Cross-watershed distribution pattern challenging the elimination of Oncomelania hupensis, the intermediate host of Schistosoma japonica, in Sichuan province, China.

BACKGROUND: Snail control is critical to schistosomiasis control efforts in China. However, re-emergence of Oncomelania hupensis is challenging the achievements of schistosomiasis control. The present study aimed to test whether the amphibious snails can spread across watersheds using a combination of population genetics and geographic statistics. METHODS: The digital maps and attributes of snail habitats were obtained from the national survey on O. hupensis. Snail sampling was performed in 45 counties of Sichuan Province. The cox1 gene of specimens was characterized by sequencing. Unique haplotypes were found for phylogenetic inference and mapped in a geographical information system (GIS). Barriers of gene flow were identified by Monmonier's maximum difference algorithm. The watercourses and watersheds in the study area were determined based on a digital elevation model (DEM). Plain areas were defined by a threshold of slope. The slope of snail habitats was characterized and the nearest distance to watercourses was calculated using a GIS platform. Spatial dynamics of high-density distributions were observed by density analysis of snail habitats. RESULTS: A total of 422 cox1 sequences of O. hupensis specimens from 45 sampling sites were obtained and collapsed into 128 unique haplotypes or 10 clades. Higher haplotype diversity in the north of the study area was observed. Four barriers to gene flow, leading to five sub-regions, were found across the study area. Four sub-regions ran across major watersheds, while high-density distributions were confined within watersheds. The result indicated that snails were able to disperse across low-density areas. A total of 63.48% habitats or 43.29% accumulated infested areas were distributed in the plain areas where the overall slope was < 0.94°. Approximately 90% of snail habitats were closer to smaller watercourses. Historically, high-density areas were mainly located in the plains, but now more were distributed in hilly region. CONCLUSIONS: Our study showed the cross-watershed distribution of Oncomelania snails at a large scale. Natural cross-watershed spread in plains and long-distance dispersal by humans and animals might be the main driver of the observed patterns. We recommend cross-watershed joint control strategies for snail and schistosomiasis control.

Interruption of schistosomiasis transmission in mountainous and hilly regions with an integrated strategy: a longitudinal case study in Sichuan, China.

BACKGROUND: Schistosomiasis remains a major public health concern in China. Since 2004, an integrated strategy was developed to control the transmission of Schistosoma japonicum in China. However, the long-term effectiveness of this integrated strategy for the interruption of schistosomiasis transmission remains unknown in the mountainous and hilly regions of China until now. This longitudinal study aims to evaluate the effectiveness of the integrated strategy on transmission interruption of schistosomiasis in Sichuan Province from 2005 through 2014. METHODS: The data regarding replacement of bovines with machines, improved sanitation, access to clean water, construction of public toilets and household latrines, snail control, chemotherapy, and health education were captured from the annual report of the schistosomiasis control programmes in Sichuan Province from 2005 to 2014, and S. japonicum infection in humans, bovines and snails were estimated to evaluate the effectiveness of the integrated strategy. RESULTS: During the 10-year period from 2005 through 2014, a total of 536 568 machines were used to replace bovines, and 3 284 333 household lavatories and 15 523 public latrines were built. Tap water was supplied to 19 116 344 residents living in the endemic villages. A total of 230 098 hm2 snail habitats were given molluscicide treatment, and 357 233 hm2 snail habitats received environmental improvements. There were 7 268 138 humans and 840 845 bovines given praziquantel chemotherapy. During the 10-year study period, information, education and communication (IEC) materials were provided to village officers, teachers and schoolchildren. The 10-year implementation of the integrated strategy resulted in a great reduction in S. japonicum infection in humans, bovines and snails. Since 2007, no acute infection was detected, and no schistosomiasis cases or infected bovines were identified since 2012. In addition, the snail habitats reduced by 62.39% in 2014 as compared to that in 2005, and no S. japonicum infection was identified in snails since 2007. By 2014, 88.9% of the endemic counties achieved the transmission interruption of schistosomiasis and transmission control of schistosmiasis was achieved in the whole province in 2008. CONCLUSION: The government-directed and multi-department integrated strategy is effective for interrupting the transmission of schistosomiasis in the mountainous and hilly regions of China.

[Oncomelania hupensis snail situation in wetlands surrounding reservoirs in hilly areas in Danling County].

OBJECTIVE: To master the Oncomelania hupensis snail situation in wetlands surrounding reservoirs in hilly areas in Danling County, Sichuan Province, so as to provide the reference for improving the snail control in these areas. METHODS: A medium-sized reservoir (Meiwan Reservoir) and a small-sized reservoir (Zhulinkan Reservoir) were chosen respectively , and the snail situation of the environments surrounding the reservoirs were investigated , the indexes such as the occurrence rate of frames with snails and the density of living snails at the upstream and downstream of the reservoirs as well as the surrounding environments were calculated and compared. Meanwhile , the data of the snail situation of the adjacent villages in the irrigation district at the downstream of the reservoirs year by year were collected to analyze the variation trend. RESULTS: The Meiwan Reservoir was located in the deep hill, the occurrence rate of frames with snails was 4.29%, the highest and average densities of living snails were 28.00 snails/0.1 m2 and 0.38 snails/0.1 m2, respectively. There was a statistically significant difference between the occurrence rates of frames with snails at the upstream and downstream, which were 0.17% and 22.16%, respectively (χ2 = 1,267.40, P < 0.05), and the rate of spillway was the highest (51.69%). The highest and average densities of living snails in the downstream were 7.00 and 656.10 times higher than those in the upstream respectively. The Zhulinkan Reservoir was located in the shallow hill, the occurrence rate of frames with snails was 17.29%, and the highest and average densities of the living snails were 38.00 snails/0.1 m2 and 0.61 snails/0.1 in 2, respectively. There was a statistically significant difference between the occurrence rates of frames with snails at the upstream and the downstream, which were 12.95% and 50.92% respectively (χ2 = 194.68, P < 0.05), and the rate of spillway was the highest (65.74%). The highest and average densities of living snails in the downstream were 5.43 and 10.00 times higher than those in the upstream respectively. After the construction of the two reservoirs, the snail area in the irrigation districts of the adjacent villages at the downstream was 57.26% of that before and after the construction (398,030 m2/695 160 m2). The snail area showed a down-ward tendency with repeatedly rebound since the 1990s. CONCLUSIONS: The wetland surrounding the reservoir in hilly region is suitable for snail breeding, and the snail situation in the shallow hill is more serious than that in the deep hill. There exists a risk for the repeatability of snail situation in this type of area where the snails can easily diffuse.

[Epidemic situation and prevention strategy of schistosomiasis in Ya' an City after Lushan Earthquake on April 20, 2013].

This paper analyzes the recently epidemic status of schistosomiasis, the change of natural and social factors, and field survey and evaluation data of schistosomiasis in Ya'an City after Lushan Earthquake on April 20, 2013, and proposes that it is necessary to strengthen the conventional schistosomiasis control measures, the control of exogenous infection sources, the control of Oncomelania hupensis snails and health education for ensuring no major epidemics after the disaster. This paper also recommends the direction and suggestions for future schistosomiasis control in Ya' an City.

[Strategy and effect of schistosomiasis emergency control after earthquake in Lushan County].

OBJECTIVE: To evaluate the effects of measures on the schistosomiasis control after the earth quake in Lushan County, so as to provide the experiences for post-disaster schistosomiasis control. METHODS: The measures taken in schistosomiasis control after the earth quake were reviewed in Lushan County in 2013, and the epidemic situation of schistosomiasis was investigated and the results were analyzed. RESULTS: The schistosomiasis control in floating population and the control of Oncomelania hupensis snails were enhanced, and no schistosome infections were found in both human and livestock. No infected snails and infested water were found. CONCLUSION: The measures of schistosomiasis control after the disaster are effective in Lushan County, and the goal to prevent major plague after the earth quake is achieved.

[Toxicity of 50% ethanol salt powder of niclosamide on growth of silkworms].

OBJECTIVE: To observe the toxity of niclosamide on the growth of silkworms. METHODS: Mulberry leaves were soaked in the different concentrations of solution of 50% ethanol salt powder of niclosamide for 10 s or 3 min, and then the leaves were fed to silkworms. The death rates of silkworms and the weight of cocoons were observed. Normal feeding control groups were established. RESULTS: The death rates were 22.5%-85.0% and 56.0%-100% in the 10-s-soaked groups and 3-min groups, respectively, which were significantly higher than those in the control groups. CONCLUSION: The 50% ethanol salt powder of niclosamide has a toxity for silkworm. Therefore, we should properly handle the relationship between the Oncomelania snail control and silkworm breeding.

[Risk assessment of schistosomiasis transmission in earthquake-stricken areas after the Lushan Earthquake in Sichuan Province on April 20, 2013].

OBJECTIVE: To assess the impact of the "4 x 20" Lushan Earthquake on the risk of schistosomiasis transmission in Lushan and Tianquan counties, so as to provide the evidence for formulating appropriate measures for schistosomiasis prevention and control. METHODS: Based on a comprehensive literature review, an analysis of schistosomiasis monitoring data in the earthquake affected counties, and a field investigation, a rapid assessment on the impact of the earthquake on schistosomiasis was conducted. RESULTS: Lushan and Tianquan counties were two endemic areas of schistosomiasis with high transmission level in history, especially Lushan County where Oncomelania snail distribution/density was the highest in Sichuan Province. After the earthquake, the streams and damaged ditches were blocked up, potentially leading to the spread of Oncomelania snails, and the damaged sanitary facilities may also lead to the release of excrement, contaminating the environment where snails resided. Meanwhile, the people who were relocated due to the earthquake may have higher exposures to contaminated environment. In addition, increasing population mobility (e.g. relief workers) also had the potential to bring infection sources in the earthquake affected areas. Further, animals, which may serve as reservoirs for the parasite such as homeless dogs, may also add the complexity of local schistosomiasis transmission. CONCLUSIONS: The epidemic risk of schistosomiasis in Lushan and Tianquan counties is high. To prevent the outbreak and epidemic of schistosomiasis, the victim settlements should be established appropriately and the excrement should be managed carefully. Meanwhile, the snail control should be carried out in the high-risk environments. The health education, monitoring, patient treatments and expanded chemotherapy should be carried out and strengthened.

[Surveillance of schistosome antibodies in population in mountainous schistosomiasis endemic regions in China].

OBJECTIVE: To understand the dynamics of schistosome antibodies in population in mountainous schistosomiasis low endemic regions, China, so as to provide the evaluation reference for immunodiagnosis. METHODS: The people who consecutively received the indirect heamagglutination assay (IHA) for schistosomiasis and Kato-Katz technique were enrolled in this study in Guixiang Village, Danling County, Sichuan Province from 2006 to 2011. The positive rates for schistosome antibodies, antibody titers and eggs per gram (EPG) were analyzed. RESULTS: A total of 353 people were investigated in this study from 2006 to 2011. The positive rates for schistosome antibodies decreased from 20.73% to 13.67%, and the geometric mean reciprocal titer (GMRT) decreased from 1.63 to 1.06. The antibodies tended to be negative in most antibody-positive people and the GMRT decreased gradually. The antibodies remained negative in most antibody-negative people. After chemotherapy in parasitology confirmed patients, the positive rate for schistosome antibodies decreased from 100% to 20%, and the GMRT decreased from 34.29 to 1.58. There was a highly positive correlation between GMRT and EPG (r = 0.94, P < 0.05). CONCLUSION: The positive rate for schistosome antibodies in population in mountainous schistosomiasis low endemic regions is relatively high (13.67%). The standardization of immunodiagnostic methods is necessary and the suitable diagnostic reagents should be developed in this region.

[Investigation on epidemic factors after schistosomiasis transmission controlled in Lushan County].

OBJECTIVE: To explore schistosomiasis endemic factors in large mountainous areas where schistosomiasis transmission has been controlled. METHODS: Qingjiang Village, Lushan County, Sichuan Province, a alpine "Pingba" type of large mountain area, Wuxing Village, a alpine hilly type of large mountainous area, and Huoju Village, a alpine canyon type of large mountainous area were selected as study areas, and the agricultural structure, health facilities, and human behavior were investi-gated. The Oncomelania snail status was surveyed by using the system sampling method combined with the environmental sampling method. The schistosome infections of population were investigated with the serum immunology method and stool hatching method, and the schistosome infections of cattle and dogs were investigated with the plastic cup top tube hatching method. RESULTS: There was a traditional agricultural structure in these villages, and the coverage rates of harmless toilets were 23.20%, 41.17%, and 41.64% in Qingjiang Village, Wuxing Village, and Huoju Village, respectively; the safe drinking water rates were 100%, 100% and 99.16% in the aforementioned villages, respectively; the rates of using ditch water for life were 22.99%, 0 and 0.85% in the aforementioned villages, respectively. The snails, wild feces, and the infection of cattle were not found. The schistosome infection rates of residents were 0.18%, 0.15%, and 6.26% in the aforementioned villages, respectively; the schistosome infection rates of dogs were 0, 0 and 2.41% in the aforementioned villages respectively. The infection rates of field rodents were all zero in the aforementioned villages. CONCLUSIONS: We should strengthen the schistosomiasis monitoring of people and cattle, strengthening the monitoring of other infectious sources, and develop a targeted snail control method in Lushan County.

[Mid-term evaluation on schistosomiasis control effect in Lushan earthquake-stricken areas in Sichuan Province].

OBJECTIVE: To evaluate the effect of schistosomiasis control in Lushan earthquake-stricken areas in Sichuan Province, so as to provide the evidence for formulating appropriate measures for schistosomiasis prevention and control. METHODS: According to the data of historical schistosomiasis prevalence, 5 villages were selected as research sites and field investigations were conducted. RESULTS: The average density of Oncomelania hupensis snails was 0.41 snails/0.1 m2, and there were no schistosome-infected snails. There were no acute schistosomiasis cases in these five villages. For local residents, the health education leaflets were more suitable than warning signs, and for migrant population, they were more concerned about the warning signs. CONCLUSION: After the implementation of effective prevention and control works, the epidemic risks of schistosomiasis have been controlled. However, the health education, surveillance, and prevention measures for schistosomiasis still need to be persisted in.

[Obstacle factors in implementation of integrated schistosomiasis prevention and control strategies with emphasis on infectious source in hilly endemic regions].

OBJECTIVE: To analyze the main obstacles existing in the implementation of integrated schistosomiasis prevention and control strategies with emphasis on infection source in hilly endemic regions, and to find out the current priority issues in schistosomiasis prevention and control, so as to provide the evidence for further solutions. METHODS: Two typical hilly schistosomiasis endemic regions in Sichuan Province, including Pujiang County of Chengdu City and Dongpo District of Meishan City, were selected as research areas. A framework of obstacle factors in the implementation of integrated schistosomiasis prevention and control strategies with emphasis on infectious source in hilly endemic regions was built by literature review, and the management and technical personnel who worked on schistosomiasis prevention and control in eight different industries (health, agriculture, forestry and so on) and five levels (provincial, city, county, township and village levels) were investigated by questionnaires in the way of nominal group. RESULTS: One hundred and fifty-three management and technical personnel in different industries and different levels were investigated. The questionnaire recovery rate (experts' positive coefficient) was 100%. The results showed that the first four problems needing to be concerned in the implementation of integrated schistosomiasis prevention and control strategies with emphasis on infection source were eliminating Oncomelania hupensis snails by projects, health education, examination and treatment for schistosomiasis persons, and harmless treatment of night-soil and safe water supply. The focuses of two counties in the implementation of integrated strategy measures were different. The harmless treatment of night-soil and safe water supply was the most important measure in Pujiang County, while the elimination of snails by projects was the most in Dong-po District. CONCLUSIONS: As the differences in the situation of epidemic areas and the existed condition of the prevention and treatment progress, the comprehensive schistosomiasis control measures should be adjusted according to the local conditions in the implementation of integrated schistosomiasis prevention and control strategies with emphasis on infection source.

[Surveilance and response for Schistosomiasis japonica based on sentinel mice examination for cercariae-infested water in risk region, 2012].

OBJECTIVE: To monitor water body infestation in schistosomiasis high-risk areas with sentinel mouse technique. METHODS: A total of 72 surveillance sites from 47 counties were selected in Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Yunnan, and Sichuan. The water infectivity of Schistosoma japonicum was determined in the surveillance sites by using sentinel mice during June-July and September, 2012. RESULTS: Among the 3,283 sentinel mice which were placed in 72 sites, 3,062 (93.3%) were recovered and dissected. Infected sentinel mice were found in six sites accounting for 8.3% (6/72) of the total surveillance sites, with an occurrence rate of sites with infected mice of 8.3% in June-July and 2.8% in September. 33 infected mice were discovered with a total infection rate of 1.08% (33/3,062). 1,085 adult worms were collected, with a mean worm burden of 32.9 worms per mouse in infected sentinel mice. 4 positive sites were in Hunan and 2 were in Jiangxi. Local acute schistosomiasis or suspected local acute cases which detected elsewhere were reported in 2 positive sites. Some follow-up activities were conducted in the 6 positive sites. CONCLUSION: Compared with those in 2010, the schistosomiasis risk areas are shrinking in 2012. However, some regions are still the schistosomiasis high-risk areas.

[Surveillance and forecast of Schistosoma japonicum-infected sentinel mice in key water regions of China in 2010].

OBJECTIVE: To explore the approach and tool for surveillance and forecast of schistosomiasis, so as to provide scientific evidence for improving the sensitivity of the surveillance and forecast system of schistosomiasis. METHODS: Two field detections were carried out in June and September by using the determination of sentinel mice in key high-risk water regions of 7 provinces of Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Yunnan and Sichuan, and the sentinel mice were raised in laboratory and dissected for observation of schistosome infections. The database regarding schisosome infections in key water regions of China was established, and the tempo-spatial distribution and environmental features of the national surveillance and forecast sites with positive sentinel mice were analyzed. RESULTS: A total of 72 surveillance and forecast sites were detected in 34 counties (cities, districts) of 7 provinces. Of the 2 667 sentinel mice placed, 2 613 were recovered, with a recovery rate of 97.98%. Among the 72 sites detected, 17 were detected with positive sentinel mice, and the occurrence rate of positive sites was 23.61%. The occurrence rate was 17.24% (10/58) in June and 14.71% (10/68) in September, and no significant difference was observed between two batches (chi2 = 0.151, P = 0.698). Of the 2 436 sentinel mice dissected, 90 were positive, and 459 schistosome worms were collected, with a total infection rate of 3.69%, and the mean worm burdens of positive mice were 5.10 worms per mouse. The infection rate of sentinel mice was 2.82% (31/1 099) in June and 4.41% (58/1 337) in September, the infection rate of sentinel mice was significantly higher in September than that in Juen (chi2 = 14.681, P < 0.01), and the mean worm burdens of infected sentinel mice were 2.45 worms per mouse in June and 6.49 worms per mouse in September. The occurrence rates of the positive sites with infected snails detected in the study year, last year and without infected snails detected in recent 3 years were 29.63%, 41.67% and 12.12%, respectively, and no significant differences were detected (chi2 = 5.227, P = 0.071). The infection rates of sentinel mice in the aforementioned 3 settings were 9.38%, 3.98% and 0.59%, respectively, and there was significant difference observed (chi2 = 20.489, P < 0.01). CONCLUSIONS: The monitoring results of sentinel mice infections in key water regions can almost reflect the endemic situation of schistosomiasis in local areas. Notably, many infections are detected in settings without infected snails detected in recent years. The monitoring of sentinel mice infections could significantly improve the sensitivity of the surveillance and forecast system of schistosomiasis.

[Surveillance of schistosomiasis in Sichuan Province, 2005-2010].

OBJECTIVE: To understand the epidemic trend of schistosomiasis in Sichuan Province so as to provide the evidence for formulating schistosomiasis control strategy. METHODS: According to the National Schistosomiasis Surveillance Protocol, the national surveillance sites in Sichuan Province were selected. The schistosomiasis surveillance was carried out continuously from 2005 to 2010. RESULTS: Nine national schistosomiasis surveillance sites were established in Pujiang, Guanghan, Zhongjiang, Fucheng, Dongpo, Danling, Renshou, Xichang and Dechang counties. The Oncomelania hupensis snail area decreased from 351 853 m2 in 2005 to 128 285 m2 in 2010, the snail density from 0.70 to 0.21 per 0.1 m2, the snail infection rate from 0.06% to 0, the positive rate of human serum schistosome antibody from 19.41% to 7.62%, the schistosome infection rate of human population from 1.93% to 0.10%, and the infection rate of livestock from 4.50% to 1.02%. The snails were found mainly in ditch, rice field and other moist field. CONCLUSIONS: Though the endemic of schistosomiasis has reached a low level in Sichuan Province, the endemic situation fluctuates at a narrow range in some surveillance sites. Therefore, the surveillance work should be carried out continuously.

[Effect of ecological civilized homestead construction on schistosomiasis control].

OBJECTIVE: To evaluate the effect of Ecological Civilized Homestead Construction on schistosomiasis control. METHODS: The data of ecological civilized homestead construction and schistosomiasis control were collected and analyzed in Meiwan Village, Shuangqiao Town, Danling County, Sichuan Province from 2004 to 2010. RESULTS: Ecological Civilized Homestead Construction was carried out from 2004 to 2010. Totally 454 bio-gas pools were built. All the farmers used well water. The popularized rates of the household bio-gas pool, sanitary toilet, sewage treatment pool reached 100%. The number of cattle was 4, which decreased by 91.30% compared with that in 2004, and all the cattle were fed in captivity. The schistosome infection rates of populations were 0.26% and 0.30% in 2005 and 2008, respectively, and nobody was infected in other years. The infection rate of cattle was 0 from 2004 to 2010. The awareness rate of knowledge about schistosomiasis control achieved 100% in the population over 6 years old. Most of the farmers could use certain protective measures while they were farming. CONCLUSION: The effect of ecological civilized homestead construction on schistosomiasis control is remarkable.

[Strengthening the achievements of schistosomiasis control in hilly regions of China].

In this paper we summarize the epidemiological characteristics, trends, and control achievements of schistosomiasis in hilly regions of China, as well as analyze the challenges of schistosomiasis control in these areas after transmission control, and further explore the control measures and strategies in the post-transmission control period to strengthen the control achievements and sustainable development with the ultimate goal of achieving transmission interruption.

[Conditions of schistosomiasis laboratories at county level].

OBJECTIVE: To understand the conditions of schistosomiasis laboratories at county level, so as to supply the information for diagnostic capacity building. METHODS: A questionnaire survey was conducted at 40 random selected counties which were in charge of national surveillance for schistosomiasis. The information of staffs, areas of laboratories, equipment configuration and diagnostic methods from each laboratory were collected. The serum specimens and Kato-Katz thick smears from the national surveillance sites were randomly selected and retested by provincial staffs to evaluate the testing ability of the personnel. RESULTS: The average age of laboratory staffs was 40.93 +/- 9.56 years old, 69.39% of staffs were older than 35 years, 86.22% of them had education background below bachelor degree. Except missed professional titles of 4 persons, the staffs with primary, middle and high professional titles accounted for 56.63%, 39.29% and 2.04%, respectively. The laboratory areas varied greatly while independent schistosomiasis stations had the lowest areas with 52.81 +/- 40.08 m2, and the equipment configurations of laboratories were in a low level. The consistency rates of primary test and reexamination for serum specimens and thick smear slides were 95.89% and 99.53%, respectively, with the Kappa value over 0.90. Nine immunodiagnostic kits were used in these laboratories, and Kato-Katz technique and miracidium hatching technique were the main parasitological methods. CONCLUSIONS: The personnel structure of laboratories at primary prevention and treatment facilities for schistosomiasis is unreasonable, while the basic infrastructure of laboratories is backward and the use of diagnostic assays/methods is disordered. The diagnostic capacity building should be strengthened, and the construction and management of schistosomiasis laboratories should be standardized.

[Spatial distribution and elimination of Schistosome japonicum intermediate hosts Oncomelania hupensis in mountainous regions].

OBJECTIVE: To explore the spatial distribution and elimination of Oncomelania hupensis in mountainous regions. METHODS: Puge County in Tezi township was selected as the study site and the quadratus were placed randomly to investigate snail. The two sods with water were selected as the sites of snail elimination. One sod with area of 1000 m2 and mean density of 9.88 snails/0.11 m2 was selected as the trial group with 'heaping' method, and the other with area of 1000 m2 and mean density of 9.80 snails/0.11 m2 as the control group with sprinkling method. The molluscacidal effect of the two methods was compared by systematic sampling (5 m x 5 m). The sample size was 40 quadratus. RESULTS: The snail distributed mainly in the sods with water, canals and farmlands. Among the three snail habitats, the area with snail was the most in the farmlands with relatively lower density of living snail; the next was the sods with water, with relatively higher density of living snail. Before killing snails, the rate of quadratus with snails was 87.50% in the trial site, and 82.50% in the control site. The mortality of snails was 3.89% in the trial site, and 4.16% in the control site. After three months, no living snails were found in the trial site, while in the control site, the rate of quadratus with snails (chi2 = 0.31, P > 0.05) and the mortality of snails (chi2 = 3.12, P > 0.05) did not decrease significantly, and the density of living snails only reduced by 8.88%. CONCLUSION: The 'heaping' method is an efficacious measure for snail control.

[Modeling transmission dynamics and control of schistosomiasis in the mountainous region, Sichuan].

OBJECTIVE: To use a mathematical model and computer simulation to study transmission dynamics and control of schistosomiasis in mountainous regions of Sichuan. METHODS: Based on studies of schistosomiasis japonica transmission in 20 villages in mountainous regions of Sichuan, a mathematical model was developed to characterize the impact of local environmental factors on transmission intensity. The model integrated site-specific factors and was calibrated to field epidemiological data from 3 subset villages. The dichotomic method was then used to predict different control measures. RESULTS: The study showed high variations in prevalence of infection and infection intensity across villages, ranging between 3%-73%, 0.1-100 epg (eggs per gram stool), respectively. Important factors including occupation of local residents, exposure to contaminated water, microclimatic characteristics were integrated in the model. The predictions of dichotomic models showed that continuing chemotherapy (coverage between 50%-60%) could reduce infection intensities to 30%-80%, but could not change local transmission potential; therefore, the termination of chemotherapy would be followed by bouncing back of transmission. Sustaining targeted environmental interventions through snail and parasite oval control at certain coverage (30%-50%, respectively) could reduce the transmission to relatively stable levels. The model predictions showed that an integrated control (e.g., including both chemotherapy and environmental interventions) could suppress the transmission to an undetectable level even interruption of transmission between 5-10 years. CONCLUSION: The study demonstrated the feasibility of using a dynamic model, calibrated to local data, to gain insights into complicated processes underlying the transmission and informing site-specific control strategies.

[Snail control by using soil pasting mixed with niclosamide].

OBJECTIVE: To evaluate the effect of snail control through soil pasting mixed with niclosamide. METHODS: Four sites were selected in different epidemic areas in Sichuan province. Soil pasting mixed with niclosamide was carried on, and the dosage was 0 g/m2, 4 g/m2, 6 g/m2, 8 g/m2 and 10 g/m2 respectively. The mortality rate of snail and the density of snail were observed after 7, 15, 30, 90 and 180 days. RESULTS: The mortality rate of snail was more than 43.3% in blank group after 30 days. The mortality rate of snail was from 75.3% to 100.0% at 4 g/m2 group after 30 days. The mortality rate of snail in 4 g/m2 group was significantly higher than that in the blank group (chi2 = 31.27, P < 0.05). There was no significant difference in the mortality rate of snail among all study groups (chi2 = 1.07, P > 0.05). The decrease rate of snail density was more than 90%. The mortality rate of snail was about 30% higher in Chantu group than Qutu group. The unit cost of Pasting-Mixing Drug with Soil was from 5 to 7 times of spray method, but the total cost was similar for the. two methods at the endpoint of the snail control. CONCLUSION: The effect of soil pasting mixed with niclosamide is good, and the dosage of 4-6 g/m2 is suggested in snail control.