DISTRIBUTION OF BULINUS AND IN THE SUDAN 949

The Distribution of Bulinus and Biomphalaria in Khartoum and Blue Nile Provinces, Sudan by S. N. WILLIAMS and P. J. HUNTER,a Department ofZoology, University ofKhartoum, Sudan

The genera of aquatic Bulinus and Biom- Vegetation type: R=reeds; G = grass; W = water- phalaria are responsible for the transmission of hyacinth (Eichhornia); V =various (mainly fila- urinary and intestinal schistosomiasis in the Sudan. mentous algae and Potamogeton); 0 = no vegeta- The last survey of these snails in Khartoum and tion. Blue Nile Provinces was in 1958, b, C and there has Vegetation density: 0 =no vegetation; 1 =sparse since been considerable development and extension vegetation; 2 = medium; 3 = thick. of the irrigation systems. It therefore seemed that a Current speed: 0 = stagnant; 1= slow; 2 = medium; new survey was required. 3 =fast. The study area A total of 150 samples was taken and the results The area studied extended from Khogalab, 23 km are shown in Table 1. Results from the Blue Nile north of Khartoum on the main Nile, to Kosti, are not shown in this table, however, as no snails 280 km south of Khartoum on the White Nile, and were found. Other samples containing no snails are across to Sennar, 250 km south of Khartoum on the also not shown in Table 1 if they were from the same Blue Nile as shown in the accompanying figure. type of habitat as the samples that are recorded. Between the two rivers, south of Khartoum, lies the The accompanying figure shows the location of the Gezira irrigation scheme which draws water from the sampling sites. Blue Nile at Sennar. The Manaqil canal, completed Geographical distribution 4 years ago, has extended the scheme further to the south-west and further development is taking place Khartoum. In the Khartoum North area (samples in the north-west. Smaller pump-irrigation systems 1-4 in Table 1) most of the canals in two small pump also take water from the Blue Nile, the White Nile schemes contained Bulinus truncatus (Audouin). A and the main River Nile. few (Krauss) were also The area surveyed can be divided conveniently recorded. into the following regions: Khartoum, Blue Nile, In the Shambat area (samples 7-10 in Table 1) Gezira and White Nile. small pump schemes serve the Ministry of Agri- culture and University farms. A successful treatment Sampling and recording nmethods of canals with copper sulfate a has reduced the Snails were sampled by making 3 sweeps with a previously large number of Bulinus truncatus to the -sampling net (20 cm x 20 cm) from the side of the present occasional occurrence of this species. river or canal. Each sweep was made for a distance Large numbers ofBiomphalaria sudanica (Martens) of 1 metre along the bottom of the river. Where were found in a drain which carries excess irrigation possible, approximately 2 cm of mud were scooped water to the main Nile. Malekb, c recorded the up in the sample and then sifted to extract the snails. species as extending only as far north as Kosti (see The number of snails from the different sites was also section on White Nile). The drain carries recorded in one of 4 categories: (1) 1 ; (2) varying amounts of water and frequently dries up for 2-5 snails; (3) 6-20 snails, and (4) > 20 snails. the greater part of its length. Snails were found Records of environmental characteristics were below the surface mud and rotting vegetation in dry noted as follows: regions of the drain. The non-vector species Bulinus forskalii (Ehren- a Present address: National Agricultural Advisory berg) was also found in the drain and to a lesser Service, Cambridge, England. extent in other canals of the scheme. b Malek, E. (1958a) Bull. Wld Hlth Org., 18, 691-734. c Malek, E. (1958b) Bull. Wld Hlth Org., 18, 785-818. d Malek, E. (1961) Bull. Wid Hith Org., 27, 41-58. 2274F 950 NOTES

THE. SURVEY AREA, SHOWING THE LOCATION OF THE SAMPLING SITES

7771717177777 AGreen Belt

Wad et Turabi

Abu Quta*On\ Abu Meheiriba. OA

ez Zaki Shubei k.

Kilo!

Eo®i)L Quardude*

EXPLANAT ION Genus Butinus Genus Biomphalaria A B. truncatus 0 B. pfeifferi L B. forskalii O B. alexandrina A B. uaandae ( B. sudanica A B. fischerianus O Intermediate alex-pfeiff

o 10 20 30 40 50 Miles 0 10 20 30 40 50 60 70 eo Kilometres TABLE I RELATIONSHIP BETWEEN THE DOMINANCE AND DENSITY OF SNAILS AND ENVIRONMENTAL FACTORS Bulinus Bulinus Biomphalaria Biomphalaria Biomphalaria Bulinus Vegetation truncatus forskalii pfeifferi alexandrina sudanica ugandae Sample No. Current Den- Domi- Den- Domi- Den- Domi- Den- Domi- Den- Domi- Den- Domi- Den- Type sity nancel sity nancel sity nanc sity nancel sity nancel sity nance sity Khartoum 1 V 3 D 2 2 0 R 3 D 3 3 2 G 3 4 1 G 2 D 3 5 0 G 1 3 6 0 V 3 D 3 2 2 7 V 3 D 4 8 0 G 1 D~~~~~~~~~ 9 1 G 3 10 1 G 2 11 0 V 3 D 4 12 0 V 2 D 4 0 Gezira east 13 3 0 3 D 2 14 0 G 3 2 D 3 15 2 V 3 4 D 4 16 0 R 3 D 1 17 1 G 3 D 2 18 1 G 3 3 D 3 19 0 G 3 2 D 4 20 3 V 2 D 2 21 3 R 3 22 0 G 3 D 4 23 2 G 2 1 D 4 24 O V 3 D 4 4 25 2 V 2 D 4 24 26 G 3 D 3 4 27 G 3 4 D Gezira west 28 2 V 3 D 29 0 G 3 D 4 1a 30 G 3 D 2_a 31 2 V 3 3 D 3 32 2 V 3 D 4 33 0 G 2 2 D 4 34 G 2 3 D 4 35 G 3 D 2 D 2 36 2 V 3 D 2 D 2 37 V 3 D 4 2 38 2 V 3 D 2 39 1 G 2 D 4 3 40 2 G 3 D 2 2 41 0 R 2 D 4 1 42 2 V 2 D 3 1 1a 43 1 V 3 D 4 2 44 2 V 2 D 3 2 45 0 G 3 D 4 4 46 G 3 D 2 47 2 V 3 D 4 3 48 1 G 1 3 1 49 1 G 2 D 4 White Nile 50 0 G 2 2 51 0 0 0 D 2 52 0 W 3 D 4 3 3 2 53 V 3 D 2 54 0 W 3 D 3 2 3 55 G 3 D 2 56 20 W 3 2 D 3 57 0 R 0 58 2 W 3 D 4 2 3 59 W 3 D 3 60 1 W 3 D 4 3 61 2 G 2 2 2 62 0 V 3 D 3 2 D 3 D 3 D 3 63 1 V 2 D 2 64 0 V 3 D 65 0 W 3 D 3 66 0 G 0 1 67 0 W 2 D 3 D 2 68 0 W 2 2 D 3 69 0 G 3 D D

a Intermediate B. alexandrinalpfeiffei types. 952 NOTES

In the Khogalab region (samples 5-6 in Table 1) border to the confluence with the White Nile at pump-irrigation canals are present and were found Khartoum the river is fast-flowing and the banks are to contain B. truncatus, B. pfeifferi and also steep. The nature of the bottom varies from rocks B. forskalii. at Roseires to sands and silt nearer Khartoum. The In the Green Belt area (samples 11-12 in Table 1) absence of snails is probably due to the shifting the Forestry Department has a small plantation of nature of the river bed, which does not allow the trees 5 km south of Khartoum. At present the canal growth of plants or algae. Bulinus truncatus and system is not extensive and no snails were found in Biomphalaria pfeifferi were found in the Sennar the eastern sector which is irrigated from the Gezira. reservoir and in pump schemes alongside the river. In the western sector large populations of a White Nile. In contrast to the fast-moving, deep, " forskalii-type " bulinid snail were found. This and relatively confined waters of the Blue Nile, the was identified by Dr G. Mandahl-Barth as possibly wide, slow-moving White Nile with its low and Bulinus fischerianus (Bourguignat). Sewage water is often swampy banks provides an excellent snail used for irrigation in the canals in this sector. habitat. An isolated population of Bulinus ugandaec Most of the surveyed part of the river, except for (Mandahl-Barth) was found in a disused swimming- the 50 km from Jebel Aulia Dam to Khartoum, is bath in the centre of Khartoum. under the immediate influence of the Jebel Aulia Gezira. The Gezira has the highest incidence of reservoir. From Kosti to Jebel Aulia the banks are intestinal schistosomiasis in the Sudan. Canal-water covered with extensive masses of floating papyrus- is used for drinking and washing so that the parasite water-hyacinth swamp. The vegetation is more is easily transmitted between its two hosts. This is dense on the west bank, the direction in which the particularly so during the cotton-picking season, reservoir tends to flood. The position of this vegeta- when workers from western and southern Sudan, tion-mass varies according to the wind strength and Chad and Nigeria come to live by the sides of the direction so that the snails amongst the vegetation canals adjacent to the cotton fields. are continually being distributed around the reservoir. In the eastern part of the Gezira (samples 13-27 This region provided the richest and most varied in Table 1), very high populations of B. pfeifferi were habitat and also the greatest number of species observed during the months February-April. As (samples 50-69 in Table 1). All the species so far well as the normal type of B. pfeifferi, an albino recorded, with the notable exception of B. pfeifferi, variety of the snail was found. This is probably were found. In addition to B. truncatus, Bulinus caused by a lack of tyrosine, important in melanin ugandae (Mandahl-Barth) was distributed from Kosti synthesis, due to a single recessive gene. Ellis f up to the dam at Jebel Aulia, much farther north recorded this as being the case with some British than previously recorded. b. c B. truncatus occurred species of planorbids. In the western Gezira sporadically in the reservoir and very large popula- (samples 28-49 in Table 1), immature specimens were tions of an unusually small race were observed near found with the shell characteristics resembling Khartoum during December, after the flood period. B. pfeifferi but with the soft parts and radula Although some of these snails were mature, none reserpbling (Ehrenberg)- was found with a height of more than 8.7 mm, well (Mandahl-Barth, personal communication). Bulinus below the size attained by the more normal type (up truncatus is also present, often in large populations, to 15 mm). By March, owing to the fall of the water particularly in the west of the region. A few Bulinus level to below the level of the vegetation, the snails forskalii were occasionally found but the distribution had disappeared. N was erratic; greater numbers were found immediately was found throughout the after the annual rains. region as far north as Jebel Aulia. This species is Blue Nile. The survey of the Blue Nile revealed well known from the south of Sudan but has not a complete absence of snails. From the Ethiopian previously been recorded from further north than Kosti. b, c Biomphalaria alexandrina was found to e Mandahl-Barth, G. (1958) Intermediate hosts of extend from Kosti to Jebel Aulia.9 Bulinus forskalii , African Biomphalaria and Bulinus, Geneva (World Health Organization: Monograph Series, No. 37). was found in great numbers at certain localities, f Ellis, A. E. (1926) British snails. A guide to the non- marine of Great Britain and Ireland, Pliocene to g Williams, S. N. & Hunter, P. J. (1967) Nature (Lond.), Recent, Oxford, Clarendon Press. 215, 1408. DISTRIBUTION OF BULINUS AND BIOMPHALARIA IN THE SUDAN 953

TABLE 2 RELATIONSHIP BETWEEN DOMINANCE OF SNAIL SPECIES AND THE SPEED OF THE WATER CURRENT

Species Total

Bulinus truncatus 27 Bulinus ugandae 4 Biomphalaria pfeifferi 15 Biomphalaria sudanica 6 Biomphalaria alexandrina 7

Total 59

particularly at cattle watering-places where the water able to withstand faster-running water than other- was rich in organic matter. species. Table 3 shows the relationship between species Ecological distribution dominance and vegetation type and it is clear that Although the sampling method and definitions of B. truncatus was more common where there was a environment were only by category and therefore mixture of vegetation types (mainly filamentous admitted a considerable degree of error, some algae and Potamogeton). B. ugandae appeared to conclusions can be drawn about the distribution of prefer water-hyacinth, but the distribution of this Bulinus and Biomphalaria species in Sudan. Tables 2, snail was limited mainly to the White Nile where 3 and 4 show the number of samples for the various water-hyacinth was dominant. B. pfeifferi seemed types of habitat in which each species was dominant commonest where the vegetation was dominated by or co-dominant (marked D in Table 1). grass, and B. sudanica and B. alexandrina, like The relationship between species dominance and Bulinus ugandae, were commonest where water- current speed is shown in Table 2 and from this hyacinth was dominant but this again may also have table it is apparent that all species prefer slower- been due to their distribution being limited by running water and also that B. truncatus was better other factors.

TABLE 3 RELATIONSHIP BETWEEN THE DOMINANCE OF SNAIL SPECIES AND VEGETATION TYPE

Species Absent Reeds Grass Eichhor-nia Various F Total

Bulinus truncatus 1 3 10 0 13 27 Bulinus ugandae 0 0 0 3 1 4 Biomphalaria pfeifferi 0 0 10 0 5 15 Biomphalaria sudanica 0 0 2 3 1 6 Biomphalaria alexandrina 1 0 1 2 3 7

Total ] 2 | 3 23 8 23 59 954 NOTES

TABLE 4 RELATIONSHIP BETWEEN DOMINANCE OF SNAIL SPECIES AND VEGETATION DENSITY

Species Absent 1 Sparse f Medium Thick Total

Bulinus truncatus 1 0 7 19 27 Bulinus ugandae 0 0 1 3 4 Biomphalaria pfeifferi 0 0 4 11 15 Biomphalaria sudanica 0 0 1 5 6 Biomphalaria alexandrina 1 0 2 4 7

Total | 2 j 0 { 15 | 42 59

From the relationship between species-dominance These species are now present as far north as and vegetation density shown in Table 4 it can be Khartoum, probably influenced by the extension concluded that all species preferred thick vegetation. north of water-hyacinth, which in 1958 h occurred in the south only. Biomphalaria alexandrina was not Discussion recorded with certainty from the Sudan by Malek, In general, the above observations confirm but now seems common throughout the White Nile Malek's b, c conclusions, that all species prefer and possibly the western region of the Gezira. reasonably stable conditions with fairly dense vegetation and that the environmental requirements * * ofthe various species are broadly similar. The minor differences in these requirements are probably not of We are very grateful to Dr G. Mandahl-Barth for his sufficient importance to merit different control meas- helpful criticism of this paper and for identifying speci- ures for the different species (at least as far as mens and to Dr C. A. Wright for help with identification. Thanks are also due to the Rockefeller Foundation for cultural control is concerned). financial assistance and to the Arid-Zone and the Hydro- It is difficult to establish whether the distribution biological Research Units of the University of Khartoum of these snails has changed in recent years but for transport facilities. Malek boc indicated that Biomphalaria sudanica and B. ugandae extended no farther north than Kosti. A Gay, P. A. (1958) Nature (Lond.), 182, 538-539.