Fasciola hepatica: A comparative survey of adult fluke resistance to triclabendazole,nitroxynil and closantel on selected upland and lowland sheep farms in Northern Ireland using faecal egg counting,coproantigen ELISA testing and fluke histology

In order to investigate the incidence and distribution of adult fluke resistance to the fasciolicide tricalbendazole (TCBZ) amongst populations of Fasciola hepatica in sheep flocks in Northern Ireland (NI), individual rectal faeces samples were collected from 3 groups of 20 sheep, before (pre-dose), and 21 days after (post-dose) treatment of the animals with TCBZ, nitroxynil or closantel, on each of 13 well-managed sheep farms distributed across the province. The efficacy of each flukicide was determined for each farm, using faecal egg count reduction (FECRT) and F. hepatica coproantigen ELISA testing. In certain flocks, 2 sheep with high pre-dose faecal egg counts (FEC) were killed 3 days and 21 days respectively after TCBZ treatment, and the histology of the fluke reproductive organs was compared with that of flukes from untreated sheep, and from sheep treated with nitroxynil or closantel 2 days prior to death, using haematoxylin and eosin (H&E) staining and an in situ hybridisation method (TdT-mediated dUDP nick end labelling [TUNEL]) to demonstrate apoptosis. Results from FECRT revealed that in all flocks with a high fluke burden, TCBZ was ineffective in treating chronic fasciolosis, and this finding was generally supported by the results of the coproantigen reduction test (CRT). The histology of reproductive organs of flukes from TCBZ-treated sheep in these flocks was normal, when compared with untreated flukes, and this, together with the FECRT and CRT findings, indicated a likely diagnosis of TCBZ resistance in all the flocks with a high fluke burden. In contrast, nitroxynil and closantel were found to be fully effective against TCBZ-resistant flukes in each of the flocks bearing a high chronic fluke burden. All of the flocks with a high fluke burden and TCBZ resistance were managed on lowland in the South and East of NI. Upland flocks, in the North and West, had low fluke burdens, or were clear of infection; and FECs were too low to allow valid resistance testing. The study highlights the high level of penetration of TCBZ resistance throughout F. hepatica populations in areas of intensively managed sheep production with a high level of fluke challenge. Further, it emphasises the importance of pre-emptive chemotherapeutic action against chronic fasciolosis, using flukicides effective against the egg-producing adult flukes to minimise pasture contamination for the next season's lamb crop. This study also exemplifies the use of several complementary methods (FECRT; CRT; fluke histology; comparative anthelmintic efficacy testing) for confirmation of a diagnosis of fluke drug resistance.     

Evaluation of the comparative efficacy of a moxidectin plus triclabendazole pour-on solution against adult and immature liver fluke, Fasciola hepatica, in cattle

The objective of this study was to evaluate the efficacy of a pour-on solution containing moxidectin plus triclabendazole (MOX plus TCBZ) against immature and adult stages of the liver fluke in cattle and compare the efficacy with other commercially available preparations. To this end, 104 male Holstein-Friesian calves aged between 3 and 4 months, were randomly allocated to 13 groups of eight animals each, and infected with approximately 500 Fasciola hepatica metacercariae. One group remained untreated, four groups were treated with MOX plus TCBZ at a dose rate of 0.1mL/kg, four other groups were treated with ivermectin (IVM) plus clorsulon injectable at a dose rate of 0.02mL/kg, and the remaining four groups were treated with IVM plus closantel pour-on at a dose rate of 0.1mL/kg. Each treatment was applied to one of the groups at 4 weeks, 6 weeks, 8 weeks and 12 weeks after the experimental infection. At necropsy (99-102 days after infection), all untreated animals were infected with a minimum of 30 flukes. The MOX plus TCBZ treated animals had significantly (P<0.0001) lower fluke counts compared to the untreated control animals at all time points after treatment. Efficacy against 8-week old and adult flukes was >99.5%. For 6-week old immature fluke, the efficacy was 98.0% and for 4-week old immature fluke the efficacy was 90.9%. The IVM plus closantel pour-on treated animals had significantly lower fluke counts compared to the untreated control animals for adult and 8-week old flukes (P<0.0001), and for 6-week old flukes (P=0.002). The efficacy was 26.8%, 68.2%, 90.6% and 99.3% against 4-week, 6-week and 8-week old immature flukes, and adult flukes respectively. The IVM plus clorsulon treated animals had significantly lower fluke counts compared to the untreated control animals for adult (P<0.0001) and 8-week old (P<0.05) flukes. The efficacy was 29.7%, 43.4%, 53.2% and 99.2% against 4-week, 6-week and 8-week old immature flukes, and adult flukes respectively. For treatments at 4, 6 and 8 weeks after infection, the fluke counts were significantly (P<0.0001) lower for the MOX plus TCBZ treatment than for IVM plus closantel or IVM plus clorsulon. The results confirm the high efficacy (>90%) of the MOX plus TCBZ pour-on combination against 4-week old to adult liver fluke in cattle. The IVM plus closantel pour-on combination was effective (>90%) against 8-week old and adult flukes, but had low efficacy against 4- and 6-week old fluke. The IVM plus clorsulon injectable combination was effective (>90%) against adult fluke only.     

Comparative efficacy of closantel and triclabendazole against Fasciola hepatica in experimentally infected sheep

The effect of closantel (10 mg/kg orally) and triclabendazole (10 mg/kg orally) on the reappearance of a patent infection of Fasciola hepatica was studied in experimentally infected sheep. The treatments resulted in the interruption of faecal egg output for 11 weeks with triclabendazole and 13 weeks with closantel. Necropsy of untreated control animals revealed a mean burden of 360 flukes with a mean (+/- se) surface area of 171 +/- 64.3 mm2, whereas the fluke burdens in the closantel and triclabendazole-treated animals 14 weeks after treatment were 61 (83 per cent reduction) and 21 (94 per cent reduction), respectively. The surface areas of the flukes in the triclabendazole-group were comparable with the untreated controls (141 +/- 51.8 mm2), but the flukes in the closantel group were markedly smaller (43.1 +/- 26.9 mm2). It is concluded that closantel has, in epidemiological terms, a potency comparable with that of triclabendazole, despite its slightly lower efficacy against the very immature stages.     

Fasciola hepatica: comparative effects of host resistance and parasite intra-specific interactions on size and reproductive histology in flukes from rats infected with isolates differing in triclabendazole sensitivity

The efficacies of putative fasciolicides and vaccines against Fasciola hepatica are frequently monitored in clinical and field trials by determination of fluke egg output in host faeces and by worm counts in the host liver at autopsy. Less often used are parameters based on fluke size and histology, yet these can provide important indications of specific effects on the development of particular germ-line or somatic tissues, especially in relation to the timing and profligacy of egg production. In this study, F. hepatica metacercariae of two distinct isolates, the triclabendazole (TCBZ)-sensitive Cullompton isolate and the TCBZ-resistant Oberon isolate, were administered to rats as single-isolate or mixed-isolate infections. At autopsy 16 weeks later individual adult flukes were counted, measured and the reproductive organs were examined histologically. The degree of development of the testis tubules in each fluke was represented by a numerical score, based on the proportion of the histological section profiles occupied by testis tissue. The level of anti-F. hepatica antibody in the serum of each rat was determined by ELISA. It was found that Cullompton flukes were significantly larger than Oberon flukes, and that significantly more Cullompton metacercariae developed to adults than Oberon metacercariae. The Cullompton flukes showed histological evidence of aspermy and spermatogenic arrest, which was reflected in quantitatively reduced testicular development, as compared with the Oberon isolate. In Cullompton flukes, parthenogenetic egg development is implied. The size of Cullompton and Oberon flukes was significantly related to the number of adult flukes recovered, to the number of metacercariae administered, and to the percentage success of infection. The testis development score in both isolates was significantly related to the number of adult flukes recovered but not to the number of metacercariae administered, or to the percentage success of infection. Fluke size was positively related to testis score for both isolates, and a significant negative relationship was found between percentage success of infection and metacercarial dose. The results are interpreted in terms of differing interactions between various numbers of young flukes and host immunity during invasion of and migration in the hepatic parenchyma, and of fluke intra-specific (possibly pheromonal) stimulatory effects in the final stages of development, within the host bile ducts. No significant relationships were found between host antibody levels and fluke size or testis score. False positive serological reactions were found in some rats that had been infected, but found to harbour no flukes at autopsy. Clearly the act of eliminating the flukes involved generation of an immune response.     

Novel insights into the pathogenic importance,diagnosis and treatment of the rumen fluke (Calicophoron daubneyi) in cattle

Recently, sharp increases in the prevalence of rumen fluke infections have been recorded throughout Western Europe. However, scarce information is available on the diagnosis, pathogenic importance and control of this parasite. We undertook 3 pilot studies to gain more insights into these aspects of rumen fluke biology in cattle. First, we evaluated the diagnostic performance of mini-FLOTAC to detect adult rumen fluke infections based on faecal egg count in an abattoir survey and found high sensitivity (0.94) and specificity (0.98). Moreover, there was an association between ruminal fluke burden (assessed by visual scoring) and faecal egg count and a cut-off of 200 eggs per gram is proposed to detect highly infected animals (>200 flukes present in the rumen and/or reticulum). There was also a significant association between ruminal fluke burden and faecal consistency. However, in a second study, we performed a case-control field survey to investigate the association between rumen fluke infection and herd-level problems with diarrhoea and no association was found. Finally, we evaluated the use of closantel (Flukiver^®, Elanco Animal Health, subcutaneous administration at 10 mg/kg) to treat rumen fluke infection on 3 herds, but no significant reduction in egg output post-treatment was found. Because this result is in contrast with a previous study using an oral dose of closantel, more research is required into the effect of administration route on the efficacy of closantel on rumen fluke.     

Impact of compound alpha treatment in vivo on egg production by the liver fluke, Fasciola hepatica

Sheep infected with the triclabendazole-susceptible Cullompton isolate of Fasciola hepatica were treated with compound alpha at a dosage of 15 mg/kg at 12 weeks post-infection. Adult flukes were recovered from the bile ducts at 24h, 48 h and 72 h post-treatment (pt). They were processed for whole mount analysis, histology and transmission electron microscopy of the female reproductive system: specifically, the uterus, Mehlis' gland, ovary and vitellaria. As judged by the appearance of the uterus, normal egg production ceased within 24h of treatment; this phenomenon preceded significant changes to the other reproductive organs. Over the 3-day pt period, there was a progressive decline in the number of oogonia in the ovary, together with an increase in the number of eosinophilic and apoptotic oocytes and vacuolation and shrinkage of the ovarian tubules. There was a shift in the cell population within the vitelline follicles at 48 h pt, with relatively greater numbers of mature vitelline cells and fewer immature cells. The follicles were vacuolated and the shell globule clusters in the mature cells were disorganised. Greater disruption was seen at 72 h pt, with a reduction in the size of the follicles and rupture of cells, releasing their content into the lumen of the follicles. These histological observations were confirmed and extended at the TEM level. Thus, examination of electron micrographs showed that disruption of the shell globule clusters was evident at 48 h pt, which coincided with the start of the breakdown of the mature cells and of the nurse cell network. These degenerative changes were more conspicuous at 72 h pt. In the Mehlis' gland, shrinkage and vacuolation of the cells and their cytoplasmic extensions became progressively greater from 48 h to 72 h pt, and secretory activity declined. The changes in the reproductive organs and inhibition of egg production are put in context of the overall time-course of drug action.     

Serum gamma glutamyl transpeptidase activity in cattle with induced fascioliasis

Six-month-old calves were inoculated with 200 metacercariae of Fasciola hepatica over a 72 day period. Their aspartic transaminase, alkaline phosphatase, arginase and gamma glutamyl transpeptidase (GGT) values were measured at two-week intervals. Infections with a final fluke count of 19 to 87 flukes did not result in an increase of serum alkaline phosphatase or arginase compared with those in control calves. Serum aspartic transaminase values were increased significantly (P less than 0.025) above those of controls but were not increased over reference values. Seemingly, measurement of these enzymes would not be useful in assessing the degree of fluke infestation. In contrast, serum values of GGT increased 56 days after preliminary inoculation and remained high for at least 83 days after infection. The initial rise coincided with the penetration of bile ducts by migrating flukes. This relationship may be useful in further studies of fluke-induced biliary damage.     

Fasciola hepatica: comparison of flukes from Korea and the United States by isoelectric focusing banding patterns of whole-body protein.

Comparisons were made between the flukes from Chonnam, Korea and Oregon, USA by isoelectric focusing (IEF) of whole-body protein. Adult Fasciola hepatica were recovered from bile ducts of Korean native cattle. Whole-body protein of the flukes was subjected to IEF, and the banding patterns of the fluke protein were compared with those of North American F. hepatica recovered from experimentally infected calves. The overall banding pattern of F. hepatica from Korea was essentially identical to that of F. hepatica from the United States. These results provide further support for the usefulness of this technique in differentiating Fasciola species in other geographical areas.     

Resistance of Fasciola hepatica against triclabendazole in cattle in Patagonia (Argentina)

In the winter of 2008, cattle on a farm in the province of Neuquen, Argentina died from subacute and chronic liver fluke disease despite four previous treatments with Triclabendazole (TCBZ). In the spring of 2009, a preliminary efficacy test revealed good performance using nitroxynil, whereas TCBZ efficacy was only 18% by egg counts of Fasciola eggs in the faeces. Resistance to Fasciola hepatica to TCBZ has never been reported in South America, so in January of 2010 a controlled trial was conducted to confirm and to define the degree of resistance in this herd. In a clinical trial, the fluke egg output was monitored on Days 14 and 21 and serum enzymes gamma-glutamyl transpeptidase (GGT) and glutamic-oxaloacetic transaminase (GOT) on Days 0 and 21 in 36 calves treated with TCBZ or with closantel. The results showed a reduction of 100% in fluke egg output at Days 14 and 21 for closantel. The mean epg in the TCBZ-treated groups did not decrease. Because of the fact that in this study TCBZ treatment in cattle had no effect, even at double the recommended dose, it is highly indicative that resistance of F. hepatica against TCBZ is present on this farm. The GGT and GOT levels decreased in the closantel-treated group as a result of the treatment at 21 days after dosing. To evaluate the importance of TCBZ resistance in F. hepatica in Argentina, a study on more farms from endemic areas is needed.     

Effects of parenteral administration of doramectin or a combination of ivermectin and clorsulon on control of gastrointestinal nematode and liver fluke infections and on growth performance in cattle

OBJECTIVE: To compare effects of an injectable doramectin preparation with those of an injectable ivermectin-clorsulon preparation on control of gastrointestinal nematodes and liver flukes and on growth performance in cattle. DESIGN: Randomized complete block design. ANIMALS: 60 crossbred calves. PROCEDURES: Calves (20/treatment group) were treated with doramectin or ivermectin-clorsulon or were not treated. Fecal samples were collected for nematode and Fasciola hepatica egg counts on day 0 and for up to 140 days after treatment. Cattle were weighed before treatment and at 28-day intervals until day 140. RESULTS: From day 7 through day 49, nematode egg counts for calves treated with doramectin or with ivermectin-clorsulon were significantly lower than those for untreated control calves. As the study progressed beyond day 56, the percentages of cattle with fluke eggs in their feces increased, but differences in regard to these percentages were not detected among the 3 groups. Average daily gain for the doramectin-treated cattle (0.79 kg/d [1.74 lb/d]) was significantly greater than that for the cattle treated with ivermectin-clorsuIon (0.71 kg/d [1.56 lb/d]); values for both groups were significantly greater than that for the control cattle (0.62 kg/d [1.37 lb/d]). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that doramectin had a greater impact on subclinical gastrointestinal tract parasitism in calves, as demonstrated by growth performance, than did ivermectin-clorsulon. In the Gulf Coast region of the United States, spring-born nursing beef calves may have minimal grazing exposure to F hepatica during the peak fluke transmission period; therefore, mature fluke burdens may be negligible at the beginning of the fall season.     

Resistance in cattle to Fasciola hepatica induced by gamma-ray attenuated larvae: results from a controlled field trial.

A significant resistance to natural infection in the field was obtained in calves inoculated with metacercariae of Fasciola hepatica attenuated at a gamma-irradiation level of 3 Krad. The mean fluke burden of vaccinated calves was 29 per cent of that of the controls. The resistance was reflected not only in reduced parasite burdens and low faecal egg counts, but also in the stability of gamma-glutamyltranspeptidase levels of the vaccinated calves compared with non-vaccinated controls. The gamma-ray dose of 3 Krad did not prevent a small proportion of the irradiated larvae reaching and maturing in the bile ducts.     

Galectin secretion and binding to adult Fasciola hepatica during chronic liver fluke infection of sheep

Galectins are increasingly recognised as important mediators of immune homeostasis and disease regulation, but comparatively little is known about their role in parasite infection. This study investigates the interaction between two ovine galectins, galectin-11 and galectin-14, and the parasitic liver fluke, F. hepatica. Galectin-14 was found in eosinophils infiltrating the tissue surrounding infected bile ducts and secreted in the connective tissue, while galectin-11 was specifically induced in epithelial cells of bile ducts from infected sheep. Strong nuclear staining was observed for galectin-11. Both galectins were found to be secreted into the bile fluid of parasite infected sheep, and were also detected in the excretory/secretory products of adult flukes, following their removal from the ovine host. Recombinant galectin-14, but not recombinant galectin-11, was found to bind specifically to the surface tegument of adult flukes in a carbohydrate dependent manner. This study shows for the first time that both galectin-14 and galectin-11 are produced in liver tissue after chronic liver fluke infection and that they can directly interact with the parasite in the bile ducts. Galectin-11 may also be involved in epithelial cell turnover and cancerogenesis.     

Morphometry on lancet flukes found in Japanese sika deer (Cervus nippon centralis) captured in Iwate Prefecture, Japan

Thirty-six flukes were collected from the livers of wild deer (Cervus nippon centralis) captured in Iwate Prefecture, Japan, and were served for morphometry. The length and/or the width of the body, suckers, testes, ovary, vitelline glands, cirrus pouch and eggs in the uterus of the flukes were measured. The distance between anterior end of the body and position of the maximal body-width or upper end of the testes were also determined. A remarked morphological characteristic was that the right and left testes did not lie tandem but lined bilaterally. Also the position of the maximal body-width did not always locate in the posterior part of the body of the fluke. The property was in accordance with those for Dicrocoelium chinensis.     

The pharmacodynamics of the flukicidal salicylanilides, rafoxanide, closantel and oxyclosanide

The pharmacokinetics of oxyclosanide, rafoxanide and closantel were investigated in sheep (n = 5). All three drugs were extensively (greater than 99%) bound to plasma proteins and the plasma concentration/time curve was best described by a tri-exponential equation. Closantel and rafoxanide had long terminal half-lives (mean 14.5 and 16.6 days, respectively) compared with oxyclosanide (mean 6.4 days). In a study of the efficacy of rafoxanide against Fasciola hepatica, a dose rate of 7.5 mg kg-1 against 6-week-old flukes appeared to be similarly effective to a dose rate of 2.5 mg kg-1 against 10-week-old flukes (86% and 88% efficacy, respectively), as assessed at autopsies carried out on all sheep when the flukes were 14 weeks old. Part of this putative efficacy against immature flukes may be due to rafoxanide persisting in the plasma and affecting the mature flukes when they reach the bile ducts.     

Effect of gastrointestinal nematode and liver fluke infections on weight gain and reproductive performance of beef heifers

Spring born, crossbred beef heifers (n=372) were utilized over four years to measure reductions in body weights, reproductive performance and calf weights caused by gastrointestinal nematodes (primarily Ostertagia ostertagi) and the bovine liver fluke (Fasciola hepatica) and to differentiate losses attributable to each type of parasitism. Each year, weaned heifers were allotted to one of the four treatment regimens: Group 1, untreated controls; Group 2, treated for nematodes; Group 3, treated for liver fluke; and Group 4, treated for both nematodes and liver fluke. Nematodes were controlled with subcutaneous injections of either ivermectin (Ivomec, Merial) or doramectin (Dectomax, Pfizer), both at the recommended dose of 200 ug/kg bodyweight. Clorsulon (Curatrem, Merial) drench was given at the recommended rate of 7 mg/kg bodyweight to control flukes. Treatments and fecal collections were initiated at allotment each year and were repeated at 28-84-day intervals until palpation for pregnancy diagnosis. Open heifers were removed from the study at this time. Treatment dates were based on expected length of treatment efficacy, the stage of growth of the heifers and the seasonal risk of infection by the parasites. Pregnant females were pooled and received their assigned treatments prior to their calving and breeding seasons and remained together until their calves were weaned. Heifers treated for nematode infections were heavier and had higher condition scores (P<0.01) than untreated control heifers at initiation of breeding, and maintained that difference through pregnancy diagnosis. Liver fluke infection did not affect heifer gains or condition scores prior to palpation (P<0.01). At palpation, heifers treated for both forms of parasitism had the highest condition scores and weight gains (P<0.01), and also higher pregnancy rates than control heifers and heifers treated for nematodes only (P<0.01). Pregnancy rates for heifers treated for flukes only were not significantly different from those treated for both nematodes and flukes. Heifers treated for nematodes weaned heavier calves than those not treated for nematodes (P<0.05).     

Comparative fluke burden and pathology in condemned and non-condemned cattle livers from selected abattoirs in Zambia

After dissecting 70 condemned and 32 non-condemned cattle livers collected from Lusaka, Chisamba, Mongu and Senanga abattoirs and Turnpike slaughter slab, significantly higher numbers of liver flukes (Fasciola gigantica) (P < 0.001) were found in the condemned livers (mean +/- SD = 100.6 +/- 16.7) than in the non-condemned livers (mean +/- SD = 0.7 +/- 0.5). Liver flukes found in 9.4% of the non-condemned livers suggest that abattoir records of liver inspection may underestimate F. gigantica infections. Average faecal fluke egg counts from animals with condemned livers (5 eggs per gram [EPG]) were significantly higher (P < 0.001) than in animals with non-condemned livers (0.8 EPG). No correlation was found between egg counts and number of flukes. Fibrosis and calcification were common in condemned livers, being severest in the vicinity of the bile ducts. Only two (6.3%) of the non-condemned livers showed pathological changes on the liver edges. The severe liver damage and high worm burden may explain low production levels experienced in cattle in Zambia maintained under traditional systems of management where worm control and good management programmes are rarely practiced.     

Fasciola hepatica: Histological demonstration of apoptosis in the reproductive organs of flukes of triclabendazole-sensitive and triclabendazole-resistant isolates,and in field-derived flukes from triclabendazole-treated hosts,using in situ hybridisation to visualise endonuclease-generated DNA strand breaks

Investigation of the triclabendazole (TCBZ) resistance status of populations of Fasciola hepatica in field cases of fasciolosis, where treatment failure has been reported, can be supported by histological examination of flukes collected from recently treated hosts. In TCBZ-sensitive flukes (TCBZ-S) exposed to TCBZ metabolites for 1–4 days in vivo, but not in TCBZ-resistant flukes (TCBZ-R), morphological changes suggestive of apoptosis occur in cells undergoing meiosis or mitosis in the testis, ovary and vitelline follicles. In order to verify or refute the contention that efficacy of TCBZ treatment is associated with apoptosis in the reproductive organs of flukes, histological sections of TCBZ-S (Cullompton isolate) flukes and TCBZ-R (Sligo isolate) flukes were subjected to the TdT-mediated dUDP nick end labelling (TUNEL) in situ hybridisation method, a commercially available test specifically designed to label endonuclease-induced DNA strand breaks associated with apoptosis. Additionally, sections of in vivo-treated and untreated flukes originating from field outbreaks of suspected TCBZ-S and TCBZ-R fasciolosis were labelled by the TUNEL method. It was found that in treated TCBZ-S flukes, strong positive labelling indicating apoptosis was associated with morphologically abnormal cells undergoing mitosis or meiosis in the testis, ovary and vitelline follicles. Background labelling in the positive testis sections was attributed to heterophagy of cell debris by the sustentacular tissue. The triggering of apoptosis was probably related to failure of spindle formation at cell division, supporting the contention that TCBZ inhibits microtubule formation. In treated TCBZ-R (Sligo Type 1) flukes, and in treated flukes from field outbreaks of suspected TCBZ-R fasciolosis, no significant labelling was observed, while sections of fluke derived from a field case of fasciolosis where TCBZ resistance was not suspected were heavily labelled. Light labelling was associated with the testis of untreated Cullompton (TCBZ-S) and Sligo Type 2 (TCBZ-R) flukes, which exhibit abnormal spermatogenesis and spermiogenesis, respectively. This was attributed to apoptosis and to heterophagy of effete germ line cells by the sustentacular tissue. It is concluded that demonstration of apoptosis by in situ hybridisation using the TUNEL method on sections of 1–4 days in vivo TCBZ-treated F. hepatica can contribute to the diagnosis of TCBZ resistance in field outbreaks of fasciolosis.     

The effects of nitroxynil on the survival, growth and morphology of Fasciola hepatica in sheep.

Groups of sheep were experimentally infected with Fasciola hepatica and treated with nitroxynil at 10 mg/kg given subcutaneously at intervals of up to 70 days later. Effects on fluke burden, weight, morphology, egg production and hatchability were recorded. The results showed that the efficacy of nitroxynil and the occurrence of structurally abnormal flukes were directly proportional to the age of infection at treatment. Treatment also deleteriously affected fluke growth and egg hatchability and reduced faecal egg counts.     

Failure to induce homologous immunity to Fasciola hepatica in sheep vaccinated with irradiated metacercariae

Vaccination of sheep with either 100 or 1000 γ-irradiated (2.5 krad) metacercariae of Fasciola hepatica, on two occasions six weeks apart, did not generate significant protection against intraruminal challenge with F. hepatica six weeks after the second vaccinating dose as measured by recovery of flukes from liver and bile ducts, twenty weeks after challenge. There was, however, a significant increase in the proportion of flukes retarded in the parenchyma of both vaccinated groups. The percentage of retarded flukes was positively correlated with the degree of liver damage and increased weight of the hepatic lymph nodes. It was not possible to determine if the retarded flukes were derived from the vaccine or challenge infections or both.Challenge infection of both vaccinated and unvaccinated sheep significantly increased the numbers of eosinophils and globule leucocytes in the parenchymal bile duct and the numbers of mast cells and globule leucocytes in the abdominal bile duct. In addition the numbers of eosinophils and globule leucocytes in the parenchymal bile duct were significantly correlated with the percentage of retarded flukes in both vaccinated groups. In the abdominal bile duct, only the numbers of eosinophils in the low level vaccination group were significantly correlated with fluke retardation.Vaccination did not protect against the pathogenic effects of challenge infection as measured by reduced packed cell volumes and weight gain.     

Host influence on the banding profiles of whole-body protein and excretory-secretory product of Fasciola hepatica (Trematoda) by isoelectric focusing.

Various protein separation techniques have been used as alternative means of differentiating species and strains of parasites. Of these techniques, isoelectric focusing (IEF) has proved to be specific and reproducible with cestodes, protozoa and trematodes. As with the traditional morphological approach, there is, however, the potential for host influence. For a particular separation technique to be useful, it is important that banding profiles differentiating parasites be consistent, regardless of host species. To test for host influence, Fasciola hepatica were maintained in four definitive hosts. Soluble proteins of flukes from different hosts and their respective excretory-secretory product (ESP) were then subjected to IEF together with respective host tissues, and the resulting banding patterns were compared. Protein banding profiles of fluke body protein from llama, rat and mouse were very similar, while those of flukes from calves were distinct. Banding patterns of fluke ESP from different hosts were dissimilar. Overall banding patterns of body protein and ESP of flukes from different hosts were distinct from those of respective host tissues. The unique banding patterns of the body protein of flukes from calves indicate that there was host influence in their protein banding patterns, and the uniqueness of the calf fluke is discussed relative to host's resistance to the fluke.