Schistosoma mansoni: the therapeutic efficacy of oxamniquine is enhanced by immune serum

Immunohistochemical Investigations of Treatment with Ro 13-3978, Praziquantel, Oxamniquine, and Mefloquine in Schistosoma mansoni-Infected Mice

To date, there is only one drug in use, praziquantel, to treat more than 250 million people afflicted with schistosomiasis, a debilitating parasitic disease. The aryl hydantoin Ro 13-3978 is a promising drug candidate with in vivo activity superior to that of praziquantel against both adult and juvenile Schistosoma mansoni organisms. Given the drug's contrasting low activity in vitro and the timing of its onset of action in vivo, it was postulated that immune-assisted parasite clearance could contribute to the drug's in vivo activity. We undertook histopathological studies to investigate this hypothesis. Infected mice were treated with an effective dose of Ro 13-3978 (100 mg/kg of body weight) and were dissected before and after the drug's in vivo onset of action. The veins and livers were excised, paraffin-embedded, and sectioned, and macrophages (IBA-1), neutrophils (Neutro), B cells (CD45R), and T cells (CD3) were stained by immunohistochemistry. For comparison, samples from infected untreated mice and mice treated with effective doses of praziquantel (400 mg/kg), oxamniquine (200 mg/kg), and mefloquine (200 mg/kg) were examined. At 24 h after treatment with Ro 13-3978, significant macrophage recruitment to the veins was observed, along with a modest increase in circulating B cells, and at 48 h, neutrophils and T cells are also present. Treatment with praziquantel and oxamniquine showed similar patterns of recruitment but with comparatively higher cellular levels, whereas mefloquine treatment resulted in minimal cell recruitment until 3 days posttreatment. Our study sheds light on the immediate immune responses to antischistosomal treatment in mice and provides further insight into immune effector mechanisms of schistosome clearance.

Acute schistosomiasis mansoni: revisited and reconsidered

Acute schistosomiasis is a systemic hypersensitivity reaction against the migrating schistosomula and eggs. A variety of clinical manifestations appear during the migration of schistosomes in humans: cercarial dermatitis, fever, pneumonia, diarrhoea, hepatomegaly, splenomegaly, skin lesions, liver abscesses, brain tumours and myeloradiculopathy. Hypereosinophilia is common and aids diagnosis. The disease has been overlooked, misdiagnosed, underestimated and underreported in endemic areas, but risk groups are well known, including military recruits, some religious congregations, rural tourists and people practicing recreational water sports. Serology may help in diagnosis, but the finding of necrotic-exudative granulomata in a liver biopsy specimen is pathognomonic. Differentials include malaria, tuberculosis, typhoid fever, kala-azar, prolonged Salmonella bacteraemia, lymphoma, toxocariasis, liver abscesses and fever of undetermined origin. For symptomatic hospitalised patients, treatment with steroids and schistosomicides is recommended. Treatment is curative in those timely diagnosed.

Current chemotherapy arsenal for schistosomiasis mansoni: alternatives and challenges

Schistosomiasis still represents a major health problem in many tropical and subtropical countries despite continuing control efforts. Due to the unavailability of a vaccine that is practically applicable to humans, the use of chemotherapy is the mainstay of schistosomiasis-associated morbidity control. This paper attempts to review the antischistosomal drugs currently used in the treatment of intestinal schistosomiasis caused by Schistosoma mansoni. Their antischistosomal properties, advantages, and disadvantages as well as issues regarding the evidence for drug resistance and combination studies are reviewed in a simple manner. The recent trends towards the identification of specific chemotherapeutic targets for the treatment of schistosomes are also discussed briefly.

Schistosomiasis mansoni and severe gastrointestinal cytomegalovirus disease in a patient with acquired immunodeficiency syndrome

The behavior of the Schistosoma mansoni infection in patients with AIDS has not been explored. The case of a young woman with schistosomiasis mansoni, AIDS, and cytomegalovirus disease is reported. The authors suggest that the helminth was not a bystander in this case, or rather, by interfering with the host's immune response, it set the stage for the development and/or aggravation of the viral infection.

The immune dependence of chemotherapy

In this review, Mike Doenhoff and colleagues discuss the immune dependency of chemotherapy and the consequences for drug resistance. They also consider the implications for the control of infections that are relatively unresponsive to drugs, such as opportunistic infections in immunosuppressed patients.

Schistosomiasis and associated infections

In hospital-based series viral hepatitis B has been frequently described in association with schistosomiasis whilst in field-based studies the association has not been confirmed. The association between schistosomiasis and Salmonella bacteraemia has been well documented. More recently, acute schistosomiasis has been shown to be a facilitating factor in the genesis of pyogenic liver abscesses caused by Staphylococcus aureus. New evidences indicate an interaction between the acquired immunodeficiency syndrome (AIDS) and schistosomiasis. In this paper, data on the association of schistosomiasis with other infections are updated.

Immunostimulation as adjuvant for the chemotherapy of experimental schistosomiasis

Immunosuppressed animals respond poorly to schistosomal chemotherapy and a proper response can be restored by the administration of immune serum. Present study attempts to search whether immunological stimulation would increase drug effectiveness. Swiss mice infected with 50 S. mansoni cercariae were later treated with complete Freund's adjuvant. Treatment with oxamniquine was made with 100 mg/kg.b.w., 25 mg/kg.b.w. and 50 mg/kg.b.w., the last two doses representing a fourth and a half of the recommended curative dose. Appropriate controls for the drug, the adjuvant and the infection were also studied. The serum-level of anti-S. mansoni antibodies (ELISA) and recovery of worms by perfusion of the portal vein system were the evaluated parameters. Statistical analysis of the results failed to reveal significant differences in worm recovery between adjuvant-stimulated animals treated with oxamniquine and any of the treated controls receiving the same amount of the drug. Although total lack of immunity interferes with curative treatment the usual immune response seems to be sufficient to allow for curative drug action in schistosomiasis and thus apparently does not need to be artificially stimulated.

Schistosomiasis. Pathophysiology, diagnosis, and treatment

Globally, schistosomes infect 1 in 30 people. Tourists travel to endemic areas, whereas students, workers, and expatriates travel to nonendemic areas. Physicians around the world need to remain aware of this common parasitic infection. Pathology results from parasite eggs that lodge in the intestines and liver. Intestinal schistosomiasis is most often asymptomatic and presents with occult gastrointestinal bleeding. Hepatosplenic schistosomiasis develops insidiously because of cumulative fibrotic injury. Stigmata of liver failure are absent unless comorbid viral or alcoholic hepatitis is present. Patients with end-stage hepatosplenic schistosomiasis die from variceal hemorrhage. Diagnosis of schistosomiasis is confirmed by finding eggs in stool or biopsy specimens. Antischistosome antibodies may identify infected tourists returning from endemic areas. Circulating schistosome antigens distinguish current from past infections. Praziquantel is the schistosomicidal drug of choice. Most cases of hepatosplenic schistosomiasis resolve after effective treatment. Prophylactic propranolol may prevent hemorrhage in praziquantel-treated patients with high-grade varices. Sclerotherapy is also efficacious. When necessary, patients with hepatosplenic schistosomiasis tolerate decompressive surgery well.

Temporal differences in praziquantel- and oxamniquine-induced tegumental damage to adult Schistosoma mansoni: implications for drug-antibody synergy

A temporal study of the effects on the tegument of Schistosoma mansoni adult worm following in vivo praziquantel and oxamniquine treatment was performed. Drug-induced damage to the tegument, exposure of surface antigens and attachment of host antibody occurred rapidly, within 1 h, following praziquantel treatment. Oxamniquine-treated worms required 4-8 days for these effects to be apparent. The 2 drugs differed in the degree and sites of damage on the worm surface. The administration of 2 different polyspecific rabbit sera with drug significantly increased the efficacy of praziquantel when administered with the drug, but not when given 6-9 days after drug treatment. In contrast, only 1 serum was synergistic with oxamniquine when administered with drug and both sera were synergistic when given 6-9 days after drug treatment. The effect of immune killing of drug-treated worms is discussed.

Efficacy of treatment of murine Schistosoma mansoni infections with praziquantel and oxamniquine correlates with infection intensity: role of host antibody

The reduction in worm burden obtained by treatment of Schistosoma mansoni with praziquantel and oxamniquine was greater in mice with heavy infections than in relatively lightly infected animals. The reduction in worm burden achieved by each drug correlated with the size of the pre-treatment worm burden (r2 = 0.82 and 0.81 for praziquantel and oxamniquine, respectively). Intensity of infection did not affect the degree of tegumental damage and drug-induced antigen exposure on worms recovered soon after treatment with praziquantel. However, praziquantel-treated worms from mice with heavy infections had significantly more murine antibody attached to the treated-worm surface than worms from praziquantel-treated lightly infected mice. Heavily infected mice had greater levels of circulating anti-worm antibodies than lighter infected mice. The correlation between infection intensity and cure rates achieved by praziquantel and oxamniquine may thus be a reflection of the higher titres of relevant antibody in heavily infected mice mediating death of drug-treated worms.

Active immunization of mice with Schistosoma mansoni worm membrane antigens enhances efficacy of praziquantel

The efficacy of praziquantel treatment was significantly enhanced (P < 0.01) in CBA/Ca mice that had been immunized prior to Schistosoma mansoni infection with a crude extract of worm membrane antigens. In Western immunoblots sera from the worm antigen-immunized animals had a polyspecific antibody response, with a 25-27 kDa antigen being reacted against with particular intensity. A molecule of similar size was also recognized by rabbit antisera raised against an antigen with esterase activity that has been previously identified as a sensitive target for drug-antibody synergy. The increase in efficacy of subcurative doses of praziquantel in immunized animals is attributed to drug-induced tegumental damage causing antigens to become exposed on the worm surface. Thus, specific antigens, including the 25-27 kDa antigen, become accessible to circulating schistosomicidal antibodies. The role of antibodies that can synergize with praziquantel to kill schistosome worms is discussed.

Immune-dependent chemotherapy of schistosomiasis

Host immune responses have been shown to enhance the efficacy of several schistosomicidal drugs. The evidence derives mainly from experiments on Schistosoma mansoni infections in the mouse with their immune status variously modulated; this review emphasises praziquantel (PZQ), which is now the main drug used for treatment of human schistosomiasis. Electron microscopy and indirect immunofluorescence indicate that PZQ disrupts the integrity of the surface membranes of S. mansoni, particularly those covering the dorsal tubercles of adult male worms, and this causes antigens which are the targets of antibody attack to be revealed. We review the evidence that two S. mansoni antigens in particular are implicated in the immune-dependent action of PZQ: a 200 kDa glycoprotein and a 27 kDa antigen with non-specific esterase activity. Consistent with the involvement of the latter antigen, increased non-specific esterase activity was demonstrated histochemically on the surface of intact PZQ-treated male worms, and we describe a chromogenic substrate assay for quantifying the amount of esterase activity that is exposed after drug treatment. The potential relevance of these observations for enhancing the efficacy of drugs currently used to treat human schistosomiasis, and for devising novel therapeutic strategies, is discussed.