Drug resistance to schistosomicides and other anthelmintics of medical significance

It is usual for people to be infected for some period in life with parasitic worms, which may cause morbidity or even kill. Anthelmintics are used for the treatment and control of the human helminthiases, since no vaccines are yet available. Despite the widespread use of these compounds, drug resistance has become apparent only with antischistosomal chemotherapy, in contrast to the situation with other anti-infective agents in human medicine and with veterinary anthelmintics, where resistance is widespread. This paper reviews research on drug resistance in human helminthiasis with emphasis on schistosomicidal drugs.

Evaluation of external-beam radiation therapy plus 5-fluorouracil (5-FU) versus external-beam radiation therapy plus hycanthone (HYC) in confined, unresectable pancreatic cancer

From March 1981 to November 1987, 87 patients with histologically confirmed pancreatic adenocarcinoma, unresectable but confined to the pancreatic region, were randomized to two treatments. The standard treatment was 40-50 Gy external-beam radiation therapy (RT) to gross tumor plus potential microscopic tumor with a 5 Gy boost to gross tumor plus a 1.5-2.0 cm margin, using multiple fields and 5-fluorouracil (5-FU) 500 mg/m2/d intravenously by rapid infusion. The 5-FU was given each of the initial 3 days of each of three 20 Gy radiation courses. The experimental treatment used identical radiation fields, but the two Gy daily radiation fractions were administered in a continuous course to a total dose of 50 Gy. Hycanthone was administered 60 mg/m2 intravenously within 2 to 4 hr during each day of the 5-day course of infusions during the first and fifth weeks of radiation therapy. There was no statistically significant difference between treatment arms in survival (p = 0.82) or disease-free survival (p = 0.27). Seven percent of hycanthone-treated patients demonstrated hepatic toxicity which was usually mild in nature. There was, however, one death due to hepatic toxicity.

Schistosoma mansoni-induced mesangiocapillary glomerulonephritis: influence of therapy

Schistosomiasis mansoni has been well documented as one of the causes of infectious glomerulopathy, with mesangiocapillary glomerulonephritis being the most frequent lesion observed in this condition. Twenty-one patients with hepatosplenic schistosomiasis mansoni and biopsy-documented mesangiocapillary glomerulonephritis (MCGN) were studied and compared with 19 patients with the idiopathic form of MCGN. Nephrotic syndrome was the most frequent clinical presentation in both groups. At the time of diagnosis nine patients with hepatosplenomegaly (4 with associated arterial hypertension) and 12 (8 with arterial hypertension) among the patients with idiopathic MCGN had renal insufficiency. At the end of the follow-up period 16 patients with hepatosplenic schistosomiasis and MCGN (75.2 months) and 15 with the idiopathic form (52.1 months) had renal failure. Also, when compared at 48 months of follow-up, no difference in renal function could be detected in both groups. No benefits related to anti-parasitic treatment in the schistosomiasis group and immunosuppression therapy in either group could be documented. The progression of the renal disease, as assessed by the reciprocal of serum creatinine versus time, and the survival curve, were not different between the two groups. It is concluded that MCGN in patients with the hepatosplenic form of schistosomiasis mansoni is a progressive disease not influenced by anti-parasitic or immunosuppressive therapy, and presents a clinical course similar to that of the idiopathic form.

Experimental chemotherapy of Schistosoma curassoni in mice

Mice experimentally infected with Schistosoma curassoni were treated with different dose regimens of praziquantel, metrifonate, oxamniquine and hycanthone. Praziquantel was the most effective drug; a dose of 100 mg/kg given orally for 5 days resulted in a 95% reduction in worm burdens. The drug produced oogram changes in all animals. Metrifonate did not result in a reduced worm burden but caused oogram changes even on a low-dose (150 mg/kg during 2 consecutive days) schedule. Oxamniquine proved to be ineffective; no reduction in worm burdens or alterations in oograms were observed. Hycanthone (80 mg/kg for 1 day) resulted in a significant reduction in worm burdens.

Effect of chemotherapy on hepatic collagen and glycosaminoglycan metabolism in Schistosoma mansoni-infected mice

The dynamics of biosynthesis and accumulation of collagenous proteins and glycosaminoglycans (GAGs) in liver granulomas induced by eggs of Schistosoma mansoni were studied in mice following eradication of adult worms by chemotherapy. The relatively synchronous granulomas around parasite eggs were isolated from the livers at ensuing 2-week intervals; the number of recoverable granulomas per liver gradually decreased and was 7% of initial values at 20 weeks. Hepatic or granuloma-associated extracellular matrix components increased for 4 weeks after treatment despite cessation of ova deposition. At 12 weeks after chemotherapy the rate of GAG biosynthesis per total liver granuloma fraction, measured by 3H-glucosamine incorporation, decreased dramatically; this was followed by a decrease in the amount of GAGs present. The rate of collagen biosynthesis per total liver granuloma fraction, measured by 3H-proline incorporation, began to decline at 14 weeks and a decrease in the amount of collagen present was noted at 16 weeks. Our results demonstrated that liver granulomas induced by S. mansoni eggs synthesize collagens and GAGs for about 4-6 weeks following parasitological cure. The subsequent resolution of granulomas proceeds first by a reduction in GAG biosynthesis followed 4-8 weeks later by decreased collagen biosynthesis, followed by accelerated resolution of both collagen and GAGs.

Preparation and antischistosomal and antitumor activity of hycanthone and some of its congeners. Evidence for the mode of action of hycanthone

The synthesis of a series of esters of hycanthone (HC) and 7-hydroxyhycanthone, their antitumor activity, and their antischistosomal effects on HC-sensitive and HC-resistant schistosomes are reported. Binding studies using tritium-labeled HC and hycanthone N-methylcarbamate (HNMC) with calf thymus DNA provided evidence that HNMC but not HC alkylated the DNA. Tritiated HNMC also bound to the DNA of intact HeLa cells exposed to the drug while very little tritiated HC bound to DNA under the same conditions. The mechanism proposed previously to account for the antischistosomal action of HC, namely, drug esterification followed by alkylation of DNA, applies also to the antitumor action of the drug as shown in Scheme I.

The influence of anti-parasitic therapy on the course of the glomerulopathy associated with Schistosomiasis mansoni

Although several aspects of the association between S. mansoni infection and renal disease are well known, the influence of the anti-parasitic therapy on the clinical course of the glomerulopathy remains undefined. With the aim of studying this aspect, 16 patients with glomerulopathy associated with schistosomiasis mansoni were evaluated (proteinuria and levels of BUN and creatinine) before therapy, 1 week, 1 month, 2-3 months and 6 months after therapy of the parasitic infections. During the follow-up of such cases no benefit could unquestionably be demonstrated in the patients. Also, no permanent deterioration of renal function related to anti-parasitic therapy could be documented. It is concluded that the treatment of the S. mansoni infection, once the consequent glomerulopathy is clinically apparent, does not influence the clinical course of the disease.

Anti-schistosomal drugs: observations on the mechanism of drug resistance to hycanthone, and on the involvement of host antibodies in the mode of action of praziquantel

This paper reports recent observations from our laboratory dealing with the anti-schistosome drugs hycanthone (HC) and praziquantel (PZQ). In particular, we discuss a laboratory model of drug resistance to HC in Schistosoma mansoni and show that drug sensitive and resistant lines of the parasite can be differentiated on the basis of restriction fragment length polymorphisms using homologous ribosomal gene probes. In addition, we summarize data demonstrating that effective chemotherapy of S. mansoni infection with PZQ in mice requires the presence of host anti-parasite antibodies. These antibodies bind to PZQ treated worms and may be involved in an antibody-dependent cellular cytotoxicity reactions which result in the clearance of worms from the vasculature.

Evolution of the schistosomal hepatic lesions in mice after curative chemotherapy

Mice with 64-day-old Schistosoma mansoni infection (+/- 27 worms, 8-12 pairs) were treated simultaneously with oxamniquine and hycanthone. The cure rate was 100%, and changes occurring thereafter in the liver were sequentially followed by means of histologic, ultrastructural, and immunofluorescence methods. Soon after treatment, hepatitic changes cleared up and periovular granulomas diminished in size. The predominant Type III collagen in granulomas was reduced, and the Type I showed no apparent increase, whereas Type IV did not seem to participate in the process. Collagen fibrils in periovular granulomas changed in texture from dense and more oriented to loose and disorganized. Fibroblasts, at first with marked signs of hyperfunction, became less so at a time when collagen fragments appeared within secondary lysosomes in macrophages and fibroblasts. Schistosomal ovular antigens remained sequestered inside the fibrotic granulomas up to the final, 39th day after treatment. Thus, specific treatment of schistosomiasis showed a beneficial effect upon the hepatic lesions from the very beginning and promoted changes in the periovular granulomas that indicated a rapid, although incomplete, resorption of fibrosis.

Schistosoma mansoni: chemotherapy of infections of different ages

Mice were treated with potassium antimony tartrate, hycanthone, oxamniquine, niridazole, or praziquantel at different times after infection with Schistosoma mansoni. The rate of cure was assessed by perfusion of surviving worms approximately 4 weeks after treatment, and the percentage reduction in worm burden was estimated relative to the number of adult worms perfused from control mice, comparably infected but untreated. All six drugs were relatively inactive against S. mansoni between 3 and 4 weeks after infection when compared with treatment at 5 to 6 weeks. However, the drugs differed in the patterns of cure they achieved in the 2-week period after administration of cercariae and in the period around the onset of patency. Worms that had been subjected to amoscanate or hycanthone in the third week after infection showed evidence of this as adults in having a reduced fecundity. Factors such as worm or host physiology, or host immune status may have had roles in the outcome of chemotherapy at different stages of maturation of S. mansoni.

Schistosoma mansoni: reduced efficacy of chemotherapy in infected T-cell-deprived mice

The effect of host immunosuppression on the efficacy of schistosomicidal chemotherapy has been tested in T-cell-deprived CBA mice infected with Schistosoma mansoni. The drugs hycanthone, oxamniquine, and praziquantel were found to kill fewer adult S. mansoni worms in deprived mice than in comparably infected strain-, age-, and sex-matched, immunologically intact controls. Inconsistent results were obtained with niridazole, and amoscanate was as effective in deprived mice as in controls. The possibility that hycanthone, oxamniquine, praziquantel, and previously studied antimony act synergistically with immune effector mechanisms in killing adult schistosomes is discussed.

The effect of repeated targeted mass treatment on the prevalence of schistosomiasis mansoni and the intensity of infection in Machakos, Kenya

In a valley in Machakos District, Kenya, the entire population was surveyed in 1976 for the presence and number of eggs of Schistosoma mansoni in their faeces. All persons with 300 or more eggs g-1 faeces were then treated with a single dose of hycanthone, 1.5 mg kg-1 body-weight. A re-survey was carried out in 1977, followed by the treatment of all persons with 200 or more eggs g-1 faeces. After another re-survey in 1978, all persons with 100 or more eggs g-1 were treated. The final survey was carried out in 1981. It was found that the treatment of persons with a high egg output had a pronounced effect on the intensity of infection in the total population, but that, after a first considerable drop in the prevalence rate, further decreases were much smaller. Continuing moderate prevalence rates in very young children were an indication of continuing transmission.

Schistosoma mansoni: an in vivo study of drug-induced autophagy in the gastrodermis

The effects of Astiban, Lucanthone, Hycanthone and Niridazole on autophagic activities in the gastrodermis of Schistosoma mansoni were determined in vivo, using different dosage levels and dosage times. With Astiban, high levels of autophagy were observed in the gastrodermis 2 hours after an injection of the drug into the mouse, and this response had declined by 20 hours, marking a recovery by the parasite from the drug. Hycanthone and Lucanthone produced an autophagic response several days after the onset of treatment, and no recovery was observed in the morphology of the gastrodermis after the drug was discontinued. The effects of Niridazole on the gastrodermis were to produce the most dramatic ultrastructural changes after high doses and over several days of treatment. With all the drugs examined, gastrodermal autophagy was characterized by the formation of vacuoles containing cell components, lipid droplets and sometimes hydrolytic enzyme reaction product. The autophagic vacuoles appeared to be formed by the sequestration of cytoplasmic material by the basal membrane infoldings, and the transfer of enzymes into the vacuole from within the limiting membrane. The residues from intracellular digestion appeared to be emptied into the caecal lumen.

Synthesis of new 8-(5-substituted amino-1,3,4-oxadiazol-2-yl) and 8-(5-substituted amino-1,3,4-thiadiazol-2-yl) methoxyquinolines with antibilharzial activity

Several 5-substituted amino-1,3,4-oxadiazol-2-yl and 5-substituted amino-1,3,4-thiadiazol-2-yl derivatives with different 8-hydroxyquinoline moieties in the 2-position were prepared and tested for their antiparasitic activity. Preliminary biological tests on mice experimentally infested with Schistosoma mansoni revealed that the new compounds show moderate schistosomicidal activity.

Genetic analysis of hycanthone resistance in Schistosoma mansoni

Interbreeding between hycanthone-resistant and hycanthone-sensitive schistosomes was achieved using a worm transfer technique which considerably reduced the length and the complexity of the operations generally involved in performing schistosome genetic crosses. A mouse was considered to harbor resistant schistosomes if, three weeks or more after a single intrasmuscular injection of 80 mg/kg hycanthone schistosome eggs were still excreted in the feces, at least one normal worm pair was obtained by perfusion, or miracidia could be seen hatching from the liver. The F1 hybrid progeny from crosses between sensitive and resistant schistosomes proved to be sensitive to hycanthone, irrespective of whether the resistant parent was the male or the female. The resistant phenotype reappeared in back-crosses and in the F2 progeny. These results could be confirmed using the traditional technique of single sex infections. It can thus be concluded that hycanthone resistance behaves like an autosomal recessive trait. These results suggest that hycanthone-resistant schistosomes are deficient in some factor, possibly an enzymatic activity which transforms hycanthone into a biologically active molecule, as suggested in a recent hypothesis on the mode of action of hycanthone.

Effect of chemotherapy on experimental pulmonary schistosomiasis

Mice with portal hypertension caused by portal vein ligation reproduced the model of severe pulmonary schistosomiasis when infected for 10 weeks with 30 cercariae of Schistosoma mansoni. Curative treatment promoted reversion, without fibrosis, of the periovular granulomatous lesions formed in the alveolar tissue. However, the arterial and arteriolar lesions were defectively repaired, with segmental vascular fibrosis, narrowing, and angiomatoid changes remaining for up to 120 days after treatment. There was also evidence that eggs are destroyed more rapidly and more completely in the lungs than in the liver.

Analogues of hycanthone and lucanthone as antitumor agents

Hycanthone analogues (5 and 6) containing 7-substituted hydroxyl groups were prepared and evaluated as antitumor agents. These compounds were significantly more active than the corresponding unsubstituted derivatives. The 7-hydroxylated 4-(hydroxymethyl)-9H-xanthen-9-ones, 11 and 12, were also active antitumor agents. However, the 7-hydroxy-9H-xanthen-9-one counterparts of the 7-hydroxylucanthones were totally devoid of antitumor activity. Results obtained thus far are consistent with the hypothesis that 4-hydroxymethyl substituents in the 9H-xanthen-9-one and 9H-thioxanthen-9-one series are required for antitumor activity.

Observations on possible immunity to reinfection among Kenyan schoolchildren after treatment for Schistosoma mansoni

In February 1977, 306 out of 409 six- to 16-year-old Kenyan schoolchildren were found to be infected with Schistosoma mansoni. Prevalence and intensity were directly related to age and indirectly to the distance between the child's home and the transmission site, but were not related to the child's sex. Most children were treated with hycanthone in July 1977. Pretreatment blood samples were taken from 100 study children for eosinophil counts and measurements of cytotoxic anti-schistosomular antibody levels. Blood and faecal samples were re-examined five times between November 1977 and July 1979. Whole school resurveys in July 1978 and 1979 confirmed the continuation of transmission after chemotherapy. 'Reinfection' rates in the study children, incorporating both failed treatment and true reinfections, were significantly reduced in children, with both detectable antibody and eosinophil counts above 400/mm3, compared with children with neither. Children with either detectable antibodies or high eosinophil counts (mainly the latter) had intermediate reinfection rates. Neither sex, age nor pretreatment intensities influenced reinfection rates, but location of dwelling did: children from distant homes had lower rates. However, the effects of residence and 'protection' were not directly linked. The implication of these results, namely that infection can confer immune protection to reinfection after treatment, is being explored in further studies.

Curative chemotherapy and resistance to reinfection in murine schistosomiasis

Complete parasitological cure was obtained by specific chemotherapy in mice with a 10-week-old infection induced by inoculating 30 cercariae of Schistosoma mansoni. By challenging the cured animals with 100 cercariae it was found that cutaneous and pulmonary reactivity to invading schistosomula, the ability to modulate periovular granulomas in the liver, and the resistance to reinfection, as measured by survival rates and recovery of worms from the portal vein system, persisted for 1 and 2 months following treatment and disappeared after 6 months. Thus, a residual immunity and reactivity to reinfection seems to persist in the host for some time after curative chemotherapy of schistosomiasis.

Use of praziquantel in patients with schistosomiasis mansoni previously treated with oxamniquine and/or hycanthone: resistance of Schistosoma mansoni to schistosomicidal agents

Fourteen patients with active schistosomiasis mansoni in spite of previous treatment with oxamniquine and/or hycanthone were treated with praziquantel, single oral dose of 45 to 50 mg/kg body-weight. All underwent clinical, laboratory and electrocardiographic examination before and after treatment. Untoward effects (dizziness, drowziness, nausea and abdominal pain) were observed in ten. Laboratory findings disclosed no significant alteration and the electrocardiograms showed no abnormalities. Monthly follow-up examinations of 13 patients for six consecutive months showed parasitological cure in all. Before praziquantel treatment strains of Schistosoma mansoni were isolated from two patients, one treated three times with oxamniquine and the other with hycanthone once and oxamniquine twice. Progenies of these strains were maintained in Biomphalaria glabrata and mice. Groups of these infected mice were then treated with oxamniquine, hycanthone, niridazole and praziquantel and results compared with the BH strain maintained in our laboratory for many years. Schistosomicidal activity was assessed by the localization of worms in the portal vein system and oogram changes. Progenies from the strains isolated in this study were resistant to oxamniquine and hycanthone but sensitive to niridazole and praziquantel. The BH strain was sensitive to all four drugs. The serial runs of S. mansoni strains through intermediate and definitive hosts have not influenced their reactions to these schistosomicides.

An assessment of anti-schistosomal treatment on physical work capacity

Acting as their own controls, village subjects from the Gezira are of the Sudan with relatively high levels of schistosomiasis infection were first tested in an exercise laboratory in Khartoum and the tests were then repeated after a period of about 1 yr during which time the subjects were treated with hycanthone and periodically monitored to ensure that they had remained free of the disease. In the meantime they were also given anti-malarial prophylaxis. Laboratory tests showed a significant improvement in physiological work capacity of up to 20% after treatment compared with untreated controls. An overall improvement in pulmonary function, particularly forced vital capacity, was observed as well as a significant increase in mean haemoglobin concentration by 1.1 g/100 ml of blood in the treated group. Apart from these improvements in physical working capacity, the treated subjects subjectively felt better after the exercise tests, as expressed by the disappearance of fatiguability.

Failure of targeted mass treatment to control schistosomiasis

An attempt was made to control schistosomiasis mansoni with mass treatment of all subjects excreting more than 100 eggs/g of faeces. No other means of control to reduce transmission were used. A very low dosage of hycanthone (0.75 mg/kg) appeared insufficient to achieve a satisfactory reduction of the worm load. A higher dosage (1.5 mg/kg) resulted in a significant reduction of the egg output. However, reappearance of eggs, probably indicating reinfection, was very rapid. One year after treatment the egg counts were at about two-thirds of the original level again.

The schistosomiasis problem in the world: results of a WHO questionnaire survey

This article presents an overview of the magnitude of the schistosomiasis problem throughout the world, and is based on information on schistosomiasis control programmes provided by 103 countries in reply to a questionnaire circulated by the World Health Organization in 1976. According to the data either given in these replies, published, or provided in internal reports to WHO, schistosomiasis is one of the most widespread parasitic infections of man. Some 500 million people are thought to be exposed to infection and four main species of schistosomes are prevalent, together with their various intermediate snail hosts, in 73 countries. Control programmes are operating in 41% of responding endemic countries although they are on a national scale only in Brazil, Dominican Republic, Egypt, Iran, Iraq, Japan, Morocco, Puerto Rico, St Lucia, Tunisia, and Venezuela. It appears that a maximum of only 1-2% of all cases have been treated, the most frequently used drugs being niridazole and hycanthone. A small number of efficient molluscicides are in regular use but their high cost precludes large-scale application. Installation of water supplies and health education are the most frequently used non-specific control measures. Nearly 50% of endemic countries use more than three different methods of control simultaneously. The national schistosomiasis control programmes in Brazil, Egypt, Iran, Japan, Puerto Rico, and Venezuela are examples of combined approaches that have resulted in a significant decline in the prevalence of schistosomiasis. Finally, some specific needs in research, control, and training of personnel are discussed.

A note on drug trials in schistosomiasis

In schistosomiasis, if the subjects of drug trials are in contact with potentially contaminated water, then differences in the chemotherapeutic response to the same dose of a drug given in the same endemic area in different seasons, may be related to different levels of transmission. Because a reduction in egg excretion may occur from causes other than chemotherapy, moderate antischistosomal activity of a drug cannot be concluded in the absence of a control group.

Susceptibility to chemotherapeutic agents of strains of Schistosoma mansoni isolated from treated and untreated patients

Seven strains of Schistosoma mansoni were isolated from the feces of patients. Three of the patients had been unsuccessfully treated with hycanthone or oxamniquine; the remaining four had not been given any specific treatment. Mice infected with these strains were treated 45 days later with niridazole (50 or 100 mg/kg body weight per day for 5 days, per os), hycanthone (single dose of 80 or 160 mg/kg, intramuscularly), or oxamniquine (single dose of 50 or 100 mg/kg, per os). Significant differences in the strains' responses to the schistosomicidal agents used were observed. Oogram changes in mice treated with the same drug ranged from 10--100%, and percentages of dead worms from 0--45. Such differences seemed to be dependent on the strain's specific characters rather than t their having been exposed to schistosomicidal drugs.

[Bilharzial myelopathies (case report) (author's transl)]

Report of a case of biharzial myelitis appearing 6/8 weeks after bathing in an infected river. Recovery was complete after medical treatment with niridazol and hycanthone. The authors review the 47 detailed cases previously reported, selected among 60 cases observed from 1905 to 1963. They consider the clinical and pathological aspects and discuss the various pathogenic problems. Treatment requires specific antibilharzial compounds and anti-inflammatory drugs and, in compressive forms, sometimes surgery.

[Drug therapy of mansoni schistosomiasis]

The various presentations of schistosomiasis mansoni are discussed, stressing the indications of parosites elimination. Parasitologic cure is necessary, although, when the infestation is recent (acute), the drug efficacy is lower than in the chronic forms. Surgery may be pertension, special care must be taken, and in the pseudotumoral form there is not enough diet regarding progression of the disease after treatment. Contraindications are linked to associated illness, and are due to toxic effects of the available drugs. The mechanism of action of such drugs are discussed, as well as the historical background. Hycantone, Oxamniquine and Praziquantel are detailed in separate, with the proposed drug schedules and possible side effects.

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse. V. Reduction in the degree of resistance to reinfection after chemotherapeutic elimination of recently patent primary infections

Effective treatment of mice with six to eight week-old patent S. mansoni infections with any one of five schistosomicidal agents (Oxamniquine, Praziquantel, potassium antimony tartrate, Niridazole and Hycanthone) resulted in a reduction in the degree of resistance to homologous challenge in the treated animals when compared with the level of resistance to reinfection observed in untreated mice with intact primary infections. Mice challenged five to six weeks after treatment with Praziquantel, Niridazole or Hycanthone demonstrated a lower level of resistance than mice challenged within 10 days of the termination of the chemotherapeutic schedules. Direct comparison of Praziquantel with potassium antimony tartrate indicated that treatment with the former drug allowed retention of a greater level of acquired resistance than the antimonial in the immediate post-treatment period. Resistance to reinfection in Hycanthone-treated mice was not restored by intravenous injection of S. mansoni eggs before challenge.

A study of the mode of action of hycanthone against Schistosoma mansoni in vivo and in vitro

Schistosomes obtained by perfusion from host animals as early as 2 hours after in vivo treatment with hycanthone and transferred into untreated recipient hamsters died in the recipient host. In contrast, unexposed schistosomes transferred into recipient hamsters treated from 7 days to 36 hours previously showed a normal survival. In vitro treatment of schistosomes with hycanthone concentrations comparable to those used in in vivo studies, followed by transfer of the parasites into normal hamsters, resulted in death of the worms. The time of lethal hycanthone exposure in vitro could be as short as 15 minutes. Hycanthone-resistant schistosomes or immature worms were not affected under similar in vitro conditions. Our data suggest that the schistosomicidal effect of hycanthone is not caused by a host-derived metabolite.

Schistosoma mansoni control in Cul de Sac Valley, Saint Lucia. II. Chemotherapy as a supplement to a focal mollusciciding programme

After an intensive area-wide mollusciciding campaign, over four and a half years, transmission of Schistosoma mansoni was reduced. A cheaper scheme suitable for the follow-up or consolidation stage of control was evaluated and two selective population chemotherapy campaigns using hycanthone (2 mg/kg b.w.) and oxamniquine (15 mg/kg b.w.) were mounted. Prevalence dropped to 6% and 3% in areas with previously high and low levels of transmission respectively. Calculations suggested that these figures were falsely low and that perhaps 20% of the population were still excreting S. mansoni ova in small numbers. The unco-operative groups in the population are probably more important in maintaining a reservoir of infection in the community than persons with light infections undetected by the sedimentation concentration stool examination technique used. The benefit of more sensitive but more costly examination techniques is not clear since the importance of very light infections in transmission is uncertain. Case detection absorbs an increasing proportion of the total cost of chemotherapy programmes with fewer cases being found amongst the same number screened. Using hycanthone (649 treated) the cost per person protected was $0.74 and using oxamniquine (264 treated) $0.94. The need to develop low cost consolidation or follow-up procedures for preventing a resurgence of transmission after successful control, when the infection is no longer of public health importance, is stressed.

Phase I study of hycanthone

Hycanthone, an antischistosomal drug possessing activity against experimental murine tumors, was administered by 20-minute infusion daily x 5 days to 12 patients with advanced cancer to determine dose-limiting toxicity and to look for therapeutic effect. No objective responses were seen. The dose-limiting toxic effect was acute hepatitis occurring in two of four patients treated at 100 mg/m2/day x 5. Moderate nausea and vomiting occurring on treatment days was the only other toxic effect. Hycanthone was not myelosuppressive. Assay of plasma concentrations of hycanthone revealed a plasma half-life of 3-5 hours and no accumulation of drug over the 5 days of treatment.

Detection of antibodies by enzyme-immunoassay in human schistosoma mansoni infections: a clinical and chemotherapeutic study

Sera from patients with S. mansoni infections, before and six weeks after successful treatment with hycanthone, were examined for antibodies reacting with S. mansoni adult worm antigen, employing the enzyme-linked immunosorbent assay (ELISA) technique. 50 local individuals who had no schistosomiasis and 48 patients with S. haematobium infection were studied for comparison. All sera from untreated patients gave positive results. Significantly higher levels of antibody were given by sera from patients with visceral enlargement than by those from patients without visceral enlargement. A rise in antibody levels was seen in 87% of treated patients and the post treatment values of antibody were significantly higher than those obtained before treatment (p less than 0.001). 94% of sera from patients with S. haematobium infection gave a cross-reaction but with a significantly lower antibody values than for the homologous infection. A weakly positive reaction was obtained in 16% of controls and the actual values of antibody were much lower in this group than in the S. mansoni and S. haematobium groups.

Serum immunoglobulin concentrations in human S. mansoni and S. haematobium infections in the Sudan, with special reference to the effect of chemotherapy

The serum immunoglobulin concentrations of IgG, IgA and IgM were studied in 111 selected Sudanese patients with S. mansoni infections and 48 with S. haematobium infections before and 6 weeks after successful treatment with hycanthone; 52 local individuals were studied as controls. Both IgG and IgM were found to be significantly raised in S. mansoni patients compared with controls, while only IgG was significantly raised in patients with S. haematobium infection. S. mansoni patients with the hepatosplenic and splenic forms had higher IgG and IgM levels than those with the intestinal and hepatic forms. No relationship could be established between the levels of immunoglobulins and parasite loads. A rise in IgG was noted in 60% of patients with S. mansoni infection 6 weeks after successful treatment with hycanthone whereas IgM decreased.