Intermediate Hosts Of Schistosomes Research Articles

Molluscicidal activity of extracts of plants from the Cerrado against Biomphalaria glabrata (Say, 1818)

Plant-derived molluscicides have been indicated as selective and low-cost strategies for the control of Biomphalaria glabrata (Say, 1818), an intermediate host of schistosomes. This study aimed to evaluate the aqueous and ethanolic extracts of leaves of plants present in the Cerrado such as Caryocar brasiliense Camb., Ximenia americana L., Piptadenia viridiflora (Kunth) Benth., and Schinopsis brasiliensis Engl. as alternatives in the control of the mollusk B. glabrata. For this, leaves were collected from plants at the in Montes Claros-MG. Extracts at concentrations of 150, 100, 75, 50, and 25 μg/mL, a positive control containing niclosamide at 3 μg/mL, and a negative control containing dechlorinated water were used to verify the molluscicidal activity. To evaluate toxicity to non-target organisms, Artemia salina was treated with extract concentrations of 10, 100, and 1000 μg/mL. The tested aqueous and ethanolic extracts showed significant mortality within 24 h of exposure. At concentrations above 75 μg/mL, the aqueous extracts of P. viridiflora, C. brasiliense, and S. brasiliensis achieved mortality higher than 90%. Regarding ethanolic extracts, mortality above 80% was observed for all tested plants at concentrations above 50 μg/mL. No toxicity was observed against A. salina. Thus, high molluscicidal activity of ethanolic and aqueous extracts of the tested plants against adult B. glabrata was observed and no toxicity was observed against A. salina.

Systematic Review and Meta-Analysis on the Infection Rates of Schistosome Transmitting Snails in Southern Africa

Efforts to interrupt and eliminate schistosomiasis as a public health problem have increased in several Southern African countries. A systematic review was carried out on the infection rates of snails that cause schistosomiasis in humans. The searches were conducted in PubMed, Web of Science, and Scopus databases, using the PRISMA guidelines from inception to 24 February 2022. The study quality was assessed by using the Joanna Briggs Institute prevalence critical appraisal checklist. Pooled infection rates were estimated by using an inverse variance heterogeneity model, while heterogeneity was determined by using Cochran’s Q test and Higgins i2 statistics. A total of 572 articles were screened, but only 28 studies were eligible for inclusion based on predetermined criteria. In the selected studies, 82,471 Bulinus spp. and 16,784 Biomphalaria spp. snails were screened for cercariae. The pooled infectivity of schistosome intermediate host snails, Biomphalaria spp., and Bulinus spp. were 1%, 2%, and 1%, respectively. Snail infection rates were higher in the 1900s compared to the 2000s. A Luis Furuya–Kanamori index of 3.16 indicated publication bias, and a high level of heterogeneity was observed. Although snail infectivity in Southern Africa is relatively low, it falls within the interval of common snail infection rates, thus indicating the need for suitable snail control programs that could interrupt transmission and achieve elimination.

The identification of alternative oxidase in intermediate host snails of Schistosoma and its potential role in protecting Oncomelania hupensis against niclosamide-induced stress

BackgroundSnail intermediate hosts are mandatory for the transmission of schistosomiasis, which has to date infected more than 200 million people worldwide. Our previous studies showed that niclosamide treatment caused the inhibition of aerobic respiration and oxidative phosphorylation, and the disruption of energy supply, in one of the intermediate hosts of schistosomiasis, Oncomelania hupensis, which eventually led to the death of the snails. Meanwhile, the terminal oxidase in the mitochondrial respiratory chain, alternative oxidase (AOX), was significantly up-regulated, which was thought to counterbalance the oxidative stress and maintain metabolic homeostasis in the snails. The aims of the present study are to identify the AOXs in several species of snails and investigate the potential activation of O. hupensis AOX (OhAOX) under niclosamide-induced stress, leading to enhanced survival of the snail when exposed to this molluscicide.MethodsThe complete complementary DNA was amplified from the AOXs of O. hupensis and three species of Biomphalaria; the sequence characteristics were analysed and the phylogenetics investigated. The dynamic expression and localisation of the AOX gene and protein in O. hupensis under niclosamide-induced stress were examined. In addition, the expression pattern of genes in the mitochondrial respiratory complex was determined and the production of reactive oxygen species (ROS) calculated. Finally, the molluscicidal effect of niclosamide was compared between snails with and without inhibition of AOX activity.ResultsAOXs containing the invertebrate AOX-specific motif NP-[YF]-XPG-[KQE] were identified from four species of snail, which phylogenetically clustered together into Gastropoda AOXs and further into Mollusca AOXs. After niclosamide treatment, the levels of OhAOX messenger RNA (mRNA) and OhAOX protein in the whole snail were 14.8 and 2.6 times those in untreated snails, respectively, but varied widely among tissues. Meanwhile, the level of cytochrome C reductase mRNA showed a significant decrease in the whole snail, and ROS production showed a significant decrease in the liver plus gonad (liver-gonad) of the snails. At 24 h post-treatment, the mortality of snails treated with 0.06–0.1 mg/L niclosamide and AOX inhibitor was 56.31–76.12% higher than that of snails treated with 0.1 mg/L niclosamide alone.ConclusionsAOX was found in all the snail intermediate hosts of Schistosoma examined here. AOX was significantly activated in O. hupensis under niclosamide-induced stress, which led to a reduction in oxidative stress in the snail. The inhibition of AOX activity in snails can dramatically enhance the molluscicidal effect of niclosamide. A potential target for the development of an environmentally safe snail control method, which acts by inhibiting the activity of AOX, was identified in this study.Graphical abstract

Snails, microbiomes, and schistosomes: a three-way interaction?

Aquatic snails, the intermediate hosts of schistosomes, harbor a diverse unexplored microbiome. We speculate that this may play a critical role in host-parasite interactions. We summarize our current knowledge of snail microbiomes and highlight future research priorities.

Spatial variation of life-history traits in Bulinus truncatus, the intermediate host of schistosomes, in the context of field application of niclosamide in C\xf4te d\u2019Ivoire

BackgroundControl of intermediate host snails using molluscicides for the control and/or elimination of schistosomiasis is a strategy in line with WHO recommendations. Niclosamide is the main chemical molluscicide recommended by WHO. However, except the immediate killing of the snail, the extent of the impact of the molluscicide application on the evolution of snail life-history traits, in relation to recolonization of treated sites is not well known. This study aimed to characterize the spatial variation of life-history traits of populations of the freshwater snail Bulinus truncatus, in relation to niclosamide spraying in the field.From 2016 to 2018, we conducted a trial, using niclosamide to control the intermediate host snails for interrupting the seasonal transmission of urinary schistosomiasis in northern and central Côte d’Ivoire. Five villages (sites) were considered, including three test and two control villages. In the test villages, the molluscicide was sprayed in habitats harboring B. truncatus snails three times a year (November, February–March and June). We sampled six B. truncatus populations: two populations from the control villages without any treatment; one collected before treatment and three sampled 2–3 months after treatment of the site with niclosamide. The snail populations were monitored for several life-history traits, including survival, growth, fecundity and hatchability, under laboratory conditions, over one generation (G1). We tested the population, region (North/Centre) and treatment status (treated/untreated) effects on the variation of the measured life-history traits and correlations between pairs of traits were estimated.ResultsOn the whole, the traits varied among populations. The risk of death was lower in northern populations compared to central ones. The age at first reproduction was reached earlier with a smaller size of snails in northern populations. Values of first reproduction features (size and fecundity) were lower in treated snail populations. The overall growth of untreated populations was higher than that of treated ones. The late fecundity and egg hatching were higher in northern than in central snails. At first reproduction, age was negatively correlated with some fecundity parameters. However, growth was positively associated with fecundity.ConclusionsOur study showed a spatial variation of life-history traits in B. truncatus snails. The mollusciciding seems to have led to the depression of some life-history traits in the snail populations. However, investigations should be carried out over several generations of snails to better clarify the impact of niclosamide on the evolution of the life-history traits.

The effect of physico chemical parameter on the distribution of fresh water snails in the Federal Capital Territory, Abuja, Nigeria

Some species of freshwater snails are known to be intermediate hosts of biomedical importance. This study was conducted to identify some physico-chemical parameters of water bodies associated with the distribution of freshwater snail species in the Federal Capital Territory, Abuja. Eight water bodies in four locations were surveyed for the presence of freshwater snails. Five physico chemical parameters (pH, temperature, dissolved oxygen content, salinity and water speed) were measured using standard water meters. A correlation matrix between the water parameters and the snail species were analysed. A total of 1,225 freshwater snails belonging to eight species and families were collected in the study area. These were Bulinus truncatus 304 (24.8%), B. umbilicatus 162 (13.2%), B. globosus 138 (11.3%), Biomphalaria pfeifferi 138 (11.3%), Aplexa waterloti 190 (15.5%), Physa acuta 96 (7.8%), Lymnea natalensis (15.8%). and Melanoides tuberculata 3 (0.2%). Three of these snail species {B. globosus, B. Pfeffeiri and L. natalensis} which are known intermediate hosts of schistosomes were reasonably present in the study area. Out of the five water parameters investigated, two (Dissolved oxygen content and salinity) were found to significantly associated with the distribution of freshwater snail species in the area (P<0.05). The study recommends freshwater snail control intervention to interrupt the transmission and spread of human and animal diseases in the area.

Species diversity and distribution of schistosome intermediate snail hosts in The Gambia.

There is a need for recent information on intermediate snail hosts of schistosomes in The Gambia; the previous studies were conducted over three decades ago. This study assessed the incidence, species diversity, distribution and infection status of schistosome intermediate snail hosts in the country. Malacological surveys were conducted in all 5 regions of The Gambia: Central River Region (CRR), Upper River Region (URR), Western Region (WR), Lower River Region (LRR) and North Bank Region (NBR). Sampling of snails was undertaken at 114 sites that included permanent water bodies such as streams (bolongs), rice fields, irrigation canals and swamps; and temporal (seasonal) laterite pools. Ecological and physicochemical factors of sites were recorded. Snails were identified morphologically and screened for schistosome infections using molecular techniques. Freshwater snails were found at more than 50% (60/114) of sites sampled. While three species of Bulinus were collected, no Biomphalaria snails were found in any of the sites sampled. Of the total 2877 Bulinus snails collected, 75.9% were identified as Bulinus senegalensis, 20.9% as Bulinus forskalii and 3.2% as Bulinus truncatus. Seasonal pools produced the largest number of snails, and CRR was the region with the largest number of snails. Bulinus senegalensis was found more in seasonal pools as opposed to permanent sites, where B. forskalii and B. truncatus were observed to thrive. Bulinus snails were more common in seasonal sites where aquatic vegetation was present. In permanent sites, the abundance of snails increased with increase in water temperature and decrease in water pH. Bulinus senegalensis was found infected with both S. haematobium and S. bovis, while B. forskalii and B. truncatus had only S. bovis infection. While the human parasite S. haematobium was restricted to just four sites, the livestock parasite S. bovis had a much more widespread geographical distribution across both CRR and URR. This new information on the distribution of intermediate snail hosts of schistosomes in The Gambia will be vital for the national schistosomiasis control initiative.

Population Dynamics of Intermediate-Host Snails in the White Nile River, Sudan: A Year-Round Observational Descriptive Study.

We aimed to explore the population dynamics of snail in 3 sites of the White Nile in Sudan. More specifically, we aimed to investigate the annual patterns of snail populations that act as intermediate hosts of schistosomes and monthly snail infection rates and ecological characteristics presumably related to snail populations. We collected snails for 1 year monthly at 3 different shore sites in the vicinity of El Shajara along the White Nile river in Khartoum State, Sudan. In addition, we measured air and water temperatures, water turbidities, vegetation coverages, and water depths and current speeds. Most of the collected snails were Biomphalaria pfeifferi and Bulinus truncatus. The population densities of snails and their infection rates varied across survey sites. The collected snails liberated S. mansoni and S. haematobium cercariae as well as Amphistome and Echinostome cercariae. Infected snails were found during March–June. The ecological characteristics found to be associated with the absence of snails population were: high turbidity, deep water, low vegetation coverage (near absence of vegetation), high water temperature, and high current speed. To our knowledge, this is the first longitudinal study of the snail population and ecological characteristics in the main basin of the White Nile river.

Resistance of Biomphalaria alexandrina to Schistosoma mansoni and Bulinus truncatus to Schistosoma haematobium Correlates with Unsaturated Fatty Acid Levels in the Snail Soft Tissue.

Only a fraction of the Biomphalaria and Bulinus snail community shows patent infection with schistosomes despite continuous exposure to the parasite, indicating that a substantial proportion of snails may resist infection. Accordingly, exterminating the schistosome intermediate snail hosts in transmission foci in habitats that may extend to kilometres is cost-prohibitive and damaging to the ecological equilibrium and quality of water and may be superfluous. It may be more cost effective with risk less ecological damage to focus on discovering the parameters governing snail susceptibility and resistance to schistosome infection. Therefore, laboratory bred Biomphalaria alexandrina and Bulinus truncatus snails were exposed to miracidia of laboratory-maintained Schistosoma mansoni and S. haematobium, respectively. Snails were examined for presence or lack of infection association with soft tissue and hemolymph content of proteins, cholesterol, and triglycerides, evaluated using standard biochemical techniques and palmitic, oleic, linoleic, and arachidonic acid, assayed by ultraperformance liquid chromatography-tandem mass spectrometry. Successful schistosome infection of B. alexandrina and B. truncatus consistently and reproducibly correlated with snails showing highly significant (up to P < 0.0001) decrease in soft tissue and hemolymph content of the monounsaturated fatty acid, oleic acid, and the polyunsaturated fatty acids, linoleic, and arachidonic acids as compared to naïve snails. Snails that resisted twice infection had soft tissue content of oleic, linoleic, and arachidonic acid similar to naïve counterparts. High levels of soft tissue and hemolymph oleic, linoleic, and arachidonic acid content appear to interfere with schistosome development in snails. Diet manipulation directed to eliciting excessive increase of polyunsaturated fatty acids in snails may protect them from infection and interrupt disease transmission in a simple and effective manner.

Changing patterns of Schistosoma host snail population densities in Maun, Botswana

Changes in the inflow of water into the Thamalakane River had been predicted to alter snail population dynamics and influence the risk of schistosomiasis transmission in Maun. We determined the abundance of schistosome intermediate host snails along the Thamalakane River and evaluated the risk of schistosomiasis infection within Maun. A retrospective study utilised snail survey data previously collected from the Thamalakane River in Maun between June 2009 and July 2012. A total of 3 563 freshwater snails were collected from 10 sentinel sites along Thamalakane River. The snails collected were Bulinus globosus, Biomphalaria pfeifferi, Lymnaea natalensis, Bellamya capillata, Pila occidentalis and Lanistes ovum. Bulinus globosus snails were more abundant than B. pfeifferi. None of the intermediate host snails (IHS) collected shed cercariae. The absence of infected IHS suggests that there was no active transmission of schistosomiasis during the study period. Furthermore, the presence of B. globosus in the Thamalakane River suggests the potential risks of Schistosoma haematobium infection when transmission conditions become conducive.

Assessment of knowledge, attitude and practices and the analysis of risk factors regarding schistosomiasis among fishermen and boatmen in the Dongting Lake Basin, the People\u2019s Republic of China

BackgroundFishermen and boatmen are a population at-risk for contracting schistosomiasis due to their high frequency of water contact in endemic areas of schistosomiasis in the People’s Republic of China (P. R. China). To develop specific interventions towards this population, the present study was designed to assess the knowledge, attitudes and practices (KAPs) towards schistosomiasis of fishermen and boatmen, and to identify the risk factors associated with schistosome infection using a molecular technique in a selected area of Hunan Province in P. R. China.MethodsA cross sectional survey was conducted in the Dongting Lake Basin of Yueyang County, Hunan Province. A total of 601 fishermen and boatmen were interviewed between October and November 2017. Information regarding sociodemographic details and KAPs towards schistosomiasis were collected using a standardized questionnaire. Fecal samples of participants were collected and tested by polymerase chain reaction (PCR). Logistic regression analysis was conducted to explore the risk factors related to the positive results of PCR.ResultsOf the 601 respondents, over 90% knew schistosomiasis and how the disease was contracted, the intermediate host of schistosomes and preventive methods. The majority of respondents had a positive attitude towards schistosomiasis prevention. However, only 6.66% (40/601) of respondents had installed a latrine on their boats, while 32.61% (196/601) of respondents defecated in the public toilets on shore. In addition, only 4.99% (30/601) respondents protected themselves while exposed to freshwater. The prevalence of schistosomiasis, as determined by PCR, among fishermen and boatmen in Yueyang County was 13.81% (83/601). Age, years of performing the current job, number of times receiving treatment, and whether they were treated in past three years were the main influencing factors of PCR results among this population.ConclusionsFishermen and boatmen are still at high risk of infection in P. R. China and gaps exist in KAPs towards schistosomiasis in this population group. Chemotherapy, and health education encouraging behavior change in combination with other integrated approaches to decrease the transmission risk in environments should be improved.

Freshwater snails of biomedical importance in the Niger River Valley: evidence of temporal and spatial patterns in abundance, distribution and infection with Schistosoma spp.

BackgroundSound knowledge of the abundance and distribution of intermediate host snails is key to understanding schistosomiasis transmission and to inform effective interventions in endemic areas.MethodsA longitudinal field survey of freshwater snails of biomedical importance was undertaken in the Niger River Valley (NRV) between July 2011 and January 2016, targeting Bulinus spp. and Biomphalaria pfeifferi (intermediate hosts of Schistosoma spp.), and Radix natalensis (intermediate host of Fasciola spp.). Monthly snail collections were carried out in 92 sites, near 20 localities endemic for S. haematobium. All bulinids and Bi. pfeifferi were inspected for infection with Schistosoma spp., and R. natalensis for infection with Fasciola spp.ResultsBulinus truncatus was the most abundant species found, followed by Bulinus forskalii, R. natalensis and Bi. pfeifferi. High abundance was associated with irrigation canals for all species with highest numbers of Bulinus spp. and R. natalensis. Seasonality in abundance was statistically significant in all species, with greater numbers associated with dry season months in the first half of the year. Both B. truncatus and R. natalensis showed a negative association with some wet season months, particularly August. Prevalences of Schistosoma spp. within snails across the entire study were as follows: Bi. pfeifferi: 3.45% (79/2290); B. truncatus: 0.8% (342/42,500); and B. forskalii: 0.2% (24/11,989). No R. natalensis (n = 2530) were infected. Seasonality of infection was evident for B. truncatus, with highest proportions shedding in the middle of the dry season and lowest in the rainy season, and month being a significant predictor of infection. Bulinus spp. and Bi. pfeifferi showed a significant correlation of snail abundance with the number of snails shedding. In B. truncatus, both prevalence of Schistosoma spp. infection, and abundance of shedding snails were significantly higher in pond habitats than in irrigation canals.ConclusionsEvidence of seasonality in both overall snail abundance and infection with Schistosoma spp. in B. truncatus, the main intermediate host in the region, has significant implications for monitoring and interrupting transmission of Schistosoma spp. in the NRV. Monthly longitudinal surveys, representing intensive sampling effort have provided the resolution needed to ascertain both temporal and spatial trends in this study. These data can inform planning of interventions and treatment within the region.

Population dynamics of fresh water snail intermediate hosts of &lt;i&gt;Schistosoma spp.,&lt;/i&gt; in the Federal Capital Territory, Abuja, Nigeria

This study was carried out to provide information on the population dynamics of the snail intermediate host of Schistosoma spp., in Abuja. A cross-sectional study was carried out on water bodies with high human contact activities in all the six area councils in Federal Capital Territory including; Narachi, Rafir shawa, Shetiko, Ushafa, Yangoji and Basa Rivers in Abaji, Gwagwalada, Kuje, Bwari, Kwali and Abuja Municipal Area Council respectively. Sampling of snail was based on convenience and presence of snail in the selected areas. Each settlement in the sample population was visited once monthly between March and September, 2017 for snail sample collection. A total of 766 fresh water snails identified to be snail intermediate hosts of schistosomiasis were collected during the study. The prevalence of fresh water snail intermediate hosts of Schistosoma spp., in Abuja comprises 30.16% Bulinus globosus, 11.75% of Bulinus truncatus and 58.09% of Biomphilaria pfeifferi. These fresh water snails were found to be more prevalent in the month of March in all the Local Government Area Council sampled with Gwagwalada Area Council having the highest prevalence of fresh water snail while Bwari Area Council had the lowest. This study revealed that there was high prevalence of snail intermediate hosts of schistosomiasis in Abuja. Hence, there is need for appropriate intervention by the Federal Ministry of Health (FMOH), in collaboration with the National Schistosomiasis Control Program (NSCP) to control snail intermediate hosts of Schistosomes spp., in the study-area using chemical or biological molluscide.Keywords: Water bodies; human contact; Schistosoma spp

Breeding and larval rearing in hatchery of Macrobrachium vollenhovenii (Herklots, 1857) in a perspective of biological control against human Schistosomiasis in tropical area

As part of an effort to use biological control against human schistosomiasis, post-larval production of the prawn Macrobrachium vollenhovenii was carried out in a hatchery. This species is a freshwater native and is fond of mollusks, intermediate hosts of schistosomes that transmit human diseases in the wild. The larval production of this species occurred in six (06) tanks - two 200 L and four 600 L. The management of brood stock took place in fresh water, with a ratio of one male to four females. Each fertilized female produced thousands of eggs attached to the abdomen until hatching about two weeks later. The larvae resulting from this reproduction were raised to the post-larval stage in brackish water at a salinity of 15 ppt. The larvae must undergo a molt between each stage. We identified 15 morphological stages between stage 1 and the post-larval stage. The duration from stage 1 until onset of the first post-larval stage in the six (06) tanks was on average 54 days after hatching. The success of larvi culture is defined by the rate of metamorphosis of the larvae into post-larvae, which, in our case, varied between 0.17% and 3.08%, depending on the production tanks, with an average of 2.8%. These results show that the production of M. vollenhovenii in hatchery is possible, presenting a possibility for aquaculture production of this species as well as for biological control against schistosomiasis in a tropical area

Molluscicidal activity of Jatropha curcas L. crude leaf extracts against Oncomelania hypensis quadrasi Mollendorf

The molluscicidal property of various leaf extracts prepared from tuba-tuba Jatropha curcas L. were tested against freshwater snail (Oncomelania hupensis quadrasi), an intermediate host of Schistosoma sp., the causative agent of schistosomiasis. Highest mortality of 80% was obtained using crude petroleum ether extract (CPE) at a concentration of 1.5 mg mL-1, and this was comparable with the positive control consisting of commercial molluscicide Niclosamide (100%) at a concentration of .002 mg mL-1. For crude ethanolic extract (CEE), snail mortalities of 92% and 84% were obtained at concentrations of 1.5 mg mL-1 and 0.75 mg mL-1, respectively, and these values were not significantly different from the commercial molluscicide Niclosamide. One-hundred percent (100%) snail mortality was achieved with the application of 1,100 mg mL-1 crude aqueous extract (CAE) of tuba-tuba leaves. Considering the test conducted to determine the concentration needed to kill 50% of the freshwater snails after 24 h (LD50), the toxicity of various extracts is in the order of CEE&gt;CPE&gt;CAE with values 0.45&gt;0.49&gt;167.23 mg mL-1, respectively. Qualitative analysis of bioactive compounds in J. curcas leaves indicated the presence of alkaloids, tannins, terpenoids, flavonoids, and saponins. Terpenoids, the most toxic compounds in J. curcas, were detected in CPE and CEE, but not in CAE. Overall, this study has demonstrated the potential of various extracts of tuba-tuba leaves as a replacement for commercially available molluscicide in eradicating the vector snail of Schistosoma sp.

The Efficiency of Two Nile Fishes as Biocontrol Agents Against Different Stages of Schistosomiasis Intermediate Host.

The present investigation is dealing with the biological control of schistosome intermediate host, two Nile fishes Debs (Labeo niloticus) and the Nile Bulti or Tilabia (Cyrinus carbio) were selected to determine their efficiency to control schistosomiasis intermediate host (snails). Six laboratory sets of experiments were designed, three for Bulinus truncatus and other three for Biomphalaria pfeifferi. The first set in each snail species were control group, while the other two provided with the two Nile fishes, to investigate the efficiency of the selected biocontrol agents. In control set, gradual reduction of egg-masses, neonates and adult snails of both schistosomiasis snails. Compared with the control set, the two fishes verified to be highly efficient predators against egg-masses and neonates of the two snails (P &lt; 0.001). While in case of the adults of both species reduced also very gradually.

Seasonal variations of PCDD/Fs in fishes: inferring a hidden exposure route from Na-PCP application for schistosomiasis control.

Japanese schistosomiasis was endemic in Dongting Lake, the second largest freshwater lake in China. The technical sodium pentachlorophenate (Na-PCP) was widely used during the period between the early 1960s and early 1990s to kill oncomelania, the intermediate host of Schistosomes. However, polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) also contaminated the environment of Dongting Lake due to trace impurities of Na-PCP. In this study, 13 species of freshwater fish were collected from Dongting Lake and analyzed in wet and dry seasons. Temporal (wet and dry season) variations in PCDD/Fs in fishes from Dongting Lake were observed. The concentration of PCDD/Fs was considerably higher in the wet season than in the dry season and in areas in China where Na-PCP was not applied. The higher level of PCDD/Fs in the wet season may be attributed to the use of Na-PCP in the past and to the increase in the migration of PCDD/Fs from sediments to water in the wet season. The results indicate that the risk of PCDD/Fs contamination is connected with prior consumption of fishes that live in the Na-PCP application area. However, there was no difference in the concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) between the wet and dry seasons.

English

Bulinid snails act as intermediate host of schistosomes and the presence of the snail gives schistosomiasis an expansive characteristics. Schistosomiasis is of medical and veterinary importance in the tropical and subtropical regions. The shell shape and structure of radula teeth of bulinids are often specific to a species or genus, and are widely used for gastropod species identification. Bulinid species collected from schistosome endemic areas of Ogun State, South-western Nigeria were used for this study. Shell morphometrics were recorded using vernier caliper while the buccal mass of each snail was removed and permanent slides of the radulae were made according to standard procedure. There was a significant difference in the shell height, width, aperture height and aperture width between Bulinus globosus and Bulinus jousseaumei (p&lt;0.05). The average shell height measurement for B. globosus was 7.6&plusmn;1.9 mm, while B. jousseaumei measured 5.1&plusmn;1.6 mm. Each transverse row of B. globosus radula had a ratio of 26:8:1:8:26 while B. jousseaumei had a ratio of 25:8:1:8:25. The marginal teeth of B. globosus possessed five cusps while B. jousseaumei possessed six cusps. The differences observed in shell, radula ratio and cusps in both species could be used to differentiate both species.&nbsp; &nbsp; Key words: Radula, shell, Bulinus species, identification, Nigeria.

Transmission patterns among freshwater snail hosts of schistosomiasis in Bauchi area of Nigeria

Schistosomiasis is endemic in the Bauchi area of Nigeria but little information is available on transmission patterns on basis of which an effective strategy for control can be developed. Consequently, a longitudinal study on the population dynamics of freshwater snails was under taken in 10 sites selected after a preliminary study. Three schistosome intermediate host snails namely Bulinus globosus, Bulinus truncatus and Biomphalaria pfeifferi all of which carried patent infections were encountered. The population of infected snails showed similar patterns of fluctuation among the different sites. Population density generally increased following the rains and peak densities occurred during the last part of the raining season and/or beginning of the dry season. This was followed by a decline during the dry season owing to an increase in temperature and dessication in some sites. Transmission was observed to be generally focal. In the temporary habitats, transmission was highly seasonal having a short duration of three months spanning from October to December. However, in the few perennial habitats, there was prolonged transmission extending from October of one year to March of the succeeding year. Findings of this study would be invaluable in planning and implementation of schistosomiasis control in Bauchi area, Nigeria.

Influence of desiccation on the survival of Bulinus globosus under laboratory conditions

Environmental changes are generally known to influence the distribution and abundance of schistosome intermediate host snails (IHs). However, the influence of hydrologic changes per ser on the length of survival of schistosome IHs is not fully understood. To explore how desiccation may influence the survival of Bulinus globosus, the main IHs of Schistosoma haematobium in southern Africa, we conducted a study under laboratory conditions where snails were subjected to periods of desiccation and their survival evaluated. Desiccation period from 28 to 49 days post-draining of water was associated with an increase in mortality of 33.2 and 42.4% in large (mean shell height 7.81 ± 0.44 mm) and small (mean shell height 5.94 ± 0.68 mm) B. globosus snails, respectively. Although the duration of desiccation had no effect on the depth of burrowing, large size snails burrowed deeper into the soil than small size snails. The LT50 and LT90 of snails designated as large (7.81 ± 0.44 mm) were 73.35 ± 10.32 and 110.61 ± 21.03 days, respectively. On the other hand, LT50 and LT90 for snails designated as small (5.94 ± 0.68 mm) were 59.64 ± 8.56 and 84.19 ± 12.09 days, respectively. The survival of B. globosus during desiccation depended on the size/age of the snail where large size snails aestivate and survive for a longer period by burrowing deeper into the soil. We therefore conclude that adult B. globosus may play a significant role in habitat recolonization after a period of drought which is a common phenomenon in schistosomiasis endemic areas when population crashes.