Social isolation in the rat enhances alpha 2-autoreceptor function in the hippocampus in vivo

This study investigated the effects of isolation rearing from weaning in rats on extracellular noradrenaline in the dorsal hippocampus in vivo, measured using microdialysis. Male Lister hooded rats were obtained at weaning and reared in social isolation or in groups for six to eight weeks. Basal noradrenaline efflux did not differ between isolation- and group-reared rats. Local K+ stimulation (50 and 100 mM) increased noradrenaline efflux in the hippocampus of both groups of rats; however, this effect was greater in group-reared rats (50 mM K+). The alpha 2-adrenoceptor agonist, clonidine (0.3 mg/kg, i.p.), reduced noradrenaline efflux in both groups of rats, but this decrease was greater in isolates. Systemic (1.0 mg/kg, i.p.) and local (via the probe; 100 microM) administration of the alpha 2-adrenoceptor antagonist, idazoxan, increased noradrenaline efflux, but these responses were also greater in isolation-reared rats. The magnitudes of the idazoxan-induced increases in noradrenaline efflux were similar for both systemic and local administration, indicating that presynaptic terminal alpha 2-adrenoceptors were predominantly involved. Furthermore, although tail pinch increased noradrenaline efflux in both isolation- and group-reared rats, there was a significant/attenuation in the response in the isolation- compared to group-reared rats. Taken together with previous findings, the present results provide evidence in favour of an isolation-induced enhancement in the function of the presynaptic terminal alpha 2-autoreceptor in the dorsal hippocampus in vivo, resulting in decreased functional responsiveness of hippocampal noradrenergic nerve terminals.

Effect of isolation-rearing on noradrenaline release in rat hypothalamus and hippocampus in vitro

A fixed volume incubation method in conjunction with HPLC-ED analysis was employed to measure endogenous NA release in vitro in slices of hippocampus and hypothalamus from rats reared in either groups of five or in social isolation from weaning. NA in release supernatants from hippocampal slices was found to be increased in response to stimulation with high K+ (30 mM), an effect which was dependent on Ca2+. Basal NA release was also Ca2+ dependent. Isolation-rearing did not significantly alter either basal or K+-stimulated release. Clonidine (10 microM) caused an inhibition of basal NA release in both regions and in both rearing groups, however there was no significant effect of isolation-rearing for this response although the response tended to be greater in the hippocampus from isolates. Idazoxan (10 microM) significantly increased basal NA release in hippocampal and hypothalamic slices in both rearing groups, but this effect was significantly greater in the hippocampus from isolation-reared rats. These findings suggest there may be a region-specific change in the sensitivity of the alpha2-adrenoceptor in isolates. Taken together with previous findings, there is evidence to suggest that isolation-rearing alters the sensitivity of the presynaptic terminal alpha2-autoreceptor in the hippocampus.

The isolation of a 22 kDa band after SDS-PAGE of Schistosoma mansoni adult worms and its use to demonstrate that IgE responses against the antigen(s) it contains are associated with human resistance to reinfection

In schistosomiasis endemic areas, intensities of reinfection after treatment are greater amongst young children than amongst adults, and high levels of parasite-specific IgE are associated with resistance to reinfection in an age-dependent manner. Previously we have reported that, in Western blots, a 22 kDa band was recognized by human IgE and that the incidence and intensity of S. mansoni reinfection were significantly lower amongst individuals who had IgE against this band, compared with those who did not (Dunne et al. 1992). Here we report the isolation of a 22 kDa SDS-PAGE band, its incorporation into ELISA and the demonstration that levels of human anti-22 kDa IgE had a significant negative correlation with intensities of subsequent reinfection. Rabbit anti-22 kDa band serum recognized the outer tegument, gut tegument, and the collecting ducts and flame cells of adult worms. The 22 kDa band antigen(s) was also present in "lung'- and "post-lung' schistosomula stages of S. mansoni, and in S. haematobium, S. bovis and S. japonicum adult worms. Metabolic labelling of schistosomula and worms demonstrated the in vitro synthesis and release of 22 kDa antigens.

Immunity and morbidity in Schistosoma mansoni infection: quantitative aspects

Immunity to Schistosoma mansoni infection in humans can be studied most easily by monitoring serially the intensity of reinfection that occurs among individuals who have undergone chemotherapeutic cure, and whose levels of exposure to contaminated water is subsequently observed. Parallel studies can then be made of those immune responses that are correlated with an observed resistance to reinfection. This paper describes some of the difficulties associated with this approach, with particular reference to the authors' own studies in Kenya, and highlights a possible role of immunoglobulin E antibodies against adult worm antigens in mediating immunity.

Human immunoglobulin E responses to a recombinant 22.6-kilodalton antigen from Schistosoma mansoni adult worms are associated with low intensities of reinfection after treatment

Schistosoma mansoni-infected individuals who have low intensities of reinfection following treatment produce immunoglobulin E (IgE) antibodies against a range of S. mansoni adult-worm antigens. One of the targets of the IgE response is an adult-worm sodium dodecyl sulfate-polyacrylamide gel electrophoresis band of 22 kDa (Sm22), which contains an antigen(s) located within the tegument and gut lining of adult worms and relatively late schistosomula life cycle stages only. A significant negative correlation between the level of anti-Sm22 IgE and the intensity of reinfection following treatment suggests that IgE responses against this antigen(s) are characteristic of individuals who are resistant to reinfection. To identify the antigen(s) in the Sm22 band that are associated with these IgE responses, we have cloned and characterized a recombinant 22-kDa protein (rSm22) that cross-reacts immunologically with Sm22. There was a high correlation between native and recombinant Sm22 isotype responses, indicating that the correct antigen had been cloned and that responses against rSm22 made up the majority of the responses against Sm22. By analyzing human isotype responses to rSm22 with human sera from a longitudinal treatment and reinfection study and correlating the anti-rSm22 isotype responses, retrospectively, with the intensity of reinfection following treatment for each individual, we observed a negative correlation between the IgE response to rSm22 and the intensity of reinfection. This relationship remained significant after allowing for age and other isotype responses to rSm22, in particular IgG4.

Age-dependent reduction of schistosome fecundity in Schistosoma haematobium but not Schistosoma mansoni infections in humans

Understanding the dynamics of schistosome infections is problematic because direct measurements of worm burden are not possible. Hitherto, the relative intensity of infection has been estimated by the number of parasite eggs excreted. Egg excretion is assumed to have a consistent relationship with worm burden with duration of infection. We have tested this assumption in Schistosoma mansoni- and S. haematobium-infected populations by looking at the relationships between a circulating parasite antigen, egg excretion level, host age, and parasite density. The study was carried out in two populations because experimental models suggested that S. haematobium but not S. mansoni suffers immune-mediated reduction of fecundity. The results were consistent with this observation, showing that S. mansoni egg output remains stable irrespective of host age or infection intensity while S. haematobium has a substantially reduced egg production with host age. This information is fundamental to understanding the immunology and epidemiology of human schistosomiasis and thus practical approaches to disease control.

Water contact observations in Kenyan communities endemic for schistosomiasis: methodology and patterns of behaviour

A descriptive analysis of observed water contact activities in seven Kenyan (Akamba) communities is presented. The patterns of contact with time of day, month of year, type of activity, degree of immersion, use of soap, use of 'kithima' and day of week are all considered, with particular attention given to how these vary with age and sex. It is noted that (a) patterns of contact vary dramatically between these culturally rather similar communities, (b) contact usually peaks in the second decade of life, (c) generally females, especially young women, spend more time at the water than males and (d) simple (unweighted) total observed duration of contact gives a relatively inflated estimate of exposure in adults, especially young women. The methodology of observation and data handling is described in some detail.

The development of an age structured model for schistosomiasis transmission dynamics and control and its validation for Schistosoma mansoni

Mathematical models are potentially useful tools to aid in the design of control programmes for parasitic diseases. In this paper, a fully age structured epidemiological model of human schistosomiasis is developed and parameterized, and used to predict trends in infection prevalence, intensity and prevalence of heavy infections over age and time during several rounds of mass and age targeted treatment. The model is validated against data from a Schistosoma mansoni control programme in Kenya.

The relationship between worm burden and levels of a circulating antigen (CAA) of five species of Schistosoma in mice

This study examines the ability of an assay which measures the amount of a schistosome specific antigen (CAA) in the host circulation to reliably reflect relative worm burden. Mice were infected with 5 species of schistosome with a range of infection dose. The levels of serum CAA increased during schistosome maturation. In all species tested CAA levels correlated well with adult worm burden once the parasites achieved sexual maturity and remained relatively stable during the establishment of egg production. The amount of CAA produced varied between species but within each species CAA levels were proportional to worm numbers: no density-dependent effects on CAA levels were observed even when mice carried worm burdens that were very large relative to host size. T-cell deprivation of the host had no effect on the CAA/worm burden relationship in either Schistosoma mansoni or S. haematobium infections and the CAA equilibrium was unaltered in intact mice when reduction of worm fecundity occurred. These data support the use of the CAA as an accurate and robust estimate of relative schistosome burden in man.

A statistical approach to schistosome population dynamics and estimation of the life-span of Schistosoma mansoni in man

Dynamic models which predict changes in the intensity of schistosome infection with host age are fitted to pre-intervention Schistosoma mansoni data from Kenya. Age-specific post-treatment-reinfection data are used to estimate the force of infection, thus enabling investigation of the rate of worm death. An empirical and statistical approach is taken to the model fitting: where possible, distributional properties and function relationships are obtained from the data rather than assumed from theory. Attempts are made to remove known sources of bias. Maximum likelihood techniques, employed to allow for error in both the pre-intervention and reinfection data, yield confidence intervals for the worm life-span (CI95% = 5.7-10.5 years) and demonstrate that the worm death rate is unlikely to vary with host age. The possibilities and limitations of fitting dynamic models to data are discussed. We conclude that a detailed, quantitative approach will be necessary if progress is to be made with the interpretation of epidemiological data and the models intended to describe them.

Observations on the effects of different chemotherapy strategies on the transmission of Schistosoma mansoni in Machakos District, Kenya, measured by long-term snail sampling and cercariometry

Transmission of Schistosoma mansoni was monitored by routine snail sampling for Biomphalaria pfeifferi and by supplementary cercariometric measurements in 4 neighbouring study areas in Machakos District, Kenya. After 1 year, extensive, population-based chemotherapy with a single dose of praziquantel was given in 3 areas, but only minimal treatment in the fourth. In the year preceding treatment, seasonal transmission of S. mansoni and other non-human trematodes occurred in all 4 areas, despite some ecological differences and the effects of earlier treatment campaigns in 1 of the study areas. After treatment of all infected subjects in one area in which there had been earlier chemotherapy campaigns, S. mansoni transmission remained very low. It was reduced for at least 2 years after chemotherapy targeted at either all heavily infected subjects or all infected school children, but it was unaffected in an area where treatment was restricted to those few very heavily infected cases at risk of developing disease. Nowhere was transmission entirely eliminated by chemotherapy and that of non-human trematodes continued unabated. The snail data correspond well with the human, parasitological data. Targeting school children was as effective as more extensive campaigns, but chemotherapy alone never stopped S. mansoni transmission: reinfection was inevitable, at rates determined by ecological factors affecting snail populations.

Evidence for altered alpha 2-adrenoceptor function following isolation-rearing in the rat

This study investigated central alpha 2-adrenoceptor function in differentially reared rats. Rats reared from weaning were either housed singly or in groups of five. Measurements of spontaneous ambulatory activity at 4 weeks postweaning showed that isolates were more hyperactive on exposure to a novel environment than grouped rats. alpha 2-Adrenoceptors were investigated using alpha 2-adrenoceptor agonist-induced behaviours, [3H]-idazoxan binding and measurement of forskolin-stimulated cyclic AMP accumulation. Clonidine (0.001-1.0 mg/kg IP) induced mydriasis in both groups with no difference observed in the response between the isolation and group-reared animals. Clonidine (0.01-0.5 mg/kg IP) induced hypoactivity in both groups, with the effect significantly greater in the isolation-reared rats. Idazoxan markedly attenuated both responses, confirming their induction by alpha 2-adrenoceptor stimulation. Clonidine-induced hypoactivity and mydriasis are mediated by pre- and postsynaptic alpha 2-adrenoceptors, respectively; therefore the results suggest rats reared in isolation have enhanced presynaptic but unchanged postsynaptic alpha 2-adrenoceptor function. Saturation binding experiments using [3H]-idazoxan were undertaken to determine alpha 2-adrenoceptor number (Bmax) and affinity (Kd) in membranes prepared from the frontal cortex and hippocampus. Analysis of binding data revealed an increase in receptor number in the hippocampus of isolates. Cyclic AMP accumulation was measured in hippocampal slices from differentially reared rats. Isolation-rearing did not affect cyclic AMP accumulation in response to stimulation by forskolin (30 microM). However, the selective alpha 2-adrenoceptor agonist, UK14304, produced a significantly greater inhibition of cyclic AMP accumulation in slices from isolated rats, confirming changes in alpha 2-adrenoceptor function following isolation rearing.

Immunity after treatment of human schistosomiasis: association between cellular responses and resistance to reinfection

Previous studies have demonstrated the development of an age-dependent resistance to reinfection after chemotherapeutic cure of the helminthic parasite Schistosoma mansoni. Here we report on a longitudinal investigation of cell-mediated responses in infected individuals before and after treatment which was designed to outline those parameters important in mediating a protective response. A well-defined study group of 89 individuals with an age range of 9 to 35 years was selected from an area of high S. mansoni transmission in the Machakos district of Kenya. Peripheral blood mononuclear cell proliferation and cytokine production (interleukin-2 [IL-2], gamma interferon IL-5, IL-4, and tumor necrosis factor) in response to different crude life cycle-stage antigens of S. mansoni were assessed longitudinally in vitro before, 3 months after, and 1 year after treatment. Detailed statistical analyses of the results from this study have indicated a clear negative association between the proliferative responses to adult- and schistosomulum-stage antigens and subsequent reinfection intensity in older individuals (14 to 35 years) which was not present in the younger individuals (9 to 13 years). This association was significant even after the effects of age, sex, and exposure had been accounted for in multiple regression analyses. Cytokines were detected predominantly in response to adult worm and egg antigen extracts. An inverse association between the two cytokines gamma interferon and IL-5 was detected in response to all antigens at the three time points investigated, indicating cross-regulation in the production of these two mediators. Differences in antigen-specific cytokine levels between the two age groups were detected, with significantly higher IL-5 levels detected in the older (more resistant) age group. An inverse correlation between this cytokine and reinfection was detected but could not be dissociated from the effects of age and exposure in multiple regression analysis.

On the use of age-intensity data to detect immunity to parasitic infections, with special reference to Schistosoma mansoni in Kenya

We consider two phenomena, related to the host age-intensity profiles of parasitic infections, which have been suggested to be indicative of acquired immunity: (i) a lower age of peak intensity among more intensely infected hosts; and (ii) a decline with age in the dispersion of the distribution of parasites between hosts. We demonstrate that these phenomena occur among Kenyan schoolchildren infected with Schistosoma mansoni, although the magnitude of both is small. We also examine the mathematical models underlying these predictions and conclude that both phenomena are possible in the absence of acquired immunity or, indeed, in the absence of any density-dependent effect. In our opinion, insufficient attention has been focused upon mathematical models, describing the null hypothesis, i.e. density-independent models. In particular, we regard the usual assumptions made for the two stochastic components of these models, describing the heterogeneity between hosts and the probabilistic nature of infection and death of parasites, as too rigid and unrealistic. We demonstrate that deviation from these assumptions undermines the qualitative distinctions between models which describe acquired immunity or density dependence and those which are density-independent.

Human immunity to Schistosoma mansoni: observations on mechanisms, and implications for control

This review summarizes the personal experiences of the authors and their colleagues during ten years of field and laboratory studies on human immunity to Schistosoma mansoni infections. There is evidence for the very slow development with age of an acquired resistance to reinfection (demonstrable after chemotherapy of the primary infection) distinguishable from a lack of reinfection due to reduced exposure. The implications of this immunity for the design of chemotherapy programs targeted at infected schoolchildren are discussed. Observational studies on the mechanisms of immunity have demonstrated a marked helminthocidal capacity of eosinophils. Subsequent correlative studies have indicated a role of IgM and IgG2 "blocking" antibodies in maintaining the continued susceptibility of young children, and of IgE antibodies in mediating protection in older individuals. Some problems in studying human immunity, and the implications for vaccine development, are also discussed.

Immunity after treatment of human schistosomiasis: association between IgE antibodies to adult worm antigens and resistance to reinfection

Previous studies in school children have demonstrated the slow development with age of resistance to reinfection after chemotherapy of Schistosoma mansoni infections, and have indicated that inappropriate ("blocking") antibody responses prevent the expression of immunity in young children. The present study was designed to investigate further the nature of the protective responses, by serological studies on a group of 151 S. mansoni-infected individuals resident in an endemic area in Machakos District, Kenya. Antibody levels against various antigens in blood samples before treatment were related to intensity of previous infections; antibodies in blood samples taken 6 months after treatment were related to cumulative reinfection rates over the following 30 months. IgE against an adult-worm antigen preparation correlated positively with age and negatively with reinfection. In contrast, IgE antibodies against other life-cycle stages showed either no relationship or the reverse correlation. Furthermore, antibodies of other isotypes against adult-worm antigens showed no correlations with reinfection. The correlation with IgE could be demonstrated for different preparations of adult worms, including a periodate-treated preparation presumptively depleted of carbohydrate epitopes. For both the intact and the periodate-treated preparations, multiple regression analysis of the results for children less than or equal to 16 years old demonstrated an IgE effect after allowing for age, although this effect was not observed in a previously studied group of school children. Western blot analysis of the adult-worm preparation revealed a limited set of antigens recognized by IgE, among which an antigen of 22 kDa was prominent. The qualitative presence of IgE against this antigen could also be shown to be related to a lack of subsequent reinfection.

Nutritional status of children with schistosomiasis mansoni in two different areas of Machakos District, Kenya

A possible association between nutritional status and Schistosoma mansoni infection or morbidity was investigated by comparing anthropometric indices among 362 children from 3 primary schools in Machakos District, Kenya. Matithini was a prosperous school in an area (Kangundo) of moderate intensity of schistosome infection but low associated morbidity. A second area (Kambu) showed more severe schistosome-associated morbidity: in this area, Kitengei school was prosperous and with high intensities of schistosome infection, while Misuuni school was less prosperous and with low intensities of infection. Nutritional status was assessed by measurement and appropriate standardization of height, weight and skinfold thickness and by questionnaires concerning diet. Children in Kangundo were better nourished than those in Kambu. Within Kambu, children from Misuuni showed low mean skinfold thickness and low mean weight-for-height ('wasting'): this was associated with a lack of dietary variety and of intake of animal products. In contrast, those from Kitengei showed low mean height-for-age ('stunting'). The relationship between intensity of schistosome infection and nutritional indices, although significant, was complex and not readily interpretable. However, intensity of infection was also correlated with hepatomegaly, which was more clearly related to nutritional status. Depending on the school, children with hepatomegaly were significantly more stunted and/or wasted than those without, and had less variety in their diet. Possible reasons for the observed associations are discussed and, of various possibilities, the hypothesis is suggested that schistosome-associated morbidity leads to a subsequent nutritional defect. This hypothesis can now be tested by appropriate intervention studies.

Human IgE responses to Schistosoma mansoni and resistance to reinfection

Schistosoma mansoni infected Kenyan patients were treated and the intensities of their reinfections were followed over the next two years. In addition, their pre- and six month post-treatment serum levels of IgG1-4, IgM, and IgE, specific for schistosomula, egg and adult worm, were measured in ELISA. No reinfection took place before six months post-treatment. Reinfection intensities varied with age; the younger children becoming reinfected at significantly higher intensities than older individuals. When antibody and reinfection levels were compared, only the six month post-treatment IgE response against adult worm correlated negatively with intensities of reinfection and, therefore, was predictive of resistance or immunity to reinfection. IgE and IgG specific Western Blots were carried out. The adult worm antigens recognized by IgE were restricted compared with the IgG responses of the same patients, although no individual antigen was uniquely recognized by the IgE isotype. A dominant 22 kDa antigen was recognized by most but not all high IgE responders. Patients with IgE responses against this antigen suffered significantly lower subsequent levels of reinfection, compared with non-responders. A monospecific rabbit antiserum against the 22 kDa adult worm antigen showed that this antigen is specifically located in the tegument of the adult worm and of 'lung' and 'liver' stage schistosomula, but is absent from the early 'skin' schistosomula. It is possible that this antigen is a target for human IgE mediated immune effector mechanisms active against the post skin stage schistosomula and that this is boosted by the death of adult worms.

Comparison of different chemotherapy strategies against Schistosoma mansoni in Machakos District, Kenya: effects on human infection and morbidity

A comparison was made of the long-term impact of different methods of administration of chemotherapy (oxamniquine, 30 mg/kg in divided doses; or praziquantel, 40 mg/kg) on prevalence and intensity of Schistosoma mansoni infection in four areas in Kangundo Location, Machakos District, Kenya. In Area A, treatment was offered in October 1983 and again in April 1985 to all infected individuals. In Area H, treatment was offered in April 1985 to individuals excreting greater than or equal to 100 eggs per gram (epg) of faeces. In Area S, treatment was offered in April 1985 to all infected school children, within the framework of the primary schools. In the witness area, Area W, treatment was given in April 1985, for ethical reasons, to a small number of individuals excreting greater than or equal to 800 epg. Prevalence and intensities of infection were subsequently monitored at yearly intervals for three complete post-treatment years. In the Area S schools, clinical examination was also carried out at yearly intervals. Treatment of all infected individuals on two occasions (Area A) was the most effective and long-lasting way of reducing prevalence and intensity of infection. In this area, however, some earlier interventions had been carried out and pre-treatment intensities were lower than in the other areas. Treatment only of infected schoolchildren (Area S) also had a marked and prolonged effect, comparable to or better than treatment of individuals with heavy infections (Area H). Treatment of infected schoolchildren also caused a persistent reduction in the prevalence of hepatomegaly, and there was suggestive evidence from intensities of infection in community stool surveys (but not from incidence rates) of an effect on transmission. In all study areas, reinfection was most rapid and most intense among children. These findings are discussed in the light of theoretical considerations and of results from other studies, both on schistosomiasis and on intestinal helminths. We conclude that, in areas of low morbidity such as Kangundo, chemotherapy of schoolchildren only, at intervals of up to 3 years, is a satisfactory way of producing a long-term reduction in both intensity of infection and morbidity.

Differences in the rate of hepatosplenomegaly due to Schistosoma mansoni infection between two areas in Machakos District, Kenya

The relationship between intensity of Schistosoma mansoni infection and the degree of related morbidity was suspected to differ locally within the Machakos district of Kenya. To test this possibility, prevalences of hepatomegaly and splenomegaly among 1483 school children were compared between 2 areas, Kangundo and Kambu, within this district. These areas, which were similar in many geographical and economic respects and populated by the same tribe (Akamba), had comparable levels of S. mansoni infection and no S. haematobium infection. A relationship was observed between the prevalence of hepatomegaly and intensity of S. mansoni infection, which showed no consistent difference between the 2 areas. In contrast, a relationship between the prevalence of splenomegaly and intensity of S. mansoni infection was observed only in the Kambu schools, and not in the Kangundo schools where the overall prevalence of splenomegaly was much lower. It was possible that part of the splenomegaly observed in Kambu was due to malaria. However, the observation that malaria and schistosomiasis in 2 Kambu schools were not positively correlated allowed approximations to be made of the relative contributions of each to the prevalence of splenomegaly. It was concluded that, in a school close to the river that formed the main transmission site of S. mansoni, schistosomiasis-related hepatosplenomegaly was present in at least 17% of children. The reason for the high prevalence in Kambu of hepatosplenic schistosomiasis remains uncertain, but it could include a synergistic interaction of schistosome infection with malaria.

Longitudinal studies on human schistosomiasis

A major difficulty in understanding the epidemiology of human schistosomiasis has been to distinguish between acquired immunity and reduced exposure as possible reasons for an observed decline, in older individuals, of levels of superinfection or of reinfection after chemotherapy. A series of studies of Schistosoma mansoni infections in Kenya has been undertaken to approach this problem, by investigation of intensities of reinfection after treatment of individuals whose levels of contact with contaminated water is subsequently observed. Intensities of reinfection are highest among younger children, thereafter declining sharply. This decline can be attributed only in part to age-related changes in the duration and nature of exposure; there is also evidence for the development of an acquired resistance to reinfection that is dependent both on age and on previous experience of infection, and that may be immunologically mediated. Evidence has been obtained that the slow development of this acquired immunity with age may be associated with the early development and subsequent slow decline of inappropriate immune responses that 'block' the effect of potentially protective responses. Implications of these findings for immunological intervention through vaccination are discussed.

Analysis of worm burdens in experimental schistosomiasis

The techniques of generalized linear modelling were applied to worm burdens of 2268 mice artificially infected with Schistosoma mansoni and treated with oxamniquine and/or praziquantel. Models which maximized the Poisson likelihood were shown to be superior to those assuming either a log Normal or negative binomial error structure. Use of the models to calculate and compare ED values of 8 strains of S. mansoni, detect abnormal dose response and synergism and to pool data from several experiments is illustrated.

Human antibody responses to Schistosoma mansoni: the influence of epitopes shared between different life-cycle stages on the response to the schistosomulum

Sera from 120 Kenyan schoolchildren who were infected with S. mansoni were individually examined, using an enzyme-linked immunoabsorbent assay (ELISA), for the presence of IgG and IgM antibodies reactive with antigens derived from adult worms, the outer membrane of the schistosomulum or from the parasite egg. In addition, antibodies against more purified egg antigens, an egg stage-specific glycoprotein preparation and a polysaccharide egg antigen known to share epitopes with the schistosomular surface were measured in ELISA, as were antibodies reactive with trichloroacetic acid-soluble and periodate-insensitive antigens derived from the outer membrane of schistosomulum and antigens shed when schistosomula were cultured in vitro. IgG subclass responses to the unfractionated egg antigen were also measured. The results from each of these assays were compared with the results of each other assay and with the number of parasite eggs excreted by each child, using Spearmans rank correlations. These comparisons revealed a number of statistically significant positive correlations. IgG4 anti-egg antibodies correlated better with intensity of infection than did other IgG subclasses. Total IgG responses against polysaccharide antigens did not correlate with intensity of infection as well as IgG responses against other antigens; epitopes shared between the schistosomulum surface and the adult worm were different to those shared with the parasite egg; and, there was antigen-directed restriction of IgG subclass responses to some egg and adult worm antigens which carried these shared epitopes. It is argued that this might have a qualitative effect on the nature of the antibodies directed against the schistosomulum by infected individuals and therefore have important consequences for the outcome of a subsequent exposure to infection with the same parasite.