Computational prediction and characterisation of miRNAs and their pathway genes in human schistosomiasis caused by Schistosoma haematobium

BACKGROUND Key genes control the infectivity of the Schistosoma haematobium causing schistosomiasis. A method for understanding the regulation of these genes might help in developing new disease strategies to control schistosomiasis, such as the silencing mediated by microRNAs (miRNAs). The miRNAs have been studied in schistosome species and they play important roles in the post-transcriptional regulation of genes, and in parasite-host interactions. However, genome-wide identification and characterisation of novel miRNAs and their pathway genes and their gene expression have not been explored deeply in the genome and transcriptome of S. haematobium. OBJECTIVES Identify and characterise mature and precursor miRNAs and their pathway genes in the S. haematobium genome. METHODS Computational prediction and characterisation of miRNAs and genes involved in miRNA pathway from S. haematobium genome on SchistoDB. Conserved domain analysis was performed using PFAM and CDD databases. A robust algorithm was applied to identify mature miRNAs and their precursors. The characterisation of the precursor miRNAs was performed using RNAfold, RNAalifold and Perl scripts. FINDINGS We identified and characterised 14 putative proteins involved in miRNA pathway including ARGONAUTE and DICER in S. haematobium. Besides that, 149 mature miRNAs and 131 precursor miRNAs were identified in the genome including novel miRNAs. MAIN CONCLUSIONS miRNA pathway occurs in the S. haematobium, including endogenous miRNAs and miRNA pathway components, suggesting a role of this type of non-coding RNAs in gene regulation in the parasite. The results found in this work will open up a new avenue for studying miRNAs in the S. haematobium biology in helping to understand the mechanism of gene silencing in the human parasite Schistosome.

Esquistosomiasis vesical urinaria: caso anatomoclínico diagnosticado en Chile / Urinary bladder schistosomiasis: a case report diagnosed in Chile

Resumen La esquistomiasis urinaria es producida por Schistosoma haematobium. Es una enfermedad endémica en muchas regiones del mundo, no existente en Chile. Se presenta el caso de un hombre joven que viajó a Malawi, en África meridional, y que a su regreso al país, años después, presentó un síndrome miccional con hematuria macroscópica. La biopsia de vejiga mostró una cistitis granulomatosa y eosinofílica con huevos de Schistosoma haematobium.

Urinary schistosomiasis is produced by Schistosoma haematobium. It is an endemic disease in many regions of the world, non-existent in Chile. We report a case of a young man who traveled to Malawi, in southern Africa, and who returned to Chile. Few years later, he presented a urinary syndrome with macroscopic hematuria. The bladder biopsy showed a granulomatous and eosinophilic cystitis with eggs of Schistosoma haematobium.

Epidemiological Survey on Schistosomiasis and Intestinal Helminthiasis among Village Residents of the Rural River Basin Area in White Nile State, Sudan

There have been some reports on schistosomiasis of school children in Sudan’s Nile River basin area; however, information about the infection status of Schistosoma species and intestinal helminths among village residents of this area is very limited. Urine and stool samples were collected from the 1,138 residents of the Al Hidaib and Khour Ajwal villages of White Nile State, Sudan in 2014. The prevalence of overall schistosomiasis and intestinal helminthiasis was 36.3% and 7.7%, respectively. Egg positive rates were 35.6% for Schistosoma haematobium, 2.6% for S. mansoni, and 1.4% were mixed. The prevalence of schistosomiasis was significantly higher in men (45.6%) than in women (32.0%), in Khou Ajwal villagers (39.4%) than in Al Hidaib villagers (19.2%), and for age groups ≤15 years old (51.5%) than for age groups >15 years old (13.2%). The average number of eggs per 10 ml urine (EP10) of S. haematobium infections was 18.9, with 22.2 eggs in men vs 17.0 in women and 20.4 in Khou Ajwal villagers vs 8.1 in Al Hidaib villagers. In addition to S. mansoni eggs, 4 different species of intestinal helminths were found in the stool, including Hymenolepis nana (6.6%) and H. diminuta (1.0%). Collectively, urinary schistosomiasis is still prevalent among village residents in Sudan’s White Nile River basin and was especially high in men, children ≤15 years, and in the village without a clean water system. H. nana was the most frequently detected intestinal helminths in the 2 villages.

Impact of Single Dose Praziquantel Treatment on Schistosoma haematobium Infection among School Children in an Endemic Nigerian Community

Schistosomiasis is prevalent in Nigeria, and the foremost pathogen is Schistosoma haematobium, which affects about 29 million people. Single dose of the drug praziquantel is often recommended for treatment but the efficacy has not been documented in certain regions. Therefore, this study was designed to assess the impact of single dose praziquantel treatment on S. haematobium infection among school children in an endemic community of South-Western Nigeria. Urine samples were collected from 434 school children and 10 ml was filtered through Nucleopore filter paper before examination for egg outputs by microscopy. The prevalence was 24.9% at pre-treatment. There was no statistically significant difference for the prevalence of infection between males (14.7%) and females (10.2%), although the mean egg count for the females (9.87) was significantly more (P < 0.05) than the males (6.06). At 6 and 12 months post-treatment there was 74.4% and 86.4% reduction in the mean egg count, respectively. Interestingly, an increased prevalence of infection from 2.1% at 6 months to 7.7% at 12 months post-treatment was observed, nonetheless the mean egg count was reduced to 0.27 at 12th month from 1.98 at 6 months post-treatment. Resurgence in the prevalence rate between 6 and 12 months post-treatment with praziquantel is herein reported and the need for a follow-up treatment in endemic areas for adequate impact on schistosomiasis control is discussed.

An unusual presentation of ovarian dermoid cyst: a case report and review of literature

Dermoid cysts or mature cystic teratoma are the most common type of ovarian germ cell tumor. It may be complicated by torsion, rupture, chemical peritonitis and malignant change but is rarely complicated by infection. We present a case of an ovarian dermoid cyst with super-infection caused by Schistosoma haematobium (S. haematobium). We present here a case of incidental finding of S. haematobium eggs in an infected cystic teratoma of the ovary because of the rare occurrence of this lesion. A 45-year-old Moroccan woman admitted to the gynecological department because of abdominal pain and fever. Gynecological examination, ultrasonography, and abdominopelvic computed tomography scan revealed an ovarian mass thought to be a dermoid cyst. The pathological evaluation suggested infected ovarian dermoid cyst with the presence of adult worm in the tumor, contains same eggs of S. haematobium. Super-infection of an ovarian dermoid cyst is a rare event, and the association with S. haematobium is extremely rare in the literature.

Comparison of ELISA and Urine Microscopy for Diagnosis of Schistosoma haematobium Infection

BACKGROUND: Schistosoma haematobium which causes urogenital schistosomiasis (UGS) is highly prevalent in African countries. Urine microscopy (UM) is the first-line diagnostic method of UGS. Enzyme-linked immunosorbent assay (ELISA) is a common method for screening many parasite infections primarily or alternatively. The present study established an in-house diagnostic system by ELISA and evaluated its diagnostic efficacy in comparison with UM for screening UGS in White Nile State, Republic of Sudan, 2011–2013. METHODS: A total of 490 participants were screened by UM or ELISA, and 149 by both. The in-house ELISA system was established employing soluble egg antigen of S. haematobium and the cut-off absorbance was set at 0.270. RESULTS: Of the 149 subjects, 58 participants (38.9%) were positive by UM, 119 (79.9%) were positive by ELISA and 82 (55.0%) showed consistently positive or negative results by both methods. The diagnostic sensitivity of ELISA was 94.8% and specificity was 29.7% based on UM results. The ELISA positive serum samples also cross-reacted with egg antigens of Schistosoma mansoni and Schistosoma japonicum. CONCLUSION: We have established in-house ELISA for screening serum immunoglobulin (Ig) G antibodies by employing soluble egg antigen of S. haematobium for diagnosis of UGS with 94.8% sensitivity and 29.7% specificity. The ELISA system can supplement the conventional diagnosis by UM.

Development of Urinary Bladder Pre-Neoplasia by Schistosoma haematobium Eggs and Chemical Carcinogen in Mice

Schistosoma haematobium is a biocarcinogen of human urinary bladder (UB). The present study investigated developing UB cancer mouse model by injecting S. haematobium eggs into the bladder wall and introduction of chemical carcinogens. Histopathological findings showed mild hyperplasia to epithelial vacuolar change, and high grade dysplasia. Squamous metaplasia was observed in the S. haematobium eggs+NDMA group at week 12 but not in other groups. Immunohistochemistry revealed significantly high expression of Ki-67 in urothelial epithelial cells of the S. haematobium eggs+BBN group at week 20. The qRT-PCR showed high expression of p53 gene in S. haematobium eggs group at week 4 and S. haematobium eggs+BBN group at week 20. E-cadherin and vimentin showed contrasting expression in S. haematobium eggs+BBN group. Such inverse expression of E-cadherin and vimentin may indicate epithelial mesenchymal transition in the UB tissue. In conclusion, S. haematobium eggs and nitrosamines may transform UB cells into squamous metaplasia and dysplasia in correlation with increased expression of Ki-67. Marked decrease in E-cadherin and increase in p53 and vimentin expressions may support the transformation. The present study introduces a promising modified animal model for UB cancer study using S. haematobium eggs.

Environmental factors influencing the distribution and prevalence of Schistosoma haematobium in school attenders of ILembe and uThungulu Health Districts, KwaZulu-Natal Province, South Africa

Schistosoma haematobium infection is reported to facilitate the development of urogenital diseases. Its symptoms include haematuria, dysuria and tiredness, and it may cause cognitive decline in children. The prevalence of S. haematobium infection needs to be known in endemic areas and a mass treatment programme against the disease implemented. The aim of this study was to investigate the prevalence and intensity of S. haematobium infection in ILembe and uThungulu health districts, using the major symptom, haematuria, as an indicator. A total of 6 265 urine samples, from 96 rural schools, was collected for analysis using dipsticks. The prevalence of haematuria in the ILembe health district was 37% (95% CI, 35­39%) for boys and 39% (95% CI, 37­41%) for girls. The prevalence of haematuria in the uThungulu health district was 56% (95% CI, 53­59%) and 53% (95% CI, 50­56%) for girls and boys, respectively. Light-intensity infection was the most common infection level in both health districts. A negative relationship was observed between prevalence and altitude (r = −0.262, p = 0.009); whereas, we found a slight, though significant, positive association with mid-summer temperatures (r = 0.234, p = 0.021). Associations between prevalence and distance of school to the nearest river were non-significant

In Vitro Schistosomicidal Activity of Phytol and Tegumental Alterations Induced in Juvenile and Adult Stages of Schistosoma haematobium

There is renewed interest in natural products as a starting point for discovery of drugs for schistosomiasis. Recent studies have shown that phytol reveals interesting in vivo and in vitro antischistosomal properties against Schistosoma mansoni adult worms. Here, we report the in vitro antischistosomal activity of phytol against Schistosoma haematobium juvenile and adult worms and alterations on the tegumental surface of the worms by means of scanning electron microscopy. The assay, which was carried out with 6 concentrations (25, 50, 75, 100, 125, and 150 μg/ml) of phytol, has shown a promising activity in a dose and time-dependent manner. There was a significant decline in the motility of the worms and a mortality rate of 100% was found at 48 hr after they had been exposed to phytol in the concentration of 150 μg/ml. Male worms were more susceptible. On the ultrastructural level, phytol also induced tegumental peeling, disintegration of tubercles and spines in addition to morphological disfiguring of the oral and ventral suckers. This report provides the first evidence that phytol is able to kill S. haematobium of different ages, and emphasizes that it is a promising natural product that could be used for development of a new schistosomicidal agent.

Renal related disorders in concomitant Schistosoma haematobium-plasmodium falciparum infection among children in a rural community of Nigeria

Schistosomiasis and malaria are two common parasitic diseases that are co-endemic in resource-poor communities of sub-Saharan Africa. This study aims to assess the effects of single and concomitant Plasmodium falciparum and Schistosoma haematobium infections on two indicators of renal injury in school children in a rural community of Nigeria. A cross-sectional epidemiological survey was carried out on a total of 173 schoolchildren between ages 6 and 18 years [mean age 11.4 +/- 2.6 years]. Urine and blood samples were collected by standard methods for concurrent microscopic diagnosis of S. haematobium and P. falciparum infections. Urinary blood [hematuria] and protein were determined using a urinalysis dipstick. The prevalence of single infections was 75.1% and 78.2% for S. haematobium and P. falciparum, respectively. A total of 57.1% individuals were infected with the two parasites. The prevalence of hematuria was significantly higher in the co-infection status [63.8%] than in single S. haematobium [52.2%] and P. falciparum [43.7%] infection statuses [p=0.04], while no significant variation was recorded in proteinuria in the three infection statuses [p=0.53]. The proportion of children with renal injury associated with the co-infection of these parasites is very high, particularly in young children, who seem to have a higher prevalence of hematuria

Genetic Diversity of Schistosoma haematobium Eggs Isolated from Human Urine in Sudan

The genetic diversity of Schistosoma haematobium remains largely unstudied in comparison to that of Schistosoma mansoni. To characterize the extent of genetic diversity in S. haematobium among its definitive host (humans), we collected S. haematobium eggs from the urine of 73 infected schoolchildren at 5 primary schools in White Nile State, Sudan, and then performed a randomly amplified polymorphic DNA marker ITS2 by PCR-RFLP analysis. Among 73 S. haematobium egg-positive cases, 13 were selected based on the presence of the S. haematobium satellite markers A4 and B2 in their genomic DNA, and used for RFLP analysis. The 13 samples were subjected to an RFLP analysis of the S. haematobium ITS2 region; however, there was no variation in size among the fragments. Compared to the ITS2 sequences obtained for S. haematobium from Kenya, the nucleotide sequences of the ITS2 regions of S. haematobium from 4 areas in Sudan were consistent with those from Kenya (> 99%). In this study, we demonstrate for the first time that most of the S. haematobium population in Sudan consists of a pan-African S. haematobium genotype; however, we also report the discovery of Kenyan strain inflow into White Nile, Sudan.

High Genetic Variability of Schistosoma haematobium in Mali and Nigeria

Schistosoma haematobium is one of the most prevalent parasitic flatworms, infecting over 112 million people in Africa. However, little is known about the genetic diversity of natural S. haematobium populations from the human host because of the inaccessible location of adult worms in the host. We used 4 microsatellite loci to genotype individually pooled S. haematobium eggs directly from each patient sampled at 4 endemic locations in Africa. We found that the average allele number of individuals from Mali was significantly higher than that from Nigeria. In addition, no significant difference in allelic composition was detected among the populations within Nigeria; however, the allelic composition was significantly different between Mali and Nigeria populations. This study demonstrated a high level of genetic variability of S. haematobium in the populations from Mali and Nigeria, the 2 major African endemic countries, suggesting that geographical population differentiation may occur in the regions.

High Genetic Variability of Schistosoma haematobium in Mali and Nigeria

Schistosoma haematobium is one of the most prevalent parasitic flatworms, infecting over 112 million people in Africa. However, little is known about the genetic diversity of natural S. haematobium populations from the human host because of the inaccessible location of adult worms in the host. We used 4 microsatellite loci to genotype individually pooled S. haematobium eggs directly from each patient sampled at 4 endemic locations in Africa. We found that the average allele number of individuals from Mali was significantly higher than that from Nigeria. In addition, no significant difference in allelic composition was detected among the populations within Nigeria; however, the allelic composition was significantly different between Mali and Nigeria populations. This study demonstrated a high level of genetic variability of S. haematobium in the populations from Mali and Nigeria, the 2 major African endemic countries, suggesting that geographical population differentiation may occur in the regions.

Cytokines and mother sporocysts in susceptible and resistant bulinus truncatus snails infected with schistosoma haematobium

The presence of immunoreactive interleukin [IL-2] interferon gamma [FN-y] and tumor necrosis factor alpha [TNF-alpha] in addition to the citation of mother sporscytes in cephalopodal musculature in the susceptible and resistance Bulinus truncatus the specific intermediate host for the trematode Schistosoma haematobium were investigated. Using ELISA tests, Results indicated that the concentration of IL-2-like activity in the susceptible and resistant snails decreased significantly after infection then persisted at low levels until the 4[th] week post exposure [WPE] in susceptible snails, while in resistant snails elevated during the second WPE, and returned to initial level at 3 and 4 WPE. Susceptible snails had low detectable levels of TNF-alpha and INF-y like-activity after infection. However, the resistant snails had significant low levels of TNF-alpha and INF-y like-activity from 3 WPE until the 4th WPE without any sign of normalization. Histological sections in the head- foot region of susceptible and resistance B, truncatus infected with S. haematobium, mother sporocysts exists froml to 7 [day post exposure] DPE, in the susceptible snail the mother sporocysts were found as single, multiple and mature types. No mother sporocysts were appear in the lip and mantle of the snail on 2, 5, 7 DPE and on 1-3, 6 DPE respectively. In the resistant snails few mother sporocysts were found in the lip, mantle and tentacles. The results showed that schistosome-resistant Bulinus can be an alternative strategy for the control of schistosomiasis

Community perceptions of schistosomiasis transmission, prevalence and control in relation to aquatic habitats in the Lake Victoria Basin of Kenya

Background: Intestinal schistosomiasis caused by Schistosoma mansoni and urinary schistosomiasis caused by Schistosoma haematobium are widely distributed parasites in several localities of the Lake Victoria basin of Kenya; the former being more prevalent. In Kenya; transmission of the intestinal form of bilharzia (S. mansoni) tends to be closely confined to narrow zones along the shores of large bodies of water such as Lake Victoria where it is endemic and the intermediate host is found. The prevalence of S. mansoni along the Kenyan Lake Victoria basin ranges between 40. Objective: To assess the community's knowledge and perceptions of schistosomiasis prevalence; transmission and control in relation to aquatic habitats in the Lake Victoria basin of Kenya. Design: Community-based cross-sectional study. Setting: The Kenyan Lake Victoria basin. Subjects: Two hundred and forty three individuals (both women and men residing in the beaches and surrounding areas) were interviewed about their knowledge and perceptions regarding schistosomiasis. Results: The community regarded schistosomiasis as a naturalistic disease not caused by supernatural forces but by an agent of contamination in water. Knowledge on schistosomiasis transmission and control was low; with 42of the respondents having no idea on how schistosomiasis is contracted; while 22 and 18of the respondents mentioned contact with contaminated water and drinking / eating dirty water / food; respectively. Most respondents were familiar with the snails' habitats; but had poor knowledge on aquatic plants harbouring snails; as 57of the respondents did not know about aquatic plants being associated with schistosomiasis snails. Only 3 of the respondents associated snails with schistosomiasis transmission. Sixty percent (60) of the respondents mentioned use of tablets and injections as means of treating schistosomiasis; while 38 had no idea how it is treated and 2 mentioned use of local herbs and services of medicine men. Conclusion: Majority of Kenyan Lake Victoria basin inhabitants had little awareness about schistosomiasis despite high prevalence of the disease in the region. There is need to adapt prevention and control strategies to the people's livelihoods. There is also need to target the less advantaged members of the community such as women; uneducated and subsistence farmers for intense health education strategies aimed at increasing participation in the control of schistosomiasis. Study to elicit divergence between biomedical and local understandings of schistosomiasis/bilharzia is suggested

Bilharzial endocervical polyp.

Schistosomiasis still represents a major threat to women's health in many developing countries. The frequency in developed countries is increasing among immigrants and tourists who have a history of freshwater exposure in endemic areas. This is a case of 43-year-old immunocompetent Egyptian woman presented by abnormal vaginal bleeding. The gynecological examination revealed an endocervical polyp measuring 3 x 2 x 1 cm. Polypectomy was done. Histopathological examination revealed several granulomas containing viable eggs of Schistosoma hematobium. Schistosomiasis is rarely presented with endocervical polyp. In developing countries, schistosomiasis may be considered in differential diagnosis of patient with endocervical polyp.

A rare case of hematuria / Um caso raro de hematúria

The infestation by Schistosoma haematobium is common in African countries and West Asia. Its chronic phase is characterized by the deposition of eggs of the parasite in various tissues of the body with inflammatory response, formation of granulomas and fibrosis. Often the disease affects the urinary tract, presenting with hematuria, and, in terminal stage, renal failure by urinary obstruction and bladder squamous neoplasia. Since chronic infection can lead to significant morbidity, its imperative that the doctors who serve this immigrant population become familiar with this disease. We present a case of an immigrant boy from Guinea-Bissau seen in consultation for monosymptomatic terminal hematuria. The diagnosis of urinary schistosomiasis was confirmed by parasitological examination of urine and the anatomopathological examination of bladder biopsies. After therapy with praziquantel, the patient was asymptomatic.

A infestação por Schistosoma haematobium é comum em países africanos e no oeste asiático. Sua fase crónica é caracterizada pela deposição de ovos do parasita em vários tecidos do organismo com resposta inflamatória, formação de granulomas e fibrose. Afecta frequentemente as vias urinárias, apresentando-se com hematúria, e, em fases terminais, com insuficiência renal por obstrução urinária e, em último caso, neoplasia escamosa da bexiga. Dado que a infecção crónica pode resultar em elevada morbilidade, é imperativo que os médicos que assistem essa população de imigrantes se familiarizem com tal doença. Apresentou-se aqui o caso clínico de uma criança natural da Guiné-Bissau observado em consulta de Nefrologia por hematúria terminal monossintomática. O diagnóstico de schistosomíase urinária foi confirmado por exame parasitológico da urina e pelo exame anatomopatológico das biópsias vesicais. Após terapêutica com praziquantel, o doente ficou assintomático.

Liver Flukes and Cholangiocarcinoma: Mechanism of Carcinogenesis / 대한내과학회지

It has been clarified that chronic infection with viruses such as hepatitis B virus, bacteria such as Helicobacter pylori and parasites contribute to carcinogenesis in human. Three helminth infections have been classified as definitely carcinogenic to humans (group I carcinogens), namely Schistosoma haematobium, which is associated with urinary bladder cancer and liver flukes Clonorchis sinensis and Opisthorchis viverrini associated with cholangiocarcinoma of the liver. Opisthorchis viverrini which has been extensively studied the association with cholangiocarcinoma is endemic in Southeast Asian countries including Thailand, Vietnam and Cambodia. Clonorchis sinensis infection which is common in rural areas of Korea and China has also been reported its definite association with cholangiocarcinoma. Carcinogenesis associated with liver flukes infections is a complex process hard to be studied because of long latency period and numerous other factors can play a role although chronic inflammation has been known as a key feature. Mechanical injury from the activities of migrating and sucking flukes contributes to biliary damage and chronic inflammation. The liver fluke also secretes or excretes metabolic products, some of which are highly immunogenic, toxic and promoting biliary epithelial cell proliferation. Host immune responses and immunopathological processes are also likely associated with chronic inflammation and carcinogenesis. Escape from host anti-tumor immune response and shift to Th2 response of Th1-Th2 balance are related with carcinogenesis. Biliary cell and its DNA damage can be induced by oxygen free radicals such as nitric oxide released from effector cells activated by inflammatory cytokines. Exogenous carcinogen suchas nitrosamine seemed also closely related with cholangiocarcinoma development in liver fluke infected individuals. In this paper, various and stepwise mechanisms of carcinogenesis by liver flukes and its potential targets can be intervene were reviewed.

Lipid profile of subjects infected with Schistosoma haematobium in South-Western Nigeria

To determine the plasma concentrations of total cholesterol, triglycerides, high-density lipoprotein cholesterol [HDL-C] and low-density lipoprotein cholesterol [LDL-C] in Schistosoma haematobium- infected subjects and healthy persons. The plasma concentration of lipids and the fractions with the urine microscopy of one hundred [100] subjects who had evidence of Schistosomiasis, selected from 14C, a rural area in Osun State, Nigeria and one hundred [100] healthy controls selected randomly in Osogbo, an urban centre in Osun State, Nigeria were determined. The age of the subjects ranged between 7-13 years with mean +/- SD of 11.00 [ +/- 1.69] years and 10.5 [ +/- 2.01] years for test subjects and controls respectively. The mean plasma concentration of triglyceride, total cholesterol, high density lipoprotein cholesterol [HDL-C] and low density lipoprotein cholesterol [LDL-C] were significantly lower among S. haematobium-infected subjects than in controls irrespective of the age and sex [p<0.01]. Significantly lower plasma lipid levels found in infected subjects lend support to the hypothesis that schistosome eggs probably contribute to alteration of lipid profile through enhancing of LDL-uptake by macrophages

ecological differences between bulinus beccari, the intermediate host of schistsoma haematobium and biomphalaria pfeifferi the intermediate host of S. mansoni in Jazan Region, Saudi Arabia

Bulinus beccari, intermediate host of Schistsoma haematobium, and Biotm-phalaria pfeifferi, intermediate host of S. mansoni have different geographical distribution in Jazan Region. The role of rain fall, ionic composition of water, water temperature and pH Grades were studied. Fluctuation of snail population densities were accompanied with corresponding fluctuation rates of rainfall. B. pfeifferi showed a wider and heavier shell than B. beccari, which might enable it to resist the effects of flash floods. B. beccari showed a higher tolerance of total dissolved solids and calcium carbonate than B. pfeifferi. Average maximum tolerated concentration of dissolved solids and calcium carbonate for B. beccari was 1254ppm and 813ppm, while that of B. pfeifferi was 455ppm and 603ppm. Average water temperature of B. beccari habitats was 25-36.3°C while that of B. pfeifferi was 25-28°C. No significant statistical difference in different pH grades was observed