Onchocerciasis in the Ivory Cost

WORLD HEALTH ORGANIZATICN ORGANISATION MONDIALE DE LA SANTE ocr/srace.s ORIGINAL: FRENCH ONCHOCERCIASIS CONTROL PROGRA},I},IE IN THE VOLTA RIVER BASIN AREA SCIEMIFIC AND TECHNICAL ADVISORY COM}trTTEE Eighth meeEing Geneva, 4-7 tember 1979 ONCHOCERCIASIS IN T'IIE IVORY COAST by A. PROST, A. ROLLAND, B. THYLEFORS The only existing summary of informaEion on onchogerciasis in the Ivory CoasE is stil1 the map compiled by Rives in 1966-. The results of extensive surveys using positive findings in the ll,azzoLti test and counts of cyst carriers enabled him to work out the distribution of this ubiquitous endemic'disease that seems to spare no area of the country. In his presentation of the results (14), however, he noted cert.ain differences suggesting that the severity of the cornplicaEions of onchocerciasis decreased from the north towards Ehe south of the country. Picq confirmed these observaLions (7,8,9,), showing that in Danan6 severe eye lesions were rare; Ehere was no blindness there due to onchocerciasis, whereas in the Korhogo, Tehini or Bouna regions the blindness rate could be as high as L2% of subject examined. It even reached L4% of males in a village in the upper Sassandra basin (L2), During surveys conducted in the Ivory Coast within the Onchocerciasis Control Progranrme in the Volta River Basin area, we have defined the characteristics of onchocerciasis in different regions of the country; the contrast between Ehe severity of the symptoms in the rrsavannatt zone and the benign nature of the symptoms in the rrforestrr zone forces us to abandon the concepE of the disease as a uniform entity and to take the Ivory Coast example as a particularly clear illusEration of the two epidemiological patterns described in Cameroon and Nigerla (2,3,15). Framework of the study and methods For this study we selected 17 hyperendemic villages in which the entire population underwent clinical, parasitological and ophthalmological examinaEions between 1976 ar.d L979, using a standardized protocol (5r11). These villages are located in the five main river basins of the country (see attached map) and in the areas r,ahere transmission is due jointly or separately to the six knor^rn vectors of onchocercj-asis in the Ivory Coast,(13). In order to ensure some degree of homogeneity in the sample, non- residents and families that had moved to the village within the last five years were excluded. Each individual examined was subjected to a double iliac biopsy (Holth-type punch) and a count was made of the microfilariae energing after 30 minutes' incubation in distilled water or after 24 hours in physiological serum if the first test proved negative. Ihe examination for microfilaruria was made by filtering 20 m1 of urine on a millipore membrane. The ophthalmological examination covered all subjects aged five years and over and included, for the two eyes separately: measurements of visuaL acuity, an examination of the anterior chamber under the biomicroscope after placing the head in an inclined position for one minute (1), an examination of the fundus oculi with the ophthalmoscope, and a measuremenE or estimate of the visual field. Irt.rr"a., of Health, Abidjan, L966. 21 To simplify the comparisons, the 3907 individuals examined in 17 villages were divided into eight analysis units, or statistical clusters, on the basis of geographical proxirnity; these units were: The Upper Sassandra zone' wtrich covers the three villages of ^ M4ssadougou, Koba1a and Mamorodougou in Odienn6 department (8045 9"o6 N - 7u20 I^I), i.e. 688 individuals. A11 six onchocerciasis vectors in the Ivory Coast are found there. to 2 Ihe Upper Bago6 zorle, which covers the two neighbouring villages of N'Gapie (9"34 N - 6'49 IAI), odienn6 department) and Gbando (9'34 N - 6"40 W, Boundiali department) i.e. 336 individuals. Transmission is due to S.damnosum s.s. and S.sirbanum , and occasionally to S.squamosum. S.yahense is predominanE at certain periods of the dry season, but seems to be of little importance Iocally as a vector. 3 Three savanna villages north of Bouak6: Longo on the Bandama (8'58 N - 5"24w, KaEiola department), F6E6kro on the N'Zi (7"49 N - 4'41 W, Bouak6 department) and Sirakoro on the Como6 (8"o5 N - 4'oo W, Dabakala department)i.e . 616 individuals. Transmission is due to S.damnosum and S.sirbanum onlv. 4 Two villages situated at the confluence of the N'Zi and the Kan: Asserekro (6"37N - 4"52 W, Dimbokro department) and Laourebo (6"3O N - 4"47 11, Toumodi subprefecture), i.e. 316 individuals. Transmission is due to S.damnosum and S.sirbanum. 5 The Cavalty focus north-east of Danan6, with the three contiguous villages of Oua, Sioba and Nimpleu centred on 7"25 N - 8'1O W, i.e. 634 individuals. S.yahense is normally the only species present. Popu lations of S.squamosum have occasionally been found. The Lower Como6 zone in the department of Abengourou, with the two villages of Assemanou (6'47 N - 3'45 W) and Bl6koum (6"22 N - 3'32 W), with 833 individuals. S.soubrense and S.sancEipauli are responsible for transmission. 7 The village of Bagro on the Sassandra (6'43 N - 6'58 w, department) , with 234 individuals. Transmission is due and S. sanctipauli. Baloa to S. soubrense 8 The village of Galegoua on Ehe N'Zi north of Tiassal6 (6"14 N - 4'5o W), with 251 individuals. Populations of S.damnosum are sometimes found in addition to the predominant sp ecies S.soubrense and S. sancEipauli . Biogeographically speaking, the first four clusters are situated in guinean savanna, clusters 5 and 6 in dense forest, and clusters 7 and 8 in fores6 v*rere the border with the savanna is not as clear-cut as simple maps would suggest. 6 3Results The results are indicated in Tables 1 and 2 No significant difference is found beEween the various clusters on examining the indicbs representing infection with O.vo1vulus: prevalence of parasite infestation, mean microfilarial density, cyst carrier raEe and prevalence of parasites in the eye, are comparable in each sampl-e. As regards ophthalmology (Table 2), for a virtually equal level of ocular parasitism, 1O-3O% of the population in the savanna suffer from severe and irreversible onchocerciasis lesions v*rereas in the forest the corresponding rate is no more than 4% it males and 2% in females. Not only are sclerosing keratitis and iridocyclitis with synechiae much less common, as was noted by Anderson (2) and Budden (3), but, there is also a significant difference for lesions of the post.erior chamber, optic atrophy and choroidoretinitis, a difference not clear in the studies by these authors. Blindness, a direci consequence of the frequency and stage of development of severe lesions, is found in 5-LO% of the savanna population, but in under 2% of forest dwellers. Mention should also be made of the non-onchocercal btindness which represents the majority of cases: 22 oul of the 24 blind persons seen in the four forest clusters owed their disability to a condition other Ehan onchocerciasis. Skin depigmentation (pretibial vitiligo) in both sexes and dermatitis lesions in males are more frequent in the savanna (see Table 1). Interpretation of the symptoms rrhanging groin and lymphadenopathytt is more tricky and the geographical difference less clear-cut. These observations contrast with the studies in Nigeria and Cameroon (2r15) which report much greater frequency of these symptoms in the foresE. Tests were made for microfilaruria in the forest villages only. Ihe rate is very low in the Danan6 Region (O-3%) as was observed earlier by Picq, (1O). On the Lower Como6 it, rises to 5% at Ass6manou and 127. at B16koum. This symptom was not looked for in the oEher rvory coast surveys but the values obtained can be compared with the 2o-3o% of subjects with microfilariae in the urine normally found in hyperendemic savanna samples in other countries. It seems that microfilaruria is a severe symPtom, rohose frequency j-s associated with that of eye lesions(Thylefors et al., study in progress) and thus indicates better tolerance of the parasite in forest areas. Di scus sion According to the conventional pattern, forest onchocerciasis is thought to cont.rast with savanna onchocerciasis by virtue of the greater frequency of cysts, higher microfilaria densities, much more vitiligo and hanging groin, fewer dermatitis lesions, fewer severe eye lesions, and less blindness. In the Ivory Coast example this pattern has to be slightly revised: there are no biogeographical differences in quantiEative infection by O.volvulus in populations subject to high transmission. With a comparable level of infection, however, all the symptoms of the disease, and especially the complications, are much less cormon in the forest. In the case of Ehe Danan6 focus, r'atrere despite very intense infection the 4various complications affect less thar. 4% of the population, the disease could almost be described as asymptomatic. The contrasE between the two epidemiological patterns is very clear between the north, vrhere the disease is severe, and the south, v*rere it is well- tolerated. These areas are either side of the geographical frontier separating the savanna frqm the forest. Ihese t\,ro biotopes rightly determine the current terminology. The present study, covering 4OOO individuals in eighE different regions of the Ivory Coast, shows that the forest pattern is found wherever transmission of the disease is due neither to Simulium damnosum sensu stricto nor to Simulium sirbanum. There is no epidemiological difference between the localities where only the vectors S.yahense S. soubrense and S.sancEipauli occur. The severe form of onchocerciasid therefore appears to be closely associated with transmission of the parasite by S.damnosum and S.sirbanum, vectors that predominat,e in the savanna and penetrate quite a long way south in the dry season. The distribution of forest onchocerciasis would seem to depend on the distribution of ecosystems that are hostile to the introduction of the two savanna species of blackfly. There are, therefore, at least two vectorfparasite complexes in the sense of Duke's hypothesis (4). It is likely that, on the pattern of Simulium damnosum s.1., which in West Africa has proved to be a complex of eight species that have now been isolated, we shall in future have to try to identify two or more parasitic strains of Onchocerca volvulus v*rich are of varying pathogenicity for man and are preferentially transmit.ted by one or more of the recognized vectors. t 12 3 4 5 6 7 B RET'ERENCES Anderson J. et Fuglsang H. Variation in numbers of microfilariae of O.volvulus in the anLerior chamber of the human eye. Trans. Roy. Soc. Trop. Med. hyg. 1973, 67, 544-548. Anderson J., Fuglsang H., Hamilton P. et Marshall T.F. de C. Studies on onchocerciasis in the UniEed Cameroon Republic. II. Compari-son of onchocerciasis in rain-forest and Sudan-savanna. Trans. Roy. Soc. Trop. Med. hyg., L974, 68, 3, 209-222. Budden F.H. Comparative Study of ocular onchocerciasis in Savannah and rain-forest Trans. Roy. Soc. Trop. Med. hyg., L963, 57, L, 64-70. Duke B.O.L., Lewis J.D. et Moore P.J. Onchocerca Simulium complexes. 1. Transmission of forest and Sudan-savanna Strains of Onchocerca volvulus from Cameroon by Simulium African bio-climatic zones. Ann. Trop. Med. Parasit., L966, 60, damnosum from various l.rIest 3 3 18-336 . Moreau J.P., Prost A. et Prod'hon J. Essai de normalisation de la m6thodologie des enqu6t.es clinico-parasitologiques sur 1'onchocercose en Afrique de 1'ouest. M6d. Trop. 1978, 38, L, 43-5L. Philippon B., Mory D., Diallo A., GuilLet P. et Sechan Y. L'onchocercose dans le bassin du Haut Sassandra (R6p. de COte d'Ivoire) 1. Les vecteurs. Doc. n6n publi6 No. 2O/OUCnO/nap.77, IRO, Bouak6, Lg77. 9 Picq J.J., Ba A. et Sellin B. Prospection sur 1'end6mie onchocerquienne dans les r6gions de Bouna et T6hini, R6publique de C6te d'Ivoire, D6cembre 1973 Doc. non pub1i6 No.5822, OCCGE, Bobo-Dioulasso, 1975. Picq J.J., Jubin R. et Plouvier S. Prospection sur 1'end6mie onchocerquienne dans la r6gion de Korhogo, R6publique de C6te d'Ivoire Doc. non pub1i6 No. 5798, OCCGE, Bobo-Dioulasso, 1974. Picq J.J., Rolland A. et Roux J. Prospection sur 1'end6mie onchocerquienne dans les r6gions de Danan6 et Man, R6publique de C6te d'Ivoire. Doc. non pub1i6 No. L29/para.73, OCCGE, Bobo-Dioulasso, Lgl3. Picq J.J. et Roux J. Sondages pr6liminaires sur 1a pr6sence de microfilaires d'Onchocerca volvulus dans les urines de sujets onchocerquiens Doc. non pub1i6 wuo/oNcuo/tz.go, oMS, GenEve, 1972. 11. Prost A. et Prod'hon J. Le diagnosEic parasitologlque de 1'onchocercose. Revue critique des m6thodes en usage. M6d.Trop. L978, 38, 5,519-532. 10 212. Prost A., Prod'hon J., Thylefors B. et Ctozafon P.H. L'onchocercose dans le bassin du Haut Sassandra (R6p. de COte d'Ivoire) 2. - La maladie. Doc . non publi6 . oMS ocp/xpt/ l7 .28, Ouagadougou, Lg17 . B. Etude du complexe Simulium damnosum II. R6partition g6ographique des cyto- m6d. et Parasitol., 1975 . Xrrr, 3, d' Ivoire L65-L72. L4 Rives I"1 . et Seri6 F. L'onchocercose en COte M6d.Afr.noire , L967, XIV, 10, 483-488. 15. Woodruff A.W., Anderson J., Pettitt L.E., Tukur M. et Woodruff A.H.W. Some aspects of onchocerciasis in Sudan-savanna and rain forest. J. Trop. Med. Hyg. 1977, 80, 4, 68'73. 13. Quill6v6r6 D. et Pendriez en Afrique de 1'ouest. Eypes en C6te d'Ivoire. Cah. ORSTOM, s6r. 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