Immunity after treatment of human schistosomiasis mansoni. I. Study design,pretreatment observations and the results of treatment

This paper describes the design of a study on immunity to reinfection after treatment of children with Schistosoma mansoni infections, the initial observations on transmission that led to the selection of the study population, the effects of treatment, and the results of immunological tests carried out before and at five weeks after treatment.Iietune village in Machakos District, Kenya, was selected on the basis of high prevalence and intensities of infection in a small preliminary survey, a stable population living in a small area amenable to detailed study, and a lack of previous intervention in the area. Subsequent observations over a pretreatment period of one year confirmed that prevalence and intensities of infection among children attending the local primary school were high. This was associated with extensive contact of members of the community with water-bodies shown to contain large numbers of infected snails.Analysis of pretreatment intensities of infection and water contact patterns in the schoolchildren allowed the selection of 129 children showing a broad scatter between: (a) high intensity, low water contact, and predicted to be non-immune, and (b) low intensity, high water contact, and predicted to be immune. These children were treated with oxamniquine, 30 mg/kg in divided doses. Five weeks after treatment, 70% of children showed apparent complete cure, and the over-all reduction in geometric mean egg output was 98·9%. Since these children represented only a small proportion of the whole community, there was no obvious reduction in transmission, as reflected by snail infection rates, during the following five-month period. Thus, we are in a position to determine whether successfully treated children do or do not become reinfected in a high transmission environment in which it will be possible to make direct estimates of exposure.Immunological tests carried out immediately before treatment were consistent with a pattern of high exposure leading to the early expression of immune responses in most infected children. Eosinophil levels were elevated in 61% of the children, all of whom showed detectable levels of antibodies against adult worm and egg antigens, as measured by ELISA. In addition, all patients showed antibodies capable of mediating eosinophil-dependent killing of schistosomula. At five weeks after treatment, eosinophil counts and anti-adult worm antibody levels had risen, whereas anti-egg antibodies remained grossly unchanged. The wide variation in the levels of responses shown by different individuals will allow us to test whether such responses are associated with resistance to reinfection during the follow-up period.     

Immunity after treatment of human schistosomiasis mansoni. II. Identification of resistant individuals, and analysis of their immune responses

Intensities of re-infection were monitored at three-monthly intervals after treatment of Schistosoma mansoni infections in a group of 119 Kenyan schoolchildren, whose levels of water contact were also observed. 22 children showed high reinfection intensities (greater than 100 eggs per gram of faeces) by 12 months after treatment, and were considered to be susceptible. Out of 70 children who showed low reinfection intensities during the same period (less than 30 eggs per gram), 35 showed high levels both of total water contact and of contact with sites containing infected snails. In these children, the relative lack of reinfection could not be attributed to a lack of exposure, and they were classified as resistant to reinfection. Comparison of the two groups, resistant and susceptible, revealed no difference in pretreatment intensities of infection. However, there was a marked difference in age, the mean age of the resistant group being two years greater than that of the susceptible group, within a restricted starting age range. These findings indicated that resistance was an acquired and age-dependent phenomenon, not obviously related to previous egg-induced pathology. Studies of immune responses revealed no clearcut correlate of resistance, but there were interesting differences between the two groups. Whereas anti-egg antigen responses declined after treatment to a greater extent in the resistant than in the susceptible group, antibodies mediating eosinophil-dependent killing of schistosomula rose markedly in both groups, strongly suggesting that the resistant children were being exposed to cercariae. Anti-adult worm antibodies rose sharply in both groups immediately after treatment, and thereafter declined to pretreatment levels. Although some individual children showed high levels of IgE anti-schistosomulum antibodies, there were no significant differences between the two groups. Since all children showed detectable levels of antibodies mediating eosinophil-dependent killing of schistosomula, the possibility was considered that such antibodies might be a necessary, but not a limiting, factor in immunity. Instead, the functional state of the effector cells mediating antibody-dependent killing might be limiting. Eosinophil levels, measured as an indirect estimate of eosinophil functional activity, did not differ between the two groups. There were, however, marked differences between different individuals in their capacity to produce eosinophil-stimulating monocyte mediators, and although this cannot yet be related to resistance, this aspect is worth further study.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunity after treatment of human schistosomiasis mansoni quantitative and qualitative antibody responses to tegumental membrane antigens prepared from adult worms

Quantitative antibody responses of individual Kenyan children to a tegument membrane preparation from adult schistosomes have been studied by enzyme-linked immunosorbent assay. Qualitative differences between patients were examined by electrophoretic fractionation of the membrane preparation followed by Western blotting analysis. All individuals had antibodies to the preparation, the level increasing twofold shortly after chemotherapy and declining to pre-treatment levels by 6 months. Susceptible children had significantly higher levels of antibody than resistant individuals at 12 and 18 months after chemotherapy. Antibody levels were positively associated with patient age (particularly over the range 8-12 years at the first bleed after chemotherapy) and the logarithm of pre-treatment egg excretion. The strongest association was observed between initial antibody level and subsequent levels. A total of 47 distinct antigens was detected in the membrane preparation. The major antigens were detected equally strongly by sera from both susceptible and resistant groups of children. At the outset the resistant group responded more strongly to 35%, and more weakly to 15%, of the antigens than the susceptible group. At the end of the study the figures were reversed, being 21% and 38% respectively, probably reflecting the reflecting the reinfection of the susceptible group. 3 antigens of molecular mass 100, 50 and 27 kDa were exceptions to the trend, being detected more strongly by the resistant than the susceptible group at one or more later times. It was concluded that the differences in total antibody level to the tegument membrane preparation were insufficient to account for the resistant or susceptible status of the children.     

Immune responses and immunoregulation in relation to human schistosomiasis in Egypt. III. Immunity and longitudinal studies of in vitro responsiveness after treatment

Immune responsiveness of schistosomiasis patients was assayed longitudinally, before and for two years after chemotherapeutic treatment with praziquantel, by in vitro peripheral blood mononuclear cell (PBMN) proliferation upon exposure to phytohaemagglutinin (PHA), or soluble schistosomal antigenic preparations from eggs (SEA), adult worms (SWAP) or cercariae (CAP). Parallel faecal and urine examinations documented the infection status of the patients during this time. Treatment resulted in substantially increased responsiveness to the schistosome-derived materials but not to PHA or C. albicans extract. The responses to SEA, SWAP, and CAP often remained elevated for one to two years after treatment. However, those patients who became reinfected had significantly lower PBMN responses to SEA or CAP at the time of the last blastogenesis assay before the observation that they were again stool-positive for Schistosoma mansoni eggs. No other demonstrable differences (such as age, sex, household location, pre-treatment intensities of infection or occupation) were observed between those who remained uninfected for at least two years (resistant?) and those who became reinfected during this time (susceptible?).     

Intestinal parameters in acute murine schistosomiasis mansoni.

Intestinal involvement is very important in acute murine schistosomiasis mansoni. Nevertheless intestinal parameters have not previously been used in assessing the severity of intestinal disease. The present observations demonstrate that in Schistosoma mansoni-infected mice, the mean total egg count of the small intestine and the mean number of eggs per g in the small and the large intestine were higher than the corresponding egg counts in the liver. The increase in weight of the small intestines of infected compared with uninfected mice was greater than the increase in weight of the corresponding livers. The small intestines from infected mice were considerably shorter than those from uninfected mice. These findings argue for the small intestine as a valuable organ for pathophysiological studies in acute murine schistosomiasis mansoni and simple parameters such as total egg count of the small intestine, the number of eggs per g tissue in small and large intestine and the weight and length of the small intestine, are recommended.     

Long-term efficacy of single-dose oral treatment in schistosomiasis haematobium

A two-year follow-up was conducted in children who had been the subjects of a six-month double-blind trial in the single-dose treatment of Schistosoma haematobium infection. The trial had assessed therapeutic efficacy of three oral preparations—praziquantel 40 mg/kg, metrifonate 10 mg/kg, and the “combination” (concurrent niridazole 25 mg/kg and metrifonate 10 mg/kg administration).Reduction in urinary egg excretion remained high up to follow-up at two years, based on a comparison of pre- and post-treatment geometric mean counts—praziquantel 96·9% (n = 96 at six months, 51 at two years); the ‘combination’ 93·9% (n = 97 at six months, 48 at two years); and metrifonate 90·3% (n = 92 at six months, 49 at two years). The differences in percentage reduction were not significant (p>0·1). However, a significantly greater reduction in egg ouput was produced by praziquantel (81·7%) and the ‘combination’ (82·5%) than by metrifonate (54·2%), on comparing pre- and post-treatment arithmetic mean counts (p<0·01).A significantly smaller percentage of subjects were excreting ≥125 ova/10 ml urine two years after treatment with praziquantel (10·3%), compared to treatment with the ‘combination’ (25·7%) and metrifonate (35·8%) (p<0·01). The cure rate was significantly higher in the praziquantel group (47·4%) compared to the ‘combination’ (24·7%) and metrifonate (17·4%) groups, for the six to 24-month follow-up period (p<0·001).The pattern and level of transmission had contributed to the long-term efficacy recorded in this study.     

Field trials of praziquantel and oxamniquine for the treatment of schistosomiasis mansoni in Burundi

Praziquantel and oxamniquine were evaluated under operational conditions for use in mass-treatment campaigns in the Rusizi Plain, Burundi. After 6 weeks, the cure rates for oxamniquine at 20, 30 and 40 mg/kg in children (less than 20 years) were respectively 47%, 67% and 86%; in adults they were 86%, 97% and 97%. The egg reduction rates were over 98% in all groups. For praziquantel at 20, 30 and 40 mg/kg the cure rates in children were respectively 58%, 63% and 78%; in adults, 55%, 87% and 91%. The egg reduction rates were respectively 92%, 96%, 98% and 91%, 98%, 98%. These results were largely confirmed by a follow-up 3 months after treatment. Oxamniquine frequently caused important dizziness and drowsiness, and in 2 cases epileptiform seizures. The side effects of praziquantel were mainly mild transient colics and diarrhoea. The cost of oxamniquine (in Burundi) was twice to three times the cost of praziquantel. Because of its better acceptability and its lower cost, with only slightly less good parasitological results, praziquantel, at 40 mg/kg in a single dose, has been selected as the drug of choice for mass-treatment campaigns in Burundi.     

Spinal cord complications of acute schistosomiasis mansoni

5 cases of clinically unsuspected involvement of the spinal cord by S. mansoni are reported. In contrast to the cases usually described in the literature, the nervous system involvement was observed during the acute phase of the infection. One of the patients exhibited a clinical picture closely resembling that of the Guillain-Barré syndrome, and cure was not dependent upon the use of corticoid hormone or antischistosomal therapy. 2 other patients improved after neurological involvement (paraparesis and paraplegia) following the completion of specific treatment (hycanthone). The sudden appearance of a polyradiculoneuritis syndrome was observed in 1 patient during treatment with niridazole. In another patient who developed a sudden transverse myelitis at T.11 with flaccid paraplegia, antischistosomal therapy apparently did not influence the course of the neurological process.It is suggested that the nervous system involvement in the reported cases cannot be explained entirely by the mechanical action of eggs and worms and the resultant granuloma formation. In the authors' opinion an anomalous response of the nervous system to the immuno-allergic products derived from dead worms and; or their eggs probably was responsible for the clinical manifestations of spinal cord involvement.     

Repeated mass treatment of schistosomiasis mansoni: experience in hyperendemic areas of Brazil. 3. Techniques for assessment and surveillance

Severe morbidity due to schistosomiasis mansoni is now quite rare in Brazil; thus it is proposed that surveillance plus selective and multidisciplinary intervention limited to areas at high risk be the next step. Such a policy has to be carried out periodically and on a state-wide scale, and therefore will have to rely upon cheap and time-saving sampling procedures. Clinical features cannot at present be used as indicators, with the exception of grossly enlarged livers, which are more frequent in areas at high risk. Overall prevalence rates for a county or even city may also be misleading, even if broken down into units of smaller size. Thus, egg counts in the young age groups remain the best indicators for the detection of areas at high risk (i.e., the main foci of transmission). Egg counts performed on pooled specimens adequately reflect the risk rating of a particular neighbourhood, and have a favourable cost-benefit ratio. In addition, it is suggested that field personnel be trained in the empirical recognition of potential foci; such 'screening by suspicion' has been tested and found to be reliable.     

Human schistosomiasis: Schistosoma mansoni antigen detection in renal glomeruli.

Twelve kidney, five biopsy and seven necropsy specimens, all from schistosomiasis mansoni patients were studied by light and immunoflurescent microscopy in an attempt to detect antigen in the glomerular walls. Deposits of IgM, IgG,I gA, IgE, complement C3 and fibrinogen were observered in most cases. Antigen was successfully detected in two cases(one biopsy and one necropsy specimen), both exhibiting proliferative glomerulonephritis. The only clinical manifestation was a slight proteinuria. IgG antibodies eluted from the sutopsy kidney homogenates showed specific binding mostly to Schistosoma mansoni gut, thus spggesting that the fixed antibodies (eluates) are, at least partially, consituted by antibodies similar to the anti-circulating antigen. These data reinfroce the hypothesis that renal injury in schistosomiasis is mediated through an immune complex disease.     

Circulating anodic antigen levels in serum before and after chemotherapy with praziquantel in schistosomiasis mansoni

The kinetics of serum levels of circulating anodic antigen (CAA) of Schistosoma mansoni were studied in patients with intestinal schistosomiasis before and after treatment with praziquantel. Day to day fluctuation in faecal egg excretion was compared with fluctuation in antigen level in 20 patients by serum and stool examination on 3 consecutive days before treatment. Antigen levels - calculated either as absorbance value of undiluted serum or as titre - showed less fluctuation than the number of eggs per gram of faeces determined by stool examinations based on single or duplicate 25 mg Kato smears. Compared with a placebo control group of 11 individuals, there was a significant reduction in CAA level in serum of 10 patients treated with praziquantel (40 mg/kg), 10 weeks after treatment. A similar decrease in serum CAA level was observed in a group of 46 patients treated with praziquantel, 6 weeks after treatment. In both groups, patients who remained seropositive after treatment still excreted eggs in their faeces. The kinetics of the antigen decrease were studied in more detail in 20 patients in hospital. Within 10 d after treatment with a double dose of 40 mg praziquantel per kg body weight, the antigen level fell to less than 10% of the original serum level, with a CAA half-life of approximately 2 d.     

Mother-child relation in human schistosomiasis mansoni: skin test and cord blood reactivity to schistosomal antigens

Reaction to schistosomal antigen was studied in children born to mothers infected with Schistosoma mansoni. Values of immediate (15 min) skin reactions were more elevated and values of delayed (24 h) skin reactions were significantly higher in children born to infected mothers than in children born to un-infected mothers. The macrophage migration inhibition test, done on cord blood cells, was positive to schistosomal antigen in 40% of children born to infected mothers and negative in all children born to uninfected mothers. These results suggest prenatal sensitization to schistosomal antigen in children born to mothers infected with S. mansoni.     

Resistance to reinfection after treatment of urinary schistosomiasis

The process of reinfection after treatment was studied in a cohort of subjects in a focus of intense Schistosoma haematobium infection. Detailed observations were made at water contact sites of cercarial densities and of water contact by members of the cohort. Individual values of a cumulative index of exposure to infection were calculated using these observations and assumptions which were made about the effect of different water contact activities on the entry of cercariae into the skin. Among groups of subjects with an apparently similar intensity of exposure to infection, reinfection tended to be much heavier in children under 10 years of age than in 10 to 14-year-olds, while only light infections were found in the few adults who became reinfected. This trend for reinfection to decrease with increasing age, after an allowance for variation in exposure, was highly significant (p less than 0.001). These observations suggest that subjects in this area slowly acquire an increasing degree of immunity to the acquisition of S. haematobium infection which is effective in the absence of a mature egg laying infection.     

Epidemiology of schistosomiasis mansoni in a low endemic area

We discuss the epidemiological patterns of schistosomiasis mansoni in areas with low transmission in Brazil. We define as areas of low endemicity those where the prevalence is less than 10%, the number Schistosoma mansoni eggs per gram of feces (epg) is less than 96, and carriers are asymptomatic. Data are from the county of Pedro de Toledo in the Ribeira Valley (S?o Paulo State) and were collected randomly according to the aggregate pattern of S. mansoni within the hosts. We suggest the replacement of parasitological methods by more sensitive and specific serological techniques. The main risk factor for infection is type of leisure activity. Infection is more frequent in the 10-14, 15-19, and 20-24-year age brackets. Geometric mean epg is 58.5. Intensity of infections correlates well (rs = 0.745) with prevalence. The highest index of potential contamination is in the 5-20-year age bracket (57.6%). Autochthonous cases show close association with Biomphalaria tenagophila, which has a low infection rate (2%). Prevalence, incidence, and intensity of infection patterns are similar to those of moderate and high endemic areas. Social and cultural aspects must be studied in order to obtain a global epidemiological view of schistosomiasis.