Prospects for the control of onchocerciasis in Africa

Bull. Org. mond. Sant)11969, 40, 843-858Bull. Wid Hlths Org. Prospects for the Control of Onchocerciasis in Africa With Special Reference to the Volta River Basin B. B. WADDY, D.M., D.P.H.1 Onchocerciasis is found in association with all the main river systems of northern tropical Africa, and there are endemic foci south of the Equator. Heavy and prolonged infection may cause blindness and intense pruritis. The vectors, Simulium damnosum and S. neavei, are also intolerable pests when they swarm. The disease and its vector together cause serious economic loss and are a main cause of the depopulation of river valleys in the savanna lands. The basin of the River Volta, in which the worst endemic area in the world is situated, is considered to be the most favourable area for a study of the problems involved in the large- scale control of onchocerciasis carried by S. damnosum. Mass treatment or prophylaxis are not practicable at present. The clinical condition progresses for many years in the absence offresh infection, and drugs capable ofmass application are needed. However, the first aim is to attack the larval stages of the vector with insecticides. DDT is idealfor this purpose in large, steadily flowing rivers, but a more suitable insecticide andformulation are needed for small, irregularly flowing streams. Research is needed into many aspects of the adult life of S. damnosum, including feeding and resting habits, dry season survival and flight range. One of the main practical problems is prevention of reinfestation ofa treated river system. INTRODUCTION Onchocerciasis is the disease resulting from infec- tion with the filarial worm Onchocerca volvulus. The filariae are carried from man to man by the bites of small flies of the genus Simulium, larval stages of which are found in running water, particularly in places where rocks break the water surface and the turbulence of the water results in a higher level of oxygenation. Rivers which cease to flow during the dry season cannot at that period support the breed- ing of Simulium, but immediately the flow of water recommences, so does breeding, and immense swarms are produced in a very short time. The nuisance and discomfort caused by these hun- gry swarms harassing man and livestock are alone, without taking into account the transmission of disease, sufficient to drive populations away from rivers in which the simuliids breed. The effects of onchocerciasis combined with the devilry of its 1 Formerly Reader in Tropical Hygiene, London School of Hygiene and Tropical Medicine, London, England. vector lead not only to human suffering but also to very severe economic damage. Effects on health Mild infections of onchocerciasis, in which the subject carries only a few worms, cause few or no symptoms. Heavy infections, specially if the first infection is acquired early in life and is followed by repeated superinfections, may result in blindness and also in a skin condition known under various names: craw-craw being the usual name in English-speaking countries of West Africa, gale filarienne in French- speaking countries. Blindness rates of over 10 %, or occasionally of over 30 %, have been found in villages subject to hyperendemic onchocerciasis. In a few instances, some sight can be restored by treatment, but mass treatment in rural surroundings has not proved to be either safe or successful enough for routine use. Craw-craw, apart from being disfiguring, causes itch- ing so intense as occasionally to lead to suicide. Elephantiasis, epilepsy and dwarfism have also been associated with onchocerciasis by some workers. 2340 -843- B. B. WADDY Economic effects Large hydro-electric installations have been con- structed or are planned in several African countries. Dam sites are naturally associated with running water and rocky gorges, and therefore with Simu- lium. The nuisance caused by fly swarms, and the danger of the spread of onchocerciasis in the labour force, necessitate the control of Simulium during construction work. The Owen Falls Dam in Ugan- da, the Volta Dam in Ghana, and the Niger Dam in Nigeria are examples. When such a dam is com- pleted, the water above it becomes static and there are no longer breeding-places for Simulium, but the spillway may provide ideal breeding conditions, to the detriment of the comfort and health of mainte- nance staff and workers in associated industrial pro- jects, such as aluminium smelting. In a rural community, the highest blindness rates are found in males over 30 years of age. At Nakong, northern Ghana, in 1948, the infection rate in child- ren reaches 100% by the age of 9 years, 9.5% of the whole population was blind, and of males over 30 years of age, nearly 20% were blind (Waddy, 1966). Males in this age-group should be the mainstay of the community's labour force, and it is unnecessary to stress the economic effects of blindness on this scale. FIG. 1 POPULATION DENSITY AROUND THE RED AND WHITE VOLTA RIVERS, NORTHERN GHANAa a From a map by Dr K. R. S. Morris. b 100 persons per square mile = 38 persons per kM2 844 PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA Moreover, onchocerciasis does not of itself shorten life, and all the economically unproductive blind have to be maintained. Not only farming but also fishing is affected since, in the presence of Simulium swarms, fishermen either cannot work at all or suffer a very high rate of blindness. Perhaps the most serious economic effect of on- chocerciasis and Simulium infestation is the depopu- lation of river valleys in the savanna lands; this can be seen to have occurred in northern Ghana, Upper Volta, Nigeria, etc. It is well known that to preserve the fertility of savanna land, the watershed areas should be kept free of deforestation and grass-burn- ing. But once Simulium establishes itself in a river, the population begins to retreat; at each new area of settlement the grass is burnt to clear land for farm- ing, soil erosion creates rocky gullies in the streams and Simulium starts to breed, a further population retreat takes place, and the process is repeated until the whole watershed has become deforested, burned, eroded and abandoned. This process is going on now, and can readily be observed in the valleys of all 3 branches of the Volta River and of its main tributaries. At the same time, improved general health services are resulting in an increasing population and more demand for land. In the Kulpawn-Sissili valley in Ghana, a statistical correlation between blindness and depopulation has been found, and a population-density map of the densely populated area around the Red and White Volta rivers indicates clearly the retreat of popula- tion from the rivers (see Fig. 1). North of the Ghana frontier, the valley of the Red Volta has become completely deserted during the last 20 years. Until the breeding of Simulium damnosum is controlled, this progressive sterilization of the West African savanna cannot be arrested or reversed. Distribution of onchocerciasis in Africa Onchocerciasis is found in association with all the main river systems of Africa south of the Sahara and north of the Equator, from near Cape Verde across to Ethiopia. The disease occurs also south of the Equator, as far as a southerly limit of about 10°S. Hyperendemic areas, having a high incidence of blindness and craw-craw, are confined to the belt of savanna which runs right across Africa, generally from about 8°N to 12°N. The environs of the Victoria Nile above Lake Victoria (only just north of the Equator) were also virtually uninhabited until a few years ago on account of the presence of S. dam- nosum. With that exception, the chief hyperendemic areas are in eastern Senegal, eastern Guinea, Mali, all the countries related to the savanna reaches of the Volta River basin (Upper Volta, Ivory Coast, Ghana, Togo and Dahomey), Nigeria, Chad, Congo (Kinshasa), Central African Republic, Sudan, north- ern Uganda and Kenya (see Fig. 2). .2 AREAS OF HYPERENDEMIC ONCHOCERCIASIS IN AFRICA 845 B. B. WADDY FIG. 3 KNOWN FOCI OF ONCHOCERCIASIS IN THE VOLTA RIVER BASIN V 0 L T A FADA. N'GOURMA TENKODOGO I/ I _-~ Site GI dam == Intemational frontiers Foci of lower intensity, some surveyed, some Hyperedemic.focus -; only known to exist IVORY COA ABIDJAN 846 PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA In parts of East Africa and Congo the vector is S. neavei. This species has a short flight range, and its breeding haunts can therefore be attacked one after the other, as isolated projects. In this way, S. neavei has actually been eradicated from Kenya (Brown, 1962), where the transmission of onchocer- ciasis has come to an end. In Ethiopia, northern Uganda and all across West Africa, the vector of onchocerciasis is S. damnosum, the control of which is very much more difficult on account of its great flight range. The range has never been precisely determined but may be more than 50 miles (80 km). As a result, if a single breeding site, or a complete river, is dealt with in isolation, it is quickly reinfested by S. damnosum from neigh- bouring rivers. For this reason, the entire area from Senegal to Ethiopia should be regarded as a single endemic focus. Nevertheless, it is possible to make rough divisions of the area according to river sys- tems, one of which is the basin of the Volta River (Fig. 3). ONCHOCERCIASIS IN THE VOLTA BASIN The Volta basin is a very favourable area for a first study of epidemiological, biological and practi- cal problems involved in large-scale control of on- chocerciasis transmitted by S. damnosum. Despite the large size of the area, it is relatively compact and well delimited, and is also smaller than other infect- ed river basins, such as those of the Niger and Nile. The Volta basin contains the worst endemic area of onchocerciasis in the world, with very high blindness rates and an acute, and growing, problem of depop- ulation. A number of incidence surveys in the several countries involved have already provided a rough picture of the distribution of the disease, and the entomological situation has been determined with considerable accuracy almost throughout the area. National or international institutions interested in onchocerciasis research, and organizations ex- perienced in the control of mass disease, are already established in all the countries concerned and it should be possible to make use of their experience and trained national staffs, to develop an onchocer- ciasis control project in the Volta basin. The population living in areas seriously affected by onchocerciasis in the Volta basin is about 51/2 million, of whom some 100 000 are blind-at least three-quarters of them being victims of on- chocerciasis. The Volta River system drains greater or lesser parts of Mali, Upper Volta, Ivory Coast, Ghana, Togo and Dahomey; even the south-western corner of Niger may be included in any Simulium control project involving the Volta River, since the eastern tributaries of the Volta may become reinfest- ed from Niger river tributaries. From the example offered by the Volta River basin, it is clear that the many problems of on- chocerciasis control-some of them fundamen- tal-which still need to be solved, as well as the practical problem of devising vector control mea- sures, are not limited by national boundaries and can be tackled only on a geographical basis. It is essential that control operations should be conduct- ed without regard to international frontiers. There- fore, inter-country co-operation is indispensable for working out, and applying, the most economical and effective control schemes. Hydrological and climatic data for the Volta basin The Volta River drains an area of some 160 000 square miles (414 398 km2) of West Africa, within the bend of the Niger (Fig. 4). The Volta itself is formed by the confluence of the Black and the White Voltas in Ghana, some 290 miles (approximately 470 km) from the river mouth where it discharges into the Atlantic at Ada (Addah). Some distance above the confluence of the Black and the White Voltas, the Red Volta flows into the White Volta. Climatically, West Africa is usually regarded as having 4 zones that merge into one another more or less according to latitude. From the coast to about latitude 8°30' N is the Libero-Dahomian, or forest, zone in which rainfall and atmospheric humidity are high and the temperature range is limited. Some- times, a coastal plain separates the forest from the sea; this is so in Ghana, around the final reaches of the Volta. At the other extreme, northwards from about 18°N is the Sahara desert in which rain sel- dom falls, humidity is very low and temperatures range from below freezing-point to over 50°C. In between these extremes lies the Sudanese, or savanna, zone (from 8°30' to about 12°N) and north of that the sahelian zone. In all zones, there is a single rainy season with a climax in September, and a prolonged dry season from November to May or July, according to latitude. Air movement during the dry season is from the north-the harmattan wind-and, even in the relatively mild savanna cli- mate, relative humidities may fall to 2% in the afternoons. The change from forest to desert is gradual and progressive; trees become smaller and fewer and the 4 847 B. B. WADDY FIG. 4 CATCHMENT BASIN OF THE RIVER VOLTA boundary between the savanna and sahelian zones is roughly 12°N, the latitude above which species of Acacia are the only trees. Temperatures range be- tween about 250C and 42°C in the savanna, with a somewhat wider range in the sahelian zone. Rainfall ranges from 50 inches (about 125 cm) in some savanna areas down to 15 or 20 inches (about 37 cm-50 cm) in sahelian regions. Even the lower end of the range represents an appreciable rainfall, which must drain away. Therefore, nearly all the rivers of West Africa rise in the north of the savanna or the sahelian zones, the constituent branches of the Volta being no exception. Although there are several ranges of hills in the savanna and sahelian zones, there are few peaks higher than about 1500 feet (about 460 m) above sea 9 level, and in general the northern part of the Volta basin lies in gently undulating plain country. The Black Volta The Black Volta is the largest of the 3 Volta rivers, and the only one to maintain its flow throughout the dry season. It arises from a number of small sources north of the Banfora scarp in Upper Volta, about 1 1ON, 5°W and its headwaters are in close proximity to those of the Comoe and Bougouriba. Thence the river runs north-east for some 160 miles (about 257 km) to a latitude of approximately 1B3N, 3°30'W, then it turns south. Between I °0N and south of 9°N, the Black Volta forms the frontier between Ghana and, successively, Upper Volta and the Ivory Coast. It then curves south-east, north- 848 PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA 849 east and east across the Ghana savanna to its con- fluence with the White Volta. The course of the river includes a number of rapids but no falls. Bobo Dioulasso, the headquarters station of the Organisation de Coordination et de Cooperation pour la Lutte contre les Grandes Endemies (OCCGE) and of its Onchocerciasis Section, is some 50 miles (80 km) from the complex of headwaters of the Black Volta, Comoe and Bougouriba rivers. At Bui, a few miles below the point at which the Black Volta curves away from the Ivory Coast fron- tier into Ghana, the river runs between hills. At various times it has been suggested that a dam might be built at Bui, and this project has received serious consideration. The Volta River Project Preparatory Commission set up hydrographic stations on the Black Volta at Lawra, Bui and Bamboi. Details of levels and flow are not given in its Report for 1956 1 but must be available from records. Noel-Buxton (1956) and Ghana Medical Field Units have experimented with the application of DDT to the river at the northern frontier of Ghana. The flow must therefore have been recorded in considerable detail. Noel-Buxton gave a value of 1600 ft3/s (45.3 m3/s) for the rate of flow in January, which is near the time when the water level is lowest. Tributaries of the Black Volta. The main tributary to the right bank is the Bougouriba, which rises close to the headwaters of the Black Volta itself and pursues a curving course eastwards to enter the Black Volta about 30 miles (50 km) south of the Northern frontier of Ghana. It drains an area of some 500 square miles (about 1300 kM2) and is perennial in flow. Its characteristics have been inves- tigated by Blanc et al. (1958) and must be known in detail. South of the Bougouriba, several other small tributaries, about which little is known in detail, drain a catchment area extending some 40 miles (about 65 km) westwards into the Ivory Coast, which adjoins the catchment area of the Comoe. East of Bamboi, small tributaries, the Oyoko and several others, drain the Kintampo highlands of Ghana, and further east the Pru drains a consider- able area of northern Ashanti, Ghana. A tributary of small size but considerable entomo- logical importance runs into the left bank of the Black Volta some 70 miles (about 110 km) north of the northern frontier of Ghana, from an origin not I Volta River Project, Preparatory Commission (1956) Report, vol. 2. Appendices; vol. 3, Engineering Report. far from the headwaters of the White and Red Volta rivers. Some 25 miles (40 km) south of this frontier, the Kamba enters, after flowing westwards for 35 miles (about 55 km). The Kamba forms pools throughout the dry season, and flows at the rate of 380 ft3/s (10.8 m3/s) in October (Noel-Buxton, 1956). The valley of the Kamba is somewhat eroded, however, and the river is liable to alternate periods of flooding and stagnation; several small dams have been constructed along the valley. South of the Kamba, many small tributaries drain into the Black Volta and after the latter has turned east- wards, the Sorri, draining an area of some size, empties into it. It is possible that some details of the flow of the Sorri are already known. The White and Red Voltas The White Volta rises in the sahelian zone of Upper Volta, about latitude 13°N, 2°W. It runs south-east, then south, to enter the north-eastern corner of Ghana. In Ghana, it continues to flow southwards for about 30 miles (50 km) before being diverted sharply westwards by the Gambaga scarp, a feature that runs east-west for some 60 miles (about 100 km) with a sheer north face about 600 feet (180 m) high. The river turns southwards again after some 50 miles (80 km), and runs a placid, meandering course down to the confluence with the Black Volta. The White Volta ceases to flow in the dry season, but in Ghana it is a big enough river to exist as a continuous linear lake rather than as a series of pools. The flow usually starts in late April or early May with the dramatic descent of a bore after rain has fallen further north. The Volta River Project Preparatory Commission set up hydrographic stations on the White Volta at Pwalagu and Yapei, so that flow records must exist. Along its course in Upper Volta, the White Volta receives many tributaries which, though small, are important entomologically. In northern Ghana it receives the Tamne before its westward bend at the Gambaga scarp, the Morago at the bend and the Red Volta some 15 miles (25 km) west of the bend. As the White Volta turns south again, it receives the Asebelika (which in its upper reaches is known successively as the Chassi and Tono) and a few miles further south the Kulpawn, both of which are on its right bank. It then receives on its left bank the Nasia, which drains the southern slopes of the Gain- baga hills. The placid southern reach of the White Volta has other tributaries-the Mole and the Nabogo. B. B. WADDY The Kulpawn rises in Ghana, and is joined by the Sissili which rises in Upper Volta. The Sissili itself has an important tributary, the Kanyanbia. All these are small rivers that flow for about 7 months a year and are either dry or limited to pools through- out the dry season. Their valleys are more or less eroded, and the river flow fluctuates violently after rain. In the flat plain country towards the con- fluence of the Black and White Voltas, the Nabogo may actually carry water away from the White Volta if the latter floods before much rain has fallen further south. About 20 miles (30 km) west of the Red Volta and the same distance north of the White Volta, in Ghana, lies Bolgatanga, at which the West African Council for Medical Research formerly had an on- chocerciasis research station with housing and a laboratory. A few miles east of Bolgatanga runs a small tributary of the White Volta in which Simu- lium formerly did not breed but (with the advance of soil erosion) may now do so. The Red Volta rises from headwaters around the junction of the savanna and sahelian zones, not very far from a tributary of the Black Volta. This river runs south-east then south into the White Volta, north of the Gambaga scarp and has no important tributaries. Even in its final reach, the Red Volta dries up to a sandy bed and small pools in the dry season, and its course being long and eroded, the flow usually begins with violent floods that are fol- lowed by stagnant periods. Some details, mainly of water levels, were recorded by Crisp (1956). The Ghana Medical Field Units (MFU) have ex- perimented with Simulium control in the Red Volta, and therefore flow records in Ghana have been made. The Volta River and the Volta Dam Before the Volta Dam was completed and filled, the Volta River ran south-east and south to Ada on the Atlantic coast. The river ran a mainly placid course through plain country but there were rapids, now submerged, at Kete Krache and in the Ajena gorge. The flow of the Volta below its lowest tribu- tary varied from about 1000 ft3/s (28.3 m3/s) from December to May to as much as 330 000 ft3/s (935 m3/s) in October. The site of the dam at Akosombo is some 60 miles (100 km) inland from Ada. The Volta Lake now extends along the entire former course of the main river and far up the Black and White Voltas, the Daka, Oti and Afram. The Afram is one, and the Pru is another, of the principal right bank tributaries of the Volta, while the Daka, another seasonal river, runs southwards to join the main river not far from the confluence of the Black and White Voltas. The Oti, which rises as the Pendjari west of the Atakora mountains in northern Dahomey, forms, together with its tributaries, the eastern boundary of the Volta basin, and drains a large area of northern Dahomey and Togo, Upper Volta and Ghana. Along the whole stretch of the lake, the water is now static and therefore offers no breeding-places for S. damnosum. The geographical relationships of the Volta with other river systems On account of the great flight range of S. damno- sum, the geographical relationships between different parts of the Volta system, and between them and other river systems, are important. In terms of Simulium flight, the Volta system divides itself naturally into 4 parts, i.e., the Black Volta and its tributaries, the White and Red Voltas and their tributaries, the Pendjari-Oti system and the Volta River itself, now the Volta Lake. The Black Volta catchment area is close to that of the Comoe; cross-infestation by S. damnosum is known to occur around the headwaters and may also occur further south. To the east, there may be cross- infestation between the headwaters of the Red and White Voltas and a Black Volta tributary in the region of Koudougou, also between the Kamba and Kulpawn and possibly between smaller Black Volta tributaries and the Kulpawn. The White Volta and Red Volta river systems can be subdivided into those of the main rivers and their tributaries north of the Gambaga scarp, and of the Kulpawn-Sissili-Asebelika complex. (The Nasia may be a separate problem but Crisp (1956) found that S. damnosum flies over the Gambaga scarp very easily.) The White and Red Voltas may be cross- infested from the unnamed tributary of the Black Volta that arises near their headwaters and from the upper reaches of the Sissili. To the east, cross- infestation may be possible from the Pendjari-Oti complex and from the Sirba, a tributary ofthe Niger. The Pendjari-Oti complex lies fairly close to several tributaries of the Niger, to the Mono in Togo, and to the headwaters of the Oueme. The Volta River itself, below the dam from Ajena to Akuse, is an isolated reach in which Simulium will presumably continue to breed until it is eradicated, probably once and for all time. 850 PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA 851 One of the most important problems of Simulium control is the prevention of reinfestation from other river systems. Therefore, the most satisfactory area for a pilot project is one containing a river system with as few zones of contact as possible. A study of the map (Fig. 3), on which the positions of head- waters are approximations only-often rough ones- indicates that the river system of choice is that ofthe White and Red Voltas, north of the Gambaga scarp, excluding the Kulpawn-Sissili-Asebelika system. DISTRIBUTION OF ONCHOCERCIASIS AND SIMULIUM DAMNOSUM The distribution of S. damnosum in the Volta River system is much more accurately known than the distribution of onchocerciasis. Since onchocer- ciasis can be presumed to be endemic in some degree wherever S. damnosum is found, the distribution of the disease is known broadly. However, the distri- bution and, especially, the degree of severity are not known with any accuracy in most areas. Onchocerciasis occurs in its most devastating form, leading to mass blindness and craw-craw, almost exclusively between latitudes 10°N and 12°N. In this zone there are 5 hyperendemic foci: (1) south of Fada N'Gourma; (2) around the Red and White Voltas north of Ghana and in Ghana as far south as the Gambaga scarp; (3) around the Kulpawn, Sissili and Asebelika rivers in Ghana-probably the worst endemic focus in the world (see Fig. 5); (4) along the Kamba and Bou- gouriba rivers and parts of the Black Volta north of 10°N; and (5) around the headwaters of the Black Volta. Between these foci, and further south, on- chocerciasis is generally endemic, though to a degree which varies from village to village, infection being associated with the Black Volta and its smaller tributaries including the Sorri. South of the junction with the Kulpawn, the White Volta and its tributar- ies probably do not provide suitable breeding-sites for S. damnosum. Surveys conducted by Ghana Medical Field Units, however, do reveal a certain amount of onchocerciasis in this area. Around the Volta River itself there is, or was, a focus near the junction of the Daka and the White Volta, a focus at Kete Krachi and a focus along the reach from Ajena to Akuse. Further east, around the area of the Ghana-Togo frontier, there is a diffuse focus in relation to tributaries of the Oti, but little detail about this focus has been published. There is diffuse endemicity of onchocerciasis in all the northern parts of Togo and Dahomey, and particular foci are described in the vicinity of Natitingou and Djou- gou, Dahomey. Surveys in this area are in progress.' Most, or all, the river systems surrounding the Volta basin are also associated with endemic on- chocerciasis. In the Ivory Coast there are foci round the Comoe and to the north-west there are impor- tant foci in relation to tributaries of the Niger. The focus at Sikasso may be continuous with that of the headwaters of the Black Volta. To the east, there are foci, not yet surveyed precisely, in relation to tributaries of the Niger and to both the Ouem6 and Mono rivers. A focus has also been found in rela- tion to the Pra in south-west Ghana. Entomological surveys have been much more pre- cise, and it can be said that the breeding haunts of S. damnosum are now known fairly accurately all over the Volta basin except in the Ivory Coast and around Banfora in Upper Volta, and in northern Togo and Dahomey, where surveys are in progress (Quelennec, 1962). Not all the information has been published, but the Onchocerciasis Section, OCCGE, has unpublished data for Upper Volta foci. THE CONTROL OF ONCHOCERCIASIS The control of an insect-borne disease may be attempted by 2 main methods. One method is to eliminate the reservoir of infection by mass treat- ment or prophylaxis; this has been used against trypanosomiasis with excellent results, and is the principle of Pinotti's method of attacking malaria by introducing an antimalarial drug into common salt. The second method is to attack the vector. Treatment Two drugs are used in the treatment of prophy- laxis of filarial infections. (A third drug, Mel W, turned out to be excessively toxic and was dropped.) Diethylcarbamazine is an effective treatment for Wuchereria bancrofti, Brugia malayi and Loa loa; it kills the microfilariae of Onchocerca volvulus rapidly, but adult worms are killed only by several courses of the drug, perhaps over a period of 3 or 4 years. The allergic reactions that accompany the death of microfilariae of any species in the human body are particularly marked during treatment of oncho- cerciasis with this drug. Diethylcarbamazine is used to treat individual patients who are eventually cured 1 Petit, J. (1961) Report on Onchocerciasis in Togoland. Unpublished WHO African Regional Office working docu- ment AFR/Onchocerciasis (1961)/i1. B. B. WADDY FIG. 5 POPULATION AND BLINDNESS DISTRIBUTION IN THE KULPAWN AND SISSILI VALLEYS, NORTHERN GHANA (1949) by it if they are persistent enough to continue a somewhat unpleasant treatment for a sufficient length of time. But the treatment should be under medical supervision, with anti-histamine or serotonin anta- gonist drugs ready to hand. Woodruff et al. (1958) have given an authoritative account of this treatment. Diethylcarbamazine has also been used, with some success, as a preventive measure against filariasis due to W. bancrofti and B. malayi. However, Jordan (1958) found that the drug had no effect on the infective larva of W. bancrofti. Therefore, the effect of mass drug-administration is not prophylactic but curative-the microfilariae in circulation are reduced by treatment and thus the cycle of infection may be broken. In Loa loa infections (the adults being perhaps more susceptible to diethylcarbamazine 852 PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA treatment than those of any other species) Duke (1963) produced evidence to show that the drug does act as a true prophylactic, killing infective larvae. There is no reason to believe that diethylcarbama- zine would act as a prophylactic against onchocer- ciasis. Nor can a campaign of preventive treatment be envisaged, bearing in mind the prolonged course required-36 months or more-the unpopularity of the normal pruritic reactions, the huge reservoir of infection and the continental distribution of the disease. Suramin sodium (hexasodium salt of 8,8'-{urey- lene bis [m-phenylene carbonylimino(4-methyl-m- phenylene) carbonylimino]}di-1,3,5-naphthalenetri- sulfonic acid) has been a principal drug for the treatment of trypanosomiasis for many years. Briefly, treatment with suramin kills adult 0. vol- vulus, while not having such an immediately lethal effect on microfilariae as diethylcarbamazine; prurit- ic reactions are therefore milder, or do not occur. The infection is frequently cured by a single course of treatment lasting 5 or 6 weeks, and there may be a dramatic recovery of useful vision in patients who had previously been totally blind (with anterior ocu- lar lesions). Unfortunately, an occasional patient under treatment with suramin is liable to die sudden- ly of kidney failure. But for this serious risk, suramin would be an almost ideal drug for mass treatment. The present situation is that, except for the few who find their way to hospitals, the great numbers of victims of onchocerciasis in Africa, blind and pruritic included, are not being offered treatment. The writer of this paper, were he still in the field, would offer suramin treatment to those blind from anterior ocular lesions and to those finding their pruritis intolerable-ex- plaining the slight risk and guarding against it by repeated urine examination. These views on drug treatment are personal and not always in complete agreement with those of others. According to Rivas et al. (1965), suramin treatment is used routinely on all onchocerciasis patients in Venezuela, with excellent clinical results and without undue toxic hazards. There is one other possible treatment, namely nodulectomy. This has been employed on a mass scale in Guatemala, both as an individual cure, or alleviation, obviating the risk of blindness, and as a preventive measure, decreasing the total number of microfilariae available for infecting the vectors. It has been an outstanding success in that country. In Africa, a campaign of nodulectomy on a scale sufficiently large to act as a preventive measure can hardly be envisaged. In addition to the great num- bers of infected persons involved, multiple nodules are the rule rather than the exception. Hissette (1932) removed 126 nodules from a single patient, who actually had more than this but refused further operations. " Je le comprends un peu ", commented Hissette. However, since nodules on the head, comparatively rare in Africa, are the most dangerous in relation to eye damage, campaigns of head nodu- lectomy might be organized; the writer has done this on a small scale in the past. It seems that mass treatment as a preventive mea- sure in Africa is not practicable, and that an attack on the vector is, therefore, the only possible method of onchocerciasis control. Nevertheless, it must not be forgotten that to terminate (or reduce) transmis- sion is not the only measure needed in a serious endemic focus. The disease continues to progress for many years in existing patients, as was found by Nelson & Grounds (1958) at Kodera, Kenya, 11 years after the local vector, S. neavei, had been eradicated. A safe form of mass treatment must be evolved. THE CONTROL OF S. DAMNOSUM Simulium larvae are intensely susceptible to DDT. In a large, steadily flowing river, a single application of as little as 1 part in 20 million maintained for 1/2 hour has been known to eliminate larvae for a distance of over 100 miles (160 km). If breeding in a few major rivers were the only problem, it would be a simple one. For example, S. damnosum was eradicated along the 45 miles (72 km) of the Victoria Nile as an incidental result of DDT being used to alleviate the nuisance the fly was causing to the labour force building the dam at Jinja in Uganda (Brown, 1962). Unfortunately, these were excep- tional conditions. The difficulties of controlling S. damnosum depend on a number of factors. Breeding habits of S. damnosum S. damnosum breeds in any suitable runnel in small rivers and streams in which the 2 variables of oxygenation (roughly dependent on current speed) and food supply (roughly dependent on turbidity) provide suitable conditions. Multiple breeding sites spread over an entire river basin must be reached and dosed every few days, giving rise to problems that may be insuperable-in particular, the expense of maintaining access tracks and the limits of physical endurance on the part of entomologists. 853 854 B. B. WADDY Reaction of S. damnosum to insecticides Neither the egg nor the pupa is susceptible to DDT (Hocking, 1950; Hocking, Twinn & McDuffie, 1949; both quoted by Davies et al., 1962), though Taufflieb (1955) considered that lindane kills pupae. The duration of the larval phase is therefore of great importance in relation to the frequency of dosing required to maintain control. There is not complete agreement on this; it seems to depend not only on temperature but also on food supply. Tables 1 and 2 show, respectively, the different durations of larval life and dosing intervals that have been suggested. Simulium resistance to DDT has been reported (Suzuki, Ito & Harada, 1968) and some degree of tolerance appears to have developed in the environs of the Kainji dam in Nigeria, after several years of control operations. The existing formulations of DDT have proved to be nearly ideal for controlling Simulium breeding in large rivers with long reaches of uninterrupted flow. In small rivers alternating between stagnant reaches and occasional rapids, the stability of DDT causes it to accumulate in the stagnant reaches, from dose to dose, until a concentration lethal to fish, and possibly even dangerous to mammalian life, is attained. For use in small streams and rivers, the insecticide should have the following qualities: (1) Persistence in water for a few days only, say 4-10 days. (2) A specific gravity less than that of water. (3) The lowest possible toxicity to plants, fish, man, and animals other than insects. (4) It should be possible to determine the con- centration in water by a test readily performed in the field or in a small field laboratory. Use of aircraft to control S. damnosum In some countries, notably the USA and Canada, where various species of Simulium are a nuisance and must be controlled, insecticides are often applied by spraying from aircraft. (Higgins 1 has reviewed the use of aircraft for the application of pesticides and has given an extensive list of references.) Aerial spraying for the control of S. damnosum would 1 Higgins, A. E. H. (1967) Use of aircraft for the aerial application of pesticides (unpublished working document WHO/Fil/67.69). A limited number of copies of this docu- ment is available to persons officially or professionally interested on request to Distribution and Sales, World Health Organization, 1211, Geneva, Switzerland. TABLE 1 DURATION OF LARVAL STAGE OF S. DAMNOSUM ACCORDING TO THEWORK OF DIFFERENT AUTHORS Period from Water Source hatching to temperature, pupation (days) if given (°C) Wanson (1950)a 5 Barnley (1953) b 6-8 26.5 Crisp (1956) 10-13 22-24 Marr (1961) 8-9 20-28.5 Wright (1957) 14 40 c 25.5 d a Quoted by Crisp (1956). b Barnley, G. R. (1953) The control of Simulium damnosum(Theobald) on the Victoria Nile, Uganda (unpublished working document WHO/Onchocerciasis/18) (quoted by Crisp, 1956). c Under laboratory conditions. d Average. eliminate some of the more arduous work but not all of it, since results would have to be checked on the ground. The possibility of using aircraft, weighed against the practical difficulties and costs, is being investigated. Flight range of S. damnosum Despite its small size (approximately 6 mm in length), the adult S. damnosum has an immense flight range. Along a river, it is now known to have a range of over 100 miles (160 km). The species reinfests the Kainji dam site along the Oli River from across the Dahomey border 70 miles (112 km) away (J. F. Walsh and H. H. Goiny, personal communications and unpublished reports.) It has no difficulty in striking out across country and Crisp (1956) demonstrated that it flies over the Gambaga scarp, 600 feet (183 m) high, in Ghana. Walsh has caught numbers of flies along the Mokwa- Kontagora road in Nigeria; this is on the watershed between the Niger and Kaduna rivers, and a con- siderable distance from both. Consequently, if a single river is dealt with in isolation, reinfestation is inevitable and immediate. Adult bionomics of S. damnosum Many of the habits of the adult fly have defied investigation by the most skilled and patient ento- mologists. Mating has never been observed; the species will not breed in the laboratory and adult males are known mostly from specimens bred out from wild-caught larvae. There are 2 biting periods, PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA TABLE 2 DOSAGE SCHEDULES FOR TREATING RIVERS WITH DDT ACCORDING TO VARIOUS AUTHORS Workers Dosage intervals No. of applica- f DDT aimned at Workers ~~~(days) tions per season (ppD am/mm)t Noel-Buxton (1956) 4 5 0.03-0.44/30 Ghana MFU (1959) 4 10 0.075-0.1/30 > 7 1011 0.2/30 Barnley (1958) J 7 12 0.4/30 Barnley & Prentice (1958) 10 12 0.5130 Browne (1960) 10 10 2/30 Garnham & McMahon (1947) 10-14 13 2-5/30 McMahon et al. (1957) 10-14 10 0.5-2/30 J. B. Davies et al. (1962) 7 12 0.5/30; 0.5/15 Crisp (1956) 4 7 0.1/15 Wanson et al. (1949) 1 26 - (banks) Crisp (unpublished data) a 14 perennial 0.5/30 Taufflieb (1955) 7 6 1.5/30 (lindane) Ovazza (personal communication) 10 ? Various Blanc et al. (1958) 8 2 2.5/30 a Quoted by Brown (1962). morning and late afternoon; between these times the flies disappear from human observation. A certain amount of information about its resting places has been given by Wanson, Courtois & Lebied (1949) and Le Berre (1966), but it is not yet possible to attack the adults with residual insecticides-a method that has given excellent results against tsetse flies in Nigeria (Kernaghan, 1961), Kenya (Fair- clough & Thomson, 1958), and Cameroon-Chad (Mouchet, 1962). Anthropophily of S. damnosum S. damnosum is anthropophilic, but by no means exclusively so. The precise determination of its feeding habits might help in the search for hiding places and resting haunts, which so far has been almost uniformly unsuccessful. The precipitin test has been used on Scottish simuliidae (Davies et al., 1962), and could be applied to S. damnosum. Survival of S. damnosum in the dry season Very little conclusive evidence on the manner of survival of S. damnosum during dry periods has been found. According to Le Berre (1966), S. dam- nosum survives longer in the dry savanna than in the humid forest climate, presumably because unfavourable conditions enforce a less active life. But the longest survival period noted by Le Berre was 23 days, which is a very short period in com- parison with the 4 or 5 months during which some of the most notorious breeding rivers do not flow. In some river systems, with a perennial main river and tributaries flowing for a few months, breeding is at its height in the main river during the dry season. During the rains (when breeding in the main river is reduced) side-streams flow and breeding sites are therefore available, well within flight range, throughout the year. The Black Volta is such a system. Other river systems are too far from dry-season breeding sites for even S. damnosum to fly to, though it appears that even in apparently dry rivers a few short stretches, of running water, fed by springs, may continue to exist and provide small perennial breeding sites. It has been observed by many workers that S. damnosum adults appear around these rivers immediately they begin to flow, or even shortly before (Crisp, 1956; Grenier, Ovazza & Valade, 855 856 B. B. WADDY 1960). From an unpublished report of the Ghana Medical Field Units (1959) a graphic example may be quoted. " At Sissili bridge no flies had been caught for four- and-a-half months when the first rain of the year fell in a storm on the night of 16th May. The Sissili started to flow about 2.30 p.m. the next day. For the first time that year a few flies were caught on the 18th but in the morning of the 19th 106 were caught by the fly boy between 8 a.m. and 10 a.m.... It is estimated that the nearest breeding site and also the apparent dry season habitat was on the Black Volta well over 100 miles away ... 106 flies caught at a single point in two hours must indicate that thousands of flies were emerging from ' hibernation ' along the Sissili alone." It can be added that the Sissili River, via the Kulpawn River, flows eastwards into the White Volta, i.e., it is not on the same watershed as the Black Volta. If infestation from the Black Volta were to occur, it could not be along a continuous river channel. S. damnosum and the valley ofthe Red Volta Onchocerciasis in the valley of the Red Volta north of Ghana was investigated during the 1930s (Richet, 1939; Puyuelo & Holstein, 1950). Blindness rates of over 30% were recorded, and the valley in this area is now completely depopulated. The 30 miles (50 km) of its course in Ghana run through one of the most densely populated areas in the whole of the West African savanna, yet the valley itself is deserted (see Fig. 1). The northerly limit of S. dam- nosum breeding is now being extended by the building of many small dams intended to provide water for agriculture; each new spillway is a poten- tial breeding site. The Red Volta is a simple river, having virtually no tributaries. No S. damnosum can be found in its environs during the dry season, yet swarms of flies have been found, repeatedly, at the moment when it begins to flow again. The dry-season breeding places downstream are known, and it will be of the greatest interest and importance to find out whether the flies will appear so promptly if these sites are subjected to control measures during the dry season. If a relatively simple dry-season operation can pre- vent the river from being reinfested, a great advan- tage will have been gained. If flies do appear, it will be known that they have come from another river system, and their source will have to be in- vestigated by means of tagging and trapping tech- niques (no easy matter with S. damnosum). The author has been familiar with the valley of the Red Volta for over 20 years, and it has always seemed to him that this valley, running deserted and eroded between dense populations of water- and land-hungry farmers (whose traditional farming land it used to be), is the ideal location for a first attempt to regenerate such a valley. The result to be aimed at is a valley full of farms, with the water- shed on each side re-afforested and protected so that the river itself can be restored to perennial flow. If this were achieved, continued Simulium control could be paid for by taxes on agricultural produce. Similium control is only one step towards this end, though an essential one. Much research has been devoted to the relevant problems of potential soil productivity and human ecology in this area. A team in which economics, agriculture, anthropo- logy, entomology and all the other relevant disci- plines were represented would find a considerable amount of data already available, certainly more than in any other comparable area. POSTSCRIPT Since this paper was first written, and partly as a result of it, a combined technical meeting was held in July 19681 under the sponsorship of the United States Agency for International Development (US-AID), the Organisation de Coordination et de Cooperation pour la Lutte contre les Grandes End6mies (OCCGE) and the World Health Organi- zation (WHO), at which economists joined epide- miologists and entomologists in agreeing that onchocerciasis control in West Africa is feasible and economically important, and that the Volta basin should be the chosen area for commencing control operations. 'Joint US-AID/OCCGE/ WHO technical meeting on the feasibility of onchocerciasis control, Tunis, 1-8 July, 1968 (unpublished working document WHO-ONCHO/69.75). A limited number of copies of this document is available to persons officially or professionally interested on application to Distribution and Sales, World Health Organization, 1211 Geneva, Switzerland. PROSPECTS FOR THE CONTROL OF ONCHOCERCIASIS IN AFRICA 857 ACKNOWLEDGEMENTS It is a pleasure to acknowledge the invaluable help in preparation of this document provided by discussion with M6decin G6n6ral P. Richet, Secr6taire g6n6ral, OCCGE, M6decin Commandant Causse, Officer in charge of Centre Muraz, Bobo Dioulasso and Dr M. Ovazza, Maitre de Recherche, Onchocerciasis Section, OCCGE. RtSUMt PERSPECTIVES DE LA LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE, ET PLUS PARTICULItREMENT DANS LE BASSIN DE LA VOLTA L'onchocercose, maladie provoquee par la filaire Onchocerca volvulus, sdvit dans les territoires draines par les grands reseaux fluviaux de l'Afrique au sud du Sahara et au nord de 1'equateur. On trouve aussi des foyers d'en- d6micite jusque vers 100 de latitude sud. Les principales zones d'hyperend6micit6 sont situees au Senegal, en Guinee, au Mali, au Nigeria, au Tchad, au Congo (Repu- blique democratique), en Republique centrafricaine, au Soudan, en Ouganda, au Kenya et dans toutes les regions de savane du bassin de la Volta (Haute-Volta, C6te d'Ivoire, Ghana, Togo et Dahomey). Les atteintes l6geres ne suscitent que peu ou pas de sympt6mes. Par contre, les infections massives, surtout si elles sont acquises precocement et entretenues par des reinfections successives, peuvent entrainer la cecite ou causer une dermatose extremement prurigineuse, la gale filarienne. Dans certains villages oui l'affection est hyper- endemique, on a releve des taux de cecite atteignant 10% et meme parfois plus de 30%. Les vecteurs de l'onchocercose en Afrique sont Simu- lium damnosum et S. neavei. En dehors de leur r6le dans la transmission de la maladie, ils representent par leurs essaims un veritable fleau. Ils sont a l'origine de serieuses difficultes lors de la realisation de certains projets, comme la construction de digues, et sont responsables de la depo- pulation des vallees fluviales dans les regions de savane. Ils entravent les travaux agricoles et la peche. S. neavei a un rayon de vol court, et on peut detruire ses gites larvaires les uns apres les autres par des campagnes distinctes. S. damnosum est beaucoup plus difficile a combattre: son aire de dispersion est tres etendue, et si l'on traite isole- ment un gite larvaire ou meme tout un cours d'eau, on assiste rapidement a une rdinfestation. Le bassin de la Volta se prete particulierement a l'etude prdliminaire des problemes epidemiologiques, biologiques et pratiques que pose la lutte a grande echelle contre l'onchocercose transmise par S. damnosum. On y trouve une zone out l'end6micite onchocerquienne est la plus forte du monde, avec des taux de c-cite tres eleves et un probleme aigu de depopulation. Des deux medicaments actifs contre les infections fila- riennes, la suramine et la di6thylcarbamazine, aucun n'est utilisable pour le traitement de masse en Afrique. Un autre compos6, le Mel W, s'est reve1l beaucoup trop toxique et a dfi etre rejete. Le seul moyen actuel de lutte contre l'onchocercose est de s'attaquer au vecteur. Les applications de DDT conviennent parfaitement a la des- truction des larves dans les grands fleuves a cours regulier; dans les petits cours d'eau a debit variable, 1'elimination des gites larvaires est plus malaisee. II est cependant indis- pensable de mettre au point une forme de traitement de masse depourvue de danger, car la maladie continue a evoluer pendant de nombreuses ann6es chez les personnes de'ja atteintes. Les connaissances sur le comportement de S. damnosum adulte sont, pour le moment, encore tres fragmentaires, notamment en ce qui regarde les habitudes d'alimentation et de repos, la survie pendant la saison seche ou la dis- tance de vol. Un des principaux problemes pratiques a resoudre est la prevention de la reinfestation des zones oui le vecteur a ete elimine. REFERENCES Bamley, G. R. (1958) Proc. Tenth. Int. Congr. Ent., 3, 535 (quoted by Brown, 1962) Barnley, G. R. & Prentice, M. S. (1958) E. Afr. med. J., 35, 475 Blanc, M., d'Aubenton, F., Ovazza, M. & Valade, M. (1958) Bull. Inst. franc. Afr. noire, 20, Serie A, p. 634 Brown, A. W. A. (1962) Bull. Wld Hlth Org., 27, 632 Browne, S. G. (1960) Bull. ent. Res., 51, 9 Crisp, G. (1956) Simulium and onchocerciasis in the Northern Territories of the Gold Coast, London, Lewis Davies, J. B., Crosskey, R. W., Johnston, M. R. L. & Crosskey, M. E. (1962) Bull. Wld Hlth Org., 27, 491-510 Davies, L., Downe, A. E. R., Weitz, B. & Williams, C. B. (1962) Trans. roy. ent. Soc. Lond., 114, 21 Duke, B. 0. L. (1963) Ann. trop. Med. Parasit., 57, 82 858 B. B. WADDY Fairclough, H. & Thomson, W. E. F. (1958) E. Afr. agric. J., 23, 186 Garnham, P. C. C. & McMahon, J. P. (1947) Bull. ent. Res., 37, 619 Grenier, P., Ovazza, M. & Valade, M. (1960) Bull. Inst. frang. Afr. noire, 22, Serie A, 892 Hissette, J. (1932) Ann. Soc. belge med. trop., 12, 433 Hocking, B. (1950) Sci. Agric., 30, 489 (quoted by J. B. Davies et al., 1962) Hocking, B., Twinn, C. R. & McDuffie, W. C. (1949) Sci. Agric., 29, 69 (quoted by J. B. Davies et al., 1962) Hughes, M. H. (1952) W. Afr. med. J., 1, 16 Hynes, H. B. N. (1960) Ann. trop. Med. Parasit., 54, 331 Jordan, P. (1958) Brit. J. Pharmacol., 13, 318 Kernaghan, R. J. (1961) J. trop. Med. Hyg., 64, 303 Le Berre, R. (1966) Contribution a' l'etude biologique et ecologique de Simulium damnosum Theobald 1903, Paris, Office de la Recherche Scientifique et Technique Outre-Mer McMahon, J. P., Highton, R. B. & Goiny, H. (1957) Bull. WId HIth Org., 19, 75 Marr, J. D. M. (1961) Bull. Wld Hlth Org., 27, 622 Mouchet, J. (1962) L'Eradication des glossines aux confins du Nord-Cameroun et du Tchad. In: Inter- national Scientific Committee for Trypanosomiasis Re- search, Ninth meeting, Conakry, Commission for Tech- nical Co-operation in Africa South of the Sahara (Publication No. 88), p. 229 Nelson, G. S. & Grounds, J. G. (1958) E. Afr. med. J., 35, 365 Noamesi, G. K. (1962) Bull. Wld Hlth Org., 27, 620 Noel-Buxton, M. B. (1956) J. W. Afr. sci. Ass., 2, 36 Puyuelo, R. & Holstein, M. R. (1950) Med. trop., 10, 397 Quelennec, G. (1962) Med. trop., 22, 463 Richet, P. (1939) Bull. Soc. Path. exot., 32, 341 Rivas, A., Gonzales, G. L., Zsogon, L., Rasi, E. & Convit, J. A. (1965) Acta med. venez., Suppl. 1 Suzuki, R., Ito, Y. & Harada, S. (1963) Jap. J. exp. Med., 33, 41 (abstract in Trop. Dis. Bull., 1964, 61, 221) Taufflieb, R. (1955) Bull. Soc. Path. exot., 48, 564-576 Waddy, B. B. (1966) Trans. roy. Soc. trop. Med. Hyg. 62, 727 Wanson, M. (1950) Contribution a l'etude de l'oncho- cercose africaine humaine, Bruxelles, Goemaere Wanson, M., Courtois, L. & Lebied, B. (1949) Ann. Soc. belge med. trop., 29, 373 Woodruff, A. W., Bell, S., Ridley, D. S. & Schofield, F. D. (1958) Trans. roy. Soc. trop. Med. Hyg., 52, 97 WHO Expert Committee on Onchocerciasis (1954) Wld Hlth Org. techn. Rep. Ser., 87