Nuclear and mitochondrial DNA analysis reveals that hybridization between Fasciola hepatica and Fasciola gigantica occurred in China

Morphometric and Molecular Characterization of Fasciola spp. in Livestock From Northwestern Provinces of Iran

BACKGROUND

Liver flukes from the genus Fasciola are the causative agents for human and livestock fascioliasis. Accurate identification of Fasciola spp. is essential to understanding the epidemiology of fascioliasis. This study aimed to determine the morphometric and molecular characterization of Fasciola spp. in livestock from Northwestern provinces of Iran.

METHODS

Five hundred adult Fasciola flukes were obtained from different definitive hosts (cattle, sheep, goats, and buffaloes) in four local abattoirs in the northwestern provinces of Iran (West-Azerbaijan, East-Azerbaijan, Ardabil, and Zanjan) from September 2021 to August 2022. All samples were examined by morphometric criteria; then, 49 samples were identified using PCR-RFLP based on ITS1 region and 23 sequence of isolates analyzed by cox1 marker. PCR-RFLP methods compared morphometric results, and cox1 gene sequences were used to confirm PCR-RFLP results and phylogenetic analysis.

RESULTS

The differences between the body length, body width, cephalic cone length, cephalic cone width, body area, and distance between the ventral sucker and posterior end of the body in two species were significant (p < 0.05). Based on the morphometric criteria, 139 samples (27.8%) were identified as Fasciola gigantica and 361 (72.2%) as Fasciola hepatica. Similarly, PCR-RFLP analysis of ITS1 region confirmed morphometric results. No hybrid forms of Fasciola were detected. Partial sequences of cox1 showed 13 variable sites with eight haplotypes in F. hepatica and 12 variable sites with five haplotypes in F. gigantica.

CONCLUSION

Based on the results of this study, the PCR-RFLP method can be used to confirm the morphological method of Fasciola species, but it is insufficient to study their genetic diversity. Also, sequences of cox1 results of the present study showed that F. hepatica and F. gigantica species in the Northern provinces of Iran have different genetic structures and haplotypes.

Fasciola hepatica and Fasciola hybrid form co-existence in yak from Tibet of China: application of rDNA internal transcribed spacer

Fasciolosis is a parasitic disease affecting humans and livestock, caused by digenean trematodes of the genus Fasciola, primarily F. hepatica and F. gigantica. This study investigates the coexistence of these species and their hybrids in yaks from Tibet, China. We analyzed the nuclear rDNA internal transcribed spacer (ITS) regions, including ITS1 and ITS2, through Sanger sequencing and Next-Generation Sequencing (NGS) to assess single-nucleotide polymorphisms (SNPs). Our results reveal that one specimen (NM008B) is identical to pure F. hepatica, while another (NM008A) contains genetic information from both F. hepatica and F. gigantica, indicating potential hybridization or introgression. The morphological analysis reveals that the collected adult F. hepatica specimens exhibit distinct characteristics, while the hybrid specimens display "intermediate" features of F. hepatica and F. gigantica. This study is the first to document the coexistence of F. hepatica and hybrid Fasciola forms in a single yak. The findings underscore the complexities of hybridization dynamics and the necessity for advanced molecular techniques in accurately identifying Fasciola species. Future research should focus on mitochondrial DNA and other nuclear gene analysis to further elucidate the nature of these hybrids and their ecological implications.

Fumarate respiration of Fasciola flukes as a potential drug target

Fascioliasis is a neglected tropical zoonotic disease caused by liver flukes belonging to the genus Fasciola. The emergence of resistance to triclabendazole, the only World Health Organization-recommended drug for this disease, highlights the need for the development of new drugs. Helminths possess an anaerobic mitochondrial respiratory chain (fumarate respiration) which is considered a potential drug target. This study aimed to evaluate the occurrence of fumarate respiration in Fasciola flukes. We analyzed the properties of the respiratory chain of Fasciola flukes in both adults and newly excysted juveniles (NEJs). Fasciola flukes travel and mature through the stomach, bowel, and abdominal cavity to the liver, where oxygen levels gradually decline. High fumarate reductase activity was observed in the mitochondrial fraction of adult Fasciola flukes. Furthermore, rhodoquinone-10 (RQ10 Em'= -63 mV), a low-potential electron mediator used in fumarate respiration was found to be predominant in adults. In contrast, the activity of oxygen respiration was low in adults. Rotenone, atpenin A5, and ascochlorin, typical inhibitors of mitochondrial enzymes in complexes I, II, and III, respectively, inhibit the activity of each enzyme in the adult mitochondrial fraction. These inhibitors were then used for in vitro viability tests of NEJs. Under aerobic conditions, NEJs were killed by rotenone or ascochlorin, which inhibit aerobic respiration (complex I-III), whereas atpenin A5, which inhibits complex II involved in fumarate respiration, did not affect NEJs. Moreover, ubiquinone-10 (UQ10 Em'= +110 mV), which is used in oxidative respiration, was detected in NEJs, in addition to RQ10. In contrast, under anaerobic conditions, rotenone and atpenin A5, which inhibit fumarate respiration (complex I-II), were crucial for NEJs. These findings demonstrate that NEJs have active hybrid respiration, in which they can properly use both oxygen and fumarate respiration, depending on oxygen availability. Thus, fumarate respiration is a promising drug target for Fasciola flukes, because it plays an essential role in both adults and NEJs.

Genetic variation and population structure of Fasciola hepatica: an in silico analysis

Fasciola hepatica is a trematode leading to heavy economic setbacks to the livestock sector globally. The population's genetic information and intimate kinship level are frequently assessed using analysis of mitochondrial DNA. In this analysis, we retrieved cox1 (n = 247) and nad1 (n = 357) sequences of F. hepatica from the NCBI GenBank database and aligned the sequences with the respective reference sequences using MEGA software. The median joining network was drawn using PopArt software while neutrality and diversity indices were estimated with the help of DnaSp software. Neighbor-joining phylogenetic tree was constructed using the MEGA software package. A total of 46 and 98 distinctive haplotypes were observed for cox1 and nad1 genes, respectively. Diversity indices indicated high haplotype and nucleotide diversities in both genes. Positive Tajima's D and Fu's Fs values were found for the entire population of both the genes under study. The cox1 and nad1 gene segments in this study showed high Tajima's D values, suggesting a low likelihood of future population growth. The Tajima's D value of the nad1 gene sequence is lower (2.14910) than that of the cox1 gene sequence (3.40314), which suggests that the former is growing at a slower rate. However, the region-wise analysis revealed that both the cox1 and nad1 genes showed deviation from neutrality suggesting a recent population expansion as a result of an excess of low-frequency polymorphism. Furthermore, the overall host-wise analysis showed positive and significant Tajima's D values for the cox1 and nad1 gene sequences. To the best of our knowledge, this is the first attempt to provide insights into genetic variations and population structure of F. hepatica at a global scale using cox1 and nad1 genes. Our findings suggest the existence of specific variants of F. hepatica in different parts of the world and provide information on the molecular ecology of F. hepatica. The results of this study also mark a critical development in upcoming epidemiological investigations on F. hepatica and will also contribute to understanding the global molecular epidemiology and population structure of F. hepatica.

The complete mitochondrial genome of Ogmocotyle ailuri: gene content, composition and rearrangement and phylogenetic implications

Trematodes of the genus Ogmocotyle are intestinal flukes that can infect a variety of definitive hosts, resulting in significant economic losses worldwide. However, there are few studies on molecular data of these trematodes. In this study, the mitochondrial (mt) genome of Ogmocotyle ailuri isolated from red panda (Ailurus fulgens) was determined and compared with those from Pronocephalata to investigate the mt genome content, genetic distance, gene rearrangements and phylogeny. The complete mt genome of O. ailuri is a typical closed circular molecule of 14 642 base pairs, comprising 12 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes and 2 non-coding regions. All genes are transcribed in the same direction. In addition, 23 intergenic spacers and 2 locations with gene overlaps were determined. Sequence identities and sliding window analysis indicated that cox1 is the most conserved gene among 12 PCGs in O. ailuri mt genome. The sequenced mt genomes of the 48 Plagiorchiida trematodes showed 5 types of gene arrangement based on all mt genome genes, with the gene arrangement of O. ailuri being type I. Phylogenetic analysis using concatenated amino acid sequences of 12 PCGs revealed that O. ailuri was closer to Ogmocotyle sikae than to Notocotylus intestinalis. These data enhance the Ogmocotyle mt genome database and provide molecular resources for further studies of Pronocephalata taxonomy, population genetics and systematics.

Identification and prevalence of fluke infection in yak and Tibetan sheep around Qinghai Lake, China

Liver flukes (Fasciola spp.) and rumen flukes (Paramphistomum spp.) are significant parasites in livestock worldwide, and Fasciola spp. are considered an important zoonotic parasite. To our knowledge, there are no reports on fluke species identification and epidemiological prevalence in yak and Tibetan sheep around Qinghai Lake, China. Therefore, this study aimed to identify the major fluke species and determine the prevalence of fluke infections among yak and Tibetan sheep in this area. A total of 307 fecal samples were collected and fluke eggs identified using morphology and molecular methods. Our study is the first to display that the predominant fluke species were F. hepatica and P. leydeni in yak and Tibetan sheep around Qinghai Lake. The overall prevalence of fluke infections in yak and Tibetan sheep was 57.7% (177/307). Specifically, the prevalences of F. hepatica and P. leydeni were 15.0% (46/307) and 31.6% (97/307), respectively, and the co-infection of both species was 11.1% (34/307). No significant difference existed in the prevalence of overall fluke infection between yak and Tibetan sheep (p < 0.05). However, F. hepatica prevalence was significantly different in yak and Tibetan sheep (p < 0.05) but not P. leydeni. The findings of this study provide useful information about the current status of natural fluke invasion in yak and Tibetan sheep around Qinghai Lake, which could be important for monitoring and controlling these parasites in the region.

Sex-inducing effects toward planarians widely present among parasitic flatworms

Various parasitic flatworms infect vertebrates for sexual reproduction, often causing devastating diseases in their hosts. Consequently, flatworms are of great socioeconomic and biomedical importance. Although the cessation of parasitic flatworm sexual reproduction is a major target of anti-parasitic drug design, little is known regarding bioactive compounds controlling flatworm sexual maturation. Using the planarian Dugesia ryukyuensis, we observed that sex-inducing substances found in planarians are also widespread in parasitic flatworms, such as monogeneans and flukes (but not in tapeworms). Reverse-phase HPLC analysis revealed the sex-inducing substance(s) eluting around the tryptophan retention time in the fluke Calicophoron calicophorum, consistent with previous studies on the planarian Bipalium nobile, suggesting that the substance(s) is likely conserved among flatworms. Moreover, six of the 18 ovary-inducing substances identified via transcriptome and metabolome analyses are involved in purine metabolism. Our findings provide a basis for understanding and modifying the life cycles of various parasitic flatworms.

Potential Hybridization of Fasciola hepatica and F. gigantica in Africa-A Scoping Review

The occurrence of Fasciola gigantica and F. hepatica in Africa is well documented; however, unlike in Asia, there is a paucity of information on the existence of hybrids or parthenogenetic species on the continent. Nonetheless, these hybrid species may have beneficial characteristics, such as increased host range and pathogenicity. This study provides evidence of the potential existence of Fasciola hybrids in Africa. A literature search of articles published between 1980 and 2022 was conducted in PubMed, Google Scholar, and Science Direct using a combination of search terms and Boolean operators. Fasciola species were documented in 26 African countries with F. hepatica being restricted to 12 countries, whilst F. gigantica occurred in 24 countries, identified based on morphological features of adult Fasciola specimens or eggs and molecular techniques. The co-occurrence of both species was reported in 11 countries. However, the occurrence of potential Fasciola hybrids was only confirmed in Egypt and Chad but is suspected in South Africa and Zimbabwe. These were identified based on liver fluke morphometrics, assessment of the sperms in the seminal vesicle, and molecular techniques. The occurrence of intermediate host snails Galba truncatula and Radix natalensis was reported in Ethiopia, Egypt, South Africa, Tanzania, and Uganda, where F. hepatica and F. gigantica co-occurrences were reported. The invasive Pseudosuccinea columella snails naturally infected with F. gigantica were documented in South Africa and Egypt. In Zimbabwe, P. columella was infected with a presumed parthenogenetic Fasciola. This suggests that the invasive species might also be contributing to the overlapping distributions of the two Fasciola species since it can transmit both species. Notwithstanding the limited studies in Africa, the potential existence of Fasciola hybrids in Africa is real and might mimic scenarios in Asia, where parthenogenetic Fasciola exist in most Asian countries. In South Africa, aspermic F. hepatica and Fasciola sp. have been reported already, and Fasciola hybrids have been reported? in Chad and Egypt. Thus, the authors recommend future surveys using molecular markers recommended to identify Fasciola spp. and their snail intermediate hosts to demarcate areas of overlapping distribution where Fasciola hybrids and/or parthenogenetic Fasciola may occur. Further studies should also be conducted to determine the presence and role of P. columella in the transmission of Fasciola spp. in these geographical overlaps to help prevent parasite spillbacks.

Dispersal direction of Malaysian Fasciola gigantica from neighboring southeast Asian countries inferred using mitochondrial DNA analysis

Fasciola gigantica and hybrid Fasciola flukes, responsible for the disease fasciolosis, are found in Southeast Asian countries. In the present study, we performed molecular species identification of Fasciola flukes distributed in Terengganu, Malaysia using multiplex PCR for phosphoenolpyruvate carboxykinase (pepck) and PCR-restriction fragment length polymorphism (RFLP) for DNA polymerase delta (pold). Simultaneously, phylogenetic analysis based on mitochondrial NADH dehydrogenase subunit 1 (nad1) was performed for the first time on Malaysian Fasciola flukes to infer the dispersal direction among neighboring countries. A total of 40 flukes used in this study were identified as F. gigantica. Eight nad1 haplotypes were identified in the F. gigantica population of Terengganu. Median-joining network analysis revealed that the Malaysian population was related to those obtained from bordering countries such as Thailand and Indonesia. However, genetic differentiation was detected using population genetics analyses. Nevertheless, the nucleotide diversity (π) value suggested that F. gigantica with the predominant haplotypes was introduced into Malaysia from Thailand and Indonesia. The dispersal direction suggested by population genetics in the present study may not be fully reliable since Fasciola flukes were collected from a single location in one state of Malaysia. Further studies analyzing more samples from many locations are required to validate the dispersal direction proposed herein.

Multiplex PCR and Sequence Analysis to Investigate Genetic Diversity of Fasciola Isolates from Cattle and Sheep in Turkey

Fasciolosis is a highly prevalent helminthic infection caused by Fasciola hepatica and F. gigantica. With the aim of identifying hybrid Fasciola flukes, multiplex PCR was performed to amplify the pepck gene. Furthermore, to determine Fasciola haplotypes, mitochondrial nad1 gene was amplified and sequenced, and phylogenetic analyses were performed. Adult Fasciola isolates were collected from 51 cattle and 51 sheep, genomic DNA was isolated, and one-step multiplex PCR was subsequently performed to amplify pepck. Isolates that generated a 510 bp band were identified as F. gigantica, those that generated a 241 bp band were identified as F. hepatica, and those that generated both bands were identified as hybrid (aspermic) flukes. Multiplex PCR data identified four isolates as F. gigantica and 84 as F. hepatica. Fourteen hybrid isolates (five cattle and nine sheep) were identified. On unidirectional DNA sequence analysis of nad1 PCR products, three sequences were identified as F. gigantica and 99 as F. hepatica. In addition, only 4 of 87 haplotypes detected for F. hepatica nad1 sequences were found to be previously reported, while the remaining 83 are unique to this study. To summarize, this study is the first to report the existence of hybrid Fasciola flukes and 83 unique haplotypes of F. hepatica in Turkey.

Development of novel DNA marker for species discrimination of Fasciola flukes based on the fatty acid binding protein type I gene

Background

Multiplex polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (RFLP) for nuclear phosphoenolpyruvate carboxykinase (pepck) and polymerase delta (pold), respectively, have been used to differentiate Fasciola hepatica, F. gigantica, and hybrid Fasciola flukes. However, discrimination errors have been reported in both methods. This study aimed to develop a multiplex PCR based on a novel nuclear marker, the fatty acid binding protein type I (FABP) type I gene.

Methods

Nucleotide sequence variations of FABP type I were analyzed using DNA samples of F. hepatica, F. gigantica, and hybrid Fasciola flukes obtained from 11 countries in Europe, Latin America, Africa, and Asia. A common forward primer for F. hepatica and F. gigantica and two specific reverse primers for F. hepatica and F. gigantica were designed for multiplex PCR.

Results

Specific fragments of F. hepatica (290 bp) and F. gigantica (190 bp) were successfully amplified using multiplex PCR. However, the hybrid flukes contained fragments of both species. The multiplex PCR for FABP type I could precisely discriminate the 1312 Fasciola samples used in this study. Notably, no discrimination errors were observed with this novel method.

Conclusions

Multiplex PCR for FABP type I can be used as a species discrimination marker in place of pepck and pold. The robustness of the species-specific primer should be continuously examined using a larger number of Fasciola flukes worldwide in the future since nucleotide substitutions in the primer regions may cause amplification errors.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05538-7.

Population structure, molecular characterization, and phylogenetic analysis of Fasciola gigantica from two locations in Uganda

Fasciola gigantica is a major pathogen that causes fasciolosis in Africa. A recent study in Uganda demonstrated that Fasciola flukes were present in 65.7% of slaughtered cattle. However, molecular identification of Fasciola species has not yet been performed in the country. In the present study, 292 Fasciola flukes were collected from Kampala and Gulu, Uganda. The samples were identified as F. gigantica using a multiplex polymerase chain reaction (PCR) assay for phosphoenolpyruvate carboxykinase (pepck) and a PCR-restriction fragment length polymorphism (RFLP) assay for DNA polymerase delta (pold). A significant genetic difference between F. gigantica obtained from cattle slaughtered at Kampala and Gulu was observed by analyzing the mitochondrial markers NADH dehydrogenase subunit 1 (nad1) and cytochrome C oxidase subunit 1 (cox1). Fasciola collected from Gulu had a more diversified population than that collected from Kampala, probably because of differences in livestock management systems. One of the possible reasons for this observation is that cattle slaughtered in Gulu were reared under an extensive communal grazing system, which is suitable for maintaining parasite diversity, whereas cattle slaughtered in Kampala mainly originated from fenced/closed farms, which limits parasite diversity. However, the cause of the difference between these two locations was not clearly defined by the results of this study. The F. gigantica population from Uganda was related to that obtained from Zambia. A star-like phylogeny was detected in a median-joining network analysis, which indicated rapid population expansion and suggested that the F. gigantica populations from both countries are maintained by domestic ruminants in eastern Africa. Interestingly, the F. gigantica population from Uganda was not related to those from Egypt and Nigeria. The results of the present study suggest that F. gigantica populations in African countries are indigenous to each country or region.

Molecular characteristics and genetic diversity of Fasciola hepatica from sheep in Xinjiang, China

Introduction

Fasciola hepatica is a trematode infecting ruminants worldwide and occasionally affecting other animal species, including humans. It causes significant economic losses. Geographic distribution and patterns of infection must be considered before control and management measures are developed for this parasite. DNA molecular markers are useful for the identification of flukes and elucidation of their genetic evolution. Therefore, the population structure of F. hepatica was studied using this method in sheep in Xinjiang, China.

Material and Methods

The molecular characteristics, genetic relationships within the population and dispersal patterns of F. hepatica isolates were analysed based on the cox1 and nad1 genes. The population structure of F. hepatica from three regions of Xinjiang was explored and a neutrality test was conducted.

Results

The cox1 and nad1 genes have 21 and 42 variable sites, respectively, which can be classified into 34 and 33 haplotypes. Median-joining network and phylogenetic tree analyses showed that there was no significant variation in F. hepatica isolates between the three geographical regions. Analysis of variance revealed that the genetic variation of F. hepatica was mainly present within the populations. The neutrality test indicated that the populations were relatively stable but the Hami population may have undergone short-term expansion.

Conclusion

This study revealed for the first time the molecular characteristics, genetic diversity and dispersal patterns of F. hepatica isolates from sheep in Xinjiang, thus providing new insights into the genetic variation and haplotype diversity of F. hepatica from indigenous sheep.

The causative agents of fascioliasis in animals and humans: Parthenogenetic Fasciola in Asia and other regions

Parthenogenetic Fasciola is the causative agent of fascioliasis in animals and humans and is widely distributed in Asian countries, such as Japan, South Korea, China, Vietnam, Thailand, the Philippines, Myanmar, Bangladesh, Nepal, and India. Parthenogenetic Fasciola geographically originated from central and eastern China, where it exists between the habitats of Fasciola hepatica and Fasciola gigantica; it likely appeared thousands of years ago following hybridization between F. hepatica and F. gigantica. Parthenogenetic Fasciola consists of diploids and triploids that possess nuclear genome of both F. hepatica and F. gigantica and mitochondrial genome of either F. hepatica or F. gigantica. Maternal parents of parthenogenetic Fasciola are either F. hepatica having Fh-C4 haplotype or F. gigantica having Fg-C2 haplotype in mitochondrial NADH dehydrogenase subunit 1 (ND1) nucleotide sequences. Parthenogenetic Fasciola flukes with the Fh-C4 haplotype have spread from China to South Korea and Japan, whereas the flukes with the Fg-C2 haplotype have not only spread to Korea and Japan but also southward to Vietnam, Thailand, the Philippines, Myanmar, Bangladesh, Nepal, and India. Parthenogenetic Fasciola can be distinguished from F. hepatica and F. gigantica using combinational DNA sequence analysis of nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) along with mitochondrial ND1 markers. The establishment of parthenogenetic Fasciola is expected as follows: parthenogenetic diploids with the Fh-C4 and Fg-C2 haplotypes first appeared based on single or multiple interspecific hybridization events; subsequently, parthenogenetic triploids emerged via backcross events between the maternal parthenogenetic diploid and either paternal bisexual F. hepatica or F. gigantica. Parthenogenetic Fasciola diploids and triploids then survived for thousands of years by clonal parthenogenetic reproduction, and generated descendants with ND1 haplotypes, which were derived from the Fh-C4 and Fg-C2 due to nucleotide substitution. Thus, the emergence of parthenogenetic Fasciola may be due to extremely uncommon and accidental events. Parthenogenetic Fasciola should be treated as a new asexual hybrid species.

Identification of Fasciola spp. based on ITS-2 reveals the Fasciola gigantica infection in buffaloes in Nanning city, South China

Fasciolosis is harmful to ruminant husbandry worldwide. Given the superficial survey on Fasciolosis infection in Guangxi, the main buffalo breeding area in China, an in-depth investigation in the infection of buffaloes in Nanning, the capital of Guangxi Zhuang Autonomous Region, with Fasciola (Platyhelminthes: Trematoda: Digenea) species will provide a theoretical support for the control and prevention of Fasciolosis infection in buffaloes. Five water buffalo livers were collected from an abattoir in Nanning every 2 weeks from June 2018 to April 2019, and a total of 101 livers were obtained. All livers were then dissected to observe the liver lesions caused by the flukes. Afterwards, Fasciola spp. collected from Fasciolosis-infected livers were numbered and measured. Then, the livers infected with more than 3 flukes were marked, and 3 flukes were picked from each liver according to their morphological differences, such as body length (BL), body maximum width (BW) and length-width ratio (BL/BW). Moreover, these Fasciola spp. worms were selected for molecular biological analysis. The second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA (rDNA) was amplified by polymerase chain reaction (PCR) and sequenced. Finally, sequential and phylogenetic analyses were also performed. The infection rate was 38.6 % according to anatomic examination, and the livers infected by Fasciola spp. were damaged seriously. The principal manifestations were the enlargement of the liver and protrusion of the bile ducts. In some cases, the bile duct wall became inflamed and rough, in which some sediment such as phosphate could be easily found. After dissection, 1243 Fasciola spp. flukes were collected from 39 out of 101 livers. The morphometric measurements obtained from the present study showed that the BL/BW ranged from 1.42-10.25. However, it might vary considerably among different geographical locations and could not be used as an accurate method for the identification of Fasciola spp.. Analysis of the ITS-2 sequences showed that 83 out of 87 flukes had 100 % homology with each other, and the other 4 flukes with 99.3 % homology possessed a nucleotide polymorphism. A unique position (271) was detected in flukes in Nanning isolates. Phylogenetic analysis indicated that all the flukes were Fasciola gigantica, and no Fasciola hepatica or the intermediate form was found in this study.

Pathogenicity and virulence of the liver flukes Fasciola hepatica and Fasciola Gigantica that cause the zoonosis Fasciolosis

Fasciolosis caused by the liver flukes Fasciola hepatica and Fasciola gigantica is one of the most important neglected parasitic diseases of humans and animals. The ability of the parasites to infect and multiply in their intermediate snail hosts, and their adaptation to a wide variety of mammalian definitive hosts contribute to their high transmissibility and distribution. Within the mammalian host, the trauma caused by the immature flukes burrowing through the liver parenchyma is associated with most of the pathogenesis. Similarly, the feeding activity and the physical presence of large flukes in the bile ducts can lead to anemia, inflammation, obstruction and cholangitis. The high frequency of non-synonymous polymorphisms found in Fasciola spp. genes allows for adaptation and invasion of a broad range of hosts. This is also facilitated by parasite’s excretory-secretory (ES) molecules that mediate physiological changes that allows their establishment within the host. ES contains cathepsin peptidases that aid parasite invasion by degrading collagen and fibronectin. In the bile ducts, cathepsin-L is critical to hemoglobin digestion during feeding activities. Other molecules (peroxiredoxin, cathepsin-L and Kunitz-type inhibitor) stimulate a strong immune response polarized toward a Treg/Th2 phenotype that favors fluke’s survival. Helminth defense molecule, fatty acid binding proteins, Fasciola-specific glycans and miRNAs modulate host pro-inflammatory responses, while antioxidant scavenger enzymes work in an orchestrated way to deter host oxidant-mediated damage. Combining these strategies Fasciola spp. survive for decades within their mammalian host, where they reproduce and spread to become one of the most widespread zoonotic worm parasites in the world.

Molecular identification and genetic-polymorphism analysis of Fasciola flukes in Dali Prefecture, Yunnan Province, China

This study aimed to identify species of Fasciola flukes in Dali Prefecture (Yunnan Province, China) and analyze their genetic diversity. Fasciola flukes (n = 122) were collected from cattle livers in a farmers' market in Xiaguan Town, Dali Prefecture. Nucleotide sequences of ribosomal internal transcribed spacer (ITS) as well as nicotinamide adenine dinucleotide dehydrogenase subunit 1 (ND1) and mitochondrial cytochrome c oxidase subunit 1 (CO1) were amplified, sequenced, and subjected to homology analysis. The heterozygosity ratios of different ITS alleles were determined using the peak-height ratio of heterozygous loci. Multiplex PCR analysis of the nuclear protein coding gene, phosphoenolpyruvate carboxykinase (pepck), was used to identify Fasciola species. Multiple ND1 sequence alignments enabled further genetic diversity analysis of regional Fasciola flukes. Seven ITS sequences belonged to F. hepatica and 115 belonged to Fh/Fg heterozygous flukes. Sequencing analysis of heterozygous flukes revealed 11 heterozygous loci with double peaks, with significantly variable ratios among individuals. ND1 and CO1 results indicated that one specimen was identical to F. hepatica, while 121 specimens were identical to F. gigantica or contained one variable site. Multiplex PCR results for pepck showed that double bands for F. hepatica and F. gigantica were amplified from Dali Fasciola specimens; hence, they were all heterozygous. By combining ITS, ND1, and CO1 sequences with multiplex pepck PCR results, all 122 specimens were identified as Fh/Fg heterozygous Fasciola flukes. Our experimental results preliminarily confirmed a high degree of Fh/Fg heterozygosity among Fasciola flukes in the Dali area. Selecting multiple molecular markers for concurrent analysis will provide more comprehensive and accurate genetic information.

Enzyme-linked immunosorbent assay (ELISA) using recombinant Fasciola cathepsin L1 for the diagnosis of human fasciolosis caused by Fasciola hepatica/gigantica hybrid type

Recombinant Fasciola cathepsin L-1 (rCatL1) was evaluated in enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of human fasciolosis in Japan. Quality characteristics of the test were accessed by receiver operating characteristic (ROC) analysis, with sera from fasciolosis patients (n = 10), patients with no evidence of parasitic infections (n = 29), and patients with other helminth infections (n = 119). Both the sensitivity and specificity of the test achieved 100% with the control samples. To test the performance of the assay in an authentic situation, 311 serum samples, which had been sent to our laboratory for the diagnosis of parasitic infections from January 2018 to February 2019, were re-assessed using the rCatL1 ELISA. In this case, the sensitivity of the rCatL1 ELISA was 100%, giving positive results to all fasciolosis sera (n = 7), and the specificity was 99.0%, in which three of the 304 non-fasciolosis samples were judged positive. Careful re-examination of the laboratory data and medical imaging of these three patients revealed that one of the patients, who had been diagnosed as having larva migrans syndrome, was judged to be infected with Fasciola, in addition to ascarid nematodes. Thus the true specificity of the assay in the authentic reached 99.3% (302/304). As the rCatL1 ELISA exhibited a highly significant positive likelihood ratio (152.0) and negative likelihood ratio (0.0), calculated from the 311 sample data, this rCatL1 ELISA can be used for routine screening and definitive diagnosis test for fasciolosis in reference laboratories.

Molecular characterization and phylogenetic analyses of Fasciola gigantica of buffaloes and goats in Punjab, Pakistan

Fasciola gigantica is considered to be a major pathogen causing fasciolosis in the Indian subcontinent, resulting in production losses of millions of dollars in the livestock industry. Understading the dispersal origin and the patterns of spread of F. gigantica is important. A total of 53 Fasciola flukes collected from buffaloes and goats in Punjab, Pakistan between 2017 and 2018 were identified as F. gigantica based on the multiplex PCR for the phosphoenolpyruvate carboxykinase (pepck) and the PCR-restriction fragment length polymorphism (RFLP) for DNA polymerase delta (pold). A significant genetic difference between F. gigantica from buffaloes and goats was indicated by the genetic analyses of mitochondrial markers, NADH dehydrogenase subunit 1 (nad1) and cytochrome C oxidase subunit 1 (cox1). Phylogenetic analysis of the seventeen nad1 haplotypes of F. gigantica from Pakistan with those in neighbouring countries of the Indian subcontinent revealed that all the haplotypes identified in Pakistan were clustered in haplogroup A. fasciola gigantica with the eight haplotypes might be expanded in Pakistan from Indian origin, along with the migration of the domestic animals, since they were related to Indian haplotypes. In contrast, the remaining nine haplotypes were not shared with any neighbouring countries, suggesting independent origin, probably from neighbouring Middle East countries. However, cautious interpretation is required due to the very limited samples size of this study. Our study provides a proof of concept for a method that could be used to investigate the epidemiology of F. gigantica.

Prevalence and distribution of livestock schistosomiasis and fascioliasis in Côte d'Ivoire: results from a cross-sectional survey

BACKGROUND

Schistosoma and Fasciola are zoonotic parasites of public health and veterinary importance. However, while the epidemiology of schistosomiasis in humans is well studied, little is known about fascioliasis and schistosomiasis in livestock in Côte d'Ivoire. This study aimed to determine the prevalence and the distribution of livestock schistosomiasis and fascioliasis across Côte d'Ivoire. In 2018, we conducted a cross-sectional survey in abattoirs and farms in 13 departments of Côte d'Ivoire. In abattoirs, the mesenteric veins and livers of slaughtered cattle, sheep and goats were examined for adult Schistosoma and Fasciola flukes. Faeces from live cattle, goats and sheep were collected and examined for Schistosoma and Fasciola eggs using a sedimentation technique.

RESULTS

A total of 386 cattle, 174 goats and 151 sheep from abattoirs and 435 cattle, 22 goats and 176 sheep from farms were sampled. The observed prevalence of schistosomiasis was higher in slaughtered animals. Fascioliasis was more prevalent in farm animals. The prevalence of schistosomiasis in slaughtered cattle varied between 5.9% (95% confidence interval (CI): 0.7-19.7%) and 53.3% (95% CI: 37.9-68.3%) with the highest prevalence observed in Ouangolodougou in the North. Cattle from farms had a relatively low prevalence of schistosomiasis, with the highest prevalence found in Ouangolodougou (2.4%, 95% CI: 0.7-6.1%). The prevalence of fascioliasis varied considerably from one department to another, ranging from nil (95% CI: 0.0-18.5%) to 50.8% (95% CI: 43.4-58.2%), with the highest prevalence found in farm cattle in Dikodougou in the North. Sheep and goats had a lower prevalence of schistosomiasis and fascioliasis than cattle. In slaughtered animals, cattle aged 4 years and older were at highest risk for schistosomiasis (odds ratio (OR): 2.4; 95% CI: 1.0-5.6) and fascioliasis (OR: 2.1; 95% CI: 1.1-3.9). In farm animals, male cattle had higher odds of being infected with Schistosoma (OR: 4.3; 95% CI: 0.7-26.9) than females.

CONCLUSIONS

Our study confirms that schistosomiasis and fascioliasis are endemic in livestock across Côte d'Ivoire. A strategic control programme should be considered, especially for cattle, including providing drinking water in troughs to reduce faecal contamination of water sources by cattle.

Molecular characterization revealed Fasciola specimens in Ecuador are all Fasciola hepatica, none at all of Fasciola gigantica or parthenogenic Fasciola species

All 225 Fasciola flukes obtained from domestic animals (73 cattle, 7 sheep and 1 pig) of 18 distinct geographic areas in Ecuador-South America, were identified as Fasciola hepatica, based on molecular analyses of nuclear pepck and pold genes, and mitochondrial nad1gene as well as the morphological observation of sperm within the seminal vesicles. Fasciola gigantica and parthenogenic Fasciola forms endemic to Asian countries were not found in this study, although zebu cattle and water buffalos have introduced into South America from Asia; this could be due to the absence of suitable intermediate host snails. The results of pepck analysis using multiplex PCR developed previously showed that 32 of the flukes could not be confirmed as F. hepatica, suggesting that the method is unreliable for the accurate discrimination of F. hepatica, and that pepck gene of the species consists of multiple loci, not a single locus. The results of genetic diversity, phylogenetic, and network analyses based on mitochondrial nad1 sequences suggest that F. hepatica populations in South America, including Ecuador, formed from the ancestral F. hepatica individuals introduced into the continent along with anthropogenic movement of livestock infected with the species.

Molecular characterization and phylogenetic analysis of Fasciola hepatica from high- plateau and steppe areas in Algeria

A previous study based on mitochondrial DNA markers reported the presence of Fasciola hepatica in Algeria. However, a precise species identification is still required. In this report, a total of 68 Fasciola isolates, collected from high-plateau (Bordj-Bou-Arreridj) and steppe (Djelfa) areas of Algeria, were identified at the species level by multiplex PCR and PCR-restriction fragment length polymorphism (RFLP) for nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold), respectively. The result of the multiplex PCR conflicted with that of the PCR-RFLP; however, subsequent nucleotide sequencing of pepck clearly showed that all isolates should be classified as F. hepatica. The two mitochondrial markers, NADH dehydrogenase subunit I (nad1) and cytochrome c oxidase subunit 1 (cox1), revealed a close relationship between the parasite populations from the plateau and those from the steppe. A dispersal direction from the high plateau to the steppe was indicated because the former population was more diversified than the latter. Moreover, these populations were more closely related to populations from Spain than those from Egypt or Afghanistan. Given the population characteristic of F. hepatica in Spain and the history of cattle trade, it seems likely that the parasite was introduced to Algeria from Europe through a route across the Mediterranean Sea.

Fasciola Species Introgression: Just a Fluke or Something More?

The threats posed by a range of viral and bacterial zoonotic diseases inevitably receive renewed attention in the wake of global pandemic events due to their overt and devastating impacts on human health and the economy. Parasitic zoonoses, however, many of which affect millions of people each day, are frequently ignored. In the case of fasciolosis, caused by infection with Fasciola hepatica or Fasciola gigantica, this oversight has allowed for the expansion of areas of parasite sympatry and thus increased the incidence of hybridization and possible introgression between the two species. Here we highlight how an increased demand for animal-derived protein, combined with a lack of appropriate tools for detection of these events, is changing the status quo of these zoonotic parasites.

Increased demand for animal-derived protein from Fasciola hepatica-endemic countries has led to a growing number of reports of hybridization between F. hepatica and Fasciola gigantica in Southeast Asia.

Hybridization and eventual introgression have been reported in a range of protozoan, helminth, and arthropod parasites and act as important drivers of evolutionary change and adaptation.

Introgression between Fasciola spp. remains unproven but has potentially serious human and animal health consequences as seen in other parasites.

New tools for the characterization of hybridization and introgression events between Fasciola spp. are needed.

Genetic diversity of Fasciola hepatica in Spain and Peru

In the present study, molecular characterization of Fasciola flukes from Spain was performed to reveal the relation with the previously reported Peruvian F. hepatica population. The nuclear DNA markers, phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold), were used for species identification of Fasciola flukes. A total of 196 Fasciola flukes were identified as F. hepatica by pepck and pold, and 26 haplotypes were detected in mitochondrial NADH dehydrogenase subunit 1 (nad1). Only one of them was previously found in Spanish samples; which indicates the existence of high genetic diversity and population structure in F. hepatica from Spain. Three haplotypes were identical to those from Peruvian F. hepatica. The pairwise fixation index value confirmed a relatively close relationship between the Spanish and Peruvian F. hepatica samples. The Spanish samples showed clearly higher genetic variability than the Peruvian population. These results are discussed in relation with the hypothesis of the introduction of the parasite in America from Europe and recent evidence of pre-Hispanic F. hepatica from Argentina revealed by ancient DNA.

Multilocus approach reveals discordant molecular markers and corridors for gene flow between North African populations of Fasciola hepatica

Fasciolosis is a foodborne trematodosis characterised by a worldwide distribution. Various approaches have been developed for the study of the causative agents of this parasitic infection: Fasciola hepatica, Fasciola gigantica and the aspermic intermediated forms (hybrid and introgressed). In the present study, novel and common molecular markers (pepck and pold, ITS, CO1, ND1 and CO1-trnT-rrnL) were used to characterise Fasciola flukes from the Tunisian-Algerian border, to estimate the gene flow between these populations and to evaluate the reliability of different molecular markers. All nuclear and mitochondrial markers, apart from pepck, supported the monophyly of the studied flukes identified as F. hepatica. Multiplex PCR for pepck revealed three different genotypes corresponding to F. hepatica (pepck-Fh), F. gigantica (pepck-Fg) and the aspermic Fasciola flukes (pepck-Fh/Fg). Sequence analysis of pepck revealed high polymorphism, length variation, within this intronic marker. The observed inconsistencies were due to the position of the forward primer within the intronic region. Pepck sequences showed different level of heterozygosity and homozygosity with length polymorphisms in the introns. Pepck multiplex PCR patterns could not differentiate between Fasciola species. All studies based on only pepck multiplex PCR with mitochondrial markers should be revised. Nuclear and mitochondrial markers revealed an important gene flow between Tunisian and Algerian populations of F. hepatica. The combination of nuclear and mitochondrial sequence analysis is still the best method to distinguish these taxa. Effective measures are needed in order to better control cross-country illegal trade of vector.

Complex and dynamic transcriptional changes allow the helminth Fasciola gigantica to adjust to its intermediate snail and definitive mammalian hosts

BACKGROUND

The tropical liver fluke, Fasciola gigantica causes fasciolosis, an important disease of humans and livestock. We characterized dynamic transcriptional changes associated with the development of the parasite in its two hosts, the snail intermediate host and the mammalian definitive host.

RESULTS

Differential gene transcription analysis revealed 7445 unigenes transcribed by all F. gigantica lifecycle stages, while the majority (n = 50,977) exhibited stage-specific expression. Miracidia that hatch from eggs are highly transcriptionally active, expressing a myriad of genes involved in pheromone activity and metallopeptidase activity, consistent with snail host finding and invasion. Clonal expansion of rediae within the snail correlates with increased expression of genes associated with transcription, translation and repair. All intra-snail stages (miracidia, rediae and cercariae) require abundant cathepsin L peptidases for migration and feeding and, as indicated by their annotation, express genes putatively involved in the manipulation of snail innate immune responses. Cercariae emerge from the snail, settle on vegetation and become encysted metacercariae that are infectious to mammals; these remain metabolically active, transcribing genes involved in regulation of metabolism, synthesis of nucleotides, pH and endopeptidase activity to assure their longevity and survival on pasture. Dramatic growth and development following infection of the mammalian host are associated with high gene transcription of cell motility pathways, and transport and catabolism pathways. The intra-mammalian stages temporally regulate key families of genes including the cathepsin L and B proteases and their trans-activating peptidases, the legumains, during intense feeding and migration through the intestine, liver and bile ducts. While 70% of the F. gigantica transcripts share homology with genes expressed by the temperate liver fluke Fasciola hepatica, gene expression profiles of the most abundantly expressed transcripts within the comparable lifecycle stages implies significant species-specific gene regulation.

CONCLUSIONS

Transcriptional profiling of the F. gigantica lifecycle identified key metabolic, growth and developmental processes the parasite undergoes as it encounters vastly different environments within two very different hosts. Comparative analysis with F. hepatica provides insight into the similarities and differences of these parasites that diverged > 20 million years ago, crucial for the future development of novel control strategies against both species.

Development of Cytochrome B, a new candidate gene for a high accuracy detection of Fasciola eggs in fecal specimens

Fasciolosis among domestic ruminants has resulted in a decrease in the production of milk products and has occasionally led to the deaths of young ruminants due to of acute infections. This study aimed to discriminate between the eggs of Fasciola gigantica and other trematode eggs in samples collected from ruminant feces specimens using PCR-based methods with the new candidate gene Cytochrome B (CYTB). A species-specific primer was developed with a high degree of sensitivity (3.285 pg). The primer was able to amplify the F. gigantica genomic DNA and there were no positive results with the other related trematodes (Paramphistomum sp., Orthocoelium sp., Fischoederius sp., Calicophoron sp., Echinostoma revolutum, E. cinetorchis, E. ilocanum and Isthmiophora hortensis), freshwater snails (Lymnaea auricularia, Bithynia siamensis, Indoplanorbis exustus, Melanoides tuberculata, Tarebia granifera) or definitive hosts (Bos primigenius and Bubalus bubalis). The minimum concentration of DNA from eggs that could be give a positive result was 3.285 pg. Moreover, the results of the study confirmed the existence of F. gigantica in Nakhon Pathom Province with a high prevalence (28.57%) and revealed the area of infection through epidemiological mapping. Thus, the species-specific primer and epidemiological data in this study may be helpful for use in epidemiological studies, phylogenetic studies and veterinary studies in the future.

Genetic Characterization of Cambodian Fasciola gigantica and Dispersal Direction of the Species in Asia

Fasciola gigantica and hybrid Fasciola are distributed throughout Asia. Herein, we investigated the species of the Fasciola fluke distributed in three hotspots of fascioliasis in Cambodia. A total of 92 flukes collected from 21 slaughtered cattle from Kandal (44), Battambang (41), and Kratie (7) Provinces were identified as F. gigantica using multiplex PCR for a nuclear phosphoenolpyruvate carboxykinase (PEPCK) gene. The overall prevalence of F. gigantica infestation was 7.14% (21/294). Phylogenetic as well as population genetics analyses were performed using the mitochondrial NADH dehydrogenase subunit 1 (ND1). The 19 ND1 haplotypes were identified from Cambodian F. gigantica (haplotype diversity, 0.83). All of the haplotypes were classified into F. gigantica haplogroup C, which includes ND1 haplotypes detected from Thailand, Vietnam, Indonesia, Myanmar, and China. Among haplogroup C, novel and unique haplotypes of Cambodia were found in the Battambang and Kandal Provinces, and the nucleotide diversity of the Cambodian population (0.00532) was the highest. Pairwise fixation indices among the F. gigantica populations from these countries indicated that the Cambodian and Thailand populations were related to each other. The highest genetic diversity in the Cambodian population suggests that F. gigantica in Cambodia may be the ancestor of the populations in Southeast Asian countries. Most likely, livestock movement, including Zebu cattle, played an important role in the transmission of F. gigantica. In this study, the hybrid Fasciola flukes that are commonly found in neighboring countries, were not found in Cambodia. Further comprehensive investigations of Fasciola prevalence should be conducted by analyzing a wider range of hosts throughout Cambodia to reach a more solid conclusion about the absence of hybrid flukes.

Molecular analysis reveals expansion of Fasciola hepatica distribution from Afghanistan to China

Recently, phosphoenol pyruvate carboxykinase (pepck) and DNA polymerase delta (pold) were established as reliable nuclear markers for species identification of Fasciola spp. in multiplex polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism-based assays, respectively. Currently, little is known about Fasciola species distribution in Central Asia. Therefore, the objective of the present study was to perform precise molecular species identification of liver flukes from Afghanistan and to reveal their dispersal route(s) via phylogenetic analysis based on mitochondrial nad1 haplotypes. Ninety-two Fasciolaflukes collected from sheep in Kabul, Afghanistan, were identified as F. hepatica based on pepck and pold screening. Although the pepck fragment pattern obtained via multiplex PCR analysis could not distinguish the species of the seven Fasciola flukes, the pepck nucleotide sequence data confirmed that they were F. hepatica.The 20 nad1 haplotypes detected among the Afghani liver flukes were closely related to those from China and Egypt, with the F_STvalue (-0.003, P = .41) between the F. hepatica populations from Afghanistan and China confirming a very close relationship. Nucleotide diversity was greater in the population from Afghanistan compared with that from China, indicating that the Afghani population was older, and that the dispersal direction of F. hepatica was from Afghanistan to China. The results of the present study contribute to our understanding of the dispersal of F. hepatica from its predicted origin, the Fertile Crescent.

New insight into genetic variation and haplotype diversity of Fasciola hepatica from Algeria

The liver fluke Fasciola hepatica is the main cause of fasciolosis in North Africa leading to significant economic losses and public health problems. In this study, the ribosomal internal transcribed spacer (ITS), cytochrome c oxidase I (COI), the mitochondrial region spanning the COI-trnT-rrnL, and the NADH dehydrogenase subunit I (NADI) markers were used to characterize Fasciola flukes from Algeria. Fasciola appeared widespread from the east to the west of Algeria. Among 1701 sampled cattle from 8 Algerian provinces, 5% were infected. Using morphological and morphometric analysis, one morphotype of Fasciola was observed. Nuclear ITS marker indicated that all collected flukes belong to F. hepatica. Multiple alignments of ITS dataset revealed two haplotypes, one described here for the first time. Analysis of molecular variance (AMOVA) of mitochondrial markers revealed weak population structure in Algeria. Mismatch distributions, neutrality tests, and median-joining network analysis all were compatible with a recent expansion of Algerian F. hepatica population. Fasciolosis appeared common in Algerian cattle, it seems that the absence of control strategy coupled to the favorable Mediterranean climate may lead to a reconstruction and dispersion of its populations. This study provides important results concerning the genetic characterization and variability of F. hepatica in Algeria as well as the significant role of cattle importation in shaping its dispersal route worldwide.

Distribution Status of Hybrid Types in Large Liver Flukes, Fasciola Species (Digenea: Fasciolidae), from Ruminants and Humans in Vietnam

The aim of this study is to delineate ‘admixed hybrid’ and ‘introgressive’ Fasciola genotypes present in the Fasciola population in Vietnam. Adult liver flukes collected from ruminants in 18 Provinces were morphologically sorted out by naked eyes for small (S), medium (M) and large (L) body shapes; and human samples (n=14) from patients. Nuclear ribosomal (rDNA) ITS1 and ITS2, and mitochondrial (mtDNA) nad1 markers were used for determination of their genetic status. Total 4,725 worm samples of ruminants were tentatively classified by their size: 6% (n=284) small (S)-, 13% (n=614) medium (M)-, and 81% (n=3,827) large (L)-forms. All the representative (n=120, as 40 each group) and 14 human specimens, possessed maternal mtDNA of only F. gigantica and none of F. hepatica. Paternally, all (100%) of the L-(n=40) and 77.5% (n=31) of the M-flukes had single F. gigantica rDNA indicating ‘pure’ F. gigantica. A majority (90%, n=36) of the S- and 15% (n=6) of the M-worms had single F. hepatica rDNA, indicating their introgressive; the rest (10%, n=4) of the S- and 7.5% (n=3) of the M-flukes had mixture of both F. gigantica and F. hepatica rDNAs, confirming their admixed hybrid genetic status. Fourteen human samples revealed 9 (64%) of pure F. gigantica, 3 (22%) of introgressive and 2 (14%) of admixed hybrid Fasciola spp. By the present study, it was confirmed that the small worms, which are morphologically identical with F. hepatica, are admixed and/or introgressive hybrids of Fasciola spp., and able to be the pathogens of human fascioliasis.

Revealing genetic hybridization and DNA recombination of Fasciola hepatica and Fasciola gigantica in nuclear introns of the hybrid Fasciola flukes

Fasciola hepatica and F. gigantica are ruminant liver flukes that are found worldwide. They can occur sympatrically and hybridize, consequently producing an intermediate form (Fasciola sp.), especially in Africa and Asia. The bridge intron (TkBridgeInt) and intron 4 of domain 2 (TkD2Int4) of the taurocyamine kinase gene were cloned and sequenced from 14 F. hepatica, 18 F. gigantica, and 12 Fasciola sp. These intron regions could be used to differentiate F. hepatica from F. gigantica and revealed genetic hybridization and DNA recombination between F. hepatica and F. gigantica in Fasciola sp. from Japan and Bangladesh. Two specimens of F. hepatica from Ecuador revealed cryptic diversity. A combination of three haplotypes observed in a Fasciola sp. specimen from Japan suggested triploidy. Thus, the intron region of the taurocyamine kinase gene is a potential marker for detecting the hybrid status of the Fasciola flukes.

Advances in Fasciola hepatica research using 'omics' technologies

The liver fluke Fasciola hepatica is an economically important pathogen of livestock worldwide, as well as being an important neglected zoonosis. Parasite control is reliant on the use of drugs, particularly triclabendazole, which is effective against multiple parasite stages. However, the spread of parasites resistant to triclabendazole has intensified the pursuit for novel control strategies. Emerging 'omics' technologies are helping advance our understanding of liver fluke biology, specifically the molecules that act at the host-parasite interface and are central to infection, virulence and long-term survival within the definitive host. This review discusses the technological sequencing advances that have facilitated the unbiased analysis of liver fluke biology, resulting in an extensive range of 'omics' datasets. In addition, we highlight the 'omics' studies of host responses to F. hepatica infection that, when combined with the parasite datasets, provide the opportunity for integrated analyses of host-parasite interactions. These extensive datasets will form the foundation for future in-depth analysis of F. hepatica biology and development, and the search for new drug or vaccine interventions.

Hybrid origin of Asian aspermic Fasciola flukes is confirmed by analyzing two single-copy genes, pepck and pold

Nuclear gene markers, phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold), have been developed for precise discrimination of Fasciola flukes instead of internal transcribed spacer 1. In this study, these two genes of 730 Fasciola flukes from eight Asian countries were analyzed. The results were compared with their mitochondrial NADH dehydrogenase subunit 1 (nad1) lineages for obtaining a definitive evidence of the hybrid origin of aspermic Fasciola flukes. All the flukes categorized into the aspermic nad1 lineages possessed both the fragment patterns of F. hepatica and F. gigantica (mixed types) in pepck and/or pold. These findings provide clear evidence for the hybrid origin of aspermic Fasciola lineages and suggest that “aspermic Fasciola flukes” should hereafter be called “hybrid Fasciola flukes”.

Molecular characterization of Fasciola flukes obtained from wild sika deer and domestic cattle in Hokkaido, Japan

The number of wild sika deer (Cervus nippon yesoensis) continues to increase in Hokkaido Prefecture, Japan. The major concern for the livestock industry is the transmission of pathogens between sika deer and cattle. Fasciolosis is an important disease that can occur in both animals. The aim of this study was to examine the possible mutual transmission of this disease in Hokkaido Prefecture. A total of 105 Fasciola flukes were obtained from sika deer and 96 from domestic cattle. The Fasciola flukes in Japan are reported to possess no mature sperm. However, in this study, 14 flukes from sika deer and eight flukes from cattle contained mature sperm in their seminal vesicles. All the Fasciola flukes from the two host animals had Fh/Fg type in nuclear phosphoenolpyruvate carboxykinase (pepck) gene, with a mixed fragment pattern derived from F. hepatica and F. gigantica, which are considered to be hybrid Fasciola flukes. However, almost all the flukes had Fsp1 haplotype in NADH dehydrogenase subunit 1 (nad1) gene, indicating that their maternal lineage was F. hepatica. A new haplotype, Fsp3, was detected in one fluke obtained from cattle and differed in one nucleotide from Fsp1. Therefore, the Fasciola flukes detected in both host species had almost identical molecular characteristics. These findings suggest the mutual transmission of Fasciola flukes between sika deer and domestic cattle in Hokkaido.