Differentiation of Bulinus senegalensis and Bulinus forskalii Snails in West Africa Using Morphometric Analysis.

PURPOSE: Accurate identification of medically important intermediate host and vector species is crucial for understanding disease transmission and control. Identifying Bulinus snails which act as intermediate host species for the transmission of schistosomiasis is typically undertaken using conchological and genital morphology as well as molecular methods. METHODS: Here, a landmark-based morphometric analysis of shell morphology was undertaken to determine its utility to distinguish the closely related and morphologically similar sister species Bulinus senegalensis and Bulinus forskalii. The method was developed to increase the accuracy of conchological morphology methods to identify Bulinus species in the field. Both species are found in West Africa, but only B. senegalensis is implicated in the transmission of urogenital schistosomiasis. RESULTS: We found when scaled down to the same length, 3-whorl and 4-whorl (juvenile) B. senegalensis shells had a longer spire, narrower body whorl and shorter aperture than B. forskalii. In contrast, 5-whorl (adult) B. senegalensis had a shorter spire, but still had a shorter aperture and narrower body whorl than B. forskalii. Canonical Variate Analysis (CVA) showed minimal overlap between B. senegalensis and B. forskalii for 3-whorl and 4-whorl shells, with a clear separation for 5-whorl shells. Overall, B. senegalensis had a consistently shorter aperture size and narrower body whorl than B. forskalii for all development stages. Spire length was variable depending on the stage of development, with 3-whorl and 4-whorl shells having the opposite trends of adult shells. CONCLUSIONS: Our study demonstrates the applicability of landmark-based morphometrics in distinguishing the medically important, Bulinus senegalensis from its morphologically similar sister species, Bulinus forskalii. We recommend using measurements based on spire length, penultimate whorl length, body whorl width and aperture size to differentiate B. senegalensis and B. forskalii, when used with the appropriate information for each shell's development stage.

DIVERSITY AND COMPARATIVE STUDIES ON BULINUS SNAILS COLLECTED FROM TWO LOCALITIES IN EGYPT.

A comparative study of the shell structure, seasonal temperature and Calcium content of Bulinus snails from two areas (Damietta and Giza) in Egypt was done and compared with laboratory snails from Schistosome Biological Supply Center (SBSC). The shells of collected snails identified as Bulinus truncatus, showed a wide variation in shape. The results showed a significant differences were detected between the populations from SBSC and Damietta (p<0.05) for mean of measured shell width, aperture length, length of spire and number of whorls. The populations from Giza and Damietta governorates showed significant differences (P<0.05) in mean of measured length of diagonal, length of body whorl above aperture, length of spire and number of whorls. There were no statically significant differences between the populations from SBSC and Giza. The seasonal temperature affected on susceptibility of snails to infection with Schistosoma haematobium. The. mean prepatent period was short in summer and long in winter. The shells of S. haematobium - infected B. truncatus snails showed hypocalcifiction from all localities.

Malacological survey and geographical distribution of vector snails for schistosomiasis within informal settlements of Kisumu City, western Kenya.

BACKGROUND: Although schistosomiasis is generally considered a rural phenomenon, infections have been reported within urban settings. Based on observations of high prevalence of Schistosoma mansoni infection in schools within the informal settlements of Kisumu City, a follow-up malacological survey incorporating 81 sites within 6 informal settlements of the City was conducted to determine the presence of intermediate host snails and ascertain whether active transmission was occurring within these areas. METHODS: Surveyed sites were mapped using a geographical information system. Cercaria shedding was determined from snails and species of snails identified based on shell morphology. Vegetation cover and presence of algal mass at the sites was recorded, and the physico-chemical characteristics of the water including pH and temperature were determined using a pH meter with a glass electrode and a temperature probe. RESULTS: Out of 1,059 snails collected, 407 (38.4%) were putatively identified as Biomphalaria sudanica, 425 (40.1%) as Biomphalaria pfeifferi and 227 (21.5%) as Bulinus globosus. The spatial distribution of snails was clustered, with few sites accounting for most of the snails. The highest snail abundance was recorded in Nyamasaria (543 snails) followed by Nyalenda B (313 snails). As expected, the mean snail abundance was higher along the lakeshore (18 ± 12 snails) compared to inland sites (dams, rivers and springs) (11 ± 32 snails) (F(1, 79) = 38.8, P < 0.0001). Overall, 19 (1.8%) of the snails collected shed schistosome cercariae. Interestingly, the proportion of infected Biomphalaria snails was higher in the inland (2.7%) compared to the lakeshore sites (0.3%) (P = 0.0109). B. sudanica was more abundant in sites along the lakeshore whereas B. pfeifferi and B. globosus were more abundant in the inland sites. Biomphalaria and Bulinus snails were found at 16 and 11 out of the 56 inland sites, respectively. CONCLUSIONS: The high abundance of Biomphalaria and Bulinus spp. as well as observation of field-caught snails shedding cercariae confirmed that besides Lake Victoria, the local risk for schistosomiasis transmission exists within the informal settlements of Kisumu City. Prospective control interventions in these areas need to incorporate focal snail control to complement chemotherapy in reducing transmission.

Identification of snails within the Bulinus africanus group from East Africa by multiplex SNaPshot trade mark analysis of single nucleotide polymorphisms within the cytochrome oxidase subunit I.

Identification of populations of Bulinus nasutus and B. globosus from East Africa is unreliable using characters of the shell. In this paper, a molecular method of identification is presented for each species based on DNA sequence variation within the mitochondrial cytochrome oxidase subunit I (COI) as detected by a novel multiplexed SNaPshotTM assay. In total, snails from 7 localities from coastal Kenya were typed using this assay and variation within shell morphology was compared to reference material from Zanzibar. Four locations were found to contain B. nasutus and 2 locations were found to contain B. globosus. A mixed population containing both B. nasutus and B. globosus was found at Kinango. Morphometric variation between samples was considerable and UPGMA cluster analysis failed to differentiate species. The multiplex SNaPshotTM assay is an important development for more precise methods of identification of B. africanus group snails. The assay could be further broadened for identification of other snail intermediate host species.

A comparison of Bulinus africanus group species (Planorbidae; Gastropoda) by use of the internal transcribed spacer 1 region combined by morphological and anatomical characters.

The morphological and anatomical characters applied to determine species identity in the Bulinus africanus group species are insufficient to unambiguously discriminate between arbitrary species of given populations. In order to solve this problem, four snail populations from Kenya have been investigated morphologically and anatomically, and the species status compared with the result of molecular methods. We have amplified the entire ITS region and found that the investigated populations showed intra-specific genetic polymorphism, thereby giving the taxa an identity which were indistinct when the region was cut with restriction enzymes. Instead, an amplification of the sub-region ITS 1 revealed an unambiguous identification. because the amplification revealed only one single fragment. We also found that the observed heterogeneity of the entire ITS region could be confined to the sub-region ITS 2. Furthermore, the micro-sculpture of the shell and penis to preputium proportion, which are normally applied as morphological characters, might be considered as inadequate, because of the lack of a significant difference in those characters between the two well established species, namely B. africanus and B. nasutus in the Kisumu area. Instead, these two taxa were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to be one single species with a highly variable morphology. This result was further confirmed by random amplified polymorphic DNA (RAPD) data and the mitochondrial cytochome oxidase subunit I (COI).

Gross histopathological effects of an extract of Agave attenuata on the epithelium of the digestive tract of Bulinus africanus.

A lethal concentration of a crude, aqueous extract of Agave attenuata was applied as a contact poison to Bulinus africanus, the intermediate host of Schistosoma haematobium, for a 24-h period. The gross histopathological effects of the extract on the epithelium of the digestive tract were then studied. A graded series of cellular injuries to the epithelial layer was observed along the length of the tract. These included the loss of cilia and brush border, disruption of the epithelial layer, cellular vacuolation, swelling and rupture, and the discharge of secretory products from mucous gland cells. The results of the microscopy show that epithelial tissue is probably a primary target of the molluscicide. The cytological injuries induced by extracts of A. attenuata indicate that the molluscicide acts by disrupting the osmoregulatory mechanisms of the epithelial cells, but further, detailed studies are required to confirm this.

Interference of Echinoparyphium elegans with the host-parasite system Bulinus truncatus-Schistosoma bovis in natural conditions.

Histological observations of Bulinus truncatus naturally infected by both Schistosoma bovis and Echinoparyphium elegans in Sardinia (Italy) have shown that E. elegans is pathogenic to the mollusc and dominant to the schistosome. The larval stages, rediae and metacercariae, acted as compressors. Rediae, mainly the young and very motile ones, also behaved as predators. The organs of the mollusc were variably affected; the ovotestis totally disappeared. The larval development of the schistosome was disturbed; cercariogenesis was strongly inhibited and gave way to high sporocystogenesis. The intensity of this interference depended on the density of echinostome larvae present.

Ultrastructural changes in the male germ cells of Bulinus truncatus during spermatogenesis.

The structure of the spermatogonia, spermatocytes, spermatids and Sertoli cells of the hermaphroditic snail Bulinus truncatus was studied by electron microscopy. The spermatogonia are small, with relatively large nuclei. The acrosome develops from a small proacrosomal granule which is probably derived from the Golgi apparatus in the spermatocyte stage. Condensation and elongation of the nuclei were found in the spermatids. The shape and components of the Sertoli cells did not change during the spermatogonium and spermatocyte stages. Before spermiation the Sertoli cells have the morphological features of steroid-producing cells. The study showed that the Sertoli cells are involved in the nutrition and transportation of the spermatogenic cells, in spermiation and in hormone production.

[Morphological, biological and biochemical study of a new species of Bulinus (Gastropoda: Planorbidae)]. / Studi morfologici, biologici e biochimici su una nuova specie di Bulinus (Gastropoda: Planorbidae).

A description is given of Bulinus yemenensis, a new species from Yemen belonging to the truncatus group. B. yemenensis is morphologically and biologically differenciated from B. truncatus truncatus, from which it is also electrophoretically distinguishable on the basis of the following enzyme loci: Est-2, Est-3, Pgm-2 and 6-Pgdh among the 26 analysed.

Present situation of schistosomiasis in the Libyan Arab Republic. I. Bilharziasis in Ubari District in Fezzan (Sebha Governorate.

A survey for urinary schistosomiasis was conducted in all the schools (18 in number) of ubari district (Sebha Governorate) of the Libyan Arab Republic. Out of 1874, school pupils examined 99 proved positive at the rate of 5.3 percent. Boys were more infected than girls and the peak of infection was at eleven years. The intensity of infection was light. New foci were detected in five towns and villages brignging up the total number to 20 out of 31. Samples of population in nine towns and villages (about one quarter) were examined covering 1435, with 34 infected at a rate of 2.4 percent. Treatment of infected pupils started with Niridazole at the standard dose, with about 60 percent cure rate. Eleven towns and villages were found to harbour Bulinus snails in some of their farms, increasing the number to 20 out of 31. These snails belong to subgenus Bulinus. However, they fall in four distinctive types based on the variation of shell morphology. Antisnail measures were introduced for the first time using copper sulphate with satisfactory preliminary results.