Schistosomiasis vaccine development--the current picture

Schistosomes: challenges in compound screening

Major progress in studying the biology of schistosomes had been achieved since the late 1960s with the successful laboratory cultivation of the parasite's life cycle stages in the vertebrate (in vivo animal models) and snail hosts. This was followed by establishment of in vitro culture techniques for cultivation of the different life cycle stages to understand the mechanisms regulating the parasite's growth, development, transformation, pathogenicity and survival, with prospects to develop and identify relevant candidate diagnostic, immunological and chemotherapeutic targets. Chemotherapeutic measures have been the mainstay in the control of schistosomiasis. The use of praziquantel, a relatively safe and orally administered drug, in targeted or mass treatment programmes had significantly reduced the prevalence of schistosomiasis in disease-endemic countries. However, with only one drug of choice for treatment, parasite resistance remains a major concern. Thus, new drug discovery against schistosomes cannot be overemphasised. Undoubtedly, this will require an integrated system that includes not only rational chemical synthesis and lead optimisation, but also appropriate drug screening strategies. This paper reviews the present state of in vitro and in vivo drug screening strategies against schistosomes. It also highlights the best practices for compound screening in the TDR-designated compound screening centres and details some of the challenges involved in in vitro and in vivo compound screening.

Genitourinary schistosomiasis: life cycle and radiologic-pathologic findings

Genitourinary schistosomiasis is produced by Schistosoma haematobium, a species of fluke that is endemic to Africa and the Middle East, and causes substantial morbidity and mortality in those regions. It also may be seen elsewhere, as a result of travel or immigration. S haematobium, one of the five fluke species that account for most human cases of schistosomiasis, is the only species that infects the genitourinary system, where it may lead to a wide spectrum of clinical symptoms and signs. In the early stages, it primarily involves the bladder and ureters; later, the kidneys and genital organs are involved. It rarely infects the colon or lungs. A definitive diagnosis of genitourinary schistosomiasis is based on findings of parasite ova at microscopic urinalysis. Clinical manifestations and radiologic imaging features also may be suggestive of the disease, even at an early stage: Hematuria, dysuria, and hemospermia, early clinical signs of an established S haematobium infection, appear within 3 months after infection. At imaging, fine ureteral calcifications that appear as a line or parallel lines on abdominopelvic radiographs and as a circular pattern on axial images from computed tomography (CT) are considered pathognomonic of early-stage schistosomiasis. Ureteritis, pyelitis, and cystitis cystica, conditions that are characterized by air bubble-like filling defects representing ova deposited in the ureter, kidney, and bladder, respectively, may be seen at intravenous urography, intravenous ureteropyelography, and CT urography. Coarse calcification, fibrosis, and strictures are signs of chronic or late-stage schistosomiasis. Such changes may be especially severe in the bladder, creating a predisposition to squamous cell carcinoma. Genital involvement, which occurs more often in men than in women, predominantly affects the prostate and seminal vesicles.

Schistosomiasis: forty years' war on the worm

Schistosome vaccine candidates are now entering phase I clinical trials. In an attempt to illustrate the progress made towards control, and the definition of potential vaccines against schistosomiasis, André Capron reviews some of the major findings and observations that have led to a significant evolution of our concepts, together with the production of novel and promising tools. It is obvious that our most important advances have proceeded from the successful integration of convergent knowledge in biology, epidemiology and biotechnology. At this stage, nobody can predict what will be the outcome of the current trials, but an important step has certainly been made towards immunointervention in human schistosomiasis.

A Vaccine for Schistosomiasis: alternative approaches

An independent trial of candidate antigens for a Schistosoma mansoni vaccine has been completed recently under the auspices of the World Health Organization TDR programme. It has been acknowledged that the results of the trial failed to meet expectations and, therefore, it is appropriate that the options for future work should be considered. In this article, Mike Doenhoff describes two S. mansoni molecules-a schistosome larval protease and a high molecular weight egg and worm antigen. Both are associated with protective immunity, but they have unusual immunological properties that distinguish them from the antigens tested so far. The results suggest that alternative approaches to a schistosomiasis vaccine are still worth exploring.

Neuroschistosomiasis

Schistosomiasis (bilharzia) is a neglected tropical disease caused by digenetic trematode platyhelminths of the genus Schistosoma. Neuroschistosomiasis is one of the most severe clinical outcomes associated with schistosome infection. Neurological complications early during the course of infection are thought to occur through in situ egg deposition following aberrant migration of adult worms to the brain or spinal cord. The presence of eggs in the CNS induces a cell-mediated Th2-driven periovular granulomatous reaction. The mass effect of thousands of eggs and the large granulomas concentrated within the brain or spinal cord explain the signs and symptoms of increased intracranial pressure, myelopathy, radiculopathy and subsequent clinical sequelae. Myelopathy (acute transverse myelitis and subacute myeloradiculopathy) of the lumbosacral region is the most common neurological manifestation of S. mansoni or S. haematobium infection, whereas acute encephalitis of the cortex, subcortical white matter, basal ganglia or internal capsule is typical of S. japonicum infection. Cerebral complications include encephalopathy with headache, visual impairment, delirium, seizures, motor deficits and ataxia, whereas spinal symptoms include lumbar pain, lower limb radicular pain, muscle weakness, sensory loss and bladder dysfunction. The finding of eggs in the stool or a positive serology, provides supportive but not direct evidence of neuroschistosomiasis. A definitive diagnosis can only be made with histopathological study showing Schistosoma eggs and granulomas. Schistosomicidal drugs (notably praziquantel), steroids and surgery are currently used for the treatment of neuroschistosomiasis. During the 'acute phase' of the disease, neuroschistosomiasis is treated with corticosteroids which are augmented with a course of praziquantel once female worm ovipositioning commences. Surgery should be reserved for special cases such as in those with evidence of medullary compression and in those who deteriorate despite clinical management.

Construction and expression of DNA vaccine pIRES-Sj97-Sj14-Sj26 and its immunogenicity in mice

To find a new preventive strategy for the infection of Schistosoma japonica, plasmid pIRES-Sj97-Sj14-Sj26 that contains fatty binding protein (Sj14), GST (Sj26) and paramyocin (Sj97) that are expressed on the membrane, was constructed. RT-PCR was used to detect the expression of Sj14 mRNA, Sj26 mRNA and Sj97 mRNA in the Hela cells, the indirect immunofluorescent test was employed for the detection of the expression of trans-membrane Sj26 after the plasmid was transfected into Hela cells. Fifty BALB/c mice were randomly divided into 5 groups and pIRES-Sj97-Sj14-Sj26 plasmid DNA, pIRES-Sj14-Sj26 plasmid DNA, pIRES-Sj26 plasmid DNA, pIRES blank vector and normal saline were respectively injected into the quadriceps muscles of thigh. Eight weeks after the immunization the mice were killed and significantly higher level of IgG was detected in the pIRES-Sj97-Sj14-Sj26 group as compared with the pIRES blank vector, normal saline and pIRES-Sj26 groups (P<0.01) and the pIRES-Sj14-Sj26(P<0.05). Single splenocyte suspension was prepared to detected the level of IFN-gamma by ELISA and the lymphocyte stimulating index (SI) by MTT. SI was significantly higher of in the pIRES-Sj97-Sj14-Sj26 group than in other groups (P<0.01), while the IFN-gamma level was significantly higher the pIRES-Sj97-Sj14-Sj26 group than in pIRES blank vector and normal saline groups (P<0.01), but no significant differences were found when compared with pIRES-Sj14-Sj26 and pIRES-Sj26 groups. Flow cytometery showed that the percent-ages of CD4+ and CD8+ T cells were much higher in the pIRES-Sj97-Sj14-Sj26 group (P< 0.01, P<0.05). It was concluded that pIRES-Sj97-Sj14-Sj26 vaccine may induce stronger immune response in BALB/c mice.

Intrahepatic Cholangiocarcinoma with Old Infestation of Schistosoma japonicum: Report of a Case

We report a rare case of intrahepatic cholangiocarcinoma associated with old infestation of Schistosoma japonicum. The patient was a 76-year-old Japanese man who had lived his childhood in an endemic area of this parasite. He presented with jaundice and computed tomography showed a 4-cm, hypodense tumor in segment VIII of the liver. Microscopically, the resected mass was composed of well-differentiated adenocarcinoma cells. Fibrosis and inflammation were seen around the dilated peripheral portal veins embolized with dead S. japonicum eggs. Our search of the literature found only one other case of cholangiocarcinoma coincident with S. japonicum, suggesting that it is not a risk factor for cholangiocarcinoma, although the inflammation and fibrosis caused by the S. japonicum eggshells may predispose to carcinogenesis. However, there is no evidence supporting this hypothesis. More data are necessary to evaluate the differences in clinicopathological findings between cholangiocarcinoma concomitant with S. japonicum and the usual type of cholangiocarcinoma.

Katayama syndrome

Katayama syndrome is an early clinical manifestation of schistosomiasis that occurs several weeks post-infection with Schistosoma spp (trematode) worms. Because of this temporal delay and its non-specific presentation, it is the form of schistosomiasis most likely to be misdiagnosed by travel medicine physicians and infectious disease specialists in non-endemic countries. Katayama syndrome appears between 14-84 days after non-immune individuals are exposed to first schistosome infection or heavy reinfection. Disease onset appears to be related to migrating schistosomula and egg deposition with individuals typically presenting with nocturnal fever, cough, myalgia, headache, and abdominal tenderness. Serum antibodies and schistosome egg excretion often substantiate infection if detected. Diffuse pulmonary infiltrates are found radiologically, and almost all cases have eosinophilia and a history of water contact 14-84 days before presentation of clinical symptoms; patients respond well to regimens of praziquantel with and without steroids. Artemisinin treatment given early after exposure may decrease the risk of the syndrome.

Schistosomiasis

Schistosomiasis is a disease that is relatively rare in the United States but has become an endemic in more than 74 countries. This disease has infected some 200 million people worldwide, particularly in developing countries. The disease is caused by parasitic worms, or flukes, which reside in contaminated or poorly sanitized fresh water. The most common effects of the disease are urinary tract and abdominal/intestinal disorders. Sonography has become an invaluable tool in detecting the clinical presentation of schistosomiasis, although lab studies of fecal and urine contents are the required to confirm infection. Although there is no current vaccine available for schistosomiasis, advances in drugs such as praziquantel, oxamniquine, and metrifonate have led to highly effective treatment. These drugs have led to a substantial reduction in morbidity in many areas. Mortality rates have also declined, but when present, it is usually due to intestinal bleeding or bladder cancer.

Schistosomiasis control in the People's Republic of China

Schistosomes, snail-transmitted trematodes (blood flukes), cause a major parasitic disease that ranks second only to malaria in terms of human suffering in the tropics. Schistosoma japonicum has occupied its ecological niche in China for thousands of years; through natural selection it has evolved survival mechanisms that make it difficult (if not impossible) to eradicate. As discussed here by Allen Ross, Li Yuesheng, Adrian Sleigh and Don McManus, vaccination, in combination with current control strategies, may significantly reduce the morbidity of this disease and ultimately improve the quality of life for those living adjacent to endemic zones. This article provides a special focus in Hunan province and examines the potential impact of the Three Gorges Super Dam Project on schistosomiasis control.

Antigenic glycans in parasitic infections: implications for vaccines and diagnostics

Infections by parasitic protozoans and helminths are a major world-wide health concern, but no vaccines exist to the major human parasitic diseases, such as malaria, African trypanosomiasis, amebiasis, leishmaniasis, schistosomiasis, and lymphatic filariasis. Recent studies on a number of parasites indicate that immune responses to parasites in infected animals and humans are directed to glycan determinants within cell surface and secreted glycoconjugates and that glycoconjugates are important in host-parasite interactions. Because of the tremendous success achieved recently in generating carbohydrate-protein conjugate vaccines toward microbial infections, such as Haemophilus influenzae type b, there is renewed interest in defining parasite-derived glycans in the prospect of developing conjugate vaccines and new diagnostics for parasitic infections. Parasite-derived glycans are compelling vaccine targets because they have structural features that distinguish them from mammalian glycans. There have been exciting new developments in techniques for glycan analysis and the methods for synthesizing oligosaccharides by chemical or combined chemo-enzymatic approaches that now make it feasible to generate parasite glycans to test as vaccine candidates. Here, we highlight recent progress made in elucidating the immunogenicity of glycans from some of the major human and animal parasites, the potential for developing conjugate vaccines for parasitic infections, and the possible utilization of these novel glycans in diagnostics.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Gastrointestinal complications of schistosomiasis

Schistosomiasis is an important disease in many parts of the world and has affected the course of human history many times over. The parasitic infection is acquired during contact with infected water. A chronic inflammatory response to schistosome eggs, mediated by both cellular and humoral mechanisms, is the root of the pathology seen in schistosomiasis. Hepatosplenic disease results in intrahepatic presinusoidal portal hypertension. The resultant esophageal and gastric varices are an important cause of morbidity and mortality. Standard treatment guidelines for managing varices can be applied to patients with schistosomiasis. Coinfection with viral hepatitis results in liver disease that progresses more rapidly and is more difficult to treat. Intestinal schistosomiasis may be confused with other disease states and can be an important cause of morbidity, especially in heavily infected patients. Diagnosis relies on demonstration of schistosome eggs in feces or tissue. Praziquantel is the treatment of choice. The development of a vaccine for schistosomiasis is an important goal in the attempt to control this disease.

HLA class II antigens positively and negatively associated with hepatosplenic schistosomiasis in a Chinese population

To identify possible associations between host genetic factors and the onset of liver fibrosis following Schistosoma japonicum infection, the major histocompatibility class II alleles of 84 individuals living on an island (Jishan) endemic for schistosomiasis japonica in the Poyang Lake Region of Southern China were determined. Forty patients exhibiting advanced schistosomiasis, characterised by extensive liver fibrosis, and 44 age and sex-matched control subjects were assessed for the class II haplotypes HLA-DRB1 and HLA-DQB1. Two HLA-DRB1 alleles, HLA-DRB1*0901 (P=0.012) and *1302 (P=0.039), and two HLA-DQB1 alleles, HLA-DQB1*0303 (P=0.012) and *0609 (P=0.037), were found to be significantly associated with susceptibility to fibrosis. These associated DRB1 and DQB1 alleles are in very strong linkage disequilibrium, with DRB1*0901-DQB1*0303 and DRB1*1302-DQB1*0609 found as common haplotypes in this population. In contrast, the alleles HLA-DRB1*1501 (P=0.025) and HLA-DQB1*0601 (P=0.022) were found to be associated with resistance to hepatosplenic disease. Moreover, the alleles DQB1*0303 and DRB1*0901 did not increase susceptibility in the presence of DQB1*0601, indicating that DQB1*0601 is dominant over DQB1*0303 and DRB1*0901. The study has thus identified both positive and negative associations between HLA class II alleles and the risk of individuals developing moderate to severe liver fibrosis following schistosome infection.

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

Schistosomiasis japonica is a serious communicable disease and a major disease risk for more than 30 million people living in the tropical and subtropical zones of China. Infection remains a major public health concern despite 45 years of intensive control efforts. It is estimated that 865,000 people and 100,250 bovines are today infected in the provinces where the disease is endemic, and its transmission continues. Unlike the other schistosome species known to infect humans, the oriental schistosome, Schistosoma japonicum, is a true zoonotic organism, with a range of mammalian reservoirs, making control efforts extremely difficult. Clinical features of schistosomiasis range from fever, headache, and lethargy to severe fibro-obstructive pathology leading to portal hypertension, ascites, and hepatosplenomegaly, which can cause premature death. Infected children are stunted and have cognitive defects impairing memory and learning ability. Current control programs are heavily based on community chemotherapy with a single dose of the drug praziquantel, but vaccines (for use in bovines and humans) in combination with other control strategies are needed to make elimination of the disease possible. In this article, we provide an overview of the biology, epidemiology, clinical features, and prospects for control of oriental schistosomiasis in the People's Republic of China.

Recent Advances in Schistosomiasis

Schistosomiasis is a major parasitic disease, affecting nearly 200 million persons, worldwide. Major advances in our knowledge-in terms of pathogenesis, improved diagnosis, therapeutics (both drugs and strategies), and morbidity assessment-now make schistosomiasis a curable, often preventable disease. In contrast to most other illnesses, most schistosomiasis pathology appears to be reversible over time. For the future, several promising vaccine candidates are already in phase-I or phase-II testing. On the other hand, the range of this disease has been increasing, as water resources are developed in several newly industrialized countries and much of schistosomiasis in sub-Saharan Africa remains largely untreated.

The Schistosoma gene discovery program: state of the art

Schistosoma are dioecious digenetic trematodes carrying a large (270 Mb) genome. Gaining knowledge about the genome of these parasites is of importance for the understanding of their biology, mechanisms of drug resistance and antigenic variation that determine escape from the host's immune system. This review will provide an update on the Schistosoma Gene Discovery Program, which is part of the Schistosoma Genome Project created in 1992. One of the main objectives of this program is the discovery and characterisation of new genes of Schistosoma mansoni and Schistosoma japonicum in an attempt to search for new targets for drugs and vaccine development. The success of the Schistosoma Gene Discovery Program is demonstrated by the number of catalogued genes, that now reaches 15 to 20% of the full gene complement of its genome.

Is there immunity to Schistosoma japonicum?

The Oriental schistosome, Schistosoma japonicum, unlike the other two major schistosomes that infect humans (S. mansoni and S. haematobium), is a zoonotic species. The transmission dynamics and the potential effects of host-related regulatory factors, including immunity, are likely to be distinct for this parasite. Here, Allen Ross and collaborators from Australia, China and the Philippines discuss recently published and established epidemiological and laboratory data bearing on anti-infection immunity to Asian schistosomiasis, and contrast these findings with the emerging picture of development of anti-infection immunity against the African schistosomes. Implications for vaccines and other control strategies for schistosomiasis japonica are also discussed.

The baboon as a non-human primate model of human schistosome infection

Over the past three decades, intensive studies of murine schistosomiasis have provided important clues to the understanding of the human disease, but growing evidence suggests that these results derived from highly inbred strains of mice might not have direct applicability to the human infection. Recent data based on the baboon indicate that infection in this non-human primate might mirror the human situation. In this review, Mramba Nyindo and Idle Farah demonstrate that baboons provide an excellent non-human primate model that produces pathology and disease closely resembling that observed in humans, and address how studies in baboons can provide insights into mechanisms regulating schistosomiasis mansoni pathology and immunity. They also address, in a general way, issues related to the use of non-human primates in biomedical research.

The search for a vaccine against schistosomiasis--a difficult path but an achievable goal

The search for an effective vaccine against schistosomiasis, a parasitic disease currently affecting over 200 million people, remains a desirable but as yet challenging and elusive goal. Progress in the area has been relatively slow but research demonstrating the ability of humans to acquire natural immunity to schistosome infection, together with the successful use in animals of attenuated vaccines, supplemented with encouraging results obtained with defined antigens, suggests that development of a vaccine is achievable. Noteworthy also are recent immune correlate findings which shed light on the complex, putatively protective immune responses in humans, which have improved the prospects of success. With the first human clinical trial having been completed with a schistosome vaccine candidate, this review examines current progress aimed at achieving the objective of a safe and effective vaccine for widespread use against schistosomiasis. The review emphasises work undertaken in the author's laboratory and those of his chief collaborators in the search for a vaccine against schistosomiasis japonica, a disease of major public health significance in The People's Republic of China and The Philippines. Schistosomiasis vaccines should not be considered as the panacea for schistosomiasis control as, when available, it is generally envisaged that they would be used as one component of an integrated strategy complementing currently available and effective tools such as chemotherapy, improvements to sanitation, piped water supply, effective sewage draining and health education.

Production of interleukin-10 by peripheral blood mononuclear cells from residents of a marshland area in China endemic for Schistosoma japonicum

Interleukin-10 (IL-10) cytokine production was assessed using peripheral blood mononuclear cells (PBMC) from 67 individuals living in an area endemic for schistosomiasis japonica in China (Dongting Lake, Hunan Province), and 11 control subjects from a non-endemic part of the same Province. Production of IL-10 was measured following in vitro stimulation of PBMC using whole parasite extract (SWAP) or a panel of recombinant Schistosoma japonicum antigens (22-kDa tegumental membrane-associated antigen, glyceraldehyde-3-phosphate dehydrogenase, paramyosin, 14-kDa fatty acid-binding protein and 28-kDa glutathione S-transferase) which are of recognized interest in the development of protective immunity to schistosomiasis. Significantly, PBMC isolated from the exposed population compared with the non-exposed population produced higher levels of IL-10. There was a trend towards higher mean levels of IL-10 release in putatively resistant (insusceptible) (consistently egg negative but highly exposed) individuals compared with susceptible (egg-positive) subjects from the exposed population. Analysis of individual exposure (the duration of water contact and the percent body surface area in contact with water, expressed as m2 h/day) vs. IL-10 production indicated a weak but consistent and statistically significant inverse correlation, with lower levels of exposure being associated with higher levels of IL-10. These results suggest an association between IL-10 production and resistance to S. japonicum in subjects from this Chinese population exposed to infection.

Genetic immunization of mice with DNA encoding the 23 kDa transmembrane surface protein of Schistosoma japonicum (Sj23) induces antigen-specific immunoglobulin G antibodies

The 23 kDa transmembrane surface protein of schistosomes is of recognized interest in studies of immune responsiveness in schistosomiasis. To examine the immunogenicity of the 23 kDa antigen of Schistosoma japonicum, Sj23, when delivered by genetic immunization, mice were immunized using a DNA construct containing the Sj23 cDNA under the control of a CMV promotor. Serological analysis of peripheral blood from immunized mice demonstrated that this construct was able to induce the production of antigen-specific IgG antibodies that recognized a schistosome antigen of 23 kDa in Western blots. Despite inducing antigen-specific antibodies, the Sj23 DNA vaccine was unable to confer protection in immunized mice subjected to challenge with S.japonicum cercariae. Appropriate engineering of the unique structure of the Sj23 kDa transmembrane protein of schistosomes may provide a novel vehicle for expressing foreign epitopes from other infectious agents or, possibly, cancer antigens, anchored to the surface of transfected cells.

Characterisation of a family of Schistosoma japonicum proteins related to dynein light chains

Dynein light chains (DLC) are components of dynein, an enzyme complex involved in various aspects of microtubule-based motility. We report here the molecular cloning and sequencing of cDNAs encoding a family of DLC-like polypeptides (SjcDLC1-5) from the human bloodfluke Schistosoma japonicum with open reading frames of 87-104 amino acids and deduced molecular masses ranging from 10.5 to 12.3 kDa. Two-dimensional Western blot analysis confirmed the presence of several S. japonicum DLC isoforms with differing pI values and molecular sizes. We also describe the molecular characterisation, genomic organisation and expression of clone SjcDLC1, and the immunological characterisation and localisation of its encoded protein. Northern blot analysis of adult worm RNA indicated SjcDLC1 is encoded by a single message of approximately 650 bp and Southern analysis suggested one SjcDLC1 gene exists in the S. japonicum genome. Immunolocalisation studies demonstrated that the SjcDLC1 protein is present in the tegument of the adult and cercarial stages of S. japonicum. SjcDLC1 and the other SjcDLC may function in the transport of specialised organelles, comprising membranous and discoid bodies, through the tegument to the schistosome-unique heptalaminate tegumental membrane at the external surface of the adult worm. As a consequence, they may provide novel targets for anti-schistosome vaccine and/or drug development.

DNA vaccines: technology and application as anti-parasite and anti-microbial agents

DNA vaccines have been termed The Third Generation of Vaccines. The recent successful immunization of experimental animals against a range of infectious agents and several tumour models of disease with plasmid DNA testifies to the powerful nature of this revolutionary approach in vaccinology. Among numerous advantages, a major attraction of DNA vaccines over conventional vaccines is that they are able to induce protective cytotoxic T-cell responses as well as helper T-cell and humoral immunity. Here we review the current state of nucleic acid vaccines and cover a wide range of topics including delivery mechanisms, uptake and expression of plasmid DNA, and the types of immune responses generated. Further, we discuss safety issues, and document the use of nucleic acid vaccines against viral, bacterial and parasitic diseases, and cancer. The early potential promise of DNA vaccination has been fully substantiated with recent, exciting developments including the movement from testing DNA vaccines in laboratory models to non-human primates and initial human clinical trials. These advances and the emerging voluminous literature on DNA vaccines highlight the rapid progress that has been made in the DNA immunization field. It will be of considerable interest to see whether the progress and optimism currently prevailing can be maintained, and whether the approach can indeed fulfil the medical and commerical promise anticipated.

Genomics and the biology of parasites

Despite the advances of modern medicine, the threat of chronic illness, disfigurement, or death that can result from parasitic infection still affects the majority of the world population, retarding economic development. For most parasitic diseases, current therapeutics often leave much to be desired in terms of administration regime, toxicity, or effectiveness and potential vaccines are a long way from market. Our best prospects for identifying new targets for drug, vaccine, and diagnostics development and for dissecting the biological basis of drug resistance, antigenic diversity, infectivity and pathology lie in parasite genome analysis, and international mapping and gene discovery initiatives are under way for a variety of protozoan and helminth parasites. These are far from ideal experimental organisms, and the influence of biological and genomic characteristics on experimental approaches is discussed, progress is reviewed and future prospects are examined.

Cloning of a cDNA encoding SjIrV1, a Schistosoma japonicum calcium-binding protein similar to calnexin, and expression of the recombinant protein in Escherichia coli

Membrane-associated proteins were isolated from adult Philippine strain Schistosoma japonicum by partitioning into the detergent phase of Triton X-114. A rabbit polyclonal antiserum raised against these proteins was used to screen an S. japonicum expression cDNA library. Positive clones were identified which encoded the species orthologue of SmIrV1, a Schistosoma mansoni protein which was initially identified by screening with sera from mice protectively vaccinated with irradiated cercariae [Hawn et al., J. Biol. Chem. 268 (1993) 7692-7698]. The S. japonicum molecule, which we term SjIrV1, is 83% identical to SmIrV1 at the predicted amino acid level and is a member of the calreticulin family of non-EF-hand, calcium-binding proteins. The Chinese strain S. japonicum orthologue of SjIrV1 was obtained by screening with the radiolabelled insert of the Philippine strain clone. Northern blot analysis revealed a single message of around 2.4 kb and gave no indication of alternative splicing. Southern blot analysis gave a simple pattern, indicating a single-copy gene, and showed a single restriction fragment length polymorphism between the genomes of Chinese and Philippine strains of S. japonicum. Recombinant, full-length SjIrV1 was expressed with a hexahistidine tag in Escherichia coli and the recombinant protein isolated by nickel-chelate chromatography. Recombinant SjIrV1 was shown to exhibit calcium-dependent, differential electrophoretic migration and to bind ruthenium red in the absence but not in the presence of calcium ions. The presence of conserved Ca(2+)-binding motifs predicted from the primary sequence, together with the Ca(2+)-dependent electrophoretic mobility of recombinant SjIrV1, confirmed that SjIrV1 was a functional calcium-binding protein.

Measuring exposure to S. japonicum in China. I. Activity diaries to assess water contact and comparison to other measures

We introduce a new method, activity diaries, in order to evaluate human water contact among fishing communities in an area moderately endemic for Schistosoma japonicum in the Dongting Lake region of Southern China. Two hundred and forty-nine subjects (76% male) were followed prospectively over a 9-month-period in order to verify exposure and reinfection. Exposure was determined crudely with questionnaires, direct 12-h water observations, and more precisely with activity diaries and an adjusted exposure model which took into account the time of day, the duration of contact and the percent body surface area in contact with water. Cohort subjects filled in activity diaries for an average of 85 days as compared with 2 days for the direct water observations. The typical unadjusted mean daily water contact (duration) based on the activity diaries was 53 min with 62% of this time spent in fishing. In contrast, the direct water observations revealed an average daily duration of 149 min with 53% of the time spent in fishing. Human water contact patterns (min/day) by site, activity and body part exposed were examined with the activity diaries. Individuals in the 36-49-year-old age range had the highest degree of water contact. Most of this daily contact occurred by males on the hands (mean+/-S.D.; 83.53+/-67.80 min/day) while fishing (mean+/-S.D.; 87.84+/-8.88 min/day) on the lake (mean+/-S.D.; 85.98+/-69.90 min/day). There was a strong positive log correlation (r=0.95) between the crude and adjusted (based on our derived exposure model) diary outcomes for the entire study sample, however, at higher exposure levels this relationship was differentially weaker (r=0.70). Results from this study suggest that current methods used in evaluating schistosomiasis exposure in China may overestimate and bias measures of the risk of infection. Activity diaries adjusted for the time of day, duration and the percent body surface area exposed are cost-effective and practical instruments to accurately quantify human exposure in the vast lake regions of Southern China where most of the endemic schistosomiasis japonica occurs.

The vaccine efficacy of native paramyosin (Sj-97) against Chinese Schistosoma japonicum

One of the promising anti-schistosome vaccine candidates currently under investigation is paramyosin, a 97-kDa myofibrillar protein located in the muscles and tegument of schistosome worms. Here we describe the results of two vaccination/challenge experiments undertaken in mice using native paramyosin isolated from adult worms of a Chinese strain of Schistosoma japonicum. In both sets of experiments, a relatively low but consistent and significant reduction in worm burden was evident in mice vaccinated subcutaneously with S. japonicum paramyosin and Freund's adjuvant. In contrast, intraperitoneal vaccination of mice with Chinese strain S. japonicum paramyosin without adjuvant did not result in any reduction in worm numbers when compared with a saline control group. These data contrast with the impressive protection figures reported by another group who used a similar intraperitoneal vaccination protocol with native paramyosin extracted from Philippine strain S. japonicum.

Five year impact of chemotherapy on morbidity attributable to Schistosoma japonicum infection in the Dongting Lake region

OBJECTIVE

To determine changes in the last 5 years of the fraction of acute and chronic symptoms attributable to schistosomiasis japonica in fishing communities with moderate endemicity in the Dongting Lake region of China.

METHOD

Complete medical histories, physical examinations, and stool samples were obtained from 1909 individuals (53% male) ranging in age from 4 to 81 years. Age, sex, occupation, frequency of water contact, number of times treated for schistosomiasis, and last year of treatment were tested as potential effect modifiers and confounders.

RESULTS

Overall, there were very few infected cases and very little variation in any prevalence ratio with infection intensity, sex, age, year of last treatment, number of times treated or frequency of water contact. The attributable fraction of liver enlargement in one village was estimated at 0.114 (11.4%), although this was not significantly > 0(95% CI; -0.008-0.237).

CONCLUSION

The chemotherapy-based schistosomiasis control programme in this locality has succeeded in reducing attributable morbidity to undetectable levels, but many uncertainties remain about sustaining control efforts in the future. Both old and new control strategies will have to be examined if the health and well-being of these people are to be maintained into the next millennium, given that periodic chemotherapy will not be accepted indefinitely.

Immunolocalisation of the glutathione S-transferases, GST-26 and GST-28, within adult Schistosoma japonicum

This paper describes the first ultrastructural immunolocalisation study of the 26-kDa and 28-kDa glutathione S-transferases within adult Schistosoma japonicum (GST-26 and GST-28). Polyclonal antibodies raised against GST-28 (in mice) and against GST-26 (in rabbits) were used to examine the distribution of the proteins within adult parasites. Both proteins were localised within the parenchymal region of the male parasite. Additionally, both proteins were present within parenchymal cells located between the vitelline glands of female parasites. There were no detectable levels of GST-26 or GST-28 on the surface or within the tegument matrix of either the male or female worms. Possible functions for GST-26 and GST-28 within S. japonicum and their significance as vaccine target molecules are addressed.

HLA class II antigens are associated with resistance or susceptibility to hepatosplenic disease in a Chinese population infected with Schistosoma japonicum

The major histocompatibility Class II alleles of 108 individuals living in an area endemic for schistosomiasis japonica in China were determined to identify possible immunogenetic associations with advanced schistosomiasis. Two alleles, HLA-DRB1*1202 (P = 0.002) and HLA-DQA*0601 (P = 0.001) were strongly associated with resistance to advanced disease. In contrast, HLA-DQB1*05031 (P = 0.02) was associated with susceptibility to advanced schistosomiasis. The remaining alleles showed no association with advanced disease. Allele DRB1*1202 co-occurred with allele DQA1*0601; therefore, their independent protective effects could not be ascertained. In contrast, alleles DQA1*0601 and DQB1*05031 never co-occurred and had opposite and significant effects on the occurrence of disease.

Differential antigen-stimulated proliferation of human mononuclear cells by recombinant Schistosoma japonicum antigens in a Chinese population

Peripheral blood mononuclear cells (PBMC) from 117 individuals living on two islands in an area (Dongting Lake) endemic for schistosomiasis japonica in China, and 15 control individuals from a non-endemic area of China, were assessed for antigen-stimulated proliferation against five recombinant Schistosoma japonicum antigens of recognized interest in the development of immunity to schistosomiasis. Two recombinant antigens, paramyosin and 28-kD glutathione-S-transferase, stimulated cellular proliferation (stimulation index > or = 3.0) in 38.5% and 42.5% of subjects, respectively, a level similar to that induced by a soluble whole parasite extract (51.3%). In contrast, three other recombinant antigens tested--a fatty acid binding protein, 22-kD tegumental membrane-associated antigen, and glyceraldehyde-3-phosphate dehydrogenase--stimulated PBMC proliferation in only 3-8% of subjects. Moreover, we also identified a positive association between the degree of exposure, and cellular proliferation following stimulation with recombinant paramyosin or whole parasite extract. Highly significant differences in antigen-stimulated proliferation were also observed between the two islands, Niangashan and Qingshan. The whole parasite extract stimulated proliferation in 90% of subjects from Niangashan island compared with only 42.1% of subjects from Qingshan island (chi2 = 16.88, P = 0.00004), while glutathione-S-transferase stimulated proliferation in 77.3% of subjects from Niangashan island compared with only 34.7% of subjects from Qingshan island (chi2 = 13.09, P = 0.003). A similar, but not significant, trend was observed for paramyosin and the fatty-acid binding protein. The identification of differential cellular proliferative responses to specific schistosome antigens within an infected human population may have important practical implications for vaccine development against schistosomiasis japonica.