Cercarial Shedding Research Articles

Exploring the evolutionary potential of parasites: Larval stages of pathogen digenic trematodes in their thiarid snail host Tarebia granifera in Thailand

Minute intestinal flukes from several distinct families of endoparasitic platyhelminths are a medically important group of foodborne trematodes prevalent throughout Southeast Asia and Australasia. Their lifecycle is complex, with freshwater snails as primary intermediate hosts, with infecting multiple species of arthropods and fish as second intermediate hosts, and with birds and mammals including humans as definitive hosts. In Southeast Asian countries, the diversity of snail species of the Thiaridae which are frequently parasitized by trematode species is extremely high. Here, the thiarid Tarebiagranifera in Thailand was studied for variation of trematode infections, by collecting the snails every two months for one year from each locality during the years 2004–2009, and during 2014–2016 when snails from the same localities were collected and new localities found. From ninety locations a total of 15,076 T.granifera were collected and examined for trematode infections. With 1,577 infected snails the infection rate was found to be 10.46 %. The cercariae were categorized into fifteen species from eight morphologically distinguishable types representing several distinct families, viz. (i) virgulate xiphidiocercariae (Loxogenoidesbicolor, Loxogenesliberum and Acanthatriumhistaense), (ii) armatae xiphidiocercariae cercariae (Maritreminoidescaridinae and M.obstipus); (iii) parapleurophocercous cercariae (Haplorchispumilio, H.taichui and Stictodoratridactyla); (iv) pleurophocercous cercariae (Centrocestusformosanus); (v) megarulous cercariae (Philophthalmusgralli); (vi) furcocercous cercariae (Cardicolaalseae, Alariamustelae and Transversotremalaruei); as well as (vii) echinostome-type cercariae, and (viii) gymnocephalous-type cercariae. In addition, a phylogenetic marker (internal transcribed spacers 2, ITS2) was employed in generic and infrageneric level classifications of these trematodes, using sequences obtained from shed cercariae isolated from T.granifera specimens of the second study period collected in various regions in Thailand. We obtained ITS2 sequences of cercariae from nine species (of seven types): Loxogenoidesbicolor, Loxogenesliberum, Maritreminoidesobstipus, Haplorchistaichui, Stictodoratridactyla, Centrocestusformosanus, Philophthalmusgralli, as well as from one species each of echinostome cercariae and gymnocephalous cercariae. Thus, this analysis combines the parasites’ data on morphology and geographical occurrence with molecular phylogeny, aiming to provide the groundwork for future studies looking into more details of the parasite-snail evolutionary relationships.

Morphological Characterization of Emerging Cercariae among Lymnaeid Snails from Barangay Cawongan, Padre Garcia, Batangas, Philippines.

Background and Objectives Lymnaeid snails are the known intermediate hosts of the liver fluke Fasciola spp. and therefore play an important role in the parasite's life cycle. The study is conducted to determine specificity of snail host-parasite interaction and to determine the snail-trematode infection rate by cercarial emergence, characterizing the emerging larvae using standardized key. Materials and Methods A total of 750 snails were collected from a rice field in Barangay Cawongan, Padre Garcia, Batangas, from November 2016 to March 2017 (n=150/month). Preliminary snail identification was based on morphological features of the shell. Each snail was acclimatized for 24 hours in a 50-ml capacity container before being exposed to strong artificial light. The 150 snails collected per month were grouped into 5 batches (n=30/batch) with each batch receiving different number of light exposures. Emerging cercariae were described and characterized using photo-referencing and standardized keys. All statistical tests were performed at p<0.05 level of significance using SPSS ver. 20. Results The total cercarial shedding rate of the snails studied, as a measure of the infected snails, was found to be 35.6% and was positively associated with the length of the snail shell [OR = 1.809; 95% CI: 1.471–2.225; p<0.001], but not with the weight [OR = 0.003; 95% CI: 0.00–0.275; p=0.012] and width of the shell [OR = 0.937; 95% CI: 0.672–1.305]. The rates varied from 29.3% to 38.0% based on the frequency of 6-hour light exposure. Appearance of encysted forms increased with increasing number of light exposures [OR = 10.27, 95% CI: 3.04–34.76, p<0.001]. Three distinct cercariae were identified, namely, echinostome, longifurcate-pharyngeate distome cercariae (Strigea cercariae), and the virgulate xiphidiocercaria, with 26.4%, 2.27%, and 0.67% infection monitored by cercarial emergence, respectively. Conclusion Local lymnaeid snails were infected with a single type of trematode larvae and coinfection with multiple larvae was rare but was encountered.

Geographical and behavioral risks associated with Schistosoma haematobium infection in an area of complex transmission

BackgroundSchistosoma haematobium infection in endemic areas varies depending on the nature and complexity of the transmission networks present. Studies of micro-geographical transmission of S. haematobium infection indicate that discrepancy in prevalence between households is associated with diverse water contact behaviors and transmission that is restricted to particular sites harboring snail intermediate hosts. Detection of variations in the transmission sources with complex transmission networks of water bodies is required for optimization of malacological control. Longitudinal parasitological and malacological surveys were conducted to investigate geographical variations in transmission of urogenital schistosomiasis in Ikingwamanoti village, Shinyanga District, Tanzania.MethodsUrine samples were collected at baseline and follow-up time points from 282 school-aged children and examined microscopically for the presence of S. haematobium eggs. Malacological surveys involved collection of Bulinus nasutus every month from 30 sites. Snails were examined for patent infections. Global positioning system was used to map household distances from S. haematobium transmission sites, while water contact behavior was assessed using a questionnaire.ResultsSchistosoma haematobium infection was observed to be prevalent among older children (12–14 years) compared to younger groups prior to treatment, but no significant difference in infection prevalence was observed at one-year. Boys were highly infected than girls at both time points. No spatial influence was observed between children’s infection and the distance from child’s residence to the nearby snail habitats nor was any significant association observed between children’s reported water contact behavior with S. haematobium infection. However, malacological surveys with cercarial shedding combined with GPS data detected significant variation among different water sources in the transmission of S. haematobium with children living in households near to ponds with high B. nasutus populations having the highest prevalence of infection.ConclusionsInteraction between malacological surveys with cercarial shedding combined with GPS mapping in endemic settings can help detection of transmission sources even in areas with complex transmission networks. Subsequent studies are needed to determine whether the combination of GPS mapping and parasitology screens can aid the detection of transmission hotspots across varied transmission settings to enhance schistosomiasis control programmes.

Epidemiological and genetic characterization of larval stages of Fasciola gigantica in snail intermediate hosts in Karnataka State, India.

Fasciolosis in ruminants in India is caused by the liver fluke Fasciola gigantica. Radix (Lymnaea) spp. are known to carry the infective stages of this parasite. Understanding the seasonal prevalence of F. gigantica infection in the intermediate host is of extreme importance in order to elucidate the transmission dynamics of the parasite. So the present study was designed to determine the bioclimatic distribution of larval stages of F. gigantica in Radix spp. snails as well as to explore the genetic diversity of F. gigantica in three geographical regions (Deccan plateau, Western Ghats and coastal region) of Karnataka. The lymnaeid snails were sampled (n = 2077) for a period of one year (June 2015 to May 2016) at 24 sites. The snails were morphologically identified and the infection status was established through cercarial shedding and nested polymerase chain reaction (PCR) based technique targeting second internal transcribed spacers (ITS-2) of nuclear ribosomal DNA. The sensitivity of PCR (8.2%) for detection of F. gigantica infection within snail is significantly higher than cercarial shedding (4.3%) with an overall prevalence of 5.1%. The prevalence of infection was higher in winter than in the rainy and summer seasons (6.2% instead of 4.6% and 4.3% respectively). Deccan plateau (5.8%) showed a higher prevalence of infection compared to Western Ghats (5.2%) and Coastal region (3.6%). The sequencing ITS-2 region permitted the identification of the parasite as F. gigantica which is having high implication in studying the population genetic structure of the parasite in the country. In conclusion, overall results indicated that Radix spp. snails harboured F. gigantica developmental stages throughout the year and nested PCR was found to be sensitive and specific for detection of F. gigantica infection in snails compared to routine parasitological techniques.

Effect of Temperature on the Release of Proterometra macrostoma (Trematoda: Digenea) Cercariae from Their Snail Intermediate Host, Pleurocera semicarinata (Gastropoda: Pleuroceridae) at North Elkhorn Creek, Kentucky

The effect of temperature on cercarial release has been well documented for several digenean species; however, there have been no prior studies assessing shedding of cercariae from snails infected with the azygiid, Proterometra macrostoma. Snails, Pleurocera semicarinata, were collected at the Lemon's Mill site on North Elkhorn Creek in Scott County, Kentucky during June and July 2016. Snails shedding cercariae (n = 453) were assigned to temperature treatments (10, 13, 15, 18, 20, 25, and 30°C) that were within the range of previously reported seasonal water temperatures at North Elkhorn Creek. Snails were acclimated to experimental temperatures for 3 d. Cercarial counts were then made at 0900 h daily over the next 7 d, and the average 7-d cercarial release was calculated for each snail. The minimum emergence threshold temperature for Pr. macrostoma cercarial release was determined to be approximately 13°C, whereas the minimum development threshold temperature was between 10 and 12°C. Notably, cercarial release increased with temperature up to 25°C, but declined at 30°C. Q10 values calculated from 10°C intervals were greatest at the lowest (13–23°C) temperature interval (Q10 = 16.1), and declined at the higher (15–25 and 20–30°C) intervals (Q10 = 4.3 and Q10 = 1.8, respectively). Snail survivorship within combined replicates ranged from 87.1 to 100% over the 10-d experiment, with the lowest survivorship observed at 30°C. These results are discussed with regard to climate change and global warming.

The life cycle of a zoonotic parasite reassessed: Experimental infection of Melanoides tuberculata (Mollusca: Thiaridae) with Centrocestus formosanus (Trematoda: Heterophyidae).

Centrocestus formosanus is a foodborne intestinal trematode that is native to Asia and has been introduced into the Americas and Europe. Although there are several studies of C. formosanus in definitive vertebrate hosts (birds and mammals, including humans), and in intermediate vertebrate hosts (fish and amphibians), there is little published information regarding interaction with its transmitting mollusc. In this study we studied the miracidial development of C. formosanus using a mouse as a source of eggs. Adult parasites were maintained in water in order to develop miracidia in intrauterine eggs. Miracidia appeared at 12 days of incubation, with no hatching observed for up to 40 days. Subsequently, we placed dead C. formosanus containing eggs with miracidia individually in contact with 48 specimens of Melanoides tuberculata, and observed the absence of the parasites after 1h of exposure, suggesting that they were ingested by the snails. Of the 33 experimentally-infected snails that were alive after 84–89 days post-infection (DPI), seven (21%) shed cercariae. We detected young C. formosanus rediae in 21/33 (64%) M. tuberculata at 90 DPI. To our knowledge, this report is the first to show that, in the life cycle of C. formosanus, infection of molluscs occurs passively by ingestion of eggs, followed by a long intramolluscan phase. We compare these data with those described for other Heterophyidae, and discuss on the phylogenetic background of the pattern of miracidial development verified in these parasites.

Three Strigeid cercariae from Littorina littorea snail, Qarun Lake, Fayoum, Egypt.

Aim:The present study aims to focus on the role of common marine snails (Littorina littorea) as a vector for some trematode parasites.Materials and Methods:A total of 327 marine water L. littorea snails were collected during the summer of 2016 from a Qarun lake in the EL-Fayoum Governorate, Egypt. The snails were investigated for infection by trematode parthenitae through induction of cercarial shedding by exposure to light and crushing the snails. The species were stored in Search Laboratory of Zoology Department, Faculty of Science, Fayoum University.Results:Three species of Strigeid littorina cercaria were identified from the infected snails. They are described here and they identified in relation to close-up morphological features and linked to its snail hosts. They give the following names: Cercaria strigeid littorina type 1, C. strigeid littorina type 2, and C. strigeid littorina type 3. The incidence of infection by these cercariae was 33%, 25.7%, and 2.4%, respectively.Conclusion:This study is clarifying the importance of this marine snail as intermediate hosts for new trematode species.

Assessing S. mansoni prevalence in Biomphalaria snails in the Gombe ecosystem of western Tanzania: the importance of DNA sequence data for clarifying species identification

BackgroundSnails are essential for the transmission and maintenance of schistosomiasis in endemic areas, as they serve as intermediate hosts for schistosome parasites. A clear understanding of the snail species present, their local distribution and infection status is therefore a prerequisite for effective control of schistosomiasis. The purpose of this study was to establish the infection status and distribution of Schistosoma mansoni in snails in the Gombe area along the shores of Lake Tanganyika in western Tanzania, using both detection of cercarial shedding and molecular approaches.MethodsSnails were collected from streams located close to human settlements in Gombe National Park, as well as from nearby villages (Kiziba, Mtanga, Mwamgongo and Bugamba) and the largest town in the region (Kigoma). Snails were individually exposed to light to induce shedding of schistosome larvae, which were examined using a compound light microscope. Additionally, the internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster was simultaneously amplified in both snails and their trematodes using a single polymerase chain reaction (PCR) and sequenced to confirm species identification.ResultsSnails morphologically identified as Biomphalaria pfeifferi were present in all streams except at Mtanga but their distribution was patchy in both time and space. Sequencing of PCR products indicated that not all snails were B. pfeifferi. None of the snails from Gombe or Bugamba shed schistosome larvae, while larvae were shed at all other sites. Overall, an infection prevalence of only 12% was observed in snails based on cercarial shedding. While 47% of the snails were PCR-positive for the 500 bp ITS fragment, which was predicted to indicate infection with S. mansoni, sequence data demonstrated that these bands are not species-specific and can be amplified from other trematode infections. In addition, a 1000 bp band was amplified in 14% of samples, which was identified as a trematode in the family Derogenidae.ConclusionsThe results support the previous assumption that B. pfeifferi snails may be involved in transmitting schistosomiasis in the area but suggest that the community structure of both snails and trematodes may be more complicated than previously thought. This emphasises the importance of confirming species identifications using sequencing, rather than relying only on PCR-based diagnostics or cercarial shedding.

In vitro Studies on the Effects of Cercariae Shedding (Schistosoma Parasitosis) on Fecundity, Hatchability and Longevity of Bulinus globosus

In vitro Studies on the Effects of Cercariae Shedding (Schistosoma Parasitosis) on Fecundity, Hatchability and Longevity of Bulinus globosus

Mapping freshwater snails in north-western Angola: distribution, identity and molecular diversity of medically important taxa

BackgroundThis study was designed to determine the distribution and identity of potential intermediate snail hosts of Schistosoma spp. in Bengo, Luanda, Kwanza Norte and Malanje Provinces in north-western Angola. This is an area where infection with Schistosoma haematobium, causing urogenital schistosomiasis, is common but little is yet known about transmission of the disease. Angola has had a varied past with regard to disease control and is revitalising efforts to combat neglected tropical diseases.MethodsSnails were sampled from 60 water-contact points. Specimens of the genera Bulinus, Biomphalaria or Lymnaea were screened for trematode infections by inducing cercarial shedding. Snails were initially identified using shell morphology; subsequently a cytochrome c oxidase subunit 1 (cox1) gene fragment was amplified from a subset of snails from each site, for molecular identification. Cercariae were captured onto FTA cards for molecular analysis. Specimens of Bulinus angolensis collected from the original locality of the type specimen have been characterised and comparisons made with snails collected in 1957 held at the Natural History Museum, London, UK.ResultsIn total snails of nine genera were identified using morphological characteristics: Biomphalaria, Bulinus, Gyraulus, Lanistes, Lentorbis, Lymnaea, Melanoides, Physa and Succinea. Significant for schistosomiasis transmission, was the discovery of Bulinus globosus, B. canescens, B. angolensis, B. crystallinus and Biomphalaria salinarum in their type-localities and elsewhere. Bulinus globosus and B. angolensis occurred in two distinct geographical areas. The cox1 sequence for B. globosus differed markedly from those from specimens of this species collected from other countries. Bulinus angolensis is more closely related to B. globosus than originally documented and should be included in the B. africanus group. Schistosoma haematobium cercariae were recovered from B. globosus from two locations: Cabungo, Bengo (20 snails) and Calandula, Malanje (5 snails). Schistosoma haematobium cercariae were identified as group 1 cox1 corresponding to the type common throughout the African mainland.ConclusionsVarious freshwater bodies in north-western Angola harbour potential intermediate snail hosts for urogenital schistosomiasis, highlighting the need to map the rest of the country to identify areas where transmission can occur and where control efforts should be targeted. The molecular phylogeny generated from the samples confirmed that considerable variation exists in B. globosus, which is the primary snail host for S. haematobium in many regions of Africa.

The efficacy of aqueous leaf extract of &lt;i&gt;Solanum tuberosum&lt;/i&gt; on &lt;i&gt;Schistosoma mansoni&lt;/i&gt;-infected albino mice

Human schistosomiasis is one of the important diseases of helminth origin; it is among the most devastating infectious parasitic disease responsible for several deaths and economic losses amongst half of the world’s population. Control of schistosomiasis is solely dependent on chemotherapy. There is need to explore other control measures to interrupt the biology of the parasite. Solanum tuberosum had been used to control the intermediate host (snail) hence the choice of plant extracts to scientifically investigate the schistosomicidal efficacy. The mature leaves of Solanum tuberosum plant were collected from the potatoe research farm of National Root Crop Research Institute, Potatoe Programme, Kuru, Vom, and identified in the Federal College of Forestry, Jos, Nigeria. The Biomphalaria pfeifferi snail vectors were collected from the Miango Irrigation Ponds in Bassa Local Government Area of Plateau State and exposed to sun light for 45 minutes for cercarial shedding. Sixty (60) albino mice of eight weeks weighing between 18 and 25 g were divided into six Groups (1, 2, 3, 4, 5 and 6), Group 1-5 were used for the experiments while Group 6 served as control. The skinned suspended tails were then immersed in the test-tube containing 150 cercariae suspension for mice infections. Group 1 was administered 1.5 mg/ kg, (2) 3 mg/kg, (3) 6 mg/kg, (4) paraziquantel 60 mg/kg divided into two doses respectively while Group 5 was infected but not treated while 6 was the uninfected control and feaces examined after 14 days post-treatment for egg recovery. The mice in the untreated Group 5 post infection (19 days) had the highest number of Schistosoma mansoni ova.Keywords: Solanum tuberosum; S. mansoni; B. pfeifferi; cercariae; albino mice and paraziquantel

Delineation of potential urban urogenital schistosomiasis transmission areas in Osogbo, south-west Nigeria

Schistosomiasis is ranked second to malaria among parasitic diseases of socio-economic and public health importance. One of the crucial factors in monitoring the current and future status and distribution of S. haematobium infection in Nigeria is to improve the knowledge on the freshwater snails that play an indispensable role in its transmission. The present study was undertaken to delineate potential transmission areas of urogenital schistosomiasis in Osogbo Metropolis using snail intermediate hosts and human-water contact as indicators. The major rivers/streams were visited bimonthly at various locations between April and July, 2016 and snail samples were collected using scoopers. The snails were identified morphologically and exposed to artificial light for cercaria shedding. Human water contact activities were observed at the sites where snails were recovered and relative index of exposure was calculated for each activity. Of the nine locations visited, only four were positive, namely; Gbodofon (Osun River), Isale Osun (Osun River), area 264 (Oniti Stream) and Gbonmi (Okoko Stream). Even though, none of the exposed snails shed cercaria, the human activities were observed at the sites. The results showed that 49.7% of the human contacts were for swimming followed by Fishing (32.2%), cloth-washing (10.1%) and spiritual/ritual bath (8.0%). Swimming has the highest relative index of exposure (RIE=30231) while spiritual/ritual bath has the least (RIE=96). The presence of the snail intermediate hosts at the four sites coupled with human water activities as observed in the present study suggest the risk of urogenital schistosomiasis at the study-area. Keywords: Bulinus species; schistosome; human water contact; Osogbo; Nigeria

Prevalence and seasonal transmission of Schistosoma haematobium infection among school-aged children in Kaedi town, southern Mauritania

BackgroundMauritania is at the fringe of transmission of human schistosomiasis, which mainly occurs in the southern and southeastern parts of the country. This study aimed to assess the influence of rainfall seasonality on the prevalence of Schistosoma haematobium infection among school-aged children in Kaedi, southern Mauritania.MethodsCross-sectional surveys (i.e. parasitological, malacological and observations on water-related human activities) were carried out in Kaedi between September 2014 and May 2015, during both the wet and dry seasons. A total of 2162 children aged 5–15 years provided a single urine sample that was subjected to S. haematobium diagnosis. Snails were sampled and checked for cercarial shedding. Water contact patterns of the local population were recorded by direct observation.ResultsThe prevalence of S. haematobium was 4.0% (86/2162, 95% confidence interval (CI): 3.2–4.9%) with a geometric mean egg count per 10 ml of urine of 3.7 (95% CI: 2.8–4.3). Being male (adjusted odds ratio (aOR) 1.78, 95% CI: 1.13–2.80), being at primary school (aOR 1.73, 95% CI: 1.04–2.87) and dry season (aOR 0.56, 95% CI: 0.35–0.89) were significantly associated with S. haematobium. Among 284 potential intermediate host snail specimens collected over the rainy and dry seasons, three species were identified: Bulinus senegalensis (n = 13) and B. forskalii (n = 161) in the rainy season, and B. truncatus (n = 157) in the wet season. No snail was shedding cercariae. On average, seven human water contacts were recorded per hour per observer over a 28-day observation period. Twelve types of water contact activities were identified among which, swimming/bathing was predominant (n = 3788, 36.9%), followed by washing clothes (n = 2016, 19.7%) and washing dishes (n = 1322, 12.9%). Females (n = 5270, 51.4%) were slightly more in contact with water than males (n = 4983, 48.6%). The average time spent in the water per person per day was 14.2 min (95% CI: 13.8–14.6 min). The frequency and duration of water contact followed a seasonal pattern.ConclusionOur findings demonstrate a low prevalence and intensity of S. haematobium among school-aged children in Kaedi. Appropriate integrated control measures, including health education among at-risk communities and snail control may help to interrupt transmission of S. haematobium in Kaedi.

Epidemiology of intestinal helminthiasis among school children with emphasis on Schistosoma mansoni infection in Wolaita zone, Southern Ethiopia

BackgroundIntestinal helminth infections are major parasitic diseases causing public health problems in Ethiopia. Although the epidemiology of these infections are well documented in Ethiopia, new transmission foci for schistosomiasis are being reported in different parts of the country. The objective of this study was to assess the prevalence of Schistosoma mansoni and other intestinal helminth infections among school children and determine the endemicity of schistosomiasis in Wolaita Zone, southern Ethiopia.MethodsCross-sectional parasitological and malacological surveys were conducted by collecting stool samples for microscopic examination and snails for intermediate host identification. Stool samples were collected from 503 children and processed for microscopic examination using Kato-Katz and formalin-ether concentration methods. Snails collected from aquatic environments in the study area were identified to species level and Biomphalaria pfeifferi snails, the intermediate host of S. mansoni,, were individually exposed to artificial light in order to induce cercariae shedding. Cercariae shed from snails were used to infect laboratory-bred Swiss albino mice in order to identify the schistosome to species level.ResultsThe overall prevalence of intestinal helminth infections was 72.2% among school children. S. mansoni infection prevalence was 58.6%. The prevalence and intensity of S. mansoni infections varied among schools and sex of children. Swimming was the only factor reported to be significantly associated with S. mansoni infection (AOR = 2.954, 95% CI:1.962-4.449). Other intestinal helminth species identified were hookworms (27.6%), Ascaris lumbricoides (8.7%), E. vermicularis (2.8%), Taenia species (2.6%), T. trichiura (1.2%) and H. nana (0.6%). Only B. pfeifferi snails collected from streams shed schistosome cercariae and 792 adult S. mansoni worms were harvested from mice exposed to cercariae shed from B. pfeifferi on the 6th week post-exposure.ConclusionThe present study found high level of intestinal helminth infections in the study area. The study also confirmed autochthonous transmission and endemicity of S. mansoni as evidenced by both parasitological and malacological findings as well as by further establishing infections in lab-bred mice. Therefore, there is a need to include the area in the control programs with anti-helminth drugs and also consider other complementary measures including sanitation, provision of clean water supply, and snail control.

Dynamics of freshwater snails and Schistosoma infection prevalence in schoolchildren during the construction and operation of a multipurpose dam in central C\xf4te d\u2019Ivoire

BackgroundThe construction and operation of small multipurpose dams in Africa have a history of altering the transmission of water-based diseases, including schistosomiasis. The current study was designed to investigate the abundance and dynamics of schistosomiasis intermediate host snails and Schistosoma infections in humans during the construction and the first years of operation of a small multipurpose dam in Côte d’Ivoire.MethodsThe study was carried out in Raffierkro and four neighbouring villages in central Côte d’Ivoire between 2007 and 2012. Snails were collected by two experienced investigators using scoops and forceps for 15 min at each site. Snails were identified at genera and, whenever possible, species level, and subjected to testing for cercarial shedding. Schoolchildren aged 6–15 years were examined once every year for Schistosoma haematobium and S. mansoni infection, using urine filtration and duplication Kato-Katz thick smears, respectively. Additionally, 551 adults were examined for Schistosoma infection before (June 2007) and 359 individuals 2 years after dam construction (June 2009).ResultsOverall, 1 700 snails belonging to nine different genera were collected from 19 sampling sites. Bulinus (potential intermediate host snails of S. haematobium) and Pila were the most common genera, whereas Biomphalaria (potential intermediate host snail of S. mansoni), Lymnaea, Physa and Melanoides were found in two villages. During the first-year sampling period, 65 snails were collected, of which 13 (20%) were schistosomiasis intermediate hosts. In subsequent years, out of 1 635 snails collected, 1 079 (66%) were identified as potential intermediate host for schistosomiasis, but none were shedding cercariae. The prevalence of S. mansoni among adults in the study area was low (0.4% in 2007 and 0.3% in 2009), whereas the prevalence of S. haematobium declined from 13.9% to 2.9% in this two-year period.ConclusionsThe low prevalence of schistosomiasis in humans and the absence of infected intermediate host snails during the construction and early phase of operation of a small multipurpose dam suggest that there was no or only very little local transmission. However, the considerable increase in the number of intermediate host snails and their dispersion in irrigation canals call for rigorous surveillance, so that adequate public health measures can be taken in case of early signs of an outbreak.

IMMUNE RESPONSE OF STIMULATED BIOMPHALARIA ALEXANDRINA SNAILS WITH SCHISTOSOMA MANSONI INFECTION

In this study, both digestive and hermaphrodite glands in Biomphalaria alexandrina snails were examined by light microscope (LM) and scanning electron microscopy (SEM) in a trial to clarify its immunological role as defense mechanism against the parasite infection. B. alexandrina snails used were exposed individually to Schistosoma mansoni miracidia; according to their responsq they were classified into infected snails (shed cercariae) and non-infected snails (failed to shed cercariae). Snails not exposed to S. mansoni miracidia used as control. LM showing great histological alteration in tissues, of the both glands in infected snails, these changes represented by degenerated both oocyte and spermatocyte in hermaphrodite gland in addition to degenerated digestive gland while non-infected snails showing mild degenerated ova with normal spermatocytes also degenerated miracidia. inside granuloma like structure with concentric layers of fibroblast and haemocyte could be observed. By SEM we could detect extensively damaged and fibrosed non-motile cilia with exfoliation of tegumental surface in in- fected B.alexandrina while non-infected ones showing attached numerous cilia with some ballooning of the folds.

Intestinal schistosomiasis in Uganda at high altitude (>1400\xa0m): malacological and epidemiological surveys on Mount Elgon and in Fort Portal crater lakes reveal extra preventive chemotherapy needs

BackgroundIntestinal schistosomiasis is of public health importance in Uganda but communities living above 1400 m are not targeted for control as natural transmission is thought unlikely. To assess altitudinal boundaries and at-risk populations, conjoint malacological and epidemiological surveys were undertaken on Mount Elgon (1139 m–3937 m), in Fort Portal crater lakes and in the Rwenzori Mountains (1123 m–4050 m).MethodsSeventy freshwater habitats [Mount Elgon (37), Fort Portal crater lakes (23), Rwenzori Mountains (8) and Lake Albert (2)] were inspected for Biomphalaria species. Water temperature, pH and conductivity were recorded. A parasitological examination of 756 schoolchildren [Mount Elgon (300), Fort Portal crater lakes (456)] by faecal microscopy of duplicate Kato-Katz smears from two consecutive stool samples was bolstered by antigen (urine-CCA dipstick) and antibody (SEA-ELISA) diagnostic assays.ResultsBiomphalaria spp. was found up to 1951 m on Mount Elgon and 1567 m in the Fort Portal crater lakes. Although no snail from Mount Elgon shed cercariae, molecular analysis judged 7.1% of snails sampled at altitudes above 1400 m as having DNA of Schistosoma mansoni; in Fort Portal crater lakes three snails shed schistosome cercariae. Prevalence of intestinal schistosomiasis as measured in schoolchildren by Kato-Katz (Mount Elgon = 5.3% v. Fort Portal crater lakes = 10.7%), CCA urine-dipsticks (18.3% v. 34.4%) and SEA-ELISA (42.3% v. 63.7%) showed negative associations with increasing altitude with some evidence of infection up to 2000 m.ConclusionsContrary to expectations, these surveys clearly show that natural transmission of intestinal schistosomiasis occurs above 1400 m, possibly extending up to 2000 m. Using spatial epidemiological predictions, this now places some extra six million people at-risk, denoting an expansion of preventive chemotherapy needs in Uganda.

Divergent Effects of Schistosoma haematobium Exposure on Intermediate-Host Snail Species Bulinus nasutus and Bulinus globosus from Coastal Kenya.

AbstractSchistosoma haematobium infection causes urogenital schistosomiasis, a chronic inflammatory disease that is highly prevalent in many parts of sub-Saharan Africa. Bulinid snails are the obligate intermediate hosts in the transmission of this parasite. In the present study, Bulinus globosus and Bulinus nasutus snails from coastal Kenya were raised in the laboratory and exposed to miracidia derived from sympatric S. haematobium specimens to assess the species-specific impact of parasite contact and infection. The snails' subsequent patterns of survival, cercarial shedding, and reproduction were monitored for up to 3 months postexposure. Schistosoma haematobium exposure significantly decreased the survival of B. globosus, but not of B. nasutus. Although both species were capable of transmitting S. haematobium, the B. globosus study population had a greater cumulative incidence of cercarial shedders and a higher average number of cercariae shed per snail than did the B. nasutus population. The effects of prior parasite exposure on snail reproduction were different between the two species. These included more numerous production of egg masses by exposed B. nasutus (as compared with unexposed snails), contrasted to decreased overall egg mass production by parasite-exposed B. globosus. The interspecies differences in the response to and transmission of S. haematobium reflect clear differences in life histories for the two bulinid species when they interact with the parasite, which should be taken into account when planning control interventions aimed at reducing each host snails' contribution to local transmission of Schistosoma infection.

Biompha-LAMP: A New Rapid Loop-Mediated Isothermal Amplification Assay for Detecting Schistosoma mansoni in Biomphalaria glabrata Snail Host.

BackgroundSchistosomiasis remains one of the most common endemic parasitic diseases affecting over 230 million people worlwide. Schistosoma mansoni is the main species causing intestinal and hepatic schistosomiasis and the fresh water pulmonate snails of the genus Biomphalaria are best known for their role as intermediate hosts of the parasite. The development of new molecular monitoring assays for large-scale screening of snails from transmission sites to detect the presence of schistosomes is an important point to consider for snail control interventions related to schistosomiasis elimination. Our work was focussed on developing and evaluating a new LAMP assay combined with a simple DNA extraction method to detect S. mansoni in experimentally infected snails as a diagnostic tool for field conditions.Methodology/Principal findingsA LAMP assay using a set of six primers targeting a sequence of S. mansoni ribosomal intergenic spacer 28S-18S rRNA was designed. The detection limit of the LAMP assay was 0.1 fg of S. mansoni DNA at 63°C for 50 minutes. LAMP was evaluated by examining S. mansoni DNA in B. glabrata snails experimentally exposed to miracidia at different times post-exposure: early prepatent period (before cercarial shedding), light infections (snails exposed to a low number of miracidia) and detection of infected snails in pooled samples (within a group of uninfected snails). DNA for LAMP assays was obtained by using a commercial DNA extraction kit or a simple heat NaOH extraction method. We detected S. mansoni DNA in all groups of snails by using no complicated requirement procedure for DNA obtaining.Conclusions/SignificanceOur LAMP assay, named Biompha-LAMP, is specific, sensitive, rapid and potentially adaptable as a cost-effective method for screening of intermediate hosts infected with S. mansoni in both individual snails and pooled samples. The assay could be suitable for large-scale field surveys for schistosomes control campaigns in endemic areas.

Malacological survey and geospatial distribution of &lt;i&gt;Indoplanor bisexutus&lt;/i&gt; (Deshayes, 1934) and &lt;i&gt;Lymnaea natalensis&lt;/i&gt; (Krauss 1848) snail vectors of trematode parasites, in Abeokuta, south-western, Nigeria

Vector snails of trematode parasites are important because of their role in the transmission of parasitic diseases. However, information on the diversity and distribution of snail hosts in Abeokuta area of Ogun State is scanty. Snails were collected from 31 water bodies including streams, rivers and dams on a monthly basis for six months. The snails were identified using shell morphology and examined for cercariae shedding. Collection sites were geo-referenced. Environmental data, Normalized Difference Vegetation Index (NDVI), Land Surface Temperature (LST), rainfall and Land cover corresponding to these locations were derived from Moderate resolution Imaging Spectroradiometer (MODIS). Binary logistic regression analysis was used to create spatial maps and predictive model map for snail species distribution. A total of 87 vector snails were collected; Lymnaea natalensis 65 (74.71%) and Indoplanor bisexutus 22 (25.29%).Nine out of 22I. exutus collected shed microcercouscercariae. Infected I. exutus, intermediate snail host of Schistosoma nasale, a cattle schistosome was found in two sites. The logistic regression analysis using remotely-sensed environmental data showed that NDVI was the significant variable influencing I. exutus distribution (B = -8.460, Sig = 0.043). Geospatial distribution maps were created to show the distribution of each snail species and potential transmission sites. This study mapped the distribution of snail hosts, identified possible transmission sites and demonstrates the presence of snail hosts of certain parasites in Abeokuta area (Abeokuta South and Abeokuta North Local Government Areas), the distribution of these snail hosts should be monitored to prevent transmission of these pathogens to humans.Keywords: geospatial, vector snails, trematode, distribution, malacological