Methods of mass epidemiological evaluation of onchocerciasis: their utilization in a vector control programme

a@ WORLD HEALTH ORGANIZATIONORGANTSATTON MONDIALE DE LA SANTE oNcrro/wP/ 75. 14 Page 2 2 L2 13 L4 19 1 EXPERT COMMITTEE ON EPIDEMIOIOGY OF ONCHOCERCIASIS Geneva, 10-18 Novenrber 1975 Item 6 of the provisional agenda MEIIIODS OF MASS EPIDEMIOLOGICAL EVALUATION OF ONCHOCERCIASIS. THEIR UTILIZATION IN A VECTOR CONTROL PROGRAMME by A. Prost, B. Thylefors and C. Palrault Epiderniological Evaluation Unit Onchocerciasis Control Prograrune in the Volta Basin, Ouagadougou CONTENTS 1. Introduction 2. Evaluation techniques Slze of the sample . Selection of clusters . Methodology of the surveys 3. Carrying out the surveys Socio-denographic picture The cllnicaI examination . Ihe parasitological examinat.ion The serological enamination . Xenodiagnosis MazzoEti test The ophthalmological examination Working up the data Conclusions Annexes References 2.L 2.2 2.3 2 2 4 5 5 7 8 8 8 9 9 3.1 3.2 3.3 3.4 3.5 3.6 3.7 4 5 I ;l{i The issue of this document does not constitute formal publication. lt should not be reviewed, abstracted or quoted without the agreement of the World Health Organization. Authors alone are responsible for views expressed rn signed articles. Ce document ne constitue pas une publication. ll ne doit faire I'objet d'aucun compte rendu ou rdsum6 ni d'aucune citation sans I'autorisation de l'Organisation Mondiale de la Sant6. Les opinions exprimdes dans les articles sign6s n'engagent que leurs auteurs. t i rl oNcrro /wP/ 75 . 14 Page 2 1. ]NTRODUCTION The purpose of making an epideroiologica 1 evaluation for a Simulium damnosum control campaign such as that being carried out in the Volta Basin is three-fold: (a) To ascertain the human impact of anti-vecEor campaigns by studying transmissi-on. Is transmission continuing or has it stopped? Is there only residual transmission? Wtrat is the diseasers incidence with vecEor control? (b) To follow the spontaneous course of the disease in the absence of transmission, when the aggravating factor of parasite accumulation ceases to operate. (c) To determine whether there is a transmission level which is tolerable for a population, i.e. a level of endemic and of parasite loads sufficiently low not to affecE the general state of the individual. Different techni.ques and survey methods may be used according to what is aimed at, and at, different times. First the basic survey has to be made, the point of departure for all subsequent comparisons. Techniques have to be devised in each case which are at once accurate, in order to obtain a scientific result, and simple and speedy so that they can be used on the spoE in mass examinations. The methods selected for making a medical evaluation in the case of the Volta Basin may be criticized. They do not use the most recent techniques. And they certainly are not such as to enabte a ful1 individual medical picture of a person who has onchocerciasis to be obtained. But the evaluation is only intended to enable Ewo situaEions separated by a given interval of time to be compared, and the function of the methodology chosen is therefore to identify key factors which are clear-cut enough to indicate the changes that occur in the epidemiological situation during a period of time studied. Much remains to be learnt from work of this kind. Every month brings new food for thought. It is not the purpose of this paper to attenpt to prescribe a single methodology which is of universal application. The account of the standards used here, however, may perhaps be useful as a guide for future epideuriological surveys and constiEute a minimr:m upon which consensus can be reached. EVALUAT rON TECHllr rQUES 1 Size of the sample This is decided upon before the plan of operations is worked ouE, and is a matter for Ehe statistician. In accordance with the population concerned and the degree of accuracy required he decides upon the minimum number of persons needed, the desirable nr:mber of clusters, and the clusterst sLze. 2.2 Selection of the clusters In onchocerciasis the distribution and seriousness of the disease are closely dependent upon the man-vector relationship. They vary greatly from place to pIace, depending upon the contour of the water-courses and the relation of human settlements with the river, but they are homogeneous within one and the same local conrnunity. It is not essential therefore to use sampling techniques: to make a map of a village, number its inhabitants, number the individuals in each family, and Lhen decide by loE which people to examine. This is a time-consuming method and very unpopular with the people who are noE exami-ned. People do not like forming part of a trial and are oblivious to the requirements of statistics. t a 2 2 ? , oNcHo/wP/7s.14 Page 3 In the Volta Basin it was therefore decided that the "villagett should be the primary uniE for the survey, the statistical cluster. Where a village is too large, one or Eore trneighbourhoodsrr are selected by lot and the whole of that neighbourhood or those neighbourhoods is examined. Slmilarly several smal1 villages can be taken together to constitute one cluster. The problerrr thus comes down to selecting villages. down for making t.his selection: A number of criteria have been laid 2.2.1 Level of endemicity For surveillance of a vecEor control prograrme it seemed essential that 75% of the villages should be in hyperendemic areas or the upper bracket of mesoendemic areas (prevalence over 5O7.), in wtrich regressi.on could be more easily objectified, and 25% of the villages in areas of low or sporadic endemicity. This means examining, before the vlllages are selected, any docr:ments and previous studies on onchocerciasis, lts dispersion and prevalence. 2.2.2 Size of the villages In order that the different age-groups should have minimum representation it would appear that 30O people is the desirable size of a cluster. It was decided Ehat v1l1ages wlth a census population of over 1OOO or 15OO should be excluded unless they consisted of easily individualized neighbourhoods. There is no lower limit however to the villagest size, because hyperendeoic villages often have only 1OO inhabitants or fewer. 2.2.3 Social homosenei ty and stability Since the surveys are longitudinal and the individuals have to be found again at intervals on each subsequent visit, i.t seeos preferable to exclude places where deoographic upheavals are going to occur: agricultural or agro-industrial projects entailing the disappearance of localities, influx of a seasonal or shifting labour force (sugar plantations), and nomadic areas. Also excluded are administrative or conmercial centres, where a proportion of the inhabitants have come from outside, only stay teuporarily and are not representative of the local endemic, and where traders and craftsmen engage in a type of activity which exposes theo less Eo the vector than is the case with peasants and so vitiate the overall findings. on the other hand lt seems advisable to include in-igration areas in which a populationthat is often rrvirginrr, and could constitute an excellent indicator of residual transmlssion,is (and w111 go on) settling in places freed from onchocerciasis. 2.2.4 Relationship with Ehe entomolosical evaluation It will be important to select certain villages in the irmediate proximity of Simuliun catching points, in order to be able to compare the parasitological observatlons with an amount of transmission identified by dissection of the f1ies. It will be no less important to selecE villages away from such catching points, in orderto check that the vectorrs disappearance and the endemicrs decline in the proximity of thepoints under surveillance are in fact attended by a simultaneous and parallel development outside the identified and treated breeding places. 2.2.5 Geosraphical dispersal The villages selected must be so distributed that all the streams thaE are carriers ofbreeding places, all the identified onchocerciasis foci, are represented in the sample.Inevitably vector control oPerations will have different results according to the contour ofthe river, and medi.cal observations made in a focus cannot be extrapolated to an entire area oNcHo/wP/75. 14 Page 4 This pinpoint aspect of evaluation means that. the points selected must be geographically dispersed. 2.2.6 Accessibility This criterion only applies to the ophthalmological exami.nation, whi.ch involves the transport of heavy equipment. Onchocerciasis has sometimes been described as an rrend of the roadrr disease, and to survey some points it may be necessary to go on foot. 2.2.7 Random selection This comes into play after lists of the villages which comply with the foregoing criteria have been drawn up. It would be useless for example to rely upon a prior selection by administrative district, or even by level of endeoicity (supposing this to be known for all the villages). The sample would not in those cases comply with the one or more of the criteria mentioned, which are considered essential. When however a large number of villages meeting those requirements has been found, a random selection to decide which shall in fact be surveyed is in place. 2.3 Methodo of the surv 2.3.L A11 of the authorsr surveys, irrespective of their nature, rest uPon a three-fold basis: (a) an exhaustive census of the population constituting the sample decided uPon, (b) a clinical and parasitological examination, with its variants, (c) an eye examination: either a full one, made by a qualified ophthalmologist, or a simple test (visual acuity). 2.3.2 There are three types of survey possible, dependent upon the object of the study being made. (a) An ordinary prevalence survey, using form S 6O2 given in Annex 1. This is what is known as the trbasicrr evaluation. The purpose of it is to investigate transmission, its continuation or its cessation. It involves: - an exhaustive census by families with identification of blood relationship including thaE of absenE mpmbers - parasitological exarnination by double biopsy - rudimentary measurement of visual acuity by a simplified test identifying the blind and the pre-blind. This type of survey both gives snapshots of the level of endemic at a Particular moment, and makes possible longitudinal surveillance of people to ascertain their degree of infestation, the aPPearance of new casea of blindness and the fate of such cases' (b) A parasitological survey. This can only deal with what is known as the r;susceptibler group, i.e. the people who are certainly negative at the beginning of vector control operations. It covers only people born since the programme started, orilvirginrt individuals from non-endemic areas settled in the surveillance area since the beginning of operations (irmigration areas). This type of survey determines solely the existence or non-existence of residual transmission. It takes less time than survey (a), and a larger number of points can be covered. (c) A detailed survey, using form S 601 given in Annex 2. This comprises: - an exhaustive census with personal identification and status - a simple medical examination: weight, height, derroal inguinal-scrotal area or of the lynphatic system, and - a parasit,ological examination - other biological investigations where necessary - exact measurement of visual acuity - examination of both eyes with an ophthalmoscope and a dilatation, covering all the existlng ocular lesions, pressure (tonometry). oNcHo/wP/75. 14 page 5 identif ication of migratory lesions, lesions of the number and site of nodules slit lamp, before and after with measurement of intraocular L The object of this last type of survey, confined to a limited number of people, is to add to knowledge of the disease and to trace its course at every level, both spontaneously in the absence of transmission, and under treatment. 2.3.3 Periodicity The interval between two surveys is at. present three years. The changes taking place in a single year do not appear to be large enough to \rarrant more frequent visits, nor do the survey techniques seem sensitive enough to detect thexo. 3. 3.1 3.1.1 To check this point several clusters are going to be surveyed annually CA,RRYING OUT TIIE SURVEYS Socio-demographic pic ture The census In each village chosen for the epidemiological evaluation the first thing to do is to mrke a census of the population (registration of residents present, residents absent, and visitors). This is a vital phase of the survey: the value of the longltudinal study made will depend upon how carefully it is carried out. This applies obviously to the first visit, but it also applies to the subsequent ones: in order to make possible easy location of the people present and the people absent at the present moment who have already been examined, together with new residents or visitors, the census of individuals is, on each occasion, carried out in family units. 3.L.2 Ordinary registration The members of several fanily units are never entered on the same sheet of form S 602(see Annex 1) used for the rrbasicrt evaluation. If the faurily group is a targe one, systenatic registration of its members rnay require trro or three sheets; on the oEher hand the name of a bachelor living in a separate dwelling on his own is given a whole sheet to itself. Each person, assigned an individual numberr.is defined by the ethnic group and village he belongs to, his neighbourhood, his sex, his agerr wheEher he is present or absent at the time 1 - While exact age is usually not ascertainable in the case of adults, even when they have identity papers, iE is considered essential to deternine age exactly in the case of the children, who are indicators of recent transmission. For this, reliance is placed exclusively, before the age of L2 years, on age determination from the dental formula, in accordance with the table given in Annex 3. oNcHo/wP/75.14 Page 6 ofthevisit, andhis bl-oodormarriage relaEionships ('rObservations" - remarks - column). People making their appearance 1ate, at Ehe end of the visit, also any absentees identified directly(i.e. ones not declared by some head of family), are registered on a special sheet, if their identity cannot be entered lruoediately on one of the already existing family forms; it stil1 rernains possible to reclassify them on a later visit, si.nce each person is always given an individual number that is transmitted to the computer after the first visit. 3.1.3 Detailed registration Unlike the form just referred Eo, form S 601 (see Annex 2), the form for detailed evaluations, does not give the members of a family together on one page; it is stricEly individual. It consists of three parts: socio-demographic, parasitological, and ophthalmological. The sociologist on the evaluation teau checks the accuracy of the information in the first part. Data additional to the initial inform:ti.on entered in form S 602 is given here type of main occupation (farmer, fisherman, craftsmrn, trader, etc.); migratory status (length of time resident in the village); mobility between t\ilo consecutive survey visits (length of time spent away from the viIlage, and where that time was spent) For the detailed evaluation an individual form is necessary because of the amount of information collected. It occupies the whole of a 2L x 29.7 cm page; the back of the page may if necessary be used for quickly jotting down, in the field, ocular diagrams for the ophthahoologist. There are two things however against using this type of form only: (a) nothing would be recorded about the family structure to which Ehe person belongs(his blood and/or marriage relationships) or, in the case of a migrant, about his place of origin or his present place of migration; (b) the splitting up of a cluster into a large number of individuals each registered on his own account greatly complicates the task of locating those people on a subsequent visit, and their identification is of course necessary for a longitudinal study. These two difficulties have been avoided by using for census of the people involved in the detailed evaluation, also forro OCP/EPT/75 (see Annex 4). Unlike forms S 601 and S 602 this does not have to be filled in completely at each visit; the first entries are added to on subsequent visits. The additional information provided by this form is not intended for daEa processing. 3.L.4 The village cards In any case the information of an individual and family nature collected during the census provides, particularly in the instance of the detailed evaluations, a substantial store of qualitative information. In so far as the level of onchocerciasis enderuic in a particular place is neither fixed nor necessarily always homogeneous, transmission dynamics (increasing, stagnant or declining) depend in part upon a kind of life and socio-economic activity which is in its turn neither simple, nor fixed, nor necessarily always homogeneous. Factors like these, irrelevant to medical diagnosis, belong nevertheless to the field of epidemiology. I oNcrro/wP/75.14 Page 7 For each village exaoined, whether it is undergoing an ordinary or a detailed investigation, the sociologist on the evaluation tearn ls.responsible for establishing a rrcardrl to which information will be added on the teamrs subsequent visits. Upon this card is entered routine information showing the date of each visit, its purpose, the onchocerciasis focus responsible, the comparative status of adminlstrative censuses and of the census rnade by the evaluation unit, access conditions and working conditlons, the name of the village chief, the history and structure of the settleoent, the type of migration(s) if any, and technologlcal innovations and local economic resources. Where it is a mrtter of detailed evaluation the sociologist. is expected as far as possible to keep the day-to-day life of the village comunity under observation, either hinself or Ehrough others. An ideal arrangement would be that an investigator living on the spoE should keep a record, between two three-yearly (or in rare cases four-yearly) vlsits by the evaluaEi.on team, of births, deaths, migratory moveoents and other outstanding events or happenings that occur in the village. 3.1.5 Relations with the villagers 0ccupying a position midway as it were between laboratory res@rch and nobile clinic rrork, an epidemiological evaluatlon aims, like laboratory research, at obcaining a scient.ific result whi1e, like mobile cllnic qrork, being required to establlsh a relationship of trust between the people studied (they are not patients) and the physicians (who do not necessarily perform any therapeuEic function). Without such trust, absenteeisn will inevitably increase. At the very beginning of the surveys the Evaluation Unit of the prograruue enjoyed the benefit of the favourable PreconcePtion which African villagers entertain of medical terms that come t,o help them. BuEto keep them favourably disposed during the 20 years of surveys whlch are being envisaged for onchocerciasis, Ehe members of the Evaluation Unit have got to be able to win lasting accePtance for theoselves. To achieve this the objects of the operaEion being undertaken and the means being employed should be clearly explained to the villagers. It is typical that in one Particular village on the Volta Noire the authors rrere the first to point out to theinhabitants the connexion between what the helicopters were doing, what the catchers weredoing, and the work of the medical tean whlch was vlsiting then. Up ti1l then the village chief and notables did not know wtry every rreek, for monEhs and monEhs, catchers had been coming to their village in a Landrover and installing theneelves on the rlver bank, apparently without doing anything, for an entire day. Nobody before had thoughr of offering that sort of explanation, or been willing to spend the time and to take the steps required for giving it. The maintenance of relations of trust and mutual information with the authorities responsible for the villagesradoinistration on the one hand (prefects, subprefecEs, heads of medical sectors or circunscriptions), and with the villagers living in the areas visited on the other, is an indispensable feature of a sound evaluation Eethod. Here rrsavoir fairerr is essential, and it must be displayed in the survey area the whole time by all the members ofthe Unit (from physicians to drivers). 3.2 Ihe clinical examination In addition ro ascertaining anthropometric data (weight and height) this examinationinvolves looking for direct or indirect onchocerciasis lesions, i.e.i - site and number of nodules (onchocerconas); - dermatological involvement (its degree and entent): papular onchodermatitis, pachyderma, lichenification, me lano leucoderna ; - involveroent of the lyuphatic systeu: elephantiasi.s, glands and hanging groin; - genital lesions: hydrocele with or without hernia. ordinary scratching leslons, atrophy of the skin, 1ocal hypertrophy of the inguinal a 0NcH0/wP/ 75. 14 Page 8 3.3 The parasitological examination Until more accurate methods have been devised (serology) this depends upon looking for 0. volvulus microfilariaeinan exsanguinated skin biopsy. In order that the findings may be comparable in all villages the examination has been codified in accordance with the following ruIes, derived from Picqts method: (a) Calibrated biopsies are taken with a 2.5 m standardized punch (Walser-type sclerectomy punch). Weighing and other measurements of the surface or volume of the biopsy (Oute, Brinkmann) "." of interest for research purposes, but are not practicable' in mass evaluations. (b) Biopsies are localized in the lliac crest, that site being recognized as the most productive one in the programme area (research performed by the Parasitological Section, Centre Muraz). (c) Two biopsies are taken from this site, one at the right of it, the other at the left. A double snip enables 67" more positive people to be detected in the general population, or even 12% more (test performed on 11OO snips, VIHO 1975). (d) The skin fragments are placed on the same slide in two drops of distilled water. Reading is easier than in physiological serum in the field: there is no salt deposit to hamper reading, the filariaeareless mobile, and it is possible to add to the liquid periodically without danger of concentratlng the solution. (e) Readings are trade with a binocular lens after 30 minutes (x 25 magnification): this is rhe time taken for 507. of the microfilariaetoemerge from the fragment (see Picq); a lens enables a broader field to be examined than a microscope, and makes possible more accurate counts. 3.4 (f) The negative slides are kept and read 30 minutes later, 6O minutes after the biopsy was taken. (g) When the slides are read as accurate a count as possible is made of the number of microfilariae observed in either fragment. (h) A certain percentage of the slides are kept for possible identification after Dipetalonema streptocerca stai.ning. (i) Ten per cenr. of the slides are double read by what is known as the blind method. Each microscopist is in this way routinely tested against the physician specialist and against his eolleagues. Findings are considered reliable when less than 1O7" of quantitative findings do not belong to the same broad numerical category as the first reading findings (see 4.3 belotr). The serological examination Methodsaresti11experimenta1,andcroSsreactions,ith@iremainconstant. These methods require improvement, and the day mey corne wtren biopsies and direct microfilaria detection are considered to be unduly gross raethods either for assessing a slight infestation and for evaluating the presence of residual transmission' 3.5 Xenodiagnosis O. volvulus microfilariae are looked for in Some authors believe this the stomach contents of Simulium engorged on examination to be more reli.able and accuratea suspected person. than a snip. The difficulty of carrying it out will prevent it from ever becoming a mass evaluation method. I oNcHo/wP/75.14 Page 9 3.6 Mazzotti test. Thls test is not reconunended without recourse to evaluaEion surveys. Apart from its inaccuracy (positlvity in the presence of W. bancrofti, etc. ), iE is not greatly liked and provides no correct information of a q,r".rtGri.r"-rrat,r-.e. 3.7 The ophthalmological examination 3.7.L Some important ophthalmological principles for the epideniological evaluation of onchocerciasis in an area, are: (a) continuous clinical and epidemiological evaluation of the total amount of blindness and impaired vision in the population. (b) estimation of the importance of onchocerci-asis as a blinding disease, related to different endemicity levels and populations. (c) estimation of the influence of other diseases on the rates of visual impairment, and their future role in relation to a changed onchocerciasis transmission. (d) continuous clinical study of the different ocular onchocerci-asis lesions and their development in relation to vari.ous degrees of transmission, or medical treatment. This will irnply a definition of variables for estimaEion of the intensity and gravity of ocular onchocerciasis. The definition of visual impairment used here, is that of the Study Groupl on the Prevention of Blindness, WIIO L972, categories 1-5. This means that|tblindnessr corresponds to category 3-5, rrsevere visual i-mpairmentrr is category 2 and rrvlsual inpairmentrr category 1. It is most important to screen population groups with visual impalrment, and many field surveys have been carried out on onchocerciasis for this purpose. It must be emphasized however, that there are many inaccuracies connected with visual acuity testing in an illiterate population. From the epidemiological point of view, it is important to find not only the blind people, but also those at risk of becoming blind. There must be a continuous follow-up of the groups at risk and their development of further visual impairmenE in relat,ion to changing transmission, and finally the sociological and economlcal Pattern they will fit into. This is fundamental for estimations of the benefit of an anti-Simullum-campaign and later medical mass-treatment actions. 3.7.2 Visual acuity tests The most conmon methodology used in the field is the illiterate rrE-testrr, or sometimes the circles of Ia.ndolt. Although some authors claim fairly good results with therrE-testtl there are some obvious disadvantages. For most of the people involved the rrErt represents an unknown geometrical figure, and the effort to recognize the figure occupies all of their attention. Also, there is a lack of a good, standardized chart with several test types for the visual acuity level of 0.1 to 0.3. It would be preferable to have separate sheets or a cube with isolated Es on each side in various sizes, and a fixed test distance related to the actual definitions and Ievels of visual impairment. The testing of visual acuity in a group of people in a village is a very complex psychological situation. There are the neighbours who have already passed the test and now are laughing, children that are afraid, shy women and traditional attitudes against this new and disturbing elernent brought into the village. A11 these factors may produce an apparent reduction in vision. It is obligatory to take your time with each case, test and re-test, tofinally find out a probable visual acuity level. There is already evidence from the field work that women and children very ofEen cannot understand the rrE-testrt. In our experience about 50% of the children aged less than 10 years can understand and cooperate in this test. Wld Hlrh Org. techn. Rep. Ser. (L973) No. 518 I oNcHo/wP/75.14 Page 10 In order to improve cooperation in the visual acuity test, vre are trying therrSjUgren Hand-testil during 1975. This test utilizes a figure of a black hand on a white background, in various si.zes on separate sheets, aE a fixed test distance of five metres. The testing procedure is Ehe same as with therrE-testrr, but as the results are given in a scale 5/5O to 5/5 LE is possible to define Ehe important levels for visual impairment. The Sjugren test has given very good results with children from the age of three to four years in Europe, and will perhaps give us more reliable results. At present we conduct in the field the visual acuity test at two different levels. For the trdetailed" evaluation (see previous chapt,er concerning sampling and methodology) with a complete ophthalmological examination, the rrE-testrr i.s used, and the results coded: finger counting at three metres finger counting at one metre percepEion of light amaurosis not able to cooperate not examined. Each eye is tested separately, without correction. The code gives the leve1 of normal, impaired and severely impaired vision, as well as three stages of blindness. For the basic, global evaluation, a much simpler methodology is used, which is still reliable and less time-consuming. As the most important thing is to find the pre-blind risk group, a preliminary screening procedure with the |tEtt or rrsjUgrenrr test at Ehe visual acuity level of 0.3 both eyes should be used. Further examination is then performed only on the group that does not pass this test level. The results are coded in four categories: blindness, severe visual i.mpairment, visual impairment and no visual impairment. The interpretation of the results from the visual acuity testing presents some problerns. With a detailed ophthalnological examination as background it is possible Eo state the probable main cause of visual impairment in the najority of cases with reduced vision code 3 or more, of the form S 601 (see Annex 2), There rernain a nr:mber of unexplained visual impairment cases, which are those cooperating poorly or with refractive anomalies or early undetectable posterior lesions. However, when a sufficient number of examinations have been conducted, it should be possible to estimate the size of this bias. Although it is time-consuming and sometimes difficult, a complete ophthalmological o(amination is necessary. An epidemiological study on onchocerciasis musE include a precise diagnosis of the individual going blind. The clinical appearance of the disease is influenced by, for instance, age, sex, exposure to transmission and other ocular disorders. This must be kept in mind to give a relevant estimation of onchocerciasis and its importance for blindness. In the OCP field surveys a standardized form (see Annex 2) is used with coding for each listed sign. 3.7.3 Examination methodology The patient, following a visual acuity test, is examined in a dark room. After having had his head dorsn for at least one minute, he is examined with the slit lamp (Haag-Streit) magnification x 16, and the number of living microfilariae (mf.) in the anterior chamber is counted, or estimated if high in both eyes. The dead and living mf. in the cornea are counted with magnification x 25. Other abnornralities in the cornea are noted, with a separate code for signs of corneal complications of trachoma. Pupillary react.ions and Ehe aPPearance of iris and eventual iritis are checked. A bilateral tonometry is then perforned on Patients of more than 10 years old. The eyes of all patients are dilated if there is no t 0 1 2 3 4 5 6 7 8 9 1.0 o.7 0.3 0.1 oNcHo/wPl75.14 Page 11 obvious contralndication, using a drop of tropicamide 17" in each eye. After minimr:ro half an hour the patient is reintroduced to the dark room, and the slit lamp examination completed by looking for mf. on the lens and in the vitreous. Finally the fundus is examined by ophthalmoscopy, direcE and indirect technique. In some selected cases the visual fields are tested by the confrontation methodology of Dondersr t.o get an approximate idea of severe restrictions. A Kowa RC2 camera is used for documentation of developing serious lesions. In case of a ralsed intra-ocular pressure, gonloscopy is performed if possible. The reverse of form S 6Ot can be used for drawings of any lesions or extra notes. The reliability of the diagnosis of ocular onchocerciasis may be relative in some cases, where there is a mixed ocular pathology from other disorders. The final diagnosis must be a conclusion of all the signs and their relevance to onchocerciasis and an eventual visual impairment. In general, onchocerciasis gives rise to a blindness in the adult population, i.e. from the third decade of life. However, in children also, serious and irreversible eye lesions are seen, especially ln those with head nodules. It is mosE important to find out the age and sex specific prevalence of impaired vision in relation t.o different endemicity levels of onchocerciasis. Even if the general correlation between the prevalences of onchocerclasis and visual impairment is well-knohrn, rre nay still find differences hard to explain. It nay be a question of geographical factors, heterogeneous exposure to transmission within a population or influence of different cytotypes of the vector. Classical1y, onchocerciasis causes more bllndness in men than in women, but there are exceptions to this ru1e. To nake an estimate of the probable total amount of visual iopairment caused by onchocerciasi.s a sufficient number of detailed eye examinatlons must be performed in different regions and populations. This will provide good baseline data Eoday, and with a continuous follow-up of the groups at risk in the future, we will be able to estimate the cost-benefit relationship of an action taken against the disease. 3.7.4 The design of the examination form S 601 (see Annex 2) is such that it should give not only a detailed diagnosis of onchocerciasis, but also of other ophthalmological diseases. Today, onchocerciasis is certainly the dominating blinding condition in the Volta River Basin Area, but this situation will probably change in the future. This will be due to not only the eradication of the vector or medical treatnent of the disease, but also due to aspects of economical develop'm.ent in an area with its concouitant change in social structure. With reinforced public health planning for instance, there will probably be a change of birth and death rates, life expectancy for the individual and Ehe general spectre of diseases in thepopulation. This may highly influence the epideniology of ocular disorders. The problem concerning the diagnosis of several diseases in a patient ls sometines very comple:<. Onchocerciasis mFy well give a secondary glaucoma, but this may also be idiopathic or caused by several other diseases. Iritis is nore cormon in onchocerciasis cases, but not at all a specific sign. The presence of an iritis in a case of ocular onchocerciasis does not necessarily uean a causal connexion. Still, in the najority of cases, it is possible to state the rrain disease and its influence on the visual acuity. The knowledge of the spectre of eye diseases in different age-roups is important. Blindness during childhood often rneans the possibility of congenital disorders, nutritionaldeficiencies, measles, trauma or trachoma, while onchocerciasis plays its role at a later stage of life. In the older age-groups one may find genuine glaucomes and senile cataracts or retinal degenerations. To evalua.te the future and final result of any action against onchocerciasis, and its relation to the prevention of blindness, \re have to know also aboutthe influence of other eye diseases in different age-groups and populations. 3.7.5 There has been much discussion about the ocular lesions of onchocerciasis, their relevance and specificity, and there is still disagreenent concerning the nature of theposterior lesions. our knowledge is sti11 limited concerning the development of existing ocular onchocerciasis lesions after Ehe transmission is terminated. The eradication of the vector will mean a new situation. As an integral part of the epideniological evaluation, itwill be necessary to conduct a continuous clinical study on the ocular lesions of oNcHo/wP/75.14 Page 12 onchocerclasis and their influence on the visual acuity in the future. In event of transmission still remeining, it will be most important to find out the ttacceptablerl transmission level in relation t.o future visual impairment. There is a need for uniform criteria for the estimation of the intensity of ocular onchocerciasis in the individual. A uniform, clinical score, based on the important eye lesions such as corneal denslty of mf., sclerosing keratitis or retinal lesi.ons, would be suitable. A system like this would also facilitate the clinical follow-up of a given medical treatxoent. Certainly, a clinical score used for evaluation of the intensity of the ocular lesions will have to be continuously revised with increasing experience of the ocular risk factors in onchocerciasis. To elucidate the nature of ocular onchocerciasis and its importance to visual impairment in a population, an index on the relative gravity of the disease would give a more distinct picture. The endemicity level nay well be the same in two adjacent regions, but the number of people going blind from onchocerciasis quite different, for several reasons. There is already in use the term ttsevere ocular onchocerciasistt, buE the problem is to define this, and its relation to future blindness. In the OCP, the same term is used to express the percentage of Ehe population with ocular onchocerciasis, and those with severe and irreversible ocular lesions of onchocerci.asis. The preliminary evaluation of Ehese lesions is based on the presence of any degree of sclerosing keraEitis, post-neuritic and consecutive optic atrophy and typical retinal lesions \dith typical distribution. In other field surveys iritis has also been included. However, to avoid confusion a uniform and well defined criEerion representing the gravity of ocular onchocerciasis should be adopted, and should also be adjusted for age and sex. Such a system would facilitate detailed analysis and direct comparisons of future clinical and epidemio logica 1 evaluations. 4. I.IORKING UP THE DATA Storing all the results in a computer is indispensable for a longitudinal study because mrnual processing of the information would be too complicated. But a nr:mber of calculations and analyses can be made at once for study of level of endenic, intensity of infestation, and comparison of villages and foci with one another. Some of these - the list is not exhaustive - are mentioned below. 4.L Calculation of prevalence by sex and age-group This is a simple percentage which objectivises the speed of individualsr positivisation and difference according to sex. Owing to peoplets uncertainty about their age the age- groups will be rather broad: five-year groups up to the age of 15 (exact dental ages), then L5-29, n-49, and 50 and over (see form for working up data, Annex 5). 4.2 Calculation of the slobaI Drevalence of onchocer ciasis by villaee The foregoing data need adjusting here for age and sex by reference to a standard population the distribution of which acts as a weighting factor. This standard population could be the national census population. Or it could be an arbitrary one, from outside the atea. For OCP progranme purposes the first 650O examinations made have been taken as the standard population. 4.3 Measurement of intensity by age-group, by sex. and by broad numerical categories of q.uantitative biopsies Since human reading error increases with the number of microfilariae t.o be counted, the numerical categories have to be ones of increasing size. The categories selected by the authors are 1 to 9, 10 to 49,50 to 99, 100 over 2OO microfilariae (total of two biopsies). Rougemont suggests categories a logarithmic progression: I to 10, 11 to 30r 31 to 70 microfilariae, etc. to 199, and increasing in 0NcH0/wP/75. 14 Page 13 4.4 Calculatlon of mean microfilaria 1o Here again comparison of two samples involves recourse to weighting by reference to a standard population. This average could be an arithmetical mean. In that case a discrepancy of a very large or very small load results in unduly large range variations. For this reason Ehe authors use the geometrical mean, which is more accuraEe since it minimizes the effect of discrepancies. It is possible to calculate this from the total number of persons in the age-grouP examined, including those who are negative. In the authorsrview however, and it is also Rougemontrs, this way of expressing the mean mixes together two different ideas: Prevalence, and intensity of infestation. lJtrat is used here therefore for measuring intensity of infestation is the geomeErical oean of microfilaria loads of positive persons, bY sex and age-group - a weighted average in the case of the overall findings for a village. 4.5 Determination in each village of the age at which 50% of people are positive This method, suggested by Knuttgen, is really useful in hypo- or mesoendemic areas, but is not a sufficiently sensitive indicator for hyperendemlc areas. 4.6 Plotting the positivisation curve in relation to age on millimetre graph paper The character of this curve varies with the endernic leve1 and shows the speed of positivisation. Calculating the slope of the curve by a mathernatical formula is a useful way of comparing a number of samples. 4.7 Statistical evaluation of ocular lesions (a) Ocular onchocercal involvement rates in the population. (b) Percentage of involvements which are serious or irreversible. (c) Pre-blindness raEes in the general population, dividing into trilo categories visual acuities between 0.3 and blindness as defined in the WHO report already referred to. (d) Blindness rates, calculated on a basls of the census population and not just of the people examined, allowing for absent people who may be blind. A11 these rates have to be weighted for age and sex to make them comparable from village to vilIage. 5. CONCLUSIONS It is not possible, six months after the cormencement of a prograrmre for control of to make a normati.ve statement as to what evaluationS. damnosum , the vector of onchocerciasis, techniques ought to be Subsequent use of computers will enable all desirable connexions to be invesEigated: the relation between ophthalnological lesj.ons and intensity of parasite infestation; longitudinal surveillance of individuals: the link between leveI of endemic, intensity of infestation and entomological findings (number of catches, n'mber of infective females, number of intective bites per tran and per day); and study of a mathemetical model of transmisslon. As the programne goes on, more will have to be done and improvements will have to be made. Lessons are learnt from each evaluation, modifying t.o a greater or lesser extent the initial line. The main thing is to take the present methodology as Ehe cormon basis for all surveys, which is essential if they are to be conparable. a o a 0 uo I o o r0s ,5 a o - i!J'!- a - il I ! ao a o o< 6d Il6 t * t€i rEd iE I - I --,,1 I + I I - + oII o F oA I 0! Eo2 o oitso9aE!20 oNcrro/wP/ 75.L4 Page 14 AI{NEX 1 { I oT a s I N 0 ct E N N Io ; IIt o IE "iIts o I c o! a a a a d I 6 a E ; J5EIots I E E zo H pj I I kJ o J tsA a E I ts 8 E Ho F rr Td Eoo E E J Ea T a 8a o t6 a t ;0 a & I I o o)g _o ot o aA o I o @ A}INEX 2 PROGBAu{! DE LUTT coNTlE LloNcHoclrcosE - !A8SIT DT I4 voLTA . rt]AI{EN DITAII.I - TOR}II,I.ATRE . IST6]6Til Dltc dr lrenquate : Dla raatc P..r.gc N' Etar : [-l vtlt.se qu.rtlcr FrEl1Ic N' Agc : Ethale : oNcHo/wP/ 7 s.L4 Page 15 l-4 5- r0 1I-19 20-28 29-tt 32-35 35-38 39-40 129- 130 Nun6ro lndivlducl : Nm dc 1r paraonnc D€Jl.nrcgtltr6?-ouI, strtut cx.nen r l-l trrltcBEt avrEt prader oor r [-l Dura6 dc rCridcncc :\-z ActlvltC prhctprlc cnEeglrtrGocnt , I--l SGrc : 1116 , E trr6quent.tlon acolalrc : Trrltco.Et dcpuh per[ge prlc.dent : EI E] E E] Autrc! cxaEana : S-p6c1ucn E E E] E Obacrv.tloEa : Ba.ultrtuarhodc tl trl E E 55-59 70-.74 7 5-79 80-84 II II 4t-43 4tF45 46 47 t8 49 50-51 52 53 54 Iftlonr cutln6ca onchoccrquleme! : .. ... Kylte! - rur k rarc rt la cou : ...... fI - rur colTa at cxtr6Eitca : Elapbrnttr.U dc3 .xtr€nltat : ..... Grorlcr.e vlslblc : .. E E EE E - autra altc : E EI Scrotu Vltl 11go 55-60 6r-64 l1op.1.! cutan€ca - cratcr lllrqurt 85-86 87-88 89-90 9L-92 93-94 95-95 97-98 99- 100 101- 102 lo3- 104 105- 106 107- 10E 109- 1 10 111-112 113-114 115-1r6 117-118 119-120 LzL-L22 t23-t24 L25-L28 Ulcrofllarl.e (x 15) ..... onchocorneal oprcltle! ... othcr opacltlea .,,..,.... Llvlng ufr. (x 25) ....... Sclerorlng kerrtltl! ..... TrachoEr Rctlnal vccrclc i .... . , Choroldo-retlnitk (oncho) : .) t{orphology b) Martin c) slre Focal chorotdltis : .. Vleual ficld : . .., .. Maln cruac of vleuel lryrlrreDt : R Vtruel aculty : ........ E E L E E tl E E E] Optlc dl.c urAc Conrca : RLEE EE Cftafact | ,..,.,. Vltreoua i....... E E E E E E r E r) b) c) d) e) f) Pupll : Ir1tl6 E fI IOP:. oNcHo/wP/75. 14 PaSe 16 AI{NEX 3 TABLE FOR DETERMINING CHILDREN'S AGE FROI'{ THE DENTAL FORMITLA (from TREBAUL) The Roman figures indicate milk teeth and the Arabic figures Permanent teeth. UnLess otherwf-se shown in this table, the four half-jaws are synmetrical. Variations in the ages of aPPearance given range from two months for milk teeth to one year for Permanent teeth. Permanent teethMilk teeth 6 to 8 monthslr 8 to 1O months 8 years12 monthsli 9 yearsL.2.Ar-r.4.V.614 months 10 yearsL .2.3.4.V.6I r.rr.rv 11 yearsL.2.3.4.5.6 t.2.3.4.5 .6.7 II I II I. II. III. IV V I I I I 1.2. rrr. rv.v.6 7 years II. I II. I rlr II.I I I.II 12 years (L2-year tooth) 6 years(6-year tooth) II L6 monEhs (lst milk molar) 18 months(milk canine) 20 to 30 months (2nd milk molar I Ir.n.rrr.ryr I.II.III.IV.V.6 I.II.III.IV.V.6 I. II. III. IV. V. 6 I. II. III. IV. V. 6 I oNcHo/t^rPl 7 5.L4 Psge 17 o cj AI{NEX 4 o{ts I9C I 0 cE@at, *-.e E . g€04 E; o D =o a4r cf I - I r 'a a .is o oh ! a > i E H!o.. d . ! ^.5 o.9a > - i c a- ,.;4 4 r O< dY! o{ 6 Hg. c3 ? 3t I a .l.ic$ =ata i , o E 4 X Ma C x g4 { > e rI . - " 3 .'3 6 E a , a aa oo o ! k aa o d -.3.-..ir8q I C 4 - I J 2F- il a i a c o q! o: 3 E r " ! '1 5i" "i ,a i klta.it 5 i a a o qca5i: ii HEt.sg!. t{ o rar_.e fle ".5 E.r3"'I.3cl-aa{la\od alo!0nelaiit ala c i otsg.:otlJt t l!r33.:i ol .- ? "'lts,f b:.lo k o d.I qj .91 5to'llBj,ts "lx g: i "ri i;'iIl{ ; e s'Ihs'z'*03 oo ada i f^Od or a > vP d!4 ,0i i!o!> .. a{ , dE ,I a 4ea c o i.i aao > o > oa 6 k .i a a oc oa4 do! ,d, to{ c a.d ! o > o E>! E OC C o , o !o ootk .d $r$ o , a oa o4 C k a4 a! o o c c!g a 4.0.-{O { E E' E O > k D $ o{ u o o a !o ! !i oa a I t a EuiN6 l6 a zo$UE <oB ! 0 t6 I 6 aokvo - It r ac{$H@l o u 5 d z^ oIAEgc <a6 L a o E o ae I E ts P a r. I .rhl aHl !-Fl o I 4 zaa cUCga 60 1a c a t I 5 a^ * T hl EIdl a u 5 ootq! l.rEE c -.,1 '- -..1 -- -.,1 .{: aha Eao GY a ot ?EcaG a o ! a x 3 nE!.d EO!.i J.4 l" 6z I I I I oaqH E.4 ,.E zE5* 5 a o - a o E aE oaG a u 5 ts lF F t I c o a, fc k o h dt d a '{,t 1 0D a ; 6 E< c I'1o e o oNcHo/wP/ 7 5.L4 Page 18 AI{NEX 5 hat) o F{ @) o F{ (U IJ oH tq o od c) Fl(! i{) H Fi E tr t fr Ol Or F{ Ioo '{ hc o\ Io rn E 14 E o\\t Io Fl la E ooN o "..1u(! rJ .r{ rJ dq,)e q) 'F{tttA o 'r'lE o\ I 14 14 E o r+t 'Fl rJ .J o oA tx E ah\0, d 'r{ e IB x rd F{ U H o\\ I o(r) onF{ Io F{ o\ N I u'l F{ o\ I rn \t Io aD(, oo o!0,t c(u @ .'{ o E oz E] Er EI q z FI z E * F o fr]H o ;;;EIr'l()urzzZHtrlii: E u2 n E X zF!oHH H A{I I s F] t-{ N lrtHH a F{ EIHt{ V) O{Hz U) t{H2 E{ frl H H rlr a I I oNcHo/wP/ 7s.L4 Page 19 i I REFERENCES Pr6vention de 1a c6c1t€, Rapport drun groupe dr6tude de 1rOlfi GenEve, L973 56r. Rapp. techn. NO 518, Programte chiffrd de 1t6va1uat1on 6pld€uiologlque du prograrune de lutte conEre lronchocercose dans le bassin de la Volta (1973) Rapp. Mlssion pAG. Annexe V-4, oMS, Genlve,27 pages . frangals/anglais Anderson, J. & Fuglsang, H. Some aspecls gf ocular onchocerc . Western Hemisphere, PAHO Sclentific Publication, L974, No 298, In: Onchocerciasfs in the 3- 10 Anderson, J., Fuglsang, H., Haurilton, P. J. S. & I'Iarshall, T. F. de C. (L974) Studies on onchocerciasis in Ehe United Cameroon Republic. I. Comparison of populations with and lrtlthouE Onchocerca volvulus, Trans. roy. Soc. trop. Med. Hyg., @, 3, 190-208 Anderson, J., Fuglsang, II., Ilamilton, P. J. S. & l,larshall, T. F. de C. (L974) Srudies on onchocerciasis in the United Casreroon Republic. II. Comparison of onchocerciasis ln rain- forest and sudan savanna, Tr'ens. rov Soc. trop. Med. Hve 68, 3, 209-222t, Anderson, J., Fuglsang, H., Ilemilton, P. J. S. & I'tarshall, T. F. de C. The Prognostic value of head nodules and microfilariae ln the skln in relation Eo ocular onchocerciasis, r{Ho/ oNcHo/ 7 4. LOg (unpublished) Brinkmann, U. K. A field method for the assessment of microfilarial densities ln onchocer- ciasis, Proc.3rd rnt. congr. Parasit., ltunich, August 1974,2, B12(9), 603-604 Brinkmann, U. K. (Lg73) Quantitative measurements on skin snips of onchocerclasis patients,Z. Tropenmed. Paraelt. , 4, 397-403 Buck, A. A. (L974) Lronchocercose : slmptomatologie, Ol,!S, f rangais /anglals anatomopathologie, diagnostic, C'enEve, Buck, A. A. Epidemlolosic features of onchocercl asis. In: Onchocerciasls in the $lesEern Hemisphere, PAHO Scientific Publicatioa, 1974, N' 298, 3-10 D,r.rke, B. o. L. (L952) A sEandard method of assessing microfilarlal density in onchocerciasis surveys, 8u11. W1d Hlth Org. , 27, 629-632 Ganley, J. P. & Biles, J. E. Prevalence of onchocerclasis, visual impairment and blindness ln six villages in the Upper Region of Ghana, PD/73.2 (unpublished) Knuttgen, II. J. & Burrner, D. W. (1969) Die alterspezifische 50 % - l,lf . Rate (Also) , Parasi tr das Onchozerkosevorko'mnen in einer Bev6lkerung, z enmed.Index fU 303-310 ein ,, 20 r{ 1 Picq, J. J. OCCGE, & Loreal, E. M6thodologie des enqu3tes 6pid6niologiques, L97O, L,173-188 Rapp. lOEme Conf. techn. Picq J. J. & Coz, J. Contrlbution A It6tude de lt6valuaEion de densit6s mlcrofilariennes chezIes onchocerqui.ens, Rapp. final lOEme Conf . Eechn. OCCGE , Bobo-Dioulasso, 20-24 avril 1970, 18O-185; PROC. 2nd Int. Congr. Parasit., L97O, L, Zg oNcHo/wP/ 75.L4 Page 20 picq, J. J., Coz, J. & Jardel, J. P. (1971) Une n6thode dr6valuaEion des densit6s microfila- riennesdrO.volvulus, Leuckart, 1893, chez les onchocerquiens : technique eE temPs de lecture des biopsles cutan€es, BulI. Ore. mond. Sant6 , 45, 5L7-52O picq, J. J. & Jardel, J. P. (1973) Une m6thode dr6valuation des densit6s microfilariennes drO. volwlus , LeuckarE, 1893, chez les onchocerquiens. R6partition des denslt6s micro- filariennes suivant les sites et niveau de pr6lEvement des biopsies cuEan6es. Variatlon des densites mlcrofilari.ennes au cours des 24 heures, WIIO/ONCHO|73.LO3 (unPublished) Rolland, A. (1968) l.[6thode dtEvaluation clinlque des campagnes de lutte conEre lronchocercose urillsable en enquate de masse, 0!6, ONCHO/WP/68.4 (unpublished) Rolland, A. (L974) R6sultats de deux examens oculaires pratiqu6s l six ans drlntervalle, dans deux vlllages onchocerqulens de llaute-Volta, WHO/ONCHO/74.112, 8 Pages, Doc. ron6oE. G.O.M. Ouagadougou Rougemont, A. (1973) Etude 6pld6niologique et clinique de I'onchocercose dans 15 villages des R6publlques du l,Iall et de llaute-Volta, RapporE OltS, non publi€ j I * t4 I l'