Detection of Fasciola gigantica infection in snails by polymerase chain reaction

Secondary Structure Analysis of Fasciola from Semi-wild Ruminants of Northeast India

PURPOSE

The objective of this study is to study the secondary structure analysis of Fasciola flukes from a rare mithun host from Manipur. Fascioliasis, a neglected tropical trematodiasis, is poorly studied in India and is widely believed to be predominantly caused by F. gigantica. Through this study, we want to assess the flukes from the rare semi-wild ruminants of Northeast India. This study is important as the mithun population is semi-wild and its population is declining in Manipur.

METHODS

Sample collected from the difficult and challenging terrain of Northeast India. The sample was collected from mithun and observed under the microscope. DNA was isolated, sequenced, and analyzed using various bioinformatics tools. The secondary structure analysis of the Internal Transcribed Spacer 2 (ITS2) region was also performed.

RESULTS

The secondary structure species tree corroborated the Bayesian inference and, hence, strengthened the phylogeny reconstructed. The annotated ITS2 sequence and RNA secondary of the Manipur isolate displayed the typical four-helix or four-domain model. Helix III reveals the presence of the UGGU motif with other deviations like UGG and GGU.

CONCLUSION

This is an in-depth analysis of the secondary structure of Fasciola species. The present study has demonstrated the usefulness of ITS2 and its secondary structures for characterizing parasites. The information on fascioliasis in the mithun's population presents itself useful with regards to their conservation strategy as their populations in both Manipur and Nagaland are dwindling.

Development of a loop-mediated isothermal amplification assay for detection of Austropeplea tomentosa from environmental water samples

Lymnaeid snails are key intermediate hosts for the development and survival of Fasciola spp., the causative agent of Fascioliasis which are economically important parasites infecting humans and livestock globally. The current control method for treating Fascioliasis is heavily reliant on anthelmintic drugs, particularly Triclabendazole (TCBZ) which has resulted in drug-resistant parasites and poses significant risk as there are no long-term efficacious alternatives available. Sustainable control measures at the farm level could include both parasite and snail control will play an important role in Fasciola spp. control and reduce the reliance on anthelmintic drugs. Implementation of such sustainable control measures requires effective identification of snails on the property however Lymnaeid snails are small and difficult to physically locate. Snail identification using an environmental DNA approach is a recent approach in which physically locating snails are not required. Austropeplea tomentosa, is the primary intermediate snail host for F. hepatica transmission in South-East Australia and we present an in-field loop-mediated isothermal amplification and water filtering method for the detection of A. tomentosa eDNA from water samples to improve current surveillance methods. This methodology is highly sensitive with a detection limit of 5 × 10^− 6 ng/μL, detected in < 20 minutes, with cumulative sample preparation and amplification time under 1 hour. This proposed workflow could assist in monitoring areas to determine the risk of Fascioliasis infection and implement strategies to manage snail populations to ultimately reduce the risk of infection for humans and livestock.

Buffalo Infection by Fasciola gigantica Transmitted by Radix acuminata in Uttar Pradesh, India: A Molecular Tool to Improve Snail Vector Epidemiology Assessments and Control Surveillance

PURPOSE

Fascioliasis is caused by Fasciola species transmitted by freshwater Lymnaeidae snails and infecting herbivorous mammals and humans worldwide. In southern Asia, fascioliasis is a problem in livestock from the Near East to Bangladesh, where recent human infection reports are worrying. In this region, Fasciola gigantica is transmitted by species of the Radix auricularia superspecies group. In the densely populated northern Indian state of Uttar Pradesh, livestock appears infected throughout. The economic importance of buffaloes highlights the need to control their very high infection rates.

METHODS

In the Gorakhpur area, a molecular method based on the two specific primer sets of genomic DNA was applied to fasciolids from buffaloes slaughtered in local abattoirs and cercariae from R. acuminata snails from freshwater collections.

RESULTS

PCR products and sequences demonstrated that the cercariae belonged to F. gigantica and that R. acuminata acts as vector for its transmission to buffaloes. The 72.0% rate found in one transmission focus appears to be the highest worldwide record of fasciolid infection in a lymnaeid population. Lymnaeid prevalences and burdens found close to human communities indicate a very high infection risk.

CONCLUSION

This method is simple, fast and cheap because there is no need for sequencing, it differentiates between fasciolid species and between fasciolids and other trematodes infecting R. acuminata, facilitates epidemiological surveys, and is useful for surveillance to evaluate the efficiency of control measures. Within climate change predictions, future increases of rain events and floods suggest the need for control and surveillance efforts in this endemic area.

Fasciolosis in India: An overview

Fasciolosis in ruminants is a relentless constraint in the livestock industry across the world. Immuno-prophylactic vaccines against fasciolosis may not come up in near future, rendering the control of this scourge with chemotherapy and snail population control. With the alarming threats of anti-fasciolid drug resistance reported from certain parts of the world; the control of fasciolosis should be directed towards the development of rapid and reliable diagnostic tools to execute the specific and discrete treatment. Understanding the epidemiology of Fasciola, its genomics and proteomics, host-parasite interplay, and advances in drug design research is vital for improving animal health that would ultimately succour to meet the ever-increasing demand for food. Due to possible differences in immune response depending on the species of the host and parasite, immuno-prophylactic studies in India should aim at achieving protective efficacy in buffalo against F. gigantica as workers from other countries concentrate primarily on vaccination of cattle and sheep against F. hepatica. This manuscript focused on the research that has been carried out in India for understanding the epidemiology, genetic diversity, immuno-diagnosis, and possible control measure in terms of immuno-prophylaxis and drug designing against tropical fasciolosis caused by Fasciola gigantica.

Development of a Molecular Snail Xenomonitoring Assay to Detect Schistosoma haematobium and Schistosoma bovis Infections in their Bulinus Snail Hosts

Schistosomiasis, a neglected tropical disease of medical and veterinary importance, transmitted through specific freshwater snail intermediate hosts, is targeted for elimination in several endemic regions in sub-Saharan Africa. Multi-disciplinary methods are required for both human and environmental diagnostics to certify schistosomiasis elimination when eventually reached. Molecular xenomonitoring protocols, a DNA-based detection method for screening disease vectors, have been developed and trialed for parasites transmitted by hematophagous insects, such as filarial worms and trypanosomes, yet few have been extensively trialed or proven reliable for the intermediate host snails transmitting schistosomes. Here, previously published universal and Schistosoma-specific internal transcribed spacer (ITS) rDNA primers were adapted into a triplex PCR primer assay that allowed for simple, robust, and rapid detection of Schistosoma haematobium and Schistosoma bovis in Bulinus snails. We showed this two-step protocol could sensitively detect DNA of a single larval schistosome from experimentally infected snails and demonstrate its functionality for detecting S. haematobium infections in wild-caught snails from Zanzibar. Such surveillance tools are a necessity for succeeding in and certifying the 2030 control and elimination goals set by the World Health Organization.

Development of a multiplex quantitative PCR assay for detection and quantification of DNA from Fasciola hepatica and the intermediate snail host, Austropeplea tomentosa, in water samples

Liver fluke (Fasciola hepatica) infection is an increasing threat to livestock production resulting in serious economic losses to the beef, dairy and sheep industries in Australia and globally. Triclabendazole (TCBZ) is the main drug used to control liver fluke infections in Australia and the widespread emergence of TCBZ resistance in cattle and sheep threatens liver fluke control. Alternative control measures to lower exposure of livestock to fluke infection would be useful to help preserve the usefulness of current chemical flukicides. Environmental DNA (eDNA) sampling methodology and associated molecular techniques are suited to rapidly assess the presence of pathogens on farms. In the present study, we developed a water sampling method in combination with a multiplex quantitative PCR assay to detect and quantify DNA of F. hepatica and Austropeplea tomentosa (A. tomentosa), a crucial intermediate snail host for liver fluke transmission in South-east Australia. The multiplex qPCR assay allows for the independent detection of F. hepatica and A. tomentosa DNA using specific primers and a probe targeting the ITS-2 region of the liver fluke or snail. The method allows the highly specific and sensitive (minimal DNA detection levels to 14-50 fg) detection of F. hepatica or A. tomentosa. The method allows the detection of both liver fluke and snail eDNA in water samples. The effective quantification of liver fluke and snail eDNA in water samples using this assay could potentially allow researchers to both identify and monitor F. hepatica transmission zones on farming properties in South-east Australia which will better inform control strategies, with potential application of the assay worldwide.

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.

Animal Fascioliasis: Perspectives from high altitudinal regions

The parasitic flukes of the genus Fasciola (Platyhelminthes: Trematoda: Digenea) cause fascioliasis or liver-rot disease in ruminant livestock in tropical and sub-tropical regions of the world. Classically, two species of Fasciola- F. hepatica and F. gigantica, are universally recognized as taxonomically valid species. Our survey studies on ovid and bovid animals including yak and mithun from high altitudinal mountainous regions in Northeast India revealed the occurrence of Fasciola gigantica and also Fasciola sp.- an intermediate form, at altitudes between 5000 and 14,085 feet above sea level (asl). Two morphotypes- F. hepatica - like and F. gigantica - like, of Fasciola species were reported from the high altitudinal areas of Northeast India; most of these locales constitute new-locality and first records for the occurrence of these liver flukes.

Fasciola hepatica infection in humans: overcoming problems for the diagnosis

Fascioliasis is a zoonosis actually considered as a foodborne trematode disease priority by the World Health Organization. Our study presents three cases of F. hepatica infection diagnosed by direct, indirect and/or imaging diagnostic techniques, showing the need of the combined use of them. In order to overcome some difficulties of the presently available methods we show for the first time the application of molecular tools to improve human fascioliasis diagnosis by employing a PCR protocol based on a repetitive element as target sequence. In conclusion, diagnosis of human fascioliasis has to be carried out by the combination of diagnostic techniques that allow the detection of infection in different disease phases, different epidemiological situations and known/new transmission patterns in the actual scenario.

Reprint of "An overview of freshwater snails in Asia with main focus on Vietnam"

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

An overview of freshwater snails in Asia with main focus on Vietnam

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

New insight in lymnaeid snails (Mollusca, Gastropoda) as intermediate hosts of Fasciola hepatica (Trematoda, Digenea) in Belgium and Luxembourg

BACKGROUND

The present study aims to assess the epidemiological role of different lymnaeid snails as intermediate hosts of the liver fluke Fasciola hepatica in Belgium and Luxembourg.

METHODS

During summer 2008, 7103 lymnaeid snails were collected from 125 ponds distributed in 5 clusters each including 25 ponds. Each cluster was located in a different biogeographic area of Belgium and Luxembourg. In addition, snails were also collected in sixteen other biotopes considered as temporary wet areas. These snails were identified as Galba truncatula (n = 2474) (the main intermediate host of F. hepatica in Europe) and Radix sp. (n = 4629). Moreover, several biological and non-biological variables were also recorded from the different biotopes. DNA was extracted from each snail collected using Chelex® technique. DNA samples were screened through a multiplex PCR that amplifies lymnaeid internal transcribed spacer 2 gene sequences (500-600 bp) (acting as an internal control) and a 124 bp fragment of repetitive DNA from Fasciola sp.

RESULTS

Lymnaeid snails were found in 75 biotopes (53.2%). Thirty individuals of G. truncatula (1.31%) and 7 of Radix sp. (0.16%) were found to be positive for Fasciola sp. The seven positive Radix sp. snails all belonged to the species R. balthica (Linnaeus, 1758). Classification and regression tree analysis were performed in order to better understand links and relative importance of the different recorded factors. One of the best explanatory variables for the presence/absence of the different snail species seems to be the geographic location, whereas for the infection status of the snails no obvious relationship was linked to the presence of cattle.

CONCLUSIONS

Epidemiological implications of these findings and particularly the role of R. balthica as an alternative intermediate host in Belgium and Luxembourg were discussed.

Development and evaluation of a single-step duplex PCR for simultaneous detection of Fasciola hepatica and Fasciola gigantica (family Fasciolidae, class Trematoda, phylum Platyhelminthes)

A single-step multiplex PCR (here referred to as a duplex PCR) has been developed for simultaneous detection and diagnosis of Fasciola hepatica and F. gigantica. These species overlap in distribution in many countries of North and East Africa and Central and Southeast Asia and are similar in egg morphology, making identification from fecal samples difficult. Based on a comparative alignment of mitochondrial DNA (mtDNA) spanning the region of cox1-trnT-rrnL, two species-specific forward primers were designed, FHF (for F. hepatica) and FGF (for F. gigantica), and a single reverse primer, FHGR (common for both species). Conventional PCR followed by sequencing was applied using species-specific primer pairs to verify the specificity of primers and the identity of Fasciola DNA templates. Duplex PCR (using three primers) was used for testing with the DNA extracted from adult worms, miracidia, and eggs, producing amplicons of 1,031 bp for F. hepatica and 615 bp for F. gigantica. The duplex PCR failed to amplify from DNA of other common liver and intestinal trematodes, including two opisthorchiids, three heterophyids, an echinostomid, another fasciolid, and a taeniid cestode. The sensitivity assay showed that the duplex PCR limit of detection for each Fasciola species was between 0.012 ng and 0.006 ng DNA. Evaluation using DNA templates from 32 Fasciola samples (28 adults and 4 eggs) and from 25 field-collected stools of ruminants and humans revealed specific bands of the correct size and the presence of Fasciola species. This novel mtDNA duplex PCR is a sensitive and fast tool for accurate identification of Fasciola species in areas of distributional and zonal overlap.

Recovery of Fascioloides magna (Digenea) population in spite of treatment programme? Screening of Galba truncatula (Gastropoda, Lymnaeidae) from Lower Austria

During the past decade, Fascioloides magna, the large American liver fluke, has spread within free-living deer in wetlands of the Danube in Lower Austria. The aim of this study was to determine the current infection rates with F. magna and other digenean parasites in the intermediate host snail Galba truncatula from risk areas in Lower Austria. A total of 3444 G. truncatula were collected and examined microscopically for the presence of digenean trematodes. A set of randomly selected snails and isolated trematode stages were also investigated molecular biologically by PCR and sequencing. Digenean parasites were detected with a prevalence of 2.41% (1.83% Paramphistomoidea; 0.46% Echinostomatoidea; 0.09% Strigeida; 0.06% Plagiorchiida). F. magna was found with an overall prevalence of 0.23%, which may indicate a recovery of the parasite population in spite of an ongoing triclabendazole treatment programme. Moreover, high risk areas and a seasonality of infections were observed.

Genetic characterization, species differentiation and detection of Fasciola spp. by molecular approaches

Liver flukes belonging to the genus Fasciola are among the causes of foodborne diseases of parasitic etiology. These parasites cause significant public health problems and substantial economic losses to the livestock industry. Therefore, it is important to definitively characterize the Fasciola species. Current phenotypic techniques fail to reflect the full extent of the diversity of Fasciola spp. In this respect, the use of molecular techniques to identify and differentiate Fasciola spp. offer considerable advantages. The advent of a variety of molecular genetic techniques also provides a powerful method to elucidate many aspects of Fasciola biology, epidemiology, and genetics. However, the discriminatory power of these molecular methods varies, as does the speed and ease of performance and cost. There is a need for the development of new methods to identify the mechanisms underpinning the origin and maintenance of genetic variation within and among Fasciola populations. The increasing application of the current and new methods will yield a much improved understanding of Fasciola epidemiology and evolution as well as more effective means of parasite control. Herein, we provide an overview of the molecular techniques that are being used for the genetic characterization, detection and genotyping of Fasciola spp..

A fluorescence-based polymerase chain reaction-linked single-strand conformation polymorphism (F-PCR-SSCP) assay for the identification of Fasciola spp

The present study aimed to establish a fluorescence-based polymerase chain reaction-linked single-strand conformation polymorphism (F-PCR-SSCP) assay for the identification of Fasciola spp. Based on the sequences of the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA, we designed a set of genus-specific primers for the amplification of Fasciola ITS-2, with an estimated size of 140 bp. These primers were labelled by fluorescence dyes, and the PCR products were analyzed by capillary electrophoresis under non-denaturing conditions (F-PCR-SSCP). Capillary electrophoresis analysis of the fluorescence-labelled DNA fragments displayed three different peak profiles that allowed the accurate identification of Fasciola species: one single peak specific for either Fasciola hepatica or Fasciola gigantica and a doublet peak corresponding to the "intermediate" Fasciola. Validation of our novel method was performed using Fasciola specimens from different host animals from China, Spain, Nigeria, and Egypt. This F-PCR-SSCP assay provides a rapid, simple, and robust tool for the identification and differentiation between Fasciola spp.

Bridging gaps in the molecular phylogeny of the Lymnaeidae (Gastropoda: Pulmonata), vectors of Fascioliasis

Background

Lymnaeidae snails play a prominent role in the transmission of helminths, mainly trematodes of medical and veterinary importance (e.g., Fasciola liver flukes). As this family exhibits a great diversity in shell morphology but extremely homogeneous anatomical traits, the systematics of Lymnaeidae has long been controversial. Using the most complete dataset to date, we examined phylogenetic relationships among 50 taxa of this family using a supermatrix approach (concatenation of the 16 S, ITS-1 and ITS-2 genes, representing 5054 base pairs) involving both Maximum Likelihood and Bayesian Inference.

Results

Our phylogenetic analysis demonstrates the existence of three deep clades of Lymnaeidae representing the main geographic origin of species (America, Eurasia and the Indo-Pacific region). This phylogeny allowed us to discuss on potential biological invasions and map important characters, such as, the susceptibility to infection by Fasciola hepatica and F. gigantica, and the haploid number of chromosomes (n). We found that intermediate hosts of F. gigantica cluster within one deep clade, while intermediate hosts of F. hepatica are widely spread across the phylogeny. In addition, chromosome number seems to have evolved from n = 18 to n = 17 and n = 16.

Conclusion

Our study contributes to deepen our understanding of Lymnaeidae phylogeny by both sampling at worldwide scale and combining information from various genes (supermatrix approach). This phylogeny provides insights into the evolutionary relationships among genera and species and demonstrates that the nomenclature of most genera in the Lymnaeidae does not reflect evolutionary relationships. This study highlights the importance of performing basic studies in systematics to guide epidemiological control programs.

Specific PCR-based assays for the identification of Fasciola species: their development, evaluation and potential usefulness in prevalence surveys

Among the helminths infecting ruminants in China are three taxa belonging to the genus Fasciola: F. hepatica, F. gigantica and the so-called 'intermediate form' that appears to lie between these two species. Based on the sequences of the second internal-transcribed spacers (ITS-2) within the parasites' nuclear ribosomal DNA (rDNA), a pair of primers (DSJf/DSJ3) specific for F. hepatica and a pair (DSJf/DSJ4) specific for F. gigantica were designed and used to develop PCR-based assays. These assays allowed the identification and differentiation of F. hepatica, F. gigantica and the 'intermediate' Fasciola, with no amplicons produced from heterologous DNA samples. The results of sequencing confirmed the species-specific identity of the amplified products. The assays showed good sensitivity, giving positive results with as little as 0.11 ng of F. hepatica DNA and 0.35 ng of F. gigantica DNA. This meant that the DNA from a single Fasciola egg or a single infected snail was sufficient for identification of the Fasciola taxon. The developed PCR assays could provide useful tools for the detection, identification and epidemiological investigation of Fasciola infection in humans, other mammals and snails.

The distribution of Fasciola hepatica and Fasciola gigantica within southern Tanzania--constraints associated with the intermediate host

In East Africa, Fasciola gigantica is generally the causative agent of fasciolosis but there have been reports of F. hepatica in cattle from highland regions of Kenya, Ethiopia, Uganda and Zaire. The topography of the Southern Highlands of Tanzania provides an environment where the climatic conditions exist for the sustenance of lymnaeid species capable of supporting both Fasciola hepatica and F. gigantica. Theoretically this would allow interaction between fasciolid species and the possible creation of hybrids. In this report we present molecular data confirming the existence of the snail, Lymnaea truncatula, at high altitude on the Kitulo Plateau of the Southern Highlands, Tanzania, along with morphometric and molecular data confirming the presence of F. hepatica in the corresponding area. At lower altitudes, where climatic conditions were unfavourable for the existence of L. truncatula, the presence of its sister species L. natalensis was confirmed by molecular data along with its preferred fasciolid parasite, F. gigantica. Analysis based on a 618 bp sequence of the 28S rRNA gene did not reveal the presence of hybrid fasciolids in our fluke samples.

Trematode infections in freshwater snails and cattle from the Kafue wetlands of Zambia during a period of highest cattle-water contact

A total of 984 snails, comprising nine species, were collected from six areas in the Kafue wetlands between August and October 2003 to assess larval trematode infections. Of these, 135 (13.7%) were positive. Most trematode infections were recorded from Lymnaea natalensis (42.8%), which harboured four of the five morphologically different cercariae found. No trematodes were recovered from Bellamya capillata, Biomphalaria pfeifferi, Melanoides tuberculata, Physa acuta and Cleopatra nswendweensis. One snail (0.2%) of 416 Bulinus snails shed brevifurcate-apharyngeate distome cercariae while three (0.7%) shed amphistomes. Gymnocephalous and longifurcate-pharyngeate distome were the commonest types of cercariae recorded while xiphidiocercaria was the least common. The highest prevalence rates of F. gigantica (68.8%) and amphistomes (50.0%) in cattle (n = 101) were in Chiyasa while those in Kaleya had the lowest (9.1 and 18.2%, respectively). In most habitats, infections were recorded in both cattle and snails. Critical determinants of infection may have been the distance of settlements and/or cattle kraals, the number of animals in nearby homesteads and the presence of susceptible host snails. This study suggests that fascioliasis and amphistomiasis could be major constraints of cattle production in the Kafue wetlands because favourable factors were available to introduce and maintain the infections. It further provides a starting point for some comprehensive studies on snail-related aspects of transmission and snail host ecology in Zambia.