Antibody-dependent eosinophil-mediated damage to 51Cr-labeled schistosomula of Schistosoma mansoni: damage by purieid eosinophils.

After earlier observations that antibody-dependent, cell-mediated damage to 51Cr-labeled schistosomula can be ablated by pretreatment of a mixed preparation of human peripheral blood leukocytes with an anti-eosinophil serum and complement, we investigated the cytotoxic effects of eosinophil-enriched cell preparations. Preparations containing up to 98.5% eosinophils and devoid of neutrophils were effective in mediating antibody-dependent damage to schistosomula. Preparations enriched in mononuclear cells or in neutrophils, and devoid of eosinophils, were inactive. Eosinophils from some patients with eosinophilia induced by schistosomiasis were less active on a cell-to-cell basis than cells from normal individuals. The possibility that such cells were initially blocked by immune complexes was considered, and it was found that reasonable cytotoxicity by purified eosinophils from patients with eosinophilia could be generated by overnight cultures. A possible requirement for cooperation between eosinophils and other cell types was also studied. Lymphocytes, neutrophils and monocytes failed to enhance eosinophil-mediated cytotoxicity. These results provide further evidence that the eosinophil is the only cell in man responsible for antibody-dependent, complement-independent damage to schistosomula in vitro. Eosinophils from individuals, however, differ in their cytotoxic potential by a mechanism yet to be elucidated. The possible relationship of these findings to immunity in vivo is discussed.

Pathology resulting from the administration of a live attenuated anti-Schistosoma haematobium vaccine in baboons.

Baboons (Papio anubis) were injected in the leg muscle with 18,000 20 Krad irradiated schistosomula of Schistosoma haematobium. Four protocols were followed: single, primary injection; single injection into animals primed by patent S. haematobium infection; secondary vaccine injection following an earlier injection; and single injection following praziquantel treatment of infected animals. Injection of the putative vaccine elicited localized mixed inflammatory infiltration at the site of injection which was both intense and prolonged. Three grades of tissue reaction were seen: the relatively mild primary response; the response in infected animals which had enhanced tissue eosinophilia; and the response in animals primed by prior injection and drug-treated prior infection. The latter 2 showed intensification of eosinophilia, stellate abscesses in the lesion centers, and perischistosomular Hoeppli precipitates. Intramuscular lesions peaked at 14 days for the primary response and at 7 days for all secondary responses. Traces of the milder lesions persisted beyond 4 weeks; more severe reactions healed more rapidly. Some schistosomula survived for 14 days in the milder reactions. A few larvae were deposited in the skin by backflushing of the injectate which produced local inflammation. Compared to mice, live schistosome vaccines injected into baboons elicited greater local inflammation; however, while evidence suggested that sporadic vaccine schistosomula did reach the lymphatic nodes draining the injection sites, no systemic lesions were found and the injection sites healed in approximately 5-6 weeks without permanent damage.

Short report: diminished susceptibility to praziquantel in a Senegal isolate of Schistosoma mansoni.

There is a recent report of low efficacy of praziquantel (PZQ) treatment of human schistosomiasis in a new Schistosoma mansoni focus in northern Senegal. Biomphalaria pfeifferi snails with patent infections were collected from the area of the focus and transported to the United Kingdom. Groups of mice were infected with cercariae from this Senegalese isolate, or with laboratory-maintained Kenyan or Puerto Rican isolates. In two separate experiments, PZQ was less effective against the parasite from Senegal than against the two other geographic isolates. The reduced susceptibility of S. mansoni to PZQ in infected human populations has important implications for current schistosomiasis control programs.

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.

Effects of borehole wells on water utilization in Schistosoma haematobium endemic communities in Coast Province, Kenya.

To determine the impact of the introduction of borehole wells on water use patterns and the consequent risk of transmission of Schistosoma haematobium in 3 endemic villages in Kenya, we performed a survey (a 1:6 sample of affected households) to identify sources of water and types of water utilization before and after well introduction. Water usage was also determined in 2 unaffected neighboring villages not given borehole wells, but having continuous access to piped water from communal taps. Prior to borehole well construction, significantly more high-risk water use occurred in the borehole villages vs. comparison villages in terms of water gathered for cooking, drinking, dish washing, and bathing; residents of both types of villages preferred high-risk sources (marshes and ponds) for clothes washing. Following well introduction, there were significant declines in the use of high-risk water for drinking, cooking, and dish washing, but not for bathing or clothes washing. A higher proportion of individuals from the 3 borehole villages reported some type of continued contact with high-risk water sources. Despite well introduction and a 3 year chemotherapy program among school-aged children, a 21-28% incidence of infection persisted among children in the villages, suggesting minimal impact on transmission. Regular monitoring for S. haematobium infected snail sites showed no decline in the number or proportion of infected snails. Borehole well introduction can significantly alter some forms of water usage, but social and water quality factors may limit the ability of communal wells to reduce S. haematobium transmission.

Identification of snails infected with schistosomes by ELISA employing monoclonal antibodies: Schistosoma mansoni in laboratory snails (Biomphalaria glabrata) and in field snails (Biomphalaria pfeifferi) from Kenya.

An enzyme-linked immunosorbent assay (ELISA) employing monoclonal antibodies was used for detecting Schistosoma mansoni antigens in hemolymph of laboratory snails (Biomphalaria glabrata) in Kenya. Infected laboratory snails shedding cercariae were differentially identified by ELISA from uninfected snails with 100% sensitivity and specificity. Prepatent infections were detected by ELISA from 2 weeks after exposure to miracidia. Thus, ELISA revealed infection 3 weeks before maximal patency was reached (5-6 weeks post-exposure). Infected field snails (B. pfeifferi) shedding cercariae were differentially identified by ELISA, with 100% sensitivity and specificity, from uninfected field snails and from snails naturally infected with other trematodes (echinostomes and strigeids). Prepatent infections with S. mansoni were readily identified by ELISA in field snails. A case is demonstrated where infection rate, as determined by shedding test alone, was 9.8%, whereas the combined figure of prepatent and patent infection rates was 22.9%

Epidemiology of Schistosoma mansoni infection in a recently exposed community in northern Senegal.

The epidemiology of Schistosoma mansoni infection was investigated in Ndombo, a village in the epicenter of a very recent outbreak of schistosomiasis in northern Senegal. Repeated fecal egg counts and antigen detection in urine and serum were carried out in a random population sample (n = 422). Eggs were found in 91% of the subjects, with 41% excreting > 1,000 eggs per gram of feces (epg) (mean egg load of 646 epg). The prevalence was almost 100% in groups greater than five years of age. In spite of the supposed absence of acquired immunity, intensities of infection decreased strongly in adults. Antigen detection confirmed the high prevalence and intensity of infection and the age-related distribution of worm loads. The emergence of this new focus is probably due to the ecologic impact of newly built dams and the extension of irrigation projects in the Senegal basin.

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.

Schistosoma haematobium in the baboon (Papio anubis): effect of vaccination with irradiated larvae on the subsequent infection with percutaneously applied cercariae.

Groups of five baboons were vaccinated three times at approximately six-weekly intervals at a rate of 1,000 organisms per kg of gamma-irradiated Schistosoma haematobium larvae. Five vaccines were tested: 3 and 20 Krad cercariae applied percutaneously; fresh 3 and 20 Krad mechanically transformed schistosomula injected intramuscularly; and cryopreserved 20 Krad schistosomula injected intramuscularly. These five groups and an unvaccinated control group were challenged percutaneously with 7,500 S. haematobium cercariae three months after the last vaccination. The efficacy of the vaccines was judged by faecal egg excretion, and by adult worm and tissue egg recoveries at necropsy 4.5 months after challenge. Significant protection, with 64 to 89% reductions in worm burden and parallel reductions in egg production, was achieved by all but the cryopreserved vaccine, although egg production was not significantly reduced in those female worms which did mature. Cercariae tended to give more protection than schistosomula and 20 Krad more protection than 3 Krad. No significant pathology could be detected in an additional baboon vaccinated with 20 Krad schistosomula but not challenged with cercariae. This is an encouraging result for the development of a live vaccine against S. haematobium.

A histological study of skin reactions of baboons to Schistosoma mansoni schistosomula.

A histological study was undertaken of the cellular reaction in the skin of baboons challenged with cercariae of Schistosoma mansoni. Control animals with no previous schistosome infection were compared with baboons that had infections of varying duration. In animals infected for 10 weeks no striking inflammatory reaction was seen, the histological picture being very similar to that of the control animals. After 8 months of infection the hosts developed a strong cellular response to the invading schistosomula. The predominant cells in these reactions were eosinophil leucocytes which sometimes closely adhered to degenerating schistosomula. However, some unaffected schistosomula were found close to these intense cellular reactions, suggesting that schistosomula possess varying ability to resist the host's immunological attack.

A note on the efficacy of a new class of compounds, 9-acridanone-hydrazones, against Schistosoma mansoni in a primate--the baboon.

Five 9-acridanone-hydrazone compounds were tested against moderately heavy Schistosoma mansoni infections in baboons. They were administered as a single oral dose at a rate of 50 mg/kg body-weight. Compared with results from an untreated control baboon, four of the compounds showed high levels of activity judged by the reduction or elimination of faecal egg production, adult worms and tissue eggs.

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.

Schistosoma mansoni in the Kenyan baboon (Papio anubis): the development and predictability of resistance to homologous challenge.

Groups of baboons were exposed to primary infections of either 500 or 2,000 Schistosoma mansoni cercariae per baboon (c.p.b.). Five from each infection level and five uninfected baboons were challenged with 2,500 c.p.b. at one of four intervals of time after primary infection and killed ten weeks later, together with unchallenged appropriate primary infection controls. Primary faecal egg excretion was related to the cercarial dose, showing some systematic fluctuations during the 78 weeks of the experiment. Challenge infections increased faecal egg excretion in certain cases only. Faecal and tissue egg production were usually suppressed in the challenge worms. In contrast to less heavily infected, challenge-control baboons bearing primary infections, the challenged baboons had minimal gross pathology and there were no deaths due to acute schistosomiasis from the challenge infection. Over-all resistance to reinfection was low and unrelated to the age or intensity of the primary infections. However, seven baboons yielded less than 50% of the expected challenge worms. An in vitro assay, measuring anti-schistosomula antibody and peripheral leucocyte cytotoxic activity, successfully identified the in vivo immune status at thetime of challenge of 14/18 baboons tested. The in vivo significance of the immunological mechanism upon which the test is based is discussed in relation to possible future baboon and human studies.

Parasitological evaluation of curative and subcurative doses of 9-acridanone-hydrazone drugs against Schistosoma mansoni in baboons, and observations on changes in serum levels of anti-egg antibodies detected by ELISA.

Derivatives in the class of 9-acridanone-hydrazones were found to be highly active against Schistosoma mansoni in baboons. Single doses of 25 mg/kg were fully effective. Data are presented showing changes detected by ELISA in antibody levels against schistosome eggs which correlated positively with the effect of chemotherapy. This approach may help to evaluate the effects of treatment of human schistosomiasis where the detection of low egg counts is problematic.

Non-specific cell mediated immunity in patients infected with Schistosoma mansoni in Kenya.

Parameters of in vitro cell-mediated immunity (CMI) have been measured in the local Kenyan population infected with Schistosoma mansoni. Lymphocyte responses to the non-specific T cell mitogens Concanavalin A (Con A) and Phytohaemagglutinin (PHA) were reduced in about 60% of schistosomiasis patients. Lymphocytes from control uninfected, and S. mansoni-infected donors formed equal numbers of spontaneous rosettes with sheep red blood cells, indicating that there was no over-all reduction in the percentage numbers of T cells in the schistosomiasis patients.

Schistosome migration in primates: a study in the olive baboon (Papio anubis).

The migration of isotopically labelled schistosomula of Schistosoma mansoni from the skin to the hepatic portal system of baboons was tracked by autoradiography of compressed organ preparations. Passage of schistosomula from skin to lungs was rapid between days 2 and 5, 72% of applied parasites being detected in the lungs at the latter time. There was an equally rapid migration from lungs to liver, 60% of the adult worm burden having arrived by day 9. Perfusion data indicated a final maturation of not less than 78%. No evidence was found to support or refute a systemic phase of migration. Thus, in comparison to rodents, schistosome migration in baboons appears to be faster and more successful, possibly because the lungs do not represent a significant obstacle to migration.

Efficacy and side effects of praziquantel treatment in a highly endemic Schistosoma mansoni focus at Lake Albert, Uganda.

The aim of the study was to assess the efficacy and side effects following single and repeated (6 weeks apart) praziquantel treatment (40 mg/kg) in a Schistosoma mansoni-endemic focus with long-standing transmission at Lake Albert in Uganda between December 1996 and January 1997. The results were based on 482 individuals, randomly representing all age and both gender groups. The cure rate following the first and second treatments was 41.9% and 69.1%, respectively. The cure rate was higher in adults than in children, irrespective of intensity of infection. In addition, the cure rate declined markedly with increasing intensity of infection. The reduction in intensity of infection was marked, being 97.7% and 99.6% after the first and second treatments, respectively. A pre- and post-treatment symptom questionnaire revealed a broad range of side effects, including abdominal pain and diarrhoea. However, no serious or long-lasting complications affecting compliance were observed. The marked reductions in faecal egg excretion and the acceptable level of side effects point to a single praziquantel treatment (40mg/kg) as the strategy of choice in such a highly endemic S. mansoni focus.

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.

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.

Schistosomiasis mansoni in Kenya: relationship between infection and anaemia in schoolchildren at the community level.

Haematological surveys were carried out in 3 schools in 2 areas where Schistosoma mansoni is endemic in Machakos District, Kenya, before and after a treatment campaign using praziquantel. Earlier clinical impressions of differences in the levels of anaemia between the 2 areas were not confirmed. Although individual haemoglobin levels and haematocrits often fell below international norms, significant anaemia with abnormal red blood cell morphology was rare (< 5%), but varied between schools. Altitude could have accounted for some of these differences, but other factors, including diet and parasitism, were involved. Anaemia was associated with splenomegaly and, to a lesser extent, hepatosplenomegaly. Epidemic malaria (mainly Plasmodium falciparum) appeared to be the main cause of parasite-induced anaemia. There was no significant association with the scarce hookworm infections (mainly Necator americanus); nor did the much commoner S. mansoni cause severe anaemia at the community level, but haemoglobin levels dropped as its intensity increased. Treatment with praziquantel eliminated this trend except in a few subjects with splenomegaly alone (probably due to malaria) or with schistosomal hepatosplenic disease. Possible pathogenic mechanisms are reviewed, including the consumption of red blood cells by adult schistosomes as a possible cause of anaemia.