Field trial on comparative efficacy of four fasciolicides against natural liver fluke infection in cattle

A controlled trial was conducted to evaluate the current efficacy of albendazole (ABZ), rafoxanide (RFX), triclabendazole (TRC) or clorsulon (CLS) against Fasciola hepatica in naturally infected cattle. This trial was conducted in Turkey during the spring, the time of year when liver fluke infection is endemic. Fifty crossbred cattle were selected for inclusion in the trial based on finding eggs of F. hepatica in the feces. The cattle were weighed and randomly allotted into five groups of 10 cattle and treatments were as follows: Group 1 served as non-treated control (CONT), Group 2 was treated orally with ABZ at 12 mg/kg, Group 3 was treated orally with RFX at 10 mg/kg, Group 4 received TRC orally at 12 mg/kg and Group 5 received CLS administered subcutaneously (s.c.) at 2 mg/kg. On day 0 (inclusion day), individual fecal samples were collected on days 0 (inclusion day), 7, 14, 28 and 56, after treatment. The drug efficacy was assessed as a percentage of the egg or fluke reduction and body weight gain relative to the untreated control. The results in the study showed a mean reduction of egg counts by 66.7%, 68.2%, 78% and 84.2% in Groups 2-5, respectively. In conclusion, our results indicate that CLS is a highly effective compound for the treatment of F. hepatica in cattle under these field conditions.

Dose-response inhibition of proteolytic activity by a cysteine protease inhibitor in a murine model of fasciolosis

Using the film in situ zymography (FIZ) technique, it has been demonstrated that N-[N-(L: -3-trans-carboxyoxirane-2-carbonyl)-L: -leucyl]-agmatine (E-64) inhibits Fasciola hepatica proteolytic activity in vivo. The aim of this study was to establish the dose-response relationship of the inhibition of proteolysis as assessed by FIZ with E-64 at different dosages in a murine model of fasciolosis. Maximum effective inhibition of proteolysis was achieved at 50 mg/kg/day (87%). Mice treated with this dose survived for a mean of 10.92 days more than untreated controls, and their ova counts and egg viability were significantly (P<0.05) lower than this latter group. These results indicate that intraperitoneal administration of E-64 not only inhibited liver proteolytic activity in a dose-dependent manner but also produced anti-fecundity and anti-embryonation effects, delaying the progression of fasciolosis. Yet, residual proteolysis may suggest that other E-64-non-sensitive enzymes are involved, or that E-64-enzyme chemical interactions are only capable of a partial agonistic-like effect.

Infection with Fasciola hepatica

Fascioliasis, caused by the liver fluke Fasciola hepatica, is an infection that occurs worldwide, although humans are accidental hosts. F. hepatica infection comprises two stages, hepatic and biliary, with different signs and symptoms. Stool examination and ELISA can be used for the initial diagnosis. Radiographic techniques, such as computerised tomography and ultrasonography, as well as magnetic resonance imaging, are used widely for confirmation and follow-up of the disease. Invasive techniques, such as percutaneous cholangiography, endoscopic retrograde cholangiography and liver biopsy, may aid in the diagnosis but are not essential. Triclabendazole is recommended as the first-line agent for the treatment of F. hepatica infection, with bithionol as an alternative.

Anthelmintic resistance – looking to the future: a UK perspective

The full extent of anthelmintic resistance in nematodes of farm animals is not known. Resistance can be detected with a faecal egg count reduction test and two in vitro tests, the egg hatch and larval development tests. The sensitivity of these two in vitro tests can be increased by using discriminating doses rather than calculating LD50 values. Only benzimidazole resistance can be detected with PCR based tests because the molecular mechanisms of resistance to levamisole and the macrocyclic lactones remain unknown. Resistance detection is important because it enables the appropriate management strategies to be put in place. The development of resistance is delayed by keeping sufficient parasites in refugia (not exposed to anthelmintic), but the necessary management details have not yet been validated in the field. It is probably too late to use combination products to delay the development of resistance, except in cattle but quarantining animals to prevent introduction of resistant helminths onto a farm is important. Dilution of resistant worms with susceptible ones is only at the preliminary research stage and the application of non-chemical methods of control to delay resistance is not yet a practical option. Extensive research is required to manage resistance, especially in the control of resistance in Fasciola hepatica.

A possible model of benzimidazole binding to beta-tubulin disclosed by invoking an inter-domain movement

Although it is well established that benzimidazole (BZMs) compounds exert their therapeutic effects through binding to helminth beta-tubulin and thus disrupting microtubule-based processes in the parasites, the precise location of the benzimidazole-binding site on the beta-tubulin molecule has yet to be determined. In the present study, we have used previous experimental data as cues to help identify this site. Firstly, benzimidazole resistance has been correlated with a phenylalanine-to-tyrosine substitution at position 200 of Haemonchus contortus beta-tubulin isotype-I. Secondly, site-directed mutagenesis studies, using fungi, have shown that other residues in this region of the protein can influence the interaction of benzimidazoles with beta-tubulin. However, the atomic structure of the alphabeta-tubulin dimer shows that residue 200 and the other implicated residues are buried within the protein. This poses the question: how might benzimidazoles interact with these apparently inaccessible residues? In the present study, we present a mechanism by which those residues generally believed to interact with benzimidazoles may become accessible to the drugs. Furthermore, by docking albendazole-sulphoxide into a modelled H. contortus beta-tubulin molecule we offer a structural explanation for how the mutation conferring benzimidazole resistance in nematodes may act, as well as a possible explanation for the species-specificity of benzimidazole anthelmintics.

The effect of the 5-chloro-2-methylthio-6-(1-naphtyloxy)-1H-benzimidazole on the tegument of immature Fasciola hepatica in their natural host

The damage to the tegument of 3-week-old Fasciola hepatica was evaluated by scanning electron microscopy (SEM) following treatment with the 5-chloro-2-methylthio-6-(1-naphtyloxy)-1H-benzimidazole (called compound alpha) in its natural host. For the present study, flukes were raised in pelibuey sheep infected orally with metacercariae of F. hepatica; the parasites were recovered from the liver of the sacrificed sheep after 6, 12 and 24 h of treatment with compound alpha. At 6 h of treatment, the flukes showed some lesions on the ventral surface of the anterior region, such as a swollen tegument and blebs. At 12 h after treatment, the specimens showed structural disorganization and spine loss in the ventral anterior region. The tegument of the flukes treated for 24 h was completely lost in some areas of the ventral surface, leaving an exposed basal lamina. The tegument of immature F. hepatica might be a target organ for compound alpha to exert its fasciolicide effect.

Ultrastructural observations on oral ingestion and trans-tegumental uptake of clorsulon by the liver fluke, Fasciola hepatica

Three experiments have been carried out in vitro to determine the effect of oral and trans-tegumental uptake of clorsulon on the fine structure of the tegument and gut of Fasciola hepatica. Changes were assessed by transmission electron microscopy. In the first experiment, the flukes were ligatured to prevent the oral ingestion of drug and treated for 24 h in clorsulon (10 microg/ml). Limited swelling of the basal infolds was observed in the tegumental syncytium. Swollen mitochondria were present in the syncytium, the underlying tegumental cells and in the gastrodermal cells. Swelling and vesiculation of the cisternae of the granular endoplasmic reticulum (ger) was evident in the gastrodermal cells, together with a reduction in secretory activity. In the second experiment, flukes were fed for 24 h on red blood cells isolated from rats dosed with clorsulon at 12.5 mg/kg body weight; this experiment was designed to prevent the exposure of the tegumental surface to the drug. There was severe swelling of the basal infolds in the tegumental syncytium and swelling of mitochondria in the syncytium, tegumental cells and gastrodermal cells. In the tegumental cells there was a decrease in the number of Golgi complexes as well. A number of changes were evident in the gastrodermal cells: swelling of the ger cisternae, an increase in the number of autophagic vacuoles, a reduction in the number of secretory bodies and disruption of the lamellae projecting from the surface of the cells. In the third experiment, flukes were incubated for 24 h in clorsulon (10 microg/ml), with both absorptive surfaces being available for drug uptake. There was severe swelling of the basal infolds in the tegumental syncytium and large autophagic vacuoles were present. Swollen mitochondria were a feature of the tegument, tegumental cells and gastrodermal cells, as were swollen cisternae of ger in the tegumental and gastrodermal cells. Fewer Golgi complexes were observed in the tegumental cells and in the gastrodermal cells there were fewer secretory bodies and an increased number of autophagic vacuoles. Overall, the gastrodermal cells were more severely affected than the tegument. Greater disruption of the tegument occurred when the oral route of uptake was available. The results support those of previous studies which point to oral uptake of clorsulon being the major route of entry into the fluke.

Response of two isolates of Fasciola hepatica to treatment with triclabendazole in vivo and in vitro

In this study, the susceptibility of two isolates of Fasciola hepatica--the Fairhurst and Oberon isolates--to treatment with triclabendazole was investigated, both in vivo and in vitro. The Fairhurst isolate originated in England, but has since been maintained in Australia; the Oberon isolate originated in Australia. Triclabendazole had a very high efficacy against the Fairhurst isolate. In sheep (dose: 10 mg/kg), the efficacy ranged from 78.4% at 2 weeks post-infection to 98.5% at 6 weeks post-infection. In cattle (dose: 12 mg/kg) efficacy was 89% at 2 weeks post-infection and 100% at 12 weeks. In contrast, against the Oberon isolate, triclabendazole had 0% efficacy against 2-week-old flukes in sheep (dose: 10 mg/kg) and 5% against 4-week-old flukes. Surface changes to flukes of the two isolates were assessed by scanning electron microscopy following treatment in vitro for 24 h in triclabendazole sulphoxide (15 and 50 microg/ml). Disruption took the form of blebbing, swelling and furrowing of the tegument and was greater in the Fairhurst than the Oberon isolate. Surface changes generally were more severe in the anterior than posterior region of the fluke and the dorsal surface was also consistently more severely affected than the ventral surface. Disruption was more severe at the higher drug concentration for both isolates. The morphological data is consistent with the efficacy data, which indicates that the Fairhurst isolate of F. hepatica is susceptible to triclabendazole treatment, whilst the Oberon isolate is refractory.

Measurement of triclabendazole and its metabolites in liver flukes: method development and full validation

The trematode parasite Fasciola hepatica is still the cause of considerable loss in livestock production all over the world. The knowledge of the pharmacological properties of the available flukicidal drugs is critical to control this parasite. Triclabendazole is an halogenated benzimidazole anthelmintic with potent flukicidal activity. A simple reversed-phase high-performance liquid chromatographic analytical method has been developed, validated and applied for the quantitative determination of the flukicidal drug triclabendazole and its sulpho- and hydroxy-metabolites in the liver fluke, F. hepatica. Triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone, hydroxy-triclabendazole, hydroxy-triclabendazole sulphoxide and hydroxy-triclabendazole sulphone were measured simultaneously in this trematode parasite. Linearity, resolution, precision, accuracy, recovery, limits of detection and quantification of the method were determined. Drug extraction from the parasite's tissue homogenate was effectively performed using liquid extraction (acetonitrile), avoiding clean up by solid phase extraction, prior to analysis by reversed-phase high-performance liquid chromatography. The resolution of all the halogenated benzimidazole thiol molecules assayed was obtained on a C(18) reversed-phase (5 microm, 250 mm x 4.6 mm) column using acetonitrile and ammonium acetate as the mobile phase and ultraviolet detection at 300 nm. Regression analyses were linear over the concentration range examined (from 0.272 to 16.331 nmol/100 mg trematode protein) and the correlation coefficients of the calibration curves ranged between 0.996 and 1.000. The calculated limits of detection of the proposed method for the parent drug and its metabolites ranged between 0.007 and 0.079 nmol/100 mg trematode protein. The extraction efficiency for the different analytes from the parasite material was greater than 71%. The results obtained indicated that the developed chromatographic method was selective, accurate and easy to reproduce. The developed procedure was successfully applied to quantify triclabendazole/metabolites in F. hepatica incubated under ex vivo conditions, demonstrating to be efficient for the determination of the most extensively used flukicidal drug available for veterinary medicine, and its metabolites. The analytical method described here is an useful tool for the measurement of this flukicidal compound in different studies addresses to evaluate drug influx/eflux and metabolism in its main target parasite.

Human fascioliasis

Fasciola hepatica, a zoonotic liver fluke, can also cause disease in humans. Common symptoms are epigastric pain, upper abdominal pain and malaise. Fever and arthralgia are common in acute fascioliasis. Eosinophilia is the predominant laboratory finding, especially in patients with the acute form of the disease. Diagnosis and treatment is not easy, as physicians rarely encounter this disease, and effective drugs are not available in many countries. Human fascioliasis may be underestimated. Patients with eosinophilia and abdominal pain should be evaluated for F. hepatica infestation by parasitological, radiological and serological tests.

Tegumental surface changes in adult Fasciola hepatica following treatment in vitro and in vivo with an experimental fasciolicide

Our objective was to determine by scanning electron microscopy the structural changes in the tegument of adult Fasciola hepatica after treatment with 5-chloro-2-methylthio-6-(1-naphtyloxy)-1 H-benzimidazole, called compound alpha, and its active metabolite sulphoxide, under in vitro and in vivo conditions. For the in vitro studies, flukes from sheep were exposed to 40 mg/l of compound alpha-sulphoxide over different incubation times. Flukes for the in vivo studies were raised in sheep treated orally with compound alpha and killed at different times post-treatment. Non-treated controls were included for each time of incubation. The results showed lesions after 6 h of treatment, such as swelling and furrows. At 12 h, the spines appeared to be surrounded by the tegument. At 24 h the tegument in some areas showed an exposed basal lamina. These changes became more severe as the incubation periods of the treated flukes increased. Compound alpha exerts a significant effect on the tegument of F. hepatica.

Transmission electron microscope study of the ultrastructural changes induced in the tegument and gut of Fasciola hepatica following in vivo drug treatment with clorsulon

Using transmission electron microscopy (TEM), both the tegument and gut of Fasciola hepatica were examined in an effort to identify and characterise the ultrastructural changes induced following treatment with the flukicidal drug clorsulon. Male Sprague-Dawley rats infected with F. hepatica were dosed orally at 8-8.5 weeks post-infection with clorsulon at a concentration of 12.5 mg/kg body weight. After 24, 48 and 72 h, rats were sacrificed by cervical dislocation and mature flukes recovered from the bile ducts. After 24 h treatment in vivo, disruption of the tegumental syncytium was concentrated at the apex of the syncytium where a dark band consisting of numerous secretory bodies was present. Some blebbing of the apex had also occurred, "open" bodies were present in this region and the mitochondria were slightly swollen. In the cell bodies, swelling of the mitochondria and their cristae had also occurred and the Golgi complexes appeared to be smaller than normal. The disruption seen after 48 h treatment in vivo was similar but more severe: the frequency of blebbing had increased, as had the number of "open" bodies and the swelling of the mitochondria. Vacuoles had begun to appear in the syncytium-both autophagic and electron-lucent-and swelling of the mucopolysaccharide masses around the basal infolds had occurred. Lipid droplets were observed occasionally. In the cell bodies, autophagic vacuoles had begun to appear and swelling of the mitochondria had increased in severity. After 72 h treatment in vivo, more severe disruption was seen in the tegumental syncytium in which widespread swelling and blebbing of the apex was apparent. The basal infolds had become very badly swollen in a number of specimens and damage to the spines was evident. The mitochondria remained swollen, as did the mucopolysaccharide masses around the basal infolds. Lipid droplets were more frequently observed in the syncytium. In the tegumental cells, swelling of the mitochondria was greater and an increase in the number of autophagic vacuoles was apparent. The gut showed signs of disruption after 24 h treatment in vivo, in that the surface lamellae were disrupted and a build-up of autophagic vacuoles at the apex of the cells had taken place. Swelling of the mitochondria and the cisternae of granular endoplasmic reticulum (gER) was evident. There was a decrease in the number of secretory bodies. After 48 h treatment in vivo, the number of autophagic vacuoles in the gastrodermal cells had increased, the mitochondria and gER remained swollen and the disruption seen to the lamellae was still evident. In the 72 h-treated specimens, the disruption seen in the gastrodermal cells had increased significantly, with severe vacuolation of the apical cytoplasm. An increase in the number of autophagic vacuoles was evident, the mitochondria and the gER remained swollen and lipid droplets were present in the cells.

Specific tyrosine phosphorylation in response to bile in Fasciola hepatica and Echinostoma friedi

Protein tyrosine phosphorylation (PY) is a well-known signalling mechanism which is also involved in host-parasite interactions. Despite its transcendence, PY has been poorly studied in parasitic helminths. The aim of this study is to examine the effect of bile salts on the PY pattern in parasitic trematodes. Two distinct adult models were analysed: Echinostoma friedi, of intestinal habitat, and Fasciola hepatica, naturally inhabitant of host biliary channels. Our results show that bile salts induce specific and distinct protein PY in both trematode species, indicating that this signalling process seems to be also involved in host-trematode relationships.

The comparative metabolism of triclabendazole sulphoxide by triclabendazole-susceptible and triclabendazole-resistant Fasciola hepatica

Benzimidazole anthelmintics are widely used against nematode, cestode and trematode parasites. The drugs undergo several enzyme-mediated reactions within the host animal that produce a number of metabolites. Although it has been shown that certain helminths, including Fasciola hepatica, can metabolise albendazole, nothing is known regarding the ability of the liver fluke to metabolise triclabendazole, which is the major flukicidal compound currently on the market. In the current study, adult triclabendazole-susceptible flukes were treated with triclabendazole sulphoxide in vitro, and the metabolism of the drug was monitored by high performance liquid chromatography. The data show that F. hepatica can metabolise triclabendazole sulphoxide into its relatively inert sulphone metabolite. Parallel experiments using triclabendazole-resistant flukes showed that the conversion of triclabendazole sulphoxide to triclabendazole sulphone was on average 20.29% greater in the resistant flukes compared with the susceptible flukes. The results are discussed with regard to the mechanism of triclabendazole resistance in F. hepatica.

Fasciola hepatica: tegumental surface alterations following treatment in vivo and in vitro with nitroxynil (Trodax)

Male Sprague-Dawley rats were dosed orally with nitroxynil at a concentration of 40 mg/kg and adult Fasciola hepatica recovered after 24 h, 48 h and 72 h. Surface changes to the flukes were monitored by means of SEM. After the 24 h treatment, extensive swelling and blebbing of the tegument was observed on both surfaces, although the dorsal anterior region was more severely affected than either the posterior dorsal region or entire ventral surface. At high magnification, microvillus-like projections were evident, giving the surface a roughened appearance. After 48 h, the changes evident at 24 h had become more severe and some tegumental loss had occurred in the oral region of the fluke. Surface disruption was particularly evident along the lateral margins of the fluke in this region. In some specimens a single large swelling was present in the dorsal midbody region. The swelling was a more typical feature of flukes recovered. After 72 h, tegumental loss was more widespread, occurring over the oral cone and anterior midbody on the dorsal surface. Overall the dorsal surface was consistently more severely affected than the ventral surface, and the anterior region of the fluke was more disrupted than the posterior region. After 24 h in vitro incubation, the oral cone and midbody exhibited considerable spine loss and swelling. Overall, the dorsal surface was more disrupted than the ventral surface and the anterior region of the fluke was more disrupted than the posterior region. Regional differences in the response of the fluke to nitroxynil will be compared to previously published data with other fasciolicides. The results indicate that the tegument is an important target for nitroxynil action. Disruption of this, the fluke's main line of defence, would allow the drug access to other internal tissues, leading to more widespread damage.

Fasciola hepatica: effects of the fasciolicide clorsulon in vitro and in vivo on the tegumental surface, and a comparison of the effects on young- and old-mature flukes

The ultrastructural changes in Fasciola hepatica induced by the fasciolicide clorsulon were assessed using scanning electron microscopy. At 8 and 44 weeks post-infection, male Sprague-Dawley rats infected with F. hepaticawere dosed orally with clorsulon at a concentration of 12.5 mg/kg and mature flukes recovered from the bile duct after 24 h, 48 h, and 72 h in both experiments. An in vitro incubation was also set up using mature fluke (8 weeks old) incubated with clorsulon for 24 h at a concentration of 10 microg/ml. After 24 h in vivo, the young-mature flukes (8 weeks old) showed significant disruption to the tegumental surface, particularly in the anterior mid-body region, where a distinct band of swelling and blebbing was evident. The band began just behind the ventral sucker and ran posteriorly along both margins. The apical cone region of the fluke was characterised by swelling and blebbing of the surface between the spines. Similar changes were evident after 48 h in vivo, but the disruption was more severe and the mid-body band had spread posteriorly. In approximately half of the specimens recovered after 72 h in vivo, widespread disruption had occurred, with sloughing of the apical membrane or the entire syncytium, over almost all of the oral cone and anterior mid-body. For all time periods, the anterior half of the fluke was more severely affected than the posterior half. No differences were seen between the dorsal and ventral surfaces. Old-mature flukes (44 weeks old) showed regionally similar, but more severe and widespread disruption than that seen in the young-mature flukes. The onset of surface changes occurred more quickly in old-mature flukes as well. Eight-week-old flukes which had been incubated for 24 h in vitro showed surprisingly little disruption, but this may be due to the method by which the drug is taken up by the fluke.

The effect of the microtubule inhibitor tubulozole-C on the tegument of triclabendazole-susceptible and triclabendazole-resistant Fasciola hepatica

The benzimidazole derivative, triclabendazole is the main drug used against Fasciola hepatica, although its precise mode of action remains to be fully determined. Previous studies have suggested that triclabendazole acts as a microtubule inhibitor in the same manner as tubulozole-C. Consequently, flukes from triclabendazole-susceptible and triclabendazole-resistant isolates were treated with tubulozole-C (1x10(-6 )M) in vitro and changes in tegumental morphology and tubulin distribution within the tegument were monitored by scanning and transmission electron microscopy, together with tubulin immunocytochemistry. Tubulozole-C caused severe disruption within the tegument of triclabendazole-susceptible flukes. Tubulin immunoreactivity diminished within the tegumental syncytium of the triclabendazole-susceptible flukes following treatment with tubulozole-C. In contrast, tubulozole-C caused only minor disruption of the tegument in triclabendazole-resistant F. hepatica and did not significantly alter the pattern of tubulin immunostaining within the tegumental syncytium. The results of the present study indicate that tubulozole-C and triclabendazole share the same target molecule and that triclabendazole-resistant flukes are also cross-resistant to tubulozole-C.

Fasciola hepatica: surface and internal tegumental changes induced by treatment in vitro with the sulphoxide metabolite of albendazole ('Valbazen')

A morphological study has been carried out to determine the effect of the active sulphoxide metabolite of the benzimidazole anthelmintic, albendazole (ABZ-SO) on the adult liver fluke, Fasciola hepatica. Whole flukes were treated with ABZ-SO for 12 and 24 h at a concentration of 10 microg/ml. The changes in response to drug treatment were examined by scanning electron microscopy (SENI), transmission electron microscopy (TEM) and tubulin immunocytochemistry (ICC). No surface changes were apparent following 12 h ABZ-SO treatment, but localized blebbing was observed after 24 h, which became more extensive towards the posterior region of both surfaces. TEM of sections from the posterior midbody region revealed that ABZ-SO caused the accumulation of secretory bodies in the tegumental cells and in their cytoplasmic connections and, after 24 h, just above the basal plasma membrane. Localized blebbing of the apical membrane also occurred. The morphology of the Golgi complexes within the tegumental cells began to change after 12 h treatment with ABZ-SO and, by 24 h, few complexes were observed. A distinct increase in tubulin immunoreactivity occurred after 12 h treatment, but this decreased after 24 h. The results obtained are consistent with those expected for microtubule inhibition. They are discussed in relation to the action of established microtubule inhibitors, as well as the benzimidazole derivative, triclabendazole.

Pre-exposure of cattle to drug-abbreviated Fasciola hepatica infections: the effect upon subsequent challenge infection and the early immune response

In this study we examined whether juvenile liver flukes are capable of stimulating protective immune responses in cattle. Four experimental groups of cattle were studied as follows: group A, a positive control, received a primary infection on day 0 and a secondary infection 28 days later; group B also received two infections but the primary infection was terminated by drug treatment on day 5; group C, received infections on days 0, 5 and 10 which were terminated by drug treatments on days 1, 6 and 11 and then a secondary infection on day 28; group D received an infection only on day 28. Juvenile flukes appear to induce protective responses because: (a) group B animals had significantly lower levels of gamma-GT (P<0.05) than group D; (b) both groups B and C exhibited lower parenchymal phase GLDH levels (P=0.006 and 0.041, respectively); and (c) both groups B and C had lower secondary phase eosinophilia (P=0.002 and 0.02, respectively) than those in group D. Sera taken from groups A-C contained antibodies reacting to a variety of proteins in adult fluke somatic antigen and excretory-secretory preparations, particularly to proteins of 52-60, 68-72 and 82-96 kDa. After secondary challenge the antibody responses of group A to these proteins declined while reactivity to proteins of 28-30 kDa increased. Antibody responses to the 28-30 kDa proteins were not detected in groups B-D until 3 weeks later than those observed in group A. Antibody responses to Fasciola hepatica cathepsin L proteases, which are known to induce protection, were monophasic, of the IgG1 isotype only and were not observed prior to secondary challenge in any of the four groups. In contrast, the response to another protective antigen fraction, a high molecular sized haem protein, was of a mixed IgG1/IgG2 nature and was detected within 14 days of primary infection. However, no significant difference in antibody titres to either protein preparation was observed after the secondary infection when groups B and C were compared to group D.

The efficacy of formulations of triclabendazole and ivermectin in combination against liver fluke (Fasciola hepatica) and gastro-intestinal nematodes in cattle and sheep and sucking lice species in cattle

OBJECTIVE

To assess the efficacy of two formulations of triclabendazole and ivermectin in combination against liver fluke (Fasciola hepatica), gastro-intestinal nematodes and sucking louse species in cattle and sheep.

PROCEDURE

A study of 540 cattle and 428 sheep at 18 sites throughout Victoria and New South Wales was undertaken. At each site, one group of cattle or sheep was treated with a combined formulation (Fasimec Cattle or Fasimec Sheep), another received ivermectin and triclabendazole separately. In trials on lice infestation, an additional group remained untreated. Samples for faecal egg counts were collected on days -7, 0 (treatment day), +7, +14 and +21 after treatment. Lice assessments were carried out on days -7, 0, +7, +14, +28, +42 and +56.

RESULTS

Both treatments were highly efficacious (> 98% efficacy) against liver fluke in cattle and sheep, against three sucking lice species of cattle and against gastro-intestinal nematodes in sheep. There was also no significant difference between treatments in efficacy. Against gastro-intestinal nematodes, Fasimec Cattle was significantly (P < 0.01) more effective than the separately applied ivermectin and triclabendazole treatment. Mean efficacy for the Fasimec Cattle and Ivomec/Fasinex 120 groups respectively, was 97.6% and 94.2% on Day +7, 98.9% and 91% on Day +14 and 98.5% and 92.6% on Day +21.

CONCLUSION

The efficacy of Fasimec' Cattle and Fasimec Sheep was at least equal to that of currently registered products (with the same active ingredients) used to control these parasites.

[Synthesis and insecticidal activity of the novel hydroxylbenzenedisulfonanilides compounds]

AIM

To synthesize novel derivatives of hydroxylbenzenedisulfonanilide with high insecticidal activity against the Fasciola hepatica.

METHODS

o-(m-, p-) Chlorphenol were used to synthesize the title compounds by sulphonation and nucleiphilic-substitution reaction. The uncoupling activity (insecticidal activity) of these compounds were tested by determining the influence on mitochondrial respiration control ratio (RCR) and the variation of inorganic phosphate in oxidative phosphorylation (delta Pi).

RESULTS

Compounds 1-14 are new compounds. The structures of the compounds were determined by IR, HNMR and elemental analysis. Most new compounds have relatively high uncoupling activities, especially compounds 3, 5, 6 and 9.

CONCLUSION

Compounds 3, 5, 6 and 9 will become novel fasciolicides and are worth further studying.

Synthesis and fasciolicidal activity of 5-chloro-2-methylthio-6-(1-naphthyloxy)-1H-benzimidazole

The synthesis and fasciolicidal activity of 5-chloro-2-methylthio-6-(1-naphthyloxy)-1H-benzimidazole (6) is described. Compound 6 showed 100% activity in vitro at 146.70 and 29.34 microM concentrations. It also completely removed 3-d and 10-week-old Fasciola hepatica in sheep at a dose of 15 mg/kg.

Fasciola gigantica: tegumental surface alterations following treatment in vitro with the sulphoxide metabolite of triclabendazole

The effect of the active sulphoxide metabolite of the fasciolicide triclabendazole on the surface morphology of the tropical liver fluke, Fasciola gigantica, was determined in vitro by scanning electron microscopy. At a concentration of 10 microg/ml, swelling and blebbing of the tegument was evident after only 6 h incubation. The blebbing was focussed on the spines. With progressively longer incubation periods, blebbing on the spines became more severe, leading to tegumental sloughing and spine loss. Tegumental loss became more widespread and, after incubation periods of 18 h and 24 h in vitro, perforations of the basal lamina were evident and, in some cases, holes penetrated through the entire fluke in the tail region. The ventral surface was consistently more severely affected than the dorsal and similarly the posterior region of the fluke was more disrupted than the anterior region. The results confirm the potent activity of triclabendazole against F. gigantica.

Triclabendazole-resistant Fasciola hepatica: beta-tubulin and response to in vitro treatment with triclabendazole

Resistance in Fasciola hepatica to triclabendazole ('Fasinex') has emerged in several countries. Benzimidazole resistance in parasitic nematodes has been linked to a single amino acid substitution (phenylalanine to tyrosine) at position 200 on the beta-tubulin molecule. Sequencing of beta-tubulin cDNAs from triclabendazole-susceptible and triclabendazole-resistant flukes revealed no amino acid differences between their respective primary amino acid sequences. In order to investigate the mechanism of triclabendazole resistance, triclabendazole-susceptible and triclabendazole-resistant flukes were incubated in vitro with triclabendazole sulphoxide (50 microg/ml). Scanning and transmission electron microscopy revealed extensive damage to the tegument of triclabendazole-susceptible F. hepatica, whereas triclabendazole-resistant flukes showed only localized and relatively minor disruption of the tegument covering the spines. Immunocytochemical studies, using an anti-tubulin antibody, showed that tubulin organization was disrupted in the tegument of triclabendazole-susceptible flukes. No such disruption was evident in triclabendazole-resistant F. hepatica. The significance of these findings is discussed with regard to the mechanism of triclabendazole resistance in F. hepatica.