Transmission control of schistosomiasis japonica: implementation and evaluation of different snail control interventions

Development of prediction models to identify hotspots of schistosomiasis in endemic regions to guide mass drug administration

Schistosomiasis is a neglected tropical disease affecting over 150 million people. Hotspots of Schistosoma transmission-communities where infection prevalence does not decline adequately with mass drug administration-present a key challenge in eliminating schistosomiasis. Current approaches to identify hotspots require evaluation 2-5 y after a baseline survey and subsequent mass drug administration. Here, we develop statistical models to predict hotspots at baseline prior to treatment comparing three common hotspot definitions, using epidemiologic, survey-based, and remote sensing data. In a reanalysis of randomized trials in 589 communities in five endemic countries, a regression model predicts whether Schistosoma mansoni infection prevalence will exceed the WHO threshold of 10% in year 5 ("prevalence hotspot") with 86% sensitivity, 74% specificity, and 93% negative predictive value (NPV; assuming 30% hotspot prevalence), and a regression model for Schistosoma haematobium achieves 90% sensitivity, 90% specificity, and 96% NPV. A random forest model predicts whether S. mansoni moderate and heavy infection prevalence will exceed a public health goal of 1% in year 5 ("intensity hotspot") with 92% sensitivity, 79% specificity, and 96% NPV, and a boosted trees model for S. haematobium achieves 77% sensitivity, 95% specificity, and 91% NPV. Baseline prevalence is a top predictor in all models. Prediction is less accurate in countries not represented in training data and for a third hotspot definition based on relative prevalence reduction over time ("persistent hotspot"). These models may be a tool to prioritize high-risk communities for more frequent surveillance or intervention against schistosomiasis, but prediction of hotspots remains a challenge.

Oncomelania hupensis Distribution and Schistosomiasis Transmission Risk in Different Environments under Field Conditions

The goal of schistosomiasis prevention and control in China is shifting from transmission interruption to elimination. However, the area inhabited by the intermediate host, the snail Oncomelania hupensis, has not changed much in recent years. Different environmental types have different impacts on snail breeding, and understanding these differences is conducive to improving the efficiency of snail monitoring and control and to saving resources. Based on previous epidemiological data, we selected 199 villages in 2020 and 269 villages in 2021 from transmission control, transmission interruption, and elimination areas of snail breeding. Snail surveys were conducted in selected villages using systematic sampling and/or environmental sampling methods in six types of snail-breeding environments (canals, ponds, paddy fields, dry lands, bottomlands, and undefined environments). All live snails collected from the field were evaluated for Schistosoma japonicum infection using the microscopic dissection method, and a subsample of snails was subjected to loop-mediated isothermal amplification (LAMP) to assess the presence of S. japonicum infection. Snail distribution data and infection rate and nucleic acid positive rate of schistosomes in snails were calculated and analyzed. The 2-year survey covered 29,493 ha of the environment, in which 12,313 ha of snail habitats were detected. In total, 51.16 ha of new snail habitats and 107.76 ha of re-emergent snail habitats were identified during the survey. The occurrence rate of snails in canals (10.04%, 95% CI: 9.88-10.20%) and undefined environments (20.66%, 95% CI: 19.64-21.67%) was relatively high in 2020, and the density of snails in bottomlands (0.39, 95% CI: 0.28-0.50) and undefined environments (0.43, 95% CI: 0.14-1.60) was relatively high in 2021. Of the 227,355 live snails collected in this study, none were S. japonicum-positive as determined by microscopy. Of the 20,131 pooled samples, however, 5 were S. japonicum-positive based on LAMP analysis, and they were distributed in three environmental types: 3 in bottomland, 1 in dry land, and 1 in a canal. The bottomland environment has a high risk of schistosomiasis transmission because it contains a large area of newly emerging and re-emerging snail habitats, and it also had the most breeding snails infected with S. japonicum. Thus, this habitat type should be the key target for snail monitoring and early warning and for the prevention and control of schistosomiasis.

The identification of alternative oxidase in intermediate host snails of Schistosoma and its potential role in protecting Oncomelania hupensis against niclosamide-induced stress

BACKGROUND

Snail intermediate hosts are mandatory for the transmission of schistosomiasis, which has to date infected more than 200 million people worldwide. Our previous studies showed that niclosamide treatment caused the inhibition of aerobic respiration and oxidative phosphorylation, and the disruption of energy supply, in one of the intermediate hosts of schistosomiasis, Oncomelania hupensis, which eventually led to the death of the snails. Meanwhile, the terminal oxidase in the mitochondrial respiratory chain, alternative oxidase (AOX), was significantly up-regulated, which was thought to counterbalance the oxidative stress and maintain metabolic homeostasis in the snails. The aims of the present study are to identify the AOXs in several species of snails and investigate the potential activation of O. hupensis AOX (OhAOX) under niclosamide-induced stress, leading to enhanced survival of the snail when exposed to this molluscicide.

METHODS

The complete complementary DNA was amplified from the AOXs of O. hupensis and three species of Biomphalaria; the sequence characteristics were analysed and the phylogenetics investigated. The dynamic expression and localisation of the AOX gene and protein in O. hupensis under niclosamide-induced stress were examined. In addition, the expression pattern of genes in the mitochondrial respiratory complex was determined and the production of reactive oxygen species (ROS) calculated. Finally, the molluscicidal effect of niclosamide was compared between snails with and without inhibition of AOX activity.

RESULTS

AOXs containing the invertebrate AOX-specific motif NP-[YF]-XPG-[KQE] were identified from four species of snail, which phylogenetically clustered together into Gastropoda AOXs and further into Mollusca AOXs. After niclosamide treatment, the levels of OhAOX messenger RNA (mRNA) and OhAOX protein in the whole snail were 14.8 and 2.6 times those in untreated snails, respectively, but varied widely among tissues. Meanwhile, the level of cytochrome C reductase mRNA showed a significant decrease in the whole snail, and ROS production showed a significant decrease in the liver plus gonad (liver-gonad) of the snails. At 24 h post-treatment, the mortality of snails treated with 0.06-0.1 mg/L niclosamide and AOX inhibitor was 56.31-76.12% higher than that of snails treated with 0.1 mg/L niclosamide alone.

CONCLUSIONS

AOX was found in all the snail intermediate hosts of Schistosoma examined here. AOX was significantly activated in O. hupensis under niclosamide-induced stress, which led to a reduction in oxidative stress in the snail. The inhibition of AOX activity in snails can dramatically enhance the molluscicidal effect of niclosamide. A potential target for the development of an environmentally safe snail control method, which acts by inhibiting the activity of AOX, was identified in this study.

Development of a loop-mediated isothermal amplification assay for detection of Austropeplea tomentosa from environmental water samples

Lymnaeid snails are key intermediate hosts for the development and survival of Fasciola spp., the causative agent of Fascioliasis which are economically important parasites infecting humans and livestock globally. The current control method for treating Fascioliasis is heavily reliant on anthelmintic drugs, particularly Triclabendazole (TCBZ) which has resulted in drug-resistant parasites and poses significant risk as there are no long-term efficacious alternatives available. Sustainable control measures at the farm level could include both parasite and snail control will play an important role in Fasciola spp. control and reduce the reliance on anthelmintic drugs. Implementation of such sustainable control measures requires effective identification of snails on the property however Lymnaeid snails are small and difficult to physically locate. Snail identification using an environmental DNA approach is a recent approach in which physically locating snails are not required. Austropeplea tomentosa, is the primary intermediate snail host for F. hepatica transmission in South-East Australia and we present an in-field loop-mediated isothermal amplification and water filtering method for the detection of A. tomentosa eDNA from water samples to improve current surveillance methods. This methodology is highly sensitive with a detection limit of 5 × 10^− 6 ng/μL, detected in < 20 minutes, with cumulative sample preparation and amplification time under 1 hour. This proposed workflow could assist in monitoring areas to determine the risk of Fascioliasis infection and implement strategies to manage snail populations to ultimately reduce the risk of infection for humans and livestock.

Molluscicides against the snail-intermediate host of Schistosoma: a review

Schistosomiasis, a neglected tropical disease (NTD), is one of the most prevalent parasitoses in the World. Certain freshwater snail species are the intermediate host in the life cycle of schistosome species. Controlling snails employing molluscicides is an effective, quick, and convenient intervention strategy to prevent the spread of Schistosoma species in endemic regions. Advances have been made in developing both synthetic molluscicides and molluscicides derived from plants. However, at present, the development of molluscicides is not adapted to the actual demand for snails and schistosoma controlling. We undertake a systematic review of exploitation and application of synthetic molluscicides and molluscicides derived from plants to combat intermediate host snails. The detailed molluscicidal activity, structure–activity relationship, structural feature, and possible mechanism of some molluscicides are also highlighted, which may afford an important reference for the design of new, more effective molluscicides with low environmental impact and realize the aim of controlling schistosome at transmission stages.

Potential impact of flooding on schistosomiasis in Poyang Lake regions based on multi-source remote sensing images

Background

Flooding is considered to be one of the most important factors contributing to the rebound of Oncomelania hupensis, a small tropical freshwater snail and the only intermediate host of Schistosoma japonicum, in endemic foci. The aim of this study was to assess the risk of intestinal schistosomiasis transmission impacted by flooding in the region around Poyang Lake using multi-source remote sensing images.

Methods

Normalized Difference Vegetation Index (NDVI) data collected by the Landsat 8 satellite were used as an ecological and geographical suitability indicator of O. hupensis habitats in the Poyang Lake region. The expansion of the water body due to flooding was estimated using dual-polarized threshold calculations based on dual-polarized synthetic aperture radar (SAR). The image data were captured from the Sentinel-1B satellite in May 2020 before the flood and in July 2020 during the flood. A spatial database of the distribution of snail habitats was created using the 2016 snail survey in Jiangxi Province. The potential spread of O. hupensis snails after the flood was predicted by an overlay analysis of the NDVI maps in the flood-affected areas around Poyang Lake. The risk of schistosomiasis transmission was classified based on O. hupensis snail density data and the related NDVI.

Results

The surface area of Poyang Lake was approximately 2207 km² in May 2020 before the flood and 4403 km² in July 2020 during the period of peak flooding; this was estimated to be a 99.5% expansion of the water body due to flooding. After the flood, potential snail habitats were predicted to be concentrated in areas neighboring existing habitats in the marshlands of Poyang Lake. The areas with high risk of schistosomiasis transmission were predicted to be mainly distributed in Yongxiu, Xinjian, Yugan and Poyang (District) along the shores of Poyang Lake. By comparing the predictive results and actual snail distribution, we estimated the predictive accuracy of the model to be 87%, which meant the 87% of actual snail distribution was correctly identified as snail habitats in the model predictions.

Conclusions

Data on water body expansion due to flooding and environmental factors pertaining to snail breeding may be rapidly extracted from Landsat 8 and Sentinel-1B remote sensing images. Applying multi-source remote sensing data for the timely and effective assessment of potential schistosomiasis transmission risk caused by snail spread during flooding is feasible and will be of great significance for more precision control of schistosomiasis.

Spatio-temporal variations of emerging sites infested with schistosome-transmitting Oncomelania hupensis in Hunan Province, China, 1949-2016

BACKGROUND

Constant emerging sites infested with Oncomelania hupensis (O. hupensis) impede the goal realization of eliminating schistosomiasis. The study assessed the spatial and temporal distributions of new Oncomelania snail habitats in Hunan Province from 1949 to 2016.

METHODS

We used the data from annual snail surveys throughout Hunan Province for the period from 1949 to 2016. Global Moran's I, Anselin local Moran's I statistics (LISA) and a retrospective space-time permutation model were applied to determine the spatial and temporal distributions of emerging snail-infested sites.

RESULTS

There were newly discovered snail-infested sites almost every year in 1949-2016, except for the years of 1993, 2009 and 2012. The number of emerging sites varied significantly in the five time periods (1949-1954, 1955-1976, 1977-1986, 1986-2003 and 2004-2016) (H = 25.35, p < 0.05). The emerging sites lasted 37.52 years in marshlands, 30.04 years in hills and 24.63 at inner embankments on average, with the values of Global Moran's I being 0.52, 0.49 and 0.44, respectively. High-value spatial clusters (HH) were mainly concentrated along the Lishui River and in Xiangyin County. There were four marshland clusters, two hill clusters and three inner embankment clusters after 1976.

CONCLUSIONS

Lower reaches of the Lishui River and the Dongting Lake estuary were the high-risk regions for new Oncomelania snail habitats with long durations. Snail surveillance should be strengthened at stubborn snail-infested sites at the inner embankments. Grazing prohibition in snail-infested grasslands should be a focus in marshlands. The management of bovines in Xiangyin County is of great importance.

Metabolic profiles of Oncomelania hupensis after molluscicidal treatment: Carbohydrate metabolism targeted and energy deficiency

Oncomelania hupensis is the intermediate host of Schistosoma japonicum, one of the Schistosoma species that can cause human schistosomiasis. Molluscicidal treatment remains the primary means to control snail. Niclosamide is the only molluscicide recommended by the World Health Organization, and it has been used throughout schistosomiasis-endemic areas in China for almost 30 years. In our previous studies on transcriptomics, morphology, and enzymology of snails after molluscicidal treatment, two effective molluscicides were used, 50% wettable powder of niclosamide ethanolamine salt (WPN) and a new molluscicide derived from niclosamide, the salt of quinoid-2', 5-dichloro-4'-nitro-salicylanilide (LDS, simplified for Liu Dai Shui Yang An). Genes involved in cell structure mintenance, inhibition of neurohumoral transmission, and energy metabolism showed significant differential expression after molluscicide treatments. Damages in the structure of liver and muscle cells were accompanied by inhibited activities of enzymes related to carbohydrate metabolism and energy supply. This study was designed to clarify the dynamic metabolic process by metabonomics, together with the previous transcriptomic and enzymological profiles, to identify potential metabolite markers and metabolism pathways that related to the toxic mechanism of the molluscicide. In total, 56 metabolites were identified for O. hupensis, and 75% of these metabolites consisted of amino acids and derivatives, organic acids, and nucleic acid components. The concentration of glucose, maltose, succinate, choline, and alanine changed significantly after molluscicide treatments. These changes in metabolites mainly occurred in the process of carbohydrate metabolism, energy metabolism, and amino acid metabolism, primarily related to glycolysis/gluconeogenesis, oxidative phosphorylation, and transamination by KEGG pathway identification. Most of the identified pathways were also related to those differentially expressed unigenes and observed enzymes from our previous studies. Inhibited aerobic respiration and oxidative phosphorylation, and energy deficiency were implied further to be the leading causes of the final death of snails after molluscicide treatments. The hypothesised mathematical model in this study identified the rational hysteresis to explain the inconsistency of responses of unigenes, enzymes, and metabolites to molluscicide treatments. This study contributes to the comprehensive understanding of the molluscicidal mechanism in the metabolic process and this could assist in improving existing molluscicide formulations or development of new molluscicides.

Oncomelania hupensis retains its ability to transmit Schistosoma japonicum 13 years after migration from permissive to non-permissive areas

Background

The East Route Project (ERP) of the South-to-North Water Diversion Project (SNWDP) stretches across schistosomiasis endemic and non-endemic areas in China, which may lead to the dispersal of Oncomelania hupensis, the intermediate host of Schistosoma japonicum, from permissive areas along the Yangtze River Basin to non-permissive areas in northern China. A previous survey demonstrated that O. hupensis could survive and breed for 13 years (12 generations) after being transferred to a non-permissive area, and could be infected by S. japonicum. However, it is not clear if the migrated snails will change their ability to transmit S. japonicum.

Methods

We infected mice with the cercariae released from the infected transferred snails bred in Jining city of Shandong Province (non-permissive areas) for 13 years. The mice in the control group were infected with cercariae derived from the snails collected in their original habitat (Jiangdu county of Jiangsu Province, permissive areas). Then, we explored the pathogenicity to mice including worm burden, liver egg count and pathology. Additionally, the gene expression profiles of the adult male and female worms recovered from the infected mice were analyzed by RNA sequencing.

Results

The worm burden, liver egg count and pathology of the mice infected with cercariae released from transferred snails bred in non-permissive areas for 13 years showed no significant differences, when compared with the control cercariae. Slight changes occurred at the transcription level between adult male and female worms recovered from mice infected with cercariae derived from snails bred in permissive and non-permissive areas. Only fourteen genes were significantly differentially expressed in the comparison of adult female worms, and no significantly differentially expressed gene was found in the comparison of adult male worms.

Conclusions

Our findings strongly suggest that transferred snails did not change their schistosomiasis transmission ability and the worms derived from them retained the original pathogenicity, even after migrating from permissive to non-permissive areas for 13 years. Therefore, a long-term surveillance system of snails along the SNWDP is urgently needed to prevent the diffusion of O. hupensis and reduce the risk of transmission of schistosomiasis.

The Stakeholders' Views on Planting Trees to Control Schistosomiasis in China

China has initiated a tree planting program in epidemic regions of schistosomiasis as a part of efforts to eliminate schistosomiasis. More than 518,900 ha of tree plantations have been planted through the program between 2006 and 2015. However, whether the planting program has fulfilled its mission or not is an open question. In this study, we intended to get the answer from the main stakeholders of the planting program through a large-scale survey. Based on interviews with 80 administrators of the planting program and 1440 farmers in 24 counties and districts in four provinces, we found that most stakeholders viewed the planting program positively. Nearly 92% of farmers and all administrators believed that the planting program had reduced snail densities, while 94.3% of farmers and all administrators believed that the program had lowered the incidences of schistosomiasis. In addition, they reported that the impacts on farmers’ living and local environments by the tree planting program were mainly positive. Based on the stakeholders’ responses, we conclude that the tree planting program has been perceived by the main stakeholders as an effective environmental control measure of schistosomiasis. However, certain places and people that may be impacted negatively by the program should be given more attention when implementing the program.

Differential Change in the Prevalence of the Ascaris, Trichuris and Clonorchis infection Among Past East Asian Populations

As we learn more about parasites in ancient civilizations, data becomes available that can be used to see how infection may change over time. The aim of this study is to assess how common certain intestinal parasites were in China and Korea in the past 2000 years, and make comparisons with prevalence data from the 20th century. This allows us to go on to investigate how and why changes in parasite prevalence may have occurred at different times. Here we show that Chinese liver fluke (Clonorchis sinensis) dropped markedly in prevalence in both Korea and China earlier than did roundworm (Ascaris lumbricoides) and whipworm (Trichuris trichiura). We use historical evidence to determine why this was the case, exploring the role of developing sanitation infrastructure, changing use of human feces as crop fertilizer, development of chemical fertilizers, snail control programs, changing dietary preferences, and governmental public health campaigns during the 20th century.

Schistosomiasis in Zambia: a systematic review of past and present experiences

Background

The speedy rate of change in the environmental and socio-economics factors may increase the incidence, prevalence and risk of schistosomiasis infections in Zambia. However, available information does not provide a comprehensive understanding of the biogeography and distribution of the disease, ecology and population dynamics of intermediate host snails. The current study used an information-theoretical approach to understand the biogeography and prevalence schistosomiasis and identified knowledge gaps that would be useful to improve policy towards surveillance and eradication of intermediate hosts snails in Zambia.

Methods

To summarise the existing knowledge and build on past and present experiences of schistosomiasis epidemiology for effective disease control in Zambia, a systematic search of literature for the period 2000–2017 was done on PubMed, Google Scholar and EBSCOhost. Using the key words: ‘Schistosomiasis’, ‘Biomphalaria’, ‘Bulinus’, ‘Schistosoma mansoni’, ‘Schistosoma haematobium’, and ‘Zambia’, in combination with Booleans terms ‘AND’ and ‘OR’, published reports/papers were obtained and reviewed independently for inclusion.

Results

Thirteen papers published in English that fulfilled the inclusion criteria were selected for the final review. The papers suggest that the risk of infection has increased over the years and this has been attributed to environmental, socio-economic and demographic factors. Furthermore, schistosomiasis is endemic in many parts of the country with infection due to Schistosoma haematobium being more prevalent than that due to S. mansoni. This review also found that S. haematobium was linked to genital lesions, thus increasing risks of contracting other diseases such as HIV and cervical cancer.

Conclusions

For both S. haematobium and S. mansoni, environmental, socio-economic, and demographic factors were influential in the transmission and prevalence of the disease and highlight the need for detailed knowledge on ecological modelling and mapping the distribution of the disease and intermediate host snails for effective implementation of control strategies.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0424-5) contains supplementary material, which is available to authorized users.

Transcriptome sequencing and differential gene expression analysis of the schistosome-transmitting snail Oncomelania hupensis inhabiting hilly and marshland regions

The freshwater snail Oncomelania hupensis is the unique intermediate host of the blood fluke Schistosoma japonicum, which is the major cause of schistosomiasis. The snail inhabits two contrasting environments: the hilly and marshland regions. The hilly snails are smaller in size and have the typical smooth shell, whereas the marshland snails are larger and possess the ribbed shell. To reveal the differences in gene expression between the hilly and marshland snails, a total of six snails, three per environment, were individually examined by RNA sequencing technology. All paired-end reads were assembled into contigs from which 34,760 unigenes were predicted. Based on single nucleotide polymorphisms, principal component analysis and neighbor-joining clustering revealed two distinct clusters of hilly and marshland snails. Analysis of expression changes between environments showed that upregulated genes relating to immunity and development were enriched in hilly snails, while those associated with reproduction were over-represented in marshland snails. Eight differentially expressed genes between the two types of snails were validated by qRT-PCR. Our study identified candidate genes that could be targets for future functional studies, and provided a link between expression profiling and ecological adaptation of the snail that may have implications for schistosomiasis control.

Establishment of first engineering specifications for environmental modification to eliminate schistosomiasis epidemic foci in urban areas

Snail control is a key link in schistosomiasis control, but no unified methods for eliminating snails have been produced to date. This study was conducted to explore an engineering method for eliminating Oncomelania hupensis applicable to urban areas. The engineering specifications were established using the Delphi method. An engineering project based on these specifications was conducted in Hankou marshland to eliminate snails, including the transformation of the beach surface and ditches. Molluscicide was used as a supplement. The snail control effect was evaluated by field investigation. The engineering results fulfilled the requirements of the design. The snail density decreased to 0/0.11m², and the snail area dropped to 0m² after the project. There was a statistically significant difference in the number of frames with snails before and after the project (P<0.05). Snails were completely eliminated through one year of continuous monitoring, and no new snails were found after a flood disaster. This study demonstrates that engineering specifications for environmental modification were successfully established. Environmental modification, mainly through beach and ditch remediation, can completely change the environment of Oncomelania breeding. This method of environmental modification combined with mollusciciding was highly effective at eliminating snails.

Apropos: critical analysis of molluscicide application in schistosomiasis control programs in Brazil

Schistosomiasis is a snail-transmitted infectious disease affecting over 200 million people worldwide. Snail control has been recognized as an effective approach to interrupt the transmission of schistosomiasis, since the geographic distribution of this neglected tropical disease is determined by the presence of the intermediate host snails. In a recent Scoping Review published in Infectious Diseases of Poverty, Coelho and Caldeira performed a critical review of using molluscicides in the national schistosomiasis control programs in Brazil. They also described some chemical and plant-derived molluscicides used in China. In addition to the molluscicides described by Coelho and Caldeira, a large number of chemicals, plant extracts and microorganisms have been screened and tested for molluscicidal actions against Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China. Here, we presented the currently commercial molluscicides available in China, including 26% suspension concentrate of metaldehyde and niclosamide (MNSC), 25% suspension concentrate of niclosamide ethanolamine salt (SCNE), 50% niclosamide ethanolamine salt wettable powder (WPN), 4% niclosamide ethanolamine salt dustable powder (NESP), 5% niclosamide ethanolamine salt granule (NESG) and the plant-derived molluscicide "Luowei". These molluscicides have been proved to be active against O. hupensis in both laboratory and endemic fields, playing an important role in the national schistosomiasis control program of China. Currently, China is transferring its successful experiences on schistosomiasis control to African countries. The introduction of Chinese commercial molluscicides to Africa, with adaptation to local conditions, may facilitate the progress towards the elimination of schisosomiasis in Africa.

Genetic Evidence of Contemporary Dispersal of the Intermediate Snail Host of Schistosoma japonicum: Movement of an NTD Host Is Facilitated by Land Use and Landscape Connectivity

BACKGROUND

While the dispersal of hosts and vectors-through active or passive movement-is known to facilitate the spread and re-emergence of certain infectious diseases, little is known about the movement ecology of Oncomelania spp., intermediate snail host of the parasite Schistosoma japonicum, and its consequences for the spread of schistosomiasis in East and Southeast Asia. In China, despite intense control programs aimed at preventing schistosomiasis transmission, there is evidence in recent years of re-emergence and persistence of infection in some areas, as well as an increase in the spatial extent of the snail host. A quantitative understanding of the dispersal characteristics of the intermediate host can provide new insights into the spatial dynamics of transmission, and can assist public health officials in limiting the geographic spread of infection.

METHODOLOGY/PRINCIPAL FINDINGS

Oncomelania hupensis robertsoni snails (n = 833) were sampled from 29 sites in Sichuan, China, genotyped, and analyzed using Bayesian assignment to estimate the rate of recent snail migration across sites. Landscape connectivity between each site pair was estimated using the geographic distance distributions derived from nine environmental models: Euclidean, topography, incline, wetness, land use, watershed, stream use, streams and channels, and stream velocity. Among sites, 14.4% to 32.8% of sampled snails were identified as recent migrants, with 20 sites comprising >20% migrants. Migration rates were generally low between sites, but at 8 sites, over 10% of the overall host population originated from one proximal site. Greater landscape connectivity was significantly associated with increased odds of migration, with the minimum path distance (as opposed to median or first quartile) emerging as the strongest predictor across all environmental models. Models accounting for land use explained the largest proportion of the variance in migration rates between sites. A greater number of irrigation channels leading into a site was associated with an increase in the site's propensity to both attract and retain snails.

CONCLUSIONS/SIGNIFICANCE

Our findings have important implications for controlling the geographic spread of schistosomiasis in China, through improved understanding of the dispersal capacity of the parasite's intermediate host.

Morphological and enzymatical observations in Oncomelania hupensis after molluscicide treatment: implication for future molluscicide development

A preparation of niclosamide named 50 % wettable powder of niclosamide ethanolamine salt (WPN), the only chemical molluscicide available in China, has been widely used for Oncomelania hupensis control over the past 20 years, but its molluscicidal mechanism has not been elucidated yet. Recently, a derivative of niclosamide, the salt of quinoid-2',5-dichloro-4'-nitro-salicylanilide (Liu Dai Shui Yang An, LDS), has been proven to have equivalent molluscicidal effects as WPN but with lower cost and significantly lower toxicity to fish than WPN. In our previous study, gene expression profiling of O. hupensis showed significantly effects after these two molluscicides had been applied. This study was designed to use morphological and enzymological analyses to further elucidate the mechanism by which these molluscicides cause snail death. After WPN or LDS treatment, the number of mitochondria of O. hupensis was reduced and their cristae appeared unclear, heterochromatin gathered to be polarized, ribosome numbers of the rough endoplasmic reticulums (rERs) decreased, myofilaments in muscle cells became disordered and loose, and cytoplasm in some liver cells was concentrated. Damage of cell structures and organelles suggested inhibited movement ability and effects on liver and energy metabolism following treatment. In parallel, activities of enzymes related with carbohydrate metabolism were inhibited except lactate dehydrogenase (LDH) increased in muscle tissue, and activities of enzymes related with stress response increased followed by decreasing to lower levels than those of the H₂O-treated group. This shift of carbohydrate metabolism patterns led to insufficient energy supply and lactic acid accumulation, and variations of nitric oxide synthase (NOS), alanine aminotransferase (ALT), and superoxide dismutase (SOD) during process of molluscicide treatment suggested a stress response of snail to the molluscicides at early stages and later fatal damage in liver and nervous system. In general, effects of WPN and LDS were similar although LDS-treated snails showed more serious damage in the liver and a stronger inhibition of enzymes related with aerobic respiration and stress response. This was consistent with the transcriptome profile obtained previously. However, considering enzyme activities at post-transcriptional and protein levels, comprehensive identification and annotation of potential enzyme-related genes and regulation pattern would be necessary to provide great benefit for understanding of potential mechanism of these molluscicides and even for future molluscicide development.

Evolution of the National Schistosomiasis Control Programmes in The People's Republic of China

Schistosomiasis japonica is caused by the parasitic trematode Schistosoma japonicum. It is endemic in The People's Republic of China and has significant impact on human health and socioeconomic development in certain regions. Over the last six decades, the national control programmes evolved in remarkable ways and brought schistosomiasis japonica largely under control. We describe the history and evolution of schistosomiasis control in The People's Republic of China, with an emphasis on shifts in control strategies that evolved with new insights into the biology of the parasite and its intermediate hosts, and the epidemiology of the disease in the country. We also highlight the achievements in controlling the disease in different socioecological settings, and identify persisting challenges to fully eliminate schistosomiasis japonica from the country. To reach the goal of schistosomiasis elimination, further integration of interventions, multisector collaboration, sensitive and effective surveillance are needed to strengthen.

Integrated Control Strategy of Schistosomiasis in The People's Republic of China: Projects Involving Agriculture, Water Conservancy, Forestry, Sanitation and Environmental Modification

Among the three major schistosome species infecting human beings, Schistosoma japonicum is the only endemic species in The People's Republic of China. Schistosomiasis is endemic in 78 countries and regions and poses a severe threat to public health and socioeconomic development. Through more than 60years of hard work and endeavour, The People's Republic of China has made considerable achievements and reduced the morbidity and prevalence of this disease to the lowest level ever recorded, especially since the introduction of the new integrated control strategy in 2004. This review illustrates the strategies implemented by giving successful examples of schistosomiasis control from the different types of remaining endemic areas. The challenge to control or eliminate S. japonicum is analysed in order to provide useful information to policy makers and scientists.

China-Africa and China-Asia Collaboration on Schistosomiasis Control: A SWOT Analysis

Schistosomiasis, a disease caused by a trematode, parasitic worm, is a worldwide public health problem. In spite of great progress with regard to morbidity control, even elimination of this infection in recent decades, there are still challenges to overcome in sub-Saharan Africa and endemic areas in Southeast Asia. Regarded as one of the most successful countries with respect to schistosomiasis control, The People's Republic of China has accumulated considerable experience and learnt important lessons in various local settings that could benefit schistosomiasis control in other endemic countries. Based on an analysis of conceived strengths, weaknesses, opportunities and threats (SWOT) of potential collaborative activities with regard to schistosomiasis in Africa and Asia, this article addresses the importance of collaborative efforts and explores the priorities that would be expected to facilitate the transfer of Chinese experience to low- and middle-income countries in Africa and Asia.

Enhancing collaboration between China and African countries for schistosomiasis control

Schistosomiasis remains an important public health issue, with a large number of cases reported across sub-Saharan Africa, and parts of Asia and Latin America. China was once highly endemic, but has made substantial progress and is moving towards elimination of schistosomiasis. Meanwhile, despite long-term, repeated, school-based chemotherapy in many African countries, more than 90% of all schistosomiasis cases are concentrated in Africa, and hence, this continent constitutes the key challenge for schistosomiasis control. Opportunities and issues for international collaboration in the fight against schistosomiasis are outlined with a focus on China's experiences, including the role of public health authorities and intersectoral collaboration, use of new and effective snail control approaches and diagnostic tools adapted to the specific stage of control, as well as the strengthening of risk mapping and surveillance-response mechanisms. Training courses targeting African governmental officials and professionals, coupled with field visits of African scientists and control programme managers to China, and vice versa, are considered important for improved schistosomiasis control and elimination. The crucial question remains whether the Chinese experience can be translated and applied in African countries to improve the effectiveness of health interventions and scale-up.

Enhancing the Capacity of Policy-Makers to Develop Evidence-Informed Policy Brief on Infectious Diseases of Poverty in Nigeria

BACKGROUND

The lack of effective use of research evidence in policy-making is a major challenge in most low- and middle-income countries (LMICs). There is need to package research data into effective policy tools that will help policy-makers to make evidence-informed policy regarding infectious diseases of poverty (IDP). The objective of this study was to assess the usefulness of training workshops and mentoring to enhance the capacity of Nigerian health policy-makers to develop evidence-informed policy brief on the control of IDP.

METHODS

A modified "before and after" intervention study design was used in which outcomes were measured on the target participants both before the intervention is implemented and after. A 4-point Likert scale according to the degree of adequacy; 1 = "grossly inadequate," 4 = "very adequate" was employed. The main parameter measured was participants' perceptions of their own knowledge/understanding. This study was conducted at subnational level and the participants were the career health policy-makers drawn from Ebonyi State in the South-Eastern Nigeria. A one-day evidence-to-policy workshop was organized to enhance the participants' capacity to develop evidence-informed policy brief on IDP in Ebonyi State. Topics covered included collaborative initiative; preparation and use of policy briefs; policy dialogue; ethics in health policy-making; and health policy and politics.

RESULTS

The preworkshop mean of knowledge and capacity ranged from 2.49-3.03, while the postworkshop mean ranged from 3.42-3.78 on 4-point scale. The percentage increase in mean of knowledge and capacity at the end of the workshop ranged from 20.10%-45%. Participants were divided into 3 IDP mentorship groups (malaria, schistosomiasis, lymphatic filariasis [LF]) and were mentored to identify potential policy options/recommendations for control of the diseases for the policy briefs. These policy options were subjected to research evidence synthesis by each group to identify the options that have the support of research evidence (mostly systematic reviews) from PubMed, Cochrane database and Google Scholar. After the evidence synthesis, five policy options were selected out of 13 for malaria, 3 out of 10 for schistosomiasis and 5 out of 11 for LF.

CONCLUSION

The outcome suggests that an evidence-to-policy capacity enhancement workshop combined with a mentorship programme can improve policy-makers' capacity for evidence-informed policy-making (EIP).

De Novo transcriptome analysis of Oncomelania hupensis after molluscicide treatment by next-generation sequencing: implications for biology and future snail interventions

The freshwater snail Oncomelania hupensis is the only intermediate host of Schistosoma japonicum, which causes schistosomiasis. This disease is endemic in the Far East, especially in mainland China. Because niclosamide is the only molluscicide recommended by the World Health Organization, 50% wettable powder of niclosamide ethanolamine salt (WPN), the only chemical molluscicide available in China, has been widely used as the main snail control method for over two decades. Recently, a novel molluscicide derived from niclosamide, the salt of quinoid-2',5-dichloro-4'-nitro-salicylanilide (Liu Dai Shui Yang An, LDS), has been developed and proven to have the same molluscicidal effect as WPN, with lower cost and significantly lower toxicity to fish than WPN. The mechanism by which these molluscicides cause snail death is not known. Here, we report the next-generation transcriptome sequencing of O. hupensis; 145,008,667 clean reads were generated and assembled into 254,286 unigenes. Using GO and KEGG databases, 14,860 unigenes were assigned GO annotations and 4,686 unigenes were mapped to 250 KEGG pathways. Many sequences involved in key processes associated with biological regulation and innate immunity have been identified. After the snails were exposed to LDS and WPN, 254 unigenes showed significant differential expression. These genes were shown to be involved in cell structure defects and the inhibition of neurohumoral transmission and energy metabolism, which may cause snail death. Gene expression patterns differed after exposure to LDS and WPN, and these differences must be elucidated by the identification and annotation of these unknown unigenes. We believe that this first large-scale transcriptome dataset for O. hupensis will provide an opportunity for the in-depth analysis of this biomedically important freshwater snail at the molecular level and accelerate studies of the O. hupensis genome. The data elucidating the molluscicidal mechanism will be of great benefit in future snail control efforts.

Evaluating the effect of a novel molluscicide in the endemic schistosomiasis japonica area of China

Oncomelania hupensis is the sole intermediate host snail of Schistosoma japonicum in China. Snail control by molluscicide remains one of the most effective measures of schistosomiasis japonica control. A 50% wettable powder of niclosamide ethanolamine salt (WPN) is widely used for snail control in China. However, WPN is costly and toxic to fish. A novel molluscicide named LDS, the salt of quinoid-2', 5-dichloro-4'-nitrosalicylanilide from niclosamide, has been developed. To evaluate the effects of large-scale field application of LDS on field snail control, tests were conducted in 15 counties of Hubei Province, China. Active adult snails, were immersed in 0.2, 0.4, and 0.6 g/m3 of 10% LDS, 1.0 g/m3 of 50% WPN was used as the molluscicide control, and then the mortality rates of snails were investigated after 1, 2, and 3 days. In addition, four active concentrations of 10% LDS (0.4, 0.6, 0.8 and 1.0 g/m2) were applied by spraying and powdering in the field. 1.0 g/m2 of 50% WPN was used as the molluscicide control, and then the mortality rates of snails were observed after 1, 3, and 7 days. The results indicated that 0.4 g/m3 LDS applied by the immersion or 0.6 g/m2 LDS applied by spraying and powdering achieved the same molluscicidal effect as that of WPN, regardless of exposure time. By using different methods, the snail mortality rates in the molluscicide groups were related to exposure time and concentration, respectively. LDS costs less than WPN; thus, LDS is suitable and applicable for use as a molluscicide in schistosomiasis japonica epidemic areas.

Resistance to niclosamide in Oncomelania hupensis, the intermediate host of Schistosoma japonicum: should we be worried?

As the currently only available molluscicide, niclosamide has been widely used for snail control for over 2 decades in China. There is therefore a concern about the emergence of niclosamide-resistant snail populations following repeated, extensive use of the chemical. The purpose of this study was to investigate the likelihood of niclosamide resistance in Oncomelania hupensis in China. Active adult O. hupensis snails derived from 20 counties of 10 schistosomiasis-endemic provinces of China, of 10 snails in each drug concentration, were immersed in solutions of 1, 0.5, 0.25, 0.125, 0.063, 0.032, 0.016 and 0.008 mg L-1 of a 50% wettable powder of niclosamide ethanolamine salt (WPN) for 24 and 48 h at 25 °C, and the median lethal concentration (LC50) was estimated. Then, the 24- and 48-h WPN LC50 values were compared with those determined in the same sampling sites in 2002. The results indicated that the 24- and 48-h WPN LC50 values for O. hupensis were not significantly different from those determined in 2002 (P = 0.202 and 0.796, respectively). It is concluded that the current sensitivity of O. hupensis to niclosamide has not changed after more than 2 decades of repeated, extensive application in the main endemic foci of China, and there is no evidence of resistance to niclosamide detected in O. hupensis.

Establishing and applying a schistosomiasis early warning index (SEWI) in the lower Yangtze River Region of Jiangsu Province, China

Background

China has made remarkable progress in schistosomiasis control over the past decades. Transmission control has replaced morbidity control as the country moves towards the goal of elimination and the current challenge is to find a sensitive measure capable of gauging transmission risk in low-prevalence areas. The study aims to develop a Schistosomiasis Early Warning Index (SEWI) and demonstrate its use in Jiangsu Province along the lower Yangtze River.

Methodology/Principal Findings

The Delphi approach, a structured communication technique, was used to develop the SEWI. Two rounds of interviews with 30 public health experts specialized in schistosomiasis control were conducted using 40 indicators that reflected different aspects of schistosomiasis transmission and control. The necessity, feasibility, and sensitivity of each indicator were assessed and the weight value of each indicator determined based on these experts' judgment. The system included 3 first-order indicators, 7 second-order indicators, and 30 third-order indicators. The 3 first-order indicators were endemic status, control measures, social and environmental factors, with the weight values 0.366, 0.343 and 0.291, respectively. For the 7 second-order indicators, the highest weight value was for control measures for snails (0.175) and the lowest for transmission route (0.110). We estimated and mapped the SEWI for endemic areas at the county scale in Jiangsu Province finding that the majority of the endemic areas were characterized as medium transmission risk (SEWI risk values between 0.3 and 0.6), while areas where transmission interruption had been officially declared showed SEWI values <0.30. A few isolated areas (e.g. endemic islands in the Yangtze River) produced SEWI values >0.60. These estimates are largely in agreement with the endemicity levels based on recent epidemiological surveys.

Conclusions/Significance

The SEWI should be useful for estimation of schistosomiasis transmission surveillance, particularly with reference to the elimination of the disease in China.

Sensitivity of Oncomelania hupensis to niclosamide: a nation-wide survey in China

Schistosomiasis japonica, transmitted by the intermediate host snail Oncomelania hupensis of the causative agent Schistosoma japonicum, remains a major public-health concern in China, and control of this snail is one of the major approaches used in attempts to interrupt the transmission of this neglected tropical disease. Niclosamide is currently the only commercial molluscicide available for the control of O. hupensis snails in China. The purpose of this study was to evaluate the current sensitivity of O. hupensis to niclosamide in China. O. hupensis snails derived from 17 sampling sites from eight schistosomiasis-endemic provinces of China were used for the molluscicidal tests. Active adult snails (10 for each drug concentration), were immersed in solutions of 1, 0.5, 0.25, 0.125, 0.063, 0.032, 0.016 and 0.008 mg/L of 50% wettable powder of niclosamide ethanolamine salt (WPN) for 24 and 48 h at 25°C, and then the snail mortality was estimated and LC50 values were calculated. All field-derived O. hupensis snails were dead following immersion in 0.5 and 1 mg/L WPN for 24 h, whereas no death was observed after immersion in 0.008 mg/L WPN for 24 h. Immersion in 0.5, 0.25, 0.125, 0.063, 0.032 and 0.016 mg/L WPN for 24 h resulted in 80%-100%, 63.33%-100%, 0%-85%, 0%-50%, 0%-15%, and 0%-5% snail mortalities, respectively. The 24 h WPN LC50 values for the O. hupensis snails derived from the 17 sampling sites in China ranged from 0.0743 to 0.2285 mg/L, and no significant difference was detected by the Kolmogorov-Smirnov test (p = 0.2). The results indicate that there is no regional variation in the current susceptibility to niclosamide in O. hupensis populations in China. It is suggested that the current sensitivity of niclosamide against O. hupensis remains high and has not changed after more than two decades of repeated, extensive application for snail control in the main endemic areas of China.

Monitoring the transmission of Schistosoma japonicum in potential risk regions of China, 2008 - 2012

Schistosomiasis japonica, caused by Schistosoma japonicum infection, remains a major public health concern in China, and the geographical distribution of this neglected tropical disease is limited to regions where Oncomelania hupensis, the intermediate host of the causative parasite, is detected. The purpose of this study was to monitor the transmission of S. japonicum in potential risk regions of China during the period from 2008 through 2012. To monitor the transmission, 10 fixed surveillance sites and 30 mobile sentinel sites were selected in 10 counties of four provinces, namely Anhui, Jiangsu, Chongqing and Hubei. There were 8, 9, 6, 2 and 3 cases infected with S. japonicum detected in the 30 mobile sentinel sites during the 5-year study period, while 27 subjects were positive for the antibody-based serum test in the 10 fixed sentinel sites; however, no infection was found. In addition, neither local nor imported livestock were found to be infected. No O. hupensis snails were detected in either the fixed surveillance or the mobile sentinel sites; however, the snail host was found to survive and reproduce at Chaohu Lake, inferring the potential of transmission of the disease. It is suggested that the continuous surveillance of schistosomiasis japonica should be carried out in both the endemic foci and potential risk regions of China, and an active, sensitive system to respond the potential risk of transmission seems justified.

Identifying host species driving transmission of schistosomiasis japonica, a multihost parasite system, in China

Understanding disease transmission dynamics in multihost parasite systems is a research priority for control and potential elimination of many infectious diseases. In China, despite decades of multifaceted control efforts against schistosomiasis, the indirectly transmitted helminth Schistosoma japonicum remains endemic, partly because of the presence of zoonotic reservoirs. We used mathematical modeling and conceptual frameworks of multihost transmission ecology to assess the relative importance of various definitive host species for S. japonicum transmission in contrasting hilly and marshland areas of China. We examine whether directing control interventions against zoonotic reservoirs could further reduce incidence of infection in humans or even eliminate transmission. Results suggest that, under current control programs, infections in humans result from spillover of transmission among zoonotic reservoirs. Estimates of the basic reproduction number within each species suggest that bovines (water buffalo and cattle) maintained transmission in the marshland area and that the recent removal of bovines from this area could achieve local elimination of transmission. However, the sole use of antifecundity S. japonicum vaccines for bovines, at least at current efficacies, may not achieve elimination in areas of comparable endemicity where removal of bovines is not a feasible option. The results also suggest that rodents drive transmission in the hilly area. Therefore, although targeting bovines could further reduce and potentially interrupt transmission in marshland regions of China, elimination of S. japonicum could prove more challenging in areas where rodents might maintain transmission. In conclusion, we show how mathematical modeling can give important insights into multihost transmission of indirectly transmitted pathogens.

The South-to-North Water Diversion Project: effect of the water diversion pattern on transmission of Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China

BACKGROUND

The South-to-North Water Diversion Project (SNWDP) is the largest national water conservancy project in China. However, the Eastern Route Project (ERP) of SNWDP will refer to the habitats of Oncomelania hupensis, the intermediate host of Schistosoma japonicum. The present study was aimed at investigating the effects of some factors relating to the water diversion pattern on the spread north of O. hupensis and transmission of S. japonicum.

METHODS

Marked snails were attached to the floating debris, and then placed on the water surface, the passage of snails through water pumps was observed. Some marked living adult snails were placed under water in the 5 spots, 15, 30, 60, 90 and 120 days later, their survival and transfer under water were investigated. 2, 4, 8, 16, 32, 64 and 128 juvenile snails, with a male: female ratio of about 1, were caged, 1 year later, their reproductions were calculated.

RESULTS

The snails attached on the floating debris at 100-, 50- and 20-cm-distance from the inlet pipe of the big pump (with a diameter of 80 cm), could be absorbed into the pumps, with passing rates of 2.45%, 3.93% and 43.46%, respectively, compared with 72.07% and 91.00% for the snails at 20 cm and 10 cm-distance from the inlet pipe of the small pump (with a diameter of 20 cm). A total of 36,600 marked living snails were put into 5 ponds and ditches, with the water depths of 1-1.6 m, 15-120 days later, no marked ones were found along the ponds and ditches or in the straw packages. The juvenile snails did not reproduce until their density reached up to 8 snails (ratio of male: female of 1)/0.16 m2.

CONCLUSIONS

During the construction of ERP of SNWDP, the risk of northward spread of schistosomiasis japonica will be decreased or eliminated as long as long-term reliable interventions for snail control are implemented.

Effectiveness of a comprehensive schistosomiasis japonica control program in Jiangsu province, China, from 2005 to 2008

The effectiveness of a comprehensive schistosomiasis japonica control program implemented in 8 villages along the Yangtze river in Jiangsu province from 2005 to 2008 was studied. Control measures included snail control, chemotherapy of humans and livestock, health education, and transmission cycle interruption using sanitation in dwellings and at anchorage sites for fishermen and sailors. The Schistosoma japonicum prevalence among residents and livestock, the total area of snail habitats, the Oncomelania hupensis snail density, and the percentage of infected snails served as indicators for the effectiveness of the control efforts. After 4 years of program implementation, the seroprevalence in humans had decreased from 9.03% to 3.24% (P < 0.001) and the parasitological prevalence among males had decreased from 0.42% to 0.12% (P = 0.004). Among females, it remained stable at a low level. The S. japonicum prevalence in livestock had decreased from 2.94% to 0% (P < 0.001). Additionally, the area where infected snails could be found had shrunk from 89.99 hectares (ha) to 16.00 ha, the snail density had decreased from 0.56 to 0.32 per 0.1m(2), and the percentage of infected snails had dropped from 0.38% to 0.12% (all P < 0.001). The results demonstrate that an integrated schistosomiasis japonica control strategy focusing on the main transmission cycles and reservoirs and combines chemotherapy, infrastructure interventions and health education combined with robust surveillance is feasible and allows to effectively control S. japonicum.

Synthesis of Ginkgolic Acid Analogues and Evaluation of Their Molluscicidal Activity

Based on the molluscicidal activity of ginkgolic acids (GAs) isolated from Ginkgo biloba L, a series of Z/E isomers of GA analogues were prepared and evaluated for their molluscicidal activities against the host snail Oncomelania hupensis. The results and analysis of the structure-activity relationship revealed that the E-isomers showed better molluscicidal activities than their Z-isomers. Molluscicidal activities decreased with the shortening of the alkenyl chain lengths.

In vitro praziquantel test capable of detecting reduced in vivo efficacy in Schistosoma mansoni human infections

Although great reductions in human schistosomiasis have been observed after praziquantel (PZQ) mass drug administration (MDA), some individuals remain infected after multiple treatments. Many MDA programs now require monitoring for drug efficacy as a key component. No molecular tools for PZQ resistance currently exist and investigations into the dose of PZQ required to kill 50% of adult worms in vivo (ED(50)) present ethical, logistical, and temporal restraints. We, therefore, assessed the feasibility and accuracy of a rapid, inexpensive in vitro PZQ test in the laboratory and directly in the field in Uganda under MDA in conjunction with highly detailed infection intensity, clearance, and reinfection data. This test strongly differentiated between subsequently cleared and uncleared infections as well as differences between parasite populations pre- and post-PZQ treatments, advocating its use for on-the-spot monitoring of PZQ efficacy in natural foci. After only a few treatments, uncleared parasites were identified to be phenotypically different from drug-sensitive parasites, emphasizing the urgent need for monitoring of these repeatedly PZQ-treated populations.

Experimental evidence of size/age-biased infection of Biomphalaria glabrata (Pulmonata: Planorbidae) by an incompatible parasite species: consequences for biological control

Because the digenetic trematode Plagiorchis elegans can elicit a rapid, severe and permanent suppression of the reproductive output in the snail Biomphalaria glabrata, it is considered as a potential biological control agent of human schistosomiasis. This assumption however is derived from laboratory experiments that are poor approximations of what occurs in a natural ecosystem. In order to recreate conditions that resemble those found in nature, we exposed B. glabrata as individual populations composed of a young, juvenile and adult snails to various concentrations of P. elegans eggs to assess the probability of encountering the parasite eggs by the different snail sizes/age groups. We demonstrated that within populations composed of different size/age classes, larger/older snails displayed the negative effects typical of exposure to P. elegans, whereas smaller individuals appeared relatively unaffected, particularly at lower levels of exposure. These findings coupled with the difficulty of producing large quantities of parasite eggs suggest that P. elegans has limited efficiency as a biological control agent of human schistosomiasis.

Microarray analysis of genes highly expressed in cercarial stage of Schistosoma japonicum and the characterization of the antigen Sj20H8

Schistosomes have a complex life cycle which alternates between two hosts and includes two short-lived water-born forms. Cercariae are the larval forms of schistosomes responsible for infection of the vertebrate hosts. The infection is initiated when the cercariae penetrate host skin. During penetration, cercariae will undergo profound changes and release excretory/secretory products to adapt to the new environment and to escape from host's immune attack. Part of these events should be determined, to some degree, by the activation of certain genes in the cercariae. In this study, we performed cDNA microarray analysis to monitor the profile of the genes actively expressed in Schistosoma japonicum cercariae. Microarray analysis showed that 76 of 3840 cDNA clones were expressed more than 20-fold in cercariae compared to adult worms. After cluster analysis, 19 non-redundant expressed sequence tags (ESTs) were obtained, 4 of which represented functionally annotated genes, 14 of which represented functionally un-characterized genes, and 1 of which represented a novel gene sequence. The full-length cDNA of the second most abundant EST, Sj20H8, was cloned and preliminarily characterized. Although the precise biological role of all cercarial actively expressed transcripts identified in this investigation awaits further functional analysis, our findings may offer insight into novel control strategies or help to develop potential vaccine candidates against schistosomiasis.

Contrasting reservoirs for Schistosoma japonicum between marshland and hilly regions in Anhui, China--a two-year longitudinal parasitological survey

Schistosoma japonicum remains highly endemic in many counties in China and has recently re-emerged, to a large extent, in previously controlled areas. To test the hypothesis that small rodents and less agriculturally important domestic animals such as dogs and cats may play an important role in the transmission and potential re-emergence of this disease, an annual investigation of S. japonicum among humans, domestic animals and rodents, combined with detailed surveys of the snail intermediate host, was performed across 3 marshland villages and 3 hilly villages in Anhui province of China over 2 consecutive years. The highest infection prevalence and intensity observed across all mammals was in rodents in the hilly region; while in the marshland, bovines were suspected as the main reservoirs. However, relatively high infection prevalence levels were also found in dogs and cats in both regions. Such results may have implications for the current human- and bovine-oriented control policy for this medically and veterinarily important disease, particularly within the hilly regions of mainland China.

Spatial epidemiology in zoonotic parasitic diseases: insights gained at the 1st International Symposium on Geospatial Health in Lijiang, China, 2007

The 1st International Symposium on Geospatial Health was convened in Lijiang, Yunnan province, People's Republic of China from 8 to 9 September, 2007. The objective was to review progress made with the application of spatial techniques on zoonotic parasitic diseases, particularly in Southeast Asia. The symposium featured 71 presentations covering soil-transmitted and water-borne helminth infections, as well as arthropod-borne diseases such as leishmaniasis, malaria and lymphatic filariasis. The work made public at this occasion is briefly summarized here to highlight the advances made and to put forth research priorities in this area. Approaches such as geographical information systems (GIS), global positioning systems (GPS) and remote sensing (RS), including spatial statistics, web-based GIS and map visualization of field investigations, figured prominently in the presentation.

Nonparametric spatial analysis to detect high-risk regions for schistosomiasis in Guichi, China

Schistosomiasis control in China is facing a new challenge due to the rebound of epidemics in many areas and the unsustainable effects of the chemotherapy-based control strategy. Identifying high-risk regions for schistosomiasis is an important first step for an effective and sustainable strategy. Direct surveillance of snail habitats to detect high-risk regions is costly and no longer a desirable approach, while indirect monitoring of acute schistosomiasis may be a satisfactory alternative. To identify high-risk regions for schistosomiasis, we jointly used multiplicative and additive models with the kernel smoothing technique as the main approach to estimate the relative risk (RR) and excess risk (ER) surfaces by analyzing surveillance data for acute schistosomiasis. The feasibility of detecting high-risk regions for schistosomiasis through nonparametric spatial analysis was explored and confirmed in this study, and two significant high-risk regions were identified. The results provide useful hints for improving the national surveillance network for acute schistosomiasis and possible approaches to utilizing surveillance data more efficiently. In addition, the commonly used epidemiological indices, RR and ER, are examined and emphasized from the spatial point of view, which will be helpful for exploring many other epidemiological indices.