Schistosomiasis in the People's Republic of China: prospects and challenges for the 21st century

Cytokine mRNA profiles in pigs exposed prenatally and postnatally to Schistosoma japonicum

The pig is a natural host for Schistosoma japonicum and a useful animal model of human infection. The aim of the present study was to assess the differences between the cytokine profiles in prenatally or postnatally S. japonicum exposed pigs. Seven prenatally exposed pigs, 7 postnatally exposed pigs and 4 uninfected control pigs were compared 27 weeks post exposure. Variables included worm burdens, tissue egg counts, liver pathology and mRNA levels of IL-2, IL-4, IL-10, IL-12, TNF-alpha, TGF-beta1 and IFN-gamma in the liver and the caecum, assessed by RT-PCR. Infection intensity and level of septal fibrosis were significantly higher in the postnatal group compared to the prenatal group (P < 0.05). A significant increase of IL-4 (P < 0.01), IL-10 (P < 0.01), IL-12 (P < 0.01) and TNF-alpha (P < 0.05) mRNA level was also observed in the caecum of prenatally infected animals compared to the control group (P < 0.01). The prenatal group showed higher levels of TGF-beta1 in the liver compared with the postnatally infected group (P< 0.05) and the control group (P< 0.01). This suppressive immune response correlated with previously reported low hepatic pathogenesis in prenatally exposed pigs.

Artificial reproduction of the Yangtze field vole: in vitro embryo development and fertilization with fresh and freeze-thawed sperm

Several research groups are using the Yangtze field vole as a model for studying schistosome infection, but relatively little is known about the species's reproductive physiology. The authors examined the vole's in vivo and in vitro embryonic development as well as the efficacy of in vitro fertilization using either fresh or cryopreserved sperm to breed these rodents.

Effect of temperature on the development of Schistosoma japonicum within Oncomelania hupensis, and hibernation of O. hupensis

The objectives of this investigation were to assess the effect of temperature on the development of Schistosoma japonicum harboured in Oncomelania hupensis and to determine the lowest temperature threshold at which the hibernation of O. hupensis occurs. In the first experiment, adult infection-free O. hupensis, collected from Jiangsu province in eastern China, were infected with S. japonicum miracidia and raised at different temperatures under laboratory conditions. The development of miracidia until the release of cercariae was monitored employing the cercarial shedding method. In the second experiment, batches of O. hupensis were kept at temperatures below 13 degrees C with the temperature gradually reduced. Snail activity was assessed by a pin puncture method. We found a positive relationship between the development of S. japonicum within O. hupensis and temperature. In snails kept at 15.3 degrees C, S. japonicum arrested their development, while the fastest development occurred at 30 degrees C. The temperature at which half of the snails were in hibernation (ET(50)) was 6.4 degrees C. Our results underscore the pivotal role temperature plays on the biological activity of O. hupensis and the development of S. japonicum within the intermediate host. These findings are likely to have implications for the transmission of schistosomiasis in a warmer future China.

Sigmoid colonic carcinoma associated with deposited ova of Schistosoma japonicum: A case report

We report a case of sigmoid colonic carcinoma associated with deposited ova of Schistosoma japonicum. A 57-year old woman presented with a 10-mo history of left lower quadrant abdominal pain and a 2-mo history of bloody stools. She had a significant past medical history of asymptomatic schistosomiasis japonica and constipation. A colonoscopy showed an exophytic fragile neoplasm with an ulcerating surface in the sigmoid colon. During the radical operative procedure, we noted the partially encircling tumor was located in the distal sigmoid colon, and extended into the serosa. Succedent pathological analysis demonstrated the diagnosis of sigmoid colonic ulcerative tubular adenocarcinoma, and showed deposited ova of Schistosoma japonicum in both tumor lesions and mesenteric lymph nodes. Three days after surgery the patient returned to the normal bowel function with one defecation per day. These findings reveal that deposited schistosome ova play a possible role in the carcinogenesis of colorectal cancer.

Human schistosomiasis

Schistosomiasis or bilharzia is a tropical disease caused by worms of the genus Schistosoma. The transmission cycle requires contamination of surface water by excreta, specific freshwater snails as intermediate hosts, and human water contact. The main disease-causing species are S haematobium, S mansoni, and S japonicum. According to WHO, 200 million people are infected worldwide, leading to the loss of 1.53 million disability-adjusted life years, although these figures need revision. Schistosomiasis is characterised by focal epidemiology and overdispersed population distribution, with higher infection rates in children than in adults. Complex immune mechanisms lead to the slow acquisition of immune resistance, though innate factors also play a part. Acute schistosomiasis, a feverish syndrome, is mostly seen in travellers after primary infection. Chronic schistosomal disease affects mainly individuals with long-standing infections in poor rural areas. Immunopathological reactions against schistosome eggs trapped in the tissues lead to inflammatory and obstructive disease in the urinary system (S haematobium) or intestinal disease, hepatosplenic inflammation, and liver fibrosis (S mansoni, S japonicum). The diagnostic standard is microscopic demonstration of eggs in the excreta. Praziquantel is the drug treatment of choice. Vaccines are not yet available. Great advances have been made in the control of the disease through population-based chemotherapy but these required political commitment and strong health systems.

Does multiple hosts mean multiple parasites? Population genetic structure of Schistosoma japonicum between definitive host species

Multi-host parasites, those capable of infecting more than one species of host, are responsible for the majority of all zoonotic, emerging or persistent human and animal diseases and are considered one of the major challenges for the biomedical sciences in the 21st century. We characterized the population structure of the multi-host parasite Schistosoma japonicum in relation to its definitive host species by genotyping miracidia collected from humans and domestic animals across five villages around the Yangtze River in Anhui Province, mainland China, using microsatellite markers. High levels of polymorphisms were observed and two main genetic clusters were identified which separated water buffalo, cattle and humans from goats, pigs, dogs and cats. We thereby believe that we present the first evidence of definitive host-based genetic variation in Schistosoma japonicum which has important epidemiological, evolutionary, medical and veterinary implications.

Reconstruction and in silico analysis of the MAPK signaling pathways in the human blood fluke,Schistosoma japonicum

At present, little is known about signal transduction mechanisms in schistosomes, which cause the disease of schistosomiasis. The mitogen-activated protein kinase (MAPK) signaling pathways, which are evolutionarily conserved from yeast to Homo sapiens, play key roles in multiple cellular processes. Here, we reconstructed the hypothetical MAPK signaling pathways in Schistosoma japonicum and compared the schistosome pathways with those of model eukaryote species. We identified 60 homologous components in the S. japonciumMAPK signaling pathways. Among these, 27 were predicted to be full-length sequences. Phylogenetic analysis of these proteins confirmed the evolutionary conservation of the MAPK signaling pathways. Remarkably, we identified S. japonicum homologues of GTP-binding protein beta and alpha-I subunits in the yeast mating pathway, which might be involved in the regulation of different life stages and female sexual maturation processes as well in schistosomes. In addition, several pathway member genes, including ERK, JNK, Sja-DSP, MRAS and RAS, were determined through quantitative PCR analysis to be expressed in a stage-specific manner, with ERK, JNK and their inhibitor Sja-DSP markedly upregulated in adult female schistosomes.

Investigation of recombinant Schistosoma japonicum paramyosin fragments for immunogenicity and vaccine efficacy in mice

Schistosoma japonicum paramyosin, a 97 kDa myofibrillar protein, is a recognized vaccine candidate against schistosomiasis. To improve its expression and to identify protective epitopic regions on paramyosin, the published Chinese Schistosoma japonicum paramyosin cDNA sequence was redesigned using Pichia codon usage and divided into four overlapping fragments (fragments 1, 2, 3, 4) of 747, 651, 669 and 678 bp, respectively. These gene fragments were synthesized and expressed in Pichia pastoris (fragments 2 and 3) or E. coli (fragments 1 and 4). The recombinant proteins were produced at high level and purified using a two-step process involving Ni-NTA affinity chromatography and gel filtration. BALB/c mice were immunized subcutaneously three times at 2-week-intervals with the purified proteins formulated in adjuvant Quil A. The protein fragments were highly immunogenic, inducing high, though variable, ELISA antibody titres, and each was shown to resemble native paramyosin in terms of its recognition by the anti-fragment antibodies in Western blotting. The immunized mice were subjected to cercarial challenge 2 weeks after the final injection and promising protective efficacy in terms of significant reductions in worm burdens, worm-pair numbers and liver eggs in the vaccinated mice resulted. There was no apparent correlation between the antibody titres generated and protective efficacy, as all fragments produced effective but similar levels of protection.

Oligonucleotide microarray analysis of strain- and gender-associated gene expression in the human blood fluke, Schistosoma japonicum

Schistosomiasis is a chronic and debilitating disease caused by blood flukes (digenetic trematodes) of the genus Schistosoma. Schistosomiasis japonica, a zoonosis caused by Schistosoma japonicum, is endemic to the Philippines and China. We utilised a 22,575 feature custom oligonucleotide DNA microarray designed from public domain databases of schistosome-expressed sequence tags to explore differential gene expression between the Philippine (SJP) and Chinese (SJC) strains of S. japonicum, and between male and female S. japonicum. We found that 593, 664 and 426 probes were differentially expressed between the two geographical strains when we compared mix sexed adults, male worms and female worms. Additionally, the study revealed that 1163 male- and 1016 female-associated probes were differentially expressed in SJP whereas 1047 male- and 897 female-associated probes were differentially expressed in SJC. The study greatly expands previously published data of strain and gender-associated differential expression in S. japonicum. Further, these new data provide a stepping stone for understanding the complexities of the biology, sexual differentiation, maturation, and development of human schistosomes, signaling new approaches for identifying novel intervention and diagnostic targets against schistosomiasis.

Immunodiagnosis and its role in schistosomiasis control in China: a review

Parasitological techniques (stool examination and/or urine filtration) are still the diagnosis of choice in national schistosomiasis control programmes the world over. However, the success of current control efforts, mainly due to the large-scale administration of praziquantel, emphasises the need for a more sensitive approach. In addition, microscopy is labour-intensive and time-consuming, while declining compliance rates after repeated chemotherapy make good coverage for the long-term increasingly problematic. China's success in the control of schistosomiasis is contributing to an enhanced understanding of the need for better and more sensitive screening methods. Immunodiagnostic techniques have a high sensitivity, are easy to perform and are an excellent epidemiological tool for the screening of target populations in schistosome-endemic areas. These assays are also useful for the surveillance of cure after chemotherapy, and for periodic control of transmission of the infection after it has been eliminated in an area. A succinct historical background of using immunodiagnosis for schistosomiasis japonica in China is given, together with a review and evaluation of the relative efficacy of the main techniques applied, i.e. the intradermal test, the circumoval precipitation test, the indirect hemagglutination assay, the dye dipstick immunoassay and different kinds of enzyme-linked immunosorbent assay applications. The important role of immunodiagnosis in the screening for schistosomiasis in China is discussed.

An economic evaluation of the national schistosomiasis control programme in China from 1992 to 2000

The World Bank Loan Project, by far the largest effort in China for schistosomiasis control since control activities were initiated in the mid 1950s, was carried out for a 9-year period commencing in 1992 in the 8 provinces where Schistosoma japonicum remained endemic when the project started. To evaluate its impact, a retrospective economic evaluation was done in 2001. Six representative counties, i.e. Huarong in Hunan province, Qianjiang in Hubei province, Yugan in Jiangxi province, Tongling in Anhui province, Xichang in Sichuan province and Dali in Yunnan province, were selected for the study. The total financial input in these counties from 1992 to 2000 was RMB Yuan 90.334 million with the World Bank loan accounting for 40.9%. Control efforts resulted in reduction of human prevalence rates in the six counties from 0.7-9.0% in 1992 to 0.1-2.7% in 2000. With regard to S. japonicum infection in bovines, a high reduction was observed in Qianjiang, and smaller decreases were noted in four counties, while there was an increase in Dali. In general, the areas infested by the intermediate host snail fluctuated around the initial level. The net benefit-cost ratio was 6.20, which means that this project gained US$ 6.20 for every dollar spent. The correlation coefficients of the net benefit-cost ratio to the human and bovine infection rates at the beginning of the project were 0.55 and 0.66, respectively. It is conceivable that further progress in schistosomiasis control is an important feature for sustained growth of the local economy, particularly in areas where control of the disease has been most challenging.

Transmission of Schistosoma japonicum by humans and domestic animals in the Yangtze River valley, Anhui province, China

The aim of the present work was to assess the relative contribution to transmission of Schistosoma japonicum by humans and domestic animals in two villages in the Yangtze River valley in Anhui province, China. A cross-sectional survey was conducted to determine the prevalence and intensity of S. japonicum in humans, cattle, water buffaloes, horses, pigs, goats, dogs and cats. Additionally, for each host species the number of individuals and the mean faecal excretion per day was determined. Results showed that both prevalence and intensity of infection varied significantly between species and between the two villages and neither of the variables gave an adequate picture of the potential transmission. Total daily egg excretion was significantly higher in Chenqiao village compared with Guanghui village. Whereas humans were the main contributors to transmission of schistosomiasis in Guanghui village (80.4%), water buffaloes accounted for nearly 90% and goats for more than 5% of the transmission in Chenqiao village. Hence, the present study suggests that schistosomiasis transmission might vary significantly within Chinese farm districts and successful control should rely on prior transmission index determinations on major potential contributors rather than routine data of prevalence and intensity of infection. Further studies should determine the value of adding other transmission variables like egg hatchability and faecal deposition habits.

A geographic information and remote sensing based model for prediction of Oncomelania hupensis habitats in the Poyang Lake area, China

A model was developed using remote sensing and geographic information system technologies for habitat identification of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum, in the Poyang Lake area, China. In a first step, two multi-temporal Landsat TM 5 satellite images, one from the wet and the second from the dry season, were visually classified into different land-use types. Next, the normalized difference vegetation index was extracted from the images and the tasseled-cap transformation was employed to derive the wetness feature. Our model predicted an estimated 709 km2 of the marshlands in Poyang Lake as potential habitats for O. hupensis. Near-ground temperature measurements in April and August yielded a range of 22.8-24.2 degrees C, and pH values of 6.0-8.5 were derived from existing records. Both climatic features represent suitable breeding conditions for the snails. Preliminary validation of the model at 10 sites around Poyang Lake revealed an excellent accuracy for predicting the presence of O. hupensis. We used the predicted snail habitats as centroids and established buffer zones around them. Villages with an overall prevalence of S. japonicum below 3% were located more than 1200m away from the centroids. Furthermore, a gradient of high-to-low prevalence was observed with increasing distance from the centroids. In conclusion, the model holds promise for identifying high risk areas of schistosomiasis japonica and may become an important tool for the ongoing national schistosomiasis control programme. The model is of particular relevance for schistosome-affected regions that lack accurate surveillance capabilities and are large enough to be detected at most commercially available remote sensing scales.

Surveillance and control of post-transmission schistosomiasis in Jiaxing prefecture, Zhejiang province, China

A surveillance system has been put in place in the Zhejiang province since achieving there the criteria for transmission interruption of schistosomiasis japonica. Suspected patients and special high-risk groups (e.g. the so called 'floating population' and children under 14 years of age) are screened for Schistosoma japonicum using serological tests. Those with positive serological result are subjected to faecal examination and if S. japonicum eggs are found they are treated with praziquantel and followed by regular re-examination until complete cure, i.e. absence of S. japonicum eggs in faecal samples. Patients with advanced schistosomiasis japonica are continuously followed-up. Implementation of the surveillance system from 1995 to 2002 detected two S. japonicum-infected persons; one came from Anhui province and the other from Jiangsu province, but no new infection occurred among local residents. The number of patients with advanced schistosomiasis japonica decreased from 1524 in 1995 to 906 by the end of 2002; a reduction of 40.6%. However, post-transmission schistosomiasis still continues to weigh on the medial resources. We conclude that the surveillance system in Zhejiang province is effective and a useful means for monitoring the endemic situation of schistosomiasis. Hence, it is recommended to be pursued in the years to come.

Evaluation on the applied value of the dot immunogold filtration assay (DIGFA) for rapid detection of anti-Schistosoma japonicum antibody

The dot immunogold filtration assay (DIGFA) is a rapid technique for the detection of anti-Schistosoma japonicum antibody. Its sensitivity with regard to sera obtained from patients with acute or chronic schistosomiasis was shown to be 100 and 96.9%, respectively. The specificity when using sera of people living in an area non-endemic for schistosomiasis japonica was 100%. Cross-reaction rates for paragonimiasis and clonorchiasis patients were 14.3% and 0%, respectively. Parallel serum tests of 1091 residents from an area endemic for S. japonicum by means of DIGFA, enzyme-linked immunosorbent assay and indirect haemagglutination test resulted in positive rates of 9.3%, 11.5% and 11.0%, respectively. Thus, there was a high level of agreement between the sets of results (P>0.05). In conclusion, DIGFA holds considerable promise for rapid and accurate diagnosis of S. japonicum, as it does not require any specific instruments and can be applied with ease. DIGFA has therefore several advantages over conventional diagnostic approaches and is useful not only for screening and sero-epidemiological surveys in the field, but also in clinical settings.

Surveillance for schistosomiasis japonica in China from 2000 to 2003

According to the protocol of the national surveillance project, longitudinal observation of the endemic situation of schistosomiasis japonica in China has been carried out at 20 sentinel surveillance sites, commencing in 2000. After four years of surveillance, the infection rate of Schistosoma japonicum gradually decreased in seven sentinel sites. In 10 sites, infection rates remained relatively stable over time, while there was a marked increase in one site. No clear trend became apparent in the remaining two sites. Significant reductions of densities of living intermediate host snails and infected snails were noted in only two sites. In turn, the endemic situation was not well controlled in most of the other sentinel sites. The infection cattle rate fluctuated yearly in the majority of the sites and maintained a high level. During the four years of surveillance, acute cases of schistosomiasis japonica among humans were found in each of the yearly cross-sectional surveys, and the number of patients with advanced schistosomiasis did not change significantly. The surveillance results obtained thus far indicate that current control strategies continue to reduce morbidity due to schistosomiasis. However, concerted control efforts must continue for a long time and the surveillance of intermediate host snail and animal reservoirs (e.g. cattle) should be strengthened.

The public health significance and control of schistosomiasis in China--then and now

The description of schistosomiasis in China dates back more than two millennia. The disease caused social and economic hardship, and the rates of morbidity and mortality were high. In the mid 1950s, when China's population was approximately 600 million, an estimated 11.6 million people were infected with Schistosoma japonicum. Hence, a national control programme was launched, with an emphasis on intermediate host snail control by means of environmental management. Over the past 50 years, the national control programme has made great progress and praziquantel-based morbidity control became the mainstay of control. In 2000, the number of infected people had been reduced to an estimated 694,788, the snail-infested area has been abridged by over 75%, and the disease had been eliminated in five of the 12 previously endemic provinces. Between the mid 1980s and 2003, the criteria of transmission interruption have been reached in 260 counties (60.0%), transmission control has been achieved in 63 counties (14.5%), but the disease was still endemic in the remaining 110 counties (25.4%). Comparison between the number of cases in 2000 and 2003 suggests that schistosomiasis has re-emerged; an estimated 843,011 people were infected with S. japonicum in 2003. Here, we provide a short historical account of the pubic health significance of schistosomiasis in China, highlight the progress made to date with the national control programme, and place particular emphasis on the most recent trends. Finally, we discuss remaining challenges for schistosomiasis control with the ultimate goal of disease elimination.

Transmission control of schistosomiasis japonica: implementation and evaluation of different snail control interventions

The great progress made in the control of schistosomiasis japonica in China is to some extent explained by successful intermediate host snail control, in particular with environmental management commencing some 50 years ago. By 1995, interruption of Schistosoma japonicum transmission had been achieved in five of the 12 schistosome-endemic provinces while endemic areas in the remaining provinces had been reduced significantly, and snail habitats had decreased by 74%. In this paper, we review the role and approaches towards control and give an account of compounds toxic to snails. Mid- and long-term national plans for schistosomiasis control are discussed, including integrated snail control approaches as an important measure. It is anticipated that implementation of these plans will accelerate snail control, which in turn will consolidate and mutually reinforce other control measures, most notably praziquantel-based chemotherapy. The ultimate aim is to eliminate schistosomiasis as a public health problem in China.

A review of geographic information system and remote sensing with applications to the epidemiology and control of schistosomiasis in China

Geographic information system (GIS) and remote sensing (RS) technologies offer new opportunities for rapid assessment of endemic areas, provision of reliable estimates of populations at risk, prediction of disease distributions in areas that lack baseline data and are difficult to access, and guidance of intervention strategies, so that scarce resources can be allocated in a cost-effective manner. Here, we focus on the epidemiology and control of schistosomiasis in China and review GIS and RS applications to date. These include mapping prevalence and intensity data of Schistosoma japonicum at a large scale, and identifying and predicting suitable habitats for Oncomelania hupensis, the intermediate host snail of S. japonicum, at a small scale. Other prominent applications have been the prediction of infection risk due to ecological transformations, particularly those induced by floods and water resource developments, and the potential impact of climate change. We also discuss the limitations of the previous work, and outline potential new applications of GIS and RS techniques, namely quantitative GIS, WebGIS, and utilization of emerging satellite information, as they hold promise to further enhance infection risk mapping and disease prediction. Finally, we stress current research needs to overcome some of the remaining challenges of GIS and RS applications for schistosomiasis, so that further and sustained progress can be made to control this disease in China and elsewhere.

Optimal combined approaches of field intervention for schistosomiasis control in China

Before the mid 1980s, the emphasis in schistosomiasis control in China was on transmission control. Thus, the aim was to eliminate the intermediate host snail by environmental management, combined with chemotherapy, water supply and sanitation, and hygiene improvement. During the last 20 years, however, control approaches mainly consisting of large-scale praziquantel-based chemotherapy and health education started to be advocated and also increasingly applied. Here, we review the literature with an emphasis on combined approaches of field interventions that have been implemented for schistosomiasis control in China over the past 50 years. The interventions consist of both pilot studies and large-scale implementation during different historical periods. The feasibility and effectiveness of the various combined approaches are examined and analysed in relation to local economic conditions and the prevailing scientific and technical expertise. Finally, a set of recommendations is put forward for contemporary schistosomiasis control readily adapted to different eco-epidemiological settings in China.

Applications and outcomes of periodic epidemiological surveys for schistosomiasis and related economic evaluation in the People's Republic of China

The great success in schistosomiasis control in China is attributable to a range of factors. Periodic epidemiological surveys (PES) used for monitoring and adapting control interventions over time are an integral feature of the national schistosomiasis control programme. PES have enabled the dynamic trends of schistosomiasis epidemics to be closely pursued and have assisted in analysing subtle changes in endemicity. The results can be summarised mathematically allowing the variation in efficacy of control measures to be readily determined and enabling control strategies to be adjusted and updated. PES have been used in both cross-sectional and longitudinal pilot studies selected by appropriate sampling methods. In the early 1990s, when the World Bank Loan Project for schistosomiasis control commenced, economic evaluations were initiated in parallel. Cost-effectiveness analysis became a necessary tool to identify the most financially feasible yet effective options among a range of alternative control strategies. There was, however, a lack of standardised approaches rendering study comparisons across sites difficult. The global burden of disease study established the disability adjusted life year (DALY) as a measure of population health, combining in a single indicator years lost from premature death and years of life lived with disability. However, a recent meta-analysis reveals that the burden of schistosomiasis is underestimated, and hence, needs to be revised. It is envisaged that after the revision of DALYs lost due to schistosomiasis japonica, they will become an essential measure in future schistosomiasis control assessments in China and in other schistosome-endemic areas of the world.

Prospects for development of a transmission blocking vaccine against Schistosoma japonicum

Despite intensive long-term control programmes, schistosomiasis japonica remains a serious public health problem in China and the Philippines. The termination of mass praziquantel-treatment has seen a dramatic recent rebound in both its prevalence and associated morbidity. Schistosomiasis japonica is a zoonosis but, despite complicating control efforts, this feature provides a practical method for attacking Schistosoma japonicum through development and deployment of a transmission blocking veterinary vaccine. A recently completed bovine drug intervention trial and mathematical modelling of the transmission of S. japonicum underpin the concept that such a vaccine, targeting water buffalo, would have major implications for future integrated schistosomiasis control in China. A major block to success is the low ceiling efficacy achieved with current vaccine molecules. To solve this challenge, an antigen discovery pipeline needs to be established for identification of new vaccine targets that induce greater potency than the current anti-S. japonicum candidate vaccines. Excretory-secretory products and molecules exposed on epithelial surfaces (including receptors) which interact directly with the host immune system warrant especial attention. Extensive schistosome genomics programmes currently underway coupled with new advances in proteomics and microarray technology provide an unparalleled opportunity to identify new molecules exploitable as vaccine targets. These will then need to be produced in quantity and rigorously tested first in the laboratory and then the field. If a transmission blocking veterinary vaccine developed for bovines can be put into practice in combination with other control strategies such as human chemotherapy, elimination of S. japonicum from China may be achievable.

Synthesis and bioactivities of two multiple antigen peptides as potential vaccine against schistosoma

Based on the two antigenic peptides, 26-43 (P26) and 116-131 (P116), derived from 28 kDa glutathione S-transferase of Schistosoma mansoni (Sm28GST), two multiple antigenic peptides (MAPs), (P26)4-MAP and (P116)4-MAP with the same oligomeric lysine core, were synthesized by stepwise solid-phase peptide synthesis method. The antigenicities and protective effects of these two MAPs were examined on experimental animals. As shown in the dot-ELISA result, the synthetic MAPs could be recognized and bound by immunoglobins in both patient's and infected-rabbit's sera. After Kunming mice were immunized with (P26)4-MAP, the worm burden reduction rate and the liver egg reduction rate were 59.9% and 61.1%. In (P26)4-MAP or (P116)4-MAP immunized BALB/c mice, the worm burden reduction rates were 37.5% and 62.5%, respectively, and the liver egg reduction rates were 35.1% and 54.0%, respectively.

Update on paramyosin in parasitic worms

Paramyosin was first identified as a structural component of invertebrate muscle. Analysis of crude, native, adult schistosome worm preparations identified a highly immunogenic protein which was later identified as paramyosin. Early vaccination/challenge studies with native paramyosin produced encouraging levels of protective efficacy against schistosomes, which led to the question as to how a sub-tegumental (muscular) protein could provide a target for vaccine-mediated immunological attack. Immunolocalisation studies of schistosomes confirmed the presence of paramyosin within the post-acetabular glands of cercariae and on the tegumental surface of lung schistosomula. Here we present an update on the more recent research on paramyosin in parasitic worms that has focused primarily in two directions: (i) further testing of the vaccine potency of paramyosin against schistosomes and other parasitic worms; and (ii) characterisation of the protein at the molecular and biochemical levels.

A Bayesian-based approach for spatio-temporal modeling of county level prevalence of Schistosoma japonicum infection in Jiangsu province, China

Spatio-temporal variations of Schistosoma japonicum infection risk in Jiangsu province, China, were examined and the relationships between key climatic factors and infection prevalence at the county level were determined. The parasitological data were collected annually by means of cross-sectional surveys carried out in 47 counties from 1990 to 1998. Climatic factors, namely land surface temperature (LST) and normalized difference vegetation index (NDVI), were obtained from remote sensing satellite sensors. Bayesian spatio-temporal models were employed to analyze the data. The best fitting model showed that spatial autocorrelation in Jiangsu province decreased dramatically from 1990 to 1992 and increased gradually thereafter. A likely explanation of this finding arises from the large-scale administration of praziquantel for morbidity control of schistosomiasis. Our analysis suggested a negative association between NDVI and risk of S. japonicum infection. On the other hand, an increase in LST contributed to a significant increase in S. japonicum infection prevalence. We conclude that combining geographic information system, remote sensing and Bayesian-based statistical approaches facilitate integrated risk modeling of S. japonicum, which in turn is of relevance for allocation of scarce resources for control of schistosomiasis japonica in Jiangsu province and elsewhere in China, where the disease remains of public health and economic significance.

The effect of colostrum on pigs pre-natally or post-natally exposed toSchistosoma japonicum

Pre-natal infection ofSchistosoma japonicumin pigs may prove to be a useful model in shedding light on human pre-natal schistosomiasis. This study describes the effects of immune colostrum on worm burdens, tissue egg counts, liver pathology and crude worm or egg antigen-specific IgG and IgA responses, in groups of pigs pre-natally, pre-natally+post-natally or post-natally exposed toS. japonicum. Results suggest that pre-natal exposure and immune colostrum did not affect the establishment of a post-natal challenge infection. However, immune colostrum seemed to increase the levels of septal fibrosis in pre-natally exposed pigs. These findings indicate that further investigations will prove valuable, elucidating the influence of the parasitological and immunological status of the sow, on pre-natally exposed pigs, and on the ability of these pigs to develop resistance againstS. japonicumlater in life.

Persistence of the protective immunity to Schistosoma japonicum in Chinese yellow cattle induced by recombinant 26kDa glutathione-S-transferase (reSjc26GST)

To observe the long lasting effect of the recombinant Sj26GST sub-unit vaccine against Schistosoma japonicum in cattle, animals aged from 5 to 12 months were vaccinated with reSjc26GST, and were challenged by natural infection 6 months or 12 months after vaccination. Worm burdens per cattle and egg burden in tissue (per gram) of cattle with or without vaccination were compared. The results showed that anti-reSjc26GST antibodies were produced in vaccinated cattle. Following natural infection, the vaccinated and the control non-vaccinated cattle were all found to be infected with S. japonicum. A 30% reduction in worm number was observed in the vaccinated cattle when compared with the control cattle. The anti-fecundity effect was characterized by an average of 60% decrease in eggs deposited in the liver of vaccinated cattle; such a decrease is obviously very significant. In addition to the anti-fecundity effect induced in the vaccinated cattle, the number of miracidum hatched per 50 g faeces and the number of eggs released in intestinal tissues per gram were reduced or decreased. Results suggested that the immune responses induced by reSjc26GST in cattle were similar to that in buffaloes and in pigs. In addition, our result demonstrated that the lasting effect of immunity to S. japonicum induced in cattle after vaccination with reSjc 26 GST could persist at least 12 months.

Research on calpain of Schistosoma japonicum as a vaccine candidate

Vaccine development by the use of calpain of Schistosoma japonicum has been tried in our laboratory. We cloned cDNA encoding the heavy chain of S. japonicum calpain, and prepared recombinant molecule of a possible vaccine region of the heavy chain. When BALB/c mice were immunized with our recombinant calpain of S. japonicum with Freund's complete adjuvant, we observed significant reduction in worm burden (41.2% reduction, P<0.05), and also significant anti-fecundity effects. In this sense, calpain of S. japonicum seems to have infection control as well as anti-disease effects. Mechanisms of vaccine effects of calpain remain to be clarified, however, several effector mechanisms are suspected. In immunized mice, raised level of iNos expression was observed, while adhesion of peritoneal exudates cells were also observed in the presence of calpain-immunized sera, suggesting the possibilities of both cellular and humoral protective mechanisms. We examined tissue distribution of calpain in various developmental stages of S. japonicum. Strong signal was observed around excretory grand of cercariae, and they secreted calpain during their migratory movement tested in vitro. Together with the findings, calpain seems to induce larvicidal effects in the immunized mice. We observed time-course kinetics of antibody production against vaccine candidates in experimental S. japonicum infection in pigs. Although significant levels of antibody production were observed for paramyosin and GST, no significant antibody production was observed for calpain. This suggests that calpain is less immunogenic, and route of immunization and/or choice of adjuvant are important in future trials of calpain vaccine.

A vaccine against Asian schistosomiasis

There is continued transmission of schistosomiasis japonica in China and Philippines despite highly effective control programs that focus on the application of the highly effective drug praziquantel (PZQ). The massive Three Gorges Dam across the Yangtze River in Southern China, soon to be completed, is expected to significantly increase schistosomiasis transmission and introduce the disease into areas currently unaffected. After long-term experience it is generally accepted that PZQ chemotherapy, although the cornerstone of current control programs, does have significant limitations. Furthermore, efficient drug delivery requires a substantial infrastructure to regularly cover all parts of an endemic area. Although there is not yet clear-cut evidence for the existence of PZQ-resistant schistosome strains, decreased susceptibility to the drug has been observed in several countries. As a result, a protective vaccine represents an essential component for the long-term control of schistosomiasis. This article briefly reviews aspects of anti-schistosome protective immunity that are important in the context of vaccine development. The current status in the development of vaccines against Schistosoma japonicum will then be discussed as will new approaches that may improve on the efficacy of available vaccines, and aid in the identification of new targets for immune attack. With new and extensive data becoming available from the S. japonicum genome project, the prospects for developing an effective vaccine are encouraging. The challenges that remain are many but it is crucial that the momentum towards developing effective anti-schistosome vaccines is maintained.

Immunoregulation and World Health Assembly resolution 54.19: why does treatment control morbidity?

World Health Assembly resolution 54.19, passed in May, 2001, declares the intent of the World Health Organization member States to implement a combined strategy for the control of morbidity caused by schistosomiasis and soil-transmitted helminths. Among other things, the resolution urges ministries to treat all clinical cases and groups at high risk of morbidity such as children, women and those exposed occupationally. The policy is predicated on the evidence that morbidity due to these infections can be controlled by periodic treatment with appropriate chemotherapeutic, anti-helminthic drugs. While it is true that annual or biannual praziquantel treatment for schistosomiasis decreases morbidity, we now question how treatment leads to this beneficial effect. It is clear that treatment kills worms, but we propose that this is only a part of how it leads to reduced morbidity in areas of ongoing transmission and reinfection. By killing worms, we postulate that treatment also effects immunologic changes to the normal host/parasite relationship, and the resulting immune responses lead to both increased resistance (protection against reinfection), and increased immunoregulatory mechanisms that control morbidity upon subsequent reinfections. If the effects of treatment contribute to morbidity control in these ways, a better understanding of how this occurs may allow optimization of these effects of treatment through appropriate periodic treatment regimens, resulting in less reinfection and better morbidity control when reinfection does occur.

Schistosome transcriptomes: new insights into the parasite and schistosomiasis

Schistosomiasis is one of the most serious parasitic diseases. More than 250 million people are infected with schistosomes in the tropics or subtropics. The parasitic flukes have some unique biological features: dioecism, complex life cycles, mechanisms to avoid host immune responses, and an apparent reliance on host endocrine and immune signals to complete their development, maturation and egg production. Recently, a large dataset of expressed sequence tags (ESTs) were generated from Schistosoma japonicum and Schistosoma mansoni, from which numerous novel genes were identified. The transcriptome analyses provide the basis for a comprehensive understanding of the molecular mechanisms involved in schistosome nutrition and metabolism, host-dependent development and maturation, immune evasion and invertebrate evolution. In addition, new potential vaccine candidates and drug targets have been predicted.

Changing health in China: re-evaluating the epidemiological transition model

This paper reviews the changing health situation in China, which has shown remarkable improvement in the 50 years since the founding of the People's Republic of China (PRC) in 1949. At first sight this improving health situation follows the classical epidemiological transition model. Just three decades ago health in China was characterised by high rates of infectious disease and early mortality (diseases of poverty) in a mainly peasant society. More recently infectious disease rates have decreased, with corresponding and extended morbidity and mortality associated with an aging population in a rapidly urbanising society. This process has given rise to new health problems, including chronic and degenerative diseases (diseases of affluence). Nonetheless, while there is some validity in the application of the epidemiological transition concept, further analysis demonstrates that China faces a new epidemiological phase, characterised by increasing life expectancy and diseases of affluence coupled with the emergence and re-emergence of infectious diseases. We demonstrate that China's state policy plays a major role in defining the parameters of health in a Chinese context. We conclude that, today, China is faced with a new set of health issues, including the impact of smoking, hypertension, the health effects of environmental pollution and the rise of HIV/AIDS; however, state policy remains vital to the health of China's vast population. The challenge for policy is to maintain health reform whilst tackling the problems associated with rapid urbanisation, widening social and spatial inequalities and the emergence of HIV/AIDS and other infectious diseases.

Epidemiological and morbidity assessment of Schistosoma japonicum infection in a migrant fisherman community, the Dongting Lake region, China

We assessed the epidemiology and morbidity related to Schistosoma japonicum infection by both parasitological (Kato-Katz method and miracidium hatching test) and ultrasound examination in a migrant fisherman community (n = 106) from the Dongting Lake region in China in 2001. A prevalence of 69.8% and a mean infection intensity of 66.5 eggs per gram (epg) were recorded for this group. Males had a higher level of infection (77%) and intensity (92.2 epg) compared with females (58% and 28.6 epg, respectively). Subjects aged 11-20 years had the highest prevalence of infection (91%) and the heaviest infection intensity (85.3 epg) among all age groups. Twenty-six percent of the subjects had not been treated previously for schistosomiasis. Parenchymal fibrosis (> or = stage II) detected by ultrasound and spleen enlargement (or splenectomy) occurred in 37% and 9% of subjects, respectively. Portal vein dilation was detected in 18% subjects, and 58% (11/19) of those patients with portal vein enlargement were shown to have parenchymal fibrosis (> or = stage II). These results indicate that S. japonicum infection and related morbidity in mobile fisherman is still unacceptably high despite the fact that China has implemented a Schistosomiasis Control Project financed by a World Bank Loan for a period of 8 years since 1992. Clearly, new approaches for schistosomiasis control, especially in communities like these mobile fishermen, should be explored.

Evolutionary and biomedical implications of a Schistosoma japonicum complementary DNA resource

Schistosoma japonicum causes schistosomiasis in humans and livestock in the Asia-Pacific region. Knowledge of the genome of this parasite should improve understanding of schistosome-host interactions, biomedical aspects of schistosomiasis and invertebrate evolution. We assigned 43,707 expressed sequence tags (ESTs) derived from adult S. japonicum and their eggs to 13,131 gene clusters. Of these, 35% shared no similarity with known genes and 75% had not been reported previously in schistosomes. Notably, S. japonicum encoded mammalian-like receptors for insulin, progesterone, cytokines and neuropeptides, suggesting that host hormones, or endogenous parasite homologs, could orchestrate schistosome development and maturation and that schistosomes modulate anti-parasite immune responses through inhibitors, molecular mimicry and other evasion strategies.

Development of a rapid, sensitive, dye immunoassay for schistosomiasis diagnosis: a colloidal dye immunofiltration assay

The colloidal dye immunofiltration assay (CDIFA) combines the concepts of the double-antigen sandwich assay, the Dot immunofiltration assay, and colloidal dye-linked antigen technique to produce a new dye immunoassay for antibody detection in schistosomiasis. The CDIFA consisted of soluble egg antigen (SEA) of Schistosoma japonicum coated onto nitrocellulose membrane, mounted on a flow-through test device to provide the assay capture matrix. SEA absorbed to a red colloidal dye, R-3, produced in China, served as the antigen-antibody complex detecting reagents. The results showed that the sensitivity of the CDIFA was 100% in 35 cases of acute schistosomiasis (35/35), 98% in 50 cases of chronic schistosomiasis (49/50). The specificity of the assay was 99.4% in 180 healthy individuals (179/180). The cross-reaction was 13.3% in 30 cases of paragonimiasis, 2.6% in 38 cases of clonorchiasis sinensis and 0% in 20 cases of hookworm infection, 20 cases of fasciolopsiasis and 16 cases of ascariasis. The results were similar to those detected by routine enzyme-linked immunosorbent assay (ELISA). In a field evaluation of the CDIFA kit, the positivity rate of the CDIFA was 97.5% in 157 cases of schistosomiasis, compared with 91.1% with the circumoval precipitin test (COPT). The dye-labeled SEA conjugate was stable at room temperature for at least 6 months. The results indicated that the CDIFA provided an economic, simple, rapid, robust test for the detection of schistosome infection, suitable for a wide variety of field applications without any instrumentation.

Five-year impact of repeated praziquantel treatment on subclinical morbidity due to Schistosoma japonicum in China

We report the 5-year impact (1996-2001) of repeated praziquantel chemotherapy on subclinical morbidity related to Schistosoma japonicum infection. We repeated stool examinations and hepatosplenic ultrasonography in a cohort of 120 individuals living on an island with endemic infection in Dongting Lake, China. Prevalence of schistosome infection fell by 43% and intensity (geometric mean eggs per gram) declined by 80% over the 5 years. However, transmission persisted at a dangerously high rate of 13% per year for re-infection or new infection in the cohort. The prevalence of left-lobe enlargement and dilated portal vein fell significantly (P < 0.01) to about half initial levels although a few patients progressed during the study period. At study endpoint, infection was nearly twice as common if the portal vein was dilated (23% versus 13%, respectively), but this association was not statistically significant (P > 0.05). However, endpoint infection was even more strongly associated with left-lobe enlargement (57% versus 15%, P < 0.01). The proportions of subjects with improved parenchymal and periportal fibrosis were much higher than the proportions of subjects that progressed (P < 0.05). Reduction of prevalence and intensity of infection, and improvement of subclinical morbidity, were benefits of repeated treatments. Further research is needed to understand why some patients developed fibrosis despite substantial reductions in egg counts and to evaluate the functional importance of residual subclinical morbidity after chemotherapy-based control in the lake and marshland area of China.

Mathematical modelling of schistosomiasis japonica: comparison of control strategies in the People's Republic of China

We present the first mathematical model on the transmission dynamics of Schistosoma japonicum. The work extends Barbour's classic model of schistosome transmission. It allows for the mammalian host heterogeneity characteristic of the S. japonicum life cycle, and solves the problem of under-specification of Barbour's model by the use of Chinese data we are collecting on human-bovine transmission in the Poyang Lake area of Jiangxi Province in China. The model predicts that in the lake/marshland areas of the Yangtze River basin: (1) once-yearly mass chemotherapy of humans is little better than twice-yearly mass chemotherapy in reducing human prevalence. Depending on the heterogeneity of prevalence within the population, targeted treatment of high prevalence groups, with lower overall coverage, can be more effective than mass treatment with higher overall coverage. Treatment confers a short term benefit only, with prevalence rising to endemic levels once chemotherapy programs are stopped; (2) depending on the relative contributions of bovines and humans, bovine treatment can benefit humans almost as much as human treatment. Like human treatment, bovine treatment confers a short-term benefit. A combination of human and bovine treatment will dramatically reduce human prevalence and maintains the reduction for a longer period of time than treatment of a single host, although human prevalence rises once treatment ceases; (3) assuming 75% coverage of bovines, a bovine vaccine which acts on worm fecundity must have about 75% efficacy to reduce the reproduction rate below one and ensure mid-term reduction and long-term elimination of the parasite. Such a vaccination program should be accompanied by an initial period of human treatment to instigate a short-term reduction in prevalence, following which the reduction is enhanced by vaccine effects; (4) if the bovine vaccine is only 45% efficacious (the level of current prototype vaccines) it will lower the endemic prevalence, but will not result in elimination. If it is accompanied by an initial period of human treatment and by a 45% improvement in human sanitation or a 30% reduction in contaminated water contact by humans, elimination is then possible.

Antibody isotype responses to Schistosoma japonicum antigens in subjects from a schistosomiasis area with repeated praziquantel chemotherapy compared with a new endemic zone in Hunan Province, P.R. China

To demonstrate the dynamics of specific antibody isotypes against schistosome adult worm (AWA) and soluble egg (SEA) antigens, we evaluated (in 1999-2000) 112 subjects infected with Schistosoma japonicum from 2 regions of Hunan Province, China. Fifty-eight subjects were from Area A, a well-known endemic area with repeated chemotherapy. Area B (n = 54) is a new endemic focus in another part of the same province. Serum samples were collected prior to praziquantel (PZQ) chemotherapy, and at 2 and 12 months post-treatment. IgM, IgA, IgG, IgG2, IgG4 and IgE antibodies to AWA and SEA were measured by quantitative enzyme-linked immunosorbent assay (ELISA). Pre-treatment antibody isotype levels from Area A, except IgA against AWA and SEA, were significantly higher than those from Area B. In response to chemotherapy, most antibody isotype levels fell or remained stable. However, in Area A there was a significant increase in the IgA, IgE and IgG4 responses to AWA 2 months after PZQ--which fell to approach pre-treatment levels by 12 months. A similar response was seen in Area B with IgE and IgG4 to AWA. Levels of all AWA-specific IgE and IgG4 were significantly higher in subjects from Area A compared with Area B at all time-points. AWA-IgE levels demonstrated significant linear correlations with age and number of previous PZQ treatments in Area A only. All SEA-specific isotypes in both areas fell significantly in response to treatment--except IgE, which remained stable in both area. All SEA-specific isotype levels (except IgA) were significantly higher from Area A at baseline. This significant difference was maintained through 12-months follow-up for IgE, IgG2 and IgG4 only. This study suggests that multiple episodes of schistosome infection may be required to generate antibody isotype levels that have been associated with resistance to re-infection in other studies. Further, a surrogate marker of successful chemotherapy (AWA-IgG4) performed less effectively in patients with previous treatment courses.

Vertical transmission of Schistosoma japonicum in the rabbit

The aim of the present study was to confirm observations on the vertical transmission of Schistosoma japonicum in the rabbit. S. japonicum-infected pregnant rabbits were used in this study. Perfusion of mother rabbits was done 9 weeks after infection in order to obtain worm burdens in relation to their initial cercarial dose. Anti-schistosoma specific IgM antibodies in serum samples collected from rabbit kittens were detected by ELISA. Our results showed that gestation period lasted the normal 29-31 days. All the exposed mother rabbits became infected with S. japonicum. Positive IgM antibody OD values were detected in 12 out of the 60 kittens examined (20.0%). In group C and A, 40.0% and 17.9% of the kitten were congenitally infected, respectively. 18.1% of the kittens born to mothers infected with a single dose of 200 cercariae per rabbit were positives; this is not significantly different from that obtained for the 600 dose group (22.2%). Three randomly selected IgM+ kittens harbored between one and two adult worms. The livers of these kittens displayed granulomatous lesions. It is concluded that congenital S. japonicum infection does occur in the rabbit and is affected by the mother stage of pregnancy and to a lesser extent by its infection load.

Recombinant paramyosin (rec-Sj-97) tested for immunogenicity and vaccine efficacy against Schistosoma japonicum in mice and water buffaloes

A primary vaccine candidate antigen against schistosomiasis is paramyosin (pmy), a myofibrillar protein found exclusively in invertebrates. Here we report the results of vaccine trials against the Asian schistosome undertaken on inbred and outbred mice and water buffaloes using a bacterially expressed and purified form of Schistosoma japonicum pmy (rec-Sj-97). Vaccination of the mice resulted in high levels of specific anti-pmy IgG antibodies when compared with adjuvant controls and significant reduction in worm burdens and in liver eggs. Furthermore, a significant reduction in liver eggs was recorded in two of the three water buffalo vaccine trials undertaken and, in all three trials, high levels of specific anti-pmy IgG antibodies were generated. There was no evidence of any toxic effects and the vaccine preparations and Quil A adjuvant were clearly well tolerated. The development of a vaccine intended for livestock animals such as bovines would be beneficial in two ways; directly by blocking transmission of schistosomiasis to humans and economically by contributing to healthier livestock. We are encouraged by the consistent efficacy in the mouse and the buffalo vaccine trials that resulted in a significant decrease in liver eggs. Indeed, predictions from mathematical models indicate that an egg reduction effect of 42-45% in buffaloes would be sufficient when combined with human treatment to control schistosomiasis japonica in the marshes and lakes along the middle and upper reaches of the Yangtze River, the most highly endemic areas for the disease in China.

The potential of artemether for the control of schistosomiasis

Schistosomiasis continues to rank--following malaria--at the second position of the world's parasitic diseases in terms of the extent of endemic areas and the number of infected people. There is yet no vaccine available and the current mainstay of control is chemotherapy with praziquantel used as the drug of choice. In view of concern about the development of tolerance and/or resistance to praziquantel, there is a need for research and development of novel drugs for the prevention and cure of schistosomiasis. Interestingly, derivatives of artemisinin, which are already effectively used in the treatment of malaria, also exhibit antischistosomal properties. Significant advances have been made with artemether, the methyl ether derivative of artemisinin. We review the discovery of the antischistosomal activity of artemether by Chinese scientists two decades ago; the detailed laboratory studies of the susceptibility of, and effect on, the different developmental stages of Schistosoma japonicum, Schistosoma mansoni and Schistosoma haematobium to artemether; the possible mechanism of action and the potential long-term toxicity. Finally, we look at the effect of combined treatment with artemether and praziquantel; and clinical findings thus far obtained from randomised controlled trials with oral artemether for the prevention of patent infections and morbidity. The review intends to create a forum for strategic discussion of how these laboratory and clinical findings could be translated into public health actions. We conclude that artemether--as part of integrated current control measures and adapted to specific socio-ecological and epidemiological settings--has considerable potential to significantly reduce the current burden of schistosomiasis in many parts of the world.