Snail Reproduction Research Articles

Effect of feed protein on reproduction, proximate composition, and hemolymph metabolite profile of snail (Achatina achatina)

Effect of feed protein on reproduction, proximate composition, and hemolymph metabolite profile of snail (Achatina achatina)

Order and timing of infection with different parasite life stages impacts host and parasite life histories.

Co-exposure to multiple parasites can alter parasite success and host life history when compared to single infections. These infection outcomes can be affected by the order of parasite arrival, the host immune response, and the interspecific interactions among co-infecting parasites. In this study, we examined how the arrival order of two trematode parasites, Schistosoma mansoni and Echinostoma caproni, influenced parasite ecology and the life history of their snail host, Biomphalaria glabrata. Snail hosts were exposed to E. caproni cercariae before, with, and after their exposure to S. mansoni miracidia. We then measured the effects of this timing on infection prevalence, infection intensity of E. caproni metacercariae, and cercarial output of S. mansoni, as well as on snail reproduction and survival. Snails infected only with S. mansoni and snails exposed to E. caproni after S. mansoni both shed more cercariae than simultaneously exposed snails. Additionally, S. mansoni prevalence was lower in snails that were first exposed to E. caproni compared to snails that were exposed to E. caproni after S. mansoni. Moreover, snails exposed to E. caproni before S. mansoni did not differ in their survival compared to control snails, whereas simultaneously exposed snails and snails exposed to E. caproni after S. mansoni had lower survival than control snails. Combined, this prevalence and survival data suggest a potential protective role of early E. caproni exposure. The timing of E. caproni exposure impacts S. mansoni establishment and reproduction, but host survival patterns are likely driven by S. mansoni prevalence alone.

Effect of Different Levels of Calcium and Addition of Magnesium in the Diet on Garden Snails’ (Cornu aspersum) Condition, Production, and Nutritional Parameters

Edible snails are an attractive protein source due to their high growth rate, cost-efficiency, and nutritional value. Calcium is crucial for snail growth, reproduction, and shell formation, while magnesium plays a role in enzyme function and muscle tone. This study aimed to optimise calcium and magnesium levels in Cornu aspersum diets to optimise the production and technological characteristics of the derived animal products. Snails were fed specific diets in controlled conditions with varying calcium and magnesium levels (44.3, 66.1, 88.7, 103.5 Ca g/kg feed and 3.3, 5.6, 7.2 Mg g/kg feed) for four months. Their growth, shell characteristics, and meat composition were evaluated. As calcium in the feed increased, carcass and shell weights were higher. Also, the crushing force of the shells was higher with increasing amount of calcium in the feed. In the group with 10.35% calcium and 0.72% magnesium, snail growth significantly slowed down after three months, with lower mortality. It is suggested that a shortened fattening cycle by 3–4 weeks compared to the magnesium-free diet is possible. However, based on meat, shell, mortality, and feed intake analysis, a 0.56% magnesium concentration in the feed seems to give better results, as magnesium content at 0.72% might be toxic to snails. Further investigation is to confirm the possibility of neutralising the negative effects of magnesium in the diet through increasing calcium and phosphorus intake.

Experimental water hyacinth invasion and destructive management increase human schistosome transmission potential.

Invasive species cause environmental degradation, decrease biodiversity, and alter ecosystem function. Invasions can also drive changes in vector-borne and zoonotic diseases by altering important traits of wildlife hosts or disease vectors. Managing invasive species can restore biodiversity and ecosystem function, but it may have cascading effects on hosts, parasites, and human risk of infection. Water hyacinth, Eichhornia crassipes, is an extremely detrimental invader in many sites of human schistosome transmission, especially in Lake Victoria, where hyacinth is correlated with high snail abundance and hotspots of human schistosome infection. Hyacinth is often managed via removal or in situ destruction, but the effects of these strategies on snail intermediate hosts and schistosomes are not known. We evaluated the effects of water hyacinth invasion and these management strategies on the dynamics of human schistosomes, Schistosoma mansoni, and snails, Biomphalaria glabrata, in experimental mesocosms over 17 weeks. We hypothesized that hyacinth, which is inedible to snails, would affect snail growth, reproduction, and cercariae production through the balance of its competitive effects on edible algae and its production of edible detritus. We predicted that destruction would create a pulse of edible detrital resources, thereby increasing snail growth, reproduction, and parasite production. Conversely, we predicted that removal would have small or negligible effects on snails and schistosomes, because it would alleviate competition on edible algae without generating a resource pulse. We found that hyacinth invasion suppressed algae, changed the timing of peak snail abundance, and increased total production of human-infectious cercariae ~6-fold relative to uninvaded controls. Hyacinth management had complex effects on algae, snails, and schistosomes. Removal increased algal growth and snail abundance (but not biomass), and slightly reduced schistosome production. In contrast, destruction increased snail biomass (but not abundance), indicating increases in body size. Destruction caused the greatest schistosome production (10-fold more than the control), consistent with evidence that larger snails with greater access to food are most infectious. Our results highlight the dynamic effects of invasion and management on a globally impactful human parasite and its intermediate host. Ultimately, preventing or removing hyacinth invasions would simultaneously benefit human and environmental health outcomes.

Opportunity or catastrophe? effect of sea salt on host-parasite survival and reproduction.

Seawater intrusion associated with decreasing groundwater levels and rising seawater levels may affect freshwater species and their parasites. While brackish water certainly impacts freshwater systems globally, its impact on disease transmission is largely unknown. This study examined the effect of artificial seawater on host-parasite interactions using a freshwater snail host, Biomphalaria alexandrina, and the human trematode parasite Schistosoma mansoni. To evaluate the impact of increasing salinity on disease transmission four variables were analyzed: snail survival, snail reproduction, infection prevalence, and the survival of the parasite infective stage (cercariae). We found a decrease in snail survival, snail egg mass production, and snail infection prevalence as salinity increases. However, cercarial survival peaked at an intermediate salinity value. Our results suggest that seawater intrusion into freshwaters has the potential to decrease schistosome transmission to humans.

The Life Histories of Intermediate Hosts and Parasites of Schistosoma haematobium and Schistosoma mansoni in the White Nile River, Sudan.

Background: The epidemiology of schistosomiasis transmission varies depending on the circumstances of the surrounding water bodies and human behaviors. We aimed to explore cercarial emergence patterns from snails that are naturally affected by human schistosomiasis and non-human trematodes. In addition, this study aimed to explore how schistosomiasis infection affects snail survival, reproduction, and growth. Methods: We measured the survival rate, fecundity, and size of Biomphalaria pfeifferi snails and the cercarial rhythmicity of S. haematobium and S. mansoni. The number of egg masses, eggs per egg mass, and snail deaths were counted for 7 weeks. The survival rate and cumulative hazard were assessed for infected and non-infected snails. Results: S. haematobium and S. mansoni cercariae peaked at 9:00–11:00 a.m. Infection significantly reduced the survival rate of B. pfeifferi, which was 35% and 51% for infected and non-infected snails, respectively (p = 0.02), at 7 weeks after infection. The hazard ratio of death for infected snails compared to non-infected snails was 1.65 (95% confidence interval: 1.35–1.99; p = 0.01). Conclusions: An understanding of the dynamics of schistosomiasis transmission will be helpful for formulating schistosomiasis control and elimination strategies. Cercarial rhythmicity can be reflected in health education, and the reproduction and survival rate of infected snails can be used as parameters for developing disease modeling.

Divergent effects of invasive macrophytes on population dynamics of a snail intermediate host of Schistosoma Mansoni

Vectors and intermediate hosts of globally impactful human parasites are sensitive to changes in the ecological communities in which they are embedded. Sites of endemic transmission of human schistosome can also be invaded by nonnative species, especially aquatic plants (macrophytes). We tested the effects on macrophyte invasions on experiment snail and schistosome populations created in 100 L mesocosm tanks. We established macrophyte-free mesocosms and those containing one of four widespread macrophyte species that are inedible to snails (duckweed, hornwort, water lettuce, or water hyacinth) and then tracked edible resources (periphyton algae) and the abundance, reproduction, and infection of snail intermediate hosts for 16 weeks. We predicted that the three floating macrophytes would reduce periphyton, thereby reducing snail reproduction, abundance, and infections. In contrast, we predicted that hornwort, which is submerged and provides substrate for periphyton growth, would increase snail reproduction and abundance. As predicted, all floating macrophytes decreased periphyton, but only water hyacinth significantly decreased snail reproduction and abundance. Snail abundance increased significantly only with water lettuce. We hypothesize that this unanticipated increase in snails occurred because water lettuce produced abundant and/or high quality detritus, subsidizing snails despite low periphyton availability. Unfortunately, we detected too few infections to analyze. Aquatic macrophytes exert strong species-specific effects on snail populations. Therefore, efforts to manage invasive plants in endemic sites should evaluate changes in resources, snails, and transmission potential. We recommend caution with management efforts that produce large amounts of detritus, which might stimulate snail populations and therefore risk of human exposure.

Combined effects of air temperature, photoperiod and humidity on Otala tingitana snails’ breeding (Mollusca, Gastropoda, Helicidae)

ABSTRACT This study investigates the reproduction of Otala tingitana (Paladilhe, 1875) snails collected from El Hajeb region (Morocco) after aestivation and reared in transparent containers under eight different combinations of air temperature, relative humidity (RH), and photoperiod [hours of light (L) and darkness (D)]. Biomass change was used to evaluate the growth of the snails. Mating, egg-laying, and hatching were monitored to assess reproduction rate in different artificial conditions. Animals that were reared under a combination of (20°C, 50% RH, 16L-8D) showed improved mating frequency, whereas the best breeding yield and reproduction rate were obtained with a combination of 20°C, 80% RH, and 16L-8D photoperiod. Except for one condition in which inhibition of laying was recorded (15°C, 50% RH, 16L-8D), O. tingitana snails showed high plasticity regarding the environmental factors tested. However, in all combinations used, none of the parameters was a limiting factor; instead, we suggest that the interaction between the three parameters modulates snail growth and reproduction. Overall, for the first time this study examined experimental evidence about the effect of environmental factors on the reproduction of Otala tingitana, thereby defining the optimal combination of temperature, humidity, and photoperiod for improved breeding of this species.

Environmental biomonitoring by snails

Background: Bio-indicator systems are vital in terms of monitoring of pollutants around the world. The impact of environmental change can be monitored by employing the responsive behaviour of snails. Heavy metal and organic pollutants affects snail reproduction, mortality, and normal metabolic activities. Various changes like a discontinuity in food intake, growth rate, twitching, and quenching of tentacles, are the biomarkers of the snails for biomonitoring. Different snails can bio-monitor eco-toxicological urban pollution, oil pollutant, terrestrial pollution, pesticide pollutants, mercury contamination, ammonia, chlorinated paraffin in soil, ethanol in water, ocean acidification pollutions. These animals can also make bio-sense about diverse environment spheres, which include the biosphere, lithosphere, anthroposphere, cryosphere, and hydrosphere. Methods: We examined the scientific literature and related articles listed in Pub-med, Google Scholar reporting on biomonitoring potential and biomarkers expression of various snail species and consequently explore the value of snails in the respective field by discussing various outcomes of a number of studies on the pollution biomonitoring and biosensing capabilities. Results: Several terrestrial, freshwater and sea snail species are characterized by the high sense of biomonitoring and biosensing potential. Various biomarkers such as expression of heat shock proteins and metallothioneins in the body are found to be the essential in-vivo biomarkers for pollution biomonitoring. Conclusion: It is observed that snails offer an environment friendly approach for the environmental bio monitoring by expressing their numerous physiological, biochemical, genetical and histological biomarkers in their body. Thus, it proved to be a critical bio monitoring tool and early warning indicators.

The effects of different water temperatures on survival and growth rate of juvenile invasive apple snail, Pomacea canaliculata (Lamarck, 1822) under controlled environment

Invasive apple snail, Pomacea canaliculata is one of the major mollusc pests affecting rice production in Malaysia. This pest not only gives fatal effects to rice but also decreases the water quality in the ecosystem due to the use of pesticides to control it. With the unpredictable changes on global climatic in Malaysia, it is important to have knowledge on the effect of water temperature on growth and survival rate of P. canaliculata in water bodies, in order to avoid loss in paddy field and its adverse effects on aquatic ecosystems. Water temperature is one of the most important environmental factors influencing the survival, growth rate, reproduction and behaviour of freshwater snails. The aim of this study is to evaluate the growth and survival rate of juvenile P. canaliculata at different temperature regimes. Growth and survival of juvenile P. canaliculata were evaluated at different constant water temperatures (15, 20, 25, 30 and 35°C). Our findings show, at 30° C the growth rate of P. canaliculata is higher compared with the other temperatures, however had low survival rate. Meanwhile, at room temperature (21 - 24°C), a higher survival rate (100%) was recorded. The results showed that different water temperatures affect the growth and survival rate of P. canaliculata and it is an important indicator for predicting and understanding the changes of water temperature when controlling this pest.

Spatial distribution and morphometry of the succineid snail Succinea baconi (Pfeiffer, 1854) in India

The spatial distribution and morphological features of the land snail Succinea baconi (Pfeiffer, 1854) (Gastropoda: Succineidae) from India were evaluated. The survey performed in gardens and bushes in Coochbehar, West Bengal, India, has made it possible to assess the abundance of the snail S. baconi on the randomly selected lemon plants (n = 18). Logistic regressions were employed to judge differences in vertical distribution, resource association and size class variation in the snails under study. Variation in shell morphology was assessed by performing the regression analysis of the sampled shells of live snails (n = 258) and vacant shells of the deceased individuals (n = 100). An overall significant difference (p < 0.05) in the vertical distribution of snails in lemon plants was observed. As to their association with resources available, snails were found to be more abundant in detritus than on living parts of the plants. The performed logistic regression revealed that the relative abundance of different S. baconi size classes was significantly different (p < 0.001). Significant correlations (p < 0.001) were found among different body size variables, with the shell length (x)-body weight (y) relationship being: y = 0.232x2.524 (for live snails) and the shell length (x)-shell weight (y) relationship being: y = 0.358x2.537 (for shells of dead snails). Various parameters of the snail shell shape could be represented through regression equations. Although reproduction and growth strategies of snails need to be explored further, the presented observations improve our understanding of the ecology of S. baconi, which may prove useful for future conservation efforts.

Supratidal existence drives phenotypic divergence, but not speciation, in tropical rocky-shore snails

AbstractThe mechanisms underlying the evolutionary adaptation of animals that transcend the ecological barrier separating the intertidal and supratidal zones of rocky shores are poorly understood. Different wetting frequencies in these zones in tropical regions (daily vs. seasonally, respectively) impose different physical stressors, which should drive phenotypic variation and ultimately speciation in the animals that inhabit them. We studied morphological, physiological and genetic variation in a tropical high-shore gastropod that transcends these zones [Echinolittorina malaccana (Philippi, 1847)]. Variation in melanization, shell features and evaporative water loss was linked to regular seawater wetting, frequent activity and feeding, and solar exposure in intertidal snails, and to inactivity and prolonged aestivation in the shade during continuous air exposure in supratidal snails. Despite selective pressure for phenotypic divergence, and reproductive isolation of the populations in either zone, their mitochondrial COI gene sequences confirmed that they represent a single species. Speciation in our study case is probably constrained by the limitation on activity, mating and reproduction of supratidal snails, such that their populations can only be sustained through intertidal pelagic larval recruitment. Comparisons with other studies suggest that supratidal speciation and specialization for life in this zone probably require moderation of the abiotic (desiccative) conditions, to facilitate greater activity and interaction of animals during air exposure.

Impact of continuous low water stage on the breeding environment of Oncomelania hupensis: a case study of Poyang Lake area in China

BackgroundOncomelania hupensis is the only intermediate host of Schistosoma japonicum and plays a decisive role in its transmission. The variation of water level greatly affects the reproduction and growth of snails. Therefore, in this paper, we analyze the variations of water level in the Poyang Lake region from 1993 to 2016 combined with satellite imagery to elucidate the evolution of the snail breeding environment.MethodsBy employing remote sensing data from 1993 to 2016 (April–June and September–November), the vegetation area of Poyang Lake and the vegetation area at different elevations were extracted and calculated. Moreover, the average daily water level data from the four hydrological stations (Hukou station, Xingzi station, Tangyin station and Kangshan station) which represent the typical state of Poyang Lake were collected from 1993 to 2016. The variance of the monthly mean water level, inundation time and the average area were analyzed by variance to find a significance level of α = 0.05.ResultsAccording to hydrological data before and after 2003, the average water level after 2003 is significantly lower than that before 2003 in Poyang Lake. After 2003, the time of inundateing the snail breeding period was later in April to June than that before 2003, while the time of wate-falling stage in September to November moved forward after 2003 than before 2003. Of them, the lowest water level affecting the breeding and growing period of O. hupensis in the northern part of Poyang Lake decreased from 11 m to 9 m. After 2003, the expansion of meadow area in the north part of Poyang Lake was mainly concentrated in the elevation of 9–11 m, and the newly increased infested-meadow in the lake area was mainly concentrated in the north part of Poyang Lake.ConclusionsBy comparing the change of water level characteristics in different parts of the Poyang Lake area as well as changes in meadow area before and after 2003, it is found that the water level changes mainly affect the snail breeding area in the northern part of Poyang Lake. The results are helpful for improving scientific measures for snail control in Jiangxi Province. This approach could also be applicible to Dongting Lake area and other lake areas affected by water level changes and can bring significant guidance for snail control in lake areas.

The South-to-North Water Diversion Project and schistosomiasis: an overview

Before and after the construction of the South-to-North Water Diversion Project, a number of studies have been conducted to assess the possibility of the northward spread of Oncomelania snails and schistosomiasis caused by the construction of the project, the survival and reproduction of snails moved north of their natural distribution, and the transmission of schistosomiasis by the survival snails moved north of their natural distribution. The effect of the South-to-North Water Diversion Project on the transmission of schistosomiasis is restricted along the Jiangsu section of the eastern route project of the South-to-North Water Diversion Project, and the Water Transfer Project from the Yangtze River to Han River of the middle route project of the South-to-North Water Diversion Project. It has been demonstrated the water diversion pattern via the pump stations and the ecological conditions in the water transfusion channels of the South-to-North Water Diversion Project are unlikely to result in the northward spread of Oncomelania snails or schistosomiasis, and no snails or schistosomiasis spread was found during the surveillance before and after the operation of the eastern route project of the South-to-North Water Diversion Project, and the Water Transfer Project from the Yangtze River to Han River of the middle route project of the South-to-North Water Diversion Project. Nevertheless, sustainable surveillance of Oncomelania snails along the South-to-North Water Diversion Project will provide scientific support and safety guarantee for the construction and operation of the subsequent projects.

Effects of salinity on survival, growth and reproduction of the invasive aquatic snail Pomacea canaliculata (Gastropoda: Ampullariidae)

Pomacea canaliculata, a freshwater snail native to tropical and temperate South America, has become an important invader and agricultural pest throughout tropical and subtropical regions around the world. Colonization of various aquatic habitats by P. canaliculata in coastal regions of South China and its establishment potential in estuaries have raised great concern, yet little is known about the biological response of the snail and its tolerance under saline environments. We first examined the salinity tolerance of P. canaliculata using a total of 30 experimental juvenile snails exposed to eight salinity levels (from 0 to 14 psu in 2 psu steps). Daily survival of the snails was measured for each salinity treatment over 30 days. Based on salinity exposure test, influence of salinity on snail reproduction was investigated for a period of 30 days using 30 adult snails exposed to four salinity treatments (0, 2, 4 and 6 psu). Each salinity test replicated three times. Pomacea canaliculata could tolerate salinity levels ranging from 0 to 6 psu in which probability of survival was greater than 72% during a 30 days exposure. Lethal time leading to 50% mortality (LT50) of the snail declined from 71 days at 0 psu to 27 days at 6 psu. Pomacea canaliculata could ingest and reproduce normally at salinities ranging from 0 to 4 psu. Average mass daily gain, specific growth rate, and the hatching of egg clutches decreased significantly with elevated salinities. Results show a general threshold response of P. canaliculata to salinity. This freshwater snail falls into “2nd degree” euryhaline limnobionts tolerating salinities of 3–8‰.

Warming alone increased exotic snail reproduction and together with eutrophication influenced snail growth in native wetlands but did not impact plants

Warming and eutrophication can have varying effects on exotic species performance and their interactions. These effects can vary with trophic level, but are rarely investigated simultaneously on exotic species from multiple trophic levels. To address this, we manipulated temperature, nutrients, and plant origin (native vs. exotic) in snail invaded wetland communities. Warming increased exotic apple snail (Pomacea maculata) reproduction (4-fold increase in egg mass) and also number of egg clutches produced while warming slowed exotic snail growth, suggesting a trade-off between reproduction and growth in exotic snails influenced by warming and nutrients. However, exotic snail size varied with warming and nutrients. Additionally, warming reduced native plant mass with no effect on exotic plants while nutrients had greater positive effects on exotic plants biomass. In combination warming and nutrient enrichment will likely increase exotic snail growth, while nutrient enrichment alone will contribute to exotic plant dominance. In conclusion, the individual and interactive effects of warming and eutrophication vary with the trophic level of exotic species with trade-offs in exotic herbivores depending on environmental conditions, making it difficult to predict effects of multiple anthropogenic factors on co-occurring exotic plants and their effects on native communities.

Laboratory-to-field extrapolation: Increase in carbamazepine toxicity in a higher tier, multiple-stress experiment

The toxicity and environmental risk of chemicals, such as the antiepileptic drug carbamazepine (CBZ), is commonly assessed using standardized laboratory tests and laboratory-to-field extrapolation. To investigate the toxicity of CBZ to aquatic key organisms in a more complex and environmentally relevant scenario, we conducted a 32-day multiple-stress experiment in artificial indoor streams. We exposed the non-biting midge Chironomus riparius, the blackworm Lumbriculus variegatus, and the New Zealand mud snail Potamopyrgus antipodarum to 80 and 400 μg CBZ/L in six artificial indoor streams. In addition to hydraulic stress, species’ interaction, and low organic content in the sediment, organisms were co-exposed to the herbicide terbutryn (TBY) as a second chemical stressor at a concentration of 6 μg/L. The exposure to CBZ under multiple stress conditions resulted in a 10- to more than 25-fold higher toxicity in C. riparius and P. antipodarum when compared to a previous, standardized laboratory experiment. The co-exposure to TBY enhanced the adverse effects of CBZ on snails (reduced production of embryos). This effect was additive as the single exposure to TBY also reduced the reproduction of snails, most likely through the reduction of biofilm biomass. The emergence of C. riparius declined at a CBZ concentration of 400 μg/L (without the co-exposure to TBY) and at 80 μg/L in combination with TBY. The difference in sensitivity between laboratory and indoor stream experiments is indicative of a potential underestimation of risk when toxicity data are extrapolated to field conditions. The present results suggest the inclusion of non-chemical and chemical stressors in environmental hazard and risk assessments.

Inbreeding does not alter the response to an experimental heat wave in a freshwater snail.

Global climate change affects natural populations of many species by increasing the average temperature and the frequency of extreme weather events (e.g. summer heat waves). The ability of organisms to cope with these environmental changes can, however, depend on their genetic properties. For instance, genetic load owing to inbreeding could alter organisms’ responses to climate change-mediated environmental changes but such effects are often overlooked. We investigated the effects of an experimental heat wave (25°C versus 15°C) on life history (reproduction, size) and constitutive immune defence traits (phenoloxidase-like and antibacterial activity of haemolymph) in relation to inbreeding by manipulating the mating type (outcrossing, self-fertilization) in two populations of a hermaphroditic freshwater snail, Lymnaea stagnalis. High temperature increased reproduction and size of snails but impaired their immune function. In one of the two study populations, inbreeding reduced reproductive output of snails indicating inbreeding depression. Furthermore, this effect did not depend on the temperature snails were exposed to. Our results suggest that L. stagnalis snails can be negatively affected by inbreeding but it may not alter their responses to heat waves.

Surveillance of potential transmission factors of schistosomiasis in Xiuzhou District of Jiaxing City from 2013 to 2015

To understand the potential risk of schistosomiasis transmission in Xiuzhou District of Jiaxing City, so as to provide the scientific evidence for consolidating schistosomiasis control achievements. Fixed and mobile surveillance sites were set up in Xiuzhou District of Jiaxing City from 2013 to 2015. Oncomelania hupensis snails was surveyed historical snail habitats, current snail habitats, and suspected snail habitats. The schistosome infections were identified using serological and parasitological testing among local residents and mobile populations. In addition, the survival and reproduction of snails imported into Xiuzhou District was observed, and the schistosome infection in wild reservoir hosts was detected. A total of 540.14 hm2 of settings were surveyed in Xiuzhou District, Jiaxing City from 2013 to 2015, and 1.65 hm2 of snail habitats were identified. The snail habitats were mainly located in dry lands, and no infected snails or importation of snails were found. During the period from 2013 to 2015, a total of 7 668 local residents and mobile populations were examined in Xiuzhou District, and no new local infections were detected; however, three imported schistosomiasis cases were identified. Field simulation experiment showed that the imported snails laid eggs and reproduced in Xiuzhou District, and no schistosome infections were found in wild animals. There are still residual Oncomelania snails and imported schistosomiasis patients in Xiuzhou District of Jiaxing City; therefore, the surveillance and management of local Oncomelania snails and imported schistosomiasis should be intensified to reduce the risk of schistosomiasis transmission.

Poison in paradise: increase of toxic effects in restored sections of two rivers jeopardizes the success of hydromorphological restoration measures

BackgroundTo date, only 8.2% of German surface waters achieve a good ecological status according to the European Water Framework Directive. This is primarily attributed to structural deficits, intensive land use, and chemical contaminations of water bodies. In this context, hydromorphological restoration measures are implemented with the aim to increase habitat and species diversity and thus improve the ecological status of water bodies. Nevertheless, existing studies show that restorations promote the reintroduction of individual species, but only in exceptional cases an improvement in the ecological status is achieved. Therefore, we examined the impact of the prevailing chemical contamination on the restoration success in the catchment of the river Nidda in Hessen (Germany) by comparing restored river sections at the rivers Nidda and Horloff with unrestored sections upstream (space-for-time-substitution) and a transect downstream the restoration measures. For this purpose, we conducted active biomonitoring campaigns with Potamopyrgus antipodarum and Gammarus fossarum and analyzed water and sediment samples with effect-based in vitro bioassays.ResultsAt the river Horloff, mortality of P. antipodarum and toxicity in water samples measured via the microtox assay were highest within the restoration. At the river Nidda, the reproduction of snails and gammarids significantly increased within the restorations, and reproduction of snails correlated positively and significantly with estrogenic activities. The microtox assay also exhibited the highest toxicities in water and sediment samples from the restorations and dioxin-like as well as estrogenic activities significantly increased compared to the unrestored reference site. On the basis of these results, the prevailing chemical contamination has negatively affected snails and gammarids in the active biomonitoring campaigns and consequently is likely to have also a negative impact on the local invertebrate community and thus endangers the restoration success.ConclusionHydromorphological restorations as a stand-alone measure are insufficient to improve the ecological status of a water body as long as the water and sediment quality remain deficient. Therefore, it is necessary to improve water and sediment quality in parallel with hydromorphological restoration measures to achieve the objectives of the EU-WFD.