The impact of schistosomiasis among rural populations in Liberia

Human infection with Schistosoma haematobium and/or Schistosoma mansoni is known to be widespread in central Liberia, but no information is available about its clinical manifestations or its significance for public health. Details of a cross-sectional morbidity study are reported. A sample from hospital out-patients and samples from 3 villages situated in areas with different transmission patterns (lack of transmission, transmission of only S. haematobium and transmission of both S. haematobium and S. mansoni) were examined. All 184 individuals were examined by standardized case history, clinical and parasitological investigations, including a skin snip for onchocerciasis and a count of schistosomal and other intestinal worm eggs from stool and urine. A complete blood count, urine analysis, urine cultures, hepatitis-B surface antigen determination and abdominal X-rays were also carried out. Schistosomal egg counts ranged from 1 to 6200/10 ml urine for S. haematobium and from 1 to 228/g stool for S. mansoni. Difficulties for the definition of accurate morbidity indices are discussed. Except for haematuria and dysuria, the overall morbidity in the study area was not striking, neither for S. haematobium nor for S. mansoni infection. No cumulative pathology was observed in patients with mixed infection. The frequency of hypertension, hepato- and splenomegaly, ascites and bacteriuria was low and no relationship to schistosomiasis could be established. Bladder calcifications were found in 10% of people living in an area of transmission of S. haematobium. Although the intensity of infection is low for both S. haematobium and S. mansoni, long-term follow-up studies are essential for a more accurate assessment of the public health importance of these parasites.     

Quantification of clinical morbidity associated with schistosome infection in sub-Saharan Africa

Health policy making in developing countries requires estimates of the (global) burden of disease. At present, most of the available data on schistosomiasis is limited to numbers of individuals harbouring the infection. We explored the relationship between the presence of schistosome infection and clinical morbidity, in order to estimate numbers of individuals with disease-specific morbidity for Schistosoma haematobium and Schistosoma mansoni infection in sub-Saharan Africa. We searched the literature for cross-sectional data from field studies reporting both schistosome infection and morbidity. This was used to derive a functional relationship between morbidity and infection. After standardisation for diagnostic method, the number of individuals with specific types of clinical morbidity or pathology was predicted. As only aggregated prevalences of infection were available for countries or areas, we adjusted for heterogeneity in infection levels within communities in those countries. In total, 70 million individuals out of 682 million (2000 estimate) in sub-Saharan Africa were estimated to experience haematuria in the last 2 weeks associated with S. haematobium infection, and 32 million dysuria. Ultrasound detected serious consequences of S. haematobium, major bladder wall pathology and major hydronephrosis, were predicted at 18 and 10 million, respectively. Infection with S. mansoni was estimated to cause diarrhoea in 0.78 million individuals, blood in stool in 4.4 million and hepatomegaly in 8.5 million. As the associations between prevalence of S. mansoni infection and prevalence of diarrhoea and blood in stool were not very clear, the resulting estimates may be underestimations. Using the very limited data available, we estimated the mortality rates due to non-functioning kidney (from S. haematobium) and haematemesis (from S. mansoni) at 150000 and 130000 per year. Given the overall high number of cases with schistosomiasis-related disease and associated death, we conclude that schistosomiasis remains an important public health problem in sub-Saharan Africa.     

Rice irrigation and schistosomiasis in savannah and forest areas of Côte d'Ivoire

Prevalence and intensity of infection of Schistosoma haematobium and Schistosoma mansoni were studied in relation to irrigated rice cultivation in C?te d'Ivoire. Urine and stool samples were collected from 4 to 15-year-old children in 24 villages in the savannah zone and 21 villages in the forest zone. Villages were classified according to surrounding inland valleys into three agro-ecosystems: (R2) full or partial water control allowing two rice cycles per year; (R1) no or partial water control allowing one harvest per year and (R0) absence of rice growing. In the savannah zone, S. haematobium prevalence was 4.8%, 2.3% and 0.7% and S. mansoni prevalence was 16.1%, 11.9% and 2.1% in R2, R1 and R0, respectively. In the forest zone, S. haematobium prevalence was 0.9%, 4.4% and 1.7% and S. mansoni prevalence was 61.3%, 46.6% and 17.5% in R2, in R1 and R0, respectively. Prevalences of S. mansoni adjusted for village effects were significantly different between agro-ecosystems in both zones. Significance of differences between agro-ecosystems of S. haematobium infection were strongly influenced by outlying villages. In savannah rice growing villages, negative binomial regression on infection intensity of each species showed significant positive relations to the surface of rice cultivated inland valleys, whereas uncultivated inland valleys showed no significant relation. However, in forest rice growing villages, S. mansoni infection intensity showed significant positive relations to the surface of uncultivated inland valleys, whereas surface water on rice cultivated land showed significant negative relations with infection intensity of each schistosomiasis species.     

Homologous and heterologous protective immunity to Egyptian strains of Schistosoma mansoni and S. haematobium induced by ultraviolet-irradiated cercariae

C57BL/6 and Balb/c mice were immunized with ultraviolet-irradiated cercariae of Egyptian strains of Schistosoma mansoni and S. haematobium , challenged with non-irradiated cercariae of the homologous or heterologous species, and assayed for protection against challenge infection by comparing the adult worm burdens of immunized and non-immunized mice. Homologous protection (per cent reduction in worm recovery) ranged from 56% to 69% for S. mansoni and 88% to 99% for S. haematobium . Significant heterologous protection was consistently induced against S. haematobium by immunization with S. mansoni , but not against S. mansoni by immunization with S. haematobium . These results are discussed in relation to those of previous studies and in terms of implications for vaccine development.     

Assessment of ultrasound morbidity indicators of schistosomiasis in the context of large-scale programs illustrated with experiences from Malian children

We assessed morbidity indicators for both Schistosoma haematobium and Schistosoma mansoni infections and evaluated the appropriateness of the World Health Organization (WHO) guidelines for ultrasound in schistosomiasis in the context of large-scale control interventions. Abdominal and urinary tract ultrasonography was performed on 2,247 and 2,822 school children, respectively, from 29 randomly selected schools in Mali before the implementation of mass anthelminthic drug administration. Using two-level logistic regression models, we examined associations of potential factors with the risk of having a positive ultrasound global score (morbidity indicative of S. haematobium infection), abnormal image pattern scores, dilatation of the portal vein, and/or enlarged liver (morbidity indicative of S. mansoni infection). The WHO protocol was found useful for detection of S. haematobium pathology but overestimated the risk of portal vein dilatation and left liver lobe enlargement associated with S. mansoni infection. We conclude that ultrasonography should be included in large-scale control interventions, where logistics allow, but cautiously.     

Swamp rice farming: possible effects on endemicity of schistosomiasis mansoni and haematobia in a population in Liberia

To obtain a better understanding of the possible influence of swamp rice farming on the patterns of Schistosoma mansoni and Schistosoma haematobium infections, the populations of two communities in rural liberia were studied. In one village, Balama (population of 435), swamp rice farms were initiated six years before the survey; in the other nearby community, Gbarta (population of 216), swamp rice farms had not yet been initiated. The prevalence of S. mansoni infection in Balama was 87% vs. 9% in Gbarta (P less than 0.01). The geometric and arithmetic mean egg counts for all infected subjects in Balama were respectively 263 and 671/g feces. in Gbarta, the geometric and arithmetic mean egg counts were 150 and 129/g feces. S. haematobium eggs were detected in 42% of subjects in Balama vs. 11% in Gbarta (P less than 0.01). Hematuria correlated with the presence of S. haematobium eggs in urine. These data indicate that there is a significantly higher prevalence and intensity of schistosomiasis mansoni and haematobia in a community where swamp rice farming has been utilized for 6 years compared to a nearby village where this water irrigation and drainage practice has not yet been implemented.     

Interactions between Schistosoma haematobium and Schistosoma mansoni in humans in north Cameroon

OBJECTIVES: To analyse the relationships between the frequency of ectopic localizations of Schistosoma haematobium and S. mansoni eggs. METHODS: Studies were conducted in 11 villages in north Cameroon, around Bessoum, a village where an epidemic of bloody diarrhoea caused by S. mansoni occurred in 1997. RESULTS: The results revealed infection prevalence rates of 70.5% for S. haematobium and 30.8% for S. mansoni. Interestingly, S. mansoni eggs were found in 14.5% of the urine samples and S. haematobium eggs in 3% of the stool samples. These ectopic eliminations of schistosome eggs resulted from sexual interactions between the two species of schistosomes, and from a spill-over of high infection loads. The clinical study showed that the morbidity was lower in individuals with mixed infections and high loads of S. haematobium than in those with S. mansoni infections only, suggesting a possible lowering effect of S. haematobium infection on S. mansoni morbidity. DISCUSSION: The results obtained in human populations are discussed in relation to the known schistosome interspecific interactions in animal models.     

Praziquantel for treatment of schistosomiasis in patients with advanced hepatosplenomegaly

We evaluated praziquantel for therapy of active Schistosoma mansoni infection in 15 rural Egyptian males with hepatosplenic schistosomiasis. Criteria for inclusion in this study were two pre-treatment S. mansoni egg counts with a mean of greater than 100 eggs g-1 faeces and an enlarged spleen. Fourteen of 15 patients had hepatomegaly, five had ascites, and six had serum albumin below 3 g dl-1. Schistosoma haematobium infection (less than 10 eggs ml-1 urine) was present in three patients. Praziquantel was administered in a single oral dose of 30 mg kg-1 body weight. Eight of the 15 patients (53%) had mild and transient reactions in the form of fever (usually one day), gastrointestinal symptoms, headache and skin rash. Criteria for parasitological cure were the absence of live eggs in two stool samples and a negative rectal snip biopsy three months after therapy. Ten patients ceased to pass live eggs (cure rate 67%). For the five who were still passing live eggs there was a mean egg reduction of 95%. The three patients with S. haematobium demonstrated parasitological cures. We conclude that praziquantel is an effective and well tolerated drug for treatment of S. mansoni infection in patients with advanced hepatosplenic schistosomiasis, and it is the drug of choice for patients with coexisting S. haematobium infection.     

The epidemiology of a recent focus of mixed Schistosoma haematobium and Schistosoma mansoni infections around the 'Lac de Guiers' in the Senegal River Basin, Senegal

A village with mixed Schistosoma mansoni and S. haematobium infections (probably in a early endemic phase) was identified around the Lac de Guiers in the Senegal River Basin. In documenting the epidemiology of both schistosomes, we focused on prevalence and intensity of infection, transmission patterns and the impact of treatment. S. mansoni prevalences (near 100%) and egg counts (overall geometric mean eggs per gram of faeces (epg) of 589 were high in all age groups, with 35% of individuals excreting > 1000 epg, and showing a slow decline in egg output only after the age of 30 years. The overall prevalence (28%) and egg counts (2% > 50 eggs/10 ml) of S. haematobium were low, with mean counts of 6.3 eggs/10 ml. Maximal mean S. mansoni egg counts were found in 5-9 year-old boys and in 15-19 year-old girls; S. haematobium maximal counts in 1-4 year-old boys and in girls aged 5-9. Extremely high Biomphalaria pfeifferi infection ratios were recorded over the whole year. Following a single treatment, re-infection was rapid with prevalences and mean egg counts of both Schistosoma species reaching pretreatment levels within 7 months.     

Immune attrition of adult schistosomes

Mouse infection models are described that demonstrate reduction in the rate of egg production in Schistosoma haematobium worms 6–10 weeks after the onset of oviposition and loss of Schistosoma bovis worms around 10 weeks after infection. Neither phenomenon has been shown in Schistosoma mansoni- or Schistosoma japonicum-infected mice. The immunological basis for these anti-adult responses was inferred by comparison with infections in T-cell deprived mice and by transferance of the ability to reduce a S. bovis worm burden in immuno-compromised hosts with immune serum. Vaccination with irradiation-attenuated parasites of S. haematobium was also shown to have consequences for the adults of challenge infections of either S. haematobium or of S. bovis, but not of S. mansoni. Thus, prior vaccination resulted in an abrogation of the reduced egg production by S. haematobium and S. bovis worms and also of the adult worm elimination that occurred in non-vaccinated S. bovis-infected mice. These models are being used to define the targets and mechanisms involved in the attrition of adult worms of schistosomes with terminal spined eggs.     

Presence of the schistosome circulating anodic antigen (CAA) in urine of patients with Schistosoma mansoni or S. haematobium infections

We investigated the presence of the circulating anodic antigen (CAA) in the urine of schistosomiasis patients. This genus specific antigen was hitherto demonstrated only in the serum of schistosomiasis patients. The urine of 80 patients with Schistosoma mansoni infections, 33 patients with S. haematobium infections, and 2 patients with mixed S. haematobium and S. mansoni infections were screened by a quantitative enzyme-linked immunosorbent assay (ELISA). CAA was demonstrated in 81% of those with intestinal schistosomiasis and in 97% of those with urinary schistosomiasis. CAA titers were less than 1:0.2-1:51.2. Results were compared with circulating cathodic antigen (CCA) titers in urine obtained in an indirect hemagglutination assay (IHA). CCA was generally not detectable in the urine of patients with S. haematobium infection, but was demonstrated in the urine of 85% of the patients with S. mansoni infection. Both CAA titers and CCA titers correlated positively with the number of S. mansoni eggs excreted in the feces, but CAA titers did not show a significant correlation with the number of S. haematobium eggs in urine. Both antigen titers showed a moderate correlation with the serum CAA level in schistosomiasis mansoni. The discovery of CAA in the urine of the majority of schistosomiasis patients tested suggests the use of urine samples for non-invasive immunodiagnosis of the disease.     

Prevalence of schistomasiasis lesions detected by ultrasonography in children in Molodo, Mali

AIM: To study schistomasiasis infection in school children in Molodo, an irrigated rice growing region of Mali, by determining the prevalence of schistomasiasis and lesions identified by ultrasonography among children living in this region. METHODS: This cross sectional study included 346 children aged 7 to 14 years selected at random from five schools in Molodo. We tested for hematuria using urine dipsticks and searched for Schistosoma haematobium eggs in urine and S. mansoni eggs in stools. Ultrasonography of the liver, spleen and urinary tract was performed. RESULTS: The prevalences of Schistosoma haematobium and S. mansoni infection were 72% (range: 66.9-76.6%) and 68.2% (range: 60.9-71.2%) respectively; 55.1% of the children had co-infection. Ultrasonography of the urinary tract revealed an irregular bladder wall as the most frequent abnormality (3.4% of children). Abdominal ultrasonography demonstrated type B hepatic fibrosis in four children (1.1%), type C in one (0.3%) and type D in one (0.3%). CONCLUSION: Few schistosomiasis lesions were detected by ultrasonography compared with the prevalence of S. haematobium and S. mansoni infections. This observation is probably related to mass treatment programs conducted during a national anti-schistosomiasis program.     

Missed treatment opportunities for schistosomiasis mansoni, in an active programme for the treatment of urinary schistosomiasis in Plateau and Nasarawa states, Nigeria

Both Schistosoma haematobium and S. mansoni are endemic in Nigeria. Since 1999 the ministries of health of Plateau and Nasarawa states, assisted by The Carter Center, have provided mass drug administrations with praziquantel to villages where >20% of the school-aged children tested with urine dipsticks have been found to have haematuria (presumed to be caused by S. haematobium). The current extent of S. mansoni in Nigeria remains relatively unknown because the tests needed to detect human infection with this parasite are difficult to perform in many endemic areas. In a cross-sectional survey involving 924 children, the prevalence of S. mansoni was determined in 30 villages (in four local government areas) that had been excluded from mass praziquantel administrations because the prevalence of haematuria in their school-aged children had been found to be <20%. Seventeen (57%) of the surveyed villages had sufficient S. mansoni (i.e. prevalences of at least 10%) to warrant treatment. The results indicated that, if both S. haematobium and S. mansoni are taken into account, 81% of the villages in the four local government areas studied require treatment, compared with 50% if only S. haematobium is considered. At the moment, the costs of the village-by-village diagnosis of S. haematobium and S. mansoni would be greater than those of the presumptive treatment of the school-aged children in all villages. Until improved and cheaper rapid diagnostic methods for S. mansoni become available, the cheapest approach to the overall problem of schistosomiasis in this part of Nigeria would therefore be wide-spread mass drug distributions, without screening for at-risk populations.     

Day-to-day variation and circadian rhythm of egg excretion in urinary schistosomiasis in the Sudan

The daily variation of urinary excretion of Schistosoma haematobium and Schistosoma mansoni ova was assessed in a group of 24 Sudanese schoolboys using the filtration Trypan blue staining technique. An intra-class correlation coefficient of r = 0.88 indicated a surprisingly low daily variation of excretion of S. haematobium ova. All patients with a median egg output of at least 100 ova per 10 ml also voided S. mansoni ova in the urine. The daily variation of S. mansoni ova was slightly greater than for S. haematobium. For an excretion rate of at least five ova per 10 ml, the lower range of mean (P = 0.95) is one, if urine filtration is done on a single day. A circadian rhythm of S. haematobium egg excretion, with a peak around noon, was confirmed. Physical exercise combined with fluid intake prior to micturition significantly increased the egg output at all time points examined.     

Specific cross-protection between Schistosoma bovis and S. haematobium induced by highly irradiated infections in mice

Significant levels of resistance against Schistosoma haematobium challenge were developed by mice exposed to highly irradiated (20 krad) cercariae of the homologous species (46-53%) or of the closely related species, S. bovis (34-56%) but not of S. mansoni (-6-28%). This ability to cross-protect reflects the phylogenetic relationships between these species; S. mansoni and S. bovis, as well as S. mansoni and S. haematobium, failed to cross-protect. The cross-protection demonstrated between S. bovis and S. haematobium in mice was non-reciprocal.     

Metrifonate trial in the treatment of various presentations of Schistosoma haematobium and S. mansoni infections in the Sudan.

The effect of metrifonate (Bilarcil Bayer) on Schistosoma haematobium and S. mansoni infections was studied in 174 patients near Khartoum. A high cure rate was obtained in S. haematobium infections, but anthelmintic efficacy was minimal in patients passing S. mansoni eggs in their stools. There was, however, a marked reduction of egg output in patients passing S. mansoni eggs in urine. This suggests that the site of infection in man, rather than the species of parasite, renders the parasite more susceptible to metrifonate. The significance of this and the possibility that these results further clarify the mode of action of metrifonate are discussed.     

Schistosoma bovis as an immunological analogue of S. haematobium

The host-parasite relationships of Schistosoma bovis and S. haematobium have been compared in normal and T-cell-deprived mice, and have been found to contrast with that of S. mansoni. Deprived mice infected with either of the former two schistosome species survived as long as, or longer than, comparably infected immunologically intact controls, and hepatocytes of infected deprived mice were not damaged in the absence of granuloma formation. S. mansoni-infected deprived mice, however, die earlier than intact controls, and suffer extensive hepatocellular abnormalities. A high degree of cross-reactivity between S. bovis, S. haematobium and S. mansoni antibodies and antigens was noted in immunoprecipitation but a greater degree of homology between S. haematobium and S. bovis egg antigens was demonstrated by enzyme immunoassay (ELISA). S. haematobium and S. bovis thus resemble each other more closely than either resembles S. mansoni, and in view of the apparent antigenic similarities between S. haematobium and S. bovis and the relatively greater ease with which the S. bovis life-cycle can be maintained in the laboratory, the animal parasite may be useful in providing material for further immunological studies of the human infection.     

Schistosomiasis and HIV-1 infection in rural Zimbabwe: implications of coinfection for excretion of eggs

BACKGROUND: Stunted development and reduced fecundity of Schistosoma parasites in immunodeficient mice and the impaired ability of human immunodeficiency virus 1 (HIV-1)-infected humans to excrete schistosome eggs have been described. This study explores the effect that HIV-1-associated immunodeficiency has on the excretion of schistosome eggs in a large cohort of coinfected individuals. METHODS: In a cross-sectional survey, urine and stool samples were obtained from and HIV-1 status was determined for 1545 individuals. More extensive data, including quantitative measures of intensity of infection in schistosomiasis and immunodeficiency, were collected in the Mupfure schistosomiasis and HIV longitudinal cohort, composed of 379 participants of whom 154 were coinfected with HIV-1 and Schistosoma parasites. RESULTS: In the cross-sectional survey, the overall prevalence of schistosomiasis was 43.4%, and 26.3% of the participants were infected with HIV-1. Schistosome infections were due to Schistosoma haematobium in 63.6% of cases, S. mansoni in 18.1% of cases, and dual infections in 18.4% of cases. Intensities of Schistosoma infections, measured by the number of eggs excreted and by the level of circulating anodic antigens, did not differ between HIV-1-negative and HIV-1-positive participants coinfected with S. haematobium, S. mansoni, or both. CD4 cell counts were significantly lower in HIV-1-positive participants and in S. mansoni-infected HIV-1-negative participants than in other participants. CONCLUSION: The present study suggests that adult HIV-1-related immunodeficiency does not impair the ability to excrete eggs in low-intensity infection with S. haematobium, S. mansoni, or both and that infection with HIV-1 may not have major implications for diagnosis and surveillance of schistosomiasis.     

Isolation and characterization of Schistosoma haematobium egg antigens

Schistosoma haematobium soluble egg antigen (ShSEA) was prepared from eggs isolated from the livers of hamsters or mice infected for at least 3 months. Immunoaffinity purified S. haematobium egg antigens (ShSh) were isolated by first passing ShSEA through a column containing anti-S. mansoni hamster IgG coupled to CNBr-activated Sepharose 4B, and recycling the unbound fraction until no more bound material could be eluted with an acid wash. The unbound fraction was then filtered through a second antibody affinity column containing anti-S. haematobium hamster IgG, and in the acid eluate the ShSh antigens were obtained. This antigenic preparation was shown by PAGE to contain at least 6 distinct bands ranging in molecular weight (Mr) from 116 to less than 31 Kd. A 40 Kd polypeptide was identified by both silver staining and EITB as specific for S. haematobium eggs. In addition, a 55 Kd worm-egg shared antigen was identified as a prominent band in EITB expressed during a primary S. haematobium hamster infection. The sera from hamsters harboring patent S. haematobium or S. mansoni infections were reacted by ELISA with ShSh antigens. The anti-Sh sera showed significantly higher absorbance values than the anti-Sm sera, demonstrating that only a minor population of S. mansoni cross-reactive egg antigens is still present in the ShSh antigens. Sera collected weekly for 13 weeks from hamsters with a primary infection of S. haematobium were then tested by ELISA against ShSh, ShSEA and SmSEA antigens. Antibody levels against both ShSEA and SmSEA were shown to increase early in infection (2 weeks). Moreover, antibody levels to ShSh did not increase until week 5 post-infection. These findings suggest that the purification procedure utilized results in the elimination of most of the S. mansoni worm antigens cross-reactive with S. haematobium eggs. The ShSh antigens had shown a high degree of sensitivity and stage-species specificity also suggesting their potential as antigens for the immunodiagnosis of schistosomiasis haematobia.     

Infection induces antibodies against the cercarial secretions, but not against the cercarial elastases of Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum and Trichobilharzia ocellata

Cercarial secretions from different species of the parasite Schistosoma and from Trichobilharzia ocellata contain a proteolytic activity, cercarial elastase, which was demonstrated by a 30 kDa band in gelatin gels. Sera of patients infected with Schistosoma mansoni, Schistosoma haematobium or Schistosoma japonicum contain immunoglobulin G which react in ELISA with cercarial secretions from all schistosomes and cross-react among the different parasite species. In Western blots, however, infection sera from patients, as well as heavily infected mice or rabbits, did not react with a 30-kDa protein. Moreover, when sections from infected snails (Biomphalaria, Bulinus and Lymnaea) were analysed by immunofluorescence using the same infection sera, only the tegument of the developing cercariae was recognized, but not the acetabular glands. In contrast, when antisera against purified cercarial elastase from either S. mansoni or S. haematobium were tested with sections of infected Biomphalaria or Bulinus, fluorescence was strong in the preacetabular glands of the cercariae of either species, but undetectable with the tegument. Cross-reactivity of both antisera extended to T. ocellata-infected Lymnaea, but not to S. japonicum-infected Oncomelania. In conclusion, although immunization with purified cercarial elastase results in antibody production, the enzyme does not induce an apparent antibody response following natural infection.