A retrospective study on the metacercarial production of Fasciola hepatica from experimentally infected Galba truncatula in central France

Population genetic analysis of the liver fluke Fasciola hepatica in German dairy cattle reveals high genetic diversity and associations with fluke size

BACKGROUND

The liver fluke Fasciola hepatica is one of the most important endoparasites in domestic ruminants worldwide and can cause considerable economic losses. This study presents the first population genetic analysis of F. hepatica in Germany and aims at providing new insights into genetic diversity and population structure.

METHODS

A total of 774 liver flukes, collected from 60 cows of 17 herds and 13 cows of unknown herd origin, were subjected to comparative analysis of two mitochondrial genes (cox1 and nad1), one nuclear region (internal transcribed spacer (ITS)-1) and eight nuclear microsatellite markers. In addition, individual fluke measurements allowed comparison of morphometric differences between genotypes.

RESULTS

The nuclear ITS-1 region showed minimal variability, with 772 of 774 flukes having identical sequences, while the mitochondrial sequences revealed a high genetic diversity, with 119 distinct haplotypes, a mean haplotype diversity (Hd) of 0.81 and a mean nucleotide diversity (π) of 0.0041. Mitochondrial phylogenetic analysis identified two clusters with no clear association with the host or farm of origin. In the microsatellite analysis, all eight loci were highly polymorphic, with a mean allele frequency of 19.0 and a mean genotype frequency of 73.5 per locus. A total of 500 unique multilocus genotypes (MLGs) were found across all fluke samples, indicating that 68.5% of all genotypes were unique. A mean expected heterozygosity of 0.71 suggested a high potential for adaptability and the number of migrants (Nm = 3.5) indicated high gene flow between farms. Population structure analysis based on microsatellite data revealed that flukes from two farms differed genetically from the others. Linear mixed model results revealed that fluke length differed significantly between the two mitochondrial clusters, although it should be noted that fluke age could not be considered in the analyses.

CONCLUSIONS

Fasciola hepatica in German dairy farms showed high genetic diversity and gene flow. The differences in population structure identified by mitochondrial sequences compared with microsatellite loci highlight the benefits of analysing genetic markers of different origins. This is the first study to correlate fluke morphometry measurements with genetic markers, indicating that the identified markers can influence fluke size.

Prevalence, Distribution and Risk Factors for Trematode Infections in Domesticated Ruminants in the Lake Victoria and Southern Highland Ecological Zones of Tanzania: A Cross-Sectional Study

Trematode infections cause long-term suffering and debilitation, posing a significant threat to global animal health and production and leading to considerable economic losses. Studies on the epidemiology and control of these infections in Tanzania are limited. The few available studies have been conducted in abattoir settings. This study aimed to fill this knowledge gap by determining the prevalence, distribution, and risk factors for trematode infections in domesticated ruminants in two different ecological zones of Tanzania. A cross-sectional study was conducted in the Lake Victoria and the Southern highlands ecological zones of Tanzania. Rectal fecal samples were collected and examined for F. gigantica, Paramphistomidae, and S. bovis infections using the sedimentation technique. A total of 1367 domesticated ruminants were sampled and examined for trematode infections. The overall prevalence of trematode infections was found to be 65.7%. The individual prevalence of F. gigantica, Paramphistomidae, and S. bovis (based on egg morphology only) was 35.1%, 60.2%, and 3.1%, respectively. Adult cattle were more likely to be infected with Paramphistomidae (adjusted odds ratio, (AOR): 1.98; 95% confidence interval, (CI): 1.40-2.78) and S. bovis (AOR: 8.5; 95% CI: 1.12-64.19) than weaners. It was observed that trematode infections in domesticated ruminants are prevalent in the two ecological zones of Tanzania; therefore, effective and community-directed prevention and control strategies are highly needed to address trematode infections of domesticated ruminants in these areas.

Risk of invasion and disease transmission by the Australasian freshwater snail Orientogalba viridis (Lymnaeidae): a field and experimental study

BACKGROUND

Biological invasions pose risks to the normal functioning of ecosystems by altering the structure and composition of several communities. Molluscs stand out as an extensively studied group given their long history of introduction by either natural or anthropogenic dispersal events. An alien population of the lymnaeid species Orientogalba viridis was first sighted in 2009 in southern Spain. In its native range (Australasian), this species is one of the main intermediate hosts of Fasciola hepatica, a major worldwide trematode parasite largely affecting humans, domestic animals and wildlife.

METHODS

We collected field populations of O. viridis from its native (Malaysia) and invaded (Spain) ranges. We performed detailed morphoanatomical drawings of the species and screened for natural infection of parasites. Individuals were molecularly characterized using ITS2 for comparison with existing sequences in a fine phylogeography study. We founded experimental populations at two different conditions (tropical, 26 °C and temperate, 21 °C) to study the life-history traits of exposed and non-exposed individuals to different F. hepatica isolates.

RESULTS

We found a 9% natural prevalence of trematode infection (98% similarity with a sequence of Hypoderaeum conoideum [Echinostomatidae]) in the Spanish field population. The haplotypes of O. viridis found in our study from Spain clustered with Australian haplotypes. Experimental infection with F. hepatica was successful in both experimental conditions but higher in tropical (87% prevalence) than in temperate (73%). Overall lifespan, however, was higher in temperate conditions (mean 32.5 ± 7.4 weeks versus 23.3 ± 6.5) and survivorship remained above 70% during the first 20 weeks. In parasite-exposed populations, life expectancy dropped from an overall 37.75 weeks to 11.35 weeks but still doubled the time for initial cercariae shedding. Cercariae shedding started at day 23 post-exposure and peaked between days 53 and 67 with an average of 106 metacercariae per snail.

CONCLUSIONS

Whether O. viridis will succeed in Europe is unknown, but the odds are for a scenario in which a major snail host of F. hepatica occupy all available habitats of potential transmission foci, ravelling the epidemiology of fasciolosis. This research provides a comprehensive understanding of O. viridis biology, interactions with parasites and potential implications for disease transmission dynamics, offering valuable insights for further research and surveillance.

Prevalence of Bovine Schistosomiasis and Associated Risk Factors in and Around Haramaya, Oromia Region, East Ethiopia

Introduction

Schistosomiasis is caused by the Schistosoma genus and is transmitted through intermediate hosts, such as snails.

Methods

A cross-sectional investigation was conducted within and surrounding Haramaya town between December 2022 and May 2023 to estimate the prevalence of schistosomiasis in cattle and associated risk factors. The degree of prevalence was estimated using surveys carried out in slaughterhouses and coprological laboratories. For statistical estimation, chi-square tests and logistic regression were utilized. A total of 390 samples were obtained through simple random sampling. In the survey that was undertaken on abattoirs, a total of 384 samples were chosen through the utilization of a systematic random sampling approach. The recovery of Schistosoma eggs from fecal specimens was achieved by sedimentation.

Results

The overall rates of schistosomiasis in cattle were estimated to be 21.28% and 18.23% through coprological and postmortem examinations, respectively. The analysis conducted through multivariable logistic regression indicated that management system, body condition, and age were significant risk factors. Cattle under extensive management (OR = 5.9, 95% CI = 2-17) and those in the young age category (OR = 2.7, 95% CI = 1.0-7.00) were more susceptible to acquiring schistosomiasis than cattle under intensive management and those in the adult age category, respectively. According to the odds ratio, there was a positive association between the incidence rate of schistosomiasis in cattle and poor body condition (OR: 3.048, 95% CI = 1.07-8.68; P = 0.00). Schistosomiasis infection was 3.048 times more likely to manifest in animals in poor physical condition. This affliction has had a profound impact on the livestock industry, as substantiated by the elevated prevalence of schistosomiasis in cattle within the studied region.

Conclusion

Consequently, an integrated approach to prevention and control that targets the parasite is needed.

Study on Cattle Trematodiasis and Related Risk Factors in Damot Sore District, Wolaita Zone, Southern Ethiopia

Trematodes are chronic, debilitating diseases in livestock, causing significant economic losses worldwide. From mid-December 2021 to May 2022, a cross-sectional study was carried out in the Damot Sore District to estimate the prevalence of trematode infections in cattle and associated risk factors. Trematode eggs were found in 100 of the 384 faecal samples tested, with an overall prevalence of 26.04% (95% CI: 21.88-30.69%). The prevalence for Fasciola, Paramphistome, and Schistosoma species were 12.50%, 5.21%, and 0, respectively. Moreover, the infection rate with two parasites was 8.33%. The data were then examined further using univariable and multivariable logistic regression analysis. As a result, age was the only potential predictor identified to influence trematode infections in cattle among the potential predictors considered. Furthermore, old cattle were more likely to be infected with trematodiasis nearly 12 times (OR = 11.5) that of young cattle, and this difference was statistically significant (p < 0.05), whereas other risk factors considered were statistically insignificant (p > 0.05). According to the findings of this study, cattle trematodiasis is a moderately common disease in the study area. As a result, additional research on the meteorological conditions of snail infection was forwarded, along with other points to reduce the disease problem in livestock production.

A machine learning approach for modelling the occurrence of Galba truncatula as the major intermediate host for Fasciola hepatica in Switzerland

Fasciolosis caused by the trematode Fasciola hepatica is an important parasitosis in both livestock and humans across the globe. Chronic infections in cattle are associated with considerable economic losses. As a prerequisite for an effective control and prevention of fasciolosis in cattle fine-scale predictive models on farm-level are needed. Since disease transmission will only occur where the mollusc intermediate host is present, the objective of our research was to develop a regression model that allows to predict the local presence or absence of Galba truncatula as principal intermediate host for Fasciola hepatica in Switzerland. By implementing generalized linear mixed models (GLMMs) a total amount of 70 variables were analysed for their potential influence on the likelihood π_i of finding Galba truncatula at a certain site. Important site-specific features could be considered by selecting suitable modelling procedures. The statistical software R was used to conduct regression analysis, performing the grplasso and the glmmLasso method. The selection of parameters was based on 10-fold cross validation and the Bayesian Information Criterion (BIC). This yielded a total number of 19 potential predictor variables for the grplasso and 13 variables for the glmmLasso model, which also included random effects. Nine variables appeared to be relevant predictors for the occurrence of Galba truncatula in both models. These included reed/humid area, spring water, water bodies within a 100 m radius, and trees/bushes as powerful positive predictors. High soil depth, temperatures frequently exceeding 30 °C in the year preceding the search for snails and temperatures below 0 °C especially in the second year before were identified to exert an adverse effect on the occurrence of Galba truncatula. Temperatures measured near ground level proved to be more powerful predictors than macroclimatic parameters. Precipitation values seemed to be of minor impact in the given setting. Both regression models may be convenient for a fine-scale prediction of the occurrence of Galba truncatula, and thus provide useful approaches for the development of future spatial transmission models, mapping the risk of fasciolosis in Switzerland on farm-level.

Coprological study of trematode infections and associated host risk factors in cattle during the dry season in and around Bahir Dar, northwest Ethiopia

This study was conducted to estimate the prevalence and identify risk factors associated with trematode infections in cattle in and around Bahir Dar, northwest Ethiopia. Fecal samples collected from randomly selected 369 cattle were examined using simple sedimentation technique for differential trematode eggs count. The animals were found shedding eggs of three groups of trematodes, namely Fasciola spp., paramphistomes and Schistosoma spp. The overall prevalence of trematodes was 61.0%, and specific prevalence for Fasciola, paramphistomes and Schistosoma was 20.1%, 48.5% and 16.5%, respectively. A substantial overlap was observed in the occurrence of Fasciola and paramphistomes. The prevalence of all the three trematodes identified in this study was significantly (P < 0.05) associated with body condition and breed, while the prevalence of Fasciola and paramphistomes was also associated with age. The mean (± SE) fecal egg count per gram of feces (EPG) for Fasciola, paramphistomes and Schistosoma was 4.3 (± 0.55), 25.7 (± 2.11) and 3.1 (± 0.42), respectively. EPG of Fasciola was significantly correlated with EPG of paramphistomes (P < 0.001). The EPG for all the three trematodes was associated with body condition and breed of animals (P < 0.05), while EPG for paramphistomes was also affected by age of the animals (P < 0.05). The prevalence of all the three major trematodes of animal health importance with high rate of mixed infection along with poor body condition, suggests substantial economic loss incurred due to reduced productivity in cattle in the study area.

Clonal amplification of Fasciola hepatica in Galba truncatula: within and between isolate variation of triclabendazole-susceptible and -resistant clones

Background

Fasciola hepatica is of worldwide significance, impacting on the health, welfare and productivity of livestock and regarded by WHO as a re-emerging zoonosis. Triclabendazole (TCBZ), the drug of choice for controlling acute fasciolosis in livestock, is also the drug used to treat human infections. However TCBZ-resistance is now considered a major threat to the effective control of F. hepatica. It has yet to be demonstrated whether F. hepatica undergoes a genetic clonal expansion in the snail intermediate host, Galba truncatula, and to what extent amplification of genotypes within the snail facilitates accumulation of drug resistant parasites. Little is known about genotypic and phenotypic variation within and between F. hepatica isolates.

Results

Six clonal isolates of F. hepatica (3× triclabendazole-resistant, TCBZ-R and 3× triclabendazole-susceptible, TCBZ-S) were generated. Snails infected with one miracidium started to shed cercariae 42–56 days post-infection and shed repeatedly up to a maximum of 11 times. A maximum of 884 cercariae were shed by one clonally-infected snail (FhLivS1) at a single time point, with > 3000 clonal metacercariae shed over its lifetime. Following experimental infection all 12 sheep were FEC positive at the time of TCBZ treatment. Sheep infected with one of three putative TCBZ-S clones and treated with TCBZ had no parasites in the liver at post-mortem, whilst sheep each infected with putative TCBZ-R isolates had 35–165 adult fluke at post-mortem, despite TCBZ treatment. All six untreated control animals had between 15–127 parasites. A single multi-locus genotype was reported for every fluke from each of the six clonal isolates. Adult F. hepatica showed considerable variation in weight, ranging from 20–280 mg, with variation in weight evident within and amongst clonal isolates.

Conclusions

A genetic clonal expansion occurs within G. truncatula, highlighting the potential for amplification of drug resistant genotypes of F. hepatica. Variation in the weight of parasites within and between clonal isolates and when comparing isolates that are either susceptible or resistant to TCBZ represent inherent variation in liver fluke and cannot be attributed to their resistance or susceptibility traits.

Fasciola and fasciolosis in ruminants in Europe: Identifying research needs

Fasciola hepatica is a trematode parasite with a global distribution, which is responsible for considerable disease and production losses in a range of food producing species. It is also identified by WHO as a re-emerging neglected tropical disease associated with endemic and epidemic outbreaks of disease in human populations. In Europe, F. hepatica is mostly associated with disease in sheep, cattle and goats. This study reviews the most recent advances in our understanding of the transmission, diagnosis, epidemiology and the economic impact of fasciolosis. We also focus on the impact of the spread of resistance to anthelmintics used to control F. hepatica and consider how vaccines might be developed and applied in the context of the immune-modulation driven by the parasite. Several major research gaps are identified which, when addressed, will contribute to providing focussed and where possible, bespoke, advice for farmers on how to integrate stock management and diagnosis with vaccination and/or targeted treatment to more effectively control the parasite in the face of increasing the prevalence of infection and spread of anthelmintic resistance that are likely to be exacerbated by climate change.

Fasciola hepatica demonstrates high levels of genetic diversity, a lack of population structure and high gene flow: possible implications for drug resistance

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Self-fertilisation does occur but is rare in field populations of Fasciola hepatica.

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Some hosts harboured genotypically identical parasites (clones).

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The presence of clones is consistent with clonal expansion and clumped transmission.

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84% of 1579 F. hepatica had unique genotypes, indicating high genetic diversity.

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We found high gene flow, no population structure and low self-fertilisation rate.

Fasciola hepatica, the liver fluke, is a trematode parasite of considerable economic importance to the livestock industry and is a re-emerging zoonosis that poses a risk to human health in F. hepatica-endemic areas worldwide. Drug resistance is a substantial threat to the current and future control of F. hepatica, yet little is known about how the biology of the parasite influences the development and spread of resistance. Given that F. hepatica can self-fertilise and therefore inbreed, there is the potential for greater population differentiation and an increased likelihood of recessive alleles, such as drug resistance genes, coming together. This could be compounded by clonal expansion within the snail intermediate host and aggregation of parasites of the same genotype on pasture. Alternatively, widespread movement of animals that typically occurs in the UK could promote high levels of gene flow and prevent population differentiation. We identified clonal parasites with identical multilocus genotypes in 61% of hosts. Despite this, 84% of 1579 adult parasites had unique multilocus genotypes, which supports high levels of genotypic diversity within F. hepatica populations. Our analyses indicate a selfing rate no greater than 2%, suggesting that this diversity is in part due to the propensity for F. hepatica to cross-fertilise. Finally, although we identified high genetic diversity within a given host, there was little evidence for differentiation between populations from different hosts, indicating a single panmictic population. This implies that, once those emerge, anthelmintic resistance genes have the potential to spread rapidly through liver fluke populations.

Fasciola gigantica transmission in the zoonotic fascioliasis endemic lowlands of Guilan, Iran: experimental assessment

The lowland flatlands around the city of Bandar-Anzali, at the Caspian Sea shore, Guilan province, are an endemic area where Fasciola gigantica appears to be the fasciolid species involved and past outbreaks affecting around 15,000 people and the highest human infection rates in Iran have been reported. Fascioliasis transmission in that area has been experimentally analysed for the first time, by means of assays of monomiracidial (Group A: 120 snails) and pentamiracidial (Group B: 96 snails) infections of local Radix lymnaeid snails with a local cattle F. gigantica isolate. Ribosomal DNA ITS-2 sequencing proved that Lymnaea (Radix) gedrosiana should henceforth be considered a synonym of Radix auricularia, the haplotype found in Bandar-Anzali being identical to that found in many European countries. Survival rates at day 30 postinfection and metacercarial productivity (both higher in Group A) and longevity of the shedding snails (higher in Group B), were affected by the miracidial dose, whereas prepatent period, patent period, infection rate, and the percentages of shedding and infected non-shedding snails did not. The higher percentage of shedding snails in Group A (51.0% versus 37.7%) counteracts the higher number of metacercariae produced in Group B (243.9 ± 259.2 versus 157.2 ± 153.2). High numbers of shedding snails in both experimental groups passed less than 100 cercariae, and 16% in Group A and 35% in Group B produced more than 300 metacercariae, while only four snails (8%) in Group A and two snails (10%) in Group B shed more than 500 metacercariae. Most metacercariae (94.7% in Group A and 85.1% in Group B) were recorded during the first 15 days of patent period. The comparison with results from other fasciolid/lymnaeid systems indicates that the F. gigantica/R. auricularia system of Guilan is highly susceptible and compatible. Results obtained suggest that increased lymnaeid vector populations and not polymiracidial snail infections most probably underlay the human outbreaks in the past. The climatic analyses suggest a long fascioliasis transmission period in the Bandar-Anzali area covering from May to the end of November regarding permanent water bodies, a transmission season window widening in rice fields and irrigation canals, and a shortening of the transmission period from only end of August to beginning of November in temporary water bodies.

Optimization of metacercarial production for three digenean species by the use of petri dishes for raising lettuce-fed Galba truncatula

Experimental infections of Galba truncatula with Fasciola hepatica, Fascioloides magna, or Paramphistomum daubneyi were carried out at 20 degrees C to determine if the use of 14-cm petri dishes for breeding lettuce-fed snails enhanced the characteristics of snail infections. Compared to infected snails raised in boxes up to day 30 post-exposure and later in individual 35-mm dishes, the survival of G. truncatula kept in 14-cm dishes and the shell height of cercariae-shedding snails during the first 45 days were higher, whatever the digenean species is. The consequence of such enhanced characteristics was a greater production of metacercariae in the case of F. hepatica (1.7 to 5.6 times higher) and P. daubneyi (2.3 times). In contrast, metacercariae of F. magna were few in number, whatever the method of snail breeding is, and this might be explained by a still incomplete adaptation between the parasite of Czech origin and the French population of G. truncatula. The use of these 14-cm dishes reduced the time necessary for snail maintenance and metacercaria collection, thus allowing a decrease in the cost price of these larvae for commercial production.

The populations of Galba truncatula, known for their natural infections with Haplometra cylindracea (Digenea, Plagiorchioidea), are better intermediate hosts for metacercarial production of Fasciola hepatica

Laboratory investigations on Galba truncatula were carried out to determine if snails coming from four populations known to be natural intermediate hosts of Haplometra cylindracea, a digenean species of frogs, would not be better hosts for experimental infections with Fasciola hepatica than those originating from two communities in which H. cylindracea was never found in the past years. Uninfected G. truncatula were used to constitute six groups of snails (one per population) before being subjected to individual monomiracidial exposures with F. hepatica. Insignificant differences between mean values were noted for snail survival at day 30 post-exposure, prevalence of snail infection with F. hepatica, and prepatent period. In contrast, the duration of cercarial shedding and the number of F. hepatica cercariae in the four groups known for natural infections with H. cylindracea were significantly greater. The use of these last lymnaeid populations for experimental infections with F. hepatica allows to have high numbers of cercariae because of long patent periods and, as a consequence, strongly reduces the cost price of these larvae for scientific purposes and/or commercial production.