The epidemiology of onchocerciasis in Ghana with special emphasis on its socio-economic aspects

EXPERT COMI"IITTEE ON EPIDEMIOLOGY OF ONCHOCERCIASIS Geneva 10-18 November 1975 Draft agenda item 5.4 The issue of thls document does not constltute formal publication. lt should not be reviewed, abstracted or quoted without the agreement of the World Health Organtzation. Authors alone are responsible for views expressed in signed articles. WORLD HEALTH ORGANIZATION ORGANTSATION MONDIALE DE LA SANTE oNCHo/WP/75. 13 ORIGINAL: ENGLISH 14r east to 3o 07r west, and It has an area of approximately Ce document ne constrtue pas une publication. ll ne doit faire I'objet d'aucun compte rendu ou r6sumd 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. THE EPIDEMIOLOGY OF ONCHOCERCIASIS IN GHANA WITH SPECIAL EMPHASIS ON ITS SOCIO-ECONOMIC ASPECTS by F. C. Grant Ministry of Health, Accra, Ghana 1. InEroduction Ghana lies on the coast of West Africa v/ithin longitude 1 within latitude 4" 45 | norEh of the equator to 11o 11' north. 240 ooo krr.z (gZ ooo square miles). rt ! '$ j The area north of latitude 8o 3Oris savanna country. IE has a short rainy season between June and october when Ehere is between 750 and 1250 mm (30-50 inches) of rainfall and the relative humidity rises above 8O%. In the dry season from November to May the tempera- ture range may be above 32'C (90'F) at noon. The relative humidity ranSes between 10% and 22%. The temperature at night may drop to as 1ow as I8oC (65'F) when the desiccating Harmattan winds blow south from the Sahara desert. The southern part of the country on the other hand is covered with forest except, for a narrow coastal strip of grassland. The mean annual temperature is 27-32'C (80-90'F) with less day and night variations. The relative humidity is uniformLy 8O%. There are tr^ro rainy seasons from April to August and from October to December. The mean annual rainfall is 2184 mm (86 inches). The country is divided into nine administrative regions. The 1970 population census results are shown in Table 1. The people are of uniform negro sEock. The northern half is economically less developed than the south. In corunon with all developing countries the major public health problems in Ghana are a high incidence of conrnunicable diseases, poor environmental sanitation, high maternal and infant mortality, and malnuErition. Among the communicable diseases is onchocerciasis of which the north takes Ehe brunt. Onchocerciasis has not in Ghana been the subject of systematic and intense study thac its prevalence and effects on human wellbeing would warrant. In particular very little investi- gaEions of the clinical aspects and treatment have been done. In contrast, the distribution of the disease and the factors influencing its transmission and distribution have been more Ehoroughly studied. The biology of the vector Simulium damnosum and methods of eliminating the fly have been investigated. '4 t !I --+ r -ir.-l!1. .d--..dr&di.Jk-'., ' t { E ryLqt I, ; *I oNcHo/wP/75.13 Page 2 TABLE 1. GHANA REGIONAL AREAS AND POPUI"A.TION ( r970) 31r)(after the Statemanrs Year-Book , 1974-75, p. Region Areak^2 /^t2 Population ( thousands) Growth rate L960-70 Wes tern Centra I Greater Accra Eas tern Volta Ashanti Brong-Aha fo Northern Upper A11 regions 24 s89/9 494 9 469/3 656 22 662/8 750 20 720/8 000 25 L23/9 700 38 59t/L4 900 70 246/27 L22 27 t38/LO 478 238 538/92 LOO 770 890 852 | 262 947 L 482 767 728 863 8 559 2.r L.7 5.6 t.4 2 2 2 3 1 2 o 9 7 1 4 4 The reasons for this situaEion are probably: (i) the disease is only encountered as a serious public health problem in t.hose parts of the country which are less well-endowed with health facilities, (ii) highly trained and experienced medical personnel have been reluctant to live and work in those parts, (iii) the indigenous population has been inclined to accept the existing situation and has not been effective in demanding improvements in the living conditions, (iv) until recently there has been little significant economic activity in the area. On Ehe contrary the tribes from the affected areas have been largely employed as migrant labour in the souEh, and (v) in the absence of safe and effective treatment for the disease, emphasis has been placed on control of the disease through the elimination of the vector. o1 of onchocerciasis in Ghana 1 Simulium damnosum The geographical distribution of the disease, as expected, fo1lo\"rs a close association r,7ith that of the vector Simulium dam3gg, which is in turn influenced by hydrological and climatic factors. rtrerE-iiEtEre a marked difference between the prevalence of the disease in the northern savanna and the southern forest country. Map 1 shows the principal rivers of Ghana in relation to the known foci of Simulium damnosum. The foci are along the Volta river and its tributaries, where b.e"diig "o=iTftiorrsare ideal as the rivers flow swiftly over rocks and floating vegetation. with the excepEion of the Black Volta, which flows throughout the year, all the other rivers in Ehe Upper region cease to flow during the long dry season from November to June or July. The White Volta {emains as long stretches of pools in March. The other rivers in the region dry up. Crisp(1956) observed the scarcity of the flies during the dry period, and their sudden appearance with the first rains. Noamesi (1966) found sma11 streams, probably originating as springs, which maintained breeding of the flies in the dry season in the Upper Region. He concluded 2 2 t e oNcHo/wPl75. 13 Page 3 that flies migrate from the wet season breeding sites Co the dry season sites and vice versa. The flies bred in the dry season formed the link between the fly population of the two seasons. He caughE flies at 183 km (114 miles) away from where they had been marked and released. Some of the flies had survived for as long as four-and-a-ha1f monEhs. Other well-known foci along the Volta river were investigated by Berner (1950) before Ehe Akosombo dam was construcEed. These have since been inundated by the Volta lake. Less well-known foci out- side the Volta basin are on the Birim, Densu, Pra and Ankobra rivers. 2.2 DistribuEion of onchocerciasis in Ghana Knowledge of the geographical distribution of onchocerciasis in Ghana has been gained from the results of surveys by the nedical field units of Ghana as well as from the work of individual investigators aE various times. But there stil1 remain other foci in southern Ghana which have as yet not been thoroughly investigated. The medical field unitsr studies aim at providing results that could give comparable information for different parts of the country. For this purpose, evidence of infection was sought in male adults aged. 2L-4O years. A single examination r{as made from a skin-snip taken from the calf of a leg. The results were plotted on a grid map. 2.2.1 Upper Region In the eastern half of the Upper Region high prevalence raEes of onchocerciasis are found along the Red Vo1ta, the White Volta and their tributaries. In the hrestern half high prevalence exists along the Black Volta, its tributaries, and the Kulpawn and Sissili ri-vers, which flow into the White Volta. Since the tributaries of these rivers branch out over the entire territory to form a network of streams' during the rainy season, onchocerciasis is highly endemic in most parts of the Upper Region. Prevalence rates range from 5% to lOO% as the large rivers are approached. Waddy (L949) drer{ attention to the high prevalence of onchocerci-asis in this part of the country and gave this as the cause of the high blindness rate he found there. 2.2.2 Northern Region The disease is endemic in the Northern Region but to a lesser extent than in the Upper Region. High prevalence rates of 60-100% are found along the larger rivers. A wide area around Tamale is free from onchocerci-asis. 2.2.3 Southern Ghana In generalronchocerciasis is not a public health problem in the rest of Ghana except amongst communities that live along the rivers that flow into the Volta lake and their tributaries. These rivers are the Daka, Oti and Dayi on Ehe eastern side of the lake and on the western side the Pru, Sene, Obosom, Afram and Pawnpawn. Prevalence rates of 60-1OO7. are found at these foci. Downstream of the dam, there exist high prevalence of onchocerciasis at the Senchi rapids and Kpong. This area was investigated by Hughes (1952). Limited investigations at Bonsra on the Ankobra river where there is a large rubber estate, at Beposo Bridge on the Pra river, at Bunso on the Birim river, have given prevalence rates of 5-35%. In a preliminary investigation by Grant (1969) before the construction of a dam at Weija to supply 180 0OO mJ (40 million gallons) of water a day to the city of Accra, only seven persons out of 723 persons examined had Onchoc iasis volvulus microfilaria in the skin-sni examination. These were adults of northern Ghana extraction and probably had the infection before migration to the souEh. P oNcHo/I.IP/75. 13 Page 4 3. Clinical manifestations of onchoc ercias i s Most of the known clinical manifestations of onchocerciasis have been observed in Ghana.But involvement of onchocerciasis with other organs besides the skin, rhe lymph glands and the eyes have not been studied. 3.1 Skin nanifestations Prurit.us, pigmentary changes, areas north of latitude 80 11t. and atrophy of the skin are observed most in highly endemic 3.2 Nodules Nodules of all sizes, some barely palpable, are common in all parts of the country where onchocerciasis is present. The pelvic region is the commonest site of occurrence. pain in various Parts of the body have been associated with the nodules. No efforE has been made sofar to exclude Pain from other causes such as the abnormal haemoglobinopathies which are cormon and yaws which still occurs. 3.3 Lymphoedema Enlargement of the ly*ph nodes of the cervical, axi1lary, and inguinal regions are cornmon in endemic areas. Senker et al. (L973) reported a higher frequency in males and in the lower age-8rouP of one to nine years. Elephantiasis of the genitalia is seen amongst adults. 3.4 Blindness The effect of onchocerciasis on visual acuity is an aspect of the clinical manifestations of the disease that has received the greatest attention in Ghana. Senker et al. (L973), in a survey of onchocerciasis in Ehe White Volta and Kulpawn river basin in 1966, observed the blindness rate in the area. They assessed visual acuity by the subjecErs ability to count fingers correctly at a distance of three metres. The subject was placed in a dark hut. and the fingers to be counted were silhouetted in the open doorway. They found blindness rates of O.75% to 25.3%, which corresponded with the prevalence and severity of infection in different cormnunities. These results were similar to those of Waddy (1949), Sarkies (1951) and Rodger (1959). In southern Ghana, Jones et aI. (1973) studied the blindness rates in three areas (i) Asukawkaw, where the onchocerciasis prevalence was 81%, (ii) Senchi/Kpong, where it was 20% to 4O%, ar,d (iii) Keta, where there r.ras no evidence of onchocerciasis transmissi-on. The investigations involved an examination by an ophthalmologist using an ophthalmoscope and a slit lamp microscope, and a test of visual acuity by an ophthalmic nursing sister using an illiterate rrErr chart. They found social blindness rates of. 1.8% at Asukawkaw, 0.9% at Senchi/Kpong and 0.18% at Keta. The Senchi/fpong results confirmed previous observations by Hughes (1952). 4. Factors that influence prevalence and severity In general the prevalence and severity of the disease increases lsith age and it is more common amongst males than females of the same locality and age. oNcHo/wP/75.13 Page 5 The prevalence and severity of the disease is higher in conrnunities that live close tothe breeding sites of Simulium damnosum. Blindness and all other clinical manifestations have been found to be more frequent and severe in the northern savanna than in the southern forest belt. But these differences have not as yet been studied in relation to differences of intensity of onchocerciasis infection inthe two geographical regions. The effect of the co-existence of onchocerciasis with other clinical conditions in a Person in relation to Ehe severiEy of clinical manifestations and tolerance to drugs have notbeen extensively investigated. Anteson (1972) has confirmed the findings of Buck (1970) by noting the co-existence of onchocerciasis with other blood helminths in his patients and the relation of microfilaruria to inEensity of onchocerciasis infection. In addition to malnutrition in the north, undernutrition is also common due to theperiods of famine towards the end of the long dry seasons. Manifestations of vitamin Adeficiency are found amongst both children and adults in many parts of the Upper Region. Butit is unconrnon in the south where diets containing such items as palnr oil are rich in vitamin A. Genetic defects such as possession of the S and SC genes and glucose-6-phosphate dehydrogenase (G6po) deficiency are frequent in Ghana and show geographical variations. Ringelhann et al. (1968) found 117. prevalence of G6PD deficiency in the norrh whilst in rhe south Owusu (I972) four.d' 24%. With regard to sickle ce11 anaemia, Konotey-Ahulu (personal cormunication, L972) found 20% of persons in southern Ghana and tO% of persons i-n northern Ghana Possess the sickle ceI1 gene. The influence of these genetic differences on theprevalence of blindness and other manifestations of onchocerciasis has not been assessed. Socio-economi.c aspects of onchocerciasis I Social The extent of social upheaval caused by onchocerciasis in past decades can never beproperly assessed. As far back as living memory goes, blind beggars in southern Ghana havebeen of northern extraction from the savanna and sahelian regions. Their cries of rlallasulalarrwhatever the etynological origin, became the childrenrs term for begging. Abandoned settlements were conrnented upon by Saunders (L929), and other workers. Tsetse flies, slave raiders, soil erosion and exhausti-on, and onchocerci-asis have each been given the discreditto variable degrees. Waddy (L949) conmenting on Ehe observation by Lynn (Lg42) that soil exhaustion \^ras animPortanE factor in the abandonment of settlements on the vast slopes towards some of thebigger rivers, blamed onchocerciasis and in some places trypanosomiasis. He noted that it vras not only on overexhausted soil that empty settlements were seen nor were all riverine soils exhausted. A map by Morris shows that the eastern half of the Upper Region is the most denselypopulated part of the northern half of Ghana yet fertile riverine valleys of the Red Volta andthe White Volta are devoid of settlements. Waddy (L949) observed that there $ras a vicious circle set uP by the pressure of Simulium whereby the human population in the fertile valleys were driven back progressively from the valleys to the watersheds, and the more watersheds were farmed, the more soil erosion resulted until it could not maintain the population. He estimated the unpopulated land as 13OO km2 (5OO square miles). Another asPecE of the combination of the presence of Simulium, over population, soil erosion and consequent inability of the soil to support tte r.sia"rt population is migrationfrom the north to the southern parts of the country. Although, in recent Eimes, Part of this population movement may be accounted for by the universal trend of rural to urban migration, it may be noted that many of the migrants io to 5 5 oNcHo/wP/75. 13 Page 6 \47ork as farm labourers on the cocoa plantations in the forest belt. The depopulation is selective of able-bodied young males, which upsets the social balance so that the remaining population is unable to support itself. General deterioration and decay set in as the females and elderly males are unable to maintain the land, and Ehe huts fall in disrepair, and the bush takes over the farms. It is notable that fishing in the Volta lake and in rivers of the north is by migrants from the coastal south. Few natives of norEhern Ghana engage in fishing as an occupation. Hunting and gathering of wild fruits however are popular occupations. Health facilities are almost non-existent in the onchocerciasis endemic areas of the savanna north. No systematic studies of the general health status of Ehe populaEion have been done. Nor are there reliable data on vital events. It is generally considered that ready availability of water is conducive to good personal and community hygiene. In the absence of any other source of water, the siting of human setElemenEs at a safe distance from rivers on account of the danger of onchocerciasis must contribute to a high burden of diseases related to poor hygiene. The records of the Ghana Leprosy Service show that the Upper Region of Ghana has the highest prevalence of leprosy in the country. 5.2 Economic aspects The economic aspects of onchocerciasis may be considered in terms of (a) illness due to onchocerciasis (b) its effects on development Projects and (c) benefits of eradication or control of the disease. the cosE of the economic 5.2.L The cost of illness The clinical manifestations of onchocerciasis in Ghana have already been discussed. The disease is not fatal and the economic loss due to the disability it causes cannot be easily assessed except with regard to loss of vision. There is little doubt however about the mental Eorture that any form of pruritus causes. The difficulty of assessing the debility due to onchocerciasis is further complicated by other concurrent infecEions such as other helminthic infections and malaria which are common in onchocerciasis areas. It is not unreasonable to assume that the disease must contribute to apaEhy and poor performance in physical and mental activities. The economic blindness raE.e due to onchocerciasis in Ghana has been assessed at 13-357. in hyperendemic areas. Blindness eliminates an i-mportant labour force from the communi-ty. The blind in the absence of retraining become an economic burden on society. There is as yet no serious demand for treatment of onchocerciasis in affected areas. But Ehis state of resignation to fate is not likely to continue for long. The demand will impose a serious economic burden on health administrations. 5.2.2 Impa ct on development projects The economic cost of transferring the siEing of development projects from a place that is ideal in all respects except for the presence of onchocerciasis to a place that is safe but less suitable economically must be taken into account when assessing the economic impact of onchocerci-a si s. Recruitment of suitable staff, especially development projects in onchocerciasis endemic introduction of financial inducement and other of the projects. Absenteeism due to sickness may affect productivity. high grade personnel, for social and economic areas is more difficult and may require the forms of incenti,ves. These increase the cost and poor morale due to fear of onchocerciasi-s \oNcHo/wP/75.13 Page 7 The construction of the Akosombo dam on the Volta river and the preParatory studies for the proposed dam at Ehe Bui Gorge r{ere preceded by Simulium control activities, which were continued during and after the conEinuation of the Akosombo dam. Workers at the intake poinE of the Kpong WaEer TreaEment Plant on the Volta river threatened industrial acEion during the high density season of Simulium in 1971 until measures were taken to remove the fly nuisance. The presence of Simulium can reduce the tourisE potential of places wiEh atEract.ive natural scenery and recreational resources. 5.2.3 The economic benefits of onchocerciasis control There is at present no safe and effective method of onchocerciasis control by mass treat- ment of the affected population. The control of the disease by the extermination of the vectors is essentially a land reclamation exercise. The high cost must therefore bejustified by economic exploitation of the reclaimed territory. The development of the land must be preceded by the preparation of a careful inventory of resources and an assessment of the potential benefits. The informat.ion available at present does not encourage industrializatLon in the irrnediate future. But there are good prospects that efficient utilization of the land for agricultural purposes would be profitable. According to the results of soil surveys by the Soil Research Institute of the Ghana Council for Scientific and Industrial Research the land along both sides of the rivers of the Northern and Upper Regions are fertile and suitable for mechanized farming for distances of from 5 to 10 km (three to six miles) from the rivers. The Northern and Upper Regions consist of land areas where more than 50% of the soils are suitable for mechanized cultivation of crops and the rest are suitable for bullock and hand cultivation. Except for the limitation of water during the long dry season much of the land area isfertile and suitable for growing of foodcrops such as rice, yamsr groundnuts, guinea corn, millet, and vegetables as well as cash crops such as sugar-cane, cotton and tobacco. Many parts of the land are also suitable for pasture grazLng and ranching. A limitingfactor is the Presence of animal trypanosomiasis. Table 2 shows the results of Ehe cattle census of L969. The Northern and Upper Regions produce the highest number of cattle. Fresh-water fishing has increased in the Volta lake and can be expanded in the rivers if these are rendered safe from onchocerciasis. The fish consumed in Ghana in 1969 rdas as shownin Table 3. 5.3 Potential revenue The Potential revenue that could be earned through agricultural developroents in onchocerciasis hyperendemic areas in the savanna north may be assessed from the import tradefigures reported by the Ghana Central Bureau of Statistics (1973). In 1973 the amount of rice imported by Ghana was 53 574 Mg (1 054 560 cwt) costing US$ 17 383 490. The number of cattle imported was 33 721 and was valued ar USg 4 g39 017. Table 4 gives an idea of the income that could be realized if agricultural development was aimed aE import substitution. one of the difficulties that will have to be overcome in order to guarantee the successful exploitation of the land concerns the resettlement of the population. oNcHo/wP/75. 13 Page 8 TABLE 2. 1969 CATTLE CENSUS ON REGIONAL BASIS TABLE 3. FISH CONSIJMPTION - 1969 TABLE 4. COST OF SOME IMPORTED FOOD ITEMS Regions No. of cattle Upper Region Northern Region Brong Ahafo Region Ashanti Region Volta Region Central Region Western Region EasEern Region Greater Accra Region 275 204 11 1 55 I 2 54 36 540 283 774 181 oo9 087 L32 897 934 Tota 1 642 837 I Category Amount in metrictons (Mg) Cash value in US$ Marine catch Inland water fishery Imported fish L8L 929 32 723 30 170.5 33 660 6L2 9 998 226 13 848 998 Total 244 822.5 57 507 836 I tem Quantity imported ValueUS$ Rice Bovine cattle Meat and meat PreParation Sugar and sugar PreParations 53 574 Mg(1 054 560 cwt) 33 721 beasts t7 383 490 4 839 0L7 2 383 444 2t 016 065 Total 45 622 0L6 \ l oNcHo/wP/75.13 Page 9 6. Resettlement The distribution of the population in the Upper Region of Ghana, which is the serious onchocerciasis problem area, shows relatively high density conglomerations in the BawkudistricE, east of the White Volta river and in the Bolgatanga district, iurnediately r47est of the Red Volta river. The rest of the region and in particular the fertile onchocerciasis affected areas in the valleys of the Sissili and the Kulpawn valleys as well as the White Volta after the entry of these major tributaries are very sparsely populated. These areas when freed from the risk of onchocerciasis will have to be settled and tilled. The economic Potential of agriculture seems promising. But. the population resettlement problems will first have to be overcome. There are already indications thaE the prospect of high profits will induce southerners to move to the north to farm and fish. Almost all fishing activities in the Volta lake are carried on by southerners. And in recent times the GovernmenE of Ghanars offer of the supply of cheap fertilizers and agricultural machinery ln Ehe north, and assured markets for rice, have induced an increasing number of southerners to start rice-farming enterprises in parts of the Northern Region which are relatively free from onchocerciasis. But it is not yet clear whether these fortune-seekers intend to settle permanently on the farms. The fishing settlements appear temporary in character. Previous att.empts at resettlement of populations with considerable difficulties. in new areas in Ghana have been fraught The Gonja resettlement scheme was an attempt in the post-Second World War period to reverse the overpopulation and consequent soil exhaustion that existed in the Kusasi and Frafra areas in the eastern parts of the present Upper Region. Able-bodied members of the tribes, including veterans of the r{ar, were encouraged to set.tle and farm in the area around Damongo in the Gonja district, a distance of about 320 km (2OO miles) south. The result was a total disaster. In spite of the good early harvests, most of the settlers returned to their areas of origin at the end of the first harvest and there were hardly any left after five years. Ihe experimenE does not appear to have been well planned and documented. It is therefore not easy to find reasons for the failure. But it is generally consldered that the migrants missed their accustomed social life and extended family contacts and returned to these. Easy comunications were non-existent in those parts during those days. Easier transPortation and the availability of radio sets, such as exist nowadays, might have produced a different story. Amarteifio et a1. (i966) described Ehe resettlement problems durlng the construction of the Tema harbour. This entailed the removal of a fishing corununity of people from their homes to a new site. The exercise was entirely successful in spite of the prolonged initial bargaining. But in this instance the social disruption was minimal, compensaEion was paid by the Government for the inconvenience and the land, and the people were provided with inproved hous ing. The third example of resettlement involved a population of 80 OOO people whose original homes were flooded by the Volta lake following the construction of the Akosombo dam. The resettlement exercise was entirely successful. Although it cannot be said that the promised better life has as yet been entirely realized, 10 years after Ehe event. It is not too easy to determi-ne the extent to which the arguments against ejection were motivated by the size of the compensation claimed by the displaced persons. Some of the arguments centred around their attachment to their ancestral gods which was bound to their ancestral land. Other difficulties required disentanglement of tribal allegiances. A11 these experiences however point to the need for the assistance of sociologists in the planning and implementation of all schemes which may require resettling of couununities. oNcHo/wP/75. 13 Page 10 7, Conclusion There are numerous gaps in knowledge about onchocerciasis in Ghana that require bridging to provide a means of effective planning and implementation of onchocerciasis control as a part of a prograume of socio-economic development. An important constraint is the lack of trained personnel. REFERENCES Amarteifio, G. W., Butcher, D. A. P. & Whitham, D. (i966) Tema Manhean - a study of resettlement Accra, Ghana University Press Anteson, R. K. (tglZ) Studies in filariasis in Ghana, Ghana Med. J. , LL, L46-L4g Berner, L. (f950) Entomological report on the development of the River Volta Basin, University of Florida, USA Buck, A A. et al. (i969) Amer. J. trop. Med. Hyg. , 18, 2L7-23o Central Bureau of Statistics (1973) External trade of Ghana ,23 Crisp, G. (1956) Simulium and onchocerciasis in the northern territories of the Gold Coast London, H. K. Lewis Grant, F. C. (1969) Survey of endemic diseases in the environs of lJeija to assess the health implications of the new Weija dam (Unpublished report) Hughes, M. H. (L952) W. Afr. Med. J. (Ns) I I ,],L6 Jones, C. R. & Quarcoopome, C. O. (1973) Unpublished report, quoted in Jones, C. R. (1973) Health component in the Volta Lake Research Projecr AFR/PHA/115; AFR/SCHIST/27, p.22 Lynn, C. W. (1942) Farm Forest, 3, 78 Noamesi, G. K. (1966) Dry season survival and associated longevity and flight range of Simulium damnosum Theobald in northern Ghana , Ghana med. J. , 5, 95-1-C.z Owusu, S. K. (1974) Glucose-6-phosphate dehydrogenase deficiency in causation of disease in Ghana, Ghana Med. J. , 13, 168-170 Ringelhann, B., Dodu, s. R. A., Konotey-Ahulu, F. r. D. & Lehmann, H. (1968) A survey for haemoglobin variants, thalassaemia and glucose-6-phosphate dehydrogenase deficiency in northern Ghana, Ghana Med. J., 7, L2O-L24 Rodger, F. C. (1959) Blindness in West Africa, London, H. K. Lewis, 8l Saunders, c. F. T. (L929) Unpublished report Sarkies, J. W. R. (fSSf) Blindness and eye disease in the northern territories, Official report to the Director of Medical Services, Accra Senker, C., Noamesi, G. K. & McRae, T. M. (L973) Onchocerciasis survey in White Volta river and the Kulpawn river in northern Ghana, Ghana Med. the J. basin of the , L2, 56-65 Waddy, B. B. (1949) Onchocerciasis and blindness in the northern territories, to the Director of Medical Services, Accra 0fficial report oNCHO/WP/75.13 Page 11 MAP 1. GHANA SHOSIING RIVER SYSTEMS AND SIMULITJM FOCI GHANA: CARTE DES RIVIERES ET DES FOYERS DE REPRODUCTION DES SIMULIES U I P t t N LT d RE a 4 a tt a t R' ^-)L.{. I I OLG PER .4.r.-.-. a t a .to { o o o aHO osombo t o r -l \ l / \ o fAHAIE N THE R : I Xp NTR A R N TE h KOFORIOU a Bul Gorge FO T! ru' I( UMASI a N )J / a !( A R I ,lt H F ta o c, E G Alrom L BROt\iG. RE E o Gu Grr\n 3 o ot aeg Qfrsr O 20 40 60 80km I a 1. t 0. 3 30' 3o' T 7. 0' b 5' 3' 30, 2' 30' 30, 0' 30, t' I E AT a a aa