Fasciola hepatica: tegumental surface changes in adult and juvenile flukes following treatment in vitro with the sulphoxide metabolite of triclabendazole (Fasinex)

Clinostomum complanatum: Anthelmintic potential of curcumin on the infective progenetic metacercarial stage

The emerging resistance against commonly used antiparasitic drugs has driven investigators to explore alternative approaches using plant-derived active ingredients. These compounds have been tested for antiviral, antibacterial, and anthelmintic properties, particularly against adult worms. However, their effects on larval forms have been neglected. Curcumin is a polyphenol that is a significant constituent of the rhizome of Curcuma longa and possesses various biological activities, including antioxidant, anti-inflammatory, anti-infectious, and anti-carcinogenic. In the present study, the anthelmintic potential of curcumin was tested in vitro for its efficacy against the zoonotically important larval form, the progenetic metacercariae of Clinostomum complanatum, which were procured from the forage fish, Trichogaster fasciatus. Curcumin produced time and concentration-dependent inhibition in the motility of treated metacercarial worms, with the maximum inhibition of motility reported at 60 μM along with a significant increase of (36-92%) in ROS and (57-112%) in GSH levels at the end of a period of 6 h. In contrast, curcumin at the highest concentration significantly inhibited the activities of the antioxidant and detoxification enzymes SOD (36%) and GST (16%), respectively, in addition to altering the polypeptide profile and inhibiting cysteine proteases. The tegumental surface appeared to be highly disrupted in curcumin-treated worms, exhibiting severe blebbing, shearing of the tegument, and spine erosion. Such changes would affect the tegumental functions and survival of worms in the hostile microenvironment. This would render worms more susceptible to host-mediated rejection responses. Based on the results of the present study, it is inferred that C. complanatum could serve as an excellent model for screening novel anthelmintic drugs against larval trematodes of great economic significance. Furthermore, we conclude that curcumin could be exploited as an excellent phytotherapeutic agent against the virulent larval form under investigation.

Efficacy of flukicides on Fasciola gigantica, a food-borne zoonotic helminth affecting livestock in Bangladesh

Fasciola gigantica, the causative agent of tropical fasciolosis, is a food-borne zoonotic trematode that affects around 80% livestock of Bangladesh. Triclabendazole (TCBZ), nitroxynil (NTON) and oxyclozanide (OCZN) are frequently used against fascioliasis; however, the current status of potency of these flukicides was unknown. In this study, in vitro efficacy of TCBZ, NTON and OCZN at various concentrations on F. gigantica has been evaluated by relative motility (RM), morphological distortions of apical cone through an inverted microscope, architectural and ultra-structural changes through histopathological and scanning electron microscopy (SEM). It is observed that TCBZ, NTON and OCZN at higher concentrations significantly (P < 0.05) reduced RM of the flukes compared to untreated control. NTON at 150 μg mL−1 was the most potent to reduce the motility within 4 h whereas TCBZ and OCZN were much delayed. Histopathological changes showed swollen, extensive cracking, numerous vacuoles and splitting of the tegument surrounding the spines; spine dislodged from its socket in treated flukes compared to untreated worms. Histopathological changes were more conspicuous at higher doses of TCBZ, NTON and OCZN. SEM has shown the disruption of the apical cone, apart from swelling of the tegument on the ventral surface corrugation and disruption of the ventral apical cone. All these changes indicate that NTON is the most potent in killing flukes in vitro among the tested flukicides and suggest the presence of TCBZ-resistant fluke populations in Bangladesh. It is imperative to explore the in vivo effects of these flukicides and subsequently their molecular mechanisms.

Egyptian propolis and selenium nanoparticles against murine trichinosis: a novel therapeutic insight

Trichinosis is a serious zoonotic disease that causes human morbidity and mortality. New effective natural remedies with minimal side effects that are well tolerated are needed to treat both enteral and parenteral trichinosis. This study evaluated the efficacy of selenium (Se), Se nanoparticles (SeNPs) and Egyptian propolis compared with albendazole as antiparasitic, anti-inflammatory and anti-angiogenic agents for treating murine trichinosis. We used parasitological, histopathological and immunohistochemical assays, as well as scanning electron microscopy, to examine adult worms. Overall, 80 Swiss albino male mice were divided into eight groups, with ten mice in each group, as follows: negative control, positive control, albendazole, propolis, Se, combination of propolis and Se, SeNPs and combination of SeNPs and propolis. Mice were slaughtered seven and 35 days after infection to examine the intestinal and muscular phases, respectively. This study demonstrated the efficacy of the combination of SeNPs and propolis. As revealed by electron microscopy, this combination caused damage to the adult worm cuticle. Additionally, compared with albendazole, it resulted in a significant reduction in adult worm and total larval counts; moreover, it caused a decrease in the number of larvae deposited in muscles, with a highly significant decrease in the inflammatory cell infiltrate around the larvae and a considerable decrease in the expression of the angiogenic marker vascular endothelial growth factor in muscles. In conclusion, the combination of SeNPs and propolis had antiparasitic, anti-inflammatory and anti-angiogenic effects on trichinosis. Consequently, this combination could be used as a natural alternative therapy to albendazole for treating trichinosis.

Spatial visualization of drug uptake and distribution in Fasciola hepatica using high-resolution AP-SMALDI mass spectrometry imaging

Understanding drug penetration, distribution, and metabolization is fundamental for understanding drug efficacy. This also accounts for parasites during antiparasitic treatment. Recently, we established matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) in blood flukes and liver flukes. This label-free technique is capable of visualizing the molecular distribution of endogenous and exogenous molecules, such as drug compounds. Here, we conducted atmospheric-pressure scanning microprobe MALDI MSI (AP-SMALDI MSI) of tissue sections of adult Fasciola hepatica that have been treated in vitro with 100 µM of triclabendazole (TCBZ), the drug of choice for treatment of fasciolosis, and its main metabolite triclabendazole sulfoxide (TCBZ-SO). Measurements covered an m/z mass range of 250–1,000 and provided a high spatial resolution using a pixel size of 10 µm. To support the interpretation of drug distribution, we first identified endogenous lipids that mark characteristic tissues such as the gastrodermis, the tegument, and the parenchyma. The obtained results suggested an early tegumental route of TCBZ uptake within 20 min, followed by spreading throughout the parasite after 4 h, and an even distribution in most tissues after 12 h. This coincided with a strong reduction of parasite vitality. TCBZ-SO treatment demonstrated the accumulation of this metabolite in the same tissues as the parent drug compound. These data demonstrate the auspicious potential of MALDI MSI to visualize uptake and distribution patterns of drugs or drug-candidate compounds in parasites, which might contribute to preclinical drug discovery in liver fluke research and beyond.

A. Immature Fasciola gigantica: Time-dependent ultrastructural changes following in vivo treatment with triclabendazole

An in vivo study was carried out to investigate the ultrastructural effects of triclabendazole (TCBZ) on immature Fasciola gigantica in a goat model. Five goats were infected with an oral gavage of 150 metacercarial cysts of F. gigantica and anthelmintic treatment occurred at 4 weeks post infection with an oral dose of 10 mg/kg. They were euthanized at 0 (untreated), 24, 48, 72 and 96 h post treatment (h pt). Juvenile flukes were recovered from each of the goat's liver and processed for transmission electron microscopy (TEM). The untreated control flukes showed normal ultrastructure and no apparent changes were observed at 24 h pt. At 48 h pt, moderate levels of disruption were observed to the tegument and minor changes to the sub-tegument which included widespread blebbing and disruption of apical tegumental membrane, swollen mitochondria, reduced number of secretory bodies, swelling of basal infolds leading to severe vacuolation, and relatively mild disruption to the subtegumental muscle fibres, parenchyma and tegumental cells, whereas the gastrodermal cells appeared less affected. By 72 h pt, sloughing of the tegumental syncytium was evident leading to the exposure of the basal lamina and the disruption was severe in the subtegument too. At 96 h pt, the flukes were totally devoid of tegument and the disruption was extremely severe, distorting the ultrastructure of the entire fluke's body. The results of the present study revealed that the flukes showed time-dependent progressive disruption to the internal tissues which became increasingly severe over time pt. This is the first study to detail the time-scale and impacts on ultrastructural morphology of the in vivo TCBZ treatment of the immature tropical liver fluke, Fasciola gigantica.

In vitro effect of curcumin on Schistosoma species viability, tegument ultrastructure and egg hatchability

Schistosomiasis remains a severe problem of public health in developing countries. The development of resistance to praziquantel (PZQ) has justified the search for new alternative chemotherapies with new formulations, more effective, and without adverse effects. Curcumin (CUR), the major phenolic compound present in rhizome of turmeric (Curcuma longa L.), has been traditionally used against various diseases including parasitic infections. Here, the antischistosomal activity of CUR (50-500 μM), evaluated in parallel against S. mansoni and S. haematobium adult worms, appeared significant (P < 0.05 to < 0.0001) in a time- and dose-dependent manner. Two h incubation with CUR (500 μM) caused 100% irreversible killing of both schistosomal species. CUR (250 μM) caused the death of S. haematobium and S. mansoni worms after 2 h and 4 h, respectively. As CUR concentration decreases (50 μM), all coupled adult worms were separated into individual male and female but the worms remained viable up to 4 h. Scanning and transmission electron microscopy revealed that S. haematobium are more sensitive than S. mansoni to CUR schistosomicidal effects. In support, CUR was found to affect the antigenicity of surface membrane molecules of S. haematobium, but not S. mansoni. Of importance, CUR significantly (P < 0.05 to < 0.0001) affected S. mansoni eggs hatchability and viability, a ground for its use in chemotherapy of schistosomiasis mansoni and japonicum because of its increased bioavailability in the gastrointestinal tract. The data together emphasize that CUR is a promising potential schistosomicidal drug.

Pleiotropic alterations in gene expression in Latin American Fasciola hepatica isolates with different susceptibility to drugs

Background

Fasciola hepatica is the main agent of fasciolosis, a zoonotic disease affecting livestock worldwide, and an emerging food-borne disease in humans. Even when effective treatments are available, drugs are costly and can result in tolerance, liver damage and normally they do not prevent reinfection. Drug-resistant strains in livestock have been reported in various countries and, more worryingly, drug resistance in human cases has emerged in South America. The present study aims to characterize the transcriptome of two South American resistant isolates, the Cajamarca isolate from Peru, resistant to both triclabendazole and albendazole (TCBZR/ABZR) and the Rubino isolate from Uruguay, resistant to ABZ (TCBZS/ABZR), and compare them to a sensitive strain (Cenapa, Mexico, TCBZS/ABZS) to reveal putative molecular mechanisms leading to drug resistance.

Results

We observed a major reduction in transcription in the Cajamarca TCBZR/ABZR isolate in comparison to the other isolates. While most of the differentially expressed genes are still unannotated, several trends could be detected. Specific reduction in the expression levels of cytoskeleton proteins was consistent with a role of tubulins as putative targets of triclabendazole (TCBZ). A marked reduction of adenylate cyclase might be underlying pleiotropic effects on diverse metabolic pathways of the parasite. Upregulation of GST mu isoforms suggests this detoxifying mechanism as one of the strategies associated with resistance.

Conclusions

Our results stress the value of transcriptomic approaches as a means of providing novel insights to advance the understanding of drug mode of action and drug resistance. The results provide evidence for pleiotropic variations in drug-resistant isolates consistent with early observations of TCBZ and ABZ effects and recent proteomic findings.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2553-2) contains supplementary material, which is available to authorized users.

Morphological and histological analysis of Cotylophoron cotylophorum treated with Acacia concinna

Objective:

Paramphistomosis (stomach fluke disease) is a parasitic infection caused by digenetic trematodes and is considered to be one of the most important parasitic diseases affecting livestock worldwide. This disease is widely prevalent in India, and the highest incidence is reported during monsoon and post-monsoon months. In the present study, in vitro effect of aqueous extract of pods of Acacia concinna (AcP E) on the morphology and the histology of the digenetic trematode Cotylophoron cotylophorum have been investigated.

Materials and Methods:

The in vitro effect of AcPE on the morphology and the histology of a digenetic trematode C. cotylophorum have been examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and light microscopic techniques.

Results:

The SEM micrograph of treated flukes showed the appearance of few blebs near the oral region and rupture of the dorsal surface of the tegument. The light and TEM observations revealed significant deleterious changes in the internal organization of the fluke. Severe injury to the tegument due to bleb formation, detachment of tubercles, and vacuolization of the subtegumental region was observed. Nuclear indentation, cytoplasmic autolysis, and mitochondrial abnormalities were the other prominent observations.

Conclusion:

The results of the present study convincingly showed that AcPE is an effective anthelmintic causing detrimental effect to C. cotylophorum and appears to be a potent phytotherapeutic agent to control paramphistomosis.

Anthelmintic Potential of Thymoquinone and Curcumin on Fasciola gigantica

Fasciolosis an economically important global disease of ruminants in the temperate and tropical regions, caused by Fasciola hepatica and F. gigantica, respectively, also poses a potential zoonotic threat. In India alone it causes huge losses to stakeholders. Anthelmintics including triclabendazole have been used to control this menace but the emerging resistance against the available compounds necessitates identification of novel and alternative therapeutic measures involving plant derived natural compounds for their anthelmintic potential. Thymoquinone (T) and curcumin (C), the active ingredients of Nigella sativa and Curcuma longa respectively have been used as antiparasitic agents but the information on their flukicidal effect is very limited. Adult flukes of F. gigantica were in vitro exposed to different concentrations of thymoquinone and curcumin separately for 3h at 37+ 1°C. A significant (p<0.05) reduction in the worm motility at 60 μM concentration of both T and C was observed though all the worms remained alive after 3h exposure, whereas the effect on egg shedding was statistically insignificant. Pronounced tegumental disruptions and erosion of spines in the posterior region and around the acetabulum was evident. A significant (p<0.05) decrease in glutathione-S-transferase and superoxide dismutase activity and reduced glutathione (GSH) level was observed, while protein carbonylation increased differentially. A significant inhibition of CathepsinL (CatL) gene expression in thymoquinone treated worms was also evident. Further, in silico molecular docking of T and C with CatL revealed a stronger interaction of curcumin with the involvement of higher number of amino acids as compared to thymoquinone that could be more effective in inhibiting the antioxidant enzymes of F. gigantica. It is concluded that both the compounds understudy will decrease the detoxification ability of F. gigantica, while inhibition of CatL will significantly affect their virulence potential. Thus, both thymoquinone and curcumin appeared to be promising anthelmintic compounds for further investigations.

Implication of artemisinin nematocidal activity on experimental trichinellosis: In vitro and in vivo studies

Benzimidazole drugs are used for treatment of trichinellosis, but they have a limited effect against encapsulated larval stages of Trichinella spiralis. Hence, there is a considerable interest in developing new anthelmintic drugs. Our aim is to investigate the possible effect of artemisinin on T. spiralis in in vitro and in vivo studies. T. spiralis worms were isolated from infected mice and transferred to 3 culture media; group I: with no drugs, group II: contained artemisinin and group III: contained mebendazole, then they were subjected to electron microscopic study. An in vivo study was done where mice were divided into three groups; group I: infected and untreated, group II: received artemisinin and group III: received mebendazole. The efficacy of treatment was assessed by adult and total larval counts, histopathological study of the small intestinal and muscle tissues and immunohistochemical staining of cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF) in muscles. Adult worm teguments showed significant degeneration and destruction with both drugs. Also, significant reduction of total adult and larval counts occurred in treated groups in comparison to the control group. Histopathological examination of the small intestine and muscles showed marked improvement with reduction in the inflammatory infiltrates with both drugs. COX-2 and VEGF expressions were reduced in both treated groups with more reduction in the artemisinin-treated group. This study revealed that artemisinin has the potential to be an alternative drug against trichinellosis.

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.

Screening anthelmintic resistance to triclabendazole in Fasciola hepatica isolated from sheep by means of an egg hatch assay

Background

In the present study, the detection of anthelmintic resistance to triclabendazole (TCBZ) in sheep infected by Fasciola hepatica was studied using an egg hatch assay (EHA). F. hepatica eggs were recovered from bile and faeces of infected animals by isolates with different grade of anthelmintic resistance to TCBZ: i) a resistant isolate (RT); ii) a susceptible isolate (ST); iii) naturally infected sheep by a susceptible field strain (FST). In the EHA the percentage of hatched eggs were calculated according to the following concentrations of TCBZ diluted in dimethyl-sulfoxide (DMSO): 0.05, 0.2, 1, 5, and 25 μg/ml.

Results

In relation to the EHAs carried out with the eggs from bile of sheep infected by ST, differences were found in the percentage of hatched eggs between the control well, only with DMSO, and the two highest concentrations of TCBZ (5 and 25 μg/m) (p < 0.05). However, when we tested the drug with the eggs from the bile of sheep infected by RT, the percentage of hatched eggs was similar among all concentrations. Since the range of hatching varied between isolates, we calculated the ratio of the results of each concentration to its control value confirming the higher hatching in RT than in ST.

We developed an EHA with eggs recovered from faeces in order to avoid the slaughter of sheep. The results of the EHAs with the isolate ST showed differences in the percentage of hatching between the highest concentration (25 μg/ml) and the control well (p < 0.05); however, these differences were not confirmed under field conditions with the strain FST.

Conclusions

The ovicidal effect of TCBZ in F. hepatica eggs from bile was shown using a commercial formulation diluted in DMSO with a minimum concentration of 5 μg/ml. However, in eggs recovered from faeces the results are not conclusive. The cleaning of eggs recovered from faeces is an important issue that should be reviewed and standardized before comparing results between susceptible and resistant isolates in this kind of EHA.

Fasciola hepatica: Histology of the Reproductive Organs and Differential Effects of Triclabendazole on Drug-Sensitive and Drug-Resistant Fluke Isolates and on Flukes from Selected Field Cases

This review summarises the findings of a series of studies in which the histological changes, induced in the reproductive system of Fasciola hepatica following treatment of the ovine host with the anthelmintic triclabendazole (TCBZ), were examined. A detailed description of the normal macroscopic arrangement and histological features of the testes, ovary, vitelline tissue, Mehlis’ gland and uterus is provided to aid recognition of the drug-induced lesions, and to provide a basic model to inform similar toxicological studies on F. hepatica in the future. The production of spermatozoa and egg components represents the main energy consuming activity of the adult fluke. Thus the reproductive organs, with their high turnover of cells and secretory products, are uniquely sensitive to metabolic inhibition and sub-cellular disorganisation induced by extraneous toxic compounds. The flukes chosen for study were derived from TCBZ-sensitive (TCBZ-S) and TCBZ-resistant (TCBZ-R) isolates, the status of which had previously been proven in controlled clinical trials. For comparison, flukes collected from flocks where TCBZ resistance had been diagnosed by coprological methods, and from a dairy farm with no history of TCBZ use, were also examined. The macroscopic arrangement of the reproductive system in flukes was studied using catechol/carmine stained whole mounts, and the histology of the main organs was examined using conventional haematoxylin-eosin stained sections. Validation of apoptosis in the fluke sections was carried out using an in situ hybridisation method designed to label endonuclease-induced DNA strand breaks. In TCBZ-S flukes exposed to TCBZ metabolites for 24–96 h in vivo, but not in TCBZ-R flukes, those tissues where active meiosis and/or mitosis occurred (testis, ovary, and vitelline follicles), were found to display progressive loss of cell content. This was due to apparent failure of cell division to keep pace with expulsion of the mature or effete products. Further, actively dividing cell types tended to become individualised, rounded and condensed, characteristic of apoptotic cell death. In the treated TCBZ-S flukes, strong positive labelling indicating apoptosis was associated with the morphologically abnormal cells undergoing mitosis or meiosis in the testis, ovary and vitelline follicles. In treated flukes from field outbreaks of suspected TCBZ-R fasciolosis, no significant histological changes were observed, nor was there any positive labelling for apotosis. On the other hand, sections of TCBZ treated flukes derived from a field case of fasciolosis where TCBZ resistance was not suspected displayed severe histological lesions, and heavy positive labelling for apoptosis. The triggering of apoptosis is considered to be related to failure of spindle formation at cell division, supporting the contention that TCBZ inhibits microtubule formation. In treated TCBZ-S flukes, protein synthesis and transport was apparently inhibited in the Mehlis’ secretory cells, perhaps due to energy uncoupling or to microtubule defects. In the uterus, successful formation of shelled eggs represents the culmination of a complex sequence of cytokinetic, cytological and synthetic activity involving the vitelline follicles, the ovary and the Mehlis’ gland. Histological evidence indicating failure of ovigenesis in TCBZ-S flukes was evident from as early as 24 h post-treatment onwards. Light labelling for apoptosis 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. The studies summarised in this review illustrate the potential utility of histological techniques for conveniently screening representative samples of flukes in field trials designed to validate instances of drug resistance. Histology can also be used to test the efficacy of new products against known drug-resistant and drug-susceptible fluke isolates. The account also provides reference criteria for drug-induced histopathological changes in fluke reproductive structures, examination of which may supplement and augment conventional coprological testing, and aid interpretation of TEM findings.

Time-dependent tegumental surface changes in juvenile Fasciola gigantica in response to triclabendazole treatment in goat

Triclabendazole (TCBZ), the anthelmintic drug active against both mature and immature liver flukes, was used to investigate the effect of in vivo treatment on the tegumental surface of juvenile Fasciola gigantica. Five goats were infected with 150 F. gigantica metacercariae each by oral gavage. Four of them were treated with single dose of TCBZ at 10mg/kg at four weeks post-infection. They were euthanized at 0 (untreated), 24, 48, 72 and 96h post treatment. Juvenile flukes were manually retrieved from the goat livers and processed for scanning electron microscopy. In control flukes, the anterior region was adorned with sharply pointed spines projecting away from the surface, while in the posterior region, spines become shorter and narrower, loosing serration and with the appearance of distinct furrows and papillae. The dorsal surface retained the same pattern of surface architecture similar to that of ventral surface. Flukes obtained from 24h post-treatment did not show any apparent change and were still very active. However, there were limited movements and some blebbing, swelling, deposition of tegumental secretions and some flattening displayed by the flukes of 48h post-treatment. All the worms were found dead 72h post-treatment and showed advanced level of tegumental disruptions, consisting of severe distortion of spines, sloughing off the tegument to expose the basal lamina, formation of pores and isolated patches of lesions. By 96h post-treatment, the disruption was extremely severe and the tegument was completely sheared off causing deeper lesions that exposed the underlying musculature. The disruption was more severe at posterior than anterior region and on ventral than dorsal surface. The present study further establishes the time-course of TCBZ action in vivo with 100% efficacy against the juvenile tropical liver fluke.

The in vitro anthelmintic effects of plumbagin on newly excysted and 4-weeks-old juvenile parasites of Fasciola gigantica

The effect of plumbagin (PB, 5-hydroxy-2-methyl-1,4-naphthoquinone) against newly excysted juveniles (NEJs) and 4-weeks-old immature parasites of Fasciola gigantica were compared with triclabendazole (TCZ). The anthelmintic efficacy of 1, 10 and 100μg/ml of PB or TCZ following incubation in vitro for 1-24h was compared using a combination of relative motility (RM), survival index (SI) and larval migration inhibition (LMI) assays for parasite viability. The RM and SI values of the PB-treated group decreased at a more rapid rate than the TCZ-treated group. For NEJs, the decreased RM values were first observed at 1h incubation with 1μg/ml PB, and 90% of flukes were killed at 24h. In contrast, in TCZ-treated groups a 10-fold higher concentration of TCZ (10μg/ml) resulted in only 9% dead parasites after 24h incubation. In 4-weeks-old juvenile parasites, PB reduced the RM value at 10μg/ml with 100% of flukes dead after 3h, while TCZ decreased RM values at the concentration of 100μg/ml but with only 5% of flukes killed at 24h. NEJs treated with PB exhibited 88%, 99% and 100% of LMIs at the concentrations of 1, 10 and 100μg/ml, respectively. NEJs incubated with TCZ have an LMI of only 32% at the highest concentration of 100μg/ml. Similarly PB had a significantly greater killing of immature 4weeks juvenile stages than TCZ at all concentrations; however, 4-weeks-old juvenile parasites were more resistant to killing by PB or TCZ at all concentrations when compared to NEJs. Further studies were carried out to investigate the alterations of the parasite tegument by scanning electron microscope (SEM). PB caused similar tegumental alterations in 4-weeks-old juveniles as those observed in TCZ treatment but with greater damage at comparative time points, comprising of swelling, blebbing and rupture of the tegument, loss of spines, and eventual erosion, lesion and desquamation of the total tegument. These data indicate that PB had a greater fasciolicidal effect against immature stages of F. gigantica parasites than TCZ and warrant further studies for use as a potential new anthelmintic against Fasciola infections.

Paramphistomum cervi: the in vitro effect of plumbagin on motility, survival and tegument structure

Paramphistomiasis causes enteritis and anemia in livestocks and result in substantial production and economic losses. It is considered a neglected tropical disease, with no effective trematodicidal compound for treatment. Plumbagin (PB), a compound founds to be rich in the roots of Plumbago indica, is a naphthoquinone derivatives which can induce oxidative stress in parasites. In this study we have evaluated the anthelmintic activity of PB against adult Paramphistomum cervi by incubating the parasites in M-199 medium containing 0.1, 1.0, 10 and 100 μg/ml of the PB, and albendazole (ABZ) at the concentration of 100 μg/ml as the positive control, for 3, 6, 12 and 24 h, using relative motility (RM) assay and observed by scanning electron microscopy (SEM). After 12 h exposure with 100 μg/ml ABZ, flukes showed decreased contraction and motility. At 24 h incubation they showed only active movement of some part of the body. The PB-treated flukes at all concentrations showed rapid decrease of motility at 3 h incubation. In 0.1, 1.0 and 10 μg/ml of PB, the RM values were decreased sharply from 3 to 12 h, and then they were killed since 12 h in the incubation with 10 μg/ml of PB. The highest parasite mortality was found as early as 3h when they were incubated with 100 μg/ml of PB. The morphological changes on the tegumental surface were similar in both flukes treated with ABZ and PB, which sequentially comprised of swelling, followed by blebbings that later ruptured, leading to the erosion and desquamation of the tegument syncytium. As the result, lesions were formed which exposed the basal lamina. The damage appeared more severe on the ventral than the dorsal surface, and earlier on the anterior part and lateral margins of middle third when compared to the posterior part of the parasites's bodies. The severity and rapidity of the damages were enhanced with increasing concentration of PB, which showed stronger activity than ABZ. Hence, PB has a potential to be an anthelmintic drug against adult P.cervi.

Fasciola gigantica: the in vitro effects of artesunate as compared to triclabendazole on the 3-weeks-old juvenile

The in vitro effect of artesunate (ATS) on the 3-week-old juveniles of Fasciola gigantica was compared with triclabendazole (TCZ) by incubating the parasites in M-199 medium containing the drugs at concentrations of 20, 40, and 80 μg/ml for 1, 3, 6, 12, and 24h. The anthelmintic activities of these drugs were evaluated based on the relative motility value (RM) and the alterations of the tegument as observed by scanning (SEM) and transmission (TEM) electron microscopy. The RM values of TCZ-treated flukes decreased significantly from 6 to 24h for all dosages. For ATS-treated flukes, RM value decreased markedly from 12 to 24h, but the rates of decline were less than TCZ at the same doses. When observed by SEM, the tegument showed similar sequence of morphological changes after treatments with both drugs, comprising of swelling of tegumental ridges, followed by blebbing and later rupturing of the blebs, leading to erosion and lesion, and disruption of the tegument. When examined by TEM, ultrastructural changes in the tegument and associated structures after treatments with TCZ and ATS were similar which comprised of swelling, blebbing of the tegument, dilation of basal infoldings, and depolymerization of the microtrabecular network. After a longer incubation time, the tegument was completely sloughed off and the tegument cell bodies became necrotic. Additionally, in ATS-treated flukes, mitochondria showed severe swelling, rupturing of outer membrane, and their interior filled with flocculent materials.

Piperonyl butoxide enhances triclabendazole action against triclabendazole-resistant Fasciola hepatica

A study has been carried out to determine whether the action of triclabendazole (TCBZ) against the liver fluke, Fasciola hepatica is altered by inhibition of the cytochrome P450 (CYP 450)-mediated drug metabolism pathway. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for these experiments, the basic design of which is given in the paper by Devine et al. (2010a). Piperonyl butoxide (PB) was the CYP P450 inhibitor used. Morphological changes resulting from drug treatment and following metabolic inhibition were assessed by means of transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with PB+TCBZ, but more particularly PB+TCBZ.SO, led to greater changes to the TCBZ-resistant isolate than with each drug on its own, with blebbing of the apical plasma membrane, severe swelling of the basal infolds and their associated mucopolysaccharide masses in the syncytium and flooding in the internal tissues. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis and production of secretory bodies were badly disrupted. The mitochondria were swollen throughout the tegumental system and the somatic muscle blocks were disrupted. With the TCBZ-susceptible Cullompton isolate, there was a limited increase in drug action following co-incubation with PB. The results provide evidence that the condition of a TCBZ-resistant fluke can be altered by inhibition of drug metabolism. Moreover, they support the concept that altered drug metabolism contributes to the mechanism of resistance to TCBZ.

Time-dependent changes to the tegumental system and gastrodermis of adult Fasciola hepatica following treatment in vivo with triclabendazole in the sheep host

Eight indoor-reared cross-bred sheep with no pre-exposure to Fasciola hepatica were infected by oral gavage with 200 metacercarial cysts of the triclabendazole (TCBZ)-susceptible Cullompton isolate of F. hepatica. At 12 weeks post-infection, sheep were dosed with 10mg/kg triclabendazole. Two sheep per time period were euthanized at 48 h, 72 h and 96 h post-treatment (pt). Two control sheep were euthanized alongside the 96 h triclabendazole-treated sheep. Flukes were recovered from each of the sheeps liver and, if present, from the gall bladder and they were processed for transmission electron microscopy (TEM). Disruption to the ultrastructure of the tegument became increasingly severe over time pt. Flukes recovered at 48 h pt showed widespread blebbing of the apical plasma membrane and swelling of the mucopolysaccharide masses surrounding the basal infolds. There was evidence of reduced secretory activity in the tegumental cells and spacing between the cells. Sloughing of the tegumental syncytium was observed at 72 h pt. The subtegumental musculature, parenchyma and tegumental cells were severely disrupted. At 96 h pt, all of the flukes were totally devoid of tegument. Disruption to the subtegumental tissue and somatic musculature was severe, and was so extreme in some specimens that the tegumental cells were barely discernible. Disruption to the gastrodermis was also progressive, though not as severe as disruption to the tegument. There was a general decline of secretory activity with time pt. Autophagic activity was apparent from 48 h pt and became more widespread with increasing time, culminating in breakdown of the gastrodermal cell cytoplasm. The mitochondria were swollen and electron-lucent and the cisternae of the granular endoplasmic reticulum were dilated and fragmented from 72 h pt.

Fasciola hepatica: histological changes in the reproductive structures of triclabendazole (TCBZ)-sensitive and TCBZ-resistant flukes after treatment in vivo with TCBZ and the related benzimidazole derivative, Compound Alpha

Twenty-four shed-reared lambs were each infected orally with 250 metacercariae of Fasciola hepatica, using either the triclabendazole (TCBZ)-sensitive Cullompton isolate or the TCBZ-resistant Sligo isolate. Twelve weeks after infection the lambs were treated with TCBZ (10mg/kg) or with the experimental fasciolicide, Compound Alpha (Cpd alpha), a benzimidazole derivative of TCBZ (15mg/kg). The lambs were euthanised 48, 72 and 96h after TCBZ treatment, or 24, 48 and 72h after Cpd alpha treatment, and flukes were collected from the liver and/or gall bladder of each animal. Untreated animals harbouring 12-week infections were euthanized 24h after administration of anthelmintic to the treatment groups, and the untreated flukes provided control material. A semi-quantitative assessment of the degree of histological change induced by the two drugs after different times of exposure was achieved by scoring the intensity of three well-defined lesions that developed in the testes and uteri of a representative sample of flukes from each lamb. In general, it was found that in those tissues where active meiosis and/or mitosis occurred (testis, ovary, and vitelline follicles), there was progressive loss of cell content due to apparent failure of cell division to keep pace with expulsion of the mature or effete products. Further, actively dividing cell types tended to become individualised, rounded and condensed, characteristic of apoptotic cell death. Protein synthetic activity was apparently inhibited in the Mehlis' secretory cells. In the uterus, where successful formation of shelled eggs represents the culmination of a complex sequence of cytokinetic, cytological and synthetic activity involving the vitelline follicles, the ovary and the Mehlis' gland, histological evidence indicating failure of ovigenesis was evident from 24h post-treatment onwards. The development of these lesions may be related to the known anti-tubulin activity of the benzimidazole class of anthelmintics, to the induction of apoptosis in cells where mitosis or meiosis has aborted due to failure of spindle formation, and to drug-induced inhibition of protein synthesis. The semi-quantitative findings indicated that Cpd alpha is slightly less efficacious than TCBZ itself in causing histological damage to the reproductive structures of TCBZ-sensitive flukes, and that, like TCBZ, it caused no histological damage in flukes of the TCBZ-resistant isolate. This study illustrates the potential utility of histological techniques for conveniently screening representative samples of flukes in field trials designed to validate instances of drug resistance or to test the efficacy of new products against known drug-resistant and drug-susceptible fluke isolates. It also provides reference criteria for drug-induced histopathological changes in fluke reproductive structures which may aid interpretation of TEM findings.

Tegumental surface changes in adult Paramphistomum microbothrium (Fischoeder 1901) following in vitro administration of artemether

The treatment of paramphistomiasis, a neglected tropical disease, has been carried out with different fasciolicidal compounds, all showing weak efficacy. Therefore, the search for alternative paramphistomicidal drugs is warranted. In the present study, the in vitro effects of artemether on adult Paramphistomum microbothrium were evaluated, for the first time, using scanning electron microscopy. After 24 h of incubation with 10 μg ml− 1 artemether, tegumental damage of both anterior and posterior ends of the fluke had occurred in the majority of the specimens examined. Sensory papillae surrounding the oral aperture were ruptured, while those at the acetabular region appeared to be sunken due to tegumental swelling. The tegumental disruption became more pronounced and both oral sucker and acetabulum were severely distorted, on increasing the concentration to 20 μg ml− 1. With higher concentration of 30 μg ml− 1, gross swellings of the body of the fluke, clearly visible to the naked eye, were observed, and damage to both oral sucker and acetabulum was so extreme that little recognizable structure remained.

Electron microscopical study to assess the in vitro effects of the synthetic trioxolane OZ78 against the liver fluke, Fasciola hepatica

Adult Fasciola hepatica were incubated for 48 h in vitro in the synthetic peroxide, OZ78 at a concentration of 100 microg/ml and then prepared for scanning and transmission electron microscopy. There was limited disruption to the external fluke surface, with only slight swelling and blebbing of the interspinal tegument in the midbody and ventral tail regions. By contrast, significant disruption was observed to the ultrastructure of the tegument and subtegumental tissues. There was severe swelling of the basal infolds in the tegumental syncytium and the flooding spread internally to affect the subtegumental tissues. In the tegumental system, there was swelling of the cisternae of granular endoplasmic reticulum and of the mitochondria, with the latter showing signs of breaking down. Autophagic vacuoles and lipid droplets were present and the synthesis of tegumental secretory bodies was much reduced. The gastrodermal cells were severely affected, with swelling and degeneration of the mitochondria and the presence of autophagic vacuoles and lipid droplets. The granular endoplasmic reticulum was swollen and vesiculated and the cells contained few secretory bodies. Both the vitelline and testis follicles showed evidence of extensive cellular disruption and degeneration. This study confirms previous data indicating the potential flukicidal activity of OZ78.

Comparative in vitro effect of artemether and albendazole on adult Toxocara canis

Since the integrity of Toxocara canis cuticle is essential for the nutritive and protective functions, light and scanning electron microscopic studies were undertaken to assess, for the first time, whether artemether had any effect on the cuticle including lips and sensory organs following 24 and 48 h incubation in vitro. The results were compared with those observed in the worm cuticle following incubation in albendazole, as it was 100% effective against adult nematode. The body cover changes seen after in vitro administration of artemether were similar to that induced by albendazole sulfoxide, active form, (ABZ-SO). However, the earlier onset of those changes was recorded with the former. The swollen appearance of the anterior end of T. canis, including the lips, distortion of some sensory papillae, and appearance of a number of lesions on the lips, were observed during in vitro action of artemether. Cuticular disruption had also been observed in adult T canis exposed to ABZ-SO. The surface changes were more severe than those observed following incubation in artemether, with which limited loss of the cuticle occurred in the lips of nematode but was not as widespread as that seen with ABZ-SO. However, the cuticular swelling of the anterior end of T canis was more pronounced than that with ABZ-SO. In the present study, artemether presented itself as a drug that might become important in nematode chemotherapy, besides its broad spectrum of activity against various trematodes.

Fasciola gigantica: anthelmintic effect of the aqueous extract of Artocarpus lakoocha

The effect of the crude extract of Artocarpus lakoocha (70% composition is 2,4,3',5'- tetrahydroxystilbene -THS) on adult Fasciola gigantica was evaluated after incubating the parasites in M-199 medium containing 250, 500, 750 and 1000 microg/ml of the crude extract, or triclabendazole (TCZ) at the concentrations of 80 and 175 microg/ml as the positive control, for 3, 6, 12 and 24h, using relative motility (RM) assay and observation by scanning electron microscope (SEM). Decreased contraction and motility were first observed after 3h incubation with TCZ at the concentration 80 and 175 microg/ml. TCZ markedly reduced the parasite's motility at the concentration of 175 microg/ml at 6h, and killed the worms after 12h exposure. The crude extract of A. lakoocha at all concentrations reduced the parasite's motility similar to TCZ at 3h incubation. In 250 and 500 microg/ml of the crude extract, the values were decreased from 3 to 12h, then they were stable between 12 and 24h and reduced to the level approximately 30-40% of the control. At 750 and 1000 microg/ml concentrations the crude extract rapidly reduced the RM values from the start to 12h and killed the parasites between 12 and 24h incubation. The crude extract also inhibited the larval migration by 75% and 100% at the concentrations of 250-500 and 750-1000 microg/ml, respectively. TCZ and the crude extract caused sequentially changes in the tegument including swelling, followed by blebbings that later ruptured, leading to the erosion and desquamation of the tegument syncytium. As the result, lesion was formed which exposed the basal lamina. The damage appeared more severe on the dorsal than the ventral surface, and earlier on the anterior part and lateral margins when compared to the posterior part. The severity and rapidity of the damages were enhanced with increasing concentration of the crude extract. Hence, the crude extract of A. lakoocha, may exert its fasciolicidal effect against adult F. gigantica by initially causing the tegumental damage.

Ultrastructural changes to the tegumental system and the gastrodermal cells in adult Fasciola hepatica following in vivo treatment with the experimental fasciolicide, compound alpha

Sheep infected with the triclabendazole-susceptible, Cullompton isolate of Fasciola hepatica were dosed with 15 mg/kg of compound alpha at 12 weeks post-infection. Adult flukes were recovered from the bile ducts at 24, 48 and 72 h post-treatment (p.t.). Ultrastructural changes to the flukes were assessed using transmission electron microscopy (TEM), with a view to gathering information on the mechanism(s) of action for compound alpha and on the possible route of its entry into F. hepatica. The tegumental syncytium was more severely affected than the gut at all time-points p.t. with compound alpha, suggesting a predominantly trans-tegumental route of uptake. Disruption to the tegumental system became increasingly severe over time. A stress response was observed at 24 h p.t. and took the form of blebbing and increases in the production and transport of secretory bodies. By 72 h p.t., extensive tegumental loss and degeneration of the tegumental cell bodies had occurred. Degeneration of subtegumental tissues and internal flooding were also observed. Changes in the gastrodermal cells were slow to develop: reduced secretory activity was evident at 72 h p.t.. There was progressive disruption to the somatic muscle layers, with disorganization of the muscle blocks and loss of muscle fibres.

A scanning electron microscope study on the route of entry of triclabendazole into the liver fluke, Fasciola hepatica

SUMMARY

Studies have been carried out to establish the relative importance of oral and trans-tegumental uptake of triclabendazole by the liver fluke, Fasciola hepatica. Experiments were designed to block either oral uptake of drug, by use of ligatures, or trans-tegumental diffusion, by allowing the drug to bind to bovine serum albumin (BSA) in the medium. Changes to the surface morphology of the tegument and gut were assessed by scanning electron microscopy. Flukes were incubated in vitro for 24 h in TCBZ.SO at a concentration of 15 microg/ml. Tegumental disruption in ligatured and non-ligatured flukes was similar, suggesting that closing the oral route did not affect drug uptake. The gut remained unaffected by drug treatment. When BSA (30 mg/ml) was present in the medium, there was a marked decline in the level of tegumental disruption. Again, the gut retained a normal morphology. Non-ligatured flukes were also incubated for 24 h in vitro in TCBZ.SO (15 microg/ml) in the presence of red blood cells. Oral ingestion of blood was demonstrated, although the gut surface retained a normal morphology. In contrast, the tegumental surface was severely affected by the drug. The findings support previous pharmacological studies which suggest that trans-tegumental uptake of triclabendazole predominates in the liver fluke.

Relative activity of triclabendazole metabolites against the liver fluke, Fasciola hepatica

A study has been carried out to determine the relative activity of triclabendazole (TCBZ) and its sulphoxide (TCBZSO) and sulphone (TCBZSO(2)) metabolites against the adult stage of the liver fluke, Fasciola hepatica. Flukes were incubated for 24h in vitro in 15mug/ml of each of the compounds and prepared for scanning and transmission electron microscopy. All three compounds induced changes to the surface morphology of the fluke, the changes comprising swelling and blebbing to a greater or lesser extent in different regions of the fluke. TCBZSO(2) was more disruptive anteriorly and TCBZSO posteriorly. Internal ultrastructural changes were evident following incubation with each of the compounds, with an order of severity TCBZSO(2)>TCBZSO>TCBZ. Swelling of the basal infolds and mitochondria were observed in the tegumental syncytium. In the tegumental cell bodies, there was a reduction in the number of secretory bodies, disruption of the Golgi complexes and swelling of the mitochondria. Severe flooding of the internal tissues was observed with TCBZSO(2) and, to a lesser extent, with TCBZSO and TCBZ. The results demonstrate that both TCBZ and TCBZSO(2) are capable of disrupting the fluke in vitro and are not the inactive compounds they were assumed to be previously. They may well contribute to drug action in vivo as well, indicating that drug action is due to the additive effects of several metabolites, rather than being due to a single active metabolite, namely, TCBZSO.

Effect of niclosamide on the tegumental surface of Haplorchis taichui using scanning electron microscopy

The effect of niclosamide on the tegument of adult Haplorchis taichui (Trematoda: Heterophyidae) exposed in vitro was observed by scanning electron microscope. Adult worms were incubated in Tyrode's solution containing 0.01, 0.1, 1.0, and 10 microg ml(-1) of niclosamide for 30 min, 1, 6, 12 and 24 h. Control groups were incubated in Tyrode's solution without niclosamide and worms remained active until 24 h. In 0.01 microg ml(-1) of niclosamide, worms showed slightly active movements up to 1 h after incubation, while in 0.1 microg ml(-1) solution a few worms showed only slightly active movements after 30 min. Tegumental changes were determined by scanning electron microscopy. Swelling and blebbing of the tegument were observed on both ventral and dorsal sides. After longer periods, extensive swelling and blebbing of the tegument became more severe and there was a loss of the apical plasma membrane in some regions. Empty spine sockets occurred, and small perforations penetrated the basal lamina, followed by some lesions. Destruction of both surfaces was more pronounced on the posterior compared with the anterior regions.

Ultrastructural changes induced in the tegument and gut of Fasciola hepatica following in vivo and in vitro drug treatment with nitroxynil (Trodax)

Male Sprague-Dawley rats were dosed orally with nitroxynil at a concentration of 40 mg/kg, and adult Fasciola hepatica were recovered after 24, 48 and 72 h. Fine structural changes to the tegument and gut were monitored by transmission electron microscopy. Flukes were also incubated for 24 h in vitro in nitroxynil at a concentration of 100 microg/ml. Following treatment in vivo, there was an accumulation and accelerated release of secretory bodies at the apex of the tegumental syncytium. Some swelling of the mucopolysaccharide masses surrounding the basal infolds was evident after 48 and 72 h. There was an initial accumulation of T1 secretory bodies at the base of the syncytium, but this decreased at 72 h, coinciding with a decline in their production in the tegumental cells. The mitochondria were consistently swollen in the tegumental cells. At 72 h, large vacuolations were observed between the muscle layers and there was flooding around the underlying tissues. Some tegumental cells were seen to be degenerating and beginning to disintegrate. After 24 h treatment in vitro, the basal infolds were swollen and the crystalline structure of the spines was disrupted. Flooding of the internal tissues was evident and, in the tegumental cells, Golgi complexes and secretory bodies were absent. The mitochondria in the tegumental cells were swollen. In the gastrodermal cells, changes were evident at the earliest time period in vivo. The lamellae were disrupted, few secretory bodies were present, the mitochondria and cisternae of granular endoplasmic reticulum (ger) were swollen and there was an increased number of secretory bodies. These changes became progressively more severe with time. Similar changes were evident following treatment in vitro; vesiculation of the ger was also seen. The results indicate that oral uptake is the predominant route of entry of nitroxynil into the fluke.

An in vitro effect of propolis on adult worms of Fasciola gigantica

The effect of Siwa propolis on adult flukes was evaluated using scanning electron microcopy. It gave an overview of the surface architecture of the tegument of Fasciola gigantica apical cone. The base of the spines appeared to be "flaking off" and showed severe blebbing after 24h incubation with 10 micro/ml propolis. This swelling became so sever and the spines were barely visible, on increasing the concentration to 20 micro/ml. Besides, there were many large blebs on the apical cone, a number of which appeared to have burst, causing lesions and the tegument was marked by a number of pits caused by the loss of spines. With the higher concentration of 30 micro/ml, erosion of the surface had occurred to such extent that no tegument remained, only a mass of fibrous structures. The tegumental changes occurred following incubation in propolis were compared with those observed with triclabendazole (TCBZ) "Fasinex" because of its high efficacy against both mature and immature flukes.

Understanding triclabendazole resistance

Triclabendazole (TCBZ) has been the drug of choice to treat liver fluke infections in livestock for >20 years, due to its high activity against both adult and juvenile flukes. More recently, it has been used successfully to treat human cases of fascioliasis. Resistance to TCBZ first appeared in the field in Australia in the mid-1990s. Since then, resistance has been reported from a number of countries throughout Europe: Ireland, Scotland, Wales, Spain and The Netherlands. The heavy reliance on a single drug puts treatment strategies for fascioliasis at risk. Should resistance develop further, the prospect is an alarming one. This review will present an overview of progress in understanding the mechanism of resistance to TCBZ, examining possible changes in the target molecule, in drug influx/efflux mechanisms and in the metabolism of TCBZ by the fluke. The review will also consider ways to deal with resistance, covering drug-oriented options such as: the use of alternative drugs, drug combinations and the search for new compounds.

Immature triclabendazole-resistant Fasciola hepatica: tegumental responses to in vitro treatment with the sulphoxide metabolite of the experimental fasciolicide compound alpha

Juvenile triclabendazole-resistant liver flukes, Fasciola hepatica, were incubated in vitro with 10 microg/ml of the sulphoxide metabolite of the experimental fasciolicide, compound alpha [5-chloro-2-methylthio-6-(1-naphthyloxy)-1H-benzimidazole], for 6 and 18 h. Following treatment, the specimens were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tubulin immunocytochemistry. The SEM results revealed a posterior-directed disruption comprised predominantly of swelling and blebbing of the tegument; these changes were more severe and extensive after the longer 18-h incubation. Along with swelling of the tegument and blebbing, the TEM results also revealed swelling of the mitochondria and basal infolds. A decrease in the number of both T1 and T2 secretory bodies was observed in the syncytium and cytoplasmic connections after the 18-h treatment. The circular muscle bundles were also disrupted, in that the organisation of the muscle fibres was irregular and the total number of muscle fibres was reduced. The immunocytochemical studies revealed no significant disruption to the distribution of tubulin immunoreactivity within the tegumental syncytium, the cytoplasmic connections or the associated tegumental cells. The results indicate that alpha.SO is capable of disrupting the tegument of 4-week-old triclabendazole-resistant liver flukes, though the morphological changes were not associated with any significant differences in tubulin immunostaining.

Fasciola hepatica: morphological effects of a combination of triclabendazole and clorsulon against mature fluke

A study has been carried out to investigate the morphological effects of half-strength triclabendazole (TCBZ), half-strength clorsulon, and a combination of these two drugs against mature Fasciola hepatica. The Cullompton TCBZ-susceptible isolate was used for these experiments. Flukes were incubated for 24 h in vitro in TCBZ sulphoxide (7.5 microg/ml), clorsulon (5 microg/ml), or a combination of the two drugs. For the in vivo experiment, rats were dosed with TCBZ (6.25 mg/kg body weight), clorsulon (5 mg/kg body weight), or a combination of the two drugs and flukes recovered after 48 h. Surface changes to the flukes were assessed by scanning electron microscopy. Treatment with the combination of drugs produced greater disruption to the flukes than the individual drugs at half-strength, both in vivo and in vitro. Disruption to the tegument of the flukes induced by the individual drugs at half-strength was relatively minor and less than that caused by the drugs at full-strength. The results suggest that there are additive effects between TCBZ and clorsulon, which may be indicative of synergy: the use of drug combinations would be of value in the treatment of triclabendazole-resistant fluke.

Adult triclabendazole-resistant Fasciola hepatica: surface and subsurface tegumental responses to in vitro treatment with the sulphoxide metabolite of the experimental fasciolicide compound alpha

Mature Fasciola hepatica of the triclabendazole-resistant Sligo isolate were incubated in vitro with 10 microg/ml of the sulphoxide metabolite of compound alpha [5-chloro-2-methylthio-6-(1-naphthyloxy)-H-benzimidazole]; the metabolite will be referred to as alpha.SO. Changes resulting from drug treatment were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tubulin immunocytochemistry (ICC). SEM revealed that disruption to the tegumental surface mainly took the form of swelling and blebbing. Extensive spine loss occurred on the ventral surface of the oral cone, and sloughing of the tegument was observed along the lateral margins of the fluke. Examination of sections from the anterior mid-body region at the TEM level revealed that treatment with alpha.SO led to swelling of the basal infolds and mitochondria within the tegumental syncytium; also, accumulations of secretory bodies beneath the apical plasma membrane. The tegumental cell bodies contained swollen mitochondria and cisternae of granular endoplasmic reticulum, but few Golgi complexes were observed. An increase in T2 secretory bodies was observed, whilst in the T1 tegumental cells, the T1 secretory bodies had decreased in number. Immunocytochemical (ICC) studies showed that incubation with alpha.SO, ABZ.SO and TCBZ.SO did not cause significant changes to the distribution of tubulin within the tegumental syncytium of the Sligo isolate. In contrast, alpha.SO, ABZ.SO and TCBZ.SO caused severe disruption to tubulin organization within the syncytial layer of the TCBZ-susceptible Cullompton isolate. The EM results confirm that compound alpha is a fasciolicide capable of disrupting the tegument of mature TCBZ-resistant F. hepatica; however, this was not accompanied by any change in tubulin immunoreactivity.

Altered drug influx/efflux and enhanced metabolic activity in triclabendazole-resistant liver flukes

Triclabendazole (TCBZ) is a halogenated benzimidazole compound that possesses high activity against immature and adult stages of the liver fluke, Fasciola hepatica. The intensive use of TCBZ in endemic areas of fascioliasis has resulted in the development of liver flukes resistant to this compound. TCBZ sulphoxide (TCBZSO) and TCBZ sulphone (TCBZSO2) are the main molecules recovered in the bloodstream of TCBZ-treated animals. In order to gain some insight into the possible mechanisms of resistance to TCBZ, the goals of the work described here were: to compare the ex vivo transtegumental diffusion of TCBZ parent drug and its sulpho-metabolites (TCBZSO and TCBZSO2) into TCBZ-susceptible and -resistant liver flukes; and to assess the comparative pattern of TCBZ biotransformation by TCBZ-susceptible and -resistant F. hepatica. For the tegumental diffusion studies, TCBZ-susceptible (Cullompton) and -resistant (Sligo) adult flukes collected from untreated infected sheep were incubated (15-180 min) in KRT buffer containing either TCBZ, TCBZSO or TCBZSO2 (5 nmol.ml-1). For the metabolism studies, microsomal fractions obtained from TCBZ-susceptible and -resistant flukes were incubated for 60 min with TCBZ (40 microM), and the amount of the formed metabolic product (TCBZSO) was measured. Drug/metabolite concentrations were quantified by HPLC. All the assayed TCBZ-related molecules penetrated through the tegument of both TCBZ-susceptible and -resistant flukes. However, significantly lower (approximately 50%) concentrations of TCBZ and TCBZSO were recovered within the TCBZ-resistant flukes compared to the TCBZ-susceptible ones over the 180 min incubation period. The rate of TCBZ sulphoxidative metabolism into TCBZSO was significantly higher (39%) in TCBZ-resistant flukes. The flavin-monooxigenase (FMO) enzyme system appears to be the main metabolic pathway involved in the formation of TCBZSO in both TCBZ-susceptible and -resistant flukes. The altered drug influx/efflux and enhanced metabolic capacity identified in TCBZ-resistant liver flukes may account for the development of resistance to TCBZ.