Entomological aspects of the devolution of the activities of the Onchocerciasis Control Programme

WORLD HEALTH ORGANIZATION ONCHOCERCIASIS CONTROL PROGRAMME ENTOMOLOGICAL ASPECTS OF THE DEVOLUTION OF THE ACTIVITIES OF THE ONCHOCERCIASIS CONTROL PROGRAMME SEPTEMBER 4, 1989 ENTOMOLOGICAL ASPECTS OF DEVOLUTION CONTENTS INTRODUCTlON 1. COLLECTION OF ENTOMOLOGICAL SAMPLES Collection of aquatic stages CaEching of adults 2. STUDY OF ENTOMOLOGICAL SAMPLES Equipment Identification of larvae Identification of pupae Identification of adults 3. SEARCH FOR INFESTATIONS 1 Equipment 2 B1ackfly dissection 3 Identificatlon of developmenEal stage 4 Calculatlon of transmisslon indices. I.t 1.2 2.1 2.2 2.3 2.4 3 3 3 3 4.1 4.2 4.3 4.4 s of O. volvulus. 4. SMALL-SCALE GROUND-BASED VECTOR CONTROL Equipment Antiblackfly insecticides Ground-based spraying technlques Evaluation of effecE of larviciding. 5 CONCLUSION INTRODUCTION The concept of Devolution demonstrates the will for a progressive transfer of the activit,ies of the Onchocerciasis Control Programrne to the public health facilities of the Participatlng Counr,ries. It was understood that Ehe birth of this Devolution, i.e., iEs progressive setting up would be nade only when onchocerciasis had been conquered as a public health problem and obstacle to socioeconomlc developnent. In principle, this objective should be attained 20 years after the sEart, of vector control and in the absence of any mass medical treatment. Devolution can therefore be put in place and will rnainly concern epidemiological survelllance and the treatment of the disease now since ivermectin is available for mass treatment,. Large-scale vector control would no longer be justified slnce t,ransmission will be reduced everywhere to the tolerable 1eve1. In addit.ion, this control which necessit.ates great financial resoures would be greatly beyond the capacity of the Participating Countries. However, ground-based llmited blackfly cont,rol activiEles should be realizable in isolated foci within Ehe framework of Devolution. It should be recalled that EI.Jo types of activities emerge from the very notion of vector control: (a) blackfly control operations proper, and (b) entotrological evaluation The enEomological evaluation is carried out before and after Ehe control oPeraEion and ls based on a rlgorous entonological survelllance which obeys scientific rules. The entomological surveillance can be carried out as and when necessary by the Participat,ing Countries as part of Devolution. WiEh Ehe cessat.lon of vector control Ehere will be a massive and undoubEedly sudden return of blackflles. The entomological surveillance based on blackfly densit.ies will no longer be neaningful, be it the search for pre- adult stages in the breeding sites or Ehe catching of biting females. The entomological activities would mainly amount to the search for developmental st,ages of 0nchocerca volvulus. Doubtlessly, it will not be necessary to lookfora11th@esoftheparasitebuttorevea1thethird stage: the infective larvae (L3) of O. volvulus which is easier to find than the fi rst or second stage. The specific identity of this metacyclic stage will prove necessary for the exclusion of all the oEher 0nchocerca species,parE,icularly Ehose of animal origin. The daEa obt,ained would be used Lo establish the rates of the blackfly populations carrying this L3 stage and if necessary draw the attention of the corDpetent authoritles to a possible recrudescence. The aim of this document is to describe certain basic principles for the attention of technicians who will be responsible for the collection of entomological data on the vectors of onchocerciasis as part of Devolution. 1 . COLLECTION OF ENTOMILOGICAL SAI'{PLES The ent.omological samples are made up of different developmental stages of the vect,ors of onchocerciasis: blackflies. It should be recalled Ehat the blackfly is a holometabolous dipterous insect. Its first three developmental stages are aquatic. They are: the egg the larva and the pupa The fourth stage is aerial and generally riverine: it is the adult insect or imago. I.1. Collection of aquaEic stages (eggs, larvae, pupae) 1.1.1. Equipmeqt tubes pure alcohol alcohol (70o-80o) pure acetic acid hatching cage entomological kit (standard conEent) : mounted needles (2) - hard forceps (1 pair) - flexible forceps (I pair) - lancet (2) scissors (2 pairs) hand lens. icebox containing ice boaE prospection notebook L.L.2. Where to find Ehe aquatic stages? In Eheir breeding sites fixed to different subsErates in the current: woody or herbaceous plants pebbly blocks surface of rocks or concrete constructions The aquatic sEages of S. damnosum s.1. are normally found in the sections of the watercourses where the current velocit,y ranges between 0.7 and 2 m/sec. During the dry season the breeding sites are generally well delimited while in Ehe ralny season Ehey are more scattered. While the rock slabs are submerged during this period, the current speed is sufficient for the fixatlon of theblackflies Eo t,he riverine vegetaEion. The rlver then becomes a more or less continuous line of breeding slt,es. They are linear breeding sites. There are two categories of breeding sites: - natural breedlng sites: rapids and cascades in the watercourses; river meanders if the speed is sufficient. artificial breedlng sites all types of modern dams; dam spillways and floodgates; irrigation canals; artificial fords and roads liable to flooding; traditional fishermen dams all the watercourse sections that have been made narrow by man. 1.I.3 IIow to collect blackf Iy aquatic st,ages This collection can only be made by entering right into t,he tater if the current and discharge al1ow it. 0therwise a boat has to be used. Once in the river: - examine most of the substrates (a hand lens is necessary for Ehe recognition of the different blackfly species); - take the subsErates (plant and/or pebble) having Ehe greatesE number of aquatic stage s of S. damnosum s.1.; - ensure the exploration of the nhole breeding site so as to have a more representative sampling; - take t.he samples collected to an appropriate place on the bank where they will not dry. I.I.4 Sampllng of aquatic sEages (a) Samples Eo be puE ln Carnoy soluEion. - Prepare the Carnoy soluEion in a tube (one part acetic acid t,o three parts pure alcohol). Only the stages 5 to 7 larvae of S. damnosum s.1. are to be put into the Carnoy solution. The volume of the larvae in the solution should be about a quart,er of the volume of the whole solution. keep the sample cool. change the Carnoy soluclon after 24 hours. The samples in the Carnoy solution should be sent to a specialized laboratory for cyt,otaxonomic identificatlon. (b) Ordinary samples Put the substrates with the blackfly eggs, larvae and pupae inEo a bottle containing 70o alcohol. (c) lupae samples Other substrates (plants or stones) colonized mainly by pupae are to be put just as t,hey are into a hatching cage. Every 24 hours the blackflies which have hatched are to be collected and identified. (d) Marking Mark all the samples correcEly according to the following nodel: River basln River Name of breeding site (coordinates) Name of invest.igators I .5.5 Recording of results Record the enEomological results in the prospection notebook: all the blackfly species observed and their quantity: (few, many, very many) according Eo the colonizatLot of the breeding sit,e and Ehe substrat,es; sketch and brief descripuion of the breeding siEe with the collection points; wat,er leve1 where possible. 1.2. Capture of adult stages This concerns Ehe disease-s vector. caP ture of t.he fernale of Simulium damnosum s.1. , the The capt,ure is made eiEher on man or by trap. L.2.1 Equipment Catching tubes (several tens) - adhesive-coated aluminium plate (Be1lec p1ate, t,he only trap operational at. presenE; one or two plates per site). | .2.2 Catches on man - The capture on man is the only nethod used aE, present to evaluate quanEit,aEively the rates of onchocerclasis Eransmisslon and relate them to the level of endemicity of the disease. - Volunteers are Eo be used. - The volunteer(s) is(are) requesEed Eo caEch on themselves all the blackflies they att,ract. - The volunteer generally takes up posiEion at the bank of the river, near a breeding site, seaEed on a chair, under a shade sufficiently isolated and far fron passers-by. - 0n1y his legs are bare. - The blackflies must be caught before they get the tirne to t,ake their blood-meal. One blackfly is puE into one tube. - The vector collector must, obey the rules in Annex 1 L.2.3 Capture on adhesive-coated aluminlulr glate (Annex 9) It is an aluminium plat,e, one metre square and 0.6 mm thlck. IE has floats which allow it to be anchored in mid-strean. It is used as a bait which aEtracts adult blackflies because of its brilliance. They are trapped in an adhesive-coated transparent plastic spread beforehand on the upper surface of the plate and thls surface is directed towards t,he downstream part of Ehe river. The time between the installatlon and the removal of the plate for Ehe collection of Ehe material eaughL is normalLy 24 hours and at mosE 96 hours. 2. STUDY OF ENTOMOLOGICAL SAMPLES The study of the entomological samples consists mainly in the morphological identification of the different developmental stages of the vectors and the evaluation of their number. To this end, "identification keys" are available in appropriat.e docunents often presented in an iconographic form. 2.1 . Equiproent needed binocular loupe - microscope with micrometer - entomological kit Perri dish - alcohol (70o-80o) identif ication documents tables, chairs. 2.2. IdentiflcaEion of larvae (Annex 3) Using the binocular loupe, the larvae of S. damnosun s.1. (a11 stages) are seprated fron Ehe larvae of the other blackfly species. Brief ly, the larvae of S. damnosum s.1. are recognized by the following characters: - Size: 0.6-0.7 to 5-6.5 mm, from the first to Ehe seventh stage. - Six pairs of dorso-lateral tubercles very visible from the Ehirdlarval stage and having a thorny aspect; - Cephalic capsule: large and round venEral notch; - Colour: the lasE sEages are generally dark with many scales except in Ehe rectal area; - Histoblasts of 5to7. the nynphal branchiae are well delimited on sEages The next st,ep is the recognition of each larval developmental stages which are grouped into two caEegories: Ist, category: stages 1 , 2, 3 and 4 for the young stages. 2nd caEegory: sE,ages 5, 6 and 7 for the old stages. - For a given breeding slte, each category ls estioated quantitatively by: - few (+): less than 10 larvae; - many (+r): between 10 and 100; - very many (++-r): more than 100 individuals; - the resulEs are recorded on the form in Annex 2. 2.3. Identification of pupae (Annex 3) The following is a brief descrlption of the pupa of s. damnosum s.r.: Cocoon in the form of a babouche with neck. Characteristics of branchial filaments: - 2 thick filaments surrounding the opening of the cocoon. 3 splndly and forked lnternal filanents, generally in a vertical posiEion. 3 external filaments towards their end. thicker than the preceding ones and curved the general aspect of the filaments is whitish. Once recogtized,, the pupae are quantified in the same way as(few, many and very many). The result,s are recorded on the that used for the larvae (Annex 2). the larvae same form as 2.4. Identificatlon of adult,s of S. damnosum s.1. (Annex 4) 2.4.L. Brief descripti on of S. damnosum s.1. (males and females) Morphologically, S. damnosum s.1. males and fernales are disfi nguished from other blackfly species by Uhe following characters: black general aspect. black legs with the exception of three-quarters of the base of theposterior basitarsus which are ye1low. tarsal claws with a basal tooth. (a) Male Like all brackflies, the eyes are holoptic, i.e., contiguous wiEh bigfacets on the upper part and snall facets on Ehe lower part; the mesonotum has three black longitudinar bands on a grey background. (b) Fenale Llke all blackflies, rhe up of small facets. eyes are well separated by a vertex and are nade the basitarsus of the hind legs is large with long hair; the mesonotum ls black without bands. 2.4.2. The S. damnosum complex The vecEors of onchocerciasis form a complex of morphologically indiscernlble species. However, in West. Afrlca there are sixprinclpal species thaE can be classified into species groups by the wing-tuft method. This method which is easy to use but, imprecise makes iE possibre to crassify these vectors lnto three main groups. species with pale wing-t.ufts, considered to be of savanna origin; species with dark wing-tufts, considered t.o be of forest, origin; species with mixed wing-tufts, having an approximately equal number of pale tufts and dark tufts. This last group is generally classified among the forest-origin species. The tufts to be taken inEo consideration are those found on the basicostal of each wing of the blackfly. Sometimes these tuft,s are absent, especially in old blackflies. Under Ehese condiEions, identification by this meEhod is impossible. 3 SEARCH FOR INFESTATIONS IN BLACKFLIES. 3.1 Equipment - binocular loupe with nicroneEer microscope with micrometer entomological kit - chloroforn - saline solut,ion (7%o) - slides. - identification document,s. 3.2 Blackf 1 dissection (Annex 5) It is t,hrough the dlssection of the S. damnosum s.l. females that, the infesEations in the blaekflies are looked for, especially the developmental sEages of the onchocerciasis parasite: Onchocerca volvulus. During t,he dissection, other filariae (ot affiilEgin) or nematodes such as the Mermithidae or ciIlates, fungi, etc.r."y be found. The dissection is made manually: either on blackflles freshly killed with chloroform (routine dissection) ; or on blackflies treated wiEh l'layer Haemalum. This latEer met,hod(known as stalning met,hod) reveals better Onchocerca which appear stained in the preparations. The search for the developnental st.ages of 0. volvulus is made sorelyin parous blackfl ies. Nulliparous blackflies are not taken into account since, not having taken a blood-mea1 which ls necessary for t,he maturation of their eggs, the probability that chey harbour O. volvulusis nil. The physiological age of the blackfly (parous/ nulliparous ) can be known only on fresh blackflies. The blackfly dissection method is described in Annex 5. The results should be recorded on a 'tdissectionform" shown in Annex 7. 3.3. Identification of developmental stages of O. volvulus (Annex 6) The onchocerciasis parasite can be found under four of morphologlcal forms in the b1ackfly. Drawing numbers show four forms which are: its different . . . . tO - microfilaria which is generally found in the stomach, peritrophic membrane or stil1 in t.he abdominal cavlty of the insect. - It should be recalled that Ehe peritrophic membrane is a sclerosed anatomical structure which is formed in and from the stomach at each blood-meal. It surrounds the latter. It is completely formed at the end of one to three hours and disappears at the end of 48 hours. _*-age_-L (Ll: 200u)(=sausage state): in the thoracic muscles, glage_3 (LZ: 450u): in rhe rhoracic muscle, stage 3 (L3: 600 to 825u)(= metacyclic stage = infecrivelarvae): usually in the thorax, abdomen and head. Because of its very great mobility, this last stage can be found indifferent parts of the blackfly's body (sometimes even in the legs and antennae, hence t,he need for a careful dissection of t.he blackfly. The identlfication of these different stages is made wlth the help of lconographic documents and by measuring their length. The respective lengths of the different developrnental stages of O. volvulus are in a range which allows them Eo be EffifrEr onchocerca. This measurement meEhod i separated "a pri6r-ri" f rom s, however, linited when it comes to separating 0. volvulus from the 0nchocerca of animal origin(0. ochengi among others). 3.4. CalculaEion of transmission quantities Two indlces are used to esEimate transmission quantities: Annual Biting Rate (ABR) and Annual Transnission Potential (ATP). Both are obtained by the addition of the corresponding monthly values. Monthly Blting Rate (MBR) and Monthly Transmission Potential (MTP). Only the catches on man make it possible to calculate the indices. the MBR for a given month is obtained by multiplying by 30 rhe mean number of daily catches for that monEh. No. of blackflies caught MBR = x30 No. of catching days Ehe MTP corresponds to the MBR multiplied by the mean of t,he total number of L3 in the head per dissected female. L3 (Total found in head I'fIP MBR X No. of flies dissected MTP or No. of flies caught x tr3 (head) x30 No. of catching days x No. of flies dissected ls larval control, the treatmenEs concern blackfly breeding Generally speaking, a minimum of four days of 11 catching hours (7 a.m. to 6 p.n.) is necessary in the month at Ehe rate of one day per week, Eo obEain a meaningful MBR (and therefore a reliable MTP). 4. SMALL-SCALE VECTOR CONTROL CAI.{PAIGN Annex 8 By thls is meant a limited conErol carried out from t,he ground in isolated blackfly foci in order to reduce the nuisance. This control can be undertaken directly from the ground or by river using an appropriateboat. It is a larval control. 4.I Equipment Insecticides - Spraying machines (Hudson or Grebaut, spray) Canoe or boat - Hydrological yearbooks Graduated contalners - 10-20 litre containers. 4.2 Blackfl insecticides (cf. utilization grid) Those most commonly used in Africa are: - temephos (Abate) (utilizable ar all discharges). - chlorphoxin (utilizable at, all discharges) Bacillus thuringiensis H-14 (urilizable at low discharge) permethrln (uti1lzable only aE high discharge) carbosulfan (utilizable at high discharge). They are products supplied in the form of emulsifiable concent.rates and like any pesEieide, have to be enployed with the great,est. necessary precautlons . 4.2 Ground-based treatment techniques Slnce it siEes. To treat a breeding siEe, one has to: to know Ehe river discharge; measure it (cf. Eechnical sheet) in Annex 8 read iE in an up-to-date hydrological yearbook, after having recorded the river height at the water-guage st,at,ion concerned. calculate the dosage from the discharge. spray the lnsecticide upstream from t.he breeding site at an appropriate distance in order to make sure that the whole breeding sit,e is covered by the waves of the insecticide. 4.4 Evaluatlon of the effecE of the larvicidins It ls made in Ewo ways: by the prospection or inspection of the breeding siEes 24 hours after Ehe larviciding and by the capture of adult blackflies ln order to monitor the eventual decrease of the blackfly populatlon. During t,he prospections (see Chapter 1.I .3), it ha that all the S. damnosum s.1. larvae have been kil sE led o be ensured after E,he passage of the insect,icide. The capture of blackflies at the t,reated site (by trapping or on man) also gives informatlon on the success of che larviclding. If t,he focus is isolated, there will be a progressive disappearance of the blackflles. In t,he contrary case, the number of bites will decrease considerably because of the elfunination of the localproduction. The resldual blackfly populations would then be from adifferent source (reinvasion or contamination). Under these condlt,ions, the parous rates would be between 85 and 1002. The nore the focus under treatmenE is far from t,he production sources Ehe lesser t[re densities of Ehese foreign populations w111 be.) 5 CONCLUSION Within t.he framework of devolution, entomological evaluation will no longer have this vanguard role. Its prlncipal task will be to undertake prospections (often on request) Ehat will make iE possible to detect apossible resumpt,ion of the transmission of river blindness. Thls meansthat the onchocerciasis entomological activities wll1 be reduced to a minlmum. To rnake the national teams which w111 be enErust,ed with such activities cost-effective, iE will be necessary for Ehem to be nultidiscipllnary. In addition to onchocerciasis, Ehey should undertake the monit,oring and control of other vectors, particularly mosquiEoes and Esetse flies, both for their nuisance and the diseases they transmit. Community partlcipation in such acEiviEies wl11 facllitate the work of these teams. ANNEXES TO THE DOCUMENT ON THE DEVOLUTION OF VCU ACTIVITIES Annex l. 9aEqhing rules What should or should not damnosum s.1. fernales. be done during the capture on man of S Annex 2. S. damnosun s.1. breeding site lnspection form It gives the total results of the prospections for the collectlon of t,he aquatic stage s of S. damnosum s.1. Annex 3. S. damnosum s.1. aeuatlc stages ldentification form This form gives at the front a descrlpt,ion of the aquat,ic stages of the onchocerciasis vectors and aE the back drawlngs of these stages. Annex 4. Adult S. damnosum s.1. identification form At the front are descrlbed the adults of the vectors (male and female) and at the back drawings of Ehe different, organs used for the identification of these vectors. Annex 5 Fema1e S. damnosum s.1. dissecEion form At the front, of che form are the dlssecEion technlques; at back, are dissection sketches and the anatomical structuresfor. Annex 6 Onchocerca volvulus developnental stages- identificatlon form Drawings of these stages: microfilaria, sausage stage, stage 2 andinfective larva with a brief descrlptlon in each case as werl as the sEandard dlmensions. Annex 7 Female S. damnosum s.1. capture and dissection form This form gives the total of the results of the dissection of a day-s catchlng at a given point. Annex 8 Ground-based S. damnosum larval breeding site Ereatment form At the fronE are t,he insecticide utilization grids and measurement of dlscharge. At the back are sketches of classic spraying machines (Grebaut spray) . Annex 9 Bellec Trap Descript.lon and use. Ehe looked