The pathogenesis of granulomatous inflammation and organ injury in schistosomiasis: interactions between the schistosome ova and the host

Matrix metalloproteinases inhibition reveals the association between inflammation, collagen accumulation and intestinal translocation of Schistosoma mansoni eggs in vivo

Schistosomiasis mansoni is a parasitic infection that causes enterohepatic morbidity associated with severe granulomatous inflammation triggered by parasite eggs. In this disease, granulomatous inflammation leads to intestinal erosion and environmental excretion of S. mansoni eggs from feces, an essential process for propagating the parasite and infecting host organisms. Metalloproteinases (MMP) are involved in S. mansoni-induced hepatic granulomatous inflammation and fibrosis. However, the relationship between MMP and collagen accumulation with the intestinal excretion of parasite eggs remains unclear. Thus, the present study investigated whether MMP inhibition is capable of modulating granulomatous inflammation, collagen accumulation and mechanical resistance to the point of influencing the dynamics between intestinal retention and excretion of S. mansoni eggs in infected mice. Our findings indicated that doxycycline (a potent MMP inhibitor) aggravates intestinal inflammation and subverts collagen dynamics in schistosomiasis. By attenuating MMP-2 and MMP-9 activity, this drug is capable of enhancing fibrosis and mechanical resistance of the intestinal wall, hindering S. mansoni eggs translocation. Although collagen content was not correlated with MMP activity, intestinal retention and fecal excretion of parasite eggs in untreated mice; these correlations were observed for doxycycline-treated animals. Thus, our study provides evidence that doxycycline is able to attenuate fecal elimination of S. mansoni eggs by inhibiting MMP-2 and MMP-9 activity, events potentially associated with excessive collagen accumulation, which increases intestinal mechanical resistance and hinders eggs translocation through the intestinal wall. Variations in intestinal collagen dynamics are relevant since they may represent changes in the environmental dispersion of S. mansoni eggs, bringing repercussions for schistosomiasis propagation.

Gastrointestinal Parasites and the Neural Control of Gut Functions

Gastrointestinal motility and transport of water and electrolytes play key roles in the pathophysiology of diarrhea upon exposure to enteric parasites. These processes are actively modulated by the enteric nervous system (ENS), which includes efferent, and afferent neurons, as well as interneurons. ENS integrity is essential to the maintenance of homeostatic gut responses. A number of gastrointestinal parasites are known to cause disease by altering the ENS. The mechanisms remain incompletely understood. Cryptosporidium parvum, Giardia duodenalis (syn. Giardia intestinalis, Giardia lamblia), Trypanosoma cruzi, Schistosoma species and others alter gastrointestinal motility, absorption, or secretion at least in part via effects on the ENS. Recent findings also implicate enteric parasites such as C. parvum and G. duodenalis in the development of post-infectious complications such as irritable bowel syndrome, which further underscores their effects on the gut-brain axis. This article critically reviews recent advances and the current state of knowledge on the impact of enteric parasitism on the neural control of gut functions, and provides insights into mechanisms underlying these abnormalities.

Hepatobiliary Schistosomiasis

Schistosomiasis is an ancient parasitic disease that has afflicted Egyptians since the time of the pharaohs. The disease is caused by lodged schistosome eggs in the host liver, evoking an immune response and leading in some patients to the development of hepatic granuloma and fibrosis. Here, we review the epidemiology, immunopathogenesis, and clinical profile of schistosomiasis. This information may aid in the development of more efficacious treatments and improved disease prognosis.

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.

T regulatory cell responses to immunization with a soluble egg antigen in Schistosoma mansoni-infected mice

The aim of the study is to characterize the phenotypes of CD4⁺ CD25⁺ T regulatory cells within the liver granulomas and association with both Foxp-3 gene expression and splenic cytokines. Naïve C57BL/6 mice were intravenously injected with multiple doses of the soluble egg antigen (SEA) 7 days before cercarial infection. The immunized and infected control groups were sacrificed 8 and 16 weeks post-infection (PI). Histopathology, parasitological parameters, splenic phenotypes for T regulatory cells, the FOXP-3 expression in hepatic granuloma using real-time PCR, and the associated splenic cytokines were studied. Histopathological examination of the liver revealed remarkable increase in degenerated ova within hepatic granuloma which decreased in diameter at weeks 8 and 16 PI (P<0.01). The percentage of T regulatory cells (CD4⁺ CD25⁺) increased significantly (P<0.01) in the immunized group compared to the infected control at weeks 8 and 16 PI. The FOXP-3 expression in hepatic granulomas increased from 10 at week 8 to 30 fold at week 16 PI in the infected control group. However, its expression in the immunized group showed an increase from 30 at week 8 to 70 fold at week 16 PI. The splenic cytokine levels of pro-inflammatory cytokines, IFN-γ, IL-4, and TNF-α, showed significant decreases (P<0.05) compared to the infected control group. In conclusion, the magnitude and phenotype of the egg-induced effects on T helper responses were found to be controlled by a parallel response within the T regulatory population which provides protection in worm parasite-induced immunopathology.

Schistosoma mansoni: effect of dietary zinc supplement on egg granuloma in Swiss mice treated with praziqantel

Schistosomiasis is one of the most important parasitic diseases in Egypt and chemotherapy is considered the most effective method of control. This study was conducted to assess the effectiveness of zinc administration against Schistosoma mansoni infection by evaluating the activities of arylesterase and paraoxonase (PON1) enzymes, and the degree of liver damage. One hundred and twenty albino mice were divided into two groups; one was an infected control and the other a treated group which was further subdivided into three according to the praziquantel and zinc supplementation given. Blood and liver samples, collected 10 weeks post-infection, were subjected to parasitological, histopathological, and enzyme assays, and immunological studies. The results showed that dietary zinc supplementation led to marked reduction in worm load, and egg deposition in the liver and intestine. Histopathological examination showed marked reduction in the number and diameter of hepatic granulomas in the treated groups. The activity of arylesterase and PON1 enzymes were partially restored in infected animals receiving zinc. IL-10 mRNA expression was higher in the treated groups than in the infection control group. In conclusion, zinc administration could be a promising adjuvant therapy for S. mansoni infection.

Hepatic changes in congenital Schistosoma japonicum infections in pigs

The inflammatory response in liver tissue from piglets congenitally infected with Schistosoma japonicum was examined at two different timepoints after infection. The piglets, which were the offspring of three sows infected with 9000 S. japonicum cercariae in the 10th week of gestation, were allocated into two groups (n=9 and 17) killed 5 or 11 weeks after birth, respectively. All piglets developed a low level infection,with no significant difference between the groups. Inflammatory lesions in the liver consisted mainly of granulomas in portal areas, often obliterating the portal veins, and frequently with central eggs or egg remnants. The granulomatous reaction consisted of epithelioid cells and occasional giant cells surrounded by layers of lymphocytes, eosinophils, plasma cells, and various amounts of collagen and fibroblasts. Mild to moderate infiltration of portal and septal connective tissue with eosinophils and lymphocytes was common, but the connective tissue was generally not increased. At the two timepoints, slight differences were observed in the numbers of eosinophils and lymphocytes in the granulomas and in the size of the granulomatous reaction. The same pattern of immunohistochemical labelling was seen in both groups. CD79alpha(+) B cells were scarce except in granuloma-associated lymphoid follicles;the majority of lymphocytes in granulomas and at other sites were CD3epsilon(+) T cells. The granulomatous reaction in the livers of piglets to schistosoma eggs from prenatal S. japonicum infection was similar to that seen in postnatal infection. Signs of immunomodulation of granulomas between the two timepoints of infection were not demonstrable.

Dynamics of collagen, MMP and TIMP gene expression during the granulomatous, fibrotic process induced by Schistosoma mansoni eggs

In schistosomiasis mansoni, granulomatous inflammation and fibrotic resolution are the major pathogenetic factors. The outcome of fibrosis is influenced by the deposition of collagen and degradation mediated by matrix metalloproteinases (MMP). There is a dearth of data on the expression of MMP and the tissue inhibitors of metalloproteinase (TIMP) during the fibrosis associated with schistosomiasis. In this study, the dynamics of collagen, MMP and TIMP gene expression were analysed during murine Schistosoma mansoni infection. Expression within the granulomatous liver tissue of the genes coding for collagen of types I, III and IV was up-regulated at the onset of granuloma development, and the dominant type-I expression peaked at the chronic, fibrotic stage. The amount of deposited hepatic collagen increased with the chronicity of the infection, indicating cumulative fibrosis. Collagenase, gelatinase, stromelysin, matrilysin-specific gene activities were similarly up-regulated, but only MMP-8 (collagenase-2) expression peaked at the height of fibrosis. TIMP-1 gene expression gradually increased during the course of the disease and, along with TIMP-2, peaked at the chronic, fibrotic stage. Granuloma myofibroblasts expressed both MMP and TIMP-1 genes. In ELISA of the splenic cytokines, high levels of fibrogenic interleukin-13 and moderate production of transforming growth factor-beta were found to be concurrent with fibrosis. These data indicate that an imbalance in MMP:TIMP expression and fibrogenic cytokine production are associated with cumulative fibrosis.

Expression of matrix metalloproteinases and their inhibitors during the resorption of schistosome egg-induced fibrosis in praziquantel-treated mice

Schistosomiasis mansoni is a tropical helminthic disease characterized by parasite egg-induced granulomatous inflammation and cumulative fibrosis. Because fibrosis is influenced by the imbalance between degradative matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), we analysed the resorption of fibrous tissue and MMP/TIMP expression in the livers of S. mansoni-infected and praziquantel-cured mice. Worm elimination significantly enhanced survival rate, ameliorated the granulomatous pathology and reduced collagen I, III and IV gene expression at 6 and 12 months post-treatment. Compared to 6 months infected, untreated controls, liver fibrous tissue was resorbed by 71.4% at 12 months after treatment. At 3 months post-treatment, expression of the MMP-2, -3, -8, -10, -13, -14 and -16 genes decreased compared with untreated controls. By 6 months, a highly significant increase in MMP-10 gene expression was manifest. At 12 months, messages for all MMP genes decreased in relation to untreated controls. TIMP-1, -2 and -3 gene expression drastically decreased between 3 and 6 months. At 1 year, only TIMP-1 expression was significantly diminished. Overall, profibrogenic tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta and inducible nitric oxide synthase (iNOS) gene expression decreased. Antigen-stimulated splenocytes secreted significantly higher levels of interleukin (IL)-4, IL-5, IL-10 and IL-13 cytokines between 3 and 12 months after treatment. Production of interferon (IFN)-gamma was higher than in untreated controls 3 and 6 months after treatment. In conclusion, praziquantel-treated mice showed a slow resorption of liver fibrous tissue. Resorption is attributed to the precipitous drop in TIMP-1 gene expression level, which shifted the balance in favour of MMP message expression and presumed enhanced collagenase activity.

Alteration of the purinergic modulation of enteric neurotransmission in the mouse ileum during chronic intestinal inflammation

1. The effect of chronic intestinal inflammation on the purinergic modulation of cholinergic neurotransmission was studied in the mouse ileum. Chronic intestinal inflammation was induced by infection of mice with the parasite Schistosoma mansoni during 16 weeks. 2. S. mansoni infection induced a chronic inflammatory response in the small intestine, which was characterised by intestinal granuloma formation, increased intestinal wall thickness, blunted mucosal villi and an enhanced activity of myeloperoxidase. 3. In control ileum and in chronically inflamed ileum, electrical field stimulation (EFS) of longitudinal muscle strips induced frequency-dependent contractions that were abolished by tetrodotoxin (TTX) and atropine. Carbachol induced dose-dependent contractions that were not affected by TTX but abolished by atropine. 4. In control ileum, adenosine and ATP dose-dependently inhibited the contractions to EFS. Theophylline and 8-phenyltheophylline, P(1) and A(1) receptor antagonists respectively, prevented this inhibitory effect of adenosine and ATP. PPADS, DMPX and MRS 1220, antagonists of P(2), A(2) and A(3) receptors, respectively, did not prevent this inhibitory effect of adenosine and ATP. Adenosine and ATP did not affect the contractions to carbachol. 5. The inhibitory effect of adenosine and ATP on contractions to EFS in control ileum was mimicked by the stable adenosine analogue methyladenosine and by the A(1)-receptor agonist N(6)-cyclohexyladenosine, but not by the A3 receptor agonist 2-Cl IB-MECA or by the ATP analogues alphabeta-methylene-ATP and ADPbetaS. The inhibitory effect of adenosine on contractions to EFS was lost after prolonged (90 min) treatment of control ileum with methyladenosine (100 micro M). 6. In chronically inflamed ileum, adenosine, methyladenosine, N(6)-cyclohexyladenosine and ATP all failed to inhibit the cholinergic nerve-mediated contractions to EFS. Also theophylline, 8-phenyltheophylline, PPADS, DMPX and MRS 1220 had no effect on the contractions to EFS and carbachol. The loss of effect of adenosine and ATP was still evident after 52 weeks of infection. 7. These results indicate that in physiological conditions neuronal adenosine A(1) receptors modulate cholinergic nerve activity in the mouse ileum. However, during chronic intestinal inflammation, this purinergic modulation of cholinergic nerve activity is impaired. This suggests that chronic intestinal inflammation leads to a dysfunction of specific neuronal regulatory mechanisms in the enteric nervous system.

When T-helper cells don't help: immunopathology during concomitant infection

Disease directly caused by immune system action is known as immunopathology. Many factors may lead the immune system to cause rather than cure disease, and autoimmune, allergic, and infection-related immunopathological diseases affect millions of people worldwide. This review presents an analysis of T-helper cell mediated, infection-related immunopathology within the framework of evolutionary ecology. A proximate cause of infection-related immunopathology is an error in the type of T-helper response induced. Distinct subsets of T-helper cells enable different effector mechanisms and therefore work optimally against different types of parasites (e.g., extracellular versus intracellular parasites). Immune responses that cure rather than cause disease require that the T-helper subset be tailored to the parasite. It is thus critical for the immunophenotype to match the "environment" of the parasitic infection. As in other cases of adaptive plasticity, a mismatch between an organism's phenotype and the selective environment can decrease fitness. T-helper response induction may be confounded by coinfection of a single host by multiple parasite species. Because of normally adaptive feedback loops that lend to polarize T-helper responses, it can become impossible for the immune system to mount effective, conflicting responses concurrently. Immunophenotype-environment mismatches may thus be inevitable when simultaneous, conflicting immune responses are required. An ultimate cause of infection-related immunopathology in a multiparasite selection regime is the T-helper response polarization that can propagate response errors and constrain the ability of the immune system to resolve conflicting response requirements. A case study is used to illustrate how coinfection can exacerbate immunopathology and to frame testable predictions about optimal responses to coinfection (e.g., is the observed joint response to coinfection accurately predicted by the average of the component single-infection optimal responses, where the single-infection optima are weighted by the contribution of each to fitness). The case study includes immunological and pathological data from mice infected by Schistosoma mansoni alone and by S. mansoni in combination with Toxoplasma gondii. Such data can inform hypothesis tests of evolutionary ecological principles, and ecological analysis can in turn clarify assumptions about responses to coinfection for a greater understanding of the immune system. The synthesis of evolutionary ecology and immunology could therefore be of mutual benefit to the two disciplines.

Effect of somatostatin on gastrointestinal contractility in Schistosoma mansoni infected mice

Schistosoma mansoni infection induces severe gastrointestinal motility disturbances which are characterised by hyperactivity of intestinal muscle, abdominal pain, diarrhoea, vomiting and nausea. During schistosomiasis, the neuropeptide somatostatin is generated within inflammatory granulomas. However, somatostatin is also an important inhibitory modulator of gastrointestinal motility. In the present study, we have investigated the potential of somatostatin to reduce schistosomiasis-induced hyperactivity of gastrointestinal smooth muscle. Organ bath experiments were performed to study the contractility of isolated smooth muscle strips of intestine from control mice and from mice that were infected with S. mansoni for 2, 4, 8 and 16 weeks. Electrical field stimulation (0.5-8 Hz) of enteric nerves induced frequency-dependent neurogenic contractions of cholinergic origin in all regions of the small intestine. Somatostatin (0.1-1 microM) concentration-dependently inhibited the contractions to enteric nerve stimulation in the small intestine from uninfected control mice and from acutely S. mansoni infected mice (2 and 4 weeks of infection). After 8 weeks of infection with S. mansoni, this inhibitory effect of somatostatin was less pronounced and after 16 weeks of infection it was completely abolished. Histology demonstrated that chronic infection of mice with S. mansoni was associated with significant alterations in the musculature of the small intestine. These alterations may be associated with physiological changes in the responsiveness to somatostatin and suggest that the somatostatin neuroregulatory circuit of enteric neurotransmission in the small intestine is disturbed during chronic schistosomiasis mansoni.

Rational basis for oligodeoxynucleotides to inhibit collagen synthesis in lung fibroblasts and primary fibroblasts from liver granulomas of Schistosoma mansoni-infected mice

Hepatocellular carcinoma is associated with liver fibrosis. Murine schistosomiasis infection offers a model to study hepatic fibrogenesis. Single-stranded phosphorothiate oligodeoxynucleotides containing the TGF-beta regulatory element have been shown to regulate the transcription of this gene and effectively inhibit collagen synthesis in primary fibroblasts isolated from schistosomiasis-induced hepatic granulomas. While the single-stranded oligos did not decrease collagen and non-collagen protein synthesis below control levels, their double-stranded modified and unmodified counterparts did. Competitive cold oligodeoxynucleotide gel mobility shift analysis using control fibroblast nuclear extract demonstrated that the single-stranded oligos diminished binding of the TGF-beta activator protein to the TGF-beta regulatory element while the double-stranded oligos totally inhibited this binding. TGF-beta element containing single-stranded phosphorothioate oligodeoxynucleotides and their double-stranded counterparts may be successful therapeutic agents to inhibit hepatic fibrogenesis and associated hepatocellular carcinoma.

Effect of Schistosoma mansoni-induced granulomatous inflammation on murine gastrointestinal motility

In Schistosoma mansoni-infected mice, gastrointestinal transit was measured in vivo and the neuromuscular function of longitudinal muscle strips of inflamed ileum and noninflamed gastric fundus was assessed in vitro. Eight weeks after infection, the ileal wall was acutely inflamed, as shown by a mucosal inflammatory infiltrate, leading to an increase in mucosal thickness, in myeloperoxidase (MPO) activity, and in interleukin (IL)-1beta production. At that time, both gastrointestinal transit and in vitro ileal contractility were normal. Twelve weeks after infection, chronic granulomatous inflammation led to proliferation of the muscle layer and to a further increase in MPO activity, whereas IL-1beta production normalized. Gastrointestinal transit was decreased, whereas in vitro ileal contractility was increased irrespective of the contractile stimulus. In vitro incubation with IL-1beta (10 ng/ml for 60 min) significantly increased ileal contractility only at 8 wk after infection. Indomethacin, tetrodotoxin, and atropine had no differential effect on ileal contractility in controls and infected mice. In vitro contractility of noninflamed gastric fundus was normal both 8 and 12 wk after infection. We conclude that intestinal schistosomiasis 8 wk after infection is associated only with structural changes of the ileum, whereas 12 wk after infection, both structural and functional changes are present. These changes are characterized by increased ileal wall thickness, decreased gastrointestinal transit, and increased smooth muscle contractility restricted to the inflamed gut segment.

Anti-miracidial effect of recombinant glutathione S-transferase 26 and soluble egg antigen on immune responses in murine schistosomiasis mansoni

The anti-miracidial potential of recombinant Schistosoma mansoni glutathione S-transferase 26 (rSmGST26) or native crude soluble egg antigens (SEA) was assessed. The associated dynamics of granuloma formation and immune responses were evaluated. Naive C57BL/6 mice were injected intravenously with multiple doses of either SEA (SEA-group) or rSmGST26 (GST-group) 7 days before cercarial infection. The immunized groups and the respective controls were sacrificed 6, 8 and 16 weeks postinfection (p.i.). Acceleration of ova destruction and reduction of granuloma diameter were greater in the GST-group than the SEA-group, mainly at 8 weeks p.i. However, the amelioration of hepatic pathology and function was more evident in the SEA-group. Concurrently, serum-specific IgG1 levels were elevated throughout the course of infection in the immunized groups compared to the infected controls. Initial rise of all splenic cytokines and serum anti-SEA IgE levels at 6 weeks p.i. was observed, followed by a dramatic drop in the levels of the proinflammatory cytokines IL-2, IFNgamma, IL-4 and TNF-alpha and IgE at 8 weeks of infection. IL-10 level was lower at 8 weeks p.i. than at 6 weeks, but was higher in immunized groups than in infected controls. Several responses may be implicated as an outcome of the present immunization protocol, such as increased levels of blocking antibody (IgG1) and IL-10 with decreased levels of proinflammatory cytokines and IgE.

Protection against Schistosoma mansoni infection with a recombinant baculovirus-expressed subunit of calpain

Infections by human schistosomes, in particular Schistosoma mansoni, account for significant morbidity and mortality every year in tropical and sub-tropical areas. The eggs of the parasite induce pathological changes in the infected host; in chronic and heavy infections, these changes may lead to death. A well-designed anti-schistosomal vaccine, alone or in concert with existing control measures such as chemotherapy, may prove to be a safe, inexpensive, and effective means of reducing the occurrence of severe disease and death in S. mansoni infection. Previous studies have demonstrated the importance of the syncytial layer containing the apical plasma membrane (APM) of S. mansoni in both the survival of the parasite in the mammalian host and as a potential source of immunogens which may be utilized as vaccine candidates. In this paper, we present evidence for the protective capacity of several schistosomal antigen preparations, including a calcium binding protein of the APM, S. mansoni calpain (GenBank accession no. M74233). We have constructed and characterized expression of a recombinant baculovirus expressing the large subunit of S. mansoni calpain, Sm-p80. This recombinant Sm-p80 is recognized by IgA, IgM, IgG1, and IgG3 isotype antibodies found in S. mansoni-infected human sera and partially-purified recombinant Sm-p80 provided a 29-39% reduction in worm burden in immunized mice challenged with S. mansoni. Our data indicate that Sm-p80 may be a useful vaccine antigen for the reduction of the morbidity associated with S. mansoni infections of mammalian hosts.

Induction of hepatic egg granuloma hyporesponsiveness in murine schistosomiasis mansoni by intravenous injection of small doses of soluble egg antigen

This work was designed to test whether hyporesponsiveness to schistosomal egg antigen (SEA) was associated with reduction in size of hepatic granulomas. Multiple small doses of SEA (10 micrograms x 4) were injected intravenously (i.v.) into C57B1/6 mice either at 7 or 30 days prior to cercarial exposure. Eight weeks postinfection, hepatic histopathology and granuloma diameter were studied. SEA-induced lympho-proliferative response, splenic cytokines (IL-2, IL-4 and IL-5) and serum antischistosomal IgG were assessed. Worm burden and tissue egg load were counted. Compared to infected controls, the SEA-treated groups showed decrease in granuloma diameter, remarkable increase in the percentage of degenerated ova within hepatic granulomas and amelioration of histopathological changes. SEA lymphoproliferative response, and levels of Il-2 and IL-4, were lower in SEA-treated groups than infected controls. The levels of IL-5 and antishistosomal IgG were comparable to the infected controls. The intensity of infection was not influenced by i.v. injection of SEA. The present data show that i.v. administration of multiple small doses of SEA induced granulomatous hyporesponsiveness with amelioration of hepatic pathology and acceleration of egg destruction.

Schistosomiasis vaccine development--the current picture

Development of a vaccine for schistosomiasis, a parasitic disease currently affecting over 200 million people worldwide, has been targeted as a priority by the World Health Organisation. Research demonstrating the ability of humans to acquire natural immunity to schistosome infection, together with the successful use of attenuated vaccines in animals both under laboratory and field conditions, suggest that development of a human vaccine is feasible. Attenuated vaccines for schistosomiasis are considered neither safe nor practicable for human use, however, and therefore other approaches must be considered. This review examines progress currently being undertaken in a number of different areas towards achieving the goal of a safe and effective human vaccine for schistosomiasis.