Yi-Biao Zhou

Identifying high-risk regions for schistosomiasis in Guichi, China: A spatial analysis

Schistosomiasis epidemic is reemerging in some areas of China. The extensive snail habitat is a major challenge for a sustainable schistosomiasis control. Direct surveillance on snails for the disease control is no longer a desirable disease control approach due to current low density of infected snails and reduced funding. In this study the benefit of indirect monitoring of acute schistosomiasis cases, using spatial methods including disease mapping and spatial clustering analysis was explored in Guichi, China. Significant global clustering existed for acute cases and two statistically significant spatial clusters were detected, and subsequently validated by field surveys. Our study indicates that the application of geographic information system (GIS) and spatial methods are useful in the epidemiologic surveillance and risk assessment for acute schistosomiasis, providing an alternative approach with minimal funds required.

A longitudinal study of comparison of the Kato-Katz technique and indirect hemagglutination assay (IHA) for the detection of schistosomiasis japonica in China, 2001-2006.

From 2001 to 2006, about one-third of the residents aged 5-65 years were selected as the subjects in a schistosome-endemic village located in Jiangxi Province, China. Every 1 year, all participants were analyzed by the Kato-Katz parasitologic examination and indirect hemagglutination assay (IHA). Statistical analysis of the results showed the k indices ranged from 0.250 to 0.347 between the two methods. Assuming the Kato-Katz results as the gold standard reference, the specificity of the IHA was from 60% to 77%, the positive predictive value of this method was from 19% to 30%, and its sensitivity and negative predictive value were more than 97%. The IHA method is unsuitable for individual screening in endemic community with relatively high prevalence (e.g. with >10% or more prevalence). A search for a better diagnostic test that can be applied in field situations in China is essential and should be given high priority.

Identifying high-risk areas of schistosomiasis and associated risk factors in the Poyang Lake region, China

The epidemiology of schistosomiasis japonicum over small areas remains poorly understood, and this is particularly true in China. We aimed to identify high-risk areas for schistosomiasis and associated risk factors in the Poyang Lake region, China. A cross-sectional study was conducted and 60 of 920 persons (6.5%) were found to be infected with Schistosoma japonicum. Locations of households and snail habitats were determined using a hand-held global positioning system. We mapped the data in a geographical information system and used spatial scan statistics to explore clustering of infection, logistic regression and Bayesian geostatistical models to identify risk factors for each individuals infection status and multinomial logistic regression to identify risk factors for living in a cluster area. The risk of schistosomiasis was spatially clustered and higher in fishermen and males, not in persons who lived in close proximity to snail habitats and infected water sources. This study has demonstrated significant spatial variation in the prevalence of schistosomiasis at a small spatial scale. The results suggest that demographic factors (gender, occupation) rather than the distance to infected water are driving human transmission at small-scale spatial levels. Such information can be used to plan locally targeted interventions based on anthelminthic drug administration, snail control and sanitation improvement.

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.

A model for the prediction of Oncomelania hupensis in the lake and marshland regions, China

A model has been developed for predicting the density of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum. The model takes into account different environmental factors, including elevation, air and soil temperature, type of vegetation, mean height of preponderant vegetation and soil humidity. Deviance and Akaike information criteria were used to determine the best model fits. Model diagnostics and internal and external validations of model efficiency were also performed. From the final prediction model, two important results emerge. First, air temperature should be used with care to study the distribution of O. hupensis and to predict its potential survival because the impact is indirect, and it is weaker and more unstable than soil temperature. Second, the more important environmental factor for O. hupensis prediction at the microscale is soil humidity, but the more important macroscale environmental factor is soil temperature. This finding might help in selecting different environmental features for studying O. hupensis at different spatial scales. Our model is promising for predicting the density of O. hupensis, and hence can provide more objective information about snail dispersal, which might eventually replace the tedious and imprecise field work for annual surveillance of O. hupensis.

Nonparametric spatial analysis to detect high-risk regions for schistosomiasis in Guichi, China.

Schistosomiasis control in China is facing a new challenge due to the rebound of epidemics in many areas and the unsustainable effects of the chemotherapy-based control strategy. Identifying high-risk regions for schistosomiasis is an important first step for an effective and sustainable strategy. Direct surveillance of snail habitats to detect high-risk regions is costly and no longer a desirable approach, while indirect monitoring of acute schistosomiasis may be a satisfactory alternative. To identify high-risk regions for schistosomiasis, we jointly used multiplicative and additive models with the kernel smoothing technique as the main approach to estimate the relative risk (RR) and excess risk (ER) surfaces by analyzing surveillance data for acute schistosomiasis. The feasibility of detecting high-risk regions for schistosomiasis through nonparametric spatial analysis was explored and confirmed in this study, and two significant high-risk regions were identified. The results provide useful hints for improving the national surveillance network for acute schistosomiasis and possible approaches to utilizing surveillance data more efficiently. In addition, the commonly used epidemiological indices, RR and ER, are examined and emphasized from the spatial point of view, which will be helpful for exploring many other epidemiological indices.

Effects of the praziquantel-based control of schistosomiasis japonica in China

Abstract In 2000–2002, the effects of the praziquantel-based control of Schistosoma japonicum (in which each subject found infected in the October of each year is given a single dose of the drug) were examined at 20 or 21 surveillance sites across China. The pre- and post-treatment prevalences and intensities of infection were compared at each site and after pooling using a random-effects method. One year after treatment, in the communities that had the higher prevalences of infection (> 10%) before treatment, the mean prevalence of infection was found to have fallen by 20.15% [95% confidence interval (CI)=6.95%–31.48%] and the geometric mean intensities of infection (measured as eggs/g faeces) in the currently infected individuals and the entire study cohort were found to have fallen, by 22.91% (CI=14.69%–30.34%) and 33.93% (CI=11.69%–50.68%), respectively (P<0.05 for each). In the communities that had lower prevalences of infection pre-treatment, however, no statistically significant reductions in the intensity of infection were observed, although the prevalences in the communities that had pre-treatment prevalences of 6%–10% did fall significantly post-treatment, by a mean of 24.50% (CI=5.35%–39.83%; P<0.05). These observations indicate that the current annual surveys for infection, in which those found infected are each given a single dose of praziquantel, should help keep the prevalence of human infection with S. japonicum low in China, although chemotherapy alone is unlikely to eradicate the parasite.

Three Gorges Dam: Impact of Water Level Changes on the Density of Schistosome-Transmitting Snail Oncomelania hupensis in Dongting Lake Area, China

Background Schistosomiasis remains an important public health issue in China and worldwide. Oncomelania hupensis is the unique intermediate host of schistosoma japonicum, and its change influences the distribution of S. japonica. The Three Gorges Dam (TGD) has substantially changed the ecology and environment in the Dongting Lake region. This study investigated the impact of water level and elevation on the survival and habitat of the snails. Methods Data were collected for 16 bottomlands around 4 hydrological stations, which included water, density of living snails (form the Anxiang Station for Schistosomiasis Control) and elevation (from Google Earth). Based on the elevation, sixteen bottomlands were divided into 3 groups. ARIMA models were built to predict the density of living snails in different elevation areas. Results Before closure of TGD, 7 out of 9 years had a water level beyond the warning level at least once at Anxiang hydrological station, compared with only 3 out of 10 years after closure of TGD. There were two severe droughts that happened in 2006 and 2011, with much fewer number of flooding per year compared with other study years. Overall, there was a correlation between water level changing and density of living snails variation in all the elevations areas. The density of living snails in all elevations areas was decreasing after the TGD was built. The relationship between number of flooding per year and the density of living snails was more pronounced in the medium and high elevation areas; the density of living snails kept decreasing from 2003 to 2014. In low elevation area however, the density of living snails decreased after 2003 first and turned to increase after 2011. Our ARIMA prediction models indicated that the snails would not disappear in the Dongting Lake region in the next 7 years. In the low elevation area, the density of living snails would increase slightly, and then stabilize after the year 2017. In the medium elevation region, the change of the density of living snails would be more obvious and would increase till the year 2020. In the high elevation area, the density of living snails would remain stable after the year 2015. Conclusion The TGD influenced water levels and reduced the risk of flooding and the density of living snails in the study region. Based on our prediction models, the density of living snails in all elevations tends to be stabilized. Control of S. japonica would continue to be an important task in the study area in the coming decade.

Oncomelania hupensis (Gastropoda: Rissooidea), Intermediate Host Of Schistosoma japonicum In China: Genetics and Molecular Phylogeny Based On Amplified Fragment Length Polymorphisms

Schistosomiasis japonica is one of the most serious parasitic diseases in China. Subspecies of the pomatiopsid snail species Oncomelania hupensis transmit the human blood fluke Schistosoma japonicum, the parasite causing the disease. In at least one study involving the subspecies Oncomelania hupensis robertsoni, there was no clear phylogenetic concordance between the mitochondrial and nuclear data, and it was strongly recommended that future studies incorporate more data from nuclear loci in order to better understand phylogeography and host-parasite coevolution (Wilke et al., 2006). In this paper, we explore genetic diversity based AFLP data involving 25 populations throughout mainland China. AFLP is a DNA fingerprinting technique that detects the polymorphism of the whole genome without prior knowledge of the nucleotide sequence, with the high degree of reproducibility and small amount of template DNA needed. Our AFLP data show that: (1) the genetic diversity within an O. hupensis population increases gradually with snail sample size, and when the sample size is more than 30 individuals, the genetic variation within one O. hupensis population trends to stabilization. (2) There is high intra-population genetic variation on the mainland of China, and these intra-population genetic variations from different areas differ significantly. (3) The considerable genetic differentiation occurs throughout China. (4) The genetic variation among populations of O. h. hupensis is higher than that of O. h. robertsoni. (5) The patterns of genetic differentiation are basically consistent with geographical distribution of snail populations. Our results are similar to the results of allozymes and COI gene sequences, excluding a snail population from Guangxi Province (Gx-1), indicating that there are three distinct subspecies in mainland China, namely O. h. hupensis, O. h. robertsoni, and O. h. tangi. However, our results do not support that the snail population from Guangxi Province belongs to O. h. hupensis.

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

BackgroundSchistosomiasis transmission is typically focal. Understanding spatial variations of Schistosoma infections and their associated factors is important to help to invent site-specific intervention strategies.MethodsA 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.ResultsThe 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.ConclusionsThe 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.