Epidemiology Of Schistosomiasis Research Articles

Profile of metabolite and biomolecule concentrations in the hemolymph of <i>Bulinus globosus</i> and <i>Bulinus rohlfsi</i> under aestivation and starvation

There is resurgence in epidemiology of schistosomiasis in Nigeria with attendant socio-economic and health impact. The agents perpetuating this disease are the Bulinus snails which employ aestivation to survive unfavourable conditions. These snails are intermediate hosts required for the aquatic stage of schistosomes thereby increasing their chances of returning to an aquatic environment to resume life cycle once favourable conditions reappear. However, mechanism of aestivation underaridity and drought is not clear. This study therefore, investigated the effects of aestivation and starvation on endogenous metabolic reserves in tissues and haemolymph of two snail species namely Bulinus globosus (Morelet) and Bulinus rohlfsi (Clessin). Aestivation, starvation, and control experiments were set up for 30 days by placing three groups of snails instandard aestivation slope, aquarium and control slope containing mixture of sand and clay (3:1) in slopes and water only for aquarium. Snails were fed on lettuce (Lactuca sativa) ad libitum for 28 days until water completely drained out. The aestivation slope and aquarium were left dry for another 30 days without lettuce while the control slope contained both lettuce and water. Quantitative analysis of protein, carbohydrate and lipid were determined in tissues and hemolymph while hemolymph creatinine,urea, total protein, glucose, total cholesterol and triglyceride were determined in aestivating, starved and control snails. Activities of lipases a-amylase alanine amino transferase (ALT) and aspartate amino transferase (AST) were determined. Data were analysed using ANOVA.Tissue macromolecules decreased in aestivating and starving snails during aestivation compared with control. Lipid and carbohydrate were significantly reduced in aestivating B. globosus and B. rohlfsi during aestivation (p

Transmission of Schistosoma mansoni in Tikur Wuha area, Southern Ethiopia

Background: Although the epidemiology of schistosomiasis is well established and the disease distribution has also been mapped in Ethiopia, discovery of new foci has continuously been reported.Objectives: The objective of this study was to assess the establishment of transmission of schistosomiasis mansoni in Tikur Wuha area, southern Ethiopia.Methods: A cross-sectional epidemiological study involving 375 school children in Tikur Wuha Elementary School was conducted in December 2007 and January 2008. Stool specimens were collected and microscopically examined using Kato-Katz method. Snail survey was also conducted using scoop in Tikur Wuha River and littoral zone of Lake Awassa on the side of Tikur Wuha Kebele (administrative unit). The snails collected were checked for trematode infection by shedding. Laboratory-bred mice were exposed to schistosome cercariae and definite identification of the schistosome was made using eggs and adult worm morphology.Results: The prevalence and intensity of schistosomiasis mansoni was 12% and 69 eggs per gram (epg) of stool, respectively. Biomphalaria sudanica collected in Tikur Wuha River shed schistosome cercariae. Adult S. mansoni worms were harvested from laboratory-bred mice after 6 weeks of laboratory maintenance.Conclusion: The prevalence and intensity of schistosomiasis mansoni among school children was low and the area represents low-risk community. The finding of S. mansoni infected young children, the collection of B. sudanica infected with schistosome cercariae, and the establishment of infection in lab-bred mice all confirmed the transmissionof schistosomiasis mansoni in Tikur Wuha area. Appropriate intervention measures need to be in place to reduce morbidity and transmission of intestinal schistosomiasis in the area.

Esquistossomose em área de transição rural-urbana: reflexões epidemiológicas

The Schistosomiasis is an endemic parasitic disease of tropical areas found in 76 countries. It is also estimated that 779 million people are at risk of infection and 207 million are infected worldwide. In northeastern Brazil, this parasitosis reaches hyperendemic rates, particularly in the states of Pernambuco, Bahia, Alagoas and Sergipe. This study proposes to reflect about the epidemiology of schistosomiasis in a Housing Complex located in Sergipe. This study is characterized as descriptive; cross-sectional qualitative and quantitative with a convenience sample comprising 200 individuals, members of a population of 142 families. Secondary data analysis from 2003 to 2008 and primary data collected in 2009/2010, obtained through interviews were used. For data analysis it was used the chi-square test, assuming a significance level of 0.05%, from the SPSS 16.0 software. The studied area presents medium endemicity for schistosomiasis with an average prevalence of 13.98%, occurring more frequently among males of all age ranges, with a greater tendency among adolescent and adults and individuals of black and mulatto ethnicity with low level of education and low income.

Vertebrate host protective immunity drives genetic diversity and antigenic polymorphism in Schistosoma mansoni

Schistosomes are gonochoric blood parasites with a complex life cycle responsible for a disease of considerable medical and veterinary importance in tropical and subtropical regions. Understanding the evolution of schistosome genetic diversity is clearly of fundamental importance to interpreting schistosomiasis epidemiology and disease transmission patterns of this parasite. In this article, we investigated the putative role of the host immune system in the selection of male genetic diversity. We demonstrated the link between genetic dissimilarity and the protective effect among male worms. We then compared the proteomes of three male clones with different genotypes and differing by their capacity to protect against reinfection. The identified differences correspond mainly to antigens known or supposed to be involved in the induction of protective immunity. These results underline the role played by host immune system in the selection of schistosome genetic diversity that is linked to antigenic diversity. We discuss the evolutionary consequences in the context of schistosome infection.

Follow-up of the genetic diversity and snail infectivity of a Schistosoma mansoni strain from field to laboratory

Schistosoma mansoni is an endoparasite causing a serious human disease called schistosomiasis. The quantification of parasite genetic diversity is an essential component to understand schistosomiasis epidemiology and disease transmission patterns but some studies on parasite genetic diversity are performed using parasite laboratory strains. However, a potential discrepancy in level of genetic variation between field populations and laboratory strains may have various implications in our deductions. In this study, 246 adult worms were analysed on 15 microsatellite markers to investigate variation of genetic diversity between a founder field isolate and the nine successive laboratory generations during three years of laboratory maintenance. In parallel, we measured a parasite life trait (snail infectivity) at each generation in order to test a potential link between inbreeding and snail infectivity. Our genetic analyses demonstrate a significant genetic differentiation between all parasite generations and a significant isolation by time associated with a decrease in neutral genetic diversity that is likely to be the result of successive bottleneck events. However, while snail infectivity decreases sharply between field isolate and the first laboratory generation, this parasite life trait does not evolve between other laboratory generations and appeared disconnected from this continuous neutral genetic diversity loss. We hypothesize that a sufficient level of compatibility polymorphism at a genomic level is maintained independently of an increase of inbreeding, ensuring the stability in the parasite life trait.

Egg excretion patterns as criterion for the determination of prevalence and intensity of infection in male and female individuals in different age groups in a schistosome endemic area in the Limpopo Province

Urinere skistosomose is ’n siekte wat deur die wurmparasiet Schistosoma haematobium veroorsaak word. Dit kom hoofsaaklik in die sub-tropiese gedeeltes van Limpopo-, Mpumalanga en KwaZulu Natal provinsies voor. Nagenoeg drie miljoen mense waarvan die meeste kinders is, is met hierdie parasiet besmet. Alhoewel daar serologiese toetse beskikbaar is om die besmetting te diagnoseer, word mikroskopiese ondersoeke van die urine vanwee die lae koste daaraan verbonde, oorwegend as diagnostiese metode gebruik. Die moontlikheid van variasie in die voorkoms van eiers in die urine wanneer urine versamel word, kan ongelukkig daartoe lei dat die getal besmette persone in ’n bepaalde gebied vanwee die voorkoms van vals negatiewe resultate onderskat kan word. Hierdie ondersoek het dit ten doel gehad om die voorkoms van sodanige variasie by skistosoombesmette manlike en vroulike individue op verskillende tye van die dag na te gaan met die doel om die graad van variasie wat mag voorkom, vas te stel, sowel as om te bepaal of daar ’n daaglikse piek in die ekskresie van die eiers voorkom wat moontlik op ’n geskikte tyd vir die versameling van urine kan dui. Urine is om 8:30, 10:30, 12:30, 14:30 en 16:30 van manlike en vroulike individue in die 4–9, 10–4 en 15–2 jaar ouderdomsgroepe versamel en mikroskopies vir die teenwoordigheid van eiers ondersoek. Die eiers is hierna getel en in verskillende intensiteitskategoriee ingedeel. Die resultate van hierdie ondersoek het aan die lig gebring dat, ongeag van wanneer die urine versamel is, vals negatiewe resultate in elke groep wat ondersoek is, voorgekom het. Dit is verder bevind dat daar geen defi nitiewe piek in eierekskresie voorgekom het wat hetsy tussen die verskillende ouderdomsgroepe of intensiteitsgroepe ooreengestem het nie.

Remote sensing, geographical information system and spatial analysis for schistosomiasis epidemiology and ecology in Africa.

Beginning in 1970, the potential of remote sensing (RS) techniques, coupled with geographical information systems (GIS), to improve our understanding of the epidemiology and control of schistosomiasis in Africa, has steadily grown. In our current review, working definitions of RS, GIS and spatial analysis are given, and applications made to date with RS and GIS for the epidemiology and ecology of schistosomiasis in Africa are summarised. Progress has been made in mapping the prevalence of infection in humans and the distribution of intermediate host snails. More recently, Bayesian geostatistical modelling approaches have been utilized for predicting the prevalence and intensity of infection at different scales. However, a number of challenges remain; hence new research is needed to overcome these limitations. First, greater spatial and temporal resolution seems important to improve risk mapping and understanding of transmission dynamics at the local scale. Second, more realistic risk profiling can be achieved by taking into account information on people's socio-economic status; furthermore, future efforts should incorporate data on domestic access to clean water and adequate sanitation, as well as behavioural and educational issues. Third, high-quality data on intermediate host snail distribution should facilitate validation of infection risk maps and modelling transmission dynamics. Finally, more emphasis should be placed on risk mapping and prediction of multiple species parasitic infections in an effort to integrate disease risk mapping and to enhance the cost-effectiveness of their control.

Introgressive hybridization of human and rodent schistosome parasites in western Kenya

Hybridization and introgression can have important consequences for the evolution, ecology and epidemiology of pathogenic organisms. We examined the dynamics of hybridization between a trematode parasite of humans, Schistosoma mansoni, and its sister species, S. rodhaini, a rodent parasite, in a natural hybrid zone in western Kenya. Using microsatellite markers, rDNA and mtDNA, we showed that hybrids between the two species occur in nature, are fertile and produce viable offspring through backcrosses with S. mansoni. Averaged across collection sites, individuals of hybrid ancestry comprised 7.2% of all schistosomes collected, which is a large proportion given that one of the parental species, S. rodhaini, comprised only 9.1% of the specimens. No F1 individuals were collected and all hybrids represented backcrosses with S. mansoni that were of the first or successive generations. The direction of introgression appears highly asymmetric, causing unidirectional gene flow from the rodent parasite, S. rodhaini, to the human parasite, S. mansoni. Hybrid occurrence was seasonal and most hybrids were collected during the month of September over a 2-year period, a time when S. rodhaini was also abundant. We also examined the sex ratios and phenotypic differences between the hybrids and parental species, including the number of infective stages produced in the snail host and the time of day the infective stages emerge. No statistical differences were found in any of these characteristics, and most of the hybrids showed an emergence pattern similar to that of S. mansoni. One individual, however, showed a bimodal emergence pattern that was characteristic of both parental species. In conclusion, these species maintain their identity despite hybridization, although introgression may cause important alterations of the biology and epidemiology of schistosomiasis in this region.

Schistosomiasis transmission at high altitude crater lakes in western Uganda.

BackgroundContrary to previous reports which indicated no transmission of schistosomiasis at altitude >1,400 m above sea level in Uganda, in this study it has been established that schistosomiasis transmission can take place at an altitude range of 1487–1682 m above sea level in western Uganda.MethodsAn epidemiological survey of intestinal schistosomiasis was carried out in school children staying around 13 high altitude crater lakes in Western Uganda. Stool samples were collected and then processed with the Kato-Katz technique using 42 mg templates. Thereafter schistosome eggs were counted under a microscope and eggs per gram (epg) of stool calculated. A semi-structured questionnaire was used to obtain demographic data and information on risk factors.Results36.7% of the pupils studied used crater lakes as the main source of domestic water and the crater lakes studied were at altitude ranging from 1487–1682 m above sea level. 84.6% of the crater lakes studied were infective with over 50% of the users infected.The overall prevalence of Schistosoma mansoni infection was 27.8% (103/370) with stool egg load ranging from 24–6048 per gram of stool. 84.3%( 312) had light infections (<100 eggs/gm of stool), 10.8%( 40) had moderate infections (100–400 eggs/gm of stool) and 4.9% (18) had heavy infections (>400 egg/gm of stool). Prevalence was highest in the age group 12–14 years (49.5%) and geometric mean intensity was highest in the age group 9–11 years (238 epg). The prevalence and geometric mean intensity of infection among girls was lower (26%; 290 epg) compared to that of boys (29.6%; 463 epg) (t = 4.383, p < 0.05). Though 61%(225) of the pupils interviewed were aware of the existence of the disease, 78% (290)didn't know the mode of transmission and only 8% (30) of those found infected were aware of their infection status. In a multivariate logistic regression model, altitude and water source (crater lakes) were significantly associated with infection.Conclusion and recommendationsThe altitudinal threshold for S. mansoni transmission in Uganda has changed and use of crater water at an altitude higher than 1,400 m above sea level poses a risk of acquiring S. mansoni infection in western Uganda. However, further research is required to establish whether the observed altitudinal threshold change is as a result of climate change or other factors. It is also necessary to establish the impact this could have on the epidemiology of schistosomiasis and other vector-borne diseases in Uganda. In addition, sensitisation and mass treatment of the affected community is urgently required.

Cheap, rapid and efficient DNA extraction method to perform multilocus microsatellite genotyping on all Schistosoma mansoni stages

Schistosomes are endoparasites causing a serious human disease called schistosomiasis. The quantification of parasite genetic diversity is an essential component to understand the schistosomiasis epidemiology and disease transmission patterns. In this paper, we propose a novel assay for a rapid, low costly and efficient DNA extraction method of egg, larval and adult stages of Schistosoma mansoni. One euro makes possible to perform 60,000 DNA extraction reactions at top speed (only 15 min of incubation and 5 handling steps).

Evaluation of IgG-ELISA for the diagnosis of Schistosoma japonicum in a high prevalence, low intensity endemic area of China

Antibody-based diagnostic methods for detecting infection with Schistosoma japonicum have been developed and integrated into the national control program in China; however, the utility of these methods compared with conventional coprological methods remains unclear. In two consecutive years, we compared the performance characteristics of Kato–Katz with a commercially available enzyme-linked immunosorbent assay (ELISA) that detects anti-egg antigen IgG antibodies in a high prevalence, low intensity village in China (1025 subjects in 2005 and 652 subjects in 2006). In comparison with Kato–Katz based on duplicate stool specimens, each read in triplicate, the sensitivity of IgG-ELISA was high, ranging from 79.3% to 87.4% but with a relatively low specificity of 38.9% to 53.5%. The positive predictive value ranged from 20.8% to 24.6% while the negative predictive value ranged from 93.1% to 94.4%. When analyzed as continuous variables, there was a poor correlation between EPG (eggs per gram feces) and antibody level in both years ( r 2005 = 0.23 and r 2006 = 0.41). We detected a trend toward reduced sensitivity at lower infection intensity as measured by Kato–Katz in 2005 ( P = 0.262) and 2006 ( P = 0.287). We evaluated changes in antibody levels and the prevalence of positive antibody in the cohort of subjects examined in both 2005 and 2006 ( n = 565). The prevalence of positive antibody but not the continuous antibody level, decreased in individuals who were uninfected at both time points or who transitioned from infected to uninfected as assessed by Kato–Katz. In this cohort, the distribution of antibody levels measured in 2006 among individuals who were positive by Kato–Katz in 2006 broadly overlapped with the distribution of antibody levels in individuals who were negative by Kato–Katz in both 2005 and 2006. Our results indicate fairly poor performance characteristics of the anti-egg antigen IgG-ELISA for the detection of active infection with S. japonicum in our community based sample and are in contrast with other reports based on more selected populations. The high prevalence but low intensity of S. japonicum in our study community reflects the evolving epidemiology of schistosomiasis in communities receiving intermittent treatment with praziquantel in China. We suggest marked caution in implementing anti-egg antigen IgG-ELISA based diagnosis for either individual level diagnosis or population-based targeting for national control programs.

Multiplex real-time PCR for the detection and quantification of Schistosoma mansoni and S. haematobium infection in stool samples collected in northern Senegal

A multiplex real-time PCR assay for the detection and quantification of Schistosoma mansoni and S. haematobium DNA in faecal samples was developed and evaluated as an alternative diagnostic method to study the epidemiology of schistosomiasis. Primers and probes targeting the cytochrome c oxidase gene were designed for species-specific amplification and were combined with an internal control. Using positive control DNA extracted from adult Schistosoma worms and negative control samples (n=150) with DNA from a wide range of intestinal microorganisms, the method proved to be sensitive and 100% specific. For further evaluation, duplicate stool specimens with varying S. mansoni egg loads were collected in northern Senegal from pre-selected individuals (n=88). The PCR cycle threshold values, reflecting parasite-specific DNA loads in faeces, showed significant correlation with microscopic egg counts both for S. mansoni in stool and S. haematobium in urine. The Schistosoma detection rate of PCR (84.1%) was similar to that of microscopy performed on duplicate stool samples (79.5%). The simple faecal sample collection procedure and the high throughput potential of the multiplex real-time PCR provide a powerful diagnostic tool for epidemiological studies on schistosomiasis in remote areas, with possibilities for extension to other helminths or protozoa using additional molecular targets.

Epidemiology of schistosomiasis in the People's Republic of China, 2004.

Results from the third nationwide cluster sampling survey on the epidemiology of schistosomiasis in the People's Republic of China, conducted by the Ministry of Health in 2004, are presented. A stratified cluster random sampling technique was used, and 239 villages were selected in 7 provinces where Schistosoma japonicum remains endemic. A total of 250,987 residents 6-65 years of age were included in the survey. Estimated prevalence rates in the provinces of Hunan, Hubei, Jiangxi, Anhui, Yunnan, Sichuan, and Jiangsu were 4.2%, 3.8%, 3.1%, 2.2%, 1.7%, 0.9%, and 0.3%, respectively. The highest prevalence rates were in the lake and marshland region (3.8%) and the lowest rates were in the plain region with waterway networks (0.06%). Extrapolation to all residents in schistosome-endemic areas indicated 726,112 infections. This indicates a reduction of 16.1% compared with a nationwide survey conducted in 1995. However, human infection rates increased by 3.9% in settings where transmission is ongoing.

Spatial epidemiology of human schistosomiasis in Africa: risk models, transmission dynamics and control

SummaryThis paper reviews recent studies on the spatial epidemiology of human schistosomiasis in Africa. The integrated use of geographical information systems, remote sensing and geostatistics has provided new insights into the ecology and epidemiology of schistosomiasis at a variety of spatial scales. Because large-scale patterns of transmission are influenced by climatic conditions, an increasing number of studies have used remotely sensed environmental data to predict spatial distributions, most recently using Bayesian methods of inference. Such data-driven approaches allow for a more rational implementation of intervention strategies across the continent. It is suggested that improved incorporation of transmission dynamics into spatial models and assessment of uncertainties inherent in data and modelling approaches represent important future research directions.

Epidemiology, burden and control of schistosomiasis with particular consideration to past and current treatment trends

Schistosomiasis, or bilharzia, is a chronic and debilitating disease caused by blood flukes of the genus Schistosoma. The most important species parasitizing humans are S. haematobium, S. japonicum and S. mansoni. While the former causes genitourinary tract lesions, the latter two affect the intestine and the liver. It is estimated that 779 million people are at risk of schistosomiasis, with 207 million people infected. Here, we summarize the epidemiology of schistosomiasis, including the life cycle, key epidemiological features and the disease burden. We discuss the shift in the global control strategy from transmission containment to morbidity control, which has been facilitated by the advent of safe and effective antischistosomal drugs, most notably praziquantel. We provide an overview of the history of schistosomiasis control, stratified by major subregions of the world where the disease is endemic, and update the current global picture of control. We review early treatment attempts and present the current arsenal of drugs, i.e., oxamniquιne, praziquantel and the artemisinins. We present recent data obtained in laboratory studies and clinical trials with triclabendazole and myrrh. Current treatment trends with praziquantel are summarized and a series of conclusions is forwarded.

The interaction of Schistosoma haematobium and S. guineensis in Cameroon

Interactions between schistosomes are complex with some different species being able to mate and hybridize. The epidemiology of schistosomiasis in specific areas of South West Cameroon has evolved remarkably over 30 years as a result of hybridization between Schistosoma guineensis and S. haematobium. Morphological and biological data suggest that S. haematobium replaced S. guineensis in areas of Cameroon through introgressive hybridization. Data are reported on the use of single stranded conformational polymorphism (SSCP) analysis of the nuclear ribosomal second internal transcribed spacer (ITS2) of individual schistosomes from hybrid zones of Cameroon. The data show that since 1990 S. haematobium has completely replaced S. guineensis in Loum, with S. haematobium and the recombinants still present in 2000. This study illustrates the complexities of the dynamics between S. haematobium and S. guineensis in South West Cameroon.

Phenotypic plasticity in the cercarial indices of human and rodent samples ofSchistosoma mansoni(Digenea: Schistosomatidae)

In the epidemiology of schistosomiasis, the cercarial index (CI) has been used for several purposes, including the identification of the species of vertebrate host involved in transmission in a particular setting. The CI of samples of Schistosoma mansoni of human (BH) and rodent (CMO) origin have now been compared, in an attempt to identify morphological markers on cercariae that would indicate whether the eggs from which the cercariae have developed were produced in humans or in rodents. After silver-nitrate impregnation of the cercariae, the CI (and their reaction norms) for the antero-dorsal (AD), antero-lateral (AL) and tail-stem (U) sensory receptors were investigated. The data analysis was based on linear-regression methods, Levene's test for the equality of variances, pooled-variance independent t-tests, and discriminant analysis. The results indicated that CI varied with vertebrate-host origin, that the AD reaction norms were more consistent and plastic than the other reaction norms investigated, that there appeared to be no simple allometric relationship between any of the CI investigated and cercarial body length, and that the BH sample gave larger standard deviations and a higher incidence of mis-classification than the CMO, indicating some developmental instability in the sample of human origin. The relative instability of the BH sample was, however, possibly the result of the experimental procedures. As the parasites used to produce the BH sample had been isolated from humans fairly recently and then routinely maintained in mice, host-induced selection could have affected the sample, altering its CI and their reaction norms. The results of the discriminant analysis indicated that, of the indices investigated, AD was the best morphological marker for distinguishing human and rodent samples of S. mansoni.

High Levels Of Selfing Are Revealed By A Parent-Offspring Analysis Of The Medically Important Freshwater Snail, Bulinus Forskalii (Gastropoda: Pulmonata)

The hermaphroditic freshwater snail Bulinus forskalii acts as intermediate host for the trematode Schistosoma guineensis, an agent of human intestinal schistosomiasis. Despite the medical importance of this snail, little is known about its mating system, even though this influences the epidemiology of schistosomiasis. Therefore, a parent-offspring analysis was carried out to elucidate its mating system. Eleven highly polymorphic microsatellites generated multilocus genotypes, enabling parentage assignment to all of the 432 offspring reared from 28 pairs of laboratory-bred B. forskalii. Ninety percent of progeny were of uniparental origin, and only six pairs (21% of parents) produced mixed clutches of crossed and selfed progeny. No pair reproduced exclusively by outcrossing. These results provide compelling evidence that B. forskalii has a mixed mating system dominated by uniparental reproduction, in agreement with indirect assessments from studies of population genetic structure and inbreeding effects. This reproductive strategy may be pivotal to the persistence of B. forskalii in its patchy, temporally unstable habitats, as well as helping it to cope with its parasitic burden.

Epidemiological and control aspects of schistosomiasis in Brazilian endemic areas.

The present work analyzes the epidemiology of schistosomiasis in Brazil, its expansion, the attempts to control the disease, and the overall difficulties. The authors present the distribution of schistosomiasis intermediary hosts in Brazil, the migration routes of the human population, and disease distribution in highly and lowly endemic areas and isolated foci. They also analyze the controlling programs developed from 1977 to 2002, indicating the prevalence evolution and the reduction of disease morbi-mortality. In addition, the authors also evaluate controlling methods and conclude that: (a) no isolated method is able to control schistosomiasis, and every controlling program should consider the need of a multidisciplinary application of existing methods; (b) in long term, basic sanitation, potable water supply, as well as sanitary education, and community effective participation are important for infection control; (c) in short term, specific treatment at endemic areas, associated with control of intermediary hosts at epidemiologically important foci, are extremely relevant for controlling disease morbidity, although not enough for interrupting infection transmission.

Applying GIS and Remote Sensing to the Epidemiology of Schistosomiasis in Poyang Lake, Jiangxi Province, China

Remote sensing, using Landsat TM imagery, has been used to classify snail habitat in the Poyang Lake marshlands, a vast area of high endemism for schistosomiasis in China (Jiangxi Province). Major findings of the study were: 1. RS images are useful for delineating snail habitat and differentiating snail habitat from total bovine grazing ranges. 2. RS enabled tracking yearly dynamic changes in lake area and snail habitat. 3. Dynamic environmental factors are responsible for the fact that some areas suitable for snails may not have snails one year, but have snails another year. 4. The critical factor for maintaining stable population structure is relative temporal stability in mean low water levels. 5. The TMRC snail survey method, employed twice a year, enables a robust statistical evaluation (especially analysis of variance) of changes in snail population density and patterns of infection over large areas. This snail collecting method involving repetitive random sampling and 4 m2 frames has resulted in reducing the adverse effects of the severe negative binomial distribution of the snails in the sampling data sets, thus enabling statistical analyses.