Transmission patterns of Fasciola hepatica to ruminants in Sweden

Estimation of diagnostic sensitivity and specificity of abattoir registrations and bulk tank milk ELISA as herd-level tests for Fasciola hepatica using Bayesian latent class modelling

The common liver fluke, Fasciola hepatica, is a trematode parasite found worldwide, typically with a focal distribution due to its requirement for suitable climatic and environmental conditions to complete its lifecycle. Bovine fasciolosis causes suboptimal production and economic losses, including liver condemnation at slaughter. The lack of reliable diagnostic methods is a disadvantage to the increasing demand for surveillance and control. The aim of this study was to evaluate the diagnostic accuracy of bulk tank milk (BTM) antibody testing and aggregated abattoir registrations (AAR) of liver fluke as herd-level tests for F. hepatica infection using Bayesian latent class models. Data from the abattoirs in 2019-2021 and BTM, sampled in the winter of 2020/2021, were collected from 437 herds on the southwest coast of Norway. The BTM samples were analysed with the SVANOVIR® F. hepatica-Ab ELISA test, with results given as an optical density ratio (ODR), and later dichotomized using the recommended cut-off value from the test manufacturer (ODR ≥0.3). Based on the BTM ELISA test, 47.8% of the herds tested positive. The AAR test was defined as the herd-level proportion of female slaughtered animals registered with liver fluke infection during the study period. For this test, three cut-offs were used (a proportion of 0.05, 0.1 and 0.2). The herds were split into two subpopulations ("Coastal" and "Inland"), which were expected to differ in true prevalence of F. hepatica infection based on climate-related and geographical factors. The diagnostic accuracies of both tests were estimated using Bayesian latent class models with minimally informative priors. Post-hoc analysis revealed that the maximum sum of sensitivity (Se) and specificity (Sp) of the tests was achieved with a herd-level proportion of ≥0.1 registered with liver fluke as the AAR test. Using this cut-off, the median estimate for the diagnostic accuracy of the BTM ELISA was 90.4% (84.0-96.2 95% Posterior Credible Interval (PCI)) for Se and 95.3% (90.6-100% PCI) for Sp, while the median estimate of Se for AAR was 87.5% (81.4-93.1% PCI) and the median estimate of Sp for AAR was 91.0% (85.2-96.5% PCI). The cut-off evaluation of the SVANOVIR® F. hepatica-Ab ELISA test for BTM confirmed the manufacturer's recommended cut-off of ODR ≥0.3 to denote positive and negative herds. This study suggests that AAR and BTM ELISA test can be used as herd-level tools to monitor liver fluke infection, so that appropriate interventions against infection can be implemented as necessary.

Exploring the utility of circulating miRNAs as diagnostic biomarkers of fasciolosis

Effective management and control of parasitic infections on farms depends on their early detection. Traditional serological diagnostic methods for Fasciola hepatica infection in livestock are specific and sensitive, but currently the earliest detection of the parasite only occurs at approximately three weeks post-infection. At this timepoint, parasites have already entered the liver and caused the tissue damage and immunopathology that results in reduced body weight and loss in productivity. Here, we investigated whether the differential abundance of micro(mi)miRNAs in sera of F. hepatica-infected sheep has potential as a tool for the early diagnosis of infection. Using miRNA sequencing analysis, we discovered specific profiles of sheep miRNAs at both the pre-hepatic and hepatic infection phases in comparison to non-infected sheep. In addition, six F. hepatica-derived miRNAs were specifically identified in sera from infected sheep. Thus, a panel of differentially expressed miRNAs comprising four sheep (miR-3231-3p; miR133-5p; 3957-5p; 1197-3p) and two parasite miRNAs (miR-124-3p; miR-Novel-11-5p) were selected as potential biomarkers. The expression of these candidates in sera samples from longitudinal sheep infection studies collected between 7 days and 23 weeks was quantified using RT-qPCR and compared to samples from age-matched non-infected sheep. We identified oar-miR-133-5p and oar-miR-3957-5p as promising biomarkers of fasciolosis, detecting infection as early as 7 days. The differential expression of the other selected miRNAs was not sufficient to diagnose infection; however, our analysis found that the most abundant forms of fhe-miR-124-3p in sera were sequence variants (IsomiRs) of the canonical miRNA, highlighting the critical importance of primer design for accurate diagnostic RT-qPCR. Accordingly, this investigative study suggests that certain miRNAs are biomarkers of F. hepatica infection and validates miRNA-based diagnostics for the detection of fasciolosis in sheep.

Histopathology and antibody responses describe the seasonal pattern of dicrocoeliosis in small ruminants in the Himalayan ranges of Pakistan

In some parts of the world, Dicrocoelium spp. lancet flukes cause significant production loss in pastoral livestock, and accurate diagnosis of infection is important. The aims of the present study were to describe the histopathology and to investigate the transmission patterns of Dicrocoelium amongst ten sheep and goat farms in Khyber Pakhtunkhwa and Gilgit Baltistan, Pakistan. The liver histology and indirect enzyme-linked immunosorbent assay (ELISA) analyses followed standard procedures. The liver histopathology showed intensive tissue destruction and biliary hyperplasia associated with presence of adult flukes, severe inflammatory cell infiltration, congestion of blood vessels, damaged hepatocytes, and sinusoids in the infected areas. The time of onset of infection was investigated by ELISA detection of antibodies in sheep (n = 164) and goats (n = 152). Colostral transfer of Dicrocoelium antibodies from seropositive mothers was detected in sheep and goats up to 16 weeks of age. In both sheep and goats, the estimated time of infection differed between farms and years. Infection was seen in both sheep flocks and goat herds, with high variation between flocks and herds, and the highest infection rate in lambs. Dicrocoelium infection was most prevalent in sheep and goats in September (n = 84) and August (n = 63) respectively. This study concluded Dicrocoelium causes severe inflammation and necrosis of liver tissues in sheep and goats. Colostral transfer of antibodies can be detected up to about ten weeks of age. Higher infection rates are observed during August and September in sheep than in goats, putatively due to effects of different grazing and browsing behaviors on the ingestion of ants. The results will aid in the development of effective disease control strategies to ensure optimal growth and productivity of sheep and goats.

Fasciolosis—An Increasing Challenge in the Sheep Industry

Simple Summary

Fasciolosis caused by Fasciola hepatica is a serious disease and a huge challenge in the sheep industry. The disease has several clinical manifestations including acute death, anemia, ill-thrift and loss of body condition. Climate change with milder temperatures and heavier rainfall will increase the risk of fasciolosis. Grazing management and treatment with flukicide are at present the only options to restrain F. hepatica infection. However, control possibilities are challenging, and resistance to flukicide drugs is increasing. Diagnostic improvements, targeted treatment and vaccines will hopefully increase animal health and welfare on fluke infested pastures in the future.

Abstract

The liver fluke Fasciola hepatica may cause severe infection in several mammalian species, including sheep and humans. Fasciolosis is a parasitic disease occurring worldwide in temperate climates and involves intermediate lymnaeid snails as vectors, in Europe the pond snail Galba truncatula in particular. In the sheep industry, the disease is a serious welfare and health problem. Fasciolosis is usually classified as acute, subacute or chronic according to the number and stage of flukes present in the liver, but with a considerable overlap. Acute disease, associated with a large number of migrating larvae, often results in sudden death due to acute and massive hemorrhage, while chronic fasciolosis is characterized by anemia, hypoalbuminaemia and weight loss. The management of fasciolosis is an increasing challenge in the sheep industry. Early diagnostic tests are limited. Protective immunity against liver flukes in sheep is low or lacking, and vaccines are not yet available. Treatment and control possibilities are challenging, and resistance to flukicide drugs is increasing. In addition, climate change with warmer and more humid weather will have a substantial effect on the establishment of both flukes and snails and will most likely increase the future distribution of F. hepatica.

Exploration of factors associated with spatial-temporal veterinary surveillance diagnoses of rumen fluke (Calicophoron daubneyi) infections in ruminants using zero-inflated mixed modelling

Rumen fluke (Calicophoron daubneyi) has emerged as a prominent parasite of ruminants in Europe over the past decades. Epidemiological questions remain regarding this observed increase in prevalence as well as the prospect for future paramphistomosis risk. This study aimed to identify factors associated with the temporal−spatial prevalence of rumen fluke as measured by veterinary surveillance in a temperate region using zero-inflated negative binomial mixed modelling. Modelling revealed that summer rainfall, raindays and sunshine hours and mean winter temperature as significant positively associated climate variables for rumen fluke prevalence over space and time (P < 0.05). Rumen fluke prevalence was also higher in counties with higher cattle/sheep densities and was positively associated with rumen fluke case rates in the previous years (P < 0.05). Equivalent models for fasciolosis prevalence revealed no significant association with winter temperature and sunshine hours, (P > 0.05). These results confirm a strong association between rainfall and the prevalence of both fluke species in a temperate environment, likely due to the role of Galba truncatula as their intermediate snail host. It also highlights the potential added importance of winter temperature and sunshine hours in rumen fluke epidemiology when compared to liver fluke.

Selective flukicide treatment of non-lactating cows and the corresponding production impact of Fasciola hepatica in dairy herds in Sweden

A control strategy against Fasciola hepatica infection based on selective treatment of non-lactating animals was evaluated in four Swedish dairy herds. The study was conducted over the course of two consecutive seasons in moderately to highly F. hepatica infected herds with robotic milking, where heifers and dry cows received an oral drench with albendazole (10 mg/kg) during three visits in January, February and March in both 2017 and 2018. This resulted in an anthelmintic coverage between 38 % and 58 % of the animals. Furthermore, on each visit, the infection status of all dewormed animals along with 15 randomly selected milking cows were monitored by detection of F. hepatica coproantigens. Individual milk samples were also collected quarterly from the whole herds for measurements of individual antibody levels against the parasite using milk ELISA. In addition, individual data on milk yield and quality were collected on a monthly basis between 2016 and 2018. To further study the impact of the infection on milk production, truly F. hepatica positive and negative cows in the first lactation were identified based on the results from coproantigen and milk ELISA assays. Total F. hepatica coproantigen prevalence in the herds varied between 28 % and 85 % in the first year, and between 27 % and 68 % in the second year of the study. We found that two years of treatments resulted in a significant decrease of coproantigen-positivity especially on the two most heavily infected farms. These results were confirmed by a similar drop in within-herd prevalences obtained by milk ELISA results. The infection had a significant negative impact on milk yields in untreated F. hepatica positive cows. No consistent long-term effect was observed at the herd level probably due to the influx of animals infected before puberty and/or adult animals that were re-infected at dry-off. This is the first study of the effects of F. hepatica infection on milk yield and quality in dairy herds in Sweden.

High parasite diversity in a neglected host: larval trematodes of Bithynia tentaculata in Central Europe

Bithynids snails are a widespread group of molluscs in European freshwater systems. However, not much information is available on trematode communities from molluscs of this family. Here, we investigate the trematode diversity of Bithynia tentaculata, based on molecular and morphological data. A total of 682 snails from the rivers Lippe and Rhine in North Rhine-Westphalia, Germany, and 121 B. tentaculata from Curonian Lagoon, Lithuania were screened for infections with digeneans. In total, B. tentaculata showed a trematode prevalence of 12.9% and 14%, respectively. The phylogenetic analyses based on 55 novel sequences for 36 isolates demonstrated a high diversity of digeneans. Analyses of the molecular and morphological data revealed a species-rich trematode fauna, comprising 20 species, belonging to ten families. Interestingly, the larval trematode community of B. tentaculata shows little overlap with the well-studied trematode fauna of lymnaeids and planorbids, and some of the detected species (Echinochasmus beleocephalus and E. coaxatus) constitute first records for B. tentaculata in Central Europe. Our study revealed an abundant, diverse and distinct trematode fauna in B. tentaculata, which highlights the need for further research on this so far understudied host-parasite system. Therefore, we might currently be underestimating the ecological roles of several parasite communities of non-pulmonate snail host families in European fresh waters.

High prevalence of fasciolosis and evaluation of the efficacy of anthelmintics against Fasciola hepatica in buffaloes in Guangxi, China

Fasciola hepatica is a common parasite of grazing livestock in Guangxi Zhuang Autonomous Region in China, but its prevalence has not been studied. While triclabendazole is commonly used to treat F. hepatica infection in China, oxyclozanide has never been used. This study investigated the prevalence of F. hepatica infections in buffaloes in the Guangxi and evaluated the efficacy of oxyclozanide and triclabendazole as treatments. In the prevalence study, a total of 767 individual faecal samples were obtained from 58 farms in Guangxi to detect the prevalence of F. hepatica, and the total rate of infection was 87.35%. A subset of 277 infected buffaloes from these farms were randomly divided into 3 groups. Group 1 (n = 101) was treated with oxyclozanide at 10 mg/kg.bw; group 2 (n = 94) was treated with triclabendazole (12 mg/kg.bw); and group 3 (n = 82) was untreated. Faecal samples were taken on days 0, 7, 14, 21 and 28. Whole blood and serum were collected on days 0 and 14. Anthelmintic efficacy was assessed using faecal egg count reduction (FECR), buffaloes positive by coprology reduction (BPCR) as well as post-treatment improvement in biochemical and haematological indicators. After 28 days treatment, group 1 and 2 showed FECR% values above 98%, and BPCR% values of 97.03% and 77.66%, respectively. In addition, the biochemical indicators and haematological parameters were improved at 14 days post-treatment compared with those before treatment. These results indicate a high prevalence of F. hepatica in Guangxi, demonstrate that oxyclozanide and triclabendazole are effective against F. hepatica infection in buffaloes, and indicate that oxyclozanide could be used in China as an alternative drug.

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The prevalence of F. hepatica infections in 767 buffaloes was 87.35% on 58 farms from 8 districts in Guangxi Zhuang Autonomous Region in China.

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Oxyclozanide and triclabendazole effectively restored the health of infected buffaloes and reduced the EPG of F. hepatica.

Patterns of Fasciola hepatica infection in Danish dairy cattle: implications for on-farm control of the parasite based on different diagnostic methods

Background

Bovine fasciolosis is an economically important livestock disease in Europe, and represents a particular challenge for organic farms, where cattle are grazed extensively and the use of anthelmintic is limited. A two-year longitudinal study was conducted on two conventional and two organic Danish dairy farms to examine the current temporal trend of F. hepatica infection on-farm, and to gather data of practical relevance for parasite control. Data were collected both at the herd and individual level using currently available diagnostic methods: a commercial serum antibody ELISA, a commercial copro-antigen ELISA, faecal egg counts, and monthly bulk tank milk (BTM) ELISA. The temporal patterns (animal age, farm-level temporal trends and seasonality) in the animal-level test results were analysed by generalised additive mixed models (GAMM).

Results

Patterns of infection differed substantially between the farms, due to different grazing management and anthelmintic use. However, animals were first infected at the age of 1.5–2 years (heifers), and most at-risk animals sero-converted in autumn, suggesting that summer infections in snails prevail in Denmark. Our results also suggest that the lifespan of the parasite could be over 2 years, as several cows showed signs of low grade infection even after several years of continuous indoor housing without access to freshly-cut grass. The serum antibody ELISA was able to detect infection first, whereas both copro-antigen ELISA and faecal egg counts tended to increase in the same animals at a later point. Decreasing BTM antibody levels were seen on the two farms that started anthelmintic treatment during the study.

Conclusions

While important differences between farms and over time were seen due to varying grazing management, anthelmintic treatment and climatic conditions, the young stock was consistently seen as the main high-risk group and at least one farm also had suspected transmission (re-infection) within the lactating herd. Careful interpretation of test results is necessary for older cows as they can show persistent infections several years after exposure has stopped. Rigorous treatment regimens can reduce BTM ELISA values, but further research is needed to develop a non-medicinal approach for sustainable management of bovine fasciolosis.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3248-z) contains supplementary material, which is available to authorized users.

A reducing trend of fasciolosis in slaughtered animals based on abattoir data in South of Iran

AIM

Fascioliasis is a zoonosis infection caused by the liver trematodes (Fasciola spp.) which have been considered to be an important disease in livestock. After several large outbreaks, fascioliasis remains one of the serious health concerns of Iran. This study was conducted to evaluate the prevalence and possible trends of fascioliasis in slaughtered animals in South of Iran based on abattoir data during a period of 5 years.

MATERIALS AND METHODS

The daily records for cattle, sheep, and goats slaughtered in the abattoir were extracted from the archived documents of the recent 5 years (2011-2015) and used as the source of data. The collected data were statistically analyzed for finding any probable correlation between the various factors associated with fasciolosis.

RESULTS

Our results showed that 3.44% of all slaughtered animals during 2011-2015 were infected with Fasciola spp. The mean prevalence of fasciolosis for cattle, sheep, and goat was 11.15%, 5.22%, and 2.15%, respectively. In addition, the highest infection rate was in winter (4.02%), and the lowest were entered in summer (2.86%).

CONCLUSION

Our findings showed a reducing trend during the 5 years. Improving the animal husbandry and increasing the awareness through fasciolosis may be a logical explanation for this trend. Since there have been suggested numerous factors associated with the epidemiology of fasciolosis, further studies seem essential for better clarifying the various aspects of fasciolosis in areas.

Fasciola hepatica: Infection Status of Freshwater Snails Collected from Gangwon-do (Province), Korea

Fasciola hepatica is a trematode that causes zoonosis, mainly in cattle and sheep, and occasionally in humans. Few recent studies have determined the infection status of this fluke in Korea. In August 2015, we collected 402 samples of freshwater snails at Hoenggye-ri (upper stream) and Suha-ri (lower stream) of Song-cheon (stream) in Daegwalnyeong-myeon, Pyeongchang-gun in Gangwon-do (Province) near many large cattle or sheep farms. F. hepatica infection was determined using PCR on the nuclear ribosomal internal transcribed spacer 2 (ITS-2). Among the 402 samples, F. hepatica 1TS-2 marker was detected in 6 freshwater snails; thus, the overall prevalence in freshwater snails was 1.5%. The prevalence varied between collection areas, ranging from 0.0% at Hoenggye-ri to 2.9% at Suha-ri. However, F. gigantica ITS-2 was not detected in the 6 F. hepatica-positive samples by PCR. The nucleotide sequences of the 6 F. hepatica ITS-2 PCR-positive samples were 99.4% identical to the F. hepatica ITS-2 sequences in GenBank, whereas they were 98.4% similar to F. gigantica ITS-2 sequences. These results indicated that the prevalence of F. hepatica in snail intermediate hosts was 1.5% in Gangwon-do, Korea; however the prevalence varied between collection areas. These results may help us to understand F. hepatica infection status in natural environments.

Relative importance of meteorological and geographical factors in the distribution of Fasciola hepatica infestation in farmed sheep in Qinghai province, China

Fasciola hepatica is an important trematode parasite of economic importance that infests sheep and cattle worldwide. We conducted a detailed investigation into the spatial distribution of F. hepatica infestation in farmed sheep in Qinghai (Wutumeiren) province, Mainland China. Mathematical modelling was used to assess the inter-relationships between meteorological and geographical factors and the risk of F. hepatica infestation across the province. A capture enzyme-linked immunosorbent assay (ELISA) test (MM3-SERO) was used to detect F. hepatica infestation. A niche model based on the maximum entropy method (MaxEnt) was used to estimate the influence of meteorological and geographical factors on the observed spatial distribution of F. hepatica infestation. Results of jackknife analysis indicated that temperature, precipitation, solar radiation, digital elevation and slope were associated with the occurrence of F. hepatica infestation, and that infestation rates were significantly higher among animals from districts with a high percentage of grassland habitat. The findings indicate that meteorological and geographical factors may be important variables affecting the distribution of F. hepatica infestation and should be taken into account in the development of future surveillance and control programmes for fascioliasis.

Comparison of molecular and conventional methods for the diagnosis of Fasciola hepatica infection in the field

The liver fluke, Fasciola hepatica, is one of the major parasite threats to livestock industries world-wide. In sheep and cattle, F. hepatica infection is commonly diagnosed using a range of methods. Aside from conventional coprological and serological diagnostic methods, there are also several molecular methods available based on the detection of liver fluke DNA in faeces. In this study, the outcomes of faecal egg count (FEC), serology and coproantigen ELISA (cELISA) were compared with the performance of polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) in diagnosis of F. hepatica from naturally infected cattle and sheep. A total of 64 individual faecal and serum samples were collected from four sheep and beef cattle herds with previous histories of F. hepatica infection. FEC and coproantigen levels were measured in faecal samples and anti-F.hepatica antibody levels were measured in serum samples. DNA samples isolated from faeces were examined both by PCR and LAMP, targeting the internal transcribed spacer 2 (ITS2) region of the F. hepatica genome. Results showed that F. hepatica eggs were present in 28 animals, while coproantigen and specific anti-F. hepatica antibodies were detected in 36 and 53 animals, respectively. Only 3 and 6 samples were positive by PCR and LAMP, respectively. To calculate method specificity and sensitivity, a combination of FEC and cELISA was selected as the composite reference standard (CRS). When compared to the CRS, PCR had a sensitivity of 10.7% and specificity of 100%, whereas LAMP had a sensitivity and specificity of 17.9% and 97.2%, respectively. PCR and LAMP in this field study were highly specific, but both had poor sensitivity compared with FEC and cELISA. Potential reasons for PCR and LAMP failure were inadequate amounts of amplifiable F. hepatica DNA, possibly due to the choice of DNA extraction procedure, amount of faecal material processed, as well as different faeces consistency and composition between different animal species.

Assessment of flukicide efficacy against Fasciola hepatica in sheep in Sweden in the absence of a standardised test

Anthelmintic resistance (AR) to Fasciola hepatica is emerging worldwide. Recently, AR to the adulticide compound albendazole (ABZ) was shown in Argentina and Spain. In Sweden, ABZ treatment failure against F. hepatica was first reported in sheep in 2012. The present study tested the efficacy of ABZ and triclabendazole (TCBZ) in sheep naturally infected with F. hepatica using a combination of three different diagnostic methods: faecal egg counts (FEC), coproantigen ELISA (cELISA) and Fasciola egg hatch test (FEHT). Two deworming trials, in November 2014 and January 2015, were performed on two sheep farms (farms A and B) in south-western Sweden. Except ABZ in November, treatment with ABZ or TCBZ achieved sufficient efficacy (97-100%) against adult F. hepatica on farm A. In contrast, ABZ treatment failed in the sheep flock on farm B, despite low initial faecal egg output. On farm B, ABZ efficacy based on FEC was 67% (95% CI: 35-84) and four of eight ewes tested were coproantigen-positive 21 days post-treatment. Ovicidal activity of ABZ against Fasciola eggs in isolates from both farms and one additional bovine isolate were tested by FEHT to exclude the presence of juvenile flukes and other factors such as dosing failure and poor quality of drug product. Irrespective of drug trial, data from FEHT showed significantly lower ovicidal activity of ABZ for the ovine farm B isolate than for the isolate from farm A. This confirms that the low efficacy of ABZ in sheep flock B was associated with ABZ resistance. Overall, the usefulness of three complementary methods for detection of ABZ resistance in the field was demonstrated.

First report of closantel treatment failure against Fasciola hepatica in cattle

Control of Fasciola hepatica infection in livestock is based on annual treatment using flukicides such as triclabendazole, albendazole and closantel. However, triclabendazole resistant F. hepatica populations are emerging worldwide and resistance is emerging to albendazole, whereas it has until now never been described for closantel. In Sweden, a topical formulation containing a combination of closantel and ivermectin (Closamectin Pour On) has been registered for use in cattle only since 2011. This study evaluated the efficacy of closantel against F. hepatica in naturally infected beef cattle using both coproantigen and faecal egg count reduction tests. Faecal egg counts (FEC) and coproantigen ELISA examinations were conducted in February 2014 in three beef cattle herds (A, B, C) in south-western Sweden. On each farm, 10 F. hepatica coproantigen-positive and F. hepatica egg-positive animals were allocated after 12-16 weeks of housing into groups and treated topically with a minimum of 20 mg closantel per kg body weight. Faecal samples were collected from selected animals on 0, 7 and 21 day post-treatment (PT). Based on FEC, closantel efficacy 21 days PT was 72% (95% CI: 65-77%) and 97% (95% CI: 95-98%) on farms A and B, respectively. No FEC reduction at all was observed on farm C. In total, 4, 1 and 6 animals remained coproantigen-positive at 21 days PT on farms A, B and C, respectively. Closantel treatment failure was confirmed on two of the farms. As the animals were housed 12-16 weeks before treatment and thereafter during the entire study, failure due to the presence of juvenile flukes was excluded. Although the cause of closantel failure currently remains unclear, development of resistance or/and absorption failure of topical administration should be considered. To our knowledge, this is the first report of closantel treatment failure against F. hepatica in cattle.

Unravelling the riddle of Radix: DNA barcoding for species identification of freshwater snail intermediate hosts of zoonotic digeneans and estimating their inter-population evolutionary relationships

Radix spp. are intermediate host snails for digenean parasites of medical and veterinary importance. Within this genus, species differentiation using shell and internal organ morphology can result in erroneous species identification, causing problems when trying to understand the population biology of Radix. In the present study, DNA barcoding, using cox1 and ITS2 sequences, identified populations of Radix auricularia and Radix balthica from specimens originally morphologically identified as Radix peregra from the UK. Assessment of cox1 and ITS2 as species identification markers showed that, although both markers differentiated species, cox1 possessed greater molecular diversity and higher phylogenetic resolution. Cox1 also proved useful for gaining insights into the evolutionary relationships of Radix species populations. Phylogenetic analysis and haplotype networks of cox1 indicated that R. auricularia appeared to have invaded the UK several times; some haplotypes forming a distinct UK specific clade, whilst others are more akin to those found on mainland Europe. This was in contrast to relationships between R. balthica populations, which had low molecular diversity and no distinct UK specific haplotypes, suggesting recent and multiple invasions from mainland Europe. Molecular techniques therefore appear to be crucial for distinguishing Radix spp., particularly using cox1. This barcoding marker also enables the population biology of Radix spp. to be explored, and is invaluable for monitoring the epidemiology of fluke diseases especially in the light of emerging diseases and food security.

Impact of meteorological and environmental factors on the spatial distribution of Fasciola hepatica in beef cattle herds in Sweden

BACKGROUND

Fasciola hepatica is a parasite with a significant impact on ruminant livestock production. Previous studies in north-west Europe have described its geographical distribution and determined potential predictors of fasciolosis using geographical information system (GIS) and regression modelling. In Sweden, however, information about the distribution of fasciolosis is limited. This study examined the geographical distribution of F. hepatica and identified high-risk areas for beef cattle in Sweden and sought to characterise potential predictors. Beef cattle serum samples were collected during winter 2006-2007 from 2135 herds which were examined for F. hepatica antibodies by enzyme-linked immunosorbent assay (ELISA). Fasciolosis distribution maps were created using GIS based on postcode location of seropositive herds. Spatial scan analysis (SaTScan) was performed to determine high-risk areas. Using datasets on animal density, temperature, precipitation and Corine land cover data, including soil type and soil mineral concentrations in Sweden, bivariate and multiple logistic regression analyses were carried out in R software to reveal potential predictors of F. hepatica infection.

RESULTS

Overall herd seroprevalence of F. hepatica in beef cattle was 9.8 % (95 % CI: 8.6-11.1). An irregular spatial distribution of F. hepatica, with two main clusters, was observed in south-west Sweden. The most northerly occurrence of F. hepatica in the world was documented. The final model explained 15.8 % of the variation in F. hepatica distribution in study herds. Absence of coniferous forest was the variable with the highest predictive value. Precipitation in July-September, Dystric Cambisol, Dystric Regosol, and P and Cu concentrations in soil were other negative predictors. Beef cattle herd density, Dystric Leptosol and Fe concentration were positive predictors.

CONCLUSIONS

The spatial distribution of F. hepatica in Swedish beef cattle herds is influenced by multi-factorial effects. Interestingly, absence of coniferous forest, herd density, specific soil type and concentration of some soil minerals are more important predictors than climate factors.

Fasciola hepatica in snails collected from water-dropwort fields using PCR

Fasciola hepatica is a trematode that causes zoonosis mainly in cattle and sheep and occasionally in humans. Fascioliasis has been reported in Korea; however, determining F. hepatica infection in snails has not been done recently. Thus, using PCR, we evaluated the prevalence of F. hepatica infection in snails at 4 large water-dropwort fields. Among 349 examined snails, F. hepatica-specific internal transcribed space 1 (ITS-1) and/or ITS-2 markers were detected in 12 snails and confirmed using sequence analysis. Morphologically, 213 of 349 collected snails were dextral shelled, which is the same aperture as the lymnaeid snail, the vectorial host for F. hepatica. Among the 12 F. hepatica-infected snails, 6 were known first intermediate hosts in Korea (Lymnaea viridis and L. ollula) and the remaining 6 (Lymnaea sp.) were potentially a new first intermediate host in Korea. It has been shown that the overall prevalence of the snails contaminated with F. hepatica in water-dropwort fields was 3.4%; however, the prevalence varied among the fields. This is the first study to estimate the prevalence of F. hepatica infection using the vectorial capacity of the snails in Korea.

Longitudinal study on the temporal and micro-spatial distribution of Galba truncatula in four farms in Belgium as a base for small-scale risk mapping of Fasciola hepatica

Background

The trematode parasite Fasciola hepatica causes important economic losses in ruminants worldwide. Current spatial distribution models do not provide sufficient detail to support farm-specific control strategies. A technology to reliably assess the spatial distribution of intermediate host snail habitats on farms would be a major step forward to this respect. The aim of this study was to conduct a longitudinal field survey in Flanders (Belgium) to (i) characterise suitable small water bodies (SWB) for Galba truncatula and (ii) describe the population dynamics of G. truncatula.

Methods

Four F. hepatica-infected farms from two distinct agricultural regions were examined for the abundance of G. truncatula from the beginning (April 2012) until the end (November 2012) of the grazing season. Per farm, 12 to 18 SWB were selected for monthly examination, using a 10 m transect analysis. Observations on G. truncatula abundance were coupled with meteorological and (micro-)environmental factors and the within-herd prevalence of F. hepatica using simple comparison or negative binomial regression models.

Results

A total of 54 examined SWB were classified as a pond, ditch, trench, furrow or moist area. G. truncatula abundance was significantly associated with SWB-type, region and total monthly precipitation, but not with monthly temperature. The clear differences in G. truncatula abundance between the 2 studied regions did not result in comparable differences in F. hepatica prevalence in the cattle. Exploration of the relationship of G. truncatula abundance with (micro)-environmental variables revealed a positive association with soil and water pH and the occurrence of Ranunculus sp. and a negative association with mowed pastures, water temperature and presence of reed-like plant species.

Conclusions

Farm-level predictions of G. truncatula risk and subsequent risk for F. hepatica occurrence would require a rainfall, soil type (representing the agricultural region) and SWB layer in a geographic information system. While rainfall and soil type information is easily accessible, the recent advances in very high spatial resolution cameras carried on board of satellites, planes or drones should allow the delineation of SWBs in the future.