Large-scale and small-scale population genetic structure of the medically important gastropod species Bulinus truncatus (Gastropoda, Heterobranchia).

BACKGROUND: Gastropod snails remain strongly understudied, despite their important role in transmitting parasitic diseases. Knowledge of their distribution and population dynamics increases our understanding of the processes driving disease transmission. We report the first study to use high-throughput sequencing (HTS) to elucidate the population genetic structure of the hermaphroditic snail Bulinus truncatus (Gastropoda, Heterobranchia) on a regional (17-150 km) and inter-regional (1000-5400 km) scale. This snail species acts as an intermediate host of Schistosoma haematobium and Schistosoma bovis, which cause human and animal schistosomiasis respectively. METHODS: Bulinus truncatus snails were collected in Senegal, Cameroon, Egypt and France and identified through DNA barcoding. A single-end genotyping-by-sequencing (GBS) library, comprising 87 snail specimens from the respective countries, was built and sequenced on an Illumina HiSeq 2000 platform. Reads were mapped against S. bovis and S. haematobium reference genomes to identify schistosome infections, and single nucleotide polymorphisms (SNPs) were scored using the Stacks pipeline. These SNPs were used to estimate genetic diversity, assess population structure and construct phylogenetic trees of B. truncatus. RESULTS: A total of 10,750 SNPs were scored and used in downstream analyses. The phylogenetic analysis identified five clades, each consisting of snails from a single country but with two distinct clades within Senegal. Genetic diversity was low in all populations, reflecting high selfing rates, but varied between locations due to habitat variability. Significant genetic differentiation and isolation by distance patterns were observed at both spatial scales, indicating that gene flow is not strong enough to counteract the effects of population bottlenecks, high selfing rates and genetic drift. Remarkably, the population genetic differentiation on a regional scale (i.e. within Senegal) was as large as that between populations on an inter-regional scale. The blind GBS technique was able to pick up parasite DNA in snail tissue, demonstrating the potential of HTS techniques to further elucidate the role of snail species in parasite transmission. CONCLUSIONS: HTS techniques offer a valuable toolbox to further investigate the population genetic patterns of intermediate schistosome host snails and the role of snail species in parasite transmission.

Antimicrobial resistance from a one health perspective in Cameroon: a systematic review and meta-analysis.

BACKGROUND: Antimicrobial resistance (AMR) is widely acknowledged as a global health problem, yet in many parts of the world its magnitude is not well elucidated. A baseline assessment of the AMR prevalence is a priority for implementation of laboratory-based AMR surveillance This review, focused on a One health approach, aimed at describing the current status of AMR in Cameroon. METHODS: PubMed, Google Scholar and African Journals Online databases were searched for articles published in English and French in accordance with the PRISMA guidelines. Retrieval and screening of article was done using a structured search string with strict inclusion/exclusion criteria. Free-text and grey literature were obtained by contacting the authors directly. The pooled prevalence and 95% confidence intervals were calculated for each pathogen-antibiotic pairs using random-effects models. RESULT: Amongst 97 full-text articles reviewed, 66 met the eligibility criteria. The studies originated from the Centre (24; 36.4%), South-West (16; 24.2%), West (13; 19.7%), Littoral (9; 13.6%) and other (4; 6.1%) regions of Cameroon. These studies reported AMR in human (45; 68.2%), animals (9; 13.6%) and the environment (12; 18.2%). Overall, 19 species of bacteria were tested against 48 antibiotics. These organisms were resistant to all classes of antibiotics and showed high levels of multidrug resistance. Escherichia coli, Klebsiella pneumoniae and Staphylococcus spp were reported in 23, 19 and 18 of the human studies and revealed multidrug resistance (MDR) rates of 47.1% [95% CI (37.3-57.2%)], 51.0% [95% CI (42.0-59.9)] and 45.2% [95% CI (38.0-54.7)], respectively. Salmonella spp was reported in 6 of the animal studies and showed a MDR rate of 46.2% [95% CI (39.2-53.5%)] while Staphylococcus spp in 8 of environment studies showed MDR rate of 67.1% [95% CI (55.2-77.2%)]. CONCLUSION: This review shows that resistance to commonly prescribed antibiotics in Cameroon is high. The findings emphasize the urgent need to address gaps in the standardization of AMR diagnostics, reporting and use of available information to optimize treatment guidelines for the arsenal of antibiotics. Effective AMR surveillance through continued data sharing, large-scale collaboration, and coordination of all stakeholders is essential to understand and manage the AMR national burden.

Population genetic structure of Schistosoma bovis in Cameroon.

BACKGROUND: Schistosomiasis is neglected tropical parasitic disease affecting both humans and animals. Due to the human health impact, population genetic studies have focused on the three main human-infecting schistosome species: Schistosoma mansoni, S. haematobium and S. japonicum. Here we present novel data on the population genetic structure of Schistosoma bovis, a highly widespread and prevalent schistosome infecting ruminants, and therefore of veterinary importance. METHODS: Adult S. bovis were sampled in the two main abattoirs of Cameroon (Yaoundé and Douala). Twenty-two cows originating from four distinct localities were sampled and a total of 218 parasites were recovered. All parasites were genotyped using a panel of 14 microsatellite markers and a sub-sample of 91 parasites were sequenced and characterized with the mitochondrial (cox1) and nuclear (ITS) genetic markers. RESULTS: No significant difference in allelic richness, heterozygosity, nucleotide diversity and haplotype diversity was observed between the populations. Additionally, no strong genetic structure was observed at the country scale. Our data also show that S. bovis is more polymorphic than its sister species, S. haematobium, and that the haplotype diversity is similar to that of S. mansoni while the nucleotide diversity does not significantly differ from that of S. haematobium. The resulting negative Tajima's D* and Fu and Li's D* indices could be a signature of population demographic expansion. No S. haematobium/S. bovis hybrids were observed in our populations, thus all samples were considered as pure S. bovis. CONCLUSIONS: This study provides novel insights into genetic diversity and population genetic structure of S. bovis. No strong genetic structure was observed at the country scale but some genetic indices could be associated as a signature of population demographic expansion.

Population genetics of the Schistosoma snail host Bulinus truncatus in Egypt.

The tropical freshwater snail Bulinus truncatus serves as an important intermediate host of several human and cattle Schistosoma species in many African regions. Despite some ecological and malacological studies, there is no information on the genetic diversity of B. truncatus in Egypt. Here, we sampled 70-100 snails in ten localities in Upper Egypt and the Nile Delta. Per locality, we sequenced 10 snails at a partial fragment of the cytochrome c oxidase subunit 1 gene (cox1) and we genotyped 25-30 snails at six microsatellite markers. A total of nine mitochondrial haplotypes were detected, of which five were unique to the Nile Delta and three were unique to Upper Egypt, indicating that snail populations may have evolved independently in both regions. Bayesian clustering and hierarchical F-statistics using microsatellite markers further revealed strong population genetic structure at the level of locality. Observed heterozygosity was much lower compared to what is expected under random mating, which could be explained by high selfing rates, population size reductions and to a lesser extent by the Wahlund effect. Despite these observations, we found signatures of gene flow and cross-fertilization, even between snails from the Nile Delta and Upper Egypt, indicating that B. truncatus can travel across large distances in Egypt. These observations could have serious consequences for disease epidemiology, as it means that infected snails from one region could rapidly and unexpectedly spark a new epidemic in another distant region. This could be one of the factors explaining the rebound of human Schistosoma infections in the Nile Delta, despite decades of sustained schistosomiasis control.

A Genome Wide Comparison to Identify Markers to Differentiate the Sex of Larval Stages of Schistosoma haematobium, Schistosoma bovis and their Respective Hybrids.

For scientists working on gonochoric organisms, determining sex can be crucial for many biological questions and experimental studies, such as crossbreeding, but it can also be a challenging task, particularly when no sexual dimorphism is visible or cannot be directly observed. In metazoan parasites of the genus Schistosoma responsible for schistosomiasis, sex is genetically determined in the zygote with a female heterogametic ZW/ZZ system. Adult flukes have a pronounced sexual dimorphism, whereas the sexes of the larval stages are morphologically indistinguishable but can be distinguished uniquely by using molecular methods. Therefore, reliable methods are needed to identify the sex of larvae individuals. Here, we present an endpoint PCR-based assay using female-specific sequences identified using a genome-wide comparative analysis between males and females. This work allowed us to identify sex-markers for Schistosoma haematobium and Schistosoma bovis but also the hybrid between both species that has recently emerged in Corsica (France). Five molecular sex-markers were identified and are female-specific in S. haematobium and the hybrid parasite, whereas three of them are also female-specific in S. bovis. These molecular markers will be useful to conduct studies, such as experimental crosses on these disease-causing blood flukes, which are still largely neglected but no longer restricted to tropical areas.

Analysis of mating system, fecundity, hatching and survival rates in two Schistosoma mansoni intermediate hosts (Biomphalaria pfeifferi and Biomphalaria camerunensis) in Cameroon.

BACKGROUND: Biomphalaria pfeifferi and Biomphalaria camerunensis are intermediate hosts of the trematode Schistosoma mansoni. Up till now, very scanty data report the life history traits of these freshwater snails. This study was therefore conducted to provide further knowledge on the mating system of these two S. mansoni intermediate hosts in Cameroon. The study was performed following a three-step experimental design as follows: (i) for each species, a sample of young snails (G1), virgin and sexually mature was constituted and divided into two groups; (ii) in the first group, individuals were maintained isolated for the evaluation of the impact of self-fertilization on life history traits while in the second group, individuals were paired for few hours for the evaluation of cross-fertilization impact; (iii) in each group, fitness parameters (fecundity of G1 snails and survival of G2 offspring) were monitored during one month. RESULTS: The sexual maturity (age at first egg-laying) was reached, on average, at 63.9 (sd: 3.0) and 103.7 (sd: 36.6) days for B. pfeifferi and B. camerunensis, respectively. Copulation was observed in all paired individuals in both species. In B. pfeifferi, the fecundity (number of egg capsules and eggs) of young G1 individuals and survival of G2 offspring on D0 and D8 were similar between selfing and outcrossing individuals, and a very low inbreeding depression (0.063) was observed. In B. camerunensis, the fecundity of outcrossed individuals was significantly higher than that of selfed individuals. The hatching rate was significantly higher and the incubation time significantly shorter for cross-fertilized eggs as compared with self-fertilized eggs, and a high inbreeding depression (0.71) was observed. CONCLUSION: These findings may explain the high adaptability to more diverse and inconstant habitats, as well as the better compatibility of B. pfeifferi to S. mansoni compared with B. camerunensis, and may support the sustainability of S. mansoni life cycle where this intermediate host prevails.

Phylogeny of seven Bulinus species originating from endemic areas in three African countries, in relation to the human blood fluke Schistosoma haematobium.

BACKGROUND: Snails species belonging to the genus Bulinus (Planorbidae) serve as intermediate host for flukes belonging to the genus Schistosoma (Digenea, Platyhelminthes). Despite its importance in the transmission of these parasites, the evolutionary history of this genus is still obscure. In the present study, we used the partial mitochondrial cytochrome oxidase subunit I (cox1) gene, and the nuclear ribosomal ITS, 18S and 28S genes to investigate the haplotype diversity and phylogeny of seven Bulinus species originating from three endemic countries in Africa (Cameroon, Senegal and Egypt). RESULTS: The cox1 region showed much more variation than the ribosomal markers within Bulinus sequences. High levels of genetic diversity were detected at all loci in the seven studied species, with clear segregation between individuals and appearance of different haplotypes, even within same species from the same locality. Sequences clustered into two lineages; (A) groups Bulinus truncatus, B. tropicus, B. globosus and B. umbilicatus; while (B) groups B. forskalii, B. senegalensis and B. camerunensis. Interesting patterns emerge regarding schistosome susceptibility: Bulinus species with lower genetic diversity are predicted to have higher infection prevalence than those with greater diversity in host susceptibility. CONCLUSION: The results reported in this study are very important since a detailed understanding of the population genetic structure of Bulinus is essential to understand the epidemiology of many schistosome parasites.

Ruminal paramphistomosis in cattle from northeastern Algeria: prevalence, parasite burdens and species identification.

Slaughterhouse samples were analysed over a two-year period (September 2010-August 2012) in Jijel (northeastern Algeria) in order to determine seasonal variations in the prevalence and intensity of bovine paramphistomosis in a Mediterranean climate and identify paramphistome species using molecular biology. In spring and summer, significantly higher prevalences and lower parasite burdens were noted in bull calves, thus indicating an effect of season on these parameters. In contrast, the differences among seasonal prevalences or among seasonal parasite burdens were not significant in the case of old cows. Eleven adult worms from the slaughterhouses of Jijel and three neighbouring departments (Constantine, El Tarf and Setif) were analysed using molecular markers for species identification. Two different species, Calicophoron daubneyi and C. microbothrium, were found. The presence of these two paramphistomids raises the question of their respective frequency in the definitive host and local intermediate hosts.

Prevalence and intensity of urinary schistosomiasis among school children in the district of Niakhar, region of Fatick, Senegal.

BACKGROUND: Urinary schistosomiasis is a parasitic disease that exists in all regions of Senegal. It is a major public health issue in this country. This study was carried out to determine the prevalence and intensity of this parasitosis in 12 villages of Niakhar (Fatick, Senegal). METHODS: A total of 210 schoolchildren, aged 7 to 15 years, were enrolled in this study, and urine samples were examined for Schistosoma haematobium eggs using a standard urine filtration technique. RESULTS: Of these children, 121 (57.6%) were found to be infected with a mean geometric count of 185 eggs per 10 ml of urine. The disease was present in all surveyed villages, and the prevalence ranged from 14.3% to 92.8%. The prevalence of infection was significantly correlated with increasing age and was higher in boys. Infection intensity was significantly higher in boys but did not significantly differ with age. Significant relationships between i) water contact or access to running water and ii) the prevalence or intensity of urinary schistosomiasis were also noted. CONCLUSIONS: The district of Niakhar is endemic for urinary schistosomiasis, with a high intensity of infection. A control program to decrease the prevalence and intensity should be implemented in this area to improve community health.