Seasonal Variations of Densities of Biomphalaria pfeifferi, the Intermediate Host of Schistosoma mansoni Parasite at the North of Senegal

Schistosomiasis is becoming more persistent because of the widespread distribution of intermediate host snails in several regions of Africa, including Senegal. The intermediate snail host of the human intestinal schistosome is Biomphalaria pfeifferi and is permanently present in northern Senegal because of the presence of the abundant freshwater habitat throughout the year. Here, we observed the seasonal variation in B. pfeifferi abundance in the Saint-louis region at the North of Senegal in West Africa. We performed snail and environmental parameter sampling across two different seasons described for Senegal: a dry season that runs roughly from mid-October to mid-June and a rainy season that spans approximately from late June to early October. We also split the dry season into two categories representing periods of time when water temperatures were either decreasing (dry1) or increasing (dry2). We used regression analyses to model snail density across the seasons and investigated which environmental variables influenced snail abundance. Results suggested that snails were more abundant and peaked during the rainy season, which lowest abundances during the dry season when temperatures were declining. The above seasonal variations of snail density were positively linked to the environmental drivers including periphyton (food resource for snails), aquatic vegetation abundance, water temperature and dissolved oxygen and negatively to both pH and water conductivity. Our findings may be useful for snail control efforts by targeting specific periods and/or site conditions when snail abundances are greatest.

Afforestation suppresses Oncomelania hupensis snail density through influencing algae in beaches of the Dongting Lake

Background Oncomelania snails serve as the sole intermediate host for Schistosoma japonicum, one of the most important neglected tropical diseases in the world. Afforestation suppression of the Oncomelania hupensis snail has been a long-term effective national strategy to decrease snail density in China. Many previous studies have made clear that vegetation (biotic factors) and soil (abiotic factors) were the basic requirements for snail survival on beaches. Moreover, a lot of research on snail control has been focused on the specific influencing environmental factors for snail survival, such as the vegetation community structure, species composition, diversity index, and the physical and chemical properties of the soil. Most of the existing research has studied the influence of a single factor on snail population density. Conversely, there have been only a few studies focused on the food sources and food composition of the snails. The current research situation on snail control has indicated that the mechanisms underlying ecological snail control have not been systematically characterized. The question of whether biotic or abiotic factors were more important in influencing snail survival remains unclear. Afforestation on beaches has significantly suppressed snail density in China so far. In this study, we proposed that the reduction of snail density was not affected by a single factor but by the interactions of multiple related factors introduced by afforestation. Moreover, different biotic and abiotic factors have significantly different effects on snail control. Therefore the goal of this study was to evaluate the relative importance and interactions of related biotic and abiotic factors on snail density. Methods: Four major vegetation communities: Sedge, Reed, Artificial poplar (3 years of age) and Artificial poplar (5 years of age), on the beaches of the Yangtze River in China were selected for vegetation and snail surveys, as well as for soil sampling. Structural Equation Model (SEM) analysis was used to assess the interactions of biotic and abiotic factors in the context of snail ecology. The soil properties were considered as abiotic factors, while algae of Chlorophyta, Cyanophyta and Bacillariophyta phyla were considered to be biotic factors. In the path analysis, the total effect between the variables was the sum of the direct and indirect effects. Results The snail density had significant correlations with soil properties, such as water content, bulk density, capillary porosity and pH value, as well as with all three types of soil algae, Chlorophyta, Cyanophyta, and Bacillariophyta. Snail density had a direct negative relationship with capillary porosity and soil bulk density, an indirect negative relationship with soil pH value and an indirect positive relationship with soil water content via soil algae. Meanwhile, as an important food source for the snail, the Chlorophyta, Cyanophyta and Bacillariophyta algae had a significant positive correlation with snail density. High soil pH had a negative impact on Chlorophyta, Bacillariophyta, while soil water content had a positive impact on Chlorophyta, and soil bulk density had a negative impact on Cyanophyta. In addition, the soil pH value and soil bulk density both had negative correlations with soil water content. Conclusion Afforestation of the beach environment can significantly reduce the snail population density by altering ecological factors. Soil algae (biological factors) might be the key element that drives ecological snail control. As important habitat determinants, the impact of the properties of the soil (non-biological factors) on the snail population was largely mediated through soil algae.

Effectiveness analysis of spatially targeted mollusciciding for Oncomelania snail control

A new developed spatially targeted mollusciciding technology for snail control was utilised in a research site. This study aims to analyse whether this technology can achieve rational effectiveness compared with the routine method. Snail density was monitored every spring and autumn from 2010 to 2017 at the research site and routine mollusciciding for snail control was then performed. After snail density monitoring in spring 2018, spatially targeted mollusciciding technology was adopted. Log-linear regression and nonlinear regression models were used for snail density prediction in autumn 2018 and the predicted value was compared with the actual snail density in autumn 2018 to verify the effectiveness of the spatially targeted mollusciciding. Monitoring results showed that overall snail density in the research site decreased from 2010 to 2018. The monitored snail density in autumn 2018 was 0.014/0.1 m2. Predicted by the log-linear regression model, the snail density in autumn 2018 would be 0.028 (95% CI 0.11–0.072)/0.1 m2. Predicted by the nonlinear regression model, the snail density growth in autumn 2018 in contrast to spring 2018 would be 79.79% (95% CI 54.81%–104.77%) and the actual value was 55.56%. Therefore, the effectiveness of the first application of spatially targeted mollusciciding was acceptable. However, the validation of its sustainable effectiveness still needs a replicated study comparing areas where targeted and untargeted methods are applied simultaneously and both snail abundance and human infection are monitored.

Determination of Tolerance Threshold Level of Golden Snail (Pomacea canaliculata) in Irrigated Rice

Determination of tolerance threshold of golden snail (Pomacea canaliculata) infestation in irrigated rice had been studied at Sumbersari Village, Moyudan District, Sleman Regency, Yogyakarta Special Teritory, in the growing season of June to October 2016. The water depth during the experiment was maintained at 1 cm. The snails of 2−3 cm in length were infested on rice plots at various ages. The snails were infested on rice plots with density rates of (1) 0, 1, 2, 3, 5, 15, 30, (2) 0, 2, 3, 5, 10, 15, 30, and (3) 0, 3, 5, 10, 15, 20, 30 individuals/m2 at (1) 0 day after planting (DAP), (2) 7 and 14 DAP, and (3) 28 DAP, respectively. These treatments were replicated three times and arranged in the randomized complete block design (RCBD). In this study the tolerance threshold is defined as the highest snail density which causes no significant effect on rice damage and yield loss as compared to control or to the lowest snail density. Therefore, determination of the tolerance threshold was based on the significant difference of damage severity, panicle number per hill, and harvesting dry-weight of rice grain. Results showed that significant rice damage occurred on age of 0, 7, and 14 DAP olds, while on age of 21 and 28 DAP the rice showed no damage. More severe damage occurred to the younger rice. The tolerance threshold values of the snail on rice plots with 1 cm water depth at 0 DAP old was approximately 2 individuals/m2 while at age of 7 and 14 DAP were approximately 3 individuals/m2, respectively. IntisariPenentuan ambang toleransi serangan keong emas (Pomacea canaliculata) pada padi sawah telah dikaji di Desa Sumbersari, Kecamatan Moyudan, Kabupaten Sleman, Daerah Istimewa Yogyakarta dalam musim tanam Juni–Oktober 2016. Kedalaman air selama percobaan berlangsung dikondisikan sedalam 1 cm. Keong berukuran 2−3 cm diinfestasikan pada berbagai umur padi. Keong dengan kepadatan (1) 0, 1, 2, 3, 5, 15, 30; (2) 0, 2, 3, 5, 10, 15, 30; dan (3) 0, 3, 5, 10, 15, 20, 30 ekor/m2 diinfestasikan berturut-turut pada plot padi (1) saat tanam (0 hari setelah tanaman (HST)), (2) umur 7 dan 14 HST, dan (3) serta umur 21, dan 28 HST. Perlakuan diulang tiga kali dan diatur dalam rancangan randomized complete block design (RCBD). Dalam penelitian ini ambang toleransi didefinisikan sebagai kepadatan keong tertinggi yang menyebabkan kerusakan tanaman padi dan kehilangan hasil tidak berbeda signifikan dengan kontrol atau dengan kepadatan populasi terendah. Oleh karena itu nilai ambang toleranasi ditentukan berdasarkan signifikansi perbedaan kerusakan tanaman, jumlah bulir per rumpun, dan berat kering panen gabah. Hasil kajian menunjukkan bahwa kerusakan signifikan terjadi pada padi umur 0, 7, dan 14 hari setelah tanam (HST), sedangkan pada umur 21 dan 28 HST padi tidak menunjukkan kerusakan. Kerusakan semakin parah pada padi semakin muda. Pada kondisi kedalaman air 1 cm, nilai ambang toleransi keong mas pada padi umur 0 HST sekitar 2 ekor/m2 sedangkan pada umur 7 dan 14 HST sekitar 3 ekor/m2.

Kepadatan dan Tingkat Infeksi Serkaria Schistosoma japonicum pada Keong Oncomelania hupensis lindoensis dengan Kasus Schistosomiasis di Daerah Endemis Schistosomiasis, Sulawesi Tengah

Schistosomiasis in Indonesia only found in Napu and Bada Highlands, Poso district and Lindu Highlandsin Sigi district, Central Sulawesi Province. Schistosomiasis in Indonesia caused by Schistosoma japonicumand Oncomelania hupensis lindoensis is the intermediate snail host. The mapping of snail foci areas in2017 showed that there was a significant change in the spread of the snail's foci. This paper aimed todescribe the density and infection rate of S. japonicum cercariae in the snail host in the endemic areasof schistosomiasis in Central Sulawesi Province. The mean O.hupensis lindoensis snail density in Napuranged from 0.9 to 6.6/m2, with mean rates of cercariae infections ranging from 0.4% to 21.4%. The snaildensity average in Lindu ranging from 3/m2 to 69,1/m2, with 4.4%-72.9% of cercariae infections. In badathe snail density ranged from 0.1 to 4.9/m2, with mean rates of cercariae infections ranging from 0% to14.9%. Bivariate analysis showed there was no correlation between snail density and cercariae infectionrate with schistosomiasis case (p value> 0.05).Keywords : Schistosomiasis, density, infection rate, Oncomelania hupensis lindoensis, Central Sulawesi AbstrakSchistosomiasis di Indonesia hanya ditemukan di Propinsi Sulawesi Tengah, yaitu Dataran Tinggi Napudan Dataran Tinggi Bada, Kabupaten Poso serta Dataran Tinggi Lindu, Kabupaten Sigi. Schistosomiasisdi Indonesia disebabkan oleh Schistosoma japonicum dengan hospes perantara keong Oncomelaniahupensis lindoensis. Pemetaan daerah fokus pada tahun 2017 menunjukkan bahwa terdapat perubahanyang signifikan dalam penyebaran fokus keong. Tulisan ini bertujuan untuk menggambarkan kepadatandan infection rate serkaria S.japonicum pada keong perantara schistosomiasis di wilayah endemisschistosomiasis di Provinsi Sulawesi Tengah. Rerata kepadatan keong O.hupensis lindoensis di Napuberkisar dari 0,9 – 6,6/m2, dengan rerata tingkat infeksi serkaria berkisar antara 0,4% sampai 21,4%, diLindu kepadatan keong berkisar antara 3/m2 sampai 69,1/m2, dengan tingkat infeksi serkaria 4,4%¬72,9%,dan di Bada kepadatan keong berkisar antara 0,1 – 4,9/m2, dengan rerata tingkat infeksi serkaria berkisarantara 0 % sampai 14,9%. Analisis bivariat menunjukkan tidak ada korelasi antara kepadatan keong dantingkat infeksi serkaria dengan jumlah kasus schistosomiasis nilai p value > 0.05.Kata kunci: Schistosomiasis, kepadatan, tingkat infeksi, Oncomelania hupensis lindoensis, SulawesiTengah

SOWING METHODS AND WATER LEVELS INFLUENCE APPLE SNAIL DAMAGE TO RICE AND ITS YIELD IN PENINSULAR MALAYSIA

SUMMARYRice productivity is limited by many pests, especially Pomacea spp. in Southeast Asia. Pomacea spp. damage to rice depends on sowing methods, flooded conditions, and snail densities in the field. Therefore, this study aims to evaluate the effect of different sowing methods, water levels, and snail density (1, 2, and 3 snails per plot) on the damage potential of Pomacea maculata and Pomacea canaliculata to rice and its yield. Both species caused complete loss of crop in direct seeding and 14 days old transplanted rice. The least damage by both species was recorded in 21 and 28 days old transplanted rice with no further damage after week five. Irrigation and snail density also influenced damage whereby highest damage was recorded in rice grown with 5 cm water level in comparison to 2 cm. At 2 cm water level, damage by various snail densities was trivial. However, in 5 cm water level, damage increased with the increasing snail density and the highest damage was observed at three snails per plot of either species. No difference in inflicted damage to various treatments was observed between two species, suggesting their equal damage potential on rice. Meanwhile, rice yields in 2 cm water level treatments were compatible with 5 cm control treatment. The least yield was recorded in treatments with three snails per plot of either species at 5 cm water level. Understanding the effect of sowing method and suitable water level is important as it can be further incorporated into rice cultivation practices to reduce damage of apple snails and ensure a high yield during harvest.

Biological and environmental factors associated with risk of schistosomiasis mansoni transmission in Porto de Galinhas, Pernambuco State, Brazil

Schistosomiasis has expanded to the coast of Pernambuco State, Brazil, where there are frequent reports of Biomphalaria glabrata snails and human cases of the disease. This study analyzes factors related to schistosomiasis transmission risk in Porto de Galinhas. A one-year malacological survey was conducted to identify biological, abiotic, and environmental factors related to the host snail breeding sites. Data analysis used Excel 2010, GTM Pro, and ArcGis 10. A total of 11,012 B. glabrata snails were captured in 36 breeding sites, and 11 schistosomiasis transmission foci were identified. A negative correlation was found between breeding site temperature and snail density and infection rate, and a positive correlation with pH and salinity. The rainy season showed a positive correlation with snail density and infection rate. The study emphasizes the factors involved in the maintenance of schistosomiasis breeding sites, in light of persistence of this disease in Porto de Galinhas for more than 10 years.