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Control of Schistosome Intermediate Hosts

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A special issue of Tropical Medicine and Infectious Disease (ISSN 2414-6366).

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 21278

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Prof. Dr. Shizhu Li

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National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, National Research Center for Tropical Diseases, Key Laboratory of Parasite and Vector Biology, National Health Commission, WHO Collaborating Center for Tropical Diseases, National Center for International Research on Tropical Diseases, Ministry of Science and Technology, Shanghai 20025, China
Interests: schistosomiasis; vector-borne diseases; transmission risk evaluation; epidemiology of parasiology; parasitic diseases control
Special Issues, Collections and Topics in MDPI journals

Dr. Qinping Zhao

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Department of Parasitology, School of Basic Medical Sciences, Wuhan University, Wuhan, China
Interests: schistosoma; trematode and snail host; population genetics; snail biology

Special Issue Information

Dear Colleagues,

Schistosomiasis, a helminth infection caused by blood flukes of the genus Schistosoma spp., which can cause either intestinal or urogenital forms of clinical illness, is considered as one of the most severe public health threats in the world. The infection occurs after exposure to freshwater that harbors cercaria, the infectious stage of Schistosoma spp., which is released from intermediate host snail species. Therefore, intermediate host snail species play a very important role in the transmission of schistosomiasis. Because of the specific selection of Schistosoma on the host snails, the distribution of the disease is strictly consistent with the intermediate host snail species' habitat. For example, Oncomelania hupensis is the only host snail of S. japonicum. Snail control has been identified as a key measure of disease control and elimination. Thus, the research into snail biology, the interaction between Schistosoma and host snails, and snail control has been a hot topic in this field. In order to update the latest progress made in the research on host snails of Schistosoma, we have established a Special Issue in the journal Tropical Medicine and Infectious Disease, and the topic is focused on but not limited to control of schistosome intermediate hosts. The fields of this Special Issue include:

The interaction between Schistosoma species and host snail species;
The temporal–spatial distribution and modeling of the snail species and the influencing factors;
Transmission risk evaluation based on snail surveys and monitoring;
The new technologies and innovations for snail control;
International cooperation for snail and schistosomiasis control based on global health and one health concepts;
Other relevant research topics.

Prof. Dr. Shizhu Li
Dr. Qinping Zhao
Guest Editors

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Keywords

host snail of Schistosoma
interaction between Schistosoma species and host snail specie
temperal-spatial distribution and modeling
transmission risk evaluation
technology and innovation for snail control
global health
one health concepts

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Published Papers (8 papers)

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Research

10 pages, 2516 KiB

Open AccessArticle

Oncomelania hupensis Distribution and Schistosomiasis Transmission Risk in Different Environments under Field Conditions

by Yinlong Li, Suying Guo, Hui Dang, Lijuan Zhang, Jing Xu and Shizhu Li

Trop. Med. Infect. Dis. 2023, 8(5), 242; https://doi.org/10.3390/tropicalmed8050242 - 23 Apr 2023

Cited by 2 | Viewed by 1882

Abstract

The goal of schistosomiasis prevention and control in China is shifting from transmission interruption to elimination. However, the area inhabited by the intermediate host, the snail Oncomelania hupensis, has not changed much in recent years. Different environmental types have different impacts on snail breeding, and understanding these differences is conducive to improving the efficiency of snail monitoring and control and to saving resources. Based on previous epidemiological data, we selected 199 villages in 2020 and 269 villages in 2021 from transmission control, transmission interruption, and elimination areas of snail breeding. Snail surveys were conducted in selected villages using systematic sampling and/or environmental sampling methods in six types of snail-breeding environments (canals, ponds, paddy fields, dry lands, bottomlands, and undefined environments). All live snails collected from the field were evaluated for Schistosoma japonicum infection using the microscopic dissection method, and a subsample of snails was subjected to loop-mediated isothermal amplification (LAMP) to assess the presence of S. japonicum infection. Snail distribution data and infection rate and nucleic acid positive rate of schistosomes in snails were calculated and analyzed. The 2-year survey covered 29,493 ha of the environment, in which 12,313 ha of snail habitats were detected. In total, 51.16 ha of new snail habitats and 107.76 ha of re-emergent snail habitats were identified during the survey. The occurrence rate of snails in canals (10.04%, 95% CI: 9.88–10.20%) and undefined environments (20.66%, 95% CI: 19.64–21.67%) was relatively high in 2020, and the density of snails in bottomlands (0.39, 95% CI: 0.28–0.50) and undefined environments (0.43, 95% CI: 0.14–1.60) was relatively high in 2021. Of the 227,355 live snails collected in this study, none were S. japonicum-positive as determined by microscopy. Of the 20,131 pooled samples, however, 5 were S. japonicum-positive based on LAMP analysis, and they were distributed in three environmental types: 3 in bottomland, 1 in dry land, and 1 in a canal. The bottomland environment has a high risk of schistosomiasis transmission because it contains a large area of newly emerging and re-emerging snail habitats, and it also had the most breeding snails infected with S. japonicum. Thus, this habitat type should be the key target for snail monitoring and early warning and for the prevention and control of schistosomiasis. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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13 pages, 3283 KiB

Open AccessArticle

The Current Distribution of Oncomelania hupensis Snails in the People’s Republic of China Based on a Nationwide Survey

by Chao Lv, Yin-Long Li, Wang-Ping Deng, Zi-Ping Bao, Jing Xu, Shan Lv, Shi-Zhu Li and Xiao-Nong Zhou

Trop. Med. Infect. Dis. 2023, 8(2), 120; https://doi.org/10.3390/tropicalmed8020120 - 14 Feb 2023

Cited by 8 | Viewed by 1992

Abstract

Schistosomiasis is a helminth infection caused by the genus Schistosoma, which is still a threat in tropical and sub-tropical areas. In the China, schistosomiasis caused by Schistosoma japonicum is mainly endemic to the Yangtze River valley. The amphibious snail Oncomelania hupensis (O. hupensis) is the unique intermediate host of S. japonicum; hence, snail control is a crucial approach in the process of schistosomiasis transmission control and elimination. In 2016, a nationwide snail survey was conducted involving all snail habitats recorded since 1950 in all endemic counties of 12 provinces. A total of 53,254 existing snail habitats (ESHs) were identified, presenting three clusters in Sichuan Basin, Dongting Lake, and Poyang Lake. The overall habitat area was 5.24 billion m², of which 3.58 billion m² were inhabited by O. hupensis. The area inhabited by snails (AIS) in Dongting and Poyang Lakes accounted for 76.53% of the population in the country. Three typical landscape types (marshland and lakes, mountains and hills, and plain water networks) existed in endemic areas, and marshland and lakes had a predominant share (3.38 billion m²) of the AIS. Among the 12 endemic provinces, Hunan had a share of nearly 50% of AIS, whereas Guangdong had no ESH. Ditches, dryland, paddy fields, marshland, and ponds are common habitat types of the ESH. Although the AIS of the marshland type accounted for 87.22% of the population in the whole country, ditches were the most common type (35,025 or 65.77%) of habitat. Six categories of vegetation for ESHs were identified. A total of 39,139 habitats were covered with weeds, accounting for 55.26% of the coverage of the area. Multiple vegetation types of snail habitats appeared in the 11 provinces, but one or two of these were mainly dominant. Systematic sampling showed that the presence of living snails was 17.88% among the 13.5 million sampling frames. The occurrence varied significantly by landscape, environment, and vegetation type. The median density of living snails in habitats was 0.50 per frame (0.33 m × 0.33 m), and the highest density was 40.01 per frame. Furthermore, two main clusters with high snail densities and spatial correlations indicated by hotspot analysis were identified: one in Hunan and Hubei, the other in Sichuan. This national survey is the first full-scale census on the distribution of O. hupensis, which is significant, as transmission interruption and elimination are truly becoming the immediate goal of schistosomiasis control in China. The study discerns the detailed geographic distribution of O. hupensis with the hotspots of snail density in China. It is beneficial to understand the status of the snail population in order to finally formulate further national control planning. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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13 pages, 3926 KiB

Open AccessArticle

Unraveling the Variation Pattern of Oncomelania hupensis in the Yangtze River Economic Belt Based on Spatiotemporal Analysis

by Lu Li, Lijuan Zhang, Yinlong Li, Zhong Hong, Qiang Wang, Wangping Deng, Shizhu Li and Jing Xu

Trop. Med. Infect. Dis. 2023, 8(2), 71; https://doi.org/10.3390/tropicalmed8020071 - 18 Jan 2023

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Abstract

The construction of the Yangtze River Economic Belt (YEB) is a great national economic development strategy in China. As the YEB covers most endemic provinces of schistosomiasis japonica featured by low endemicity, this study aimed to investigate the spatiotemporal distribution pattern of Oncomelania hupensis (O. hupensis), which serves as the only intermediate host of Schistosoma japonicum in the YEB. Annual data reflecting the distribution of O. hupensis from 2015 to 2021 were collected from the National Institute of Parasitic Disease, Chinese Center for Disease Control and Prevention. Spatial autocorrelation analysis, hotspot analysis and space–time scan analysis were performed to explore the aggregation features and spatiotemporal dynamics of the snail distribution. The distribution of both total snail habitats (during 2015–2021) and emerging snail habitats (in 2016, 2018 and 2020) showed spatial autocorrelation (Z = 15.8~16.1, p < 0.05; Z = 2.3~7.5, p < 0.05). Hotspot (high-value areas in space) counties were mainly clustered in the alluvial plain of the middle and lower reaches of the YEB. Eight spatial and temporal clusters of snail habitats were scanned and were mainly concentrated in the counties of Anhui, Jiangxi, Hubei, Hunan and Jiangsu provinces along the Yangtze River. The YEB carries a tremendous burden of O. hupensis. Surveillance and risk identification based on the snail presence should be strengthened to provide reference for protecting humans and public health security in the YEB. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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12 pages, 2768 KiB

Open AccessArticle

Population Genetics of Oncomelania hupensis Snails from New-Emerging Snail Habitats in a Currently Schistosoma japonicum Non-Endemic Area

by Yu-Heng Cheng, Meng-Tao Sun, Ning Wang, Chang-Zhe Gao, Han-Qi Peng, Jie-Ying Zhang, Man-Man Gu and Da-Bing Lu

Trop. Med. Infect. Dis. 2023, 8(1), 42; https://doi.org/10.3390/tropicalmed8010042 - 5 Jan 2023

Cited by 2 | Viewed by 2309

Abstract

Schistosomiasis is still one of the most significant neglected tropical diseases worldwide, and China is endemic for Schistosoma japonicum. With its great achievement in schistosomiasis control, the government of China has set the goal to eliminate the parasitic disease at the country level by 2030. However, one major challenge is the remaining huge areas of habitats for the intermediate host Oncomelania hupensis. This is further exacerbated by an increasing number of new emerging snail habitats reported each year. Therefore, population genetics on snails in such areas will be useful in evaluation of snail control effect and/or dispersal. We then sampled snails from new emerging habitats in Taicang of Jiangsu, China, a currently S. japonicum non-endemic area from 2014 to 2017, and performed population genetic analyses based on nine microsatellites. Results showed that all snail populations had low genetic diversity, and most genetic variations originated from within snail populations. The estimated effective population size for the 2015 population was infinitive. All snails could be separated into two clusters, and further DIYABC analysis revealed that both the 2016 and the 2017 populations may derive from the 2015, indicating that the 2017 population must have been missed in the field survey performed in 2016. These findings may have implications in development of more practical guidelines for snail monitoring and control. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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13 pages, 2235 KiB

Open AccessArticle

Transmission Risk Predicting for Schistosomiasis in Mainland China by Exploring Ensemble Ecological Niche Modeling

by Jingbo Xue, Xiaokang Hu, Yuwan Hao, Yanfeng Gong, Xinyi Wang, Liangyu Huang, Shan Lv, Jing Xu, Shizhu Li and Shang Xia

Trop. Med. Infect. Dis. 2023, 8(1), 24; https://doi.org/10.3390/tropicalmed8010024 - 28 Dec 2022

Cited by 7 | Viewed by 2453

Abstract

Schistosomiasis caused by Schistosoma japonicum is one of the major neglected tropical diseases worldwide. The snail Oncomelania hupensis is the only intermediate host of S. japonicum, which is recognized as an indicator of the schistosomias occurrence. In order to evaluate the risk of schistosomiasis in China, this work investigate the potential geographical distribution of host snail habitus by developing an ensemble ecological niche model with reference to the suitable environmental factors. The historical records of snail habitus were collected form the national schistosomiasis surveillance program from the year of 2005 to 2014. A total of 25 environmental factors in terms of the climate, geographic, and socioeconomic determinants of snail habitats were collected and geographically coded with reference to the snail data. Based on the correlations among snail habitats and the geographically associated environmental factors, an ensemble ecological niche model was developed by integrating ten standard models, aiming for improving the predictive accuracy. Three indexes are used for model performance evaluation, including receiver operating characteristic curves, kappa statistics, and true skill statistics. The model was used for mapping the risk of schistosomiasis in the middle and lower reaches of the Yangtze River. The results have shown that the predicted risk areas were classified into low risk (4.55%), medium risk (2.01%), and high risk areas (4.40%), accounting for 10.96% of the land area of China. This study demonstrated that the developed ensemble ecological niche models was an effective tool for evaluating the risk of schistosomiasis, particularly for the endemic regions, which were not covered by the national schistosomiasis control program. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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16 pages, 1745 KiB

Open AccessArticle

Environmental Factors Affecting Freshwater Snail Intermediate Hosts in Shenzhen and Adjacent Region, South China

by Fengyang Min, Jiasheng Wang, Xiaoguang Liu, Yi Yuan, Yunhai Guo, Kongxian Zhu, Zhaohui Chai, Yunchao Zhang and Shizhu Li

Trop. Med. Infect. Dis. 2022, 7(12), 426; https://doi.org/10.3390/tropicalmed7120426 - 9 Dec 2022

Cited by 8 | Viewed by 3523

Abstract

Sound knowledge of the local distribution and diversity of freshwater snail intermediate hosts and the factors driving the occurrence and abundance of them is crucial to understanding snail-borne parasitic disease transmission and to setting up effective interventions in endemic areas. In this study, we investigated the freshwater snails, water quality parameters, physical characteristics of habitats, predators and competitors, and human activity variables at 102 sites during December 2018 and August 2019 in Shenzhen and adjacent areas in China. We used decision tree models and canonical correspondence analysis to identify the main environmental and biotic factors affecting the occurrence and abundance of snail species. A total of nine species of snail were collected throughout the study area, with Biomphalaria straminea, Sinotaia quadrata, and Physella acuta being the most predominant species. Our study showed that the most important variables affecting the abundance and occurrence of snail species were the presence of predators and competitors, macrophyte cover, chlorophyll-a, substrate type, river depth, and water velocity. In terms of human activities, snail species occurred more frequently and in larger numbers in water bodies affected by human disturbances, especially for sewage discharge, which may reduce the occurrence and abundance of snail predators and competitors. These findings suggest that proper management of water bodies to reduce water pollution may increase the abundance of snail predators and competitors, and should be considered in integrated snail control strategies in the study area. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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12 pages, 1516 KiB

Open AccessArticle

The Indispensability of Snail Control for Accelerating Schistosomiasis Elimination: Evidence from Zanzibar

by Mtumweni Ali Muhsin, Xinyao Wang, Fatma Mohammed Kabole, January Zilabumba and Kun Yang

Trop. Med. Infect. Dis. 2022, 7(11), 347; https://doi.org/10.3390/tropicalmed7110347 - 3 Nov 2022

Cited by 7 | Viewed by 3918

Abstract

Schistosomiasis is a serious and neglected global tropical disease, affecting upwards of 230 million people, with more than 95% of infections concentrated in Africa. For many years, the main schistosomiasis control strategy in Africa focused on mass drug administration (MDA). The aim of this study was to compare the difference between MDA alone and alongside another intervention, namely snail control, by exploring effective measures for eliminating schistosomiasis. Retrospective data of human prevalence on Schistosoma haematobium and major control measures were collected from the China-Zanzibar-WHO Cooperation Project for Schistosomiasis Elimination (CZW) and the Zanzibar Elimination of Schistosomiasis Transmission (ZEST) project since 2012. The optimal order polynomial regression fitting model and joinpoint regression model (JRM) were used to analyze trends in schistosomiasis prevalence and the consistency of change points with strengthening of the control measures. In Unguja Island, the main control measure was MDA, and prevalence decreased to a nadir in 2019, and then rebounded. The R² value of the optimal fitting model was 0.6641. There was a single JRM changepoint in 2019, the annual percent change (APC) was −19.3% (p < 0.05) from 2012 to 2019, and the APC was 59.7% (p > 0.05) from 2019 to 2021. In Pemba Island, the main control measures until 2016 was MDA, while integrated measures of MDA and snail control were implemented from 2017, the prevalence continuously decreased, and the R² value was 0.8673. There was also a single JRM changepoint in 2017, the APC was −22.2% (p < 0.05) from 2012 to 2017, and was maintained at −8.6% (p > 0.05) from 2017 to 2021. Our data indicate that, while it is challenging to eliminate schistosomiasis by MDA alone, integrated measures, including both MDA and snail control, can prevent reinfection and help to eliminate the diseases in Africa. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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10 pages, 1366 KiB

Open AccessArticle

The Biosafety Evaluation for Crustaceans: A Novel Molluscicide PBQ Using against Oncomelania hupensis, the Intermediate Host of Schistosoma japonica

by Qianwen Shi, Liping Duan, Zhiqiang Qin, Weisi Wang, Lu Shen, Xuetao Hua, Ling’e Shen, Jiaqian Cao, Fukang Zhu, Jingzhi Wu and Shizhu Li

Trop. Med. Infect. Dis. 2022, 7(10), 294; https://doi.org/10.3390/tropicalmed7100294 - 11 Oct 2022

Cited by 4 | Viewed by 1746

Abstract

A new formulation (suspension concentrate, SC) of PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl) urea] was used in water network schistosomiasis-endemic areas to test its molluscicidal efficacy and the acute toxicity to crustaceans. PBQ (20% SC), 26% metaldehyde, and niclosamide suspension concentrate [MNSC (26% SC)] were used both in ditch and field experiments for the molluscicidal efficacy comparison. Acute toxicity tests of two molluscicides were conducted using Neocaridina denticulate and Eriocheir sinensis. Both in the field and ditch experiments, PBQ exhibited comparable molluscicidal efficacy with MNSC. At doses of 0.50 g/m³ and 0.50 g/m², the snail mortalities were more than 90% three days after PBQ (20% SC) application. Compared with previous tests, PBQ (20% SC) exhibited higher molluscicidal activity than PBQ (25% wettable powder, 25% WP) used in Jiangling and showed similar mollucicidal activity to PBQ (25% WP) used in Dali and Poyang Lake. The 96 h LC₅₀ value of MNSC against Eriocheir sinensis was 283.84 mg a.i./L. At the concentration of PBQ (20% SC) 1000 mg a.i./L, all Eriocheir sinensis were alive. The 96 h LC₅₀ values of PBQ and MNSC against Neocaridina denticulate were 17.67 and 14.05 mg a.i./L, respectively. In conclusion, PBQ (20% SC) had a comparable molluscicidal efficacy with MNSC (26% SC) and PBQ (25% WP). Furthermore, it showed lower toxicity to the crustacean species, better solubility, no floating dust, and convenience for carriage. PBQ (20% SC) was suitable for controlling snails in the water network schistosomiasis-endemic areas. Full article

(This article belongs to the Special Issue Control of Schistosome Intermediate Hosts)

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