Vector control in urban areas

WORLD HEALTH ORGANIZATION VBC/ECV/EC/82.22 ORGANISATION MONDIALE DE LA SANTE ENGLISH ONLY . r{ ~ v1Al 11,tf'-l S ... EXPERT COMMITTEE ON VECTOR CONTROL - ,.. ,, t (- ('6.U. ~ ,. . INDEX::.:.- .). .t > (1 . • .;· ( It· ~ I . ( (.,t,- Geneva, 7-13 December 1982 '"'ir( i (? 1,: t: ,., ;.l· ., tlA_,IL 71.t(l·. ,o,HEQu,,.~. ' <"\~ fi •, v ..._ ~ ' ·'S (~ Jt1 ':t.-VECTOR CONTROL IN URBAN AREAS t.11 by Dr P.B. Deobhankar Insecticide Officer, Municipal Corporation of Greater Bombay Bombay, India 1. Introduction The growth of urban centres where large populations are crowded in compact areas has brought severe stress on liquid/solid waste disposal systems, water supply and was;e water management. Rapid urbanization of periurban areas has resulted in an increase of Culex pipiens fatigans, a nuisance species which also is a vector of Bancroftian filariasis in tropical countries of South-east Asia and Africa; other species associated with the sewage lagoons in the temperate regions are the hosts of encephalitis viruses (Smith 1969, Sudia et al 1967, 1967a). Inadequate piped water supply necessitates domestic water storages causing an increase in Aedes aegypti prevalence in close association with man which has resulted in the extension of dengue and dengue haemorrhagic fever into newer areas in South-east Asia. A large number of man-made water containers which cannot be emptied by upturning as can the domestic utensil-barrel type containers, thereby constitute a formidable breeding source of the urban malaria vector An. stephensi. Constraints on the proper drainage of surface water due to the lack of required degree of gradient in the seaport cities further complicate the problem. High per capita generation of unsegregated wet and dry garbage and rising transport costs to carry it far away from human habitations create house fly breeding situations close to where infiltration occurs into the inhabited zones. The urban ecological set up is thus conducive to vector abundance. Defining the problems through geographical/entomological surveys, establishment of a suitable organization commensurate with the workload and norms, and adoption of appropriate methodology are the key factors for accomplishing satisfactory and sustained vector control. 2. Geographical-Entomological Reconnaissance Although the gross characteristics of urban situations everywhere are more or less identical, each one presents special features of its own with reference to vector species, their breeding habitats and their distribution. Geographical and entomological surveys are intended to meet the following objectives: 2.1 Delineation of area of influence of different vectors A variety of vector distribution and vector preponderance patterns are discernible in the different urban areas. In Bombay, for example, the malaria vector An. stephensi is so far strictly confined to 68.71Km2 of city proper, whereas 369Km2 of the suburbs occasionally record the occurrence of An. culicifacies. Likewise Cx. p. fatigans and the incidence of filariasis, albeit at a low level, is a striking suburban feature. J.e. aegypti, however, has The issue of this document does not constitute formal publication. It should not be reviewed, abstracted or quoted without the agreement of the World Health Organization. Authors alone are responsible for views expressed in signed articles. Ce document ne constitue pas une publication. II ne doit faire l'objet d'aucun compte rendu ou resume ni d'aucune citation sans l'autorisation de !'Organisation Mondiale de la Sante. Les opinions exprimees dans les articles signes n'engagent que leurs auteurs. VBC/ECV/EC/82.22 page 2 uniform seasonal distribution all over. In Delhi, the distribution of An. stephensi and An. culicifacies overlap, while in Madras, An. stephensi and Cx. p. fatigans are uniformly distributed. Such spatial distribution has a definite bearing on data collection, control strategy and staffing pattern. In urban areas where areas of influence of different vectors coincide, uniformity of operation may be possible. Entomological data on the occurrence of different vector species, their spatial dis- tribution, seasonal variation, if any, in densities and records on infection as well as infectivity rates amongst mosquito vectors of filariasis are necessary to identify problem areas and to enable organizing appropriate measures on priority. 2.2 Listing of premises, open lands with precise details of potential breeding places of various vectors Collection and quantification of data on the actual and potential breeding places of vector species through house to house surveys is an essential prerequisite for determining workload and setting up a suitable organization. 2.2.1 Anopheline vectors In urban areas where An. stephensi is involved in malaria transmission, the survey information needs to be collected and classified under two categories, in view of its proclivity of breeding at ground level and also at heights. In Bombay, this species has been found breeding in deep wells and also in the water storage tanks and building con- struction sites up to 30th floor i.e. about lOOm high. Enumeration of vector breeding places is accordingly done in respect of all premises in two categories, i.e. ground work including wells, garden tanks, water fountains, ground cisterns, textile mill ponds, seepages from water reservoirs and aquaducts etc. and cistern work at upper levels. Building construction sites present a peculiar feature in urban malaria epidemiology in view of numerous water storages and accumulations associated with the construction activities constituting the most vulnerable breeding places of An. stephensi. This coupled with the migratory labour, importing infection from outstations, create conditions conducive to focal outbreaks. 2.2.2 Culicine vectors Many breeding situations overlap and are jointly shared by malaria vectors and other vector species. Likewise, the control methods are also almost identical. Therefore, it is desirable to include culicine species under the survey of breeding places such as the number of septic tanks, cesspools, soak pits, aqua privies in unsewered areas. Quantification of other breeding places in open lands is necessary e.g. number and length of natural water courses and drains; number and area of creek and grass lands. 3. Estimation of Workload-Fixation of Norms of Work-Organization The total work-load of the operational area is computed on the basis of the survey information. Norms of work i.e. the exp~cted output of work by each worker or squad for every activity or combination of activities are determined under the pilot studies to be carried out by technically qualified personnel. Norms of work are, however, dependent upon the objective, nature of work, frequency of inspection/treatment, composition of the squad, appliances, fund resources, local conditions, etc. 4. Control Strategy VBC/ECV/EC/82.22 page 3 Integrated control strategy envisages employment of source reduction comprised of engineering, legislation, biological and chemical control in appropriate combinations, as no method is adequate in itself in controlling vector population to a desired degree and over a prolonged period. Important adjuncts to these basic components are intersectoral coordination and community participation. 4.1 Source reduction Source reduction covers a wide range of activities. They encompass major engineering projects from town planning, drainage, filling, flushing or sluicing etc. involving engineering skills and small financial commitments such as channelisation of surface drains, removal of aquatic and marginal vegetation and mosquito proofing of cisterns, septic tanks etc. Major engineering source reduction measures requLrLng large allocation of funds can therefore be implemented under a phased programme in consideration of the severity of the vector problem. Source reduction measures, to be effective, must be ably supported by intersectoral coordination and legislation. 4.1.1 Anopheline vectors In India, most of the metropolitan centres and cities do not have adequate legislation conducive to source reduction. In Bombay, however, mosquito proofing of wells-cisterns is enforced. A definite policy in respect of other breeding sites is operative for avoiding vector breeding possibilities. Cisterns and overhead tanks are required to provide safe, easy and permanent access and to be mosquito proof. Digging of new surface wells is not permitted unless they are mosquito proof. Sinking of tube wells is encouraged. Disused and neglected water fountains are demolished and the erection of new ones is regulated. 4.1.2 Culicine vectors Source reduction measures for culicine control require waste and storm water management through extension of underground sewage and storm water systems to all areas. When financial constraints do not render this immediately possible, priority areas and problems are defined. Work may include training-desilting-cleaning of drains, giving proper outlets to sewage effluents, extending drainage outfalls up to the lowest tide mark etc. Minor source reduction measures within the scope of vector control organizations include: channelling of surface drains to clear obstructions and to remove marginal grass removal of aquatic vegetation to enhance wave action, predation and spread and penetration of larvicides draining of stagnant water mosquito proofing of septic tanks, filling of low lands, ponds, disused wells, borrow pits. VBC/ECV/EC/82.22 page 4 4.1.3 Aedine vectors Source reduction measures against Aedes species control is not a practicable proposition in view of numerous containers taRt are available for breeding particularly during the rainy season. Chemical methods of control are therefore relied upon. 4.1.4 House flies Resistance to practically all groups of insecticides render imperative envirolUllental sanitation as a tool in house fly control. speedy and efficient removal of garbage bulldozing and compacting refuse at refuse dumping sites. Spreading a layer of earth over freshly dumped garbage, although ideal, is impractical in urban areas in view of the quantity of garbage and the area involved. 4.2 Legislation Enactment of appropriate legislation is an important component of a public health programme including delegation of certain powers of the competent authority to trained officers and proper definition of "nuisance" to provide wider base for instituting legal action. 4.2.1 Source reduction Eliminating where mosquito breeding occurs or is likely to occur e.g. filling in of pools, ditches, tanks, disused wells or mosquito proofing of water containers e.g. wells, cisterns, septic tanks etc. Regulating new works by the competent authority, e.g. digging new wells, installation or construction of water storage tanks, swimming pools etc. Granting special provision under which temporary water storages can be authorized such as at building construction sites. 4.2.2 Inspection of cisterns and water storage tanks Provision for safe, easy and permanent means of access (e.g. an iron ladder) for cistern inspection. Granting water connexion is subject to complia~ce to the rules. 4.2.3 Enforcement of orders to execute work etc., in the event the landlord/occupier fails to carry out required work. 4.2.4 Eliciting cooperation for carrying out proper malaria control programmes. 4.2.5 Deterrent penalties should be provided for offences, punishable with fine. 4.3 Biological control Under normal and non-epidemic conditions appropriate methods of biological control are to be explored and applied before resorting to the use of pesticides. Among the methods are the introduction of predatory fish, Gambusia affinis, Poecilia reticulata and Panchax and the use of microbial formulations, Bacillus thuringiensis israelensis (serotype H-14) and Bacillus sphaericus. VBC/ECV/EC/82.22 page 5 Predatory fish: Pending realisation of source reduction measures and particularly of mosquito proofing of cisterns and wells, introduction of Gambusia affinis and Poecilia reticulata in adequate numbers is often useful. It has been more effective in An. stephensi breeding places than in those of Cx. p. fatigans, perhaps owing to pH variation, high pollution and aquatic vegetation encountered in the latter. Open wells, cellars holding water, non-mosquito proof overhead water storage tanks and cisterns are stocked with Poecilia and replenished whenever necessary. 150 fish/m2 is an ideal'._ density. An. stephensi larvae have never been found in water bodies with Poecilia in Bombay although the latter have been found co-existing with Cx. p. fatigans larvae. Introduction of exotic fish in newer areas at times affects the local fauna and needs thorough study of all parameters before introduction. 4.3.1 Microbial agents/formulations Bacillus thuringiensis Berliner, var. israelensis, serotype 14 of 1500 AA units (Ae. aegypti units)/mg, and supplied by Sandoz under their code name SAN 402 1 WDC, was field tested against Cx. p. fatigans breeding in the ground pools of varying pollutions. 3ppm of the material suitably diluted for application was tested. 92.4% reduction in larvae density was noticed after 24 hours. However,, after one week the densities rose beyond the original numbers. As the test areas totalled 218.9m2 and because the formulation is not active against eggs, egg hatching and oviposition by females from other areas increased the larval density. Bacillus sphaericus strain 1321 (SSll-1) and B. sphaericus strain 1593, are also being developed as microbial agents for mosquito control. Their introduction in large scale operations is not yet feasible. 4.4 Chemical control Chemical control assumes an important place in the vector control programmes where rapid suppression of vector populations or of nuisance species is essential, particularly during epidemic situations. It is an important adjunct to source reduction and biological control. 4.4.1 Larvicides Despite the disadvantages: frequent weekly applications, high cost of operations and likelihood of missed breeding places, larviciding continues to be the method of choice in the urban-periurban set up. The larvicides which are commonly used are: Name Dermal LO Formulation Use rate-range 50 (rat) (mg/kg) 1 or kg/ha (a,i,J Petroleum oils MLO oil 170-225 or (50m/1) Flit M:.,Q oil 9-27 Pyrethrum based oil emulsions Pvrethrum 1500 oil emulsion 11.2 Inorganic compound Paris Green 2400 dust 0.50-0.75 Emulsifiable concentrate of Q, P, compounds Temephos 500 E >4000 E, C, Q,056-0, 112 Fenthion 1 OOO E 330 EC, 0, 111 Chlorpyrifos 2000 E,c, 0,056 Controlled release formulations Temephos >4000 granules 0,056-0, 11 2 Fe nth ion 330 granules Q, 111 VBC/ECV/EC/82.22 page 6 A.G.L.F. (Aviation Gasoline Lead Free) is used in drinking water storages like wells at the rate of 910ml/10m2 during evenings as the smell lingers for 2 hours. Various other larvicides like pirimiphos methyl, chlorpyrifos and synthetic pyrethroids have not yet been introduced under routine larvicide prograUDI1es in India. Although the dosages of various larvicides have been worked out and their effective ranges are known through laboratory and field experiments, the application of correct and recOUDI1ended dosages under routine progranmes by field workers requires careful planning to avoid sublethal or excessive dosages. Volumetric and surface considerations, thus pose problems in applying accurate dosages. Surface active oils can be applied fairly accurately with ease owing to the visible spread of the film. Oils are usually applied to non-drinking, unusable water bodies and hence pose no toxicity hazards, even if excess dose results. Application of oil emulsions, solutions and sinking type of granular formulations demand volumetric measurement. In the case of treatment to drinking water storages like cisterns and wells, however, such approximations are hazardous and it is necessary to calculate volumes by trained personnel. Suitable "charges" of the chemical temephos, diluted in water at the time of treatment, can be used to ensure correct dosages and safety. 4.4.2 Adulticides The use of adulticides is primarily intended for reducing the survival rate of vectors and for quick suppression of vector population or of nuisance species. Intradomiciliary residual spraying is used against endophilic species, whereas space spraying is beneficial in outdoor situations. 4.4.3 Residual spraying Residual spraying which forms the mainstay of rural malaria control programmes has limited utility in urban areas on the grounds of feasibility and cost. In areas of focal outbreaks and particularly at large housing projects, comprising of structures 20 to 25 storeys high, it is impracticable to resort to residual spraying. However, wherever feasible, DDT 2g/m2, HCH 0.2g/m2 or malathion 2g/m2 is used depending upon the susceptibility status. Fenitrothion, pirimiphos methyl have also been used and recently synthetic pyrethroids like Decamethrin 25 mg/m2 is also suggested for residual application. 4.4.4 Space spraying Space spraying envisages dispersal of toxicants, usually of "knock-down" category for sudden effect on impingement. The smaller droplets disperse in space and therefore do not possess residual action. Hence space applications need sequential treatments, properly synchronized with larviciding. The droplet size and the reach of the toxicant in space varies with the equipment. Depending upon the target situation, therefore, the equipment is chosen. 4.4.5 Thermal fogging Thermal fogs are generated either by low discharge swing fog machines (11-25 1/hr) or by high discharge vehicle mounted units (50-200 1/hr). Owing to their small droplet size (10 microns) and lighter particles, the fog occupies relatively more volume for a given discharge rate. Hence, in indoor situations thermal fogs are more effective than in outdoor situations where they are subjected to horizontal or vertical drifts because of wind or temperature. In urban areas such enclosed places exist as covered surface drains which are inaccessible to larviciding. High adult densities are effectively controlled by thermal fogging at the discharge rate of 200 ml/min. covering about 90m3 of interior space. VBC/ECV/EC/82.22 page 7 Dichlorvos 1%, pyrethrum extract 0.1% and malathion 5% in diesel oil give rapid knockdown action in that order. However, fogging treatments must be repeated every three days to maintain reduction of Cx. p. fatigans in such covered drains. Intradomiciliary fogging with 5% malathion and 0.1% pyrethrum is resorted to in lieu of residual focal spraying in the areas where malaria cases are reported, and where filaria infected Cx. p. fatigans are recorded. Thermal fogging with 4% malathion at 220 ml/ha concurrently with larviciding by temephos has also been used in urban areas (Bangkok) for the control of Ae. aegypti. Vehicle mounted fog generators with high discharge rates are useful outdoors and particularly under Regional Emergency Units for Vector Abatement (REUVA) during dengue or DHF epidemics. Thermal fogging however has severe limitations and is being rapidly displaced by more effective ULV applications. 4.4.6 Ultra-Low-Volume (ULV) applications ULV implies application of minimum volume of insecticides per unit area. This is achieved by means of portable aerosol/mist generators, vehicle mounted ULV generators or aerial ULV equipment. Undiluted concentrates of the special ULV formulations are used in volumes less than 1 kg - 1 1/ha. although by definition the dispensation rate is 4.7 1/ha. Ground LV application of dichlorvos 0.4% at the discharge rate of 1.5 to 2 1/minute by mist blowers has been adopted for house fly control at refuse dumping grounds. These space sprays are applied daily and area coverage intensified at refuse dumping sites during rainy seasons to maintain satisfactory fly reduction. In India the use of dichlorvos is restricted to house fly control at dumping grounds and outdoor situations. ULV applications have been successful in dramatically reducing Ae. aegypti and house fly populations in large-scale treatments. Yet, particularly in the case of Cx. p. fatigans, unless ULV applications are concurrently supplemented by larviciding, sustained reduction is difficult. 4.4.7 Aerial LV - ULV spraying Aerial application of insecticides has been resorted to for vector abatement under many programmes. The ULV applications of various insecticides, unless backed by proper larviciding, have only limited effect lasting for not more than three days. Sustained reduction, therefore, requires sequential treatments appropriately spaced. In urban areas, aerial applications have limited use but in nuisance situations they may offer an effective remedy. Highly polluted mangrove swamps of Bandra-Kurla creek complex in suburban Bombay covering 6.25 sq.km. occasionally or seasonally show unprecedented growth of Cx. gelidus, a non-vector species of high annoyance potential. These swamps are inaccessible to ground application of larvicides and adulticides. Aerial spraying (LV) of a combined dose of dichlorvos and fenthion is found to be effective in reducing breeding potential as well as mangrove resting hordes of adult mosquitos. Sequential treatments every 10 days reduce infestations to about 85 to 90% at the dosage rate of 124 ml+ 500 ml 6.75 1/ha. However, owing to restrictions in the use of dichlorvos, this procedure had to be discontinued. 4.5 Intersectoral coordination and community participation Functionally effective coordination committees, sub~ommittees and technical committees are required for implementation of vector control components of the programme. The involve- ment of various sectors in the integrated system of vector control lies primarily in the area of source reduction. The technical committees will identify field problems requiring intersectoral action, review the progress of work through regular field inspections and monitor data to the main committee. The action/coordination committee structure may be different for metropolitan cities and smaller municipalities. In Bombay, a high level ''Mosquito Abatement Committee" functions under the chairmanship of the Mayor. For smaller municipalities a three tier system comprising of locaidistrict and provincial committees may be useful in consideration of the scope of executive powers at each level. VBC/ECV/EC/82.22 page 8 In most of the urban vector control progranunes, the potential of conmunity participation has not been explored effectively. Establishment of informative and educative links through field health personnel with the community creates awareness of the progranme ideology. 5. Other Vector Species 5.1 Aedes aegypti The limited hours of water supply in urban areas has affected the population dynamics of Aedes aegypti which bred primarily in the rain water collections and hence was seasonal in occurrence. Paucity of water, however, necessitated its storage in earthern pots, drums and barrels within the living quarters which are not necessarily emptied before refilling. This has not only enhanced its breeding potential but has also rendered its detection and control beyond the scope of weekly inspections, organized under the existing vector control progranunes. Larviciding of domestic water storages by temephos or methoprene is useful but practicable only during disease emergencies. 10 ml of 50% E.C. temephos "charge" diluted at the time of treatment in 1 litre of water is applied at the rate of 10 ml of dilution to 50 1 of water storage. Different charges could, however, be made according to convenience. Operational constraints encountered in intradomiciliary larviciding, however, do not apply to peridomestic and outdoor breeding situations. Emptying small containers and treating other rain water collections by M.L.O., Pyrosene Oil, or granular formulations of temephos or fenthion is effective and practised under existing malaria/mosquito control progranunes in Bombay. Fenthion granules 2% have been found to be effective for more than 20 days in such containers. Special situations like large vehicle-tyre dumps and articles stacked improperly in industrial establishments are kept under control through larviciding with fenthion E.C. 0.2% by suitable appliances. Space spraying and thermal fogging with dichlorvos, malathion at and around large breeding places of Ae. aegypti synchronized with larviciding is effective. 5,2 Houseflies Physiological resistance by the predominant urban species Musca domestica to a wide range of insecticides and particularly to organochlorines requires more emphasis on sanitation. The system of proper storage of domestic refuse, its quick removal and disposal constitutes the essentials of solid waste management and enables the reduction of fly breeding potential. Bulldozing and compacting refuse at the dumping sites is necessary although spreading a layer of earth is not practicable. Chemical control comprises mainly space sprays at refuse collections and dumping sites. Insecticides used are dichlorvos 336 g/ha, malathion 650 g/ha or fenthion 224 g/ha. Mistblowers or vehicle mounted power equipment is suitable for large coverage. Refuse carrying vehicles are treated at their exit point at dumping grounds by using propoxur or diazinon for residual action. Impregnated cords and wet gunny sacks sprinkled with propoxur 2% scatter bait and kept at vulnerable points are supplementary to space sprays. Insecticides used for cord impregnation are diazinon, fenthion, malathion, propoxur. Pyrethrin + piperonyl butoxide or bioresmethrin + piperonyl butoxide in 1:5 ratio as aerosols are effective in controlling fly infestation but the synthetic pyrethroids have not as yet been used in routine progranunes in India. Screening of doors and windows is beneficial in eating establishments, hospitals, dairies and pharmaceutical units. 5.3 Cockroaches VBC/ECV/EC/82.22 page 9 Paradoxically, the cockroach infestation of the species Periplaneta americana, spreads with the extension of underground sewer systems in the urban areas. The drainage line and its inspection covers are the places where heavy infestations of more than 1000 cockroaches can be frequently noticed in the area of 0.75m3 of the interior of inspection chambers. Inspection chambers and manholes of the sewer line are residually sprayed with propoxur 0.1%. The residual effect lasts for about 2 months. Thermal fogging with 0.5% dichlorvos so that the fog permeates through the system of drain and ventshafts coupled with residual application of propoxur in inspection chambers is a desirable combination. However, indoor cockroach control is primarily organized and executed by private pest control services, whereas municipal programnes relate more to sewer infestation. 6. References (1) Cardarelli, Nate. (1976) Controlled Release Pesticides Formulations. CRC Press, 133-145. (2) Covell, Major G. (1928) Malaria in Bombay. (3) Gratz, N.G. (1973) Critical Reviews in Environmental Control, 3(4), 455-495. (4) Pal, R. and Gratz, N.G. (1968) Pest Articles and News SUJIIID8ries, 477-485. (5) Subba Rao, S. (1981) SEA/MI.A Meet. 12/WP 8. (6) Surtees, G. (1971) Abstracts on Hygiene Vol. 46, No. 2, 121-1~4. = = =