method is most effective but also most hazardous as it may damage crops or cause undesirable environmental effects. Various herbicides of contact, translocated, or soil-applied types are available. Great care needs to be exercised in their selection and application, with full consideration being given to the types of plants to be controlled and human and environmental factors. Some details were given of the nation-wide application of herbicides for the control of Pistia and Salvinia in Sri Lanka. Of a number of herbicides tested for Pistis clearance, Phenoxylene 30 and 2, 4-D amine salt of the chlorphenoxy compounds were found to be the most effective, cheapest, and easiest to handle. They proved to be much more effective in controlling young Pistia, which was killed in about a week. For Salvinia control, pentachlorophenol was found to be a satisfactory herbicide. This killed all the young plants and most of those in the middle stage of development in 7-10 days. Two applications were necessary for full-grown plants. 4.5 Aircraft disinsection
Increasing interest in and attention to aircraft disinsection have recently been noted. This was one of the subjects under discussion during the 1972, 1973 and 1974 meetings of the WHO Regional Committee for the Western Pacific. Aircraft disinsection was emphasized in many countries and areas in the South Pacific during the recent outbreaks of dengue fever. Methods of aircraft disinsection were reviewed. The dichlorvos vapour system was recommended during the 1974 World Health Assembly, and almost all the countries and areas in the Western Pacific Region have accepted this system as valid. However, there is so far no single airline or country in the world that has actually implemented it, although testing has continued under operational conditions. Complaints have been received from two countries in the Region about the unpleasant odours of newly recommended aerosol formulations based on resmethrin and bioresmethrin. A search is being made by WHO for other suitable pyrethroids; 5-2539 Forte (d-phenothrin OMS-l8l0) which has been found very effective and does not have an offensive odour. The final results of the tests on this new formulation are awaited. 4.6 Safe use of pesticides
Since a WHO Technical Report Series on "Safe use of pesticides" had been distributed to the participants, only certain highlights, such as protection of spraymen and environmental pollution, were
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discussed. The education of the users, particularly spraymen and farmers, in the safe use and proper handling of pesticides is essential. Cleanliness is necessary so that they are protected from toxic material, and soap should always be provided for frequent washing and bathing. protection equipment such as hats, clothing, gloves, and rubber boots should be used; however, there is a big gap between theory and practice, particularly in tropical areas. Environmental pollution by pesticides can be minimized by the use of minimum recommended dosages, improved application equipment and formulations, and the use of alternative methods for mosquito control. Serious consideration should be given to the enactment and enforcement of legislation for controlling and regulating the manufacture, transportation, importation, sale and application of pesticides. It was noted that many pesticides for sale in the markets have only trade names and no mention of their actual contents. It is important that the label on the package should clearly indicate the chemical name of the toxicant and the quantity or percentage of toxicant in the product. and give basic instructions to ensure the product is properly used. Mention was also made of a system of pesticides classified into 4 categories: "extremely". "highly". "moderately" and "slightly" hazardous. as recommended by the Twenty-eighth World Health Assembly held in 1975. WHO and FAO have recently issued data sheets on pesticides. Each issue deals with one pesticide and provides general information. information on toxicology and risks, recommendations on the regulation of pesticides. prevention of poisoning in man and emergency aid, and information on the diagnosis and treatment of cases of poisoning and on laboratory tests. It was noted that the WHO Regional Office for the Western Pacific would organize its first seminar on the safe use of pesticides in Manila from 30 August to 3 September 1976. 5. BIOLOGICAL CONTROL
Biological control is the direct or indirect manipulation of the natural enemies (i.e •• predators. pathogens or parasites) of mosquitoes in order to increase mortality in the mosquito popUlation. 5.1 Larvivorous fish
Recent developments in the use of larvivorous fish in anti-malaria programmes were reviewed. It was noted that an epidemiological and entomological evaluation of the large-scale use of Gambusia affinis had been made in Afghanistan and Iran and the results had been very satisfactory. When the optimum density of fish was maintained. a drastic reduction in the mosquito larval population was observed. •
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The guppy, Poecilia reticulata, is known to occur in certain breeding sites of f.£. fatigans in several large cities in the WHO South-East Asia and the Western Pacific Regions. Observations in Rangoon and elsewhere have revealed that guppies have provided good control in only a small proportion of the breeding sites. In Indonesia, it is commonly found in ricefields, but its density is normally too low for an effective control of mosquito larvae. When chironomid and mayfly nymphs are present, the guppy may prefer these insects to mosquito larvae. In the Republic of Korea, two small larvivorous fish, Aplocheilus latipes and Zacco platypus, are found in the ricefieldsj the former species is most prevalent. The dosage of pesticides used for controlling rice pests was found to have no harmful effects on the fish. However, certain herbicides, such as pentachlorophenol had, on occasion, drastically reduced this fish popUlation. Mention was made of recent trials on the introduction of the annual fish (Nothobranchius guentheri and Cynolebias bellottii) in anti-malaria programmes. A letter was sent a year ago to the countries and areas in the Western Pacific Region about the use of larvivorous fish in mosquito control. The replies showed that larvivorous fish of many species are found in many countries and areas, but there has been no large-scale application of the fish for mosquito control. Gambusia affinis exists in Australia, Gilbert and Ellice Islands, GUam, Hong Kong, Malaysia, New Hebrides, New Zealand and Papua New Guinea. Poecilia reticulata is present in Australia, Hong Kong, Japan, Malaysia, Philippines and Singapore. 5.2 Predacious plants and insects
Spirogyra. Chara, Azolla and Lemna can prevent the development of mosquito larvae if they fully cover the surface of breeding sites. Utricularia can trap mosquito larvae. Although ants, dragon flies and certain mayflies have been reported as playing a role as mosquito predators, only few predacious mosquitoes are worthy of consideration at this stage. Toxorhynchites inornatus was introduced into Fiji in 1931 to control ~. polynesiensis. Field trials of the Toxorhynchites larvae for the contro 1 of f.ilariasis vectors in the South Pacific are planned. 5.3 Pathogens and parasites
Among different pathogens and parasites, only fungi and nematodes have been tried in the field in the Western Pacific Region. Coelomomyces stegomyiae was tested in one of the Tokelau Islands for control of ~. polynesiensis, and more trials will be made in other areas in the South Pacific. Many species of Coelomomyces have been found in mosquitoes in Australia, Samoa and the Solomon Islands. Reesimermis nielseni is considered at present the most promising control agent of nematode for mosquito larvae. Preliminary field trials have been undertaken in the Republic of Korea.
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6.
GENETIC CONTROL
Genetic control means the use of any condition or treatment that can reduce the reproductive potential of mosquitoes by altering or replacing their hereditary material. The successful application of the sterile-male technique for the control of screw-worms has given impetus to the use of this method for the control of mosquitoes. An advantage of genetic control is that the target species is selectively controlled by procedures that carry no hazard to any living organisms in the area. The genetic control of mosquitoes is not limited to the use of mosquitoes sterilized by radiation or chemicals, but includes other mechanisms such as cytoplasmic incompatibility, hybrid sterility, chromosome translocation, meiotic drive, etc. 6.1 Sterile-male technique
The mosquito is exposed to an amount of irradiation or chemosterilants sufficient to damage the DNA in the sperm chromosome without impairing its mating activity. 6.2 Cytoplasmic inCOmpatibility
With certain species complexes of mosquitoes. the cytoplasm of the egg of one population is incompatible with the sperm of another population, causing the disintegration of the male pronucleus before its fusing with the female pronucleus and thus no offspring are produced. The crossing type is determined not by nuclear factors but by cytoplasmic factors. A new hypothesis was mentioned that the cause of cytoplasmic incompatibility might be due to the presence of a rickettsia-like micro-organism. possible Wolbachia pipientis. in the maternal cytoplasm and its ovarial transmission. 6.3 Hybrid sterility
Within the species complex of Anopheles gambiae. the hybrid offspring produces sterile males. Because of heterosis. the hybrid males are much more vigorous than normal males. 6.4 Chromosome trans locations
By means of irradiation. the chromosomes undergo breakage and the fragments rejoin in abnormal arrangements. The rearranged chromosomes can yield healthy and competitive. but sterile, mosquitoes. On release of the males (and/or females) of these strains into natural populations. sterility of 50% or more can be achieved. Mention was made of the research directed at finding or developing strains of vector mosquitoes refractory of filarial infection in the f.£. fatigans complex and the~. scutellaris complex. The activities of the WHO/lCMR Research Unit on Genetic Control of Mosquitoes in New Delhi were briefly reviewed.
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7.
PLANNING AND ORGANIZATION OF ANTI-LARVAL OPERATION
Planning for public health programmes and. more particularly, for vector-borne disease control programmes needs: (a) to determine the problem. (b) to establish priorities, (c) to study feasibilities (d) to decide on what programme to implement, (e) to prepare a detaiied plan, (f) to implement and organize the planned activities, and (g) to evaluate the performance and results. The above principles were presented and discussed. Special emphasis was placed on the feasibility studies and their importance. These are claSSified under: (a) technical feasibility - to assess whether the objectives can be achieved with available control measures, (b) operational feasibility - to examine the practicability of applying control methods, (c) administrative feasibility - to examine the ability of the local administrations to manage the planned activities, (d) financial feasibility - to determine whether the resources of the Government and outside agencies are sufficient to finance the programme, (e) social-economic feasibility - to evaluate the social and economic structure of the country and the cost/benefit results expected to be obtained from the project, and (f) political feasibility - to find out the role and view of the decision-making group towards realization of the project. For planning and organizing field larviciding operations, the area to be treated needs to be identified and sketch maps prepared showing the locations of all breeding sites - their size, types, accessibility. and possibly seasonal variations. Estimates of requirements for larviciding include: (a) chemicals and formulations, which will be estimated on the basis of the dosage recommended. frequency of application (usually one week). and the extent of the area involved; (b) equipment to be used, which depends on availability, types of breeding places and their extent, and the skill of the operators; (c) personnel needed, which depends on the type of organization and frequency of application; (d) transport needed for the insecticide, equipment and personnel. and (e) materials and supplies, including protective equipment, mixing equipment, and reporting forms. needed.
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8.
EPIDEMIOLOGICAL. ENTOMOLOGICAL AND OPERATIONAL EVALUATION
The component of evaluation must be clearly defined in tn~ plan before launching the project. In a public health programme employing anti-mosquito measures, evaluation is a continuous process covering field operations as well as the entomological and epidemiolog,,: 1 activities. However. it is important that clost; "oo~;,,,,,~',ion exists among the three disciplines in order to enable an aC,;;H:l:':;", collective and sensitive assessment to be made of the efHc:","v and benefit of the project. The objectives and benefits expected to arise from the implementation of the project. short- or long-term. must be clearly defined for the longitudinal assessment. The collection of baseline data. not only in respect of epidemiological infcrmation concerning the disease and the vector but also on the __ - '61 of the population under control. is essential for project pla.nning and evaluation. Longitudinal evaluations are required to measure the accomplishm.nt of the programme in relation to the situation existing before it is launched. The challenge for the epidemiologist is to select those methods of evaluation that will provide the rE,w~red information. All control programmeR must have a built-in evaluation component. Such an organizational setup at cen~~~! and intermediate levels was reviewed. It was considered essential for the senior professional staff at central level to provide evaluation guides and to have frequent contact with the staff at intermediate and field levels so as to ensure thdt the evaluation data are reliable and meaningful. For qualitative evaluations proper evaluation tools should be selected with attention to simplicity. cost and the validity of the information obtained. Basic methods for epidemiological assessment of malaria control and eradication were briefly discussed. Operational evaluation should be a routine procedure based on proper supervision to ensure that the quality of operational performance is maintained at the optUDum level. The operational objective of chemical control is to achieve uniform insecticidal coverage with the pr~yer application of techniques and equipment. Tbe elements which need to be checked and evaluated during the process of the operation include: (a) correct strength of the concentrate and of the spray liquid of the insecticide. its proper storage. handling and transportation. Chemical testing of the concentrate is required when this is newly supplied and this should be repeated periodically; (b) equipment should always be in good operating condition. Periodic checks of the discharge rate and spray pattern is essential to avoid wastage;
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(c) application techniques and uniform coverage can be checked by direct supervision at the time of application. In the case of space application by fog or mist. the physical performance of the equipment can be evaluated by sampling the spray droplet spectra at representative points in the treated area. using magnesium oxide coated slides and dye cards; (d) analysis of reported data and checking their significance; and
(e) external factors. such as climatic conditions or the people's behaviour. which may reduce the efficiency of application. When environmental management is applied, evaluation will be on the basis of its effectiveness in eliminating or reducing potential breeding places and of its side effects on the environment. The efficiency of sub-soil lines can be checked by the flow of water at the inspection chambers and the outlets. and by the elimination of seepage. Biological control by larvivorous fish can be operationally evaluated by checking the density of fish in each habitat. The efficiency of breeding. packing. transportation and distribution of fish at the various sites needs always to be checked. An important element in the evaluation of all anti-mosquito measures is good geographical reconnaissance and the availability of detailed operational maps of the area. Checking of maps and up-dating them periodically are essential.
The cost element of any measure is of utmost importance and should always be checked and maintained within planned limits. The objectives of entomological evaluation of anti-mosquito measures are: (a) to assess the susceptibility status of the vector mosquitoes and the biologically effective area of the operations; (b) to determine the efficacy of anti-mosquito measures and their impact on the endemicity or interruption of transmission of the disease; (c) if there should be adverse results. to determine the reasons for the failure of the anti-mosquito measures. The methods and techniques for larval and adult surveys need to be carefully selected to ensure that they are in conformity with the methode and techniques used for the collection of baseline date so that comparable data can be obtained. This methodology should include data on the ecology, distribution, breeding places. seasonal variation. bionomics and susceptibility of the vector (or vectors),as well as an accurate recording of the meteorological conditions.
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Generally, dipping is used for larval surveys. For adult surveys, appropriate techniques, which will give information on resting habits, man-vector contact and longevity of the vectors, should be selected. Two types of observations may be used for evaluation. They are (a) fixed-capture-station observations (or trend observations), and (b) random surveys (or spot checks). It was emphaSized that the personnel should be well trained and superviled frequently.
9.
CRITICAL REVIEW OF THE DIFFERENT CONTROL METHODS
A critical review was made of the different methods of mosquito control - their practicability, effectiveness, cost and limitations, during group discussions and then in plenary sessions. 9.1 Environmental management
The group felt that source reduction and environmental management mealurel should be the first priority in vector-borne disease control programmes. It is realized that certain engineering methods may require large capital investmentl and perhaps constant maintenance. However. certain measures for source reduction involve only minor operation. such as the proper disposal of excess of waste water or discarded tins, cans, automobile tires, etc., which would help a great deal in reducing the breeding sites of a number of mosquito species. The benefits of environmental management include not only the control of vectors and pests but also land and water economy and improvement. 9.2 Chemical control
Chemical control methods will remain an important component of vector-borne disease control programmes, particularly during outbreaks, until other more permanent and safer measures can be developed to replace them. Newer insecticides may have to be used for indoor residual spraying when the local malaria vector mosquitoes develop resistance to older compounds but the costs may be much higher. Propoxur, a carbamate with airborne effect, may be tried in areas with a highly exophilic vector such as Anopheles balabacensis.
ULV application is reported to be more economical in most situations than thermal fogging. Many types of equipment were demonstrated and their advantages and disadvantages, as well as costs, were compared. It was suggested that portable equipment should also be made available to complete the coverage in areas inaccessible by vehicles. It was considered difficult to make suggestions on the amount of equipment and insecticides to be purchased for such a programme. Insecticides should be tested first under local conditions at the lowest recommended dosage before they are purchased. The
- u WHO~
and WHO/VBC series periodically provide information about new equipment and insecticides for vector control. The WHO Manual on Anti-larval Operations in Malaria Eradication Programmes provides useful data on the planning of such operations. Space spraying by fogs or mists is mainly intended for mosquito adult control. For larval control larger droplet sizes of the insecticide formulations are necessary.
In malaria eradication, larviciding is usually applied as a supplement in rural areas. The insecticides used for larval control should not be the same as those used for adult control in the same locality. Larviciding is, however, a major attacke measure in urban areas for the control of Anopheles stephensi, £.£. fatigans, Ae. aegypti, etc. Health education should be emphasized in order to obtain good public cooperation. If possible, legislation on vector surveillance and control and on the safe use of pesticides should be promulgated and enforced. 9.3 Biological and genetic control
Among the available biological agents for mosquito control, larvivorous fish is the most promising one and has yielded good results in some anti-malaria programmes. The cost involved is low. The average daily consumption of a single Gambusia is estimated at about 100 mosquito larvae and a population of 4-5 fish per square metre can achieve good control when conditions are favourable. Local larvivorous fish, if any, should be appraised before introducing exotic species. The introduction of new fish should be preceded by field trials to ensure their compatibility and the Fisheries Department should be consulted about the importation of exotic species. It was stated that the paucity or loss of some species of fish in the Philippines was due to the introduction of Gambusia. On the other hand, the introduction of guppies may not endanger the indigenous fish species which are seldom found in highly polluted waters. The adult guppy can also eat egg-rafts, pupae and the dead adults of £.£. fatigans. No breeding of the mosquito larvae has been noted in pools where the fish density exceeds 10 per square metre. It was observed that in Manila, the Philippines, a female guppy can eat 25 mosquito larvae in two hours, and in Japan it can consume as many as 123 fourth-stage larvae of f.£. fatigans. At this stage, the most promising genetic control techniques are the use of cytoplasmic incompatibility and chromosome trans locations. Strains of £.£. fatigans containing both trans locations and cytoplasmic incompatible factors were produced by the WHO/ICMR Research Unit on Genetic Control of Mosquitoes. The advantages of trans locations are that it is unnecessary to separate the sex of pupae before releasing the adult mosquitoes and that there is a sterilizing effect on subsequent generations since the trans locations may be passed on through the males.
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It is realized that many of the techniques for biological and genetic control may not become operational in the near future. Proper techniques for mass production and for the release of some organisms used for biological or genetic control have still to be developed. Furthermore, a number of ecological problems have first to be solved. Consideration might be given to employing some of the techniques as an adjunct to other methods, such as the application of insecticides. which can be used first to suppress the mosquito density to a very low level. 10.
INTEGRATED CONTROL AND C<H'REHENSIVE APPROACH IN PLANNING VECTOR CONTROL PROGRAMMES
Integrated control means the utilization of all known technology and an intelligent selection of the methods of control which gives maximum efficacy under local conditions. Malaria eradication programmes. where the sole reliance is on residual spraying for vector control has, in some cases, gradually shifted towards the integrated or combined use of control methods. For example. spraying supplemented by larviciding, the use of larvivorous fish, adu1ticiding by space application, or filling and drainage. The exophilic tendency of some vectors and the resistance of others to insecticides were cited as the principal factors behind the change. More recently. concern about the environment and the increasing cost of pesticides together with a decrease in government expenditure in outside aid have led to the consideration of a more rational approach, that is a comprehensive approach to vector/disease control. The planning of a comprehensive approach should be preceded by extensive studies to define problems and priorities and to plan feasible programmes of a multi-beneficial nature. Therefore, a comprehensive mosquito control programme for anti-malaria purposes would mean that in any situation. all the known control technology should be considered and applied as appropriate. The control methods selected should ensure primarily the control of malaria and, to the greatest extent possible. the control of other mosquito-borne diseases. In many cases, a minor modification. adaptation or addition in the control measures selected may be adequate to produce expanded results. Taking examples in this region, DDT indoor residual spraying for anti-malaria purposes should also have an effect on filariasis control in the New Hebrides, Papua New Guinea and the Solomon Islands where the vectors are the same. Investigations might be undertaken in rural areas of Malaysia on the simultaneous effectiveness of DDT residual spraying, as an anti-malaria meaaure. on ~. aegypti. although this mosquito was found to be resistant to DDT in the laboratory. ULV application might be employed as a supplementary method in the New Resettlement Area in Malaysia to control the vectors of malaria,
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filariasis and dengue haemorrhagic fever. In the South Pacific studies will be carried out on source reduction and ULV application for'control of the vectors of filariasis and dengue fever.
11.
CONCLUSIONS
The following is a summary of the conclusions drawn from the presentation and discussions at the workshop. The participants requested that these be outlined in this report for the gUidance of national vector control programmes. (a) Environmental management and source reduction should be first considered as these methods are safe, of long-duration and often with important side benefits. It was proposed that every vector control programme should devote a portion of its budget to source reduction and elimination, as over the years results accumulate and great economy in expenditures would be achieved. (b) Chemical control must be regarded as an intermediary measure to provide rapid control until other suitable measures are developed to take over the control activities. The increasing east of pesticides, concern about their effect on the environment and their toxic effect on humans are listed as limiting factors in their use. It was. however, agreed by all participants that pesticides for years to come will be the principal methods for vector control and, therefore, WHO and other international and bilateral agencies should help to make available an adequate supply of pesticides at reasonable costs. Assistance in the provision of local pesticides manufacturing and formulation plants il needed urgently. This would eliminate or reduce greatly the high COlt involved in the transportation of pesticides. (c) Anti-larval operations, including the use of larvivoroul fish, have a special place in vector control programmes and should be taken into serious consideration at the time of planning. (d) A rational approach to planning, including the carrying out of feasibility, cost/effectiveness and cost/benefit studies, il considered an essential step to ensure a successful vector control programmes. Systematic and integrated control and a comprehensive approach must be introduced in programme planning, espeCially at this time when governmental and outside financial resources are becoming more restricted. (e) Most participants indicated their interest in being kept informed regularly of developments in the field of vector control, on pesticides, equipment, etc. They requested WHO to make such information available to individual workers and not only to scientific and official institutions.
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(f) All participants agreed that the workshop had been very useful in bringing them up-to-date knowledge on newer methods of control, new equipment, chemicals and their use, as well as on the policies governing vector control programmes. They wished other similar meetings to be arranged to deal in more depth with specific aspects. ACKNOWLEDGEMENT Acknowledgement is made to: (a) The Ministry of Health, Government of Malaysia, for hosting the Workshop and the Organizing Committee of the Workshop for local arrangements; (b) The Director of Public Health Institute and his staff for providing faCilities, transport and secretarial assistance; (c) The Director of the Malaria Eradication Programme, the Directors of Medical and Health Services of Penang and Selangor, the Director of the Institute for Medical Research, the Chief Health Officer, City of Kuala Lumpur, and their staff, for arranging field demonstration programmes; (d) Tifa Ltd. for airfreighting eqUipment, on loan, and for sending their engineer, Mr G.L. Bull, to demonstrate the equipment, and (e) Buffalo Turbine Agricultural Equipment Co., Harvey & Co., London Fog Co., pulsfog Co., Spraying Systems Co., Sumitomo Chemical Co., Wellcome Foundation Ltd., and Zuellig Inc., for providing literature, display of equipment, or supplying free samples of nozzles and insecticides.
I I
I
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ANNEX I
LIST OF PARTICIPANTS I OBSERVERS AND SECRETARIAT 1. National participants Country/Area MALAYSIA Name/title/official address Dr Abdul Talib bin Latiff Director Malaria Eradication Programme Kuala Lumpur Ungku Abu Bakar bin Abdul Rahman Chief Public Health Inspector Malaria Eradication Programme Kuala Lumpur Dr Eddy K.C. Lo Head Epidemiology Division and METePublic Health Institute Kuala Lumpur Dr P.K. Roy Malariologist Medical Department Kuching, Sarawak Dr I.K. Singh Entomologist Institute for Medical Research Kuala Lumpur
NEPAL
Dr K.A. Dixit Chief Officer Malaria Eradication Organization Kathmandu Mr C. Asinas Chief Sanitary Engineer Malaria Field Services Malaria Eradication Service Department of Health Manila Mr C.A. Galicia Unit Chief, Sanitary Engineer Malaria Unit F-35 Butuan City
PHILIPPINES
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Annex I SOLClttON ISLANDS Mr B. SeiJama Malaria Field Operations Officer Malaria Eradication Programme Honiara
2.
WHO staff members Name
Title and official address Entomologist Malaria Control Programme Port Moresby, Papua New Guinea Technical Officer Malaria Control Programme Port Moresby, Papua New Guinea Sanitarian Malaria Control Programme Vientiane, Laos Sanitarian Malaria Eradication Programme Honiara, Solomon Islands Technical Officer Malaria Control Programme Kota Klnabalu, Sabah Malaysia Sanitary Engineer Malaria Eradication Programme Kuala Lumpur, Malaysia Sanitarian Malaria Control Programme Port-Vila, New Hebrides Entomologist (Training Adviser) Malaria Eradication Programme Manila. Philippines Technical Officer Malaria Control Programme Kuching, Sarawak MalaySia Sanitarian c/o WHO!WPRO Manila, Philippines
Dr S.E. Afifi
Mr C. Allen
Mr A. Gouliouras
Mr O. Habash
Mr Y.S. Huang
Mr S. Kolta
Mr P. Lietaert
Dr M.A. Rao
Mr H. Soong
Mr L. Swlllen
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Annex I
Dr E.S. Thevasagayam
Entomologist Malaria Eradication Programme Kuala Lumpur, Malaysia
3.
Observers Name Mr CHAN Seng Thim Title and official address Laboratory Assistant Institute for Medical Researcb Kuala LumpUr, Malaysia Entomologist Malaria Eradication Programme Kuala Lumpur, Malaysia Chief Medical & Health Officer Malayan Railway Kuala Lumpur, Malaysia Health and Malaria Advisor United States Agency for International Development (USAID) P.O. Box, Islamabad Pakistan Health Inspector Public Health Institute Kuala Lumpur, Malaysia Assistant Health Officer City Health Department Kuala Lumpur, Malaysia Deputy Assistant Director of Medical Services (Health) Ministry of Defence Kuala Lumpur, Malaysia
Mr CHOOl Chin Khoon
Dr A.K. Datta-Sarma
Mr Howard B. Keller
Mr 1001 Choon Hong
Dr J.N. Soosaipillai
Major (Dr) V. Supramaniam
4.
Secretariat Name Dr C.T. Chien Professor C.Y. Chow Title and official address Regional Malaria Adviser WHO;WPRO, Manila, Philippines Regional Adviser on Vector Biology and Control WHO;WPRO, Manila, Philippines
- 22 -
Annex I Mr T.D. Mulhern WHO Consultant Executive Director American Mosquito Control Association 908 West Fairmont Avenue Fresno. California 93705 United States of America Sanitary Engineer Planning and Programme Development Division of Malaria and Other Parasitic Diseases WHO. Geneva. Switzerland Acting Project Leader WHO Vector and Rodent Control Research Unit P.O. Box 302 Jakarta. Indonesia
Mr H.A. RafatJah
Dr L.S. Self
- 23 -
ANNEX II PROGRAMME
Subject 1-
Number of sessions 1
Panel members
Introduced
~y
OPENING INTRODUCTION
2.
2
2.1 Objectives of the workshop 2.2 Orientation 2.3 Review of mosquito-borne diseases and their control in the Western Pacific Region
Chfen Thevasagayam
Chow Mulhern 11
2.4 Definition of control methods 3· ENVIRONMENTAL MANAGEMENT Kolta Mulhern Rafatjah
Mulhern
3.1 Source reduction and water management (engineering methods) Mulhern Mulhern
3.2 Equipment 4. CHEMICAL CONTROL
14
Chow Kolta Mulhern Rafatjah Self
Self
4.1 Recent development in pesticides and their formulations and their field evaluation
. Selt Mul.hel'l'l
I
4.2 Recent development in spraying operation and equipment (including ULV application) l\at..tJah
4.3 4.4 4.5 4.6
Larvicides Herbicides Aircraft disinsection Safe use of pesticides
Kol" . Rafatjah Chow Chow
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Annex II
"
Subjeot
Number of sessions Panel members
Introduoed by Mulhern
5.
BIOLOGICAL CONTROL
3
Chow Mulhern RafatJah Self
5.1 Larvivorous fish in veotor oontrol programme
5.1.1 In general 5.1.2 In the Western Paoifio Region 5.1.3 In Korea and Indonesia
RafatJah Chow Self Chow
5.2 Pathogens, parasites and predators
6.
GENETIC aONl'ROL
1 and
Afifi Chow Thevasagayam
Thevasagayam
6.1 Radiosterilization chemosterilization
6.2 6.3 6.4 6.5
Cytoplasmio inoompatibility Hybrid sterility Translocation Aotivities of the WHQ/ICMR Mosquito Genetio Control Researoh Unit in India 1
7. PLANNING AND ORGANIZATION OF ANTILARVAL MEASURES AGAINST MALARIA AND OTHER MOSQUITO-BORNE DISEASES
Chow Kolta Mulhern RafatJah Ch'en Kolta Rao Ch'en Chow Kolta Mulhern Rafatjah Ch'en Chow Kolta Mulhern Rafatjah
RafatJah
8.
EPIDEMIOLOGICAL, ENTOMOLOGICAL AND OPERATIONAL EVALUATION CRITICAL REVIEW OF THE AOOVEMENTIONED DIFFERENT CONl'ROL METHOD, AND PRACTICABILITY, EFFECTIVENESS, COSTS AND LIMITATIONS INl'EGRATED AND COMPREHENSIVE VECTOR CONl'ROL
2
Ch'en
9.
4
Mulhern
10.
1
Mulhern
- 25/26 -
ANNEX III
LIST OF DOCUMENTS DISTRIBUTED WHO publications 1. 2. 3. 4. 5. 6. 7. 8. 9. Insecticide resistance and vector control (TRS No. 443, 1970) Application am dispersal of pesticides (TRS No. 465, 1971) Vector control in international health (1972) WHO manual on larval control operations in malaria programmes (WHO Offset Publ. No.1, 1973) Safe use of pesticides (TRS No. 513, 1973) Equipment for vector control (1974) Technical guides for diagnosis, treatment, surveillance. prevention and control of dengue haemorrhagic fever (1975) Sequential application of ultra-low-volume ground aerosols of fenitrothion for sustained control of Aedes aegypti - Pant. C.P. et al., 1973, Bull. WId Hlth Org., 48, 455-459 Recent developments in methods of mosquito control - Lofgren, C.S., 1974, Bull. WId Hlth Org., 50, 323-328
Unpublished WHO documents 1. 2. 3. 4. 5. 6. Alternative methods of mosquito control - ChOW, C.Y., 1972. WPfl/YBCI8 Control of vectors of mosquito-borne diseases in the Western Pacific Region - Chow, C.Y., 1972, WPR/VOC/9 Aedes aegypti surveillance and control, with special reference to the South Pacific - Chow, C.Y., 1973, WPR/VEC/13 A critical review of certain ground equipment and insecticides for Aedes aegypti control - Chow, C.Y., 1975. WPR/VBC/16 Residual effectiveness of ULV aerosols against__Aedesaegyptl in Bangkok: a study of Sumithion and malathion apprte.rby a portable ULV machine - Pant, C.P. & H.L. Mathis, 1972, WHO/VBC/T2.)40 Sequential application of ULV Sumithion for sustained control of Aedes aegypti Linn. Use of Fontan, a back pack portable mist blower - Samutrapongse, W. & C.P. Pant, 1973, WHO/VBCI73.432 A comprehensive approach to vector control in malaria and other parasitic diseases' control programmes - Rafatjah, H.A., 1973, RAMOPD!WP/73.2.6 Weed control in programmes for the control of parasitic diseases Rafatjah, H.A., 1975, SEM/ANT. LARV/75/50 Observations on mosquito control activities and related research in the United States of America, 1967, WH0!MAL/67.598
7. 8. 9.