A comparison of modelling the spatio-temporal pattern of disease: a case study of schistosomiasis japonica in Anhui Province, China.

The construction of spatio-temporal models can be either descriptive or dynamic. In this study we aim to evaluate the differences in model fitting between a descriptive model and a dynamic model of the transmission for intestinal schistosomiasis caused by Schistosoma japonicum in Guichi, Anhui Province, China. The parasitological data at the village level from 1991 to 2014 were obtained by cross-sectional surveys. We used the fixed rank kriging (FRK) model, a descriptive model, and the integro-differential equation (IDE) model, a dynamic model, to explore the space-time changes of schistosomiasis japonica. In both models, the average daily precipitation and the normalized difference vegetation index are significantly positively associated with schistosomiasis japonica prevalence, while the distance to water bodies, the hours of daylight and the land surface temperature at daytime were significantly negatively associated. The overall root mean square prediction error of the IDE and FRK models was 0.0035 and 0.0054, respectively, and the correlation reflected by Pearson's correlation coefficient between the predicted and observed values for the IDE model (0.71; p<0.01) was larger than that for the FRK model (0.53; p=0.02). The IDE model fits better in capturing the geographic variation of schistosomiasis japonica. Dynamic spatio-temporal models have the advantage of quantifying the process of disease transmission and may provide more accurate predictions.

Dynamic evolution of schistosomiasis distribution under different control strategies: Results from surveillance covering 1991-2014 in Guichi, China.

BACKGROUND: Since the founding of the China, the Chinese government, depending on the changing epidemiological situations over time, adopted different strategies to continue the progress towards elimination of schistosomiasis in the country. Although the changing pattern of schistosomiasis distribution in both time and space is well known and has been confirmed by numerous studies, the problem of how these patterns evolve under different control strategies is far from being understood. The purpose of this study is, therefore, to investigate the spatio-temporal change of the distribution of schistosomiasis with special reference to how these patterns evolve under different control strategies. METHODOLOGY / PRINCIPAL FINDINGS: Parasitological data at the village level were obtained through access to repeated cross-sectional surveys carried out during 1991-2014 in Guichi, a rural district along the Yangtze River in Anhui Province, China. A hierarchical dynamic spatio-temporal model was used to evaluate the evolving pattern of schistosomiasis prevalence, which accounted for mechanism of dynamics of the disease. Descriptive analysis indicates that schistosomiasis prevalence displayed fluctuating high-risk foci during implementation of the chemotherapy-based strategy (1991-2005), while it took on a homogenous pattern of decreasing magnitude in the following period when the integrated strategy was implemented (2006-2014). The dynamic model analysis showed that regularly global propagation of the disease was not present after the effect of proximity to river was taken into account but local pattern transition existed. Maps of predicted prevalence shows that relatively high prevalence (>4%) occasionally occurred before 2006 and prevalence presents a homogenous and decreasing trend over the study area afterwards. CONCLUSIONS: Proximity to river is still an important determinant for schistosomiasis infection regardless of different types of implemented prevention and control strategies. Between the transition from the chemotherapy-based strategy to the integrated one, we noticed a decreased prevalence. However, schistosomiasis would remain an endemic challenge in these study areas. Further prevention and control countermeasures are warranted.

Assessment of the national schistosomiasis control program in a typical region along the Yangtze River, China.

Schistosomiasis remains a major public health problem in eastern China, particularly along the Yangtze River Basin. The latest national schistosomiasis control program (NSCP) was implemented in 2005 with the main goal of reducing the rate of infection to less than 5% by 2008 and 1% by 2015. To assess the progress, we applied a Bayesian spatio-temporal model to describe dynamics of schistosomiasis in Guichi, Anhui Province, China, using annual parasitological and environmental data collected within 41 sample villages for the period 2005-2011. Predictive maps of schistosomiasis showed that the disease prevalence remains constant and low. Results of uncertainty analysis, in the form of probability contour maps (PCMs), indicated that the first goal of "infection rate less than 5% by 2008" was fully achieved in the study area. More longitudinal data for schistosomiasis are needed for the assessment of the second goal of "infection rate less than 1% by 2015". Compared with the traditional way of mapping uncertainty (e.g., variance or mean-square error), our PCMs provide more realistic information for schistosomiasis control.

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.

Human infections and co-infections with helminths in a rural population in Guichi, Anhui Province, China.

Helminth infections are believed to be common in tropical and subtropical countries. A cross-sectional study was carried out in two villages located in Guichi District in Anhui Province, the People's Republic of China, where multiparasitism was investigated using parasitological tests. The data collected were fitted to Bayesian multi-level models to profile risk factors for helminth infections. The prevalence of Schistosoma (S.) japonicum, Ascaris (A.) lumbricoides and Trichuris (T.) trichiura were 0.43% (range: 0-0.87% at the village level), 2.28% (range: 1.69-2.88%), and 0.21% (range: 0-0.42%), respectively. No hookworm infection was found. With regard to multiparasitism, only a 33-year-old female was found to be co-infected with S. japonicum and A. lumbricoides. Multiparasitism was unexpectedly rare in the study area, which contrasts with results from other studies carried out elsewhere in the country. The long-term usage of albendazole for individuals serologically positive for schistosomiasis may be the main reason, but this needs to be confirmed by future studies.

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.