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Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best.

ABSTRACT: BACKGROUND:Despite control efforts, human schistosomiasis remains prevalent throughout Africa, Asia, and South America. The global schistosomiasis burden has changed little since the new anthelmintic drug, praziquantel, promised widespread control. METHODOLOGY:We evaluated large-scale schistosomiasis control attempts over the past century and across the globe by identifying factors that predict control program success: snail control (e.g., molluscicides or biological control), mass drug administrations (MDA) with praziquantel, or a combined strategy using both. For data, we compiled historical information on control tactics and their quantitative outcomes for all 83 countries and territories in which: (i) schistosomiasis was allegedly endemic during the 20th century, and (ii) schistosomiasis remains endemic, or (iii) schistosomiasis has been "eliminated," or is "no longer endemic," or transmission has been interrupted. PRINCIPAL FINDINGS:Widespread snail control reduced prevalence by 92 ± 5% (N = 19) vs. 37 ± 7% (N = 29) for programs using little or no snail control. In addition, ecological, economic, and political factors contributed to schistosomiasis elimination. For instance, snail control was most common and widespread in wealthier countries and when control began earlier in the 20th century. CONCLUSIONS/SIGNIFICANCE:Snail control has been the most effective way to reduce schistosomiasis prevalence. Despite evidence that snail control leads to long-term disease reduction and elimination, most current schistosomiasis control efforts emphasize MDA using praziquantel over snail control. Combining drug-based control programs with affordable snail control seems the best strategy for eliminating schistosomiasis.

SUBMITTER: Sokolow SH

PROVIDER: S-EPMC4956325 | biostudies-other | 2016 Jul

REPOSITORIES: biostudies-other

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Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best.

Sokolow Susanne H SH Wood Chelsea L CL Jones Isabel J IJ Swartz Scott J SJ Lopez Melina M Hsieh Michael H MH Lafferty Kevin D KD Kuris Armand M AM Rickards Chloe C De Leo Giulio A GA

PLoS neglected tropical diseases 20160721 7

<h4>Background</h4>Despite control efforts, human schistosomiasis remains prevalent throughout Africa, Asia, and South America. The global schistosomiasis burden has changed little since the new anthelmintic drug, praziquantel, promised widespread control.<h4>Methodology</h4>We evaluated large-scale schistosomiasis control attempts over the past century and across the globe by identifying factors that predict control program success: snail control (e.g., molluscicides or biological control), mas ...[more]

PMID: 27441556

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Project description:BackgroundThe control of schistosomiasis is particularly difficult in sub-Saharan Africa, which currently harbours 95% of this disease. The target population for preventive chemotherapy (PC) is expanded to all age group at risk of infection, thus increasing the demands of praziquantel (PZQ) tablets according to the new released guideline by World Health Organization. Due to the gap between available PZQ for PC and requirements, alternative approaches to assess endemicity of schistosomiasis in a community, are urgently needed for more quick and precise methods. We aimed to find out to which degree the infection status of snails can be used to guide chemotherapy against schistosomiasis.MethodsWe searched literature published from January 1991 to December 2022, that reported on the prevalence rates of Schistosoma mansoni, S. haematobium in the intermediate snails Biomphalaria spp. and Bulinus spp., respectively, and in humans. A random effect model for meta-analyses was used to calculate the pooled prevalence estimate (PPE), with heterogeneity assessed using I-squared statistic (I2), with correlation and regression analysis for the exploration of the relationship between human S. mansoni and S. haematobium infections and that in their specific intermediate hosts.ResultsForty-seven publications comprising 59 field investigations were included. The pooled PPE of schistosomiasis, schistosomiasis mansoni and schistosomiasis haematobium in humans were 27.5% [95% confidence interval (CI): 24.0-31.1%], 25.6% (95% CI: 19.9-31.3%), and 28.8% (95% CI: 23.4-34.3%), respectively. The snails showed an overall infection rate of 8.6% (95% CI: 7.7-9.4%), with 12.1% (95% CI: 9.9-14.2%) in the Biomphalaria spp. snails and 6.9% (95% CI: 5.7-8.1%) in the Bulinus spp. snails. The correlation coefficient was 0.3 (95% CI: 0.01-0.5%, P < 0.05) indicating that the two variables, i.e. all intermediate host snails on the one hand and the human host on the other, were positively correlated.ConclusionsThe prevalence rate of S. mansoni and S. haematobium is still high in endemic areas. Given the significant, positive correlation between the prevalence of schistosomes in humans and the intermediate snail hosts, more attention should be paid to programme integration of snail surveillance in future.

Project description:If we try to draw conclusions about events, analyse data or results (in one or a certain area) and clarify our unknown points in standard or non-standard ways, this leads to the transfer of experience from one area to another. How do we want to follow guidelines, while the most of the obligatory laws are not followed, for example? The aim of prescriptions or recommendations in medicine, for example, (or the laws of a country that do not usually apply to particular classes or castes, as well as business rules) is to give guidance on how it would be appropriate to help people or ourselves (as we have already mentioned) and the people themselves. Unfortunately, this behaviour is also characteristic of developed societies that dictate the rules and try to help … to people, as well. If we come deeper into the system of mutual aid in medicine, it is unfortunate that sometimes the condition of this kind of "ecosystem" (or any of the ecosystems described) is worse than the best tragic-comedy. Unfortunately, the "ecosystem of medicine" is also subordinate and slaves somehow to the stronger "ecosystems" as politics and business and is dependent on them, but for evil or good, these ecosystems have glimpsed at times, no matter what are the motives, which provoke them! And they are most often … once again personal. Although in a number of Eastern European countries, it was unthinkable to even undesirable until recently, that dermasurgery and dermatooncology to be part of modern dermatological societies, the insatiable thirst for growth of young specialists, as well as the impact of Western schools, on their formation as a kind of new hope proved to be stronger in the formation of dermatosurgery, not only all over the world, but also in particular in the Balkans and Bulgaria. These units are gradually being introduced as an indispensable part of any modern clinic, and this part guarantees the best results (in patients with dermatosurgical or dermatooncological needs). The globalisation of dermatology and dermatological science has led to the introduction and involvement of additional auxiliary units, based on a more global concept of the interdisciplinary concept that encompasses psycho-neuroendocrine dermatology which provides a good explanation for some unexplained diseases, such as vitiligo, for example.

Project description:BACKGROUND:With the closure of the Three Gorges Dam in 2003 the hydrology of Poyang Lake was altered dramatically leading to significant changes in the environment. In order to assess the impact on schistosomiasis this study assessed the spatial and temporal patterns of the snail intermediate host, Oncomelania hupensis in the Poyang Lake tributaries. The results of the study have important implications for future snail control strategies leading to disease elimination. METHODS:The marshland area surrounding Poyang Lake was divided randomly into 200 × 200 m vector grids using ArcGIS software, and the surveyed grids were randomly selected by the software. The snail survey was conducted in each selected grid using a survey frame of 50 × 50 m with one sideline of each grid serving as the starting line. No less than ten frames were used in each surveyed grid with Global Positioning System (GPS) recordings for each. All snails in each frame were collected to determine infection status by microscopy. Altitude data for all frames were extracted from a lake bottom topographic map in order to analyze the average altitude. All snail survey data were collected and statistically analyzed with SPSS 20.0 software in order to determine the difference of the percentage of frames with living snails and mean density of living snails in different regions of Poyang Lake. The altitude of the snail-infested marshlands and snail dens were subsequently identified. RESULTS:A total of 1159 potential snail sampling grids were surveyed, of which 15 231 frames (0.1 m2/frame) were investigated. 1241 frames had live Oncomelania snails corresponding to 8.15% of the total number of frames. The mean density of living snails was 0.463/0.1 m2 with a maximum of 57 snails per frame. The percent of frames with snails in the southern sector (8.13%) of Poyang Lake did not differ statistically from the north (8.21%). However, the mean density of live snails in the northern sector (0.164/0.1 m2) of the lake was statistically higher (F = 6.727; P = 0.010) than the south (0.141/0.1 m2). In the south of the lake, the elevation of snail-inhabited marshland ranged between 11 - 16 m, and could be further subdivided into two snail-concentrated belts at 12-13 m of elevation and 15-16 m of elevation respectively. In the north of the lake, the elevation of snail-inhabited marshland ranged between 9- 16 m with the elevation of 12-14 m being the snail-concentrated zone. CONCLUSIONS:The elevation of snail-infested marshlands in the Poyang Lake region ranged from 9 to 16 m. The snail distribution and habitat has moved north of the lake and to a lower altitude due to changes in the water level post dam closure. Based on the current geological features of the snail habitant focused mollusciciding should occur in snail dense northern regions with frequent bovine and human traffic. Targeting these identified 'hotspots' of transmission will assist in elimination efforts.

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Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best.

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Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best.

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