Name: Tsafack, F. Home Country: Cameroon Research Country: Cameroon Project period: 1994-1997 Type: Ph.D. Thesis Title Ecology of schistosome intermediate hosts in the Benue Upper-Valley area Abstract A hydroelectric dam began operating at Lagdo, Benue Division, Far Northern Province of Cameroun in 1984. In 1987, a large-scale irrigation project was started covering an area of200 ha at Gounougou (about l km from the Lagdo Dam). Recently, i.e. in 1994, an additional 800 ha was added covering three villages (Labare, Ouro-Doukoudje and Bessoum at 5 to 10 km away from the dam). Previous studies have shown that schistosome intermediate hosts quickly started to colonise the new habitats. Urinary schistosomiasis is highly prevalent in the area and it is becoming an increasingly important public health problem. For example, in the village Gounougou located in the area which was first brought under irrigation, the prevalence of Schistosoma haematobium infection increased from 21% in 1986, to 29% in 1989, to 45% in 1993 and recently, it was reported to be 53.3%. Despite this increasingly alarming situation, little work has been done on the transmission pattern of the disease in the area. The study area provides a great variety of ecological situations within relatively short distances, i.e. the lake environment, the irrigated area for rice cultivation and the area with traditional rainfed farming. Transmission patterns of urinary schistosomiasis were believed to be highly variable between the environments. The present work was undertaken to compare the ecology of the intermediate hosts and transmission patterns of schistosomes among the different environments in the Benue Upper- Valley area. This work is summarised in six manuscripts, which are in preparation for publication. Manuscript 1 concerns the distribution of freshwater snails in the Lagdo Dam area, Northern Cameroun detailing the results from three surveys carried out at three different periods of the year between March 1994 and December 1995. The study was undertaken to determine the distribution of freshwater snails within each of the three areas, with special reference to the intermediate hosts of schistosomiasis, and to relate distribution patterns to ecological factors such as habitat and various biological, physical and chemical factors. A total number of 13 snail species were recorded in the area among which five were potential schistosome intermediate hosts, namely Bulinus globosus, B. truncatus, B. forskalii, B. senegalensis, and Biomphalaria pfeifferi. Biomphalaria pfeifferi was commonly found in the lake and in the irrigation scheme. This species was also found in one of the seasonal streams outside the irrigated area. High densities of B. pfeifferi occurred in irrigation canals but schistosome infected specimens were only found in the sites along the lakeshores, close to fishermen settlements. Bulinus truncatus was limited to the lake area and the irrigation scheme where it occurred in all types of canals and rice fields. Schistosome infected B. truncatus were collected both in the lake and in the drains. B. globosus was common in temporary habitats both within the irrigation scheme and in the area outside the scheme. B. forskalii was widely spread from the lake area to the area outside the irrigation scheme. Density of aquatic macrophytes was high in almost all types of the irrigation canals. This was mainly due to the poor maintenance status of the canals and the Jack of a proper management of the irrigation water by farmers. The lake and the irrigation canals play an important role in the transmission of schistosomiasis in the area, but the possible contribution to the transmission by temporary habitats where B. globosus and B. senegalensis occur most, needs further elucidation. The present Study reports for the first time the colonisation of the Lagdo irrigation scheme by B. pfeifferi and B. globosus and the occurrence of naturally infected B. truncatus and B. pfeifferi. Manuscript 2 deals with the rapid colonisation of an irrigation scheme at Lagdo (Benue Valley, Northern Cameroun) by B. pfeifferi (Krauss, 1848) and B. globosus (Morelet, 1866) intermediate hosts of Schistosoma mansoni and S. haematobium respectively. The population densities, size distributions and the permanency of populations of B. pfeifferi, an intermediate host snail of S. mansoni in Cameroun, and B. globosus, an intermediate host of S. haematobium, were Studied in the two parts of the irrigation scheme in the Lagdo Dam area from March 1994 to December 1995. In one part (Gounougou) irrigation started in 1987 and in the other (Ouro-Doukoudje) irrigation started in 1994. The purpose was to determine and to compare the state of colonisation of the two schemes by B. pfeifferi and B. globosus. The findings of this study revealed that B. pfeifferi and B. globosus have been introduced into the two schemes. B. pfeifferi has succeeded in establishing permanent populations in the irrigation canals at Gounougou and is rapidly colonising the newly irrigated area at Ouro-Doukoudje where permanent populations are established in same canals. Apparently, B. globosus is still making its way into the two schemes. The overall density of B. pfeifferi is higher in the irrigation canals at Gounougou than in those at Ouro-Doukoudje. This species showed a great variation among sites in both density and fluctuation patterns. The density of B. globosus was higher in the newly irrigated scheme. Weed clearance of irrigation canals and drains is neglected and they are often overgrown with aquatic plants at their middle or terminal parts. B. pfeifferi seems to be associated with Potamogeton sp. and filamentous algae, particularly in the main canal where high densities of B. pfeifferi were found regularly in the floating mats of Potamogeton sp. At Ouro-Doukoudje, B. globosus was associated with Cyperus sp. and Echinocloa sp. Manuscript 3 deals with the ecology of freshwater snails in the Lagdo lake, Northern Cameroun, with special reference to schistosome intermediate hosts. The study was undertaken to investigate the density fluctuations in the populations of intermediate host snails and the fluctuation in the number of schistosome infected snails in relationship to ecological parameters in the man-made lake and thereby to identify the most important transmission period in the lake. The Study was done during the period March 1994 to December 1995, in three selected villages along the shore of the man-made Lagdo lake. Schistosome intermediate hosts, B. pfeifferi and B. truncatus underwent great seasonal variation in density. Low densities were found at the end of the rally season, just before the lake reached its maximum level. The density increased during the cold part of the dry season and the peak densities were reached during the early draw-down phase of the lake level. The two species differed in their patterns with the population density increase for B. truncatus starting one to two months earlier than that of B. pfeifferi. The main factors responsible for these fluctuations were related to the fluctuations in the lake level, rainfall, inflow of snails during the early torrential rains, temperature and aquatic vegetation. Transmission of S. haematobium by B. truncatus and that of S. mansoni by B. pfeifferi takes place almost during the same period of the year, i.e. from September to April, which is throughout the dry season. In same swamps close to the lake B. senegalensis was found. It was also found sporadically in the lake. The implications of these findings on schistosomiasis control through snail control are discussed and recommendations are given with regard to a snail control programme. Manuscript 4 deals with the ecology of schistosome intermediate hosts in irrigation canals in the Lagdo scheme, Northern Cameroun. This study was carried out to provide detailed information on the density fluctuation patterns of the intermediate hosts in the irrigation system at Lagdo, in relation to environmental factors. Snail sampling was done at monthly interval s from March 1994 to December 1995. Biomphalaria pfeifferi, B. globosus, B. truncatus and B. forskalii varied greatly in population densities between habitats but the seasonal density fluctuations showed the same pattern. The most important factor affecting the fluctuation in density of snails is the fluctuation in water level in the canals associated with the rice cycles. The lack of proper water management by the farmers and the poorly maintained state of the canals have led to a permanent presence of water and an overgrowth of aquatic plants in the canals. Consequently, high densities of snails were found in all the canal types. Potamogeton sp. and Ceratophyllum sp., previously found only in the lake, have rapidly colonised the whole irrigation scheme. The density of B. pfeifferi showed a positive correlation with the density of Potamogeton sp. Schistosome infected B. truncatus were found once in a drainage canal close to the village Gounougou. However, schistosome transmission might be taking place throughout the year in the irrigation scheme even though infected snails were found only on one occasion. Recommendations are given regarding snail control, such as proper water management and weed clearance of canals, among other measures. Manuscript 5 deals with density fluctuations of schistosome intermediate hosts in seasonal ponds and streams around the Lagdo Dam area, Northern Cameroun. The study was undertaken to investigate the density fluctuations in the populations of intermediate host snails in relationship to ecological parameters in temporary ponds and streams. The results show that B. senegalensis is widely spread in the temporary habitats where it often occurs in mixed populations with B. forskalii. In fact B. senegalensis occurred alone only in one site. B. globosus was common and it occurred in ponds and seasonal streams. B. truncatus does not occur in temporary habitats but seems to prefer permanent breeding sites and may tolerate only short periods of desiccation. In the ponds and marshes, snail densities are affected by rainfall and desiccation of the sites. Moreover, human interactions in many of the ponds and marshes in terms of brick making introduced an important factor. In the seasonal streams, the flushing out of snails by the torrential rains and the high temperatures in the small water pockets are the main factors affecting snail populations. The present data suggest that B. globosus is responsible for the transmission of S. haematobium in the area outside the irrigation scheme. However, the presence of B. senegalensis in the temporary habitats adds to the complexity of the transmission of schistosomiasis in the area. There is a need for further investigations to determine the role of this species in the transmission of urinary schistosomiasis in the Lagdo area. Manuscript 6 deals with the separation of B. senegalensis Müller 1781 and B. forskalii (Ehrenberg 1831), two closely related snail species of the B. forskalii group in the Benue Upper- Valley area, the sub-sahelian semi-arid Northern Cameroun. This work was an attempt to segregate two closely resembling snail species B. senegalensis and B. forskalii on the basis of shell morphology, in order to contribute to the development of useful tools for field taxonomy in areas where these species are present. During the period of March 1994-December 1995, snails were collected from different habitats including the lake, irrigation canals, rice fields, seasonal streams, ponds, marshes and burrow pits. The following shell characteristics were examined: the shoulder angle (carination), the degree of costulation (ribs) and the overall shape of the shell. After segregation on the basis of shell morphology, enzyme electrophoresis was used for confirmation. The results showed that B. senegalensis and B. forskalii presented considerable morphological variations within species. All the snails classified as B. forskalii on the basis of shell morphology (i.e. the presence of a more or less pronounced shoulder angle), were confirmed as belonging to this species by the electrophoresis. Two out of a total of 44 specimens were wrongly identified (absence of shoulder angle) as B. senegalensis. Involved research institutions Faculty of Medicine and Biomedical Sciences, University of Yaoundé, Cameroun Department of Population Biology, Zoological Institute, University of Copenhagen Institute for Health Research and Development Supervisor(s) A. Same-Ekobo, Centre Hospitalier et Universitaire de Yaoundé, Cameroun H. Madsen, DBL Correspondence