Fasciola hepatica: disruption of spermatogenesis by the fasciolicide compound alpha

Evaluation of Reproductive Histology Response of Adult Fasciola hepatica in Goats Vaccinated with Cathepsin L Phage-Exposed Mimotopes

Fasciolosis, a globally re-emerging zoonotic disease, is mostly caused by the parasitic infection with Fasciola hepatica, often known as the liver fluke. This disease has a considerable impact on livestock productivity. This study aimed to evaluate the fluke burdens and faecal egg counts in goats that were administered phage clones of cathepsin L mimotopes and then infected with F. hepatica metacercariae. Additionally, the impact of vaccination on the histology of the reproductive system, specifically related to egg generation in adult parasites, was examined. A total of twenty-four goats, which were raised in sheds, were divided into four groups consisting of six animals each. These groups were randomly assigned. The goats were then subjected to two rounds of vaccination. Each vaccination involved the administration of 1 × 1013 phage particles containing specific mimotopes for cathepsin L2 (group 1: PPIRNGK), cathepsin L1 (group 2: DPWWLKQ), and cathepsin L1 (group 3: SGTFLFS). The immunisations were carried out on weeks 0 and 4, and the Quil A adjuvant was used in combination with the mimotopes. The control group was administered phosphate-buffered saline (PBS) (group 4). At week 6, all groups were orally infected with 200 metacercariae of F. hepatica. At week 22 following the initial immunisation, the subjects were euthanised, and adult F. hepatica specimens were retrieved from the bile ducts and liver tissue, and subsequently quantified. The specimens underwent whole-mount histology for the examination of the reproductive system, including the testis, ovary, vitellaria, Mehlis' gland, and uterus. The mean fluke burdens following the challenge were seen to decrease by 50.4%, 62.2%, and 75.3% (p < 0.05) in goats that received vaccinations containing cathepsin L2 PPIRNGK, cathepsin L1 DPWWLKQ, and cathepsin L1 SGTFLFS, respectively. Animals that received vaccination exhibited a significant reduction in the production of parasite eggs. The levels of IgG1 and IgG2 isotypes in vaccinated goats were significantly higher than in the control group, indicating that protection is associated with the induction of a mixed Th1/Th2 immune response. The administration of cathepsin L to goats exhibits a modest level of efficacy in inducing histological impairment in the reproductive organs of liver flukes, resulting in a reduction in egg output.

Microscopic alterations in Fasciola hepatica from sheep treated with albendazole

Currently, albendazole is one of the most commonly used drugs because of its affordability. The objective was to evaluate the histopathology of Fasciola hepatica specimens. For this, the efficacy test was performed on sheep treated with albendazole at the dose recommended for F. hepatica, in which the helminths recovered at necropsy were counted and separated for histology. Spermatogenic cells from parasites recovered from treated and control sheep were examined by microscopy. The fecal egg-count reduction test revealed 97.06% efficacy of albendazole in the treatment of F. hepatica. Changes in testicular tubule cells started 48 hours after treatment and became evident within 72 hours, at which point it became difficult to identify cell types. Primary and secondary spermatogonia became increasingly rare and intercellular vacuolization was more evident. Signs of apoptosis, with pycnotic nuclei and evidence of keriorrexia were observed at all times. Cell debris was identified 96 hours after treatment. The results indicated that parasitic spermatogenesis was severely affected by albendazole and demonstrated the importance of the use of histopathology for the diagnosis of therapeutic efficacy in field strains.

Assessment of the effective dose of an experimental intramuscular formulation against immature and adult Fasciola hepatica in sheep

The effective dose of an injectable prodrug, named compound alpha prodrug, against immature and adult Fasciola hepatica in experimentally infected sheep was determined. In a first experiment, 30 sheep were infected with Fasciola hepatica on day 0 and 50. After microscopic detection of faecal eggs on day 80, groups (n = 6) 1 to 3 were treated with 6, 8 and 10 mg/kg of the experimental water-soluble prodrug compound alpha intramuscularly, respectively. Group 4 was treated with closantel and group 5 remained untreated. Copromicroscopical examinations were made on day 0, 80 and 108. On day 110, trematodes were collected from the bile ducts. Fasciolicide efficacy was assessed as a percentage of fluke-egg and adult-fluke reduction. Fluke length was also recorded. In a second experiment aimed to assess the fasciolicide activity of compound alpha prodrug against four-week-old flukes, 12 sheep were infected on day 0 and allocated into two groups (n = 6). On day 50 post infection, group A was treated with the experimental water-soluble prodrug compound alpha at 6 mg/kg/IM and B remained untreated. Fasciolicide activity was assessed on day 80 after collection, microscopic observation and measurement of flukes present in the parenchyma for immature stages and on day 108 for adults. Egg output decreased 91.2, 96.0, 98.8 and 94.9% for groups 1, 2, 3 and 4, respectively. Compound alpha prodrug cleared 97.6%, 98.51% and 100% of adult stages in a dose-dependent manner. Closantel killed 81.95% flukes. Regarding the second experiment, 81.2% efficacy was achieved. Immature flukes were significantly smaller in the treated group. It is concluded that the intramuscular application of compound alpha prodrug exerted fasciolicide efficacy against adults of Fasciola hepatica.

Disruption of spermatogenesis in the liver fluke, Fasciola hepatica by two artemisinin derivatives, artemether and artesunate

An in vivo study in the laboratory rat model has been carried out to monitor changes to the spermatogenic cells in the testis tubules of adult Fasciola hepatica following treatment with the artemisinins, artemether and artesunate. Rats infected with the triclabendazole (TCBZ)-resistant Sligo isolate were dosed orally with artemether at a concentration of 200 mg/kg and flukes recovered at 24, 48 and 72 h post treatment (pt). Rats infected with the TCBZ-resistant Oberon isolate were dosed orally with artesunate at a concentration of 200 mg/kg and flukes recovered 24, 48, 72 and 96 h pt. The flukes were processed for histological and transmission electron microscope (TEM) examination. Changes to the spermatogenic cells were evident at 24 h pt with artemether. The spermatogonial and spermatocyte cells contained abnormal mitochondria, there were fewer spermatids and spermatozoa in the tubules than normal, and a number of cells showed signs of apoptosis. There was a further decline in cell numbers at 48 h pt and the organization of the spermatocyte and spermatid rosettes was atypical. Sperm formation had become abnormal and those spermatozoa present possessed only a single axoneme. By 72 h pt, the testis tubules were vacuolated and filled with abnormal cells and cell debris. Only spermatogonial cells could be identified and there was widespread evidence of apoptosis in the cells. Distinct cellular changes following artesunate treatment did not become apparent until 48 h pt. The changes seen were similar to those described for artemether, but were generally less severe at matching time-periods. The fine structural changes occurring in the spermatogenic cells were compared to those observed in other cell types and fluke tissues and the overall information was collated to identify the cellular targets for artemisinin action and to establish the time-line for drug action.

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.

A highly water soluble benzimidazole derivative useful for the treatment of fasciolosis

This study describes the synthesis of compound (7), a highly hydrosoluble phosphonooxymethyl prodrug of compound alpha (4). Compound (7) improved the aqueous solubility of its precursor compound (4) by 50,000 times and it is stable at neutral pH. The prodrug showed faciolicidal activity when evaluated in vitro against excysted Fasciola hepatica metacercariae. The in vivo evaluation of (7) was carried out via oral, intramuscular and subcutaneous administration in sheep artificially infected with F. hepatica metacercariae. At an intramuscular dose of 4 mg/kg, the activity of (7) was similar to that of compound alpha (4) at an oral dose of 15 mg/kg.

Disruption of vitellogenesis and spermatogenesis by triclabendazole (TCBZ) in a TCBZ-resistant isolate of Fasciola hepatica following incubation in vitro with a P-glycoprotein inhibitor

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Sligo TCBZ-resistant fluke isolate was used for these experiments and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. In the first experiment, flukes were initially incubated for 2 h in R(+)-VPL (100 μm), then incubated in R(+)-VPL+triclabendazole sulphoxide (TCBZ.SO) (50 μg mL−1, or 133·1 μm) until flukes ceased movement (at 9 h post-treatment). In a second experiment, flukes were incubated in TCBZ.SO alone and removed from the incubation medium following cessation of motility (after 15 h). In the third experiment, flukes were incubated for 24 h in R(+)-VPL on its own. Changes to the testis tubules and vitelline follicles following drug treatment and following Pgp inhibition were assessed by means of light microscope histology and transmission electron microscopy. Incubation of the Sligo isolate in either R(+)-VPL or TCBZ.SO on their own had a limited impact on the morphology of the two tissues. Greater disruption was observed when the drugs were combined, in terms of the block in development of the spermatogenic and vitelline cells and the apoptotic breakdown of the remaining cells. Sperm formation was severely affected and abnormal. Large spaces appeared in the vitelline follicles and synthesis of shell protein was disrupted. The results of this study support the concept of altered drug efflux in TCBZ-resistant flukes and indicate that drug transporters may play a role in the development of drug resistance.

5-Chloro-2-methyl-sulfanyl-6-(naphtha-len-1-yl-oxy)-1H-benzimidazole methanol monosolvate

In the title compound, C18H13ClN2OS·CH3OH, the dihedral angle between the benzimidazole group and the naphth-yloxy moiety [82.89 (5)°] very near to orthogonality. The H atom in the five-membered ring is disordered with equal occupancies at the two N atoms and the H atom of the methano-lic hy-droxy group is disordered with equal occupancies over two sites at the O atom. The methanol mol-ecule acts as a hydrogen-bond acceptor for the amino H atom and donates a hydrogen bond to the nonprotonated ring N atom. As a result, chains are formed running along the a axis.

Current status of food-borne trematode infections

Food-borne trematodiases constitute an important group of the most neglected tropical diseases, not only in terms of research funding, but also in the public media. The Trematoda class contains a great number of species that infect humans and are recognized as the causative agents of disease. The biological cycle, geographical distribution, and epidemiology of most of these trematode species have been well characterized. Traditionally, these infections were limited, for the most part, in populations living in low-income countries, particularly in Southeast Asia, and were associated with poverty. However, the geographical limits and the population at risk are currently expanding and changing in relation to factors such as growing international markets, improved transportation systems, and demographic changes. The diagnosis of these diseases is based on parasitological techniques and only a limited number of drugs are currently available for treatment, most of which are unspecific. Therefore, in-depth studies are urgently needed in order to clarify the current epidemiology of these helminth infections and to identify new and specific targets for both effective diagnosis and treatment. In this review, we describe the biology, medical and epidemiological features, and current treatment and diagnostic tools of the main groups of flukes and the corresponding diseases.

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

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

Liver fluke isolates: a question of provenance

A survey of literature on experimental infections with the liver fluke, Fasciola hepatica published between 2005 and 2009 has revealed a general lack of information on where fluke material (i.e. metacercariae) was sourced from. Even less information was given on the drug status of the fluke isolate used, which is a particular concern for those studies that involved anthelmintics. In these two respects, information on the liver fluke lags far behind that for nematodes, where such information is given almost as a matter of course. Of additional concern is that, at times, information about the source and drug history of fluke isolates was incorrect. The overall aim of the review is to demonstrate why it is important to provide as much information as possible on what fluke material is being used. It also attempts to correct some of the errors in the literature and gather together what information is available about the provenance of those isolates that have been used in recent experimental studies.

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.