BACKGROUND: Preventive chemotherapy represents a powerful but short-term control strategy for soil-transmitted helminthiasis. Since humans are often re-infected rapidly, long-term solutions require improvements in water, sanitation, and hygiene (WASH). The purpose of this study was to quantitatively summarize the relationship between WASH access or practices and soil-transmitted helminth (STH) infection. METHODS AND FINDINGS: We conducted a systematic review and meta-analysis to examine the associations of improved WASH on infection with STH (Ascaris lumbricoides, Trichuris trichiura, hookworm [Ancylostoma duodenale and Necator americanus], and Strongyloides stercoralis). PubMed, Embase, Web of Science, and LILACS were searched from inception to October 28, 2013 with no language restrictions. Studies were eligible for inclusion if they provided an estimate for the effect of WASH access or practices on STH infection. We assessed the quality of published studies with the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach. A total of 94 studies met our eligibility criteria; five were randomized controlled trials, whilst most others were cross-sectional studies. We used random-effects meta-analyses and analyzed only adjusted estimates to help account for heterogeneity and potential confounding respectively. Use of treated water was associated with lower odds of STH infection (odds ratio [OR] 0.46, 95% CI 0.36-0.60). Piped water access was associated with lower odds of A. lumbricoides (OR 0.40, 95% CI 0.39-0.41) and T. trichiura infection (OR 0.57, 95% CI 0.45-0.72), but not any STH infection (OR 0.93, 95% CI 0.28-3.11). Access to sanitation was associated with decreased likelihood of infection with any STH (OR 0.66, 95% CI 0.57-0.76), T. trichiura (OR 0.61, 95% CI 0.50-0.74), and A. lumbricoides (OR 0.62, 95% CI 0.44-0.88), but not with hookworm infection (OR 0.80, 95% CI 0.61-1.06). Wearing shoes was associated with reduced odds of hookworm infection (OR 0.29, 95% CI 0.18-0.47) and infection with any STH (OR 0.30, 95% CI 0.11-0.83). Handwashing, both before eating (OR 0.38, 95% CI 0.26-0.55) and after defecating (OR 0.45, 95% CI 0.35-0.58), was associated with lower odds of A. lumbricoides infection. Soap use or availability was significantly associated with lower infection with any STH (OR 0.53, 95% CI 0.29-0.98), as was handwashing after defecation (OR 0.47, 95% CI 0.24-0.90). Observational evidence constituted the majority of included literature, which limits any attempt to make causal inferences. Due to underlying heterogeneity across observational studies, the meta-analysis results reflect an average of many potentially distinct effects, not an average of one specific exposure-outcome relationship. CONCLUSIONS: WASH access and practices are generally associated with reduced odds of STH infection. Pooled estimates from all meta-analyses, except for two, indicated at least a 33% reduction in odds of infection associated with individual WASH practices or access. Although most WASH interventions for STH have focused on sanitation, access to water and hygiene also appear to significantly reduce odds of infection. Overall quality of evidence was low due to the preponderance of observational studies, though recent randomized controlled trials have further underscored the benefit of handwashing interventions. Limited use of the Joint Monitoring Program's standardized water and sanitation definitions in the literature restricted efforts to generalize across studies. While further research is warranted to determine the magnitude of benefit from WASH interventions for STH control, these results call for multi-sectoral, integrated intervention packages that are tailored to social-ecological contexts.

https://edoc.unibas.ch/34012/1/20140512122808_5370a23851a65.pdf

Water, Sanitation, Hygiene, and Soil-Transmitted Helminth Infection: A Systematic Review and Meta-Analysis

This review considers the current status of urinary schistosomiasis, caused by infection with Schistosoma haematobium, and argues that greater research effort and focus are needed to improve understanding of this neglected tropical disease (NTD). The inappropriateness of relying solely on data concerning the much more extensively studied intestinal form of schistosomiasis caused by S. mansoni is highlighted. The current lack of genome and transcriptome information for S. haematobium is directly hindering further targeted research and must be quickly rectified. Recent molecular phylogenies caution the expectation of similarities between schistosome species and highlight the close relationships of species within the S. haematobium group. Treatment, current and prospective drugs and vaccines, together with diagnosis are considered, highlighting the differences associated with urinary schistosomiasis. This infection has a significant and specific impact on the urino-genital system and has a strong association with bladder cancer, leading to severe and chronic morbidity. There is a clear need for new clinical initiatives in this area to better quantify the disease burden. Furthermore, emerging associations with HIV and other pathogens need to be closely monitored. Research is urgently needed to improve current knowledge in order to develop the next generation of control tools.

A Wake Up Call for Urinary Schistosomiasis: Reconciling Research Effort With Public Health Importance

Cercariae are non-feeding free-living stages in the life cycles of trematodes, highly influenced by temperature. Their life span is brief, limited by the depletion of a non-renewable glycogen store. Warmer temperatures under the influence of climate change may promote the transmission of parasites and therefore understanding their thermobiology forms an important step in discerning the future dynamics of parasite populations. An empirical relationship exists between cercarial mean expected life span and the half-life of the population (t0·5) and therefore t0·5 is a good indicator of glycogen utilization. In this study experimental data on the effects of temperature on cercarial survival is compiled from the scientific literature and evaluated in terms of metabolism using Q10 and Arrhenius activation energy (E* or μ), common measures of temperature-mediated reaction rates. Cercariae have a variable response to temperature, which does not appear to be influenced by their life-history attributes or size. There were little differences in Q10 and E* values between most temperature ranges. In almost half the studies examined (7 of 16) cercariae demonstrated a discrete zone of thermostability over a range equivalent to typical individual mean summer temperatures. Distinct intraspecific differences in temperature responses between 3 laboratory strains of Schistosoma mansoni and 2 natural strains of Echinoparyphium recurvatum sensu stricto were apparent. The importance of these results for cercarial biology under global climate change is discussed.

Thermodynamics of cercarial survival and metabolism in a changing climate.

https://hal.archives-ouvertes.fr/hal-01598398/document

Emerging Schistosomiasis in Europe: A need to quantify the risks

Background: This is the first study in Morocco to estimate snail infection rates at the last historic transmission sites of schistosomiasis, known to be free from new infection among humans since 2004. Screening of large numbers of snails for infection is one way to confirm that Schistosoma haematobium transmission has stopped and does not resurge. Methods: A total of 2703 Bulinus truncatus snails were collected from 24 snail habitats in five provinces of Morocco: Errachidia, El Kelaa des Sraghna, Tata, Beni Mellal, and Chtouka Ait Baha. All visible snails were collected with a scoop net or by hand. We used waders and gloves as simple precautions. Snails were morphologically identified according to Moroccan Health Ministry guide of schistosomiasis (1982). All snails were analyzed in pools by molecular tool, using primers from the newly identified repeated DNA sequence, termed DraI, in the S. haematobium group. To distinguish S. bovis and S. haematobium, the snails were analyzed by Sh110/Sm-Sl PCR that was specific of S. haematobium. Results: The results showed that snails from Errachidia, Chtouka Ait Baha, sector of Agoujgal in Tata and sector of Mbarkiya in El kelaa des Sraghna were negative for DraI PCR; but, snails from remaining snail habitats of El Kelaa des Sraghna, Tata and Beni Mellal were positive. This led to suggest the presence of circulating schistosome species (S. haematobium, S. bovis or others) within these positive snail habitats. Subsequently, confirmation with S. haematobium species specific molecular assay, Sh110/Sm-Sl PCR, showed that none of the collected snails were infected by S. haematobium in all historic endemic areas. Conclusion: The absence of S. haematobium infection in snails supports the argument of S. haematobium transmission interruption in Morocco.

/pdf/schistosoma-haematobium-detection-in-snails-by-drai-pcr-and-2e618ykp7c.pdf

Schistosoma haematobium detection in snails by DraI PCR and Sh110/Sm-Sl PCR: further evidence of the interruption of schistosomiasis transmission in Morocco

Planorbarius metidjensis infected with Schistosoma haematobium were subjected, from the first day of shedding, to a 5- or 10-day period of desiccation in order to study its effect on the cercarial release occurring after reactivation of snails in water. These results were compared to those of infected controls that were not subjected to desiccation. Compared to controls, the duration of shedding following reactivation was shorter and the total number of cercariae shed by each infected snail was smaller in the 5- and 10-day groups. The rhythm occurring in the daily cercarial production of the 5-day group was shorter (11 days only) at the beginning of the shedding period and lengthened to 17–18 days at the end of the patent period. In the 10-day group, no rhythm was found. These results could be explained by the length of the desiccation period and its consequences on the development of S. haematobium sporocysts in the body of snails.

Effect of a short period of desiccation during the patent period on cercarial shedding of Schistosoma haematobium from Planorbarius metidjensis.

Since Bulinus truncatus and Planorbarius metidjensis are the intermediate hosts of Schistosoma haematobium in southwestern Morocco, five rivers were investigated to identify sites colonized by either of both species and determine the characteristics of their habitats via the study of 12 physicochemical parameters in running water. P. metidjensis was observed in the upper valleys of three rivers, whereas B. truncatus was found in sites of lower altitude. A component analysis demonstrated that altitude (from 4 to 1,380 m), water pH (from 5.9 to 9.2), and electric conductivity (from 120 to 6,020 microS/cm) were the main descriptors of environment. A multiple correspondence analysis showed that P. metidjensis was associated to Ancylus fluviatilis, high altitude, and possibly low electric conductivity. B. truncatus was associated to Melanoides tuberculata and was found in lower altitude sites with medium electric conductivity in water. Using logistic regressions, the main characteristics were altitude and dissolved oxygen for B. truncatus, and chlorides and CaCO3 for P. metidjensis. As the habitats of both S. haematobium intermediate hosts differed from each other by altitude and the frequency of snails, which cohabited with them, these findings may be used to detect the presence of either of both intermediate hosts in numerous spring heads which are present on the western slope of the Anti Atlas mountains and the corresponding valleys.

Habitats of Bulinus truncatus and Planorbarius metidjensis, the intermediate hosts of urinary schistosomosis, under a semiarid or an arid climate.

Planorbarius metidjensis measuring 2 or 3 mm in diameter and originating from three populations in the Agadir province (Ida Ou Gnidif, Imouzzer, and Sidi Belkacem) were experimentally infected with Schistosoma haematobium to determine if the complete larval development of the parasite might be ensured by any snail population of the Agadir province and to compare the general characteristics of infection. No significant difference between the three populations was noted in the survival rates of snails when the first shedding occurred or in the prevalence of infection. The mean duration of the shedding period was significantly higher in the Imouzzer population (111 days versus 53–58 days). The total number of cercariae shed per mollusc was significantly lower in the Ida Ou Gnidif planorbids (1,398/snail versus 3,346 and 3,343/snail in the other 2 groups). The same rhythm in daily cercarial production was noted in the three snail groups, with the periodicity being 18–20 days. Despite some differences in parasite development between the three snail populations, the different populations of P. metidjensis can ensure the complete development of S. haematobium and maintain local transmission in the South of Morocco.

Schistosoma haematobium: comparative studies on the characteristics of infection in three populations of Planorbarius metidjensis from the Agadir province in South Morocco.

Since Planorbarius metidjensis was recently found to be an experimental intermediate host of Schistosoma haematobium in the South-West of Morocco, a study on planorbid and B. truncatus was carried out from 1997 to 2005. Eleven planorbid populations were identified in 1997 in the Agadir province, all living at high altitude (from 340 to 1380 m). In contrast, most of the seven bulinid populations inhabited low-lying zones. Three annual generations of P. metidjensis (April-July June-September, and August-March) were noted in two populations (living in perennial bodies of water) in Imouzzer so that juvenile snails were present throughout the year. The dissection of numerous snails collected from these 18 populations between 1999 and 2005 revealed the absence of natural infections with S. haematobium. As most cases of human bilharziosis detected in the Agadir region between 1993 and 1997 are located in highlands, P. metidjensis might be the principal intermediate host of S. haematobium in districts at 500 m above sea level.

[Bulinus truncatus, Planorbarius metidjensis and endemic bilharziosis in the southwestern Morocco].

Experimental infections of Planorbarius metidjensis by Schistosoma haematobium were carried out under controlled conditions to determine whether there was a size limit after which the snail could not longer sustain Schistosoma infection. Snails measuring 1–6 mm in diameter were exposed to two miracidia each and were raised at 24–26 °C until their death. The frequency of snails with cercarial shedding was 63% in the 2.1- to 3-mm group. In the other groups the frequencies were lower, decreasing to 2.8% in the 5.1- to 6- mm group. The periodicity of S. haematobium cercarial shedding was not modified by the snail diameter at miracidial exposure.

Schistosoma haematobium: comparative studies on prevalence and cercarial shedding according to the shell diameter of Planorbarius metidjensis at miracidial exposure.

B. Yacoubi

Papers

Effect of a short period of desiccation during the patent period on cercarial shedding of Schistosoma haematobium from Planorbarius metidjensis.

Habitats of Bulinus truncatus and Planorbarius metidjensis, the intermediate hosts of urinary schistosomosis, under a semiarid or an arid climate.

Schistosoma haematobium: comparative studies on the characteristics of infection in three populations of Planorbarius metidjensis from the Agadir province in South Morocco.

[Bulinus truncatus, Planorbarius metidjensis and endemic bilharziosis in the southwestern Morocco].

Schistosoma haematobium: comparative studies on prevalence and cercarial shedding according to the shell diameter of Planorbarius metidjensis at miracidial exposure.