Schistosoma Haematobium Transmission Research Articles

Vector snail fauna and Schistosoma haematobium transmission patterns in freshwater systems of Ishielu Local Government Area, Ebonyi State, Nigeria

Freshwater snails are widespread in tropical and temperate regions of the world where they serve as intermediate hosts for larval stages of parasitic trematodes which cause schistosomiasis that is endemic in Nigeria. Snail fauna and patterns of Schistosoma haematobium transmission were determined in flowing water habitats (FWH) and stagnant water habitats (SWH) in Ishielu, Local Government Area, Ebonyi State, Nigeria. Snail collection was done using scoop-net and hand-picking techniques. Bulinus species collected were exposed to sunlight/light-induced in laboratory for cercarial shedding. Cercariae were then observed under microscope. 923 snails were collected, 67.7% Lymnaea natalensis, 23.1% Bulinus globosus and 9.2% Bulinus truncatus. Their relative abundance was significantly different (P<0.05). 31.6% Bulinus snails from FWH were infected by S. haematobium whereas 18.5% from SWH were infected. Infectivity of Bulinus spp in each habitat group was not significantly different but was when compared the two groups of habitats (P<0.05). Highest infectivity (45.8%) occurred during dry season peaking in February (45.8%) for FWH and for SWH, highest infectivity occurred during rain peaking in July (26.8%). The transmission potential (T.P) was very high during dry season (93.0%) peaking in February (34.9%) in FWH and very low (0%) for SWH. During rain, the T.P was very high (100%) peaking in July (50%) in SWH and very low (7.0%) for FWH. Pools and rivers in Ishielu are suitable habitats for vector snails wherein season and habitat type influence snail abundance and transmission of Schistosomiasis, the findings of which can help in establishing programmes for proper health awareness and snail control.

Evaluation of a urogenital schistosomiasis behavioural intervention among students from rural schools in Unguja and Pemba islands, Zanzibar

Urogenital schistosomiasis is a common experience among children in Zanzibar. There is a paucity of behavioural science-based, health education and behaviour change (HEBC) interventions for school-aged children, those at greatest risk for urogenital schistosomiasis. We assessed the influence of a HEBC intervention, guided by the Health Belief model, among rural schoolchildren on Pemba and Unguja islands in Zanzibar, Tanzania. From 2012 to 2016, a cluster-randomized trial to assess three different interventions against urogenital schistosomiasis was conducted in 90 schools and shehias across Zanzibar. The HEBC intervention was implemented in 15 schools per island. In 2017, at the trial conclusion, we administered written questionnaires to schoolchildren from 4 HEBC intervention schools and 4 not HEBC exposed schools on each island, respectively. Responses were compared between students that were exposed or not exposed to the HEBC intervention using a Fisher's exact test. A total of 1451 students, 708 from intervention and 743 from non-intervention schools completed the questionnaire. Noting some between island differences, students who had received the HEBC interventions reported significant improvements in knowledge about Schistosoma haematobium transmission and personal risk, strategies for schistosomiasis prevention, and self-reported changes in risk behaviours: stopped washing laundry/dishes 49.4% (350/708) versus 5.8% (43/743), stopped bathing in streams/ponds 49.4% (350/708) versus 4.2% (31/743), and stopped playing in streams/ponds 40.8% (289/708) versus 10.8% (80/743). HEBC exposed children also reported a significant increase in swallowing tablets during mass drug administration (MDA) campaigns (when they had not before) 30.2% (214/708) versus 4.6% (34/743). The school based HEBC interventions were associated with desirable positive behaviour change among students. Data suggest that scaling up HEBC interventions to all schools in high-risk areas, augmented with bi-annual MDA, can help to reduce prevalence of urogenital schistosomiasis in Zanzibar, strengthening the possibility for future disease elimination.

Impact of community piped water coverage on re-infection with urogenital schistosomiasis in rural South Africa.

Previously, we demonstrated that coverage of piped water in the seven years preceding a parasitological survey was strongly predictive of Schistosomiasis haematobium infection in a nested cohort of 1976 primary school children (Tanser, 2018). Here, we report on the prospective follow up of infected members of this nested cohort (N = 333) for two successive rounds following treatment. Using a negative binomial regression fitted to egg count data, we found that every percentage point increase in piped water coverage was associated with 4.4% decline in intensity of re-infection (incidence rate ratio = 0.96, 95% CI: 0.93-0.98, p=0.004) among the treated children. We therefore provide further compelling evidence in support of the scaleup of piped water as an effective control strategy against Schistosoma haematobium transmission.

A 5-Year intervention study on elimination of urogenital schistosomiasis in Zanzibar: Parasitological results of annual cross-sectional surveys.

BackgroundThe Zanzibar Elimination of Schistosomiasis Transmission (ZEST) project aimed to eliminate urogenital schistosomiasis as a public health problem from Pemba and to interrupt Schistosoma haematobium transmission from Unguja in 5 years.MethodologyA repeated cross-sectional cluster-randomized trial was implemented from 2011/12 till 2017. On each island, 45 shehias were randomly assigned to receive one of three interventions: biannual mass drug administration (MDA) with praziquantel alone, or in combination with snail control or behavior change measures. In cross-sectional surveys, a single urine sample was collected from ~9,000 students aged 9- to 12-years and from ~4,500 adults aged 20- to 55-years annually, and from ~9,000 1st year students at baseline and the final survey. Each sample was examined for S. haematobium eggs by a single urine filtration. Prevalence and infection intensity were determined. Odds of infection were compared between the intervention arms.Principal findingsPrevalence was reduced from 6.1% (95% confidence interval (CI): 4.5%-7.6%) to 1.7% (95% CI: 1.2%-2.2%) in 9- to 12-year old students, from 3.9% (95% CI: 2.8%-5.0%) to 1.5% (95% CI: 1.0%-2.0%) in adults, and from 8.8% (95% CI: 6.5%-11.2%) to 2.6% (95% CI: 1.7%-3.5%) in 1st year students from 2011/12 to 2017. In 2017, heavy infection intensities occurred in 0.4% of 9- to 12-year old students, 0.1% of adults, and 0.8% of 1st year students. Considering 1st year students in 2017, 13/45 schools in Pemba and 4/45 schools in Unguja had heavy infection intensities >1%. There was no significant difference in prevalence between the intervention arms in any study group and year.Conclusions/SignificanceUrogenital schistosomiasis was eliminated as public health problem from most sites in Pemba and Unguja. Prevalence was significantly reduced, but transmission was not interrupted. Continued interventions that are adaptive and tailored to the micro-epidemiology of S. haematobium in Zanzibar are needed to sustain and advance the gains made by ZEST.

Contextualizing Schistosoma haematobium transmission in Ghana: Assessment of diagnostic techniques and individual and community water-related risk factors

ObjectivesThe study assessed associations between Schistosoma haematobium infection (presence of parasite eggs in urine or hematuria) and self-reported metrics (macrohematuria, fetching surface water, or swimming) to evaluate their performance as proxies of infection in presence of regular preventive chemotherapy. It also examined community water characteristics (safe water access, surface water access, and groundwater quality) to provide context for schistosomiasis transmission in different types of communities and propose interventions. MethodsLogistic regression was used to assess the associations between the various measured and self-reported metrics in a sample of 897 primary school children in 30 rural Ghanaian communities. Logistic regression was also used to assess associations between community water characteristics, self-reported water-related behaviors and S. haematobium infection. Communities were subsequently categorized as candidates for three types of interventions: provision of additional safe water sources, provision of groundwater treatment, and health education about water-related disease risk, depending on their water profile. ResultsMicrohematuria presence measured with a reagent strip was a good proxy of eggs in urine at individual (Kendall’s τb = 0.88, p < 0.001) and at school-aggregated (Spearman’s rs = 0.96, p < 0.001) levels. Self-reported macrohematuria and swimming were significantly associated (p < 0.05) with egg presence, but self-reported fetching was not. Of the community water characteristics, greater surface water access and presence of groundwater quality problems were significantly associated with increased likelihood of fetching, swimming, and S. haematobium infection. Access to improved water sources did not exhibit an association with any of these outcomes. ConclusionsThe study illustrates that in presence of regular school-based treatment with praziquantel, microhematuria assessed via reagent strips remains an adequate proxy for S. haematobium infection in primary schoolchildren. Community water profiles, in combination with self-reported water-related behaviors, can help elucidate reasons for some endemic communities continuing to experience ongoing transmission and tailor interventions to these local contexts to achieve sustainable control.

COMBINING REMOTELY SENSED ENVIRONMENTAL CHARACTERISTICS WITH SOCIAL AND BEHAVIORAL CONDITIONS THAT AFFECT SURFACE WATER USE IN SPATIOTEMPORAL MODELLING OF SCHISTOSOMIASIS IN GHANA

Abstract. Schistosoma haematobium transmission is influenced by environmental conditions that determine the suitability of the parasite and intermediate host snail habitats, as well as by socioeconomic conditions, access to water and sanitation infrastructure, and human behaviors. Remote sensing is a demonstrated valuable tool to characterize environmental conditions that support schistosomiasis transmission. Socioeconomic and behavioral conditions that propagate repeated domestic and recreational surface water contact are more difficult to quantify at large spatial scales. We present a mixed-methods approach that builds on the remotely sensed ecological variables by exploring water and sanitation related community characteristics as independent risk factors of schistosomiasis transmission.

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

BackgroundThis 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.MethodsA 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.ResultsThe 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.ConclusionThe absence of S. haematobium infection in snails supports the argument of S. haematobium transmission interruption in Morocco.

Atopy Is Inversely Related to Schistosome Infection Intensity: A Comparative Study in Zimbabwean Villages with Distinct Levels of Schistosoma haematobium Infection

Background: The hygiene hypothesis suggests that parasitic infections protect against allergic diseases by modulating the host’s immune responses. Experimental studies indicate that this protection depends on the intensity of parasitic infection, but this observation has not been tested in human populations. The aim of this study is to investigate whether the intensity of Schistosoma haematobium infection is related to atopic responses and whether this relationship differs between populations with distinct parasite transmission dynamics. Methods: The study was conducted in two villages with different Schistosoma haematobium transmission dynamics, i.e. high (n = 365) and low (n = 307) transmission. Allergic reactivity to the common house dust mite (Dermatophagoides pteronyssinus) was measured by skin prick tests and allergen-specific IgE and IgG4 quantified by enzyme-linked immunosorbent assay. Atopic responses were related to current infection intensity and schistosome transmission levels. Results: Schistosome infection intensity was negatively associated with the skin prick reactivity, mite-specific IgE and the ratio IgE/IgG4 in the high-transmission village. However, when only low levels of infection were analyzed in the 2 villages, there was no correlation between mite-specific responses and infection intensity. Conclusion: The relationship between schistosome infection and atopic responses is dependent on the intensity of current schistosome infection. Thus, consistent with results from animal models, with an increasing parasite burden, the immunoregulation of immune responses to allergens appears to become more pronounced.

SPATIAL PATTERNS OF URINARY SCHISTOSOMIASIS INFECTION IN A HIGHLY ENDEMIC AREA OF COASTAL KENYA

Urinary schistosomiasis remains a major contributor to the disease burden along the southern coast of Kenya. Selective identification of transmission hot spots offers the potential for more effective, highly-focal snail control and human chemotherapy to reduce Schistosoma haematobium transmission. In the present study, a geographic information system was used to integrate demographic, parasitologic, and household location data for an endemic village and neighboring households with the biotic, abiotic, and location data for snail collection/water contact sites. A global spatial statistic was used to detect area-wide trends of clustering for human infection at the household level. Local spatial statistics were then applied to detect specific household clusters of infection, and, as a focal spatial statistic, to evaluate clustering of infection around a putative transmission site. High infection intensities were clustered significantly around a water contact site with high numbers of snails shedding S. haematobium cercariae. When age was considered, clustering was found to be significant at different distances for different age groups.

Recent urban growth and urinary schistosomiasis in Niamey, Niger.

A cluster sample survey was conducted in 1998 in 30 schools to assess the effect of the growth of Niamey during the last decade on a urinary schistosomiasis urban focus described in 1989. Two thousand and forty-two children (11.0 + 0.1 years old) had a urine filtration test and answered a behavioural questionnaire. Snail populations of the sites used by schoolchildren were followed up in 1999. The global prevalence was 15.7% in 1998, as opposed to 23.7% in 1989. The prevalence was very low in schools far from the river and higher in those along the Niger banks, particularly in villages on the periphery of the urban area. Geographical factors were more important than socio-economic ones in explaining the distribution of the disease. Only 46% of the children in Niamey reported water contact; mainly in the river, rarely in pools and the canal. The infection risk was low in pools (RR = 1.6), high in the river (RR = 3.5) and very high in the canal (RR = 12.5). Malacological studies confirmed the location of transmission sites obtained through parasitological studies and the questionnaire. Sixty-one per cent of the children travelled outside Niamey to the hyperendemic surrounding areas. However, these movements did not increase their infection level. The results are discussed in relation to water contact behaviour and Schistosoma haematobium transmission features.

Focal mollusciciding: an effective way to augment chemotherapy of schistosomiasis

Fig. 3. Technician spraying niclosamide into a site o f Schistosoma haematobium transmission in the Volta Lake, Ghana The demise of mollusciciding as the primary means of controlling schistosome transmission in endemic areas has been a consequence of the appearance of cheap, safe, and effective oral drugs, which have revolutionized control strategies during the last 15 years. The increase in cost of the molluscicide of choice, niclosamide, to over US$18 per kg (70% wettable powder) has also been a factor in the decline of chemical snail control. A third reason has been the failure of blanket or area-wide mollusciciding to control schistosome transmission in major control projects6,14,15. But the medical estabkishment may now be placing too much faith in the use of chemotherapy alone in control schemes and primary health care to diminish morbidity and control the transmission of schistosomiasis. This optimism has grown with the increasing availability of the 'new wonder drug', praziquantel, and its continuing reduction in price. Similarly, immunologists may be overly optimistic about the prospects for producing and delivering an effective anti-schistosome vaccine in the near future. A balanced approach to schistosomiasis control should not be overlooked. Properly designed preventive control measures such as improving water supply, sanitation, health education, and environmental management, though expensive in the short run, will reduce the long-term risks not only of schistosomiasis,

Ecological studies on the snail hosts of schistosomiasis in the South Chad Irrigation Project Area, Borno State, northern Nigeria

Qualitative and quantitative samples of aquatic snails were collected over a two year period in the South Chad Irrigation Project Area, northern Nigeria. The area and its climate are described. Lake Chad, the irrigation channels and temporary pools are defined as three major categories of snail habitat and an account of the seasonal abundance of their snail populations is given. Bulinus rohlfsi, Bulinus forskali, a form of Bulinus globosus and Biomphalaria sudanica occurred in Lake Chad. Bulinus rohlfsi, Bulinus forskali, Bulinus senegalensis and another form of Bulinus globosus were found in irrigation channels. Bulinus senegalensis was the only bulinid recovered from temporary pools. The seasonal patterns of the snails are considered in relation to climatic and habitat changes. The possible roles of the bulinids in Schistosoma haematobium transmission are discussed.

Malumfashi Endemic Diseases Research Project XII

Slaughter-slab surveys of livestock within the human schistosomiasis study area of Malumfashi revealed a very low prevalence of snail-borne trematode infections. The drought of 1973 was responsible for a decline in Schistosoma haematobium transmission, but there were other factors responsible for the less than 5% prevalence of bovine schistosomiasis and fascioliasis in the surveyed animals. The husbandry method of the settled farmers accounted for a low prevalence of trematode infections in their goats and sheep, and most of the infected animals probably acquired S. bovis and Fasciola gigantica outside the study area. The dry seasonal conditions had been unfavourable for fascioliasis transmission, but there may have been the added factor of S. bovis incompatibility with available snail hosts to account for the low level of bovine schistosomiasis transmission.The recent construction of several low earth dams in this dry part of northern Nigeria is likely to sustain the recent upward trend in S. haematobium...