Schistosomiasis and soil-transmitted helminthiasis: common drugs for treatment and control

Trematocidal activity of praziquantel and artemisinin derivatives: in vitro and in vivo investigations with adult Echinostoma caproni

We examined the effects of praziquantel and the artemisinins on adult Echinostoma caproni. In vitro, both praziquantel and the artemisinins exhibited exposure-response relationships. In vivo, worm burden reductions of 100% were achieved with single oral doses of praziquantel, artesunate, and artemether at 50, 700, and 1,100 mg/kg of body weight, respectively.

New initiatives against Africa's worms

Since 1999, the funding available for the control of diseases of poverty (neglected diseases) has increased mainly due to leverage resulting from donations by the Bill and Melinda Gates Foundation and loans from the World Bank. Many countries have embarked on control programmes on a national scale due to drug donations by pharmaceutical companies through vertical programmes. The Schistosomiasis Control Initiative has expanded its operations to cover six countries in sub-Saharan Africa, but overlap of treatments between different vertical programmes is now a reality, and so care is needed to ensure that too many different drugs are not given together. Dialogue between programme managers has increased, and integration of some programmes may offer chances of synergy.

Risk factors and spatial patterns of hookworm infection among schoolchildren in a rural area of western Côte d'Ivoire

This study is aimed at investigating the risk factors for hookworm infection among schoolchildren in a rural area of western Côte d'Ivoire and predicting and mapping the spatial distribution of infection. We used demographic and socio-economic data from a cross-sectional survey of 6-16-year-old schoolchildren from 56 schools. Infection with hookworm was determined by microscopic examination of stool samples employing the Kato-Katz technique and an ether-concentration method. Environmental data were derived from satellite images and digitised maps. Bayesian variogram models were applied to investigate the variation of hookworm infection in relation to demographic, socio-economic and environmental factors. The overall hookworm infection prevalence, based on the pooled microscopic diagnoses, was 43.3% and ranged from 5.4 to 79.1% in the schools surveyed. Bivariate analyses showed that sex, age, socio-economic status, elevation, rainfall and land cover were significantly associated with the spatial distribution of hookworm infection. The final multivariate spatial model consisted of the covariates age, sex, socio-economic status, elevation and land cover. When assuming non-stationary underlying spatial dependency, the results of the model suggested that spatial correlation depended on the location only marginally. We conclude that, at the current resolution, it seems more reasonable to target interventions based on well-established epidemiologic risk factors, rather than on spatial factors.

Emerging foodborne trematodiasis

Foodborne trematodiasis is emerging because of increased aquaculture.

Foodborne trematodiasis is an emerging public health problem, particularly in Southeast Asia and the Western Pacific region. We summarize the complex life cycle of foodborne trematodes and discuss its contextual determinants. Currently, 601.0, 293.8, 91.1, and 79.8 million people are at risk for infection with Clonorchis sinensis, Paragonimus spp., Fasciola spp., and Opisthorchis spp., respectively. The relationship between diseases caused by trematodes and proximity of human habitation to suitable freshwater bodies is examined. Residents living near freshwater bodies have a 2.15-fold higher risk (95% confidence interval 1.38–3.36) for infections than persons living farther from the water. Exponential growth of aquaculture may be the most important risk factor for the emergence of foodborne trematodiasis. This is supported by reviewing aquaculture development in countries endemic for foodborne trematodiasis over the past 10–50 years. Future and sustainable control of foodborne trematodiasis is discussed.

Necator americanus: Optimization of the golden hamster model for testing anthelmintic drugs

Laboratory golden hamsters (Mesocricetus auratus) were infected with Necator americanus under several different parasite and host conditions to optimize the model for testing anthelminthic drugs. The results confirmed that male hamsters were more susceptible to infection than females. Host age in the range of 5-15 weeks was not a factor that impacted on adult worm burden, and similar worm burdens were achieved using doses of 150, 250 or 500 N. americanus L3 (NaL3). The largest numbers of adult hookworms were recovered on days 21-28 post-infection, with a significant decrease at days 40-50 post-infection. Therefore adult worm recovery is maximal approximately 11-18 days prior to patency and host blood loss. From these studies a drug evaluation protocol was developed using 150 NaL3 as the infectious dose and then evaluating the anthelminthic effects of the drugs albendazole, tribendimidine, and pyrantel pamoate on days 21-28 post-infection. The model confirms the anthelminthic activity of albendazole, tribendimidine, and pyrantel pamoate and has the potential as a laboratory animal model to detect emerging drug resistance.

Use of praziquantel for clinical treatment and morbidity control of schistosomiasis japonica in China: a review of 30 years' experience

Chemotherapy is widely acknowledged as the most important, rapid and cost-effective method of reducing morbidity due to schistosome infections. The discovery of praziquantel in the 1970s has been a breakthrough for treatment of patients infected with schistosomes, including Schistosoma japonicum in China, and entire communities at risk of schistosomiasis. Praziquantel is usually administered in a single oral dose and has no or only mild and transient side effects. The drug is highly efficacious against S. japonicum, both in patients with acute and chronic stages of the infection, among subjects with extensive hepatosplenic involvement, and in patients with other complicated diseases. The cost of praziquantel has been reduced significantly over the past years. Hence, praziquantel has become the backbone of the national schistosomiasis control programme in China and in other countries where the disease remains endemic, most notably in sub-Saharan Africa. Chemotherapy with praziquantel also plays a role in transmission control of schistosomiasis, although transmission interruption cannot be reached by chemotherapy alone. Here, I review 30 years' of experiences gained with the use of praziquantel for clinical treatment and larger-scale control of schistosomiasis japonica in China.

School-based interventions to enhance knowledge and improve case management of schistosomiasis: a case study from Hunan, China

This paper discusses an intersectoral health-related intervention, using cartoons and video-recording, print materials and face-to-face educational methods, to increase children's knowledge of schistosomiasis, which in turn might improve the case management of early diagnosis and treatment. The main components of the project were (i) the collaboration between the departments of public health and education and (ii) a randomized, controlled, school-based field trial conducted in the Dongting Lake region, China. Children in the experimental group (n=604) and their parents participated in the educational programme. Control children (n=527) received a 2 hour lecture about the disease. All participants were pre-tested, and retested five months after the conduct of the educational intervention. The results show significant changes among children and their parents in the experimental group related to knowledge about schistosomiasis and beliefs towards screening and treatment of the disease. Children in the experimental group also had better compliance than children in the control group for regular screening for schistosomiasis. These findings indicate that carefully designed education programmes are useful for providing both children and their families with information about the prevention and treatment of schistosomiasis. Intersectoral collaboration holds promise to deliver research-based interventions for enhanced knowledge of schistosomiasis and improved case management.

A double-blind field trial on the effects of artemether on Schistosoma japonicum infection in a highly endemic focus in southern China

To further strengthen the evidence-base of artemether for the control of schistosomiasis japonica, a randomised controlled trial was carried out in the Poyang Lake region, a highly endemic area in southern China. A total of 783 individuals, aged 6-60 years, were enrolled. They were first given a single oral dose of praziquantel (50 mg/kg). Then, they were randomly assigned oral artemether (6 mg/kg) or placebo, administered once every 2 weeks for 9-11 doses, covering the entire transmission season for Schistosoma japonicum in 2004. Stool examination 1 month after the final dosing revealed eggs of S. japonicum in 3/373 (0.8%) of the artemether recipients and 56/361 (15.0%) in placebo recipients (chi2=53.69, P<0.001). Compared to the baseline, the geometric mean intensity of S. japonicum infection had decreased by 96.1% in the artemether group, and increased by 50.8% in the placebo group. No acute cases of schistosomiasis japonica were observed in the artemether group, whereas three such cases were reported from the placebo group. Compliance with regard to multi-doses of artemether and placebo was 84.9, and 77.9%, respectively. This study confirms that repeated oral artemether produces no drug-related adverse effects, significantly reduces incidence and intensity of patent S. japonicum infection and results in high compliance. Hence it can be used as an additional tool for the control of schistosomiasis japonica in the lake regions of China.

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.

Development of antischistosomal drugs in China, with particular consideration to praziquantel and the artemisinins

Remarkable achievements have been made in the control of schistosomiasis in China, with chemotherapy playing a seminal role. From the early 1950s through the early 1980s, Chinese scientists made considerable progress in discovery and development of compounds with antischistosomal properties, including antimonials, non-antimonials and various effective principles stemming from traditional herbs. However, only few compounds entered clinical testing, while others were abandoned mainly due to their toxicity and poor efficacy. The advent of praziquantel in the 1970s changed the landscape of research and development of drugs for treatment and morbidity control of schistosomiasis. The main Chinese contributions to enhance the understanding of the antischistosomal drug praziquantel are reviewed here, including issues of metabolism, antibody-dependency, host immune factors, stage-specific susceptibility and resistance. Over the past 25 years, researchers from China successfully developed artemether and artesunate, two derivatives from the antimalarial artemisinin, as promising drugs against Schistosoma japonicum. Laboratory investigations showed that the artemisinins display their highest activity against the juvenile stages of the parasite. These findings were consistently confirmed in randomised controlled trials; repeated oral administration of artemether or artesunate was safe and efficacious in the prevention of patent S. japonicum infections. The key findings are reviewed here, and emphasis is placed on how it stimulated research outside of China on other human schistosome species.

Short communication: Soil-transmitted helminthiasis in Uganda: epidemiology and cost of control

A country-wide description of the distribution of soil-transmitted helminths in Uganda is reported, based on data for 20-185 school-children from 271 schools. The overall prevalence of Ascaris lumbricoides, Trichuris trichiura and hookworm was 6.3%, 5.0% and 43.5%, respectively. The prevalence of A. lumbricoides and T. trichiura was unevenly distributed in the country with prevalence greatest in south-western Uganda whereas hookworm was generally more homogeneously distributed. Based on preliminary cost analysis of an ongoing school-based control programme, the financial delivery cost per school-child treated with albendazole is estimated to be between US dollar 0.04 and 0.08 in different districts.

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.

Effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice

The effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice were compared using scanning electron microscopy (SEM). Forty-two mice infected with S. mekongi for 49 days were treated intragastrically with either 300 mg/kg praziquantel or 300 mg/kg artesunate. Mice were sacrificed 1 or 3 days post-treatment. Worms were collected by perfusion and examined by SEM. One to 3 days after administration of artesunate, the tegument of S. mekongi showed severe swelling, vacuolization, fusion of the tegumental ridges and loss or shortening of the spines on the trabeculae, collapse and peeling. Praziquantel induced similar tegumental alterations as those observed after administration of artesunate, but they were less severe. Three days post-treatment, there was evidence of recovery only in the case of praziquantel. The results of our study suggest that artesunate is more effective than praziquantel in causing tegumental damage in adult S. mekongi, and provides a basis for subsequent clinical trials.

Vaccine-linked chemotherapy: can schistosomiasis control benefit from an integrated approach?

The present strong emphasis on gross organ pathology (liver, kidneys, bladder) in schistosomiasis needs to be replaced with a more balanced view of the disease that also takes into account systemic symptoms that are less easy to assess, such as retarded growth, cognitive development and the effect of continuing low-level blood loss. Access to better estimates of disease burdens, morbidity and mortality is delivering results that bring into question the wisdom of downgrading the impact of the disease. In this scenario, the simplistic approach of exclusive drug treatment might not be sufficient and, in the worst-case scenario, might even exacerbate pathology. To meet this challenge, the repositioning of vaccines within the totality of disease control through the combined use of chemotherapy and vaccination is recommended as the basis for a novel, more-versatile approach to control. Studies on human correlate responses in endemic areas have opened the way to assess the protective value of specific antigens through the cytokine responses and antibodies they elicit. Moreover, vaccine formulations based on novel adjuvants could improve the final outcome through selective manipulation of the immune response. Thus, the tools of vaccine-linked chemotherapy are in principle already available and could shortly be put to the test in clinical trials.

Chemotherapy for major food-borne trematodes: a review

Food-borne trematode infections, caused by liver flukes (Clonorchis, Fasciola, Opisthorchis), lung flukes (Paragonimus) and intestinal flukes (Echinostoma, Fasciolopsis, heterophyids), are significant public health problems, most notably in Southeast Asia and the Western Pacific. Globally, it is estimated that > 40 million people are infected among the 750 million people who live in endemic areas. The epidemiology of food-borne trematodiasis has changed over the past few decades, and now presents a dual picture. On the one hand, increasing numbers of infections are reported from non-endemic areas, and endemic areas are expanding due to larger areas utilised for aquaculture, domestic migration, declining socioeconomic conditions, lack of improved sanitation, and increasing availability of aquatic foods through wider distribution networks often without proper food inspections. On the other hand, social and economic advances in many Asian countries, going hand-in-hand with urbanisation, use of chemical fertilisers and, above all, the administration of safe, efficacious and inexpensive drugs, have significantly reduced the prevalence of food-borne trematode infections. In this review, the taxonomy, life cycle, and geographical distribution of the major food-borne trematodes, including issues of diagnosis and clinical disease manifestations, is summarised. The discovery, chemistry, pharmacological properties, safety, therapeutic efficacy and adverse effects of the current drugs of choice, namely praziquantel and triclabendazole, is then discussed. Recent advances on other drugs and contemporary investigations on novel compounds that might become important players in chemotherapy are highlighted. Finally, the need for research and development of new trematocidal drugs that - employed in concert with health education, improved sanitation and enhanced food safety - are key factors for sustainable control of food-borne trematodiasis, is highlighted.

Tribendimidine: a promising, safe and broad-spectrum anthelmintic agent from China

We review, for the first time, a 20-year Chinese story of research and development pertaining to tribendimidine, a promising anthelmintic agent that is safe and exhibits a broad spectrum of activity. Tribendimidine was first synthesized at the National Institute of Parasitic Diseases in Shanghai in the mid 1980s. In laboratory studies, tribendimidine showed high efficacy against Nippostrongylus braziliensis in rats, Necator americanus in hamsters, Ancylostoma caninum and Toxocara canis in dogs, and Syphacia mesocriceti in mice. Activity was also found against several species of cestodes in chicken. In clinical trials, a single oral dose of 400 mg tribendimidine, administered to patients infected only with N. americanus, or with N. americanus and Ancylostoma duodenalis, resulted in cure rates of 85.7% (132/154) and 89.8% (53/59), respectively. In comparison, a single oral dose of 400 mg albendazole resulted in significantly lower cure rates, namely 65.5% (91/139; chi(2) = 16.47, P < 0.001) and 71.7% (43/60; chi(2) = 6.29, P = 0.012), respectively. Single oral doses of tribendimidine (300 mg) and albendazole (400mg) were equally effective against Ascaris lumbricoides infections; cure rates were 96.0% (97/101) and 98.1% (101/103), respectively. In 5-14-year-old children with an Enterobius vermicularis infection, treated with a single oral dose of 200 mg tribendimidine, a cure rate of 81.6% (93/114) was observed. Tribendimidine was well-tolerated as only mild and transient side effects were observed. It would be of great public health significance if these findings are confirmed in other epidemiological settings, as more than one-quarter of the world population is currently affected by intestinal nematodes, with only very few drugs currently available on the market.

Morbidity in schistosomiasis: an update

PURPOSE OF REVIEW

Schistosomiasis is an important poverty-related health problem and more than 200 million people are infected. This review summarizes papers from April 2003 to June 2004 with a focus on schistosomiasis morbidity and the various factors that affect the level of morbidity in endemic populations. The aim is to provide an update on the current state of knowledge and, hopefully, thereby stimulate continued research interest in this important area.

RECENT FINDINGS

Research into the immune responses associated with severe morbidity has provided new insights into the mechanisms of immune regulation as well as the role of genetic predisposition to periportal fibrosis. Malaria and schistosomiasis are co-endemic and co-infection with malaria may increase the level of morbidity in hepatosplenic schistosomiasis, and alter the host immune response towards schistosome antigens. Schistosome infections may render the host more susceptible to human immunodeficiency virus infection by either interfering with immune responses or increasing the risk of transmission due to genital lesions. An important advance in schistosomiasis research, and parasite genomics, is the recent availability of two major Schistosoma mansoni and Schistosoma japonicum DNA bioinformatic resources.

SUMMARY

Significant advances have been achieved in our understanding of the epidemiology, immunology and genetics of schistosomiasis, and the various factors that may influence morbidity. However, good research is vital for sustainable disease control, and continued progress requires a critical mass of researchers with a range of expertise from basic parasite biology to public-health interventions. It is therefore important to strengthen research capacity in endemic countries.

Schistosomiasis--an unusual cause of ureteral obstruction: a case history and perspective

A male, 32 years of age, presented with dysuria and abdominal pain, but no gross hematuria. He emigrated three years earlier from Somalia, East Africa, and was currently employed as a poultry processor in a rural Wisconsin community. The patient denied any trauma, sexual activity, or family history of significant illness. Abdominal and genitourinary exams were normal with negative tests for gonococcus and chlamydia. Urinalysis demonstrated microhematuria. A urogram and retrograde pyelogram revealed a mildly dilated right ureter down to the ureterovesical junction. Cystoscopy showed punctate white lesions on the bladder urothelium. Ureteroscopy was used to biopsy abnormal tissue in the distal ureter and bladder. Biopsy tissue demonstrated deposits of Schistosoma haematobium eggs. No ova were seen in collected urine specimens. The patient was successfully treated with praziquantel and will be monitored for sequelae of the disease. Schistosomiasis (Bilharziasis) can be expected to be seen with increasing frequency in the United States with the continuing influx of immigrants and refugees, as well as the return of travelers and soldiers from endemic areas. While no intermediate snail host exists for the transmission of Schistosoma sp. in the United States, the continued importation of exotic animals including snails from Africa, as well as the ability of schistosomes to shift host species warrants concern. Additionally, increasing disease associated with non-human bird schistosomes of the same genus seen in the midwestern United States is occurring throughout Europe. One should be aware that praziquantel may not always be available or effective in the treatment of schistosomiasis. It behooves the practicing clinician to remain updated on the status of this widespread zoonosis.

Metabonomic investigations in mice infected with Schistosoma mansoni: an approach for biomarker identification

Schistosomiasis, a chronic and debilitating parasitic disease, affects approximately 200 million people in the developing world and imposes a substantial public health and economic impact. Accurately diagnosing at the individual level, monitoring disease progression, and assessing the impact of pharmacological interventions at the population level are of prime importance for controlling schistosomiasis. Using a Schistosoma mansoni-mouse model, we present a characterization of a parasitic infection by metabolic profiling, employing (1)H NMR spectroscopy and multivariate pattern recognition techniques. We infected 10 mice with 80 S. mansoni cercariae each and collected urine samples 49 and 56 days postinfection. Urine samples were also obtained from 10 uninfected control mice at the same time. The metabolic signature of an S. mansoni infection consists of reduced levels of the tricarboxylic acid cycle intermediates, including citrate, succinate, and 2-oxoglutarate, and increased levels of pyruvate, suggesting stimulated glycolysis. A disturbance of amino acid metabolism was also associated with an S. mansoni infection, as indicated by depletion of taurine, 2-oxoisocaproate, and 2-oxoisovalerate and elevation of tryptophan in the urine. A range of microbial-related metabolites, i.e., trimethylamine, phenylacetylglycine, acetate, p-cresol glucuronide, butyrate, propionate, and hippurate, were also coupled with an S. mansoni infection, indicating disturbances in the gut microbiota. Our work highlights the potential of metabolic profiling to enhance our understanding of biological responses to parasitic infections. It also holds promise as a basis for novel diagnostic tests with high sensitivity and specificity and for improved disease surveillance and control.

Human hookworm infection in the 21st century

The scientific study of human hookworm infection began at the dawn of the twentieth century. In recent years, there have been dramatic improvements in our understanding of many aspects of this globally widespread parasite. This chapter reviews recent advances in our understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century. Advances in molecular biology has lead to the identification of a variety of new molecules from hookworms, which have importance either in the molecular pathogenesis of hookworm infection or in the host-parasite relationship; some are also promising vaccine targets. At present, relatively little is known about the immune responses to hookworm infection, although it has recently been speculated that hookworm and other helminths may modulate specific immune responses to other pathogens and vaccines. Our epidemiological understanding of hookworm has improved through the development of mathematical models of transmission dynamics, which coupled with decades of field research across multiple epidemiological settings, have shown that certain population characteristics can now be recognised as common to the epidemiology, population biology and control of hookworm and other helminth species. Recent recognition of the subtle, but significant, impact of hookworm on health and education, together with the simplicity, safety, low cost and efficacy of chemotherapy has spurred international efforts to control the morbidity due to infection. Large-scale treatment programmes are currently underway, ideally supported by health education and integrated with the provision of improved water and sanitation. There are also on-going efforts to develop novel anthelmintic drugs and anti-hookworm vaccines.