PCR-RFLP analysis of the ITS2 region to identify Schistosoma haematobium and S. bovis from Kenya

Development and utilization of a visual loop-mediated isothermal amplification coupled with a lateral flow dipstick (LAMP-LFD) assay for rapid detection of Echinostomatidae metacercaria in edible snail samples

Trematodes belonging to the family Echinostomatidae are food-borne parasites which cause echinostomiasis in animals and humans. This is a global public health issue, particularly in East and Southeast Asia. A method to detect the infective stage of Echinostomatidae species is required to prevent transmission to humans. In this study, a loop-mediated isothermal amplification coupled with a lateral flow dipstick (LAMP-LFD) assay was developed for visual detection of the metacercarial stage in edible snails of the genus Filopaludina from local markets in Thailand. The LAMP-LFD method can be performed within 70 min at a consistent temperature of 66 °C, and the results can be interpreted with the naked eye. The detection limits of the assay using Echinostoma mekongi, E. macrorchis, E. miyagawai and Hypoderaeum conoideum genomic DNA were equal between the four species at 50 pg/μL. A specificity evaluation demonstrated that the LAMP-LFD assay had no cross-reaction with another parasite (Thapariella species) or with the snail host species (Filopaludina martensi martensi, F. sumatrensis speciosa, and F. s. polygramma). Clinical test assessments were compared to microscopic examination in 110 edible snail samples. The clinical sensitivity and specificity of the tests were 84.62 % and 100 %, respectively, with a strong level of agreement based on the kappa statistic and the results of both methods were not significantly different (p > 0.05) per McNemar's test. The test successfully developed in this study may be useful for the detection of the metacercarial stage in edible snails for epidemiological investigations, control, surveillance, and to prevent future echinostomiasis health issues.

Assay for the simultaneous detection of Raillietina spp. (R. echinobothrida, R. tetragona, and R. cesticillus) and Ascaridia galli infection in chickens using duplex loop-mediated isothermal amplification integrated with a lateral flow dipstick assay

Raillietina species and Ascaridia galli are two of the significant intestinal parasites that affect chickens in a free-range system production. They destroy the intestinal mucosa layer, leading to several clinical symptoms such as weight loss, a slowed growth rate, and economic value loss. Thus, the objective of this study was to develop an assay for simultaneously detecting Raillietina spp. (R. echinobothrida, R. tetragona, and R. cesticillus) and A. galli in a single reaction using duplex loop-mediated isothermal amplification (dLAMP) coupled with a lateral flow dipstick (LFD) assay. The analytical specificity of the dLAMP-LFD assay showed a high specific amplification of Raillietina spp. and A. galli without non-target amplification. Regarding the analytical sensitivity, this approach was capable of simultaneously detecting concentrations as low as 5 pg/μL of mixed-targets. To evaluate the efficiency of the dLAMP assay, 30 faecal samples of chickens were verified and compared through microscopic examination. The dLAMP-LFD assay and microscopic examination results showed kappa values of Raillietina spp. and A. galli with moderate (K= 0.615) to high (K= 1) agreements, respectively, while the McNemar's test indicated that the efficiency between assays was not significantly different. Therefore, the developed dLAMP-LFD assay can be used as an alternative screening method to the existing classical method for epidemiological investigation, epidemic control, and farm management, as well as for addressing poultry health problems.

Assessment of the genetic diversity of lymnaeid (Gastropoda: Pulmonata) snails and their infection status with trematode cercariae in different regions of Thailand

Lymnaeid snails are some of the most widespread snails and are the first intermediate host of trematode parasites that affect human and livestock health. A full understanding of the genetic relationship of hosts and parasites is of paramount importance for effective parasite management. The present study assessed the prevalence of trematode larvae in lymnaeid snails and examined the genetic diversity of these snails collected across Thailand. We collected 672 lymnaeid snails from 39 locations in 22 provinces of six regions in Thailand. Subsequently, cercarial infection in the snails was observed by using the shedding method. Lymnaeid snails released 5 types of trematode cercariae, namely, xiphidiocercariae, echinostome cercariae I, echinostome cercariae II, furcocercous cercariae, and strigea cercariae. The phylogenetic analysis based on ITS2 and 28S rDNA sequences revealed 5 cercaria types assigned to four trematode families, of which two belong to the group of human intestinal flukes. Combination of shell morphology and sequence analysis of the mitochondrial COI and 16S rDNA genes, the lymnaeid snails were classified into two species, Radix rubiginosa and Orientogalba viridis. Moreover, the combined dataset of mtDNA genes (COI + 16S rDNA) from R. rubiginosa and O. viridis revealed 32 and 15 different haplotypes, respectively, of which only a few haplotypes were infected with cercariae. The genetic diversity and genetic structure revealed that R. rubiginosa and O. viridis experienced a bottleneck phenomenon, and showed limited gene flow between populations. Population demographic history analyses revealed that R. rubiginosa and O. viridis experienced population reductions followed by recent population expansion. These findings may improve our understanding of parasite-lymnaeid evolutionary relationships, as well as the underlying molecular genetic basis, which is information that can be used for further effective control of the spread of trematode disease.

Environmental influence on abundance and infection patterns of snail intermediate hosts of liver and intestinal flukes in North and Central Vietnam

Liver and intestinal flukes (LIF) are important groups of foodborne zoonotic trematodes (FZTs) in Southeast Asia, including Vietnam. Their complex life cycles require specific freshwater snail species as the obligatory first intermediate hosts. In 2019, we conducted a longitudinal study in Yen Bai and Thanh Hoa provinces in North and Central Vietnam, respectively, to investigate the diversity of LIF and their infection prevalence in relation to snail host abundance and environmental factors. Using a combination of morphological and molecular identification techniques, we identified 10 LIF species infecting 11 snail host species. We observed significant seasonal variation in the mean abundance of several snail host species, with the majority of snails collected during the spring. We also detected seasonal changes in LIF species composition, with the highest species richness reported in the spring. Clonorchis sinensis and Fasciola gigantica, two medically important human liver flukes in Asia, were found only in the spring in Yen Bai. Our study revealed that not all snail host species have the same probability of becoming infected, and we recorded seasonal variations in the prevalence of LIF infection in different snail species in relation to water parameters.

Population genetic structure of Indoplanorbis exustus (Gastropoda: Planorbidae) in Thailand and its infection with trematode cercariae

Indoplanorbis exustus is a freshwater gastropod belonging to the family Planorbidae. This snail is widely distributed across the tropics and plays an important role as the intermediate host for trematodes. However, relatively little is understood regarding the genetic relationship between I. exustus and trematodes. The goals of this study were to investigate the current transmission status of trematode cercariae in I. exustus in Thailand and to examine the genetic diversity, genetic structure, and demographic history of I. exustus. We collected 575 I. exustus from 21 provinces across six regions of Thailand and investigated cercarial infections by using the shedding method. I. exustus from two provinces were infected with cercarial trematodes, and two types of cercarial stages were molecularly identified as furcocercous cercaria and xiphidiocercariae. Phylogenetic tree analysis based on 28S rDNA and ITS2 sequences demonstrated that furcocercous cercaria and xiphidiocercariae were closely clustered with a clade of Euclinostomum sp. and Xiphidiocercariae sp., respectively. Phylogenetic and network analyses of I. exustus haplotypes based on the COI, 16S rDNA, and ITS1 genes demonstrated four main clades. Only snails in clade A were distributed in all regions of Thailand and harbored trematode cercariae. The level of genetic diversity of I. exustus was relatively high, but most populations were not genetically different, thus suggesting the appearance of gene flow within the I. exustus populations. Overall, the haplotype network was star-shaped, thus suggesting the recent demographic expansion of populations. This result was also supported by the unimodal mode of the mismatch distribution graph and the large negative values of the neutrality tests. Therefore, the I. exustus snail was likely another freshwater snail of the invasive species in Thailand. This information will aid in monitoring the spread of the parasitic trematodes carried by I. exustus from different populations.

Morphological and molecular identification of lymnaeid snail and trematodes cercariae in different water bodies in Perak, Malaysia

Lymnaeid snails play a crucial role in the transmission of trematode cercariae as an intermediate host that can infect humans, ruminants like buffalo, and other animals, resulting in serious economic losses. The purpose of the study was to identify the morphological and molecular characteristics of snails and cercariae collected from water bodies near buffalo farms that were integrated with palm oil in Perak, Malaysia. The presence or absence of snails in 35 water bodies was examined via cross-sectional study. From three marsh wetlands, 836 lymnaeid snails were gathered in total. Each snail's shell was morphologically identified to determine its family and species. The cercarial stage inside each snail's body was observed using the crushing method and trematode cercariae types were determined. In addition, the target gene Cytochrome c oxidase subunit 1 (Cox1) and the ribosomal internal transcribed spacer 2 (ITS2) region were used to identify the snail species and cercarial types according to the species level. The findings indicated that the collected snails belong to the family lymnaeidae and Radix rubiginosa species. In snails, the cercarial emergence infection rate was 8.7%. Echinostome, xiphidiocercariae, gymnocephalous, brevifurcate-apharyngeate distome cercariae (BADC), and longifurcate-pharyngeal monostome cercariae (LPMC) are the five morphological cercarial types that were observed. The cercariae were identified using morphological and molecular techniques, and they are members of the four families which are Echinostomatidae, Plagiorchiidae, Fasciolidae, and Schistosomatidae. Interestingly, this is the first study on R. rubiginosa and several trematode cercariae in Perak water bodies near buffalo farms that are integrated with palm oil. In conclusion, our research shown that a variety of parasitic trematodes in Perak use R. rubiginosa as an intermediate host.

The determination and relationship of four coexisting paramphistomes in perspective of integrative taxonomic investigation

Co-infections with Orthocoelium species and other paramphistomes were found in different ruminant hosts from two provinces of Thailand. Whilst O. parvipapillatum coexisted with Paramphistomum epiclitum in the same cattle (Bos taurus) from Pathum Thani Province, Thailand, O. dicranocoelium and Fischoederius elongatus were found in water buffalo (Bubalus bubalis) from Chiang Mai Province. Morphological, histological, and tegumental surface features of both Orthocoelium species were intensively investigated for species differentiation. Statistical analysis of eight morphometric ratios presented morphological differences for three paramphistomes in the Paramphistomidae family and some relationships among paramphistomes in different definitive hosts. The genetic relationships of the co-infecting paramphistomes were investigated using p-distance and phylogenetic tree analyses. Genetic variations in the Orthocoelium co-infecting paramphistomes, P. epiclitum and F. elongatus, were calculated and compared to DNA sequence alignments based on internal transcribed spacer 2 (ITS2) and cytochrome c oxidase subunit I (COI) DNA markers. In addition, the phylogenetic tree constructions from both DNA markers and their concatenated sequence (ITS2 + COI) were used for species confirmation and the presentation of genetic relationships between co-infecting paramphistomes and other paramphistomes. This study improves the basic taxonomical description and understanding of parasite-parasite and host-parasite interactions from the perspectives of morpho-histological, morphometric, and genetic variation in co-infecting paramphistomes and Orthocoelium species in different hosts.

Feasibility of a DNA biosensor assay based on loop-mediated isothermal amplification combined with a lateral flow dipstick assay for the visual detection of Ascaridia galli eggs in faecal samples

Ascaridia galli is an important nematode that causes ascaridiasis in free-range and indoor system chicken farms. Infection with A. galli may damage the intestinal mucosa and inhibit nutrient absorption, leading to a reduced growth rate, weight loss and a decreased egg production. Consequently, A. galli infection is a significant health problem in chickens. In this study, we developed a loop-mediated isothermal amplification coupled with a lateral flow dipstick (LAMP-LFD) assay for the visual detection of A. galli eggs in faecal samples. The LAMP-LFD assay consists of six primers and one DNA probe that recognize the internal transcribed spacer 2 (ITS2) region; it can be performed within 70 min and the results can be interpreted with the naked eye. Using the LAMP-LFD assay developed in this study, A. galli DNA was specifically amplified without any cross-reactions with other related parasites (Heterakis gallinarum, Raillietina echinobothrida, R. tetragona, R. cesticillus, Cotugnia sp., Echinostoma miyagawai) and definitive hosts (Gallus gallus domesticus, Anas platyrhynchos domesticus). The minimum detectable DNA concentration was 5 pg/μl, and the detectable egg count was 50 eggs per reaction. The assay can be performed in a water bath, without the need for post-mortem morphological investigations and laboratory instruments. It is therefore a viable alternative for the detection of A. galli in chicken faeces and can replace classical methods in field screening for epidemiological investigations, veterinary health and poultry farming management. RESEARCH HIGHLIGHTSThis is the first study using the LAMP-LFD assay for Ascaridia galli detection.The results can be observed by the naked eye.The developed assay can be used to detect Ascaridia galli eggs in faecal samples.

Bulinus snails in the Lake Victoria Basin in Kenya: Systematics and their role as hosts for schistosomes

The planorbid gastropod genus Bulinus consists of 38 species that vary in their ability to vector Schistosoma haematobium (the causative agent of human urogenital schistosomiasis), other Schistosoma species, and non-schistosome trematodes. Relying on sequence-based identifications of bulinids (partial cox1 and 16S) and Schistosoma (cox1 and ITS), we examined Bulinus species in the Lake Victoria Basin in Kenya for naturally acquired infections with Schistosoma species. We collected 6,133 bulinids from 11 sites between 2014-2021, 226 (3.7%) of which harbored Schistosoma infections. We found 4 Bulinus taxa from Lake Victoria (B. truncatus, B. tropicus, B. ugandae, and B. cf. transversalis), and an additional 4 from other habitats (B. globosus, B. productus, B. forskalii, and B. scalaris). S. haematobium infections were found in B. globosus and B. productus (with infections in the former predominating) whereas S. bovis infections were identified in B. globosus, B. productus, B. forskalii, and B. ugandae. No nuclear/mitochondrial discordance potentially indicative of S. haematobium/S. bovis hybridization was detected. We highlight the presence of Bulinus ugandae as a distinct lake-dwelling taxon closely related to B. globosus yet, unlike all other members of the B. africanus species group, is likely not a vector for S. haematobium, though it does exhibit susceptibility to S. bovis. Other lake-dwelling bulinids also lacked S. haematobium infections, supporting the possibility that they all lack compatibility with local S. haematobium, thereby preventing widespread transmission of urogenital schistosomiasis in the lake's waters. We support B. productus as a distinct species from B. nasutus, B. scalaris as distinct from B. forskalii, and add further evidence for a B. globosus species complex with three lineages represented in Kenya alone. This study serves as an essential prelude for investigating why these patterns in compatibility exist and whether the underlying biological mechanisms may be exploited for the purpose of limiting schistosome transmission.

Geographical distribution and molecular survey of freshwater snail intermediate hosts of Schistosoma haematobium by DraI/Sh73 PCR in eliminated foci of Morocco

Morocco had reached the level of schistosomiasis elimination 16 years ago. However the spread of freshwater snails in several breeding sites, and imported schistosome infection, still exist. Therefore, snail survey is a crucial component to sustain elimination progress. This study aimed to evaluate and to incorporate DraI/Sh73 PCR, for detecting early prepatent Schistosoma haematobium infection in snail host, into epidemiologic surveillance for schistosomiasis, particularly in reportedly eliminated foci where S.bovis overlaps with S. haematobium. The geographical distribution and the density of Bulinus truncatus and Planorbarius metidjensis were monitored for six years (2014-2019) and snail sampling were conducted in Fkih Ben Saleh province. All snails were analyzed in pools by DraI/Sh73 PCR. Results showed absence of Planorbarius metidjensi and none of the collected Bulinus truncatus snails were infected by S. haematobium. DraI/Sh73 PCR using pooled snail extracts is specific, feasible and suitable in routine malacological survey in the post elimination phase of schistosomiasis in Morocco.

Prevalence and Molecular Identification of Schistosoma haematobium among Children in Lusaka and Siavonga Districts, Zambia

Schistosomiasis remains a public health concern in Zambia. Urinary schistosomiasis caused by Schistosoma haematobium is the most widely distributed infection. The aim of the current study was to determine the prevalence and risk factors of urinary schistosomiasis and identify the strain of S. haematobium among children in the Siavonga and Lusaka districts in Zambia. Urine samples were collected from 421 primary school children and S. haematobium eggs were examined under light microscopy. A semi-structured questionnaire was used to obtain information on the socio-demographic characteristics and the potential risk factors for urinary schistosomiasis. DNA of the parasite eggs was extracted from urine samples and the internal transcribed spacer gene was amplified, sequenced and phylogenetically analysed. The overall prevalence of S. haematobium was 9.7% (41/421) (95% CI: 7.16–13.08), male participants made up 6.2% (26/232) (95% CI: 4.15–9.03), having a higher burden of disease than female participants who made up 3.5% (15/421) (95% CI: 2.01–5.94). The age group of 11–15 years had the highest overall prevalence of 8.3% (35/421) (5.94–11.48). Participants that did not go fishing were 0.008 times less likely to be positive for schistosomiasis while participants whose urine was blood-tinged or cloudy on physical examination and those that lived close to water bodies were 9.98 and 11.66 times more likely to test positive for schistosomiasis, respectively. A phylogenetic tree analysis indicated that S. haematobium isolates were closely related to pure S. haematobium from Zimbabwe and hybrids of S. haematobium × S. bovis from Benin, Senegal and Malawi. The current study shows that urinary schistosomiasis is endemic in the study areas and is associated with water contact, and S. haematobium isolated is closely related to hybrids of S. bovis × S. haematobium strain, indicating the zoonotic potential of this parasite.

A Novel PCR-RFLP to Detect and Differentiate Schistosoma spindale and S. indicum, the Pathogenic Schistosomes in Indian Cattle

PURPOSE

Visceral schistosomosis is an economically important trematode infection caused by Schistosoma spindale and S. indicum in among ruminants. The lack of sensitive diagnostic tools has often led to underestimation of the prevalence in live animals. A sensitive copro-PCR targeting partial mitochondrial gene was developed to detect Schistosoma spp. However, this protocol could not differentiate between the two species. This study was conducted to explore the possibility of species differentiation using restriction fragment length polymorphism of PCR products (PCR- RFLP).

METHODS

Polymerase chain reaction was carried out to amplify mitochondrial gene of adult S. spindale and S. indicum. Copro PCR was done with schistosome-positive faecal samples. A novel PCR-RFLP was designed targeting the Hpy166II recognition sequence in the mitochondrial gene sequence of S. indicum.

RESULT

The PCR using primers targeting the mitochondrial gene of S. spindale and S. indicum amplified a distinct product of approximately 454 bp with adult fluke as well as faecal DNA, which upon RFLP with Hpy166II yielded 330 bp and 124 bp products with S. indicum amplicons alone.

CONCLUSION

The novel PCR-RFLP possesses the potential to be used in epidemiological surveys among bovines and in snail intermediate hosts to screen for S. spindale and S. indicum infection.

High-performance triplex PCR detection of three tapeworm species belonging to the genus Raillietina in infected poultry

Chickens and ducks are important sources of essential proteins and nutrition for global consumption, especially their eggs and meat. Tapeworm infections in chickens and ducks are the cause of serious poultry health and economic problems in the processing of livestock and food production systems. Raillietina are cosmopolitan in distribution and are possibly the most common tapeworm parasites. There are three important species regarding avian infection, with different pathogenicity, including Raillietina echinobothrida, R. tetragona, and R. cesticillus. Co-infection diagnosis of these tapeworms using morphological analysis can be performed, but this is time-consuming and complicated. Therefore, this study aimed to develop a triplex PCR for the detection and discrimination of three Raillietina species. The triplex PCR assay specifically amplified target DNAs with no inter-specific interference and produced a specific band for each species. According to the specificity test, there was no cross-amplification with the DNA template of related parasites and their hosts. The lowest detectable DNA concentrations were evaluated and provided sensitivities of 0.5 pg/μL for R. echinobothrida, 5 pg/μL for R. tetragona, 50 fg/μL for R. cesticillus, and 5 pg/μL for the combination of DNA from all three species. Simultaneous detection limits of egg capsules and gravid proglottids was also performed, with and without feces. The interference of feces in the reaction was related to a decrease in sensitivity, but simultaneous detection of three Raillietina species in amounts lower than one gravid proglottid and ten egg capsules was still successful. Thus, this study is the first triplex PCR assay for Raillietina detection and can be utilized as an alternative diagnostic tool for the detection and discrimination of R. echinobothrida, R. tetragona, and R. cesticillus infection in poultry through the verification of fecal specimens. In addition, it could improve the performance of specific treatments and promote veterinary healthcare.

Morphological and molecular characterization of larval trematodes infecting the assassin snail genus Anentome in Thailand

The assassin snail genus Anentome is widespread in Southeast Asia, and is distributed all over the world via the aquarium trade. One species of genus Anentome, Anentome helena, is known to act as intermediate host of parasitic trematodes. This study investigates the taxonomic diversity of larval trematodes infecting A. helena and Anentome wykoffi in Thailand. Larval trematodes were identified by combining morphological and DNA sequence data (cytochrome c oxidase I and internal transcribed spacer 2). Species delimitation methods were used to explore larval trematode species boundaries. A total of 1107 specimens of Anentome sp. were collected from 25 localities in Thailand. Sixty-two specimens of A. helena (n = 33) and A. wykoffi (n = 29) were infected by zoogonid cercariae, heterophyid metacercariae and echinostome metacercariae, with an overall prevalence of 5.6% (62/1107) and population-level prevalences in the range of 0.0-22.3%. DNA sequence data confirmed that the larval trematodes belong to the families Echinostomatidae, Heterophyidae and Zoogonidae. As such, this is the first report of zoogonid cercariae and heterophyid metacercariae in A. helena, and echinostome metacercariae in A. wykoffi. Moreover, this study provides evidence of tentative species-level differentiation between Thai Echinostoma sp. and Cambodian Echinostoma mekongi, as well as within Echinostoma caproni, Echinostoma trivolvis and Echinostoma revolutum.

Simplifying Schistosome Surveillance: Using Molecular Cercariometry to Detect and Quantify Cercariae in Water

Avian schistosomes are considered a public health nuisance due to their ability to cause swimmer’s itch when accidentally encountering humans rather than their intended avian hosts. Researchers have been monitoring their presence and abundance through snail collections and cercariometry. Cercariometry methods have evolved over the last several decades to detect individual schistosome species from a single water sample, simplifying the monitoring of these parasites. This methodological evolution coincides with the development of the field of environmental DNA (eDNA) where genetic material is extracted from environmental samples, rather than individual organisms. While there are some limitations with using molecular cercariometry, notably the cost and its inability to differentiate between life cycle stages, it substantially reduces the labor required to study trematode populations. It also can be used in complement with snail collections to understand the composition of avian schistosomes in an environment.

Complex morphological characterization and morphometric-molecular discrimination of two paramphistome species co-infecting cattle, Orthocoelium sp. and Paramphistomum epiclitum

Co-infection by two paramphistome species, Orthocoelium sp. and Paramphistomum epiclitum, is found in cattle in Thailand. The morphological features of these and other paramphistomes under a light microscope are similar, resulting in misidentification and misdiagnosis. We classified these paramphistomes into three morphological variation types, namely Orthocoelium sp., P. epiclitum MV1 (immature), and P. epiclitum MV2 (matured). Ten morphological characteristics were investigated, and the values were transformed into 25 ratio criteria for statistical investigation. Morphometric analysis can classify the variation of these specimens using differences in the bifurcal level, the vitellaria starting level, the starting level of the anterior testis, and the center level of the posterior testis positions by body length ratios. These ratios can separate the samples into three morphologically different groups, whereas molecular analysis based on the nuclear internal transcribed spacer 2 (ITS2) region and the mitochondrial cytochrome c oxidase subunit I (COI) gene could only distinguish two specific groups. In addition, the Orthocoelium specimen, related to O. dicranocoelium and O. parvipapillatum according to morphological and histological analysis, was monophyletic grouped via ITS2 analysis. Our study provides a scientific basis for the taxonomic classification and clustering of morphologically varying species, improving the identification, detection, and diagnosis of co-infecting paramphistomes.

Hybridization increases genetic diversity in Schistosoma haematobium populations infecting humans in Cameroon

Background

Hybrids between Schistosoma haematobium (Sh) and S. bovis (Sb) have been found in several African countries as well as in Europe. Since the consequences of this hybridization are still unknown, this study aims to verify the presence of such hybrids in Cameroonian humans, to describe the structure of S. haematobium populations on a large geographic scale, and to examine the impact of these hybrids on genetic diversity and structure of these populations.

Methods

From January to April 2019, urine from infected children was collected in ten geographically distinct populations. Miracidia were collected from eggs in this urine. To detect the presence of hybrids among these miracidia we genotyped both Cox1 (RD-PCR) and ITS2 gene (PCR-RFLP). Population genetic diversity and structure was assessed by genotyping each miracidium with a panel of 14 microsatellite markers. Gene diversity was measured using both heterozygosity and allelic richness indexes, and genetic structure was analyzed using paired Fst, PCA and Bayesian approaches.

Results

Of the 1327 miracidia studied, 88.7% were identified as pure genotypes of S. haematobium (Sh_Sh/Sh) while the remaining 11.3% were hybrids (7.0% with Sh_Sh/Sb, 3.7% with Sb_Sb/Sh and 0.4% with Sb_Sh/Sb). No miracidium has been identified as a pure genotype of S. bovis. Allelic richness ranged from 5.55 (Loum population) to 7.73 (Matta-Barrage) and differed significantly between populations. Mean heterozygosity ranged from 53.7% (Loum) to 59% (Matta Barrage) with no significant difference. The overall genetic differentiation inferred either by a principal component analysis or by the Bayesian approach shows a partial structure. Southern populations (Loum and Matta Barrage) were clearly separated from other localities but genetic differentiation between northern localities was limited, certainly due to the geographic proximity between these sites.

Conclusions

Hybrids between S. haematobium and S. bovis were identified in 11.3% of miracidia that hatched from eggs present in the urine of Cameroonian schoolchildren. The percentages of these hybrids are correlated with the genetic diversity of the parasite, indicating that hybridization increases genetic diversity in our sampling sites. Hybridization is therefore a major biological process that shapes the genetic diversity of S. haematobium.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-022-00958-0.

Spatial variation of life-history traits in Bulinus truncatus, the intermediate host of schistosomes, in the context of field application of niclosamide in Côte d’Ivoire

Background

Control 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.

Results

On 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.

Conclusions

Our 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.

Morphological and molecular identification of trematode cercariae related with humans and animal health in freshwater snails from a lake and a dam in Myanmar

Freshwater snails play an essential role in the transmission of trematode parasitic flatworms that can infect wild and domestic animals, as well as humans. This study aimed to investigate the rate of cercarial infections in freshwater snails collected from two study areas, Inlay Lake and Yezin Dam, in Myanmar. A total of 4,740 snail samples were collected from Inlay Lake (n = 3,837) and Yezin Dam (n = 903), and infection rate by cercarial emergence was examined. Cercarial DNA samples were analysed by PCR. Based on morphological characteristics, eleven snail species and eight cercarial types were identified. Snails of Melanoides tuberculata in the family Thiaridae were found as the most abundant, followed by Indoplanorbis exustus of the family Planorbidae, in both study areas. The infection rate by cercarial emergence in snails in Inlay Lake and Yezin Dam was 5.8% (224/3,837) and 48.6% (439/903), respectively. Echinostome cercariae showed the highest infection rate in both study areas. Phylogenetic analysis of cercarial internal transcribed spacer 2 (ITS2) sequences revealed that at least seven cercaria types belonged to five digenean trematode families, two of which were zoonotic trematodes in the families of Opisthorchiidae/Heterophyidae and Schistosomatidae. Furthermore, cercarial 28S ribosomal RNA gene analysis showed that the furcocercous cercariae in Yezin Dam were identified as Schistosoma spindale, a causative agent of ruminant schistosomiasis. This is the first report on zoonotic trematode cercariae in snails in Myanmar. The findings indicate that various snail species act as intermediate host for trematode species that infect aquatic animals, mammals and humans in the country.

Internal transcribed spacer region 1 as a promising target for detection of intra-specific polymorphisms for Strongyloides stercoralis

Background:

Strongyloides stercoralis, the causative agent of strongyloidiasis, is a parasitic worm that has larvae capable of reinfecting the same host. This nematode infection is therefore difficult to treat and to achieve total cure. Information about genetic variation and differences in drug susceptibility between strains is needed to improve treatment outcomes.

Aim:

To develop a polymerase chain reaction (PCR) to identify the intra-species variation among 13 S. stercoralis isolates collected from Bangladesh, USA and Australia.

Material & Methods:

PCR assays were designed by using primers targeting S. stercoralis internal transcribed spacer (ITS) regions 1 and 2. Sequence data generated by these PCR products were compared to the existing ITS1/2, 18S and 28S rRNA gene sequences in GenBank for phylogenetic analysis.

Results:

Intra-species single nucleotide polymorphisms (SNPs) were identified in ITS1 and in the 5.8S rRNA gene. The generated phylogram grouped the 13 isolates into dog, Orangutan and human clusters.

Conclusion:

This method could be used as an epidemiological tool to study strain differences in larger collections of S. stercoralis isolates. The study forms the basis for further development of an ITS-based assay for S. stercoralis molecular epidemiological studies

Molecular detection of three intestinal cestode species (Raillietina echinobothrida, R. tetragona, R. cesticillus) from poultry in Thailand

RESEARCH HIGHLIGHTS

This study established specific primers for Raillietina species detection.The ITS2 region is an effective molecular marker for Raillietina identification.

Mastomys natalensis (Smith, 1834) as a natural host for Schistosoma haematobium (Bilharz, 1852) Weinland, 1858 x Schistosoma bovis Sonsino, 1876 introgressive hybrids

Cercarial emission of schistosomes is a determinant in the transmission to the definitive host and constitutes a good marker to identify which definitive host is responsible for transmission, mainly in introgressive hybridization situations. Our goal was to test the hypothesis that micro-mammals play a role in Schistosoma haematobium, S. bovis, and/or S. haematobium x S. bovis transmission. Small mammal sampling was conducted in seven semi-lacustrine villages of southern Benin. Among the 62 animals trapped, 50 individuals were investigated for Schistosoma adults and eggs: 37 Rattus rattus, 3 Rattus norvegicus, 9 Mastomys natalensis, and 1 Crocidura olivieri. Schistosoma adults were found in four R. rattus and two M. natalensis, with a local prevalence reaching 80% and 50%, respectively. Two cercarial chronotypes were found from Bulinus globosus experimentally infected with miracidia extracted from naturally infected M. natalensis: a late diurnal and nocturnal chronotype, and an early diurnal, late diurnal, and nocturnal chronotype. The cytochrome C oxidase subunit I mtDNA gene of the collected schistosomes (adults, miracidia, and cercariae) belonged to the S. bovis clade. Eleven internal transcribed spacer rDNA profiles were found; four belonged to S. bovis and seven to S. haematobium x S. bovis. These molecular results together with the observed multi-peak chronotypes add M. natalensis as a new host implicated in S. haematobium x S. bovis transmission. We discuss the origin of the new chronotypes which have become more complex with the appearance of several peaks in a 24-h day. We also discuss how the new populations of offspring may optimize intra-host ecological niche, host spectrum, and transmission time period.

Transmission sites for Schistosoma haematobium and Schistosoma bovis identified in localities within the Athi River basin of Kenya using a PCR-RFLP assay

Background

The epidemiology of human urinary schistosomiasis caused by Schistosoma haematobium can be complicated by the presence of ruminant schistosomiasis caused, primarily by S. bovis. The two schistosome species may be transmitted by the same Bulinus species, they may occur sympatrically in the same habitat, and their cercariae are very similar in morphology and therefore, difficult to tell them apart. Screening of snails collected from freshwater habitats for schistosome infections is often used to identify transmission sites or to evaluate success or failure of interventions. However, pin-pointing sites involved in S. haematobium transmission can be complicated by the presence of other mammalian schistosomes such as the bovine schistosome, which is a fairly common parasite. A PCR-RFLP method targeting a unique segment of the second internal transcribed spacer (ITS2) region of the ribosomal DNA (rDNA) in the schistosomes was used to identify mammalian schistosome cercariae shed by bulinid snails collected from endemic freshwater habitats located within Machakos county in south-eastern Kenya, with the aim to identify the transmission sites and assess the distribution each of the parasite species in the study area.

Results

A total of 5,034 bulinid snails were collected from 41 different sites and screened for schistosome infections, and out of these, 43 (<1%) were found to be shedding mammalian schistosome cercariae. On analysis using the Polymerase chain reaction- Restriction Fragment Length Polymorphisms (PCR-RFLP) assay, cercariae from 32 snails were identified as S. haematobium while cercariae from 11 snails turned out to be S. bovis. Only two sites out of 40 namely Kisukioni and Katiwa, were active transmission sites. Both sites were active transmission sites for both S. haematobium and S. bovis. The assay reliably identified and distinguished between S. haematobium and S. bovis cercariae, even when only a few cercariae (5–10) were present in the sample, or when the parasite DNA concentrations were as low as five pico grammes (5pg). The FTA® paper offered a more reliable way of collecting, transporting and storing DNA material, and the samples.

Conclusion

The PCR-based assay can potentially be used to support schistosomiasis control efforts, in epidemiological studies of urinary schistosomiasis, or in transmission ecology studies of S. haematobium and S. bovis.

Cercarial trematodes in freshwater snails from Bangkok, Thailand: prevalence, morphological and molecular studies and human parasite perspective

We investigated the prevalence, morphological characters and molecular classifications of trematode cercariae in freshwater snails randomly collected from 59 sampling localities in Bangkok from May 2018 to March 2019. We used a crushing technique to observe the cercarial stage inside each snail body and amplified the internal transcribed spacer 2 regions of cercarial DNA using polymerase chain reaction methodology. The associated phylogenetic tree was reconstructed using Bayesian inference analyses. A total of 517 of 15 621 examined snails were infected with trematode cercariae, and the infected snails were classified into 11 species of seven families with a 3.31% overall prevalence of the infection. The Bithynia siamensis siamensis snail displayed the highest prevalence of infection (16.16%), whereas the Physella acuta snail exhibited the lowest prevalence (0.08%) of infection. Eight morphological types of cercariae were observed. The highest prevalence of infection was observed in mutabile cercaria (1.86%). Based on molecular investigations, the phylogram revealed eight cercaria types assigned to at least nine digenean trematode families, of which five belong to groups of human intestinal flukes. Although, with the exception of schistosome cercaria, trematode cercariae are not known to directly damage humans, understanding the general biology of trematode cercariae (including diversity, distribution, infection rates and host range) is important and necessary for the prevention and control of parasitic transmission that impacts aquatic cultivations, livestock farming and human health.

Novel high-performance detection of Raillietina echinobothrida, Raillietina tetragona, and Raillietina cesticillus using loop-mediated isothermal amplification coupled with a lateral flow dipstick (LAMP-LFD)

Cestodes belonging to the genus Raillietina are a major veterinary health problem in the poultry industry, especially in chickens (Gallus gallus domesticus) and ducks (Anas playtrhynchos domesticus). In this study, loop-mediated isothermal amplification coupled with a lateral flow dipstick (LAMP-LFD) assay was established and validated for the detection of R. echinobothrida, R. tetragona, and R. cesticillus in one reaction. The LAMP-LFD assay can be completed in 75 min under isothermal conditions at 66 °C and the results can be obtained by observation with the naked eye. This assay was very specific and had no cross-amplification with other closely related parasites (Cotugnia sp., Diorchis formosensis, Fimbriaria sp., Echinostoma sp., E. miyagawai, Hypoderaeum conoideum, Prosthogonimus cuneatus, and Ascaridia galli) or their definitive hosts (G. g. domesticus, A. p. domesticus). The sensitivity of the LAMP-LFD assay was detected with three Raillietina species at 0.5 ng, which was enough for gravid proglottid DNA detection. The accuracy test showed that the LAMP-LFD assay demonstrated accurate verification results when compared to morphological results. This is a novel LAMP-LFD assay that is highly specific and sensitive for the detection of Raillietina species. It can be applied to detection for epidemiological investigations, monitoring programs, surveillance, control, and to solve veterinary health problems for the poultry industry in Raillietina endemic areas.

Diverging patterns of introgression from Schistosoma bovis across S. haematobium African lineages

Hybridization is a fascinating evolutionary phenomenon that raises the question of how species maintain their integrity. Inter-species hybridization occurs between certain Schistosoma species that can cause important public health and veterinary issues. In particular hybrids between Schistosoma haematobium and S. bovis associated with humans and animals respectively are frequently identified in Africa. Recent genomic evidence indicates that some S. haematobium populations show signatures of genomic introgression from S. bovis. Here, we conducted a genomic comparative study and investigated the genomic relationships between S. haematobium, S. bovis and their hybrids using 19 isolates originating from a wide geographical range over Africa, including samples initially classified as S. haematobium (n = 11), S. bovis (n = 6) and S. haematobium x S. bovis hybrids (n = 2). Based on a whole genomic sequencing approach, we developed 56,181 SNPs that allowed a clear differentiation of S. bovis isolates from a genomic cluster including all S. haematobium isolates and a natural S. haematobium-bovis hybrid. All the isolates from the S. haematobium cluster except the isolate from Madagascar harbored signatures of genomic introgression from S. bovis. Isolates from Corsica, Mali and Egypt harbored the S. bovis-like Invadolysin gene, an introgressed tract that has been previously detected in some introgressed S. haematobium populations from Niger. Together our results highlight the fact that introgression from S. bovis is widespread across S. haematobium and that the observed introgression is unidirectional.

Hybridization is a fascinating evolutionary phenomenon that raises the question of how species maintain their integrity. Inter-species hybridization occurs between certain Schistosoma species that can cause important public health and veterinary issues. In particular hybrids between Schistosoma haematobium and S. bovis associated with humans and animals respectively are frequently identified in Africa. Recent genomic evidence indicates that some S. haematobium populations show signatures of genomic introgression from S. bovis. Here we conducted a comparative genomic study to assess the genomic diversity within S. haematobium and S. bovis species and genetic differentation at the genome scale between these two sister species over the African continent. We also investigated traces of possible ancient introgression from one species to another. We found that S. haematobium display low genetic diversity compared to S. bovis. We also found that most S. haematobium samples harbor signature of past introgression with S. bovis at some genomic positions. Our results strongly suggest that introgression occurred long time ago and that such introgression is unidirectional from S. bovis within S. haematobium. Such introgresssion event(s) result in diverging patterns of genomic introgression across S. haematobium lineages.

Insights on foodborne zoonotic trematodes in freshwater snails in North and Central Vietnam

Foodborne zoonotic trematode (FZT) infections are common neglected tropical diseases in Southeast Asia. Their complicated life cycles involve freshwater snails as intermediate hosts. A cross-sectional study was conducted in Yen Bai and Thanh Hoa provinces in North and Central Vietnam, to investigate the diversity of cercariae of potential FZT and to construct the phylogenetic relationship of trematode cercariae based on the Internal Transcribed Spacer 2 (ITS2) region. Among 17 snail species collected from various habitats, 13 were infected by 10 cercarial groups among which parapleurolophocercous, pleurolophocercous, and echinostome cercariae were of zoonotic importance. The monophyletic tree separated cercarial sequences into different groups following the description of the cercariae families in which Haplorchidae, Opisthorchiidae, Echinochasmidae, and Echinostomatidae are important families of FZT. The overall prevalence was different among snail species and habitats and showed a seasonal trend. Parapleurolophocercous and echinostome cercariae emerged as the most common cercariae in snails in Yen Bai, while monostome, echinostome, and megalura cercariae were most common in Thanh Hoa. Using a molecular approach, we identified Parafossarulus striatulus as the first intermediate snail host of Clonorchis sinensis in Thac Ba Lake. Melanoides tuberculata and Bithynia fuchsiana were we identified preferred intermediate snail hosts of a diverse range of trematode species including intestinal flukes (i.e., Haplorchis pumilio and Echinochasmus japonicus) in Yen Bai and Thanh Hoa, respectively.

Very low prevalence of Opisthorchis viverrini s.l. cercariae in Bithynia siamensis siamensis snails from the canal network system in the Bangkok Metropolitan Region, Thailand

The liver fluke Opisthorchis viverrini s.l. is associated with a long-term public health problem in Thailand. However, O. viverrini s.l. infection in Bithynia snails in the canal network system (CNS) in the Bangkok Metropolitan Region (BMR) has never been assessed. This study aimed to investigate the occurrence of B. siamensis siamensis and the prevalence of O. viverrini s.l. infection in this snail in the CNS in BMR along with morphological examination and molecular analyses on O. viverrini s.l. cercariae. The snails were randomly sampled from the CNS in all BMR areas from January 2018 to July 2019. Snail specimens were identified and examined for digenean infection by shedding and dissection. The cercariae were identified using morphology and molecular methods, including PCR with a species-specific primer and a Bayesian phylogenetic analysis of ITS2 sequences. Bithynia siamensis siamensis was found in almost all sampling localities, with different quantities and detected frequencies. From a total of 7473 B. s. siamensis specimens, O. viverrini s.l. infections were detected in the Northern Bangkok, Muang Nakhon Pathom, Krathum Baen, and Lam Luk Ka areas with an overall prevalence of 0.05% (4/7473) and prevalence of 0.22% (1/455), 0.21% (1/469), 0.40% (1/253), and 0.16% (1/614) in individual localities with positive snails, respectively. This study is the first investigation of digenean infection in the canal network system-type habitat in Thailand and revealed extremely low O. viverrini s.l. prevalence.

A new second intermediate host and phylogenetic relationships based on the ITS2 sequence of Isoparorchis sp. (Digenea: Isoparorchiidae) in Thailand

The genus Isoparorchis (Family: Isoparorchiidae) contains trematodes infecting the air bladder of freshwater catfishes in Asia and Australia. Isoparorchis spp. rely on freshwater shrimps and fishes as intermediate hosts. There is limited information about parasitic infections in freshwater shrimp in Thailand, and Isoparorchis infection in an intermediate host in this country has never been reported. Thus, this study reports infections in freshwater shrimp (Macrobrachium lanchesteri and Caridina sp.), including overall prevalence, mean intensity, morphological characters and molecular analyses. The parasite specimens were analysed by studying their morphological characters, together with a molecular approach based on internal transcribed spacer 2 (ITS2) sequence data. The overall prevalence and mean intensity of Isoparorchis infections were 92% and 1.89, respectively. The metacercariae were identified as Isoparorchis sp. based on their morphological characters and supported by the comparison with published ITS2 sequences of Isoparorchis species. The phylogenetic studies based on the ITS2 region demonstrated that all of the Isoparorchis sp. specimens in this study are distinct from Isoparorchis species in previous reports. Moreover, we show for the first time that the freshwater shrimp M. lanchesteri serves as a second intermediate host of Isoparorchis sp. and we provide a morphological description and molecular characterization of Isoparorchis sp. metacercariae based on ITS2 sequence data to clarify the status of Isoparorchis sp. in Thailand.

Cattle as natural host for Schistosoma haematobium (Bilharz, 1852) Weinland, 1858 x Schistosoma bovis Sonsino, 1876 interactions, with new cercarial emergence and genetic patterns

Schistosomiasis remains a parasitic infection which poses serious public health consequences around the world, particularly on the African continent where cases of introgression/hybridization between human and cattle schistosomiasis are being discovered on a more frequent basis in humans, specifically between Schistosoma haematobium and S. bovis. The aim of this paper is to analyze the occurrence of S. bovis in cattle and its relationship with S. haematobium in an area where cattle and humans share the same site in Benin (West Africa). We used the chronobiology of cercarial emergence as an ecological parameter and both molecular biology (COI mtDNA and ITS rDNA) of the larvae and morphology of the eggs as taxonomic parameters. The results showed a chronobiological polymorphism in the cercarial emergence rhythm. They showed for the first time the presence of S. bovis in Benin, the presence of introgressive hybridization between S. bovis and S. haematobium in domestic cattle, and the presence of atypical chronobiological patterns in schistosomes from cattle, with typical S. haematobium shedding pattern, double-peak patterns, and nocturnal patterns. Our results showed that the chronobiological life-history trait is useful for the detection of new hosts and also may reveal the possible presence of introgressive hybridization in schistosomes. Our results, for the first time, place cattle as reservoir host for S. haematobium and S. bovis x S. haematobium. The consequences of these results on the epidemiology of the disease, the transmission to humans, and the control of the disease are very important.

High prevalence of Schistosoma haematobium × Schistosoma bovis hybrids in schoolchildren in Côte d'Ivoire

Schistosomiasis is a neglected tropical disease, though it is highly prevalent in many parts of sub-Saharan Africa. While Schistosoma haematobium-bovis hybrids have been reported in West Africa, no data about Schistosoma hybrids in humans are available from Côte d'Ivoire. This study aimed to identify and quantify S. haematobium-bovis hybrids among schoolchildren in four localities of Côte d'Ivoire. Urine samples were collected and examined by filtration to detect Schistosoma eggs. Eggs were hatched and 503 miracidia were individually collected and stored on Whatman® FTA cards for molecular analysis. Individual miracidia were molecularly characterized by analysis of mitochondrial cox1 and nuclear internal transcribed spacer 2 (ITS 2) DNA regions. A mitochondrial cox1-based diagnostic polymerase chain reaction was performed on 459 miracidia, with 239 (52.1%) exhibiting the typical band for S. haematobium and 220 (47.9%) the S. bovis band. The cox1 and ITS 2 amplicons were Sanger sequenced from 40 randomly selected miracidia to confirm species and hybrids status. Among the 33 cox1 sequences analysed, we identified 15 S. haematobium sequences (45.5%) belonging to seven haplotypes and 18 S. bovis sequences (54.5%) belonging to 12 haplotypes. Of 40 ITS 2 sequences analysed, 31 (77.5%) were assigned to pure S. haematobium, four (10.0%) to pure S. bovis and five (12.5%) to S. haematobium-bovis hybrids. Our findings suggest that S. haematobium-bovis hybrids are common in Côte d'Ivoire. Hence, intense prospection of domestic and wild animals is warranted to determine whether zoonotic transmission occurs.

No barrier breakdown between human and cattle schistosome species in the Senegal River Basin in the face of hybridisation

Schistosomiasis is widely distributed along the Senegal River Basin (SRB), affecting both the human population and their livestock. Damming of the Senegal River for irrigation purposes in the 1980s induced ecological changes that resulted in a large outbreak of Schistosoma mansoni, followed a few years later by an increase and spread of Schistosoma haematobium infections. The presence of hybrid crosses between the human and cattle schistosomes, S. haematobium and Schistosoma bovis, respectively, is adding complexity to the disease epidemiology in this area, and questions the strength of the species boundary between these two species. This study aimed to investigate the epidemiology of S. haematobium, S. bovis and their hybrids along the Senegal River basin using both microsatellite genetic markers and analysis of mitochondrial and nuclear DNA markers. Human schistosome populations with a S. haematobium cox1 mtDNA profile and those with a S. bovis cox1 mtDNA profile (the so-called hybrids) appear to belong to a single randomly mating population, strongly differentiated from the pure S. bovis found in cattle. These results suggest that, in northern Senegal, a strong species boundary persists between human and cattle schistosome species and there is no prolific admixing of the populations. In addition, we found that in the SRB S. haematobium was spatially more differentiated in comparison to S. mansoni. This may be related either to the presence and susceptibility of the intermediate snail hosts, or to the colonisation history of the parasite.

Phylogenetic studies of larval digenean trematodes from freshwater snails and fish species in the proximity of Tshwane metropolitan, South Africa

The classification and description of digenean trematodes are commonly accomplished by using morphological features, especially in adult stages. The aim of this study was to provide an analysis of the genetic composition of larval digenean trematodes using polymerase chain reaction (PCR) and sequence analysis. Deoxyribonucleic acid (DNA) was extracted from clinostomatid metacercaria, 27-spined echinostomatid redia, avian schistosome cercaria and strigeid metacercaria from various dams in the proximity of Tshwane metropolitan, South Africa. Polymerase chain reaction was performed using the extracted DNA with primers targeting various regions within the larval digenean trematodes' genomes. Agarose gel electrophoresis technique was used to visualise the PCR products. The PCR products were sequenced on an Applied Bioinformatics (ABI) genetic analyser platform. Genetic information obtained from this study had a higher degree of discrimination than the morphological characteristics of seemingly similar organisms.

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.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3307-0) contains supplementary material, which is available to authorized users.

Barcoding hybrids: heterogeneous distribution of Schistosoma haematobium × Schistosoma bovis hybrids across the Senegal River Basin

Hybridization events between Schistosoma species (Digenea, Platyhelminthes) are reported with increasing frequency, largely due to improved access to molecular tools. Nevertheless, little is known about the distribution and frequency of hybrid schistosomes in nature. Screening for hybrids on a large scale is complicated by the need for nuclear and mitochondrial sequence information, precluding a 'simple' barcoding approach. Here we aimed to determine and understand the spatiotemporal distribution of Schistosoma haematobium × Schistosoma bovis hybrids in the Senegal River Basin. From ten villages, distributed over the four main water basins, we genotyped a total of 1236 schistosome larvae collected from human urine samples using a partial mitochondrial cox1 fragment; a subset of 268 parasites was also genotyped using ITS rDNA. Hybrid schistosomes were unevenly distributed, with substantially higher numbers in villages bordering Lac de Guiers than in villages from the Lampsar River and the Middle Valley of the Senegal River. The frequency of hybrids per village was not linked with the prevalence of urinary schistosomiasis in that village. However, we did find a significant positive association between the frequency of hybrids per village and the prevalence of Schistosoma mansoni. We discuss the potential consequences of adopting a barcoding approach when studying hybrids in nature.

The substructure of three repetitive DNA regions of Schistosoma haematobium group species as a potential marker for species recognition and interbreeding detection

Background

Schistosoma haematobium is the causative agent of human urogenital schistosomiasis affecting ~112 million people in Africa and the Middle East. The parasite is transmitted by snails of the genus Bulinus, which also transmit other closely related human and animal schistosomes. The accurate discrimination of S. haematobium from species infecting animals will aid effective control and elimination programs. Previously we have shown the utility of different repetitive nuclear DNA sequences (DraI, sh73bp, and sh77bp) for the identification of S. haematobium-group species and inter-repeat sequences for discriminating S. haematobium from S. bovis.

Results

In this current study we clarify the structural arrangement and association between the three repetitive sequences (DraI, sh73bp, and sh77bp) in both S. haematobium and S. bovis, with a unique repeat linker being found in S. haematobium (Sh64bp repeat linker) and in S. bovis (Sb30bp repeat linker). Sequence data showed that the 3′-end of the repeat linker was connected to the DraI repetitive sequence array, and at the 5′-end of the repeat linker sh73bp and sh77bp were arranged in an alternating manner. Species-specific oligonucleotides were designed targeting the species-specific repeat linkers and used in a reverse line blot (RLB) hybridization assay enabling differentiation between S. haematobium and S. bovis. The assay was used to discriminate natural infections in wild caught Bulinus globosus.

Conclusion

This research enabled the characterisation of species-specific DNA regions that enabled the design of species-specific oligonucleotides that can be used to rapidly differentiate between S. haematobium and S. bovis and also have the potential to aid the detection of natural hybridization between these two species.

A review of bovine fasciolosis and other trematode infections in Nigeria

Trematode infections cause serious economic losses to livestock worldwide. Global production losses due to fasciolosis alone exceed US$3 billion annually. Many trematode infections are also zoonotic and thus a public health concern. The World Health Organization has estimated that about 56 million people worldwide are infected by at least one zoonotic trematode species, and up to 750 million people are at risk of infection. Fasciolosis caused by the fluke Fasciola gigantica is endemic in Nigeria and is one of the most common causes of liver condemnation in abattoirs. Total cattle losses from Fasciola infection in Nigeria have been estimated to cost £32.5 million. Other trematode infections of cattle, including paramphistomosis, dicrocoeliasis and schistosomiasis, have all been reported in various parts of Nigeria, with varying prevalence. Most publications on trematode infections are limited to Nigerian local and national journals, with very few international reports. This paper therefore summarized the current data on distribution, control and zoonotic trematode infections in Nigeria and other African countries. We also identified research gaps and made recommendations for future research and areas for funding for policy/planning.

Morphological Characteristics and Phylogenetic Trends of Trematode Cercariae in Freshwater Snails from Nakhon Nayok Province, Thailand

The prevalence of cercarial infection in freshwater snails and their evolutionary trends were studied in Nakhon Nayok province, Thailand. A total of 2,869 individual snails were examined for parasitic infections. The results showed that 12 snail species were found to host larval stages of trematodes with an overall prevalence of 4.7%. The infected specimens included 7 types at the cercarial stage; cercariae, megalurous cercariae, echinostome cercariae, furcocercous cercariae, parapleurolophocercous cercariae, virgulate cercariae, and xiphidiocercariae. Regarding molecular identification, ITS2 sequence data of each larval trematode were analyzed, and a dendrogram was constructed using the neighbor-joining method with 10,000 replicates. The dendrogram was separated into 6 clades (order/family), including Echinostomatida/Echinostomatidae, Echinostomatida/Philophthalmidae, Opisthorchiida/Heterophyidae, Plagiorchiida/Prosthogonimidae, Plagiorchiida/Lecithodendriidae, and Strigeatida/Cyathocotylidae. These findings were used to confirm morphological characteristics and evolutionary trends of each type of cercariae discovered in Nakhon Nayok province. Furthermore, this investigation confirmed that the ITS2 data of cercariae could be used to study on phylogenetic relationships or to determine classification of this species at order and/or family level when possible.

Detecting hybridization in African schistosome species: does egg morphology complement molecular species identification?

Hybrid parasites may have an increased transmission potential and higher virulence compared to their parental species. Consequently, hybrid detection is critical for disease control. Previous crossing experiments showed that hybrid schistosome eggs have distinct morphotypes. We therefore compared the performance of egg morphology with molecular markers with regard to detecting hybridization in schistosomes. We studied the morphology of 303 terminal-spined eggs, originating from 19 individuals inhabiting a hybrid zone with natural crosses between the human parasite Schistosoma haematobium and the livestock parasite Schistosoma bovis in Senegal. The egg sizes showed a high variability and ranged between 92·4 and 176·4 µm in length and between 35·7 and 93·0 µm in width. No distinct morphotypes were found and all eggs resembled, to varying extent, the typical S. haematobium egg type. However, molecular analyses on the same eggs clearly showed the presence of two distinct partial mitochondrial cox1 profiles, namely S. bovis and S. haematobium, and only a single nuclear ITS rDNA profile (S. haematobium). Therefore, in these particular crosses, egg morphology appears not a good indicator of hybrid ancestry. We conclude by discussing strengths and limitations of molecular methods to detect hybrids in the context of high-throughput screening of field samples.

Nucleic acid detection in the diagnosis and prevention of schistosomiasis

Schistosomiasis is an important zoonotic parasitic disease that causes serious harms to humans and animals. Surveillance and diagnosis play key roles in schistosomiasis control, however, current techniques for surveillance and diagnosis of the disease have limitations. As genome data for parasites are increasing, novel techniques for detection incorporating nucleotide sequences are receiving widespread attention. These sensitive, specific, and rapid detection methods are particularly important in the diagnosis of low-grade and early infections, and may prove to have clinical significance. This paper reviews the progress of nucleic acid detection in the diagnosis and prevention of schistosomiasis, including such aspects as the selection of target genes, and development and application of nucleic acid detection methods.

Molecular characterization of Stictodora tridactyla (Trematoda: Heterophyidae) from Kuwait Bay using rDNA ITS and mtCO1

Stictodora tridactyla is an intestinal fluke in the family Heterophyidae that parasitizes shorebirds and mammals, including humans. Its metacercarial cyst stage was reported in the Arabian killifish, Aphanius dispar, at Kuwait Bay. In the present study, Cerithidea cingulata was found to serve as the first intermediate host of S. tridactyla. In order to establish the snail-fish link in the life cycle of S. tridactyla, complete sequences of ribosomal DNA internal transcribed spacer region 1 and 2 (rDNA ITS1 and ITS2) and partial sequence of cytochrome oxidase subunit 1 were obtained for metacercarial cysts isolated from the fish A. dispar and rediae isolated from the snail C. cingulata. Sequence alignment demonstrated that these larval stages belong to the same heterophyid species, S. tridactyla. Phylogenetic analysis based on rDNA ITS1, ITS2, and mtCO1 confirmed the position of S. tridactyla within the Heterophyidae and found it to cluster with Haplorchis spp. The present study represents the first molecular study correlating the larval stages of S. tridactyla using rDNA ITS1, ITS2, and mtCO1 and examining the phylogenetic relationships of S. tridactyla with different heterophyid species.

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.

Developmental and Phylogenetic Characteristics of Stellantchasmus falcatus (Trematoda: Heterophyidae) from Thailand

This study aimed to investigate the infection status, worm development, and phylogenetic characteristics of the intestinal trematode, Stellantchasmus falcatus. The metacercariae of S. falcatus were detected only in the half-beak (Dermogenus pusillus) out of the 4 fish species examined. Their prevalence was 90.0%, and the intensity of infection was 919 metacercariae on average. Worms were recovered from 33 (97.1%) of 34 chicks that were experimentally infected with 200 S. falcatus metacercariae each, and the average recovery rate was 43.0%. The body size and inner organs of S. falcatus quickly increased in the experimental chicks over days 1-2 post-infection (PI). In addition, ITS2 sequence data of this parasite were analyzed to examine the phylogenetic relationships with other trematodes using the UPGMA method. The results indicated that the ITS2 sequence data recorded from trematodes in the family Heterophyidae appeared to be monophyletic. This study concluded that D. pusillus serves as a compatible second intermediate host of S. falcatus in Thailand and that S. falcatus can develop rapidly in the experimental chicks. Data collected from this study can help to close the gap in knowledge regarding the epidemiology, biology, and phylogenetic characteristics of S. falcatus in Thailand.

Problematic barcoding in flatworms: A case-study on monogeneans and rhabdocoels (Platyhelminthes)

Some taxonomic groups are less amenable to mitochondrial DNA barcoding than others. Due to the paucity of molecular information of understudied groups and the huge molecular diversity within flatworms, primer design has been hampered. Indeed, all attempts to develop universal flatworm-specific COI markers have failed so far. We demonstrate how high molecular variability and contamination problems limit the possibilities for barcoding using standard COI-based protocols in flatworms. As a consequence, molecular identification methods often rely on other widely applicable markers. In the case of Monogenea, a very diverse group of platyhelminth parasites, and Rhabdocoela, representing one-fourth of all free-living flatworm taxa, this has led to a relatively high availability of nuclear ITS and 18S/28S rDNA sequences on GenBank. In a comparison of the effectiveness in species assignment we conclude that mitochondrial and nuclear ribosomal markers perform equally well. In case intraspecific information is needed, rDNA sequences can guide the selection of the appropriate (i.e. taxon-specific) COI primers if available.

Hybridisation between the two major African schistosome species of humans

It is generally accepted that Schistosoma mansoni and Schistosoma haematobium, causing intestinal and urinary schistosomiasis, respectively, are not able to hybridise, due to the high phylogenetic distance between them. Cloning of nuclear internal transcribed spacer rDNA and partial mitochondrial cytochrome c oxidase 1 fragments revealed two internal transcribed spacer rDNA genotypes within single eggs and miracidia, one identical to S. mansoni and the other identical to S. haematobium, suggesting hybrid ancestry. The cytochrome c oxidase 1 clones always belonged to only one of the parental species. This demonstrates that offspring of heterologous pairing between these two species is not (always) parthenogenetic.

Molecular diagnosis of Schistosoma infections in urine samples of school children in Ghana

Recent studies using an internal transcribed spacer (ITS)-based real-time polymerase chain reaction (PCR) for the detection of Schistosoma DNA in urine samples has shown high sensitivity and specificity when performed on controls and known microscopy-positive samples. In this study, using 730 urine samples collected from children in five primary schools from different communities in the Greater Accra region of Ghana, specific detection of Schistosoma DNA showed excellent sensitivity of 100% and 85.2% in urines with > 50 eggs/10 mL urine and ≤ 50 eggs/10 mL of urine, respectively. Additionally, Schistosoma-specific DNA was amplified in 102 of 673 samples in which Schistosoma eggs could not be detected with microscopy. Taking microscopy and/or PCR-positive samples as true positives, the negative predictive value calculated was 94.6-100% for each school sampled as compared with 54.3-95.7% using microscopy. This ITS-based real-time PCR proves to be a powerful tool in epidemiological surveys of schistosomiasis providing more precise and sensitive results than microscopy.

PCR-based molecular discrimination between Maritrema eroliae and Probolocoryphe uca (Digenea: Microphallidae) in Kuwait Bay

Microphallid trematodes are common parasites in marine snails and crustacean hosts at Kuwait Bay. The larval stages of two microphallids, Maritrema eroliae and Probolocoryphe uca, are difficult to differentiate morphologically. In this study, two PCR-based techniques were established for quick and accurate discrimination between the larval stages of the two microphallid species, employing restriction fragment length polymorphism (PCR-RFLP) and species-specific primers. Both techniques utilized nucleotide differences in the second internal transcribed region (ITS2) of the ribosomal DNA (rDNA) in the two species. For the PCR-RFLP technique, restriction enzyme AvaII was selected and it generated different restriction profiles among the two microphallids. In addition, species-specific primers were prepared for each microphallid species that amplified distinctive fragments. Both techniques showed that the larval stages of the two microphallid species can be identified accurately. However, direct PCR amplification using species-specific primers was more advantageous than the PCR-RFLP technique since it allowed rapid and specific discrimination between the two species. This technique provides a useful tool that can be used in future studies for the study of the distribution of microphallid species and their definitive hosts at different localities of Kuwait Bay.