Protein undernutrition reduces the efficacy of praziquantel in a murine model of Schistosoma mansoni infection.

BACKGROUND: Undernutrition and schistosomiasis are public health problems and often occur in low and middle-income countries. Protein undernutrition can alter the host-parasite environment system and aggravate the course of schistosomiasis. This study aimed to assess the impact of a low-protein diet on the efficacy of praziquantel. METHODOLOGY/PRINCIPAL FINDINGS: Thirty-day-old mice were fed with a low-protein diet, and 40 days later, they were individually infected with fifty Schistosoma mansoni cercariae. A 28-day-treatment with praziquantel at 100 mg/kg for five consecutive days followed by distilled water begins on the 36th day post-infection. Mice were sacrificed on the 64th day post-infection. We determined the parasitological burden, liver and intestine histomorphometry, liver injury, and immunomodulation parameters. Praziquantel treatment of infected mice fed with a standard diet (IN-PZQ) resulted in a significant reduction of worm and egg burdens and a normalization of iron and calcium levels. The therapy also improved schistosomiasis-induced hepatopathy and oxidative stress. The anti-inflammatory and immunomodulatory activities of praziquantel were also significant in these mice. When infected mice receiving the low-protein diet were treated with praziquantel (ILP-PZQ), the body weight loss and hepatomegaly were not alleviated, and the worm and liver egg burdens were significantly higher than those of IN-PZQ mice (P < 0.001). The treatment did not reduce the increased activities of ALT and γ-GGT, the high malondialdehyde concentration, and the liver granuloma volume. The iron and calcium levels were not ameliorated and differed from those of IN-PZQ mice (P < 0.001 and P < 0.05). Moreover, in these mice, praziquantel treatment did not reverse the high level of IL-5 and the low mRNA expression of CCL3/MIP-1α and CXCL-10/IP-10 induced by S. mansoni infection. CONCLUSION/SIGNIFICANCE: These results demonstrated that a low-protein diet reduced the schistosomicidal, antioxidant, anti-inflammatory, and immunomodulatory activities of praziquantel.

Pathological and immunological evaluation of different regimens of praziquantel treatment in a mouse model of Schistosoma mansoni infection.

BACKGROUND: One of the considerable challenges of schistosomiasis chemotherapy is the inefficacy of praziquantel (PZQ) at the initial phase of the infection. Immature schistosomes are not susceptible to PZQ at the curative dose. Here, we investigated the efficacy of different PZQ regimens administered during the initial stage of Schistosoma mansoni infection in mice. METHODOLOGY/PRINCIPAL FINDINGS: Two months-old mice were individually infected with 80 S. mansoni cercariae and divided into one infected-untreated control group (IC) and four PZQ-treated groups: PZQ at 100 mg/kg/day for five consecutive days (group PZQ1), PZQ at 100 mg/kg/day for 28 days (group PZQ2), PZQ at 18 mg/kg/day for 28 days (group PZQ3) and a single dose of PZQ at 500 mg/kg (group PZQ4). The treatment started on day one post-infection (p.i), and each group of mice was divided into two subgroups euthanized on day 36 or 56 p.i, respectively. We determined the mortality rate, the parasitological burden, the hepatic and intestinal granulomas, the serum levels of Th-1, Th-2, and Th-17 cytokines, and gene expression. The treatment led to a significant (p < 0.001) reduction of worm burden and egg counts in the intestine and liver in groups PZQ2 and PZQ3. On 56th day p.i, there was a significant reduction (p < 0.001) of the number and volume of the hepatic granulomas in groups PZQ2 and PZQ3 compared to group PZQ1 or PZQ4. Moreover, in group PZQ3, the serum levels of IFN-γ, TNF-α, IL-13, and IL-17 and their liver mRNA expressions were significantly reduced while IL-10 and TGF-ß gene expression significantly increased. The highest mortality rate (81.25%) was recorded in group PZQ2. CONCLUSION/SIGNIFICANCE: This study revealed that the administration of PZQ at 18 mg/kg/day for 28 consecutive days was the optimal effective posology for treating S. mansoni infection at the initial stage in a murine model.

Reduction of testosterone levels in Schistosoma haematobium- or Schistosoma mansoni-infected men: a cross-sectional study in two schistosomiasis-endemic areas of the Adamawa region of Cameroon.

BACKGROUND: The incidence of schistosomiasis-induced male reproductive dysfunction and infertility is probably underestimated compared to female genital schistosomiasis. This study aimed to investigate the impact of Schistosoma haematobium or S. mansoni infection on the reproductive function of men of reproductive age in Tibati and Wouldé, two endemic schistosomiasis areas in the Adamawa region of Cameroon. METHODS: A total of 89 men of reproductive age (range 14-56 years) from two localities were enrolled in the study, with 51 in Tibati and 38 in Wouldé. Each participant was submitted to a questionnaire to document data on sociodemographic and stream contact behaviors. A medical examination was performed to measure the testes' circumference and evaluate genital tract pathologies. Stool and urine samples were collected and screened for the presence of S. haematobium or S. mansoni ova. Blood serum was used to assess the levels of transaminases and testosterone. RESULTS: Schistosoma haematobium was present only in Tibati, with a prevalence of 31.37%. The S. mansoni prevalence was 3.92% at Tibati and 44.71% at Wouldé. The intensity of infection was 22.12 ± 9.57 eggs/10 mL for S. haematobium and 128.10 ± 3.76 epg for S. mansoni. Serum transaminase activity and the mean testicular circumference of Schistosoma-positive individuals were close to Schistosoma-negative individuals. However, the testes size was more prominent in S. mansoni-positive individuals than in S. haematobium-positive individuals (P < 0.05). The serum testosterone levels of S. haematobium- and S. mansoni-positive men were significantly reduced by 56.07% (P < 0.001) and 51.94% (P < 0.01), respectively, in comparison to those of Schistosoma-negative men. A significant and negative correlation was established between schistosomiasis and the low serum testosterone level. Male genital tract pathologies such as scrotal abnormalities, varicocele, nodular epididymis, inguinal hernia, and hydrocele were recorded in both Schistosoma-positive and Schistosoma-negative men. However, no significant link was established between schistosomiasis infection and these pathologies. CONCLUSION: These results demonstrated that infection with S. haematobium or S. mansoni is associated with low production of the reproductive hormone testosterone and may be a significant cause of male infertility.

In Vitro Assessment of the Cercaricidal Activity of Sida acuta Burm. F. and Sida rhombifolia Linn. (Malvaceae) Hydroethanolic Extracts, Cytotoxicity, and Phytochemical Studies.

Despite the global efforts, schistosomiasis remains a public health problem in several tropical and subtropical countries. One of the major challenges in the fight against schistosomiasis is the interruption of the parasite life cycle. Here, we evaluated the anticercarial, cytotoxicity, and phytochemical profiles of Sida acuta (HESa) and Sida rhombifolia (HESr) hydroethanolic extracts (Malvaceae). Schistosoma mansoni cercaria was collected from fifteen Biomphalaria pfeifferi-infected snails. Twenty-five cercariae were incubated in duplicate with different concentrations (31.25-1,000 µg/mL) of HESa or HESr. The cercaria viability was monitored at 30 min time intervals for 150 min, and the concentration-response curve of each plant extract was used to determine their respective lethal concentration 50 (LC50). Additionally, the cytotoxicity profile of each plant extract was evaluated on the Hepa 1-6 cell line at a concentration range of 15.625-1,000 µg/mL using the WST-8 assay method and its inhibitory concentration 50 (IC50) was calculated. Moreover, phytochemical characterization of each plant extract was carried out by HPLC-MS. Both extracts exhibited cercaricidal activity in a time- and concentration-dependent manner. At 30 min time point, HESa (LC50 = 28.41 ± 3.5 µg/mL) was more effective than HESr (LC50 = 172.42 ± 26.16 µg/mL) in killing S. mansoni cercariae. Regarding the cytotoxicity effect of both extracts, the IC50 of HESa (IC50 = 109.67 µg/mL) was lower than that of HESr (IC50 = 888.79 µg/mL). The selectivity index was 3.86 and 5.15 for HESa and HESr, respectively. Fifteen compounds were identified from HESa and HESr after HPLC-MS analysis. N-Feruloyltyramine, a polyphenol, and thamnosmonin, a coumarin, were identified in both extracts. HESa and HESr displayed cercaricidal activity and were not toxic on Hepa 1-6 cell line. Based on the selectivity index of these extracts, S. rhombifolia extract could be more effective on S. mansoni cercariae than S. acuta extract. This study could provide baseline information for further investigations aiming to develop plant-based alternative drugs against S. mansoni.

Genome-wide insights into adaptive hybridisation across the Schistosoma haematobium group in West and Central Africa.

Schistosomiasis remains a public health concern across sub-Saharan Africa; current control programmes rely on accurate mapping and high mass drug administration (MDA) coverage to attempt disease elimination. Inter-species hybridisation can occur between certain species, changing epidemiological dynamics within endemic regions, which has the potential to confound control interventions. The impact of hybridisation on disease dynamics is well illustrated in areas of Cameroon where urogenital schistosomiasis, primarily due to Schistosoma haematobium and hybrid infections, now predominate over intestinal schistosomiasis caused by Schistosoma guineensis. Genetic markers have shown the ability to identify hybrids, however the underlying genomic architecture of divergence and introgression between these species has yet to be established. In this study, restriction site associated DNA sequencing (RADseq) was used on archived adult worms initially identified as; Schistosoma bovis (n = 4), S. haematobium (n = 9), S. guineensis (n = 3) and S. guineensis x S. haematobium hybrids (n = 4) from Mali, Senegal, Niger, São Tomé and Cameroon. Genome-wide evidence supports the existence of S. guineensis and S. haematobium hybrid populations across Cameroon. The hybridisation of S. guineensis x S. haematobium has not been demonstrated on the island of São Tomé, where all samples showed no introgression with S. haematobium. Additionally, all S. haematobium isolates from Nigeria, Mali and Cameroon indicated signatures of genomic introgression from S. bovis. Adaptive loci across the S. haematobium group showed that voltage-gated calcium ion channels (Cav) could play a key role in the ability to increase the survivability of species, particularly in host systems. Where admixture has occurred between S. guineensis and S. haematobium, the excess introgressive influx of tegumental (outer helminth body) and antigenic genes from S. haematobium has increased the adaptive response in hybrids, leading to increased hybrid population fitness and viability.

Effect of preventive chemotherapy with praziquantel on schistosomiasis among school-aged children in sub-Saharan Africa: a spatiotemporal modelling study.

BACKGROUND: Over the past 20 years, schistosomiasis control has been scaled up. Preventive chemotherapy with praziquantel is the main intervention. We aimed to assess the effect of preventive chemotherapy on schistosomiasis prevalence in sub-Saharan Africa, comparing 2000-10 with 2011-14 and 2015-19. METHODS: In this spatiotemporal modelling study, we analysed survey data from school-aged children (aged 5-14 years) in 44 countries across sub-Saharan Africa. The data were extracted from the Global Neglected Tropical Diseases database and augmented by 2018 and 2019 survey data obtained from disease control programmes. Bayesian geostatistical models were fitted to Schistosoma haematobium and Schistosoma mansoni survey data. The models included data on climatic predictors obtained from satellites and other open-source environmental databases and socioeconomic predictors obtained from various household surveys. Temporal changes in Schistosoma species prevalence were estimated by a categorical variable with values corresponding to the three time periods (2000-10, 2011-14, and 2015-19) during which preventive chemotherapy interventions were scaled up. FINDINGS: We identified 781 references with relevant geolocated schistosomiasis survey data for 2000-19. There were 19 166 unique survey locations for S haematobium and 23 861 for S mansoni, of which 77% (14 757 locations for S haematobium and 18 372 locations for S mansoni) corresponded to 2011-19. Schistosomiasis prevalence among school-aged children in sub-Saharan Africa decreased from 23·0% (95% Bayesian credible interval 22·1-24·1) in 2000-10 to 9·6% (9·1-10·2) in 2015-19, an overall reduction of 58·3%. The reduction of S haematobium was 67·9% (64·6-71·1) and that of S mansoni 53·6% (45·2-58·3) when comparing 2000-10 with 2015-19. INTERPRETATION: Our model-based estimates suggest that schistosomiasis prevalence in sub-Saharan Africa has decreased considerably, most likely explained by the scale-up of preventive chemotherapy. There is a need to consolidate gains in the control of schistosomiasis by means of preventive chemotherapy, coupled with other interventions to interrupt disease transmission. FUNDING: European Research Council and WHO.

Estimating true prevalence of Schistosoma mansoni from population summary measures based on the Kato-Katz diagnostic technique.

BACKGROUND: The prevalence of Schistosoma mansoni infection is usually assessed by the Kato-Katz diagnostic technique. However, Kato-Katz thick smears have low sensitivity, especially for light infections. Egg count models fitted on individual level data can adjust for the infection intensity-dependent sensitivity and estimate the 'true' prevalence in a population. However, application of these models is complex and there is a need for adjustments that can be done without modeling expertise. This study provides estimates of the 'true' S. mansoni prevalence from population summary measures of observed prevalence and infection intensity using extensive simulations parametrized with data from different settings in sub-Saharan Africa. METHODOLOGY: An individual-level egg count model was applied to Kato-Katz data to determine the S. mansoni infection intensity-dependent sensitivity for various sampling schemes. Observations in populations with varying forces of transmission were simulated, using standard assumptions about the distribution of worms and their mating behavior. Summary measures such as the geometric mean infection, arithmetic mean infection, and the observed prevalence of the simulations were calculated, and parametric statistical models fitted to the summary measures for each sampling scheme. For validation, the simulation-based estimates are compared with an observational dataset not used to inform the simulation. PRINCIPAL FINDINGS: Overall, the sensitivity of Kato-Katz in a population varies according to the mean infection intensity. Using a parametric model, which takes into account different sampling schemes varying from single Kato-Katz to triplicate slides over three days, both geometric and arithmetic mean infection intensities improve estimation of sensitivity. The relation between observed and 'true' prevalence is remarkably linear and triplicate slides per day on three consecutive days ensure close to perfect sensitivity. CONCLUSIONS/SIGNIFICANCE: Estimation of 'true' S. mansoni prevalence is improved when taking into account geometric or arithmetic mean infection intensity in a population. We supply parametric functions and corresponding estimates of their parameters to calculate the 'true' prevalence for sampling schemes up to 3 days with triplicate Kato-Katz thick smears per day that allow estimation of the 'true' prevalence.

Evaluation of the schistosomicidal, antioxidant and anti-inflammatory activities of the ethyl acetate fraction from Ozoroa pulcherrima Schweinf. Roots on Schistosoma mansoni-induced liver pathology in mice and its phytochemical characterization.

ETHNOPHARMACOLOGICAL RELEVANCE: Ozoroa pulcherrima Schweinf. (syn.: Heeria pulcherrrima Schweinf.) is a small shrub belonging to the family Anacardiaceae. In Africa, the stem and the leaves are used to treat dystocia, hyperthermia, and conjunctivitis, while the root is used to treat dysmenorrhea and intestinal helminthiasis. AIM OF THE STUDY: The aim of this study was to assess the schistosomicidal, antioxidant and anti-inflammatory effects of the ethyl acetate fraction from O. pulcherrima roots methanolic extract (EAOp) on S. mansoni- induced liver pathology in mice. Additionally, its phytochemical composition was elucidated. MATERIAL AND METHODS: The phytochemical characterization of EAOp was carried out by High-Performance Liquid Chromatography-Mass spectrometry (HPLC-MS). Total phenolic and flavonoid contents were also quantified in the fraction. S. mansoni-infected mice received daily and per os, for 28 days, EAOp at 200 or 400 mg/kg, starting from the 36th day post-infection. Praziquantel was used as reference drug. Uninfected-untreated, uninfected-treated and infected-untreated mice served as controls. At the 65th day post-infection mice were sacrificed and parasitological burden monitored. Transaminases, total bilirubin, and total proteins levels were determined in the plasma. Malondialdehyde (MDA), nitrites, superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) levels were measured in the liver as biomarkers of the oxidative stress. Liver histology and morphometric analysis of granulomas were also conducted. RESULTS: The HPLC-MS analysis data of EAOp revealed the presence of four triterpenes namely oleaterminaloic acid, hydroxyoleanolic acid, moronic acid, and oleanolic acid; a flavonoid dipentoxybenzoic acid and two alkaloids. Its total phenolic content was 76.46 ±â€¯0.01 mg GAE/g and total flavonoid content 6.26 ±â€¯0.31 mg rutin equivalent/g. The reductions of worm burden (48.89 and 75.56%), fecal egg count (77.76 and 69.52%) and egg load in the liver (65.33 and 77.18%) and intestine (78.06 and 84.63%) were significant after EAOp treatment. EAOp at all doses significantly (p < 0.001) reversed the increasing transaminases activities and total bilirubin level induced by the infection. A normalization of total proteins concentration was also recorded. Treatment of S. mansoni-infected mice with EAOp at 200 or 400 mg/kg resulted in a significant reduction (p < 0.001) of MDA concentration by 73.20% and 67.78% respectively. The level of nitrites which was reduced by the infection significantly increased after the treatment. EAOp significantly increased by 4.67 and 5.69-fold the CAT activity and by 126.67% the GSH level. Histologically, a significant reduction of the number (66.39 and 57.82%) and the volume (52.25 and 34.81%) of liver inflammatory granulomas was recorded after EAOp treatment at all doses. CONCLUSIONS: These results suggest that the liver pathology in S. mansoni infection is improved by EAOp which disclosed good schistosomicidal, antioxidant and anti-inflammatory activities. Its effects on the liver dysfunction and the hepatic oxidative stress were comparable to that of praziquantel. These findings justified the traditional use of O. pulcherrima for the treatment of intestinal helminthiasis. This fraction can be considered as a promising source for schistosomicidal agents.

Translating preventive chemotherapy prevalence thresholds for Schistosoma mansoni from the Kato-Katz technique into the point-of-care circulating cathodic antigen diagnostic test.

BACKGROUND: Intervention guidelines against Schistosoma mansoni are based on the Kato-Katz technique. However, Kato-Katz thick smears show low sensitivity, especially for light-intensity infections. The point-of-care circulating cathodic antigen (POC-CCA) is a promising rapid diagnostic test detecting antigen output of living worms in urine and results are reported as trace, 1+, 2+, and 3+. The use of POC-CCA for schistosomiasis mapping, control, and surveillance requires translation of the Kato-Katz prevalence thresholds into POC-CCA relative treatment cut-offs. Furthermore, the infection status of egg-negative but antigen-positive individuals and the intensity-dependent sensitivity of POC-CCA should be estimated to determine its suitability for verification of disease elimination efforts. METHODOLOGY: We used data from settings in Africa and the Americas characterized by a wide range of S. mansoni endemicity. We estimated infection intensity-dependent sensitivity and specificity of each test at the unit of the individual, using a hierarchical Bayesian egg-count model that removes the need to define a 'gold' standard applied to data with multiple Kato-Katz thick smears and POC-CCA urine cassette tests. A simulation study was carried out based on the model estimates to assess the relation of the two diagnostic tests for different endemicity scenarios. PRINCIPAL FINDINGS: POC-CCA showed high specificity (> 95%), and high sensitivity (> 95%) for moderate and heavy infection intensities, and moderate sensitivity (> 75%) for light infection intensities, and even for egg-negative but antigen-positive infections. A 10% duplicate slide Kato-Katz thick smear prevalence corresponded to a 15-40% prevalence of ≥ trace-positive POC-CCA, and 10-20% prevalence of ≥ 1+ POC-CCA. The prevalence of ≥ 2+ POC-CCA corresponded directly to single slide Kato-Katz prevalence for all prevalence levels. CONCLUSIONS/SIGNIFICANCE: The moderate sensitivity of POC-CCA, even for very light S. mansoni infections where the sensitivity of Kato-Katz is very low, and the identified relationship between Kato-Katz and POC-CCA prevalence thresholds render the latter diagnostic tool useful for surveillance and initial estimation of elimination of S. mansoni. For prevalence below 10% based on a duplicate slide Kato-Katz thick smear, we suggest using POC-CCA including trace results to evaluate treatment needs and propose new intervention thresholds that need to be validated in different settings.

A pilot study using wearable global positioning system data loggers to compare water contact levels: Schistosoma haematobium infection in pre-school-age children (PSAC) and their mothers at Barombi Kotto, Cameroon.

Background: Barombi Kotto, Cameroon serves as a reference location for assessing intervention strategies against Schistosoma haematobium. Methods: As part of a pilot study, the whole community was treated with praziquantel, inclusive of pre-school-age children (PSAC) and their mothers. One year later, egg-patent infections were reassessed and water contact patterns of 12 pairs of PSAC and their mothers were measured with global positioning system (GPS) data loggers. Results: A substantial reduction in general infection prevalence, from 44.8% to 12.2%, was observed but certain PSAC and mothers continued to have egg-patent infections. Analysis of GPS data demonstrated similar water contact levels between the child and mother groups, although certain individuals were numerical outliers. Conclusions: This study shows the potential of GPS data loggers to clarify the at-risk status of PSAC and mothers.

Mapping of schistosomiasis and soil-transmitted helminthiasis in the regions of Littoral, North-West, South and South-West Cameroon and recommendations for treatment.

BACKGROUND: The previous nationwide mapping of schistosomiasis and soil-transmitted helminthiasis (STH) in Cameroon was conducted 25 years ago. Based on its results, mass drug administration (MDA) of praziquantel was limited to the three northern regions and few health districts in the southern part of Cameroon. In 2010, we started the process of updating the disease distribution in order to improve the control strategies. Three of the ten regions of Cameroon were mapped in 2010 and the data were published. In 2011, surveys were conducted in four additional regions, i.e. Littoral, North-West, South and South-West. METHODS: Parasitological surveys were conducted in March 2011 in selected schools in all 65 health districts of the four targeted regions, using appropriate research methodologies, i.e. Kato-Katz and urine filtration. RESULTS: The results showed significant variation of schistosomiasis and STH prevalence between schools, villages, districts and regions. Schistosoma haematobium was the most prevalent schistosome species, with an overall prevalence of 3.2%, followed by S. mansoni (3%) and S. guineensis (1.2%). The overall prevalence of schistosomiasis across the four regions was 7.4% (95% CI: 6.7-8.3%). The prevalence for Ascaris lumbricoides was 19.5% (95% CI: 18.3-20.7%), Trichuris trichiura 18.9% (95% CI: 17.7-20.1%) and hookworms 7.6% (95% CI: 6.8-8.4%), with an overall STH prevalence of 32.5% (95% CI: 31.1-34.0%) across the four regions. STH was more prevalent in the South region (52.8%; 95% CI: 48.0-57.3%), followed by the South-West (46.2%; 95% CI: 43.2-49.3%), the North-West (35.9%; 95% CI: 33.1-38.7%) and the Littoral (13.0%; 95% CI: 11.3-14.9%) regions. CONCLUSIONS: In comparison to previous data in 1985-87, the results showed an increase of schistosomiasis transmission in several health districts, whereas there was a significant decline of STH infections. Based on the prevalence data, the continuation of annual or bi-annual MDA for STH is recommended, as well as an extension of praziquantel in identified moderate and high risk communities for schistosomiasis.

Efficacy of praziquantel and reinfection patterns in single and mixed infection foci for intestinal and urogenital schistosomiasis in Cameroon.

The regular administration of the anthelminthic drug praziquantel (PZQ) to school-aged children (and other high-risk groups) is the cornerstone of schistosomiasis control. Whilst the performance of PZQ against single schistosome species infections is well-known, performance against mixed species infections is less so, as are patterns of re-infection following treatment. To address this, a study using a double treatment with PZQ, administered at 40 mg/kg spaced by 3 weeks, took place in two mixed intestinal-urogenital schistosomiasis foci in northern Cameroon (Bessoum and Ouro-Doukoudje) and in one single intestinal schistosomiasis infection focus (Makenene). A total of just under 1000 children were examined and the Schistosoma-infected children were re-examined at several parasitological follow-ups over a 1-year period posttreatment. Overall cure rates against Schistosoma spp. in the three settings were good, 83.3% (95% confidence interval (CI)=77.9-87.7%) in Bessoum, 89.0% (95% CI=79.1-94.6%) in Ouro Doukoudje, and 95.3% (95% CI=89.5-98.0%) in Makenene. Interestingly, no case of mixed schistosome infection was found after treatment. Cure rates for S. mansoni varied from 99.5% to 100%, while that for S. haematobium were considerably lower, varying from 82.7% to 88.0%. Across transmission settings, patterns of re-infection for each schistosome species were different such that generalizations across foci were difficult. For example, at the 6-month follow-up, re-infection rates were higher for S. haematobium than for S. mansoni with re-infection rates for S. haematobium varying from 9.5% to 66.7%, while for S. mansoni, lower rates were observed, ranging between nil and 24.5%. At the 12-month follow-up, re-infection rates varied from 9.1% to 66.7% for S. haematobium and from nil to 27.6% for S. mansoni. Alongside these parasitological studies, concurrent malacological surveys took place to monitor the presence of intermediate host snails of schistosomiasis. In the two northern settings, three species of Bulinus (intermediate host snail of S. haematobium) were collected; i.e. Bulinus truncatus, B. globosus and B. senegalensis, however, Biomphalaria pfeifferi (intermediate host snail of S. mansoni) was much rarer despite repeated and intensive searching and was suggestive of limited local transmission potential of S. mansoni during this time. While this study highlights that performance of PZQ was satisfactory in this region, with somewhat greater impact upon intestinal than urogenital schistosomiasis, the dynamics of local transmission are shown, however, to be complex.

Schistosomiasis control: keep taking the tablets.

Despite the limited reports of praziquantel resistance, the relative success of chemotherapy-based control programmes for schistosomiasis has prompted overdue efforts to expand the use of cheap, generic, praziquantel in sub-Saharan Africa. The likely impact of such programmes on the development and spread of praziquantel resistance is uncertain, but this possibility reinforces the need for monitoring the spectrum of praziquantel sensitivity of schistosome populations and for an improved knowledge of the precise targets for the action of the drug. The search for alternatives to praziquantel and other tools for control of schistosomiasis must continue.

Recent studies on Schistosoma intercalatum: taxonomic status, puzzling distribution and transmission foci revisited

Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity indice allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum