The introduction of Melanoides tuberculata (Mollusca: Thiaridae) to the island of Saint Lucia (West Indies) and its role in the decline of Biomphalaria glabrata, the snail intermediate host of Schistosoma mansoni.
ABSTRACT A malacological survey was carried out in May 1992 in the whole hydrographic system of Saint Lucia 11 years after the end of a biological control programme to eliminate Biomphalaria glabrata, the snail intermediate host of Schistosoma mansoni. A competitor snail, Melanoides tuberculata, was introduced to Saint Lucia in 1978 and field experiments in several habitats were conducted by Prentice between 1978 and 1986. At the present time M. tuberculata is the most common freshwater snail in Saint Lucia. The results of the survey, undertaken in sites where B. glabrata occurred in large populations in the past showed (i) the absence of the snail hosts from seven sites now extensively colonized by the competitor (ii) the presence of B. glabrata in low or very low densities in 17 sites together with the competitor and (iii) the presence of the intermediate hosts in large populations in only two sites where M. tuberculata was absent. These results confirm the positive results observed by Prentice. The presence of another planorbid snail, B. straminea, is reported for the first time in Saint Lucia.
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ABSTRACT: A survey on the preponderance of Mollusca in Owan River, Edo State, Nigeria was conducted to ascertain the composition, distribution and diversity of Mollusca for a period of twelve (12) months spanning from September, 2010 to August, 2011, in four well marked out stations. Monthly samples of mollusca were collected using the kick sampling method with a D-frame net (800 μm mesh) size and also hand picking was done randomly in each station. Water samples for physicochemical parameters were also collected monthly at the four stations. The water pH was slightly acidic (6.1 – 7.6), water temperature ranged from 23.2 – 27.6oC, salinity, 0.01 – 0.0350/00 and alkalinity 28.7 – 38.9 mgl-1. A total of 3630 Mollusca were collected during the study period. The Mollusca were represented by four species which include; Potadoma moerchi, Melanoides tubaculata and Melanoides moerchi of the family Thiaridae and Pseudospatha sp. of the family Unionidae. Potadoma moerchi was represented by 2309 individuals which is the most abundant species during the entire survey, followed immediately by Melanoides tuberculata (1145). More Mollusca were recorded in station 4, followed by station 3 and the least composition was found in station 1. Melanoides tuberculata was found mostly in the clayey and loamy substrate as was observed in station 4. Analysis of species diversity revealed that the highest number of taxa richness was recorded in station 4 while stations 2, 3 and 4 showed no significance differences (p>0.05) in species diversity. The study reveals the abundance of Mollusca in Owan River. The presence of Melanoides tuberculata which is an intermediate host to the trematode; Centrocetus species, Paragonimus species and Clonorchis species may spread infection to fish, aquatic birds and humans in the study area. On the other hand it presence may also help in the biological control of schistosomiasis agent because it competes and prey on the Planorbid snails, Biomphalaria, an intermediate host of Schistosoma mansoni. From the foregoing, it can be inferred that, the absence of the genus Biomphalaria in the study area may be attributed to the abundance of Melanoides tuberculata. Key words: Owan River, Mollusca, Melanoides tuberculata, Biological Control, Schistosomiasis
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ABSTRACT: Biomphalaria glabrata snails play an integral role in the transmission of Schistosoma mansoni, the causative agent for human schistosomiasis in the Western hemisphere. For the past two decades, tremendous advances have been made in research aimed at elucidating the molecular basis of the snail/parasite interaction. The growing concern that there is no vaccine to prevent schistosomiasis and only one effective drug in existence provides the impetus to develop new control strategies based on eliminating schistosomes at the snail-stage of the life cycle. To elucidate why a given snail is not always compatible to each and every schistosome it encounters, B. glabrata that are either resistant or susceptible to a given strain of S. mansoni have been employed to track molecular mechanisms governing the snail/schistosome relationship. With such snails, genetic markers for resistance and susceptibility were identified. Additionally, differential gene expression studies have led to the identification of genes that underlie these phenotypes. Lately, the role of schistosomes in mediating non-random relocation of gene loci has been identified for the first time, making B. glabrata a model organism where chromatin regulation by changes in nuclear architecture, known as spatial epigenetics, orchestrated by a major human parasite can now be investigated. This review will highlight the progress that has been made in using molecular approaches to describe snail/schistosome compatibility issues. Uncovering the signaling networks triggered by schistosomes that provide the impulse to turn genes on and off in the snail host, thereby controlling the outcome of infection, could also yield new insights into anti-parasite mechanism(s) that operate in the human host as well.Frontiers in Genetics 07/2014; 5:230. DOI:10.3389/fgene.2014.00230