Multi-host model and threshold of intermediate host Oncomelania snail density for eliminating schistosomiasis transmission in China.

Schistosomiasis remains a serious public health issue in many tropical countries, with more than 700 million people at risk of infection. In China, a national integrated control strategy, aiming at blocking its transmission, has been carried out throughout endemic areas since 2005. A longitudinal study was conducted to determine the effects of different intervention measures on the transmission dynamics of S. japonicum in three study areas and the data were analyzed using a multi-host model. The multi-host model was also used to estimate the threshold of Oncomelania snail density for interrupting schistosomiasis transmission based on the longitudinal data as well as data from the national surveillance system for schistosomiasis. The data showed a continuous decline in the risk of human infection and the multi-host model fit the data well. The 25th, 50th and 75th percentiles, and the mean of estimated thresholds of Oncomelania snail density below which the schistosomiasis transmission cannot be sustained were 0.006, 0.009, 0.028 and 0.020 snails/0.11 m(2), respectively. The study results could help develop specific strategies of schistosomiasis control and elimination tailored to the local situation for each endemic area.

Spatial-temporal variations of Schistosoma japonicum distribution after an integrated national control strategy: a cohort in a marshland area of China.

BACKGROUND: Schistosomiasis transmission is typically focal. Understanding spatial variations of Schistosoma infections and their associated factors is important to help to invent site-specific intervention strategies. METHODS: A five-year longitudinal study was carried out prospectively in 12 natural villages, Guichi district of Anhui province. A GIS-based spatial analysis was conducted to identify geographic distribution patterns of schistosomiasis infections at the household scale. RESULTS: The results of the spatial autocorrelation analysis for 2005 showed that there were significant spatial clusters of human infections at the household level, and these results were in agreement with that of the spatial scan statistic. As prevalence of infections in humans decreased over the course of control, the spatial distribution of these infections became less heterogeneous. CONCLUSIONS: The findings imply that it may be necessary to re-assess risk factors of S. japonicum transmission over the course of control and to adjust accordingly control measures in the communities.

[Molluscicidal effects of nano-silver biological molluscicide and niclosamide].

OBJECTIVE: To evaluate the molluscicidal effect of a novel nano-silver biological molluscicide in the field and its toxicity to other aquatic organisms. METHODS: A marshland of the Qiupu River was selected as the study site. Four 1 m3 pools were excavated. Four groups, including 300 g/m3 and 600 g/m3 nano-silver biological molluscicide groups, a 2 g/m3 50% niclosamide group, and a natural water (control) group were assigned to the four pools which had 100 Oncomelania hupensis snails and 100 crucian seedlings. The molluscicidal effects and toxicity to the aquatic organisms were observed. RESULTS: The snail death rates were 100% and crucian seedling death rates were 6% in the 600 g/m3 nano-silver biological molluscicide group and 300 g/m3 nano-silver biological molluscicide group in 7 days and 14 days. The snail death rate was 100% in the niclosamide group in 7 days, and the crucian seedling death rate was 100% in the niclosamide group in 3 days. The snail death rates were 7% and 14% in the control group in 7 and 14 days respectively, and the crucian seedling death rate was 22% in the control group. CONCLUSIONS: The novel nano-silver biological molluscicide possesses an excellent molluscicidal capability and non-toxicity to the other aquatic organisms. Therefore, it may become a new, efficient and environment-friendly bio-molluscicide for extensive application.

[Evaluation on the effect of comprehensive control strategy of schistosomiasis with emphasis on infection source control in Anhui province].

OBJECTIVE: To evaluate the effect of comprehensive control strategy of schistosomiasis with emphasis on infection source control in Anhui province. METHODS: Forty endemic villages in Guichi district, Chizhou city, Anhui province were selected as national pilot villages in the years from 2006 to 2008, and another 10 provincial pilot villages were respectively selected from 10 highly endemic villages in 7 cities in 2007. The comprehensive infection source control measures, including "replace cattle with machines", "raise livestock in pens", "improve the sanitary toilets", "supply safe water " and so on were carried out among the above pilot villages. At the end of 2008, 13 national pilot villages and 6 provincial pilot villages were selected to investigate the popularity of schistosomiasis, and the effect of the comprehensive control strategy in those villages were compared. RESULTS: After implementing the comprehensive control strategy, the infectious rate of schistosomiasis in national pilot villages decreased from 4.57% (487/10 659) to 1.76% (147/8370), with the reduction rate at 61.49%, whose difference showed statistical significance (χ(2) = 115.16, P < 0.01); and the density of infected snails decreased from 0.0067/0.1 m(2) to 0.0008/0.1 m(2), the infectious rate of snails decreased from 0.28% to 0.04%, whose reduction rates were 88.06% and 85.71% respectively. While as to the provincial pilot villages, the infectious rate of schistosomiasis decreased from 1.27% (54/4254) to 0.21% (14/6592), with the reduction rate at 83.46%, whose difference showed statistical significance (χ(2) = 94.57, P < 0.01); and the density of infected snails decreased from 0.0025/0.1 m(2) to 0.0003/0.1 m(2), the infection rate of snails decreased from 0.13% to 0.05%, whose reduction rates were 88.00% and 61.54% respectively. CONCLUSION: The comprehensive control strategy with emphasis on infection source control implemented in marshland and lake regions can effectively control the transmission of schistosomiasis.

[Investigation on prevalent trends and analysis of control period among floating population in schistosomiasis endemic areas of Guichi District].

OBJECTIVE: To understand the characteristics of the floating population infected with Schistosoma japonicum, so as to provide the evidence for constituting and optimizing control strategy. METHODS: By the cluster random sampling method, six highly endemic villages from the different endemic types in Guichi District were selected as the research areas . The basic information and infected status of the floating population were surveyed by questionnaires and examination between 2000 and 2009. RESULTS: The time when the floating population returned to their homes mainly focused on Spring Festival between 2000 and 2009, and more than 83% of people returned. The infection rate of the floating population was similar to or more than that of the local residents. During the ten years, the reduction of the infection rates in the floating populations (from 5.29% to 2.63%) was consistent with the reduction of the infection rates in the local residents (from 5.28% to 2.68%). However, the reduction of the infection rates in the floating population who worked in the non-endemic areas was more than that in the local residents. CONCLUSION: Spring Festival is the optimal time for detecting and treating schistosomiasis in the floating population.

An integrated strategy for transmission control of Schistosoma japonicum in a marshland area of China: findings from a five-year longitudinal survey and mathematical modeling.

In 2004 an aggressive plan was instituted aiming to achieve nationwide transmission control of schistosomiasis by 2015. Here, we report a longitudinal study on the control of schistosomiasis in Anhui province, China. Using a mathematical model, we compared the effects of different control strategies implemented in the study area. During the 5-year study period, a 60.8% reduction in human prevalence was observed from 2005 (7.95%) to 2009 (3.1%), and snail infection decreased from 0.063% in 2005 to zero in 2009. Results of the model agree well with the first 3-year field observations and suggest continuous decrease in human infections in the last 2 years, whereas the last 2-year field observations indicated that human infections appeared to be stable even with continuous control. Our findings showed that the integrated control strategy was effective, and we speculated that other factors besides bovines might contribute to the local transmission of the disease.

[Scan statistic method with moving window and its application in the temporal clustering detection of acute schistosomiasis].

Acute schistosomiasis cases from 2001 to 2006 in Guichi District, Chizhou City, Anhui Province, were collected and analyzed by scan statistic method with moving window, central degree approach and circular distribution method in order to detect the temporal clustering of schistosomiasis. The analyzed data provided by the method showed that the temporal clustering of acute schistosomiasis from 2001 to 2003 in Guichi District became more concentrative, and then disperse, resulting in a final disappearance of the clustering in 2006 (LLR = 4.14, P > 0.05). The temporal clustering for all cases in the six years detected by scan statistic method was between August to September in 2002 (LLR = 18.5, P < 0.01), which was consistent with the real condition. Whereas the results from the central degree and the circular distribution methods could only provide limited information and were biased in the analysis in 2002, indicating that the scan statistic method with moving window can provide ample information with more robust and credible results.