Snail Vectors Research Articles

Global warming induced spread of the highest human fascioliasis hyperendemic area

BackgroundClimate change is driving the occurrence of several infectious diseases. Within a One Health action to complement the ongoing preventive chemotherapy initiative against human fascioliasis in the Northern Bolivian Altiplano hyperendemic area, field surveys showed a geographical expansion of its lymnaeid snail vector. To assess whether climate change underlies this spread of the infection risk area, an in-depth analysis of the long-term evolution of climatic factors relevant for Fasciola hepatica development was imperative.MethodsWe used monthly climatic data covering at least a 30-year period and applied two climatic risk indices, the water-budget-based system and the wet–day index, both of verified usefulness for forecasting fascioliasis transmission in this endemic area. To reveal the long-term trends of the climatic factors and forecast indices, we applied procedures of seasonal-trend decomposition based on locally weighed regression and trend analysis on the basis of linear models. To further demonstrate the changes detected, we depicted selected variables in the form of anomalies.ResultsThis study revealed a notorious climatic change affecting most of the hyperendemic area, with a strong impact on crucial aspects of the fascioliasis transmission. Trends in maximum and mean temperatures show significant increases throughout the endemic area, while trends in minimum temperatures are more variable. Precipitation annual trends are negative in most of the localities. Trends in climatic risk indices show negative trends at lower altitudes or when farther from the eastern Andean chain. However, monthly and yearly values of climatic risk indices indicate a permanent transmission feasibility in almost every location.ConclusionsWarmer temperatures have enabled lymnaeids to colonize formerly unsuitable higher altitudes, outside the endemicity area verified in the 1990s. Further, drier conditions might lead to an overexploitation of permanent water collections where lymnaeids inhabit, favoring fascioliasis transmission. Therefore, the present preventive chemotherapy by annual mass treatments is in need to widen the area of implementation. This study emphasizes the convenience for continuous monitoring of nearby zones for quick reaction and appropriate action modification.Graphical

Chemical Control of Snail Vectors as an Integrated Part of a Strategy for the Elimination of Schistosomiasis-A Review of the State of Knowledge and Future Needs.

WHO promotes the implementation of a comprehensive strategy to control and eliminate schistosomiasis through preventive chemotherapy, snail control, clean water supply, improved sanitation, behaviour change interventions, and environmental management. The transmission of schistosomiasis involves infected definitive hosts (humans or animals) excreting eggs that hatch (miracidia), which infect freshwater snail vectors (also referred to as intermediate snail hosts) living in marshlands, ponds, lakes, rivers, or irrigation canals. Infective larvae (cercariae) develop within the snail, which, when released, may infect humans and/or animals in contact with the water. Snail control aims to interrupt the transmission cycle of the disease by removing the vector snails and, by so doing, indirectly improves the impact of the preventive chemotherapy by reducing reinfection. Snail control was, for many years, the only strategy for the prevention of schistosomiasis before preventive chemotherapy became the primary intervention. Snails can be controlled through various methods: environmental control, biological control, and chemical control. The chemical control of snails has proven to be the most effective method to interrupt the transmission of schistosomiasis. The current review aims to describe the vector snails of human schistosomiasis, present the chemicals and strategies for the control of snails, the challenges with the implementation, and the future needs. Snail control can play a key role in reducing schistosomiasis transmission and, thus, complements other interventions for disease control. There is a need to develop new molluscicide products or new formulations and methods of applications for existing molluscicides that would target snail vectors more specifically.

Immune targets for schistosomiasis control identified by a genome-wide association study of East African snail vectors.

Schistosomiasis, afflicting >260 million people worldwide, could be controlled by preventing infection of freshwater snail vectors. Intestinal schistosomiasis, caused by Schistosoma mansoni, occurs predominantly in Sub-Saharan Africa and is vectored by Biomphalaria sudanica and related Biomphalaria species. Despite their importance in transmission, very little genomic work has been initiated in African snails, thus hindering development of novel control strategies. To identify genetic factors influencing snail resistance to schistosomes, we performed a pooled genome-wide association study (pooled-GWAS) on the offspring of B. sudanica collected from a persistent hotspot of schistosomiasis in Lake Victoria, Kenya, and exposed to sympatric S. mansoni. Results of the pooled-GWAS were used to develop an amplicon panel to validate candidate loci by genotyping individual snails. This validation revealed two previously uncharacterized, evolutionarily dynamic regions, SudRes1 and SudRes2, that were significantly associated with resistance. SudRes1 includes receptor-like protein tyrosine phosphatases and SudRes2 includes a class of leucine-rich repeat-containing G-protein coupled receptors, both comprising diverse extracellular binding domains, suggesting roles in pathogen recognition. No loci previously tied to schistosome resistance in other snail species showed any association with compatibility suggesting that loci involved in the resistance of African vectors differ from those of neotropical vectors. Beyond these two loci, snail ancestry was strongly correlated with schistosome compatibility, indicating the importance of population structure on transmission dynamics and infection risk. These results provide the first detail of the innate immune system of the major schistosome vector, B. sudanica, informing future studies aimed at predicting and manipulating vector competence.

Different metazoan parasites, different transcriptomic responses, with new insights on parasitic castration by digenetic trematodes in the schistosome vector snail Biomphalaria glabrata

BackgroundGastropods of the genus Biomphalaria (Family Planorbidae) are exploited as vectors by Schistosoma mansoni, the most common causative agent of human intestinal schistosomiasis. Using improved genomic resources, overviews of how Biomphalaria responds to S. mansoni and other metazoan parasites can provide unique insights into the reproductive, immune, and other systems of invertebrate hosts, and their responses to parasite challenges.ResultsUsing Illumina-based RNA-Seq, we compared the responses of iM line B. glabrata at 2, 8, and 40 days post-infection (dpi) to single infections with S. mansoni, Echinostoma paraensei (both digenetic trematodes) or Daubaylia potomaca (a nematode parasite of planorbid snails). Responses were compared to unexposed time-matched control snails. We observed: (1) each parasite provoked a distinctive response with a predominance of down-regulated snail genes at all time points following exposure to either trematode, and of up-regulated genes at 8 and especially 40dpi following nematode exposure; (2) At 2 and 8dpi with either trematode, several snail genes associated with gametogenesis (particularly spermatogenesis) were down-regulated. Regarding the phenomenon of trematode-mediated parasitic castration in molluscs, we define for the first time a complement of host genes that are targeted, as early as 2dpi when trematode larvae are still small; (3) Differential gene expression of snails with trematode infection at 40dpi, when snails were shedding cercariae, was unexpectedly modest and revealed down-regulation of genes involved in the production of egg mass proteins and peptide processing; and (4) surprisingly, D. potomaca provoked up-regulation at 40dpi of many of the reproduction-related snail genes noted to be down-regulated at 2 and 8dpi following trematode infection. Happening at a time when B. glabrata began to succumb to D. potomaca, we hypothesize this response represents an unexpected form of fecundity compensation. We also document expression patterns for other Biomphalaria gene families, including fibrinogen domain-containing proteins (FReDs), C-type lectins, G-protein coupled receptors, biomphalysins, and protease and protease inhibitors.ConclusionsOur study is relevant in identifying several genes involved in reproduction that are targeted by parasites in the vector snail B. glabrata and that might be amenable to manipulation to minimize their ability to serve as vectors of schistosomes.

Historic water quality patterns in endemic schistosomiasis regions of southern Africa: Implications for disease vector distribution

Alterations in atmospheric temperature and rainfall have a major influence on the distribution patterns of vector-borne diseases, including schistosomiasis, by changing the optimum habitat of the intermediate hosts (vectors) that transmit these diseases. Water quality degradation and the creation of artificial freshwater habitats may widen or restrict the distribution of disease vectors. Understanding the influence of water quality on ecosystems is essential in determining the environments that vectors thrive in and where potential outbreaks of the disease they carry will occur. This study aims to analyse the changes in various water quality variables between 1977 and 2009 in the Mbombela river systems and how this may have altered the presence of schistosomiasis snail vectors in these areas. Historical water quality data for the Sabie, Kaap, Komati and Crocodile rivers were obtained from the Department of Water and Sanitation monitoring stations and separated into three decades (1977–1987; 1988–1998 and 1999–2009). The Physicochemical Driver Assessment Index (PAI) was used to determine the ecological category of the rivers in each decade. A Principal Component Analysis was also created for the different river systems to identify possible changes in water quality over the 3 decades. According to the PAI, the Sabie River remained in a relatively good state while the Crocodile, Komati and Kaap rivers had a low water quality to begin with and became further degraded over the three decades. The PCAs indicated the Sabie and Crocodile rivers had increased levels of salts, nutrients and pH between 1988-1998 and 1999–2009 while the Kaap River had high salt content and pH between 1977 and 1998 and high nutrients during the decade of 1999–2009. These results indicate that there has been a change in the water quality of Mbombela river systems with notable increases in salt, pH and nutrient levels. As a result, the aquatic biota have likely been negatively affected and this poses severe impacts on the presence and abundance of schistosomiasis vectors as the snails are sensitive to changes in salinity, nutrients and pH.

Potentilla fulgens: organic column purified extract and its effect on enzyme inhibition in the vector snail Lymnaea acuminata

Fasciola hepatica and F. gigantica are parasitic trematode that causes fascioliasis in cattle and humans. The vector snail Lymnaea acuminata is an intermediate host of the Fasciola species. The major preventive step against fascioliasis is the control of the host snail L. acuminata. Effect of sub-lethal concentration of (20% and 60% of 96h LC50) column purified extract of Potentilla fulgens on acid phosphatase (ACPase), alkaline phosphatase (ALPase), and acetylcholinesterase (AChE) inhibition in nervous tissue of host L. acuminata were studied. Alteration in the enzymes of ACPase, ALPase, and AChE in nervous tissue was time and concentration-dependent. Withdrawal experiment demonstrates that there was a significant recovery in ACPase, ALPase, and AChE inhibition in nervous tissues of L. acuminata were withdrawn from 7 days and treated with 20 and 60% of 96h LC50 for 96h. A significant recovery in the levels of ACPase, ALPase, and AChE was observed in the nervous tissue of L. acuminata. . KEYWORDS :Lymnaea acuminata; Potentilla fulgens; ACPase; ALPase; AChE; Fasciola

Trematode infection in ruminants and diversity of snail hosts across three agro-ecological zones in Ethiopia

The occurrence of trematodes among ruminants and their snail vectors is a major concern across various agro-ecological regions of Ethiopia. Trematodes pose significant threats to animals, causing considerable economic losses and impacting public health. In this study, we have investigated 784 ruminant fecal samples, and 520 abattoir samples, alongside the collection and identification of snail vectors from various agro-ecological regions. Fecal examinations revealed Fasciola, Paramphistomum and Schistosoma species infected 20.5% (95% CI: 17.6, 23.8), 11.7% (95% CI: 9.6, 14.2), and 6.3% (95% CI: 4.1, 9.1) of the animals, respectively. The overall prevalence of trematodes among ruminants was 28.8% (95% CI: 25.7, 32.1%), with 6.0% (95% CI: 4.3, 7.7) showing mixed infections. Fasciola was more prevalent in Asela (26%) compared to Batu (19%) and Hawassa (11.5%), while a higher proportion of animals in Batu were infected with Paramphistomum. Schistosoma eggs were detected only in Batu (12.5%), but not in other areas. Sheep and cattle exhibited higher infection rates with Fasciola, Paramphistoma, and Schistosoma compared to goats. Significant associations were observed between trematode infections and risk factors including agro-ecology, animal species, body condition score, and deworming practices. About 20.8% and 22.7% of the slaughtered animals harbored Fasciola and Paramphistomum flukes, respectively, with a higher prevalence in Asela and Hawassa abattoirs compared to Batu abattoir. Additionally, a total of 278 snails were collected from the study areas and identified as lymnae natalensis, lymnae trancatula, Biomphalaria pffiferi, Biomphlaria sudanica, and Bulinus globosus. In conclusion, the study highlights the widespread occurrence of trematode infections, emphasizing the need for feasible control measures to mitigate their economic and public health impacts.

Impacts of water physicochemical parameters on schistosomiasis vector snail distributional-abundance and infectivity rate in South-Eastern Nigeria.

Schistosomiasis, an NTD, poses public health problems for rural communities. The parameters controlling its intermediate hosts are scarcely studied. 24 human-water contacts were sampled for 12 months to understand the impacts of water parameters on the vector. Sampling was done by monthly handpicking of the snail vector with a net to analyze the water parameters (temperature, dissolved oxygen, conductivity, depth, and rainfall). 546 snails recovered from the water sites showed that Bulinus globosus had the highest occurrence (50.5%), followed by Lanistes varicus (27.7%), and Bulinus truncatus species (3.7%). Ohaukwu LGA recorded the highest occurrence of freshwater snails at 55.3%, while Amovu stream had the highest number of snails with an overall abundance of 35.9%. May had the highest cercariae shedding at 26%, followed by June at 20%. No shedding occurred in September, November, December, and January. The infectivity rate of freshwater snails collected showed a significant difference based on the month (X2=6590.079, p- value=0.006). The study reveals that water physicochemical parameters significantly influence the abundance of intermediate snail hosts, with all parameters positively correlated except for temperature, conductivity, and TDS. This poses a significant public health threat due to vector snails' presence.

A haplotype-like, chromosome-level assembled and annotated genome of Biomphalaria glabrata, an important intermediate host of schistosomiasis and the best studied model of schistosomiasis vector snails.

Schistosomiasis is one of the world's most devastating parasitic diseases, afflicting 251 million people globally. The Neotropical snail Biomphalaria glabrata is an important intermediate host of the human blood fluke Schistosoma mansoni and a predominant model for schistosomiasis research. To fully exploit this model snail for biomedical research, here we report a haplotype-like, chromosome-level assembled and annotated genome of the homozygous iM line of B. glabrata that we developed at the University of New Mexico. Using multiple sequencing platforms, including Illumina, PacBio, and Omni-C sequencing, 18 sequence contact matrices representing 18 haploid chromosomes (2n = 36) were generated (337x genome coverage), and 96.5% of the scaffold sequences were anchored to the 18 chromosomes. Protein-coding genes (n = 34,559), non-coding RNAs (n = 2,406), and repetitive elements (42.52% of the genome) were predicted for the whole genome, and detailed annotations for individual chromosomes were also provided. Using this genomic resource, we have investigated the genomic structure and organization of the Toll-like receptor (TLR) and fibrinogen-domain containing protein (FReD) genes, the two important immune-related gene families. Notably, TLR-like genes are scattered on 13 chromosomes. In contrast, almost all (39 of 40) fibrinogen-related genes (FREPs) (immunoglobulin superfamily (IgSF) + fibrinogen (FBG)) are clustered within a 5-million nucleotide region on chromosome 13, yielding insight into mechanisms involved in the diversification of FREPs. This is the first genome of schistosomiasis vector snails that has been assembled at the chromosome level, annotated, and analyzed. It serves as a valuable resource for a deeper understanding of the biology of vector snails, especially Biomphalaria snails.

The genome and transcriptome of the snail Biomphalaria sudanica s.l.: immune gene diversification and highly polymorphic genomic regions in an important African vector of Schistosoma mansoni.

Control and elimination of schistosomiasis is an arduous task, with current strategies proving inadequate to break transmission. Exploration of genetic approaches to interrupt Schistosoma mansoni transmission, the causative agent for human intestinal schistosomiasis in sub-Saharan Africa and South America, has led to genomic research of the snail vector hosts of the genus Biomphalaria. Few complete genomic resources exist, with African Biomphalaria species being particularly underrepresented despite this being where the majority of S. mansoni infections occur. Here we generate and annotate the first genome assembly of Biomphalaria sudanica sensu lato, a species responsible for S. mansoni transmission in lake and marsh habitats of the African Rift Valley. Supported by whole-genome diversity data among five inbred lines, we describe orthologs of immune-relevant gene regions in the South American vector B. glabrata and present a bioinformatic pipeline to identify candidate novel pathogen recognition receptors (PRRs). De novo genome and transcriptome assembly of inbred B. sudanica originating from the shoreline of Lake Victoria (Kisumu, Kenya) resulted in a haploid genome size of ~ 944.2Mb (6,728 fragments, N50 = 1.067Mb), comprising 23,598 genes (BUSCO = 93.6% complete). The B. sudanica genome contains orthologues to all described immune genes/regions tied to protection against S. mansoni in B. glabrata, including the polymorphic transmembrane clusters (PTC1 and PTC2), RADres, and other loci. The B. sudanica PTC2 candidate immune genomic region contained many PRR-like genes across a much wider genomic region than has been shown in B. glabrata, as well as a large inversion between species. High levels of intra-species nucleotide diversity were seen in PTC2, as well as in regions linked to PTC1 and RADres orthologues. Immune related and putative PRR gene families were significantly over-represented in the sub-set of B. sudanica genes determined as hyperdiverse, including high extracellular diversity in transmembrane genes, which could be under pathogen-mediated balancing selection. However, no overall expansion in immunity related genes was seen in African compared to South American lineages. The B. sudanica genome and analyses presented here will facilitate future research in vector immune defense mechanisms against pathogens. This genomic/transcriptomic resource provides necessary data for the future development of molecular snail vector control/surveillance tools, facilitating schistosome transmission interruption mechanisms in Africa.

Yolk proteins of the schistosomiasis vector snail Biomphalaria glabrata revealed by multi-omics analysis

Vitellogenesis is the most important process in animal reproduction, in which yolk proteins play a vital role. Among multiple yolk protein precursors, vitellogenin (Vtg) is a well-known major yolk protein (MYP) in most oviparous animals. However, the nature of MYP in the freshwater gastropod snail Biomphalaria glabrata remains elusive. In the current study, we applied bioinformatics, tissue-specific transcriptomics, ovotestis-targeted proteomics, and phylogenetics to investigate the large lipid transfer protein (LLTP) superfamily and ferritin-like family in B. glabrata. Four members of LLTP superfamily (BgVtg1, BgVtg2, BgApo1, and BgApo2), one yolk ferritin (Bg yolk ferritin), and four soma ferritins (Bg ferritin 1, 2, 3, and 4) were identified in B. glabrata genome. The proteomic analysis demonstrated that, among the putative yolk proteins, BgVtg1 was the yolk protein appearing in the highest amount in the ovotestis, followed by Bg yolk ferritin. RNAseq profile showed that the leading synthesis sites of BgVtg1 and Bg yolk ferritin are in the ovotestis (presumably follicle cells) and digestive gland, respectively. Phylogenetic analysis indicated that BgVtg1 is well clustered with Vtgs of other vertebrates and invertebrates. We conclude that, vitellogenin (BgVtg1), not yolk ferritin (Bg yolk ferritin), is the major yolk protein precursor in the schistosomiasis vector snail B. glabrata.

Predicting the potential nationwide distribution of the snail vector, Oncomelania hupensis quadrasi, in the Philippines using the MaxEnt algorithm

Predicting the potential nationwide distribution of the snail vector, Oncomelania hupensis quadrasi, in the Philippines using the MaxEnt algorithm

Community composition of invasive, outbreak, and non-pest snail species along a source spring-to-fishpond gradient in a spatially structured aquacultural region

Agricultural lands are integrated into and interact with natural areas. Such is the case of Emek HaMa'ayanot, northern Israel, comprising a springs-rich area characterized by multiple land-uses, including spring-water-based aquaculture, recreational springs, and nature reserves. Aquacultural farms suffer from pest snails that carry fish disease; in the study region, these species are invasive (Thiara scabra, Tarebia granifera, Pseudosuccinea columella) and outbreak endemic (Melanoides tuberculata). Previous snail control efforts have focused on individual fishponds without considering management on larger environmental scales in the waterways from the source springs to the fish farms. To broaden our understanding of the status of the pest snail problem in the study area prior to suggesting environmental managerial solutions, we quantified changes in the community composition of snail species along the springs-to-fishponds gradients in a spatially explicit system. We found a remarkable increase in pest snail abundances along these gradients, indicating that pest snails might be invading upstream towards the springs. There were always nearly 100% pest snails in the endpoint sites for water tracks that ended in fishponds. Moreover, pest snails dominated the site when it was used as a fishpond, even though the site was also a spring. In contrast, in a water track that does not end in a fish farm, the relative abundances of non-pest snail species was similar between the source spring and the downstream endpoint, in spite of an increase in pest snail abundance at a midpoint site. These results suggest that invasive pest snails are actively moving upstream and that the fishponds have a marked upstream effect on the ability of non-pest snails to resist pest species invasions. We suggest further investigation of possible strategies for biocontrol of the observed invasion of the snails into natural areas as a basis for environmental management efforts. Finally, the observations made during this study could have practical global implications for snail management in aquaculture and agriculture, and for the control of snails and snail vectors implicated in animal and human diseases.

Molluscicidal Efficacy of Essential oils of Syzygium aromaticum Clove and Tachyspermum ammi Seeds against Lymnaea acuminata, a Vector Snail

In eastern Uttar Pradesh, fascioliasis, an endemic zoonotic disease, is quite prevalent. Essential oils that are produced from various plants are extremely important to human health. The current study found that the essential oils from Tachyspermum ammi seeds and Syzygium aromaticum cloves are effective herbal molluscicides against the vector snail Lymnaea acuminata. Syzygium aromaticum cloves and Tachyspermum ammi seeds are used to extract their essential oils using both conventional and unconventional techniques, such as solvent extraction (SE) and hydrodistillation (HD). The results section makes it evident that both of the essential oils from Syzygium aromaticum clove and Tachyspermum ammi seeds have a high level of molluscicidal activity (24-hour LC50 values are 3.01 and 2.35), particularly against the vector snail Lymnaea acuminata. The current investigation unequivocally showed that the exposed vector snails to the essential oils are extremely harmful. The aim of the present investigation is to establish the molluscicidal activity of the essential oils of Syzygium aromaticum clove and Tachyspermum ammi seeds against the vector snail Lymnaea acuminata.

Fluorescent non transgenic schistosoma to decipher host-parasite phenotype compatibility.

Schistosomiasis is considered as a significant public health problem, imposing a deeper understanding of the intricate interplay between parasites and their hosts. Unfortunately, current invasive methodologies employed to study the compatibility and the parasite development impose limitations on exploring diverse strains under various environmental conditions, thereby impeding progress in the field. In this study, we demonstrate the usefulness for the trematode parasite Schistosma mansoni, leveranging a fluorescence-imaging-based approach that employs fluorescein 5-chloromethylfluorescein diacetate (CMFDA) and 5-chloromethylfluorescein diacetate (CMAC) as organism tracker for intramolluscan studies involving the host snail Biomphalaria glabrata. These probes represent key tools for qualitatively assessing snail infections with unmatched accuracy and precision. By monitoring the fluorescence of parasites within the snail vector, our method exposes an unprecedented glimpse into the host-parasite compatibility landscape. The simplicity and sensitivity of our approach render it an ideal choice for evolutionary studies, as it sheds light on the intricate mechanisms governing host-parasite interactions. Fluorescent probe-based methods play a pivotal role in characterizing factors influencing parasite development and phenotype of compatibility, paving the way for innovative, effective, and sustainable solutions to enhance our understanding host-parasite immunobiological interaction and compatibility.

All-female crayfish populations for biocontrol and sustainable aquaculture

Snail control in aquaculture and control of snail vectors implicated in animal and human diseases are global challenges. Potential biocontrol agents could be species of crayfish, which are known to be voracious predators of snails. However, at present, the use of crayfish as biocontrol agents is limited due to their invasive nature. A promising candidate biocontrol agent is the Australian redclaw crayfish, Cherax quadricarinatus, a key species in the aquaculture industry. However, the downside of using this species for biocontrol is that C. quadricarinatus aquaculture escapees – being highly robust, fast growing, and ferocious omnivores – have become invasive, establishing feral populations around the world. Here we suggest the production of monosex C. quadricarinatus populations that open two exciting biotechnology applications—as a possible sustainable solution for snail control and as a means to improve yields and management in crayfish aquaculture, without the inherent danger of establishing invasive populations of aquaculture escapees. In the first part of this study, C. quadricarinatus was tested as a snail eradicator. Both males and females were highly efficient in predation experiments, eliminating 89% and 98% of Thiara scabra snails, respectively. The superior efficiency of the females in the predation experiments and the possible advantage for aquaculture of all-female crayfish populations provided the rationale for the second part of the study—the development of an economically feasible and non-labor-intensive biotechnology for the production of all-female C. quadricarinatus populations. To this end, we leveraged the naturally occurring intersexuality in C. quadricarinatus populations to produce female-biased populations. Females bearing only the W sex chromosome isolated from such populations using W and Z-specific genomic markers were found to be reproductive when bred with WZ intersexuals. Resulting progenies from the above crosses were 100% female populations including 50% WW females, thus paving the way to the establishment of an all-female producing brood stock. We present a quantitative scheme that demonstrates how our approach, which does not include any genomic intervention, can be implemented both for sustainable aquaculture and to fight harmful snails damaging aquaculture, agriculture, and human health.

Vector snail fauna and Schistosoma haematobium transmission patterns in freshwater systems of Ishielu Local Government Area, Ebonyi State, Nigeria

Freshwater snails are widespread in tropical and temperate regions of the world where they serve as intermediate hosts for larval stages of parasitic trematodes which cause schistosomiasis that is endemic in Nigeria. Snail fauna and patterns of Schistosoma haematobium transmission were determined in flowing water habitats (FWH) and stagnant water habitats (SWH) in Ishielu, Local Government Area, Ebonyi State, Nigeria. Snail collection was done using scoop-net and hand-picking techniques. Bulinus species collected were exposed to sunlight/light-induced in laboratory for cercarial shedding. Cercariae were then observed under microscope. 923 snails were collected, 67.7% Lymnaea natalensis, 23.1% Bulinus globosus and 9.2% Bulinus truncatus. Their relative abundance was significantly different (P<0.05). 31.6% Bulinus snails from FWH were infected by S. haematobium whereas 18.5% from SWH were infected. Infectivity of Bulinus spp in each habitat group was not significantly different but was when compared the two groups of habitats (P<0.05). Highest infectivity (45.8%) occurred during dry season peaking in February (45.8%) for FWH and for SWH, highest infectivity occurred during rain peaking in July (26.8%). The transmission potential (T.P) was very high during dry season (93.0%) peaking in February (34.9%) in FWH and very low (0%) for SWH. During rain, the T.P was very high (100%) peaking in July (50%) in SWH and very low (7.0%) for FWH. Pools and rivers in Ishielu are suitable habitats for vector snails wherein season and habitat type influence snail abundance and transmission of Schistosomiasis, the findings of which can help in establishing programmes for proper health awareness and snail control.

A Place-Based Conceptual Model (PBCM) of Neotricula aperta/Schistosoma mekongi habitat before and after dam construction in the Lower Mekong River.

In 1971, scientists from Mahidol University in Thailand and the Smithsonian Institution in the USA formed a research team to study a new species of Schistosoma in the Mekong River in Thailand and Laos. The studies, completed during 1971-1973, prior to the construction of any dams or restrictions to the natural flow regime of the Mekong River, provide a unique description of the natural ecological state of the river that can serve as a baseline for current research. The natural transmission of Schistosoma japonicum, Mekong Strain, was first reported on Khong Island, Laos in 1973 using sentinel mice. The first detailed description of the habitat ecology of the snail vector Neotricula aperta was done on-site in 1971 simultaneously with that research and is unique in providing the only description of the river shoreline habitat before any dams were built and any alteration of the natural flow regime was in place. Aggregating current information in a Place-Based Conceptual Model (PBCM) as an organizing template, along with current habitat models that combine ecological data with e-flows, can be developed and used as a tool to predict suitable habitats for snails. The natural flow regime of the Mekong River prior to any impoundments is described with current updates on the potential impacts of climate change and dams with flow-related snail habitat characteristics, including sediment drift and water quality. The application of the PBCM to describe and compare descriptive information on current and potential future N. aperta/S. mekongi habitat is discussed.

Towards an integrated vector management approach for sustainable control of schistosomiasis and malaria in Mwea, Kirinyaga County, Kenya: Baseline epidemiological and vector results

BackgroundVector control is an important approach in the control of most parasitic and vector-borne diseases including malaria, and schistosomiasis. Distribution of these two infections often overlaps and in such areas it’s more economically viable to employ an integrated approach in the control of their vectors which largely shares the same breeding ecosystem. We carried out a baseline epidemiological and vector surveys for malaria and schistosomiasis in Mwea, Kirinyaga County, in preparation for the upscaling of integrated vector management (IVM) for the two diseases. MethodsThis was a repeated cross sectional survey, where mosquito and snails were sampled during dry and wet seasons in three different ecological zones, Kiamaciri, Thiba and Murinduko to identify possible breeding sites. Mosquito larvae were collected using standard dippers, adults using CDC miniature light traps while snail vectors were sampled using standard snail scoops in different breeding habitats. A total of 1200 pupils from 12 primary schools were tested for malaria using rapid diagnostic tests (Malaria Pf/PAN Ag combo). Stool samples were processed using the Kato Katz technique for intestinal schistosomiasis. ResultsThe overall prevalence of intestinal schistosomiasis was 9.08 % (95 % CI: 07.00–11.00), with Kiamaciri zone recording the highest prevalence at 19 % (95%CI: 15.00–23.00) and Murinduko zone the least at 0.17 % (95%CI: 0.00–0.01). Majority of the infections were of light intensity 78.9 % (95%CI: 70.04–86.13). There was no positive malaria case detected in this study. Of the 3208 adult mosquitoes sampled during the dry season, 20.6 % (95 % CI: 19.25–22.08) were Anopheles gambiae s.l while 79.4 % (95 % CI: 77.92–80.75) were culicines. During the wet season, 3378 adult mosquitoes were collected, of which 14.7 % (95 % CI: 13.56–15.98) were Anopheles gambiae s.l and 85.3 % (95 % CI: 84.02–86.44) culicines. Overall, 4085 mosquito larvae were collected during the two seasons, of which, 57.3 % and 42.7 % were anopheles and culicine respectively. Majority of the larvae (85.1 % (95%CI: 84.01–86.10) were collected during the wet season, with only 14.9 % (95%CI: 14.10–16.00) being collected during the dry season. A total of 2292 fresh water vector snails were collected with a majority (69.6 % (95%CI: 68.00–71.10) being Biomphalaria pffeiferi responsible for transmission of intestinal schistosomiasis. ConclusionThis study demonstrates that intestinal schistosomiasis is prevalent in Kiamaciri and Thiba zones, and points to the possibility of active transmission of schistosomiasis in Murinduko zone. Malaria vectors were predominantly observed in all sites despite there being no malaria positive case. Culex quinquefaciatus responsible for the spread of several arboviruses was also observed. The presence of these vectors may lead to future disease outbreaks in the area if concerted control initiatives are not undertaken. The disease vectors shared the same breeding sites and thus its economical and feasible to adopt an integrated vector management approach in control efforts for these disease in the study area.

Influence of Abiotic Factors and Umbelliferone Toxicity in Snail Attractant Pellets Against the Vector Snail <i>Lymnaea acuminata</i>

Background and Objective: Fasciolosis is a zoonotic disease, which is transmitted by Lymnaea acuminata snails of the Lymnaidae family and causes the disease in human and herbivorous mammals in all over the world. One of the suitable approaches for the control of fasciolosis is the snail control. The snail control by snail attractant pellets is a new technique because there is no any side effect on other biota/human/natural environment. Material and Methods: The influence of various abiotic factors and umbelliferone toxicity in bait against the vector snail Lymnaea acuminata was checked in different months of the years 2018-2019. Result: After 24h of molluscicide exposure, it was found that LC50 values 4.37, 4.22 and 5.66 % in SAP containing starch + umbelliferone and 4.02, 4.33, and 4.76 % in SAP containing proline + umbelliferone during May, June and July, respectively, were most effective treatments in killing the snails. While SAP containing starch + umbelliferone was 9.84% and proline + umbelliferone was 8.94% were minimum effective in January in 24h toxicity. Conclusion: This study indicates that various abiotic factors significantly changed the toxicity of umbelliferone; so, the snails can be controlled by snail attractant pellets containing umbelliferone will be applied in a particular month rather than the whole month of the year.