Assessment of metal contamination in the Hun River, China, and evaluation of the fish Zacco platypus and the snail Radix swinhoei as potential biomonitors.

The Hun River is a major tributary of the Liao River in the northeast area of China and provides drinking water for 23 million local residents. This study was designed to assess the severity of metal contamination in the Hun River and the potential use of indigenous organisms (the fish Zacco platypus and the snail Radix swinhoei) as biomonitors of metal contamination. Water, sediment, and the native fish and snails were collected at four sampling sites that differed in their physicochemical characteristics and their contamination levels. The samples were analyzed for Cd, Cr, Cu, Ni, Pb, and Zn by ICP-MS. The results showed that although the overall potential ecological risks of the metals were low at our sampling sites, Cd posed a noteworthy ecological risk. Strong correlations were obtained between Cd concentrations in the organisms and in the environment. The results indicated that Z. platypus and R. swinhoei can be useful biomonitoring species for assessing Cd contamination. Biomonitoring with the snail may be most effective when focused on the gonad/digestive tissue (because of the high metal accumulation there), but further work is needed to confirm this.

Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best.

BACKGROUND: Despite control efforts, human schistosomiasis remains prevalent throughout Africa, Asia, and South America. The global schistosomiasis burden has changed little since the new anthelmintic drug, praziquantel, promised widespread control. METHODOLOGY: We evaluated large-scale schistosomiasis control attempts over the past century and across the globe by identifying factors that predict control program success: snail control (e.g., molluscicides or biological control), mass drug administrations (MDA) with praziquantel, or a combined strategy using both. For data, we compiled historical information on control tactics and their quantitative outcomes for all 83 countries and territories in which: (i) schistosomiasis was allegedly endemic during the 20th century, and (ii) schistosomiasis remains endemic, or (iii) schistosomiasis has been "eliminated," or is "no longer endemic," or transmission has been interrupted. PRINCIPAL FINDINGS: Widespread snail control reduced prevalence by 92 ± 5% (N = 19) vs. 37 ± 7% (N = 29) for programs using little or no snail control. In addition, ecological, economic, and political factors contributed to schistosomiasis elimination. For instance, snail control was most common and widespread in wealthier countries and when control began earlier in the 20th century. CONCLUSIONS/SIGNIFICANCE: Snail control has been the most effective way to reduce schistosomiasis prevalence. Despite evidence that snail control leads to long-term disease reduction and elimination, most current schistosomiasis control efforts emphasize MDA using praziquantel over snail control. Combining drug-based control programs with affordable snail control seems the best strategy for eliminating schistosomiasis.

[Cost-effectiveness evaluation on comprehensive control measures carrying out in schistosomiasis endemic areas with regard to different layers of administrative villages stratified by infection situation of human and domestic animals. II Correlation analysis of costs and inputs with changes of schistosomiasis endemic situation in inner embankment of marshland and lake regions from 2006 to 2013].

OBJECTIVE: To investigate the correlations between inputs and costs and endemic situation of schistosomiasis in inner embankment, so as tb provide the references for the strategy optimization of schistosomiasis control. METHODS: Jiangling County was selected as the study field. The correlatibn and regression analyses were applied to analyze the endemic situation of schistosomiasis in Jiangling County from 2006 to 2013. The methods of two-stages least squares and path analysis were applied to analyze the impacts between costs and inputs and endemic situation of schistosomiasis. RESULTS: The adjusted infection rate of population, number of bovines and Oncomelania hupensis snail areas reduced by 77.42%, 76.34% and 19.43%, respectively in Jiangling County from 2006 to 2013. The correlations between the infection rate of snails and the population positive rates of blood and fecal exams, and the infection rate of bovines were significant (all P < 0.05); and there was a significant linear regression between the infection rates of snails and bovines (P < 0.05). There were statistically significant regressions between inputs at different levels and the population positive rates of blood and fecal exams, and the infection rates of bovines and snails, as well as between the costs and the population positive rate of fecal exams and the infection rates of bovines and snails (all P < 0.05), whereas there was no statistically significant regression between the costs and the population positive rate by blood exams (P > 0.05). The inputs at county level had an impact on the population positive rate of blood exams; the costs of comprehensive treatment had an impact on the population positive rate of fecal exams; the costs of human labor and measures for exams and treatments had an impact on the infeiction rate of bovines; the inputs at national level and the costs of measures for exams and treatments had an impact on the infection rate of snails (all P < 0.05). CONCLUSION: The inputs and costs of schistosomiasis control were related to the epidemic situation of schistosomiasis in Jiangling County from 2006 to 2013; therefore, it is necessary to develop a comprehensive surveillance system as substitute for the current indexes on schistosomiasis control.

[Measures and effectiveness of comprehensive schistosomiasis control along Xinglong River in Qianjiang City].

OBJECTIVE: To evaluate the effect of comprehensive control of schistosomiasis along the Xinglong River in Qianjiang City, so as to provide the evidence for improving schistosomiasis control. METHODS: The comprehensive control measures including infection source control and Oncomelania hupensis snail eradication were surveyed along the Xinglong River in Qianjiang City. RESULTS: The prevalence of schistosomiasis was under control, that was the human and cattle infection rates decreased by 53.77% and 100% respectively, the snail area decreased by 26.9%, the mean density of living snails decreased by 25.5%, and no infected snails was found. CONCLUSIONS: The comprehensive control measures along the Xinglong River are effective, and the management and surveillance of snail environments still should be strengthened.

[Effect of water storage and aquaculture on Oncomelania hupensis control in tidal flats wetlands of islet-beach type area of Dantu section of lower reaches of Yangtze River].

OBJECTIVE: To evaluate the effect and the benefits of the projects of water storage and aquaculture on Oncomelania hupensis snail control in the tidal flats wetlands of islet-beach type area of lower reaches of the Yangtze River. METHODS: The projects of water storage and aquaculture on 0. hupensis snail control were implemented in the tidal flats wetlands of islet-beach type of lower reaches of the Yangtze River. The breed situation of the snails was investigated by the conventional method before and after the project implementation and the effect of control and elimination of the snails by the projects were evaluated. At the same time, the cost-benefit analysis of two projects among them was performed by the static benefit-cost ratio method. RESULTS: All of 0. hupensis snails were eliminated in the first year after the implementation of seven water storage and aquaculture projects. The costs of detection and control of snails saved by each project was 69.20 thousand yuan a year on average. The annual net benefits of the "Nanhao Group 10 beach" project and "Wutao Group 6-14 beach" project were 2 039.40 thousand yuan and 955.00 thousand yuan respectively, and the annual net benefit-cost ratios were 1.09: 1 and 1.07: 1 respectively. CONCLUSION: The O. hupensis snails could be rapidly eliminated by the water storage and aquaculture, and the economic benefit is obvious, but the wetland ecological protection and flood control safety should be considered in the tidal flats wetlands of islet-beach type area of lower reaches of the Yangtze River.

Mercury contamination and exposure assessment of fishery products in Korea.

In this study, total (T-Hg) and methyl mercury (Me-Hg) contamination was investigated in fishery products including canned fish, fish sauces, dried bonito and frozen tuna sashimi, collected from retail markets in Korea, to assess dietary exposure. Direct mercury analyser and gas chromatography-electron captured detector were employed to measure T-Hg and Me-Hg, respectively. The highest T-Hg and Me-Hg contamination was present in tuna sashimi, followed by dried bonito, respectively. Canned tuna showed more frequent detection and higher content than other canned fishery products. The weekly exposure estimate indicates that exposure to mercury from fishery products is safe, showing 2.59% provisional tolerable weekly intake (PTWI) for T-Hg, 1.82% PTWI for Me-Hg and 4.16% reference dose for Me-Hg. However, it should be addressed to monitor the mercury contamination in fish and fishery products regularly, to safeguard vulnerable population such as children, to limit intake of these food products.

Caged mudsnail Potamopyrgus antipodarum (Gray) as an integrated field biomonitoring tool: exposure assessment and reprotoxic effects of water column contamination.

This study highlights the usefulness of gastropods for water quality monitoring. Gastropods were caged upstream and downstream of an effluent discharge. Exposure was assessed by measurement of organic contaminants in water. Contamination of the Potamopyrgus antipodarum mudsnail was also measured using innovative techniques at the end of the 42 days of exposure. Biological effects were measured at the individual level (growth, reproduction) and subindividual level (energy reserves, vitellin-like proteins, steroid levels, expression of genes involved in estrogen signaling pathways), thus providing a better understanding of reprotoxic effects. The effluent was mainly contaminated by pharmaceutical compounds, as was the mudsnail. The highest concentrations were measured for oxazepam and were higher than 2 mg/kg downstream of the effluent discharge. Alkylphenols, bisphenol A, and vertebrate-like sex-steroid hormones were also bioaccumulated by the mudsnail downstream of the effluent. The combined use of water and snail contamination provided a complete exposure assessment. Exposure was further linked to biological effects. The mudsnail was shown to be a better adapted species for in situ exposures than Valvata piscinalis. Reproduction was sharply decreased after 6 weeks of exposure in the mudsnail. Feeding issues were excluded, confirming the toxic origin. These effects were related to estrogen signaling pathways using genomic analysis. Genes coding for proteins involved in nongenomic signaling pathways were inhibited, and those of genomic pathway repressors were induced. These results suggest that the chemical contamination due to the effluent discharge altered steroid control of reproduction and blocked the transition between oocyte and unshelled embryo, resulting in a drastic decrease of embryo production, while survival was not affected.

[Surveillance and risk assessment system of schistosomiasis in Jiangsu Province. I. Distribution of surveillance site and effectiveness of the system].

OBJECTIVE: To establish the surveillance and risk assessment system of schistosomiasis in Jiangsu Province, so as to provide technical support for timely understanding of the risk of schistosomiasis transmission and implementation of targeted control measures. METHODS: The surveillance sites of schistosomiasis were assigned according to the epidemic status and endemic type of schistosomiasis as well as the characteristics of the water system, and the prevalence of Schistosoma japonicum in humans and domestic animals, and snail status were investigated. In addition, the quality control of serum detection of S. japonicum infections was performed. The prevalence of human and animal S. japonicum infections, snail status and missing diagnosis of serum detection were analyzed and compared among regions. RESULTS: A total of 27 surveillance sites of schistosomiasis were set up in 26 counties of 10 cities, Jiangsu Province, including 14 sites in transmission-interrupted villages and 13 sites in transmission-controlled villages, and 15 sites in marshland and lake regions, 9 sites in plain regions with water network and 3 sites in mountainous region. In the 27 surveillance sites, a total of 16 617 residents were screened for S. japonicum infection by using dipstick dye immunoassay (DDIA), and 326 were sero-positive, with a sero-prevalence of 1.96% (2.17% for men and 1.8% for women). Of the 326 individuals undergoing parasitological examination, 2 positive cases were detected in the marshland and lake region, with a S. japonicum human prevalence of 0.01%. Of the 762 floating population detected, 10 were positive for blood test, with a sero-prevalence of 1.31%, and no egg-positive individuals were detected. No infection was found in the 476 domestic animals. Of the 746 settings surveyed, a total of 240.7 hm2 snail area was detected, with a mean snail density of 0.06 snails/0.1 m2, and no infected snails were found. There were 780 quality-control sera detected in 26 surveillance sites of schistosomiasis, and the gross coincidence rate was 95.13%, with misdiagnosis rate of 1.28% and missing diagnosis rate of 19.23%. CONCLUSION: The surveillance sites of schistosomiasis show reasonable distribution in Jiangsu Province, and the endemic situation of schistosomiasis appears a low level in the whole province.

[Surveillance and risk assessment system of schistosomiasis in Jiangsu Province. II. Surveillance pattern and effect of Oncomelania hupensis snail status in Dongtai City, Jiangsu Province].

OBJECTIVE: To explore the method of Oncomelania hupensis snail surveillance in transmission-interrupted regions of schistosomiasis, so as to provide a new pattern for the surveillance of snail status in the transmission-interrupted areas. METHODS: In Dongtai County, north of Jiangsu Province where the transmission of schistosomiasis was interrupted, the surveillance of snail status was performed by means of the village-level general survey, village-level sampling survey, snail survey in key settings of township and county, and snail reporting by residents. In addition, quality-control snail sites were set up for quality control. The effectiveness and cost of the four methods of snail surveillance was compared. RESULTS: A total of 163 079 settings and 22 785.62 hm2 were surveyed in Dongtai County from 2008 to 2013, and 89 residual snail breeding sites were found, with a snail area of 1.48 hm2. The patterns of village-level general survey, village-level sampling survey, and snail survey in key settings of township and county were employed for investigation of 94 550, 45 033 and 23 496 settings, consisting of 57.98%, 27.61% and 14.41% of total settings, and 2, 0 and 6 settings were found with snails, with 0.021/thousand, 0, and 0.255/thousand detection rates of settings with snail breading sites, respectively. The pattern of snail survey in key settings of township and county was more effective than that of village-level survey to detect-snail breeding sites (χ2 = 19.158, P = 0). The recovery rate of quality-control snail breeding sites was 52.56%, 38.27% and 73.62% for the three patterns of snail survey, respectively, and the pattern of snail survey in key settings of township and county showed a higher quality for snail survey than that of village-level survey (χ2 = 111.597 and 85.991, both P = 0). During the period from 2008 to 2013, 289 person-times reported 279 suspected snail habitats and 1 501 living snails, and no Oncomelania snails were found. During the 6-year period, there were 1617.5, 964.7 and 527.7 thousand RMB invested for village-level general survey, village-level sampling survey, and snail survey in key settings of township and county, and the cost of snail survey per hm2 was 129.88, 133.6 and 162.57 RMB/hm2, respectively. The cost of village-level general survey and snail survey in key settings of township and county to detect a snail-breeding site was 808 800 and 88 000 RMB, respectively (t = 12.850, P = 0.000), and the cost of snail survey in key settings of township and county was 10.88% of that of village-level general survey. CONCLUSION: The snail survey in key settings of township and county is a highly effective and high-quality method for snail surveillance, which miay serve as a prior way for the surveillance of snail status in the transmission-interrupted areas of schistosomiasis.

[Assessment and analysis of risks of realizing schistosomiasis transmission control in Jiangxi Province].

OBJECTIVE: To evaluate the situation of realizing schistosomiasis transmission control in Jiangxi Province. METHODS: The situation of reaching the criteria of schistosomiasis transmission control was evaluated by using the method of field surveys combined with retrospective investigations. RESULTS: The schistosome infection in human was kept at a stable low level, and the infection rate in residents was below 1% in 90.24% (536/594) of whole epidemic controlled villages. There were 45 spots with schistosome infected Oncomelania hupensis snails in 38 pieces of marshland. The epidemic situation in livestock showed less optimistic than that in human, and the infection rate in bovine was higher than 1% in 19.87% (118/594) of the whole epidemic controlled villages. CONCLUSIONS: Currently, the prevalence of schistosomiasis is at a low level in 9 infection-controlled counties of Jiangxi Province. More favorable situation has emerged to the realization of schistosomiasis transmission control. However, it is necessary to strengthen the infectious sources control with emphasis on bovine so as to achieve the goal of transmission control in whole province in 2015.

[Assessment of schistosomiasis transmission interruption in Beichuan County, Sichuan Province].

OBJECTIVE: To assess whether Beichuan County reaches the national standard of schistosomiasis transmission interruption. METHODS: Three villages in Beichuan County were sampled as assessment spots, and the schistosomiasis infections of residents and domestic animals, the status of Oncomelania snails and the past records were assessed according to the Criteria for Control and Elimination of Schistosomiasis in China. RESULTS: No local schistosome infections were found in residents and cattle for successive 5 years and no snails were found for 2 successive years in the 3 villages. The files were documented completely. All the indices reached the national standard of schistosomiasis transmission being interrupted. CONCLUSION: Beichuan County has reached the national standard of schistosomiasis transmission interruption. However, the endemic surveillance of schistosomiasis still needs to continue.

[Molluscicidal effect and cost-effectiveness of suspension concentrate of metaldehyde and niclosamide in the field in Honghu City].

OBJECTIVE: To assess the molluscicidal effect and cost-effectiveness of suspension concentrate of metaldehyde and niclosamide (MNSC) in the field, so as to evaluate the possibility of popularization and application value. METHODS: 26% MNSC and 50% wettable powder of niclosamide (WPN) were used for Oncomelania snail control with the spraying method in the field, and the 15-d molluscicidal effects and costs were investigated. RESULTS: Fifteen days after the spraying, in the beach of Dongjing River, the snail death rates of MNSC and WPN were 89.40% and 88.08%, respectively, and the density reduction rates of MNSC and WPN were 92.35% and 91.67%, respectively. In the marshland of Honghu Lake, the snail death rates of MNSC and WPN were 86.59% and 87.01%, respectively, and the density reduction rates of MNSC and WPN were 90.05% and 91.71%, respectively. There was no significant difference in the molluscicidal effect between two drugs (P > 0.05). The cost of MNSC used in 100 m2 was 15.03 Yuan, while the cost of WPN used in 100 m2 was 16.29 Yuan. CONCLUSION: MNSC has high molluscicidal efficacy, low cost and low impact on environments, which possesses of popularization and application value in the field.

Life stage-specific effects of the fungicide pyrimethanil and temperature on the snail Physella acuta (Draparnaud, 1805) disclose the pitfalls for the aquatic risk assessment under global climate change.

It can be suggested that the combined stress of pesticide pollution and suboptimal temperature influences the sensitivity of life stages of aquatic invertebrates differently. The embryo, juvenile, half- and full-life-cycle toxicity tests performed with the snail Physella acuta at different concentrations (0.06-0.5 or 1.0 mg L(-1)) of the model fungicide pyrimethanil at 15, 20 and 25 °C revealed, that pyrimethanil caused concentration-dependent effects at all test temperatures. Interestingly, the ecotoxicity of pyrimethanil was higher at lower (suboptimal) temperature for embryo hatching and F(1) reproduction, but its ecotoxicity for juvenile growth and F(0) reproduction increased with increasing temperature. The life-stage specific temperature-dependent ecotoxicity of pyrimethanil and the high fungicide susceptibility of the invasive snail clearly demonstrate the complexity of pesticide-temperature interactions and the challenge to draw conclusions for the risk of pesticides under the impact of global climate change.

[Evaluation of molluscicidal effects of contracted responsibility system in Changshan County].

OBJECTIVE: To explore a new molluscicidal pattern suitable for the complicated environments in hilly regions, so as to provide the evidence for making the strategy of Oncomelania snail control. METHODS: The contracted responsibility system for snail control was implemented by government. The quality of control work was evaluated in the same year and the recent molluscicidal effect was assessed in the next spring. RESULTS: After the intervention, the decline rate of snail areas increased from 53.4% to 100%; the compression rate of snail spots increased from 54.6% to 100%; the input of fund for snail control decreased from 2.03 Yuan/m2 to 0.69 Yuan/m2; the cost of snail control decreased from 3.73 Yuan/m2 to 0.75 Yuan/m2; the work efficiency increased from 12.0 m2/(man x day) to 36.7 m2/(man x day); the molluscicide decreased from 7.50 tons/year to 3.20 tons/year and the decline rate was 57.3%. The awareness rate and recognized rate of the contracted responsibility system for snail control were both 92.5%. CONCLUSION: The contracted responsibility system for snail control can increase financing efficiency, molluscicidal quality and work efficiency, and save molluscicide in complicated environments of hilly regions.

[Effect and cost-benefit of Oncomelania snail control by plowing and planting in Jiaobei Beach of Zhenjiang City].

OBJECTIVE: To evaluate the effect and cost-benefit of Oncomelania snail control by plowing and planting in Jiaobei Beach of Zhenjiang City. METHODS: In 2009, the measures of building low dike and plowing and planting were implemented in the experimental area of the east part of Jiaobei Beach, while in the control area of the west part of the beach, the molluscacide (niclosamide) was used to control snails. Then, the snail control effects and the cost-benefits of the two groups were compared. RESULTS: In the experimental area, the density of living snails decreased by 99.75% in the year when the measures were implemented, and no living snails were found from the second year. Though that the density of living snails in the control area decreased by 70% around, it aroused again in the second year. The net cost-benefit ratios of the experimental area and the control area were 2.18 and -0.92, respectively. CONCLUSION: Building low dike and plowing and planting in the beaches along the middle and lower reaches of the Yangtze River can effectively control snails, meanwhile, it is economic.

[Study on surveillance and early-warning system of schistosomiasis in first phase of east route of South-to-North Water Diversion Project. III. Indexes of surveillance and early-warning and risk assessment].

OBJECTIVE: To establish the index system of surveillance and early-warning on schistosomiasis and to provide the scientific basis for risk assessment and emergency plan in first phase of east route of South-to-North Water Diversion Project. METHODS: The Delphi method and the multidimensional synthetic evaluation were used in the evaluation of indexes of surveillance and early-warning on schistosomiasis in the east route of the project. RESULTS: There were 53 indexes evaluated in the index system, and among them, there were 3 first grade indexes, 10 second grade indexes and 40 third grade indexes. The indexes on Oncomelania snails were the most important. According to the habitation position of snails, the four grades on surveillance and early-warning of schistosomiasis were established in the east route. The grade I of the early-warning meant that snails crossed the first level of the pumping station. The grade II meant that snails crossed N 32 degrees 54'. The grade III meant that snails crossed N 33 degrees 03' or Jinhu pumping station. The grade IV meant that snails crossed N 33 degrees 15' or Hongze Station. Other 4 indexes on schistosome infection in people and livestock were confirmed as indicative indexes. According to the relationship among the indexes, the evaluation methods were determined on the risk of schistosomiasis transmission. CONCLUSIONS: The index system of surveillance and early-warning and the methods of risk assessment of schistosomiasis have been confirmed in first phase of east route of South-to-North Water Diversion Project. The primary index is related to snails and the supplementary is related to schistosome infection in people and livestock in the system.

[Evaluation on cost-effectiveness of snail control project by environmental modification in hilly regions].

OBJECTIVE: To evaluate the cost-effectiveness of the snail control project by environmental modification in order to provide the evidence for quickly interrupting the transmission of schistosomiasis in hilly regions. METHODS: Field investigations were carried out. The changes of the snail habitat areas were compared before and after the snail control project. The direct costs of the snail control were calculated. The reduction rates of snail area and snail density were regarded as the evaluation indexes of the effectiveness. The costs for reduction of 1% of snail area and 1% of snail density were used as the unit for cost-effectiveness analysis. RESULTS: After the 15 projects were implemented, there were no snails in 12 areas. The reduction rates of snail areas were 72.22% to 100%. The reduction rates of the snail area and density were both 100% in the areas with digging new ditches to fill up the old ones and building reservoirs. The total cost of 15 projects was 1 450 800 Yuan. The average cost per unit was 0.56 Yuan/m2. After the snail control project by digging new ditches to fill up the old ones was implemented, the costs of snail area and density decreased by one unit were 300 -700 Yuan, by building reservoirs, the costs were 600 -2 600 Yuan, by building fishpond, the costs were 1 200 - 1 500 Yuan, by watershed comprehensive measures, the costs were 900 - 2 700 Yuan. The cost of digging new ditches to fill up the old ones was significantly lower than that of building reservoirs or watershed comprehensive measures, but there was no significant difference between building reservoirs and watershed comprehensive measures. CONCLUSIONS: In hilly regions, the implementation of snail control project by environmental modification combined with construction of water conservancy is effective, and the cost-effectiveness of the snail control with digging new ditches to fill up the old ones is excellent.

[Technology of preventing Oncomelania snail diffusion in east route of South-to-North Water Diversion Project. I. Field test of blocking diffusion of Oncomelania snails with blocking network via collecting water from middle layer].

OBJECTIVE: To evaluate the effectiveness of blocking diffusion of Oncomelania snails with the blocking network via collecting water from middle layer. METHODS: According to the principle of the installation preventing snails via collecting water from middle layer without snails, the blocking network was manufactured. The field test of the blocking diffusion of snails with the blocking network was carried out in the electric pumping station and the irrigation located in the area with snails. The snails stained were put into the water inlet of the pump when the pump was actuating, and the snails pumped were observed during the test period. The cost of the test was also calculated. RESULTS: The rate of blocking diffusion of snails with the blocking network was 100%, and the direct costs were only 11 030 CNY. CONCLUSIONS: The blocking network via collecting water from middle layer has good effect for prevention of snail dispersal. It is simple for manutacturing and installation, and suitable for emergency blocking diffusion of snails in the east route of South-to-North Water Diversion Project and the electric pumping station with snails.

[Retrospective investigation on national endemic situation of schistosomiasis I analysis of changes of endemic situation in transmission-interrupted counties].

OBJECTIVE: To analyze the changing rules of schistosomiasis endemic situation in the area of transmission that has been interrupted before and after they reach the criteria of transmission interruption, so as to offer the basis of amending to the criteria of schistosomiasis transmission interruption and a more scientific, standardized assessment and evaluation of the effects of schistosomiasis control in the future. METHODS: Nineteen counties of transmission that has been interrupted in 9 provinces nationwide were selected and investigated with the retrospective research method to collect and record the endemic detailed data 10 years before they reach the criteria of transmission interruption and several years later (ended in 2008 or 2009) and then a database was established. The changing rules of various disease indices in different endemic areas before and after reaching the criteria of transmission interruption were analyzed and compared. RESULTS: The average time from the transmission control to the transmission interruption was 17 years in the 17 counties. After reaching the criteria of transmission interruption, the infection rates of people turned down to a minimum level in various endemic areas, the infection rates in a few numbers of lake endemic areas and hilly endemic areas increased slightly after the transmission interruption 4-9 years later, but all of them were below 1%. The densities of living Oncomelania snails in lake endemic areas and water-network endemic areas were high and the changes were great each year, and the densities of living snails were much lower in hilly endemic areas than in the above two types of areas and they came to the lowest 4 years before and after the transmission interruption. The infected snails appeared occasionally in lake endemic areas, and they recurred 6 years and 10 years after the transmission interruption in water-network endemic areas and hilly endemic areas, respectively. The continued time without infected snails found before reaching transmission interruption was 2.71 +/- 1.10 years averagely in transmission-interrupted counties with endemic stable, and was 3. 80 +/- 1.43 years in lake endemic areas. CONCLUSIONS: It is possible to maintain a low level of population schistosome infection, and the endemic rebound is shown as snail rebound after the endemic areas reach the criteria of transmission interruption, The infected snails could be the comprehensive index reflecting the control achievement and the risk of schistosomiasis transmission. So the persistent control of infected snails is the fundament of schistosomiasis transmission interruption. It is suggested that in our current social and economic development and science and technology capacity conditions, the status of no infected snails found continuously for 5 years would be one of the criteria of schistosomiasis transmission interruption.

[Effect of project of afforestation for schistosomiasis prevention on snail control in marshland and lake regions].

OBJECTIVE: To evaluate the effect of the project of afforestation for schistosomiasis prevention on Oncomelania hupensis control. METHODS: The situation of afforestation for schistosomiasis prevention in the field and the snail distribution in marshland regions were surveyed with the systematic sampling method in the spring, 2009. The database of snail distribution was established and the status of afforestation was investigated, and the effect of the project on snail control was evaluated. RESULTS: The rates of frames with living snails in the environment with plantations and the environment without a plantation were 14.9% and 19.7%, respectively, and there was a significant difference (Chi2 = 2 267, P < 0.01). The rate of frames with living snails in agroforestry model was lower than that in other models except for fishery-husbandry-forestry model. The average densities of living snails in the environment with plantations and the environment without a plantation were 0.552 snails/0.1 m2 and 0. 989 snails/0.1 m2, respectively. The average densities of living snails in the cultivating group and un-cultivating group were 0.354 snails/0.1 m2 and 0.653 snails/0.1 m2, respectively. The rate of frames with living snails and the average density of living snails were the lowest in the environment of long-term afforestation. CONCLUSIONS: The project of afforestation for schistosomiasis prevention has a good effect on snail control in Anhui Province. Long-term afforestation could stably maintain the effect on snail control.