The effects of farm management practices on liver fluke prevalence and the current internal parasite control measures employed on Irish dairy farms

Prevalence, coinfection, and risk factors associated with Fasciola hepatica and other gastrointestinal parasites in cattle from the Peruvian Amazon

Background and Aim

Extensive cattle rearing is a major source of economy for the inhabitants of the Amazon region of Peru. Milk and meat production is generally affected by the prevalence of various parasites, including hepatic and gastrointestinal parasites, as these products provide ideal conditions for parasitic growth. This poses a serious public health threat. This study aimed to estimate the prevalence, coinfection, and risk factors associated with the liver fluke (Fasciola hepatica) and other gastrointestinal parasites in cattle from the Amazon region of Peru.

Materials and Methods

Fecal samples obtained from 1450 bovine specimens were analyzed using flotation and sedimentation methods to identify parasites, including Eimeria spp., strongyle-type eggs (STEs), and F. hepatica. We collected information about the specimens, including age, sex, origin, breed, category, frequency of deworming, farm size, herd size, water sources, and rearing system by conducting simple inspections and interviewing owners. The data obtained were statistically evaluated using the Chi-square test (p < 0.05) to determine the association between the qualitative variables. We also calculated the odds ratio at a 95% confidence interval to identify the risk factors.

Results

We observed that F. hepatica, Eimeria spp., and STEs were 45.6%, 39.8%, and 35.3% prevalent, respectively. We found risk factors related to distomatosis in the animals from Huambo, where the drinking water sources are mainly streams, ditches, and rivers, while the specimens from Valle Chico were predisposed to coccidiosis. Further, the risk factors related to the presence of STEs in feces were age (61-90 months), origin (Valle Chico), herd size (<50 animals), and type of extensive rearing. Furthermore, significant coinfection was observed between Eimeria spp. and STEs.

Conclusion

The high percentages of parasites in cattle observed were related to epidemiological factors, such as the origin of the sample, water sources, age, herd size, and extensive breeding. Similarly, the presence of STEs was a risk factor for contracting coccidiosis. Our future goals include investigating these parasites using a larger sample size and identifying more risk factors using more sensitive and specific diagnostic tests.

A survey of sheep and/or cattle farmers in the UK shows confusion over the diagnosis and control of rumen fluke and liver fluke

Calicophoron daubneyi (rumen fluke) is an emerging parasitic infection of livestock across Europe. Despite increasing in prevalence, little is known about the level of awareness of rumen fluke or current control practices used by UK farmers. Fasciola hepatica (liver fluke) is a common parasitic infection of cattle and sheep in the UK. Co-infections with these parasites can present in sheep and cattle, but the only drug with reported efficacy against rumen fluke is oxyclozanide. Between December 2019 and March 2020, 451 sheep and/or cattle farmers completed an online questionnaire, capturing their awareness and current means of control for liver fluke and rumen fluke. Most respondents (70%) were aware of rumen fluke, with 14% recording its presence on their farms and 18% having previously treated for rumen fluke. Almost all respondents (99%) were aware of liver fluke and higher numbers of respondents reported its presence on farm (67%) with 88% having previously treated for liver fluke. Respondents who were aware of rumen fluke said they were concerned about the parasite (81%), although rumen fluke was less of a concern than liver fluke (p < 0.05). Of respondents who reported rumen fluke presence on their farm, 42% cited incorrect diagnostic methods, including those traditionally used to detect liver fluke. Respondents were more likely to treat annually for liver fluke, as opposed to rumen fluke (p < 0.05). The most frequently used drug for the treatment of liver fluke infection was triclabendazole (53% sheep treatments, 34% cattle treatments) and only a minority of farmers treated with a product effective against rumen fluke (oxyclozanide; 42% cattle treatments, 35% sheep treatments). A small proportion of farmers stated that they used a non-flukicide drug to treat sheep for liver fluke infection (1.6% sheep treatments). These results demonstrate a broad awareness of liver and rumen fluke in sheep and cattle, but reveal confusion amongst farmers about their diagnosis and treatment, highlighting the need to provide best practice advice to the livestock industry for the control of both parasites.

Grazier perceptions and management practices for liver fluke control in north eastern NSW, Australia

A survey of livestock producers (graziers) located in north eastern NSW Australia, collected information on perceptions and management practices for liver fluke control in livestock. The total area farmed by the 161 respondents was 195,600 ha (ranging in size from 4 to 10,522 ha) with cattle and sheep being the dominant livestock enterprises. Overall, 80% of graziers relied exclusively on anthelmintics for liver fluke control and few of these graziers (9%) integrated parasite management (IPM) strategies to reduce disease prevalence. Of those relying on anthelmintic control, triclabendazole (TCBZ) was preferentially chosen by 75% of graziers. Fifty five percent of these graziers used TCBZ in combination with oxfendazole (46%), ivermectin (5%) or abamectin (4%) whilst 45% used TCBZ as a single active ingredient. Thirty eight percent of graziers drenched livestock one or more times per year for liver fluke despite claiming they had no liver fluke or confirmed knowledge of infection. Fifty one percent of graziers based anthelmintic dose on the known weight of the heaviest animal in the herd whilst 43% visually guessed livestock bodyweight to calculate anthelmintic dose. Choice of anthelmintic was predominately based on perceived efficacy (45%) despite very few graziers (2%) having conducted post-treatment fluke egg counts. The majority of graziers (76%) were unsure if they had anthelmintic resistance, 21% claimed they had no resistance whilst 3% of graziers had confirmed resistance. Most graziers (97%) also reported farms were cohabited by kangaroos highlighting additional grazing pressures on-farm. This current survey has revealed that graziers rely on anthelmintics as their primary choice for liver fluke control. Reluctance to adopt IPM strategies and a continued heavy reliance on TCBZ, whilst basing anthelmintic decisions on perception rather than measurement and testing, pose threats for the future control of liver fluke in livestock within this endemic area.

Gastrointestinal nematodes and Fasciola hepatica in Norwegian cattle herds: a questionnaire to investigate farmers' perceptions and control strategies

Background

Pasture management influences the prevalence and impact of the pasture parasites (PP) in cattle herds, which cause production-limiting disease worldwide. Evaluating farmer management strategies is vital when considering sustainable PP control practices. The aim of this questionnaire-based study was to describe the pasture management and control strategies regarding PP in Norwegian beef cattle (BC) and dairy cattle (DC) production systems with a focus on gastrointestinal nematodes (GIN) and Fasciola hepatica.

Results

A total of 745 responses from BC (return rate 20.5%) and 1347 responses from DC farmers (30.7%) were included. The mean total pasture time for DC was 4.2 months for first-season grazers and 4.3 months for second-season grazers and cows, while the corresponding finding in BC was 5.4 months. Home pasture was used for most of the pasture period, particularly for first-season grazer dairy heifers (81%), which were also commonly grazed on the same pasture every year (79%). For most farmers it was necessary for grazing areas to be used for cattle for more than one season (77% of BC farmers and 89% of DC farmers). However, changing the pasture during the season was common in both DC (67%) and BC (70%) herds. The majority of DC farmers (60%) stated that they did not consider that they had a problem with PP. Of the remaining 40%, few respondents could specify whether their herds had a problem due to infection by GIN (11%) or liver flukes (12%). Treatment for GIN was performed by 52% of DC and 34% of BC farmers. Diagnostic faecal samples were collected upon suspicion of parasitic disease by 5% of DC and 16% of BC farmers. Veterinarians were stated as a central source of information about parasite management and treatment.

Conclusions

Potential risks for exposure to PP were identified, such as use of the same pasture every year for first-season grazers and frequent use of home pasture. The perception of problems related to PP appeared low. Regular anthelmintic treatment without concurrent use of diagnostic faecal samples seems to be common practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13028-021-00618-7.

Fasciola hepatica Control Practices on a Sample of Dairy Farms in Victoria, Australia

In Australia, little is known about the strategies used by farmers to control Fasciola hepatica (F. hepatica) infection in dairy cattle. Triclabendazole-resistant F. hepatica have recently been found on several dairy and beef properties in Australia. It is difficult to draw conclusions about how widespread resistance is in Australian dairy cattle because we have little information about flukicide usage, drug resistance testing, and alternative flukicide usage on-farm. The study objectives were to determine how dairy farmers are currently controlling F. hepatica and to identify knowledge gaps where F. hepatica control strategies need to be communicated to farmers to improve management. The survey was distributed online or by hard copy and 36 dairy farmers completed the survey. There were 34 questions including closed, open-ended, multicheck box, demographic, and text questions. Descriptive statistics were used to quantify each response. The survey results showed high use of clorsulon, limited rotation of flukicides, and limited use of diagnostic tests to inform treatment options and timing. There was poor adherence to best management practice in determining the dose of flukicides administered to cattle, with farmers often relying on estimating body weights or average body weights, suggesting that underdosing of animals is likely to be prevalent. Most respondents in this study did not isolate and quarantine treated and newly returned or purchased animals before joining them with the main herd. The research identified four knowledge gaps where communication needs to be enhanced to improve control of F. hepatica: diagnostic testing to inform flukicide use, rotation of flukicide actives, flukicide administration, and increased testing of replacement animals.

Discovering environmental management opportunities for infectious disease control

Climate change and emerging drug resistance make the control of many infectious diseases increasingly challenging and diminish the exclusive reliance on drug treatment as sole solution to the problem. As disease transmission often depends on environmental conditions that can be modified, such modifications may become crucial to risk reduction if we can assess their potential benefit at policy-relevant scales. However, so far, the value of environmental management for this purpose has received little attention. Here, using the parasitic disease of fasciolosis in livestock in the UK as a case study, we demonstrate how mechanistic hydro-epidemiological modelling can be applied to understand disease risk drivers and the efficacy of environmental management across a large heterogeneous domain. Our results show how weather and other environmental characteristics interact to define disease transmission potential and reveal that environmental interventions such as risk avoidance management strategies can provide a valuable alternative or complement to current treatment-based control practice.

Economic model of bovine fasciolosis in Nigeria: an update

Bovine fasciolosis is a zoonotic infection transmitted by infected freshwater snail-Lymnaea (Radix) natalensis-in tropical regions. The prevalence of bovine fasciolosis in Nigeria is overwhelming with huge financial cost. In the chronic form of the disease, hyperplastic cholangitis and calcification of bile ducts occur with severe liver damage. The aim of the study was to estimate annual economic losses of bovine fasciolosis in Nigeria. Disease prevalence was estimated at 18.3% (8.5-30.6), average annual disease incidence is maintained at 2.5%, an estimated mortality rate of 1.5%, a total liver condemnation rate of 11.1% were estimated from affected liver due to fasciolosis, annual slaughter rate of 10.5% and a total cattle population of 20 million. A total of 7.3% livestock owners consider fasciolosis as a threat, while only 4.3% have ever used molluscicide. Treatment cost of controlling fasciolosis is estimated at US$375,000, which puts the total annual loss due to fasciolosis at US$26.02 million. Both direct and indirect sources of production losses have an impact on the livestock industry in Nigeria. Bovine fasciolosis threatens food security in Nigeria; therefore, further awareness among livestock owners is needed on control strategies to improve the income base for small-scale livestock farmers.

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.

The impact of liver fluke infection on steers in Ireland: A meta-analytic approach

Post-mortem liver inspection results together with production parameters are often used to estimate the impact of liver fluke infection on farm animal populations. However, post mortem liver inspection is an imperfect method of determining the liver fluke infection status of cattle. This work estimates the difference in mean lifetime weight gain at 819 days (ΔLWG₈₁₉) between steers assigned liver fluke negative (LFN) and liver fluke positive (LFP) status at post-mortem meat inspection, quantifies the potential impact of imperfect sensitivity and specificity on these results and estimates the economic impact of these differences. The study population is 32,007 steers that never moved from their birth herd in the Republic of Ireland and were slaughtered in one of two Irish meat processors in 2014. Individual animal-level data are used to generate 46 county - processor level estimates of ΔLWG₈₁₉. Standard errors and confidence intervals for these estimates are derived using bootstrapping. A meta-analytic approach is then used to obtain 3 overall estimates of the effect of liver fluke status on the ΔLWG₈₁₉ in all the county - processor combinations, assuming post - mortem liver inspection Se = Sp = 1, 0.99 and 0.95. A random effects model is used and 95% prediction intervals (95% PI) are calculated. Assuming Se = Sp = 1 for post - mortem liver inspection, the random effects summary estimate of ΔLWG₈₁₉ (ΔLWG_819(RE)) is 36 kg (95% PI: -1, 73). There is a minor change in ΔLWG_819(RE) (38 kg, 95% PI: -1, 77) when Se = Sp = 0.99 is assumed but this increases to 46 kg (95% PI: -2, 94) assuming Se = Sp = 0.95. The corresponding cost in euros of these differences between the LFN and LFP steers, assuming a price per kg of €3.90, are €77.01 (95% PI: -2.57, 156.37), €80.65 (95% PI: -3.43, 164.74) and €98.67 (95% PI: -5.15, 202.27) respectively. Our results demonstrate an association between liver fluke infection and reduced weight gain. We show that the effect of liver fluke infection on weight gain in cattle is underestimated due to misclassification resulting from imperfection in post mortem meat inspection. These findings will aid researchers, farmers and veterinary practitioners to make informed decisions on the control of liver fluke on farms.

Genome-wide association study of endo-parasite phenotypes using imputed whole-genome sequence data in dairy and beef cattle

BACKGROUND

Quantitative genetic studies suggest the existence of variation at the genome level that affects the ability of cattle to resist to parasitic diseases. The objective of the current study was to identify regions of the bovine genome that are associated with resistance to endo-parasites.

METHODS

Individual cattle records were available for Fasciola hepatica-damaged liver from 18 abattoirs. Deregressed estimated breeding values (EBV) for F. hepatica-damaged liver were generated for genotyped animals with a record for F. hepatica-damaged liver and for genotyped sires with a least one progeny record for F. hepatica-damaged liver; 3702 animals were available. In addition, individual cow records for antibody response to F. hepatica on 6388 genotyped dairy cows, antibody response to Ostertagia ostertagi on 8334 genotyped dairy cows and antibody response to Neospora caninum on 4597 genotyped dairy cows were adjusted for non-genetic effects. Genotypes were imputed to whole-sequence; after edits, 14,190,141 single nucleotide polymorphisms (SNPs) and 16,603,644 SNPs were available for cattle with deregressed EBV for F. hepatica-damaged liver and cows with an antibody response to a parasitic disease, respectively. Association analyses were undertaken using linear regression on one SNP at a time, in which a genomic relationship matrix accounted for the relationships between animals.

RESULTS

Genomic regions for F. hepatica-damaged liver were located on Bos taurus autosomes (BTA) 1, 8, 11, 16, 17 and 18; each region included at least one SNP with a p value lower than 10^-6. Five SNPs were identified as significant (q value < 0.05) for antibody response to N. caninum and were located on BTA21 or 25. For antibody response to F. hepatica and O. ostertagi, six and nine quantitative trait loci (QTL) regions that included at least one SNP with a p value lower than 10^-6 were identified, respectively. Gene set enrichment analysis revealed a significant association between functional annotations related to the olfactory system and QTL that were suggestively associated with endo-parasite phenotypes.

CONCLUSIONS

A number of novel genomic regions were suggestively associated with endo-parasite phenotypes across the bovine genome and two genomic regions on BTA21 and 25 were associated with antibody response to N. caninum.

Development and validation of a protocol to identify and recruit participants into a large scale study on liver fluke in cattle

Background

Liver fluke infection caused by the parasite Fasciola hepatica is a major cause of production losses to the cattle industry in the UK. To investigate farm-level risk factors for fluke infection, a randomised method to recruit an appropriate number of herds from a defined geographical area into the study was required. The approach and hurdles that were encountered in designing and implementing this study are described. The county of Shropshire, England, was selected for the study because of the variation between farms in exposure to fluke infection observed in an earlier study.

Results

From a sampling list of 569 holdings in Shropshire randomly drawn from the RADAR cattle population dataset, 396 (69.6%) holdings were successfully contacted by telephone and asked if they would be interested in taking part in the study. Of 296 farmers who agreed to receive information packs by post, 195 (65.9%) agreed to take part in the study. Over the period October 2014 – April 2015 visits were made to 100 dairy and 95 non-dairy herds. During the farm visits 40 faecal samples +/− bulk-tank milk samples were collected and a questionnaire administered. Composite faecal samples were analysed for the presence of F. hepatica eggs by sedimentation and bulk tank milk samples were tested with an antibody ELISA for F. hepatica. Forty-five (49%) of non-dairy herds were positive for liver fluke infection as determined by the finding of one or more fluke eggs, while 36 (36%) dairy herds had fluke positive faecal samples and 41 (41%) dairy herds were positive for F. hepatica antibody. Eighty-seven (45.8%) farmers said that they monitored their cattle for liver fluke infection and 118 (62.1%) reported that they used flukicide drugs in their cattle.

Conclusions

Using a protocol of contacting farmers directly by telephone and subsequently sending information by post, 79% of the target sample size was successfully recruited into the study. A dataset of farm-specific information on possible risk factors for liver fluke infection and corresponding liver-fluke infection status was generated for the development of statistical models to identify risk factors for liver fluke infection at the farm-level.

Seasonal variation of Fasciola hepatica antibodies in dairy herds in Northern Ireland measured by bulk tank milk ELISA

Bovine fasciolosis, caused by the infection of the trematode parasite Fasciola hepatica, remains a problem in dairy herds causing significant production losses. In this study, bulk milk tank samples were utilised to generate a comprehensive survey of the variation in liver fluke exposure over the four seasons of 2016 in Northern Ireland (NI). Samples were tested using an antibody ELISA test; within-herd prevalence levels were categorised relative to sample-to-positive ratio (S/P%). Overall, 1494 herds (~ 50% of all active dairy farms in NI) were sampled. In total, 5750 samples were tested with 91% of herds having a sample result for each season. The proportion of herds with evidence of liver fluke exposure was very high across the year, with 93.03% of all bulk milk samples having some indication of liver fluke antibody presence. A high proportion of samples (2187/5750; 38.03%) fell within the highest infection class (indicating high within-herd prevalence). There was significant seasonal variation in the mean S/P%. A multivariable random effect ordinal logit model suggested that the greatest probability of being in a higher infection class was in winter, whilst the lowest was recorded during summer. There was a significant negative association between increasing herd liver fluke infection class and herd size. Furthermore, there was significant variation in infection levels across regions of Northern Ireland, with higher infection levels in northern administrative areas. This study demonstrates the very high liver fluke exposure in this region of Europe, and that risk is not equally distributed spatially or across seasons in dairy herds.

Bovine fascioliasis in Brazil: Economic impact and forecasting

Fasciola hepatica causes liver damage and poor growth in cattle and other animals, including humans. Although the disease occurs throughout the country, it is hyperendemic in cattle in the South of Brazil. This work aimed to determine the economical loss by carcass weight variance using data from all the states where F. hepatica is found, as well as to run a disease forecast analysis for the Rio Grande do Sul State. We found a direct loss of approximately US$ 210 million/year from infected cattle in Brazil and the ARIMA model analysis revealed that an increase of fascioliasis is most probable if no parasite control program is adopted.

Paramphistomosis of Ruminants: An Emerging Parasitic Disease in Europe

Whilst historically regarded as being of minor importance in European livestock, recent evidence suggests that the prevalence of paramphistomosis is greater than that of fasciolosis in parts of the UK. In order to address this emerging threat to ruminant farming systems, and associated risks for food security posed by rumen fluke infection, it is imperative that we develop a better understanding of the basic biology of this parasite and how it interacts with its ruminant host. In this Opinion article we review recent progress in tracking the spread of rumen fluke infection in Europe, and propose some research questions that should be addressed if we are to develop tools to diagnose and treat paramphistomosis more effectively in the future.

A review on epidemiology, global prevalence and economical losses of fasciolosis in ruminants

Fasciolosis is an important plant borne trematode zoonosis in ruminants caused by the Fasciola hepatica and Fasciola gigentica, It is classified as a neglected tropical disease and found in more than 50 countries especially where sheep and cattle are reared. Fasciolosis is a serious animal health problems in many rural and urban areas of world, causing significant financial losses due to decrease in production and viscera condemnation in animals. Accurate diagnosis of fasciolosis is always remained a challenging task for the field practitioners. There is no comprehensive summary on the occurrence and distribution of the infection at international level. Therefore, we intended to provide a complete overview on the prevalence and epidemiology of fasciolosis in farm animals from a global prospective. It includes to map the global distribution of fasciolosis in different areas of the world to identify the endemic regions which may be a source of potential disease outbreak. The financial liability related to fasciolosis on the livestock production has also been addressed. For this purpose, the published data during 2000-2015 (15 years) on fasciolosis was reviewed and collected by electronic literature search of four databases including Google, PubMed, Science Direct, and Web of Science. Data presented are contemplated to enhance our current understanding of the parasite's geographical distribution, host range, and economic losses. Information provided would be useful for the application of more effective control strategies against fasciolosis in different geo-economics regions of the world.

Associations between fasciolosis and milk production, and the impact of anthelmintic treatment in dairy herds

Liver fluke is a ubiquitous parasite that causes extensive production losses in cattle and is a zoonosis. The aims of this study were to determine the prevalence of fasciolosis in 178 dairy cattle herds in Styria (federal state of Austria) and its influence on production, to detect the risk factors for infection, and to explore effective strategies in management and control. A questionnaire on farm management, prophylaxis, and therapy was developed and applied. Furthermore, production parameters (milk yield, milk protein content, butter fat content, non-return rate 90, calving to conception interval, service period) were recorded for 2014 and 2015, and a commercial ELISA for detection of Fasciola hepatica antibodies was applied in bulk tank milk in March 2014 and March 2015. Analysis of bulk tank milk samples showed a prevalence of 61.3% in 2014 and 45.5% in 2015. No associations could be found between F. hepatica exposure and farm structure or pasture management. Farms with highly positive (optical density ratio (ODR) ≥ 0.6 and lying above the upper interquartile range) antibody levels had a significantly lower annual milk yield of 438 kg per cow per year (p = 0.045), butterfat content of 0.091% (p = 0.004), and milk protein content of 0.046% (p = 0.024). However, fertility parameters were not significantly associated with liver fluke exposure. Anthelmintic treatment led to significantly lower antibody levels in the subsequent year (p = 0.042) and had a significant influence on protein content in milk (p = 0.003). This study highlighted the importance of fasciolosis in Austria and its influence on milk production and the need for veterinary advice regarding prophylactic measures to reduce economic losses.

Genetic parameters for both a liver damage phenotype caused by and antibody response to phenotype in dairy and beef cattle

is a helminth parasite of economic importance to the global cattle industry, with documented high international herd prevalence. The objective of the present study was to generate the first published genetic parameter estimates for liver damage caused by as well as antibody response to in cattle. Abattoir data on the presence of live , or -damaged livers, were available between the years 2012 and 2015, inclusive. A second data set was available on cows from 68 selected dairy herds with a blood ELISA test for antibody response to in autumn 2015. Animals were identified as exposed by using herd mate phenotype, and only exposed animals were retained for analysis. The abattoir data set consisted of 20,481 dairy cows and 75,041 young dairy and beef animals, whereas the study herd data set consisted of 6,912 dairy cows. (Co)variance components for phenotypes in both data sets were estimated using animal linear mixed models. Fixed effects included in the model for both data sets were contemporary group, heterosis coefficient, recombination loss coefficient, parity, age relative to parity/age group, and stage of lactation. An additional fixed effect of abattoir by date of slaughter was included in the model for the analysis of the abattoir data. Direct additive genetic effects and a residual effect were included as random effects for all analyses. After data edits, the prevalence of liver damage caused by in cows and young cattle was 47% and 20%, respectively. The prevalence of a positive antibody response to in cows from the study herd data was 36% after data edits. The heritability of as a binary trait for dairy cows in abattoir data and study herd data was 0.03 ± 0.01 and 0.09 ± 0.02, respectively; heritability in young cattle was 0.01 ± 0.005. The additive genetic SD of as a binary trait was 0.069 and 0.050 for cows and young cattle from the abattoir data, respectively, and 0.112 from the study herd cows. The genetic correlation between liver damage caused by in young cattle and cows from the abattoir data was 0.94 ± 0.312 and the genetic correlation between liver damage caused by in cows and positive antibody response to in cows in the study herd data was 0.37 ± 0.283.

Seroprevalence and Risk Factors of Fascioliasis in Yaks, Bos grunniens, from Three Counties of Gansu Province, China

The aim of this study was to determine the seroprevalence and risk factors of fascioliasis in yaks, Bos grunniens, from 3 counties of Gansu Province in China. A total of 1,584 serum samples, including 974 samples from white yaks from Tianzhu, 464 from black yaks from Maqu, and 146 from black yaks from Luqu County, were collected and analyzed using ELISA to detect IgG antibodies against Fasciola hepatica. The overall F. hepatica seroprevalence was 28.7% (454/1,584), with 29.2% in white yaks (284/974) and 27.9% in black yaks (170/610). The seroprevalence of F. hepatica in yaks from Tianzhu, Luqu, and Maqu was 29.2%, 22.6%, and 29.5%, respectively. Female yaks (30.9%) had higher F. hepatica seroprevalence than male yaks (23.4%). Also, F. hepatica seroprevalence varied by different age group from 24.1% to 33.8%. Further, the seroprevalence ranged from 21.8% to 39.1% over different seasons. Interestingly, the season and age of yaks were associated with F. hepatica infection in yaks in the investigated areas. These findings provided a basis for further studies on this disease in yaks from 3 counties of Gansu Province in northwestern China, which may ultimately support the development of effective control strategies of fascioliasis in these areas.

Effects of albendazole, artesunate, praziquantel and miltefosine, on Opisthorchis viverrini cercariae and mature metacercariae

OBJECTIVE

To explore larvicidal effects of anthelmintic drugs on Opisthorchis viverrini (O. viverrini) for alternative approach to interrupting its cycle for developing a field-based control program.

METHODS

The larvicidal activities of albendazole (Al), artesunate (Ar), praziquantel (Pzq) and miltefosine (Mf) on O. viverrini cercariae and mature metacercariae were investigated. Lethal concentrations (LC₅₀ and LC₉₅) of these drugs were determined. Mature metacercariae previously exposed to various concentrations of the drugs were administered to hamsters. Worms were harvested 30 d post infection and worm recovery rates calculated. Al, Ar, Pzq and Mf produced morphological degeneration and induced shedding tails of cercariae after 24 h exposure.

RESULTS

The LC₅₀ and LC₉₅ of Al, Ar, Pzq and Mf on cercariae were 0.720 and 1.139, 0.350 and 0.861, 0.017 and 0.693, and 0.530 and 1.134 ppm, respectively. LC₅₀ and LC₉₅ of Ar on mature metacercariae were 303.643 and 446.237 ppm and of Mf were 289.711 and 631.781 ppm, respectively but no lethal effect in Pzq- and Al-treated groups (up to 1 ppt). No worms were found in hamsters administered Pzq-treated metacercariae. The adult worms from Al-treated metacercariae were significantly bigger in size compared to the control group (P < 0.05). Fecundity and body width were greater in adults from Mf-treated metacercariae compared to the control group (P < 0.05).

CONCLUSIONS

The larvicidal effects of these drugs were high efficacy to O. viverrini cercariae but lesser efficacy to metacercariae. It should be further studied with the eventual aim of developing a field-based control program.

Liver fluke (Fasciola hepatica) infection in cattle in Northern Ireland: a large-scale epidemiological investigation utilising surveillance data

Background

Liver fluke (Fasciola hepatica) is a widespread parasite of ruminants which can have significant economic impact on cattle production. Fluke infection status at the animal-level is captured during meat inspection of all animals processed for human consumption within Northern Ireland. These national datasets have not been analysed to assess their utility in uncovering patterns in fluke infection at animal- and herd-levels in Northern Ireland.

Methods

We utilised a dataset of 1.2 million animal records from ~18,000 herds across 3 years (2011–2013) to assess animal- and herd-level apparent prevalence and risk-factors associated with fluke infection. Animal-level apparent prevalence was measured as the proportion of animals exhibiting evidence of fluke infection at slaughter; between herd-level infection prevalence was measured by binary categorisation of herds (infected or not). “Within herd” infection prevalence was measured using the proportion of animals within a herd that showed evidence of fluke infection per year (ranging from 0–100 %). “Within herd” infection prevalence at the herd level was investigated using multivariable modelling.

Results

At the animal level, the proportion of animals slaughtered that exhibited evidence of infection was 21–25 % amongst years. Across herds, the proportion of herds with at least one infected animal, varied between 61 and 65 %. However, there was a significant sampling effect at the herd-level; all herds where at least 105 animals slaughtered over the study period exhibited evidence of fluke infection (100 %). There was significant variation in terms of within-herd infection prevalence. Risk factors included herd type, long-term weather variation, geographic location (region) and the abattoir.

Conclusions

Liver fluke apparent prevalence was high at the herd-level across years. However, there was lower prevalence at the animal level, which may indicate significant variation in the exposure to fluke infection within herds. The proportion infected within-herds varied significantly in time and space, and by abattoir, herd-type and some weather variables. These data are a useful source of information on a widespread endemic disease, despite known limitations in terms of test performance (low sensitivity). As well as informing on the distribution and severity of liver fluke infection, these analyses will be used to investigate the effect of co-infection on risk for bovine tuberculosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1489-2) contains supplementary material, which is available to authorized users.

Current Threat of Triclabendazole Resistance in Fasciola hepatica

Triclabendazole (TCBZ) is the only chemical that kills early immature and adult Fasciola hepatica (liver fluke) but widespread resistance to the drug greatly compromises fluke control in livestock and humans. The mode of action of TCBZ and mechanism(s) underlying parasite resistance to the drug are not known. Due to the high prevalence of TCBZ resistance (TCBZ-R), effective management of drug resistance is now critical for sustainable livestock production. Here, we discuss the current status of TCBZ-R in F. hepatica, the global distribution of resistance observed in livestock, the possible mechanism(s) of drug action, the proposed mechanisms and genetic basis of resistance, and the prospects for future control of liver fluke infections using an integrated parasite management (IPM) approach.

Liver fluke control on sheep farms in Northern Ireland: A survey of changing management practices in relation to disease prevalence and perceived triclabendazole resistance

Reports of resistance to triclabendazole (TCBZ) among fluke populations have increased in recent years. Allied to this, there has been a rise in the prevalence of the disease, which has been linked to climate change. Results from questionnaire surveys conducted in Northern Ireland (NI) in 2005 (covering the years 1999-2004) and 2011 (covering the years 2008-2011) have provided an opportunity to examine the extent to which fluke control practices have changed over a prolonged time-frame, in light of these changes. A number of differences were highlighted. There was a significant shift away from the use of TCBZ over time, with it being replaced largely by closantel. The timing of treatments had moved earlier in the year, perhaps in response to climate change (and an altered pattern of disease). In relation to the frequency of drug treatments, there were no major changes in the overall pattern of drug treatments between the two survey points, although on both occasions approximately one-third of flock owners gave more than 3 treatments per year to ewes. In lowland areas in 2011, flock owners were rotating drug classes more often (each year and at each treatment) than in 2005, whereas in upland areas, flock owners were rotating less often and more were not rotating at all. Between 2005 and 2011, the percentage of flock owners giving quarantine treatments to bought-in stock had halved, to a very low level (approximately 10%). Using data from a complementary TCBZ resistance survey (Hanna et al., 2015), it has been shown that the way in which data are selected and which efficacy formula is applied can influence the calculation of drug efficiency and impact on diagnosis of resistance.

Detection of major climatic and environmental predictors of liver fluke exposure risk in Ireland using spatial cluster analysis

Fasciolosis caused by Fasciola hepatica (liver fluke) can cause significant economic and production losses in dairy cow farms. The aim of the current study was to identify important weather and environmental predictors of the exposure risk to liver fluke by detecting clusters of fasciolosis in Ireland. During autumn 2012, bulk-tank milk samples from 4365 dairy farms were collected throughout Ireland. Using an in-house antibody-detection ELISA, the analysis of BTM samples showed that 83% (n=3602) of dairy farms had been exposed to liver fluke. The Getis-Ord Gi* statistic identified 74 high-risk and 130 low-risk significant (P<0.01) clusters of fasciolosis. The low-risk clusters were mostly located in the southern regions of Ireland, whereas the high-risk clusters were mainly situated in the western part. Several climatic variables (monthly and seasonal mean rainfall and temperatures, total wet days and rain days) and environmental datasets (soil types, enhanced vegetation index and normalised difference vegetation index) were used to investigate dissimilarities in the exposure to liver fluke between clusters. Rainfall, total wet days and rain days, and soil type were the significant classes of climatic and environmental variables explaining the differences between significant clusters. A discriminant function analysis was used to predict the exposure risk to liver fluke using 80% of data for modelling and the remaining subset of 20% for post hoc model validation. The most significant predictors of the model risk function were total rainfall in August and September and total wet days. The risk model presented 100% sensitivity and 91% specificity and an accuracy of 95% correctly classified cases. A risk map of exposure to liver fluke was constructed with higher probability of exposure in western and north-western regions. The results of this study identified differences between clusters of fasciolosis in Ireland regarding climatic and environmental variables and detected significant predictors of the exposure risk to liver fluke.