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1.
Vet Parasitol ; 330: 110244, 2024 Jun 26.
Article in English | MEDLINE | ID: mdl-38964116

ABSTRACT

Application of 'omics' technology, and advances in in vitro methods for studying the growth of Fasciola hepatica, have highlighted the central role of migrating neoblasts in driving forward development and differentiation towards the adult-like form. Neoblast populations present molecular heterogeneity, morphological variation and changes associated with recruitment of these stem cells into their final tissue locations. However, terminal differentiation towards function, has received much less attention than has been the case for the free-living Platyhelminths. An actively replicating neoblast population, comprising cells with heterochromatic nuclei consistent with regulation of gene expression, has been identified in the parenchyma of juvenile Fasciola gigantica migrating in the liver of experimentally infected mice. In some of these cells, early cytoplasmic differentiation towards myocyte function was noted. Neoblasts have also been identified close to, and incorporated in, the subtegumental zone, the gastrodermis and the excretory ducts. In these locations, progressive morphological differentiation towards terminal function has been described. This includes the appearance of specific progenitors of type-1, type-2 and type-3 tegumental cells, the latter possibly contributing to tegumental spine development. 'Cryptic' surface molecular differentiation is postulated to account for recognition and 'docking' of migrating neoblasts with their final site for terminal differentiation.

2.
Article in English | MEDLINE | ID: mdl-32179499

ABSTRACT

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.


Subject(s)
Anthelmintics/pharmacology , Drug Resistance , Fasciola hepatica/drug effects , Liver/parasitology , Animals , Benzimidazoles/pharmacology , Fasciola hepatica/classification , Fascioliasis/diagnosis , Fascioliasis/drug therapy , Fascioliasis/parasitology , Triclabendazole/pharmacology
3.
Vet Parasitol ; 274: 108923, 2019 Oct.
Article in English | MEDLINE | ID: mdl-31542719

ABSTRACT

Cytochemical staining techniques were carried out en bloc with in vitro excysted and gut-penetrated Fasciola gigantica larvae in order to visualise the glycocalyx of the tegument, a structure which comprises the parasite component of the host-parasite interface, yet is incompletely preserved by conventional fixation and preparation techniques for electron microscopy. Positive reactivity with ruthenium red and periodic acid-thiocarbohydrazine-osmium (PATCO) techniques revealed that the glycocalyx is polyanionic and carbohydrate-rich throughout its depth. It comprises a trilaminate arrangement, with a thin dense zone and fibrillar layer closely apposed to the outer aspect of the apical plasma membrane, invested by an irregular thick mucopolysaccharide capsule. The latter, not recorded in adult flukes, may represent a specific adaptation to facilitate invasion in the face of host immunity, and may also protect the parasite surface from the action of host- and parasite-derived proteases. Early in the invasion of a naïve host, the glycocalyx may be partly responsible for triggering the responses of innate immunity, while later in infection, or when an anamnestic response is initiated in an immunocompetent host, the antibodies and activated lymphocytes of specific acquired immunity are invoked to interact with the parasite surface. The cytochemical properties of the glycocalyx, together with its potential for dynamic turnover due to exocytosis of the T0 tegumental secretory bodies, are likely to aid neutralisation of potentially damaging immune effectors and ensure their removal from the vicinity of the parasite by sloughing in complex with glycocalyx components.


Subject(s)
Fasciola/physiology , Fasciola/ultrastructure , Histocytochemistry/methods , Animals , Fasciola/chemistry , Glycocalyx/chemistry , Glycocalyx/physiology , Host-Parasite Interactions , Metacercariae/chemistry , Metacercariae/physiology , Metacercariae/ultrastructure
4.
Vet Parasitol ; 265: 38-47, 2019 Jan.
Article in English | MEDLINE | ID: mdl-30638519

ABSTRACT

Using in vitro procedures to prepare newly excysted metacercariae and gut-penetrated juvenile Fasciola gigantica, the ultrastructural features of the tegumental syncytium and perikarya of these ephemeral stages in the host-invasion process were compared. The T0-type tegumental cells in newly excysted metacercariae are packed with stored T0 granules which, following transport to the surface membrane of the syncytium, discharge by exocytosis to maintain the glycocalyx. The T0 cells become depleted of T0 granules during the penetration process, shrink in size, and initiate autophagy in the cytoplasm to facilitate metamorphosis from a storage function to active biosynthesis. The novel products appear to include lysosomes which contribute to the autophagosomes, and T1 granules, necessary for maintenance of the glycocalyx and immunoprotection, as the invasion process continues into the host liver. Residual bodies, the end-products of autophagy, are eliminated from the apical membrane of the tegumental syncytium into the host-parasite interface. There they may present a transient source of parasite-derived molecules, including lysosomal cathepsin-type proteases, with potential for interaction with the host's immune system, and so might be exploited as targets for vaccinal and immunomodulatory studies.


Subject(s)
Fasciola/ultrastructure , Fascioliasis/veterinary , Immunologic Factors/chemistry , Integumentary System/anatomy & histology , Metacercariae/ultrastructure , Vaccines/immunology , Animals , Fascioliasis/prevention & control , Immunologic Factors/pharmacology
5.
J Helminthol ; 91(1): 55-71, 2017 Jan.
Article in English | MEDLINE | ID: mdl-26979164

ABSTRACT

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.


Subject(s)
Anti-Infective Agents/administration & dosage , Artemisinins/administration & dosage , Fasciola hepatica/drug effects , Fascioliasis/drug therapy , Administration, Oral , Animals , Anti-Infective Agents/pharmacology , Apoptosis , Artemether , Artemisinins/pharmacology , Artesunate , Cell Count , Cell Survival/drug effects , Disease Models, Animal , Fasciola hepatica/physiology , Histocytochemistry , Male , Microscopy, Electron, Transmission , Mitochondria/drug effects , Mitochondria/ultrastructure , Rats , Spermatogenesis/drug effects , Spermatozoa/drug effects , Spermatozoa/physiology , Spermatozoa/ultrastructure , Time Factors
6.
Vet Parasitol Reg Stud Reports ; 7: 14-18, 2017 Jan.
Article in English | MEDLINE | ID: mdl-31014650

ABSTRACT

A questionnaire to obtain information on tapeworm control practices was sent to 252 sheep farmers in Northern Ireland (NI) in 2012. Replies were received from 228 flock owners. Most farmers considered that tapeworm infections had less impact on productivity than gastrointestinal nematodes, flukes and ectoparasites. The majority of respondents (61.8%) did not treat for tapeworms. Of those that did, the average number of treatments given per year was 2.3, with some owners treating up to 6 times a year. The highest percentages of treatments were given over the period May-July. Benzimidazole compounds were the predominant class of drugs used (48.2%), followed by macrocyclic lactones (MLs) (31.2%). Levamisole, oxyclozanide, closantel and Monepantel were also used; together with MLs, their combined use accounted for 51.9% of all treatments given, and represents inappropriate product choice. Diagnostic data for tapeworm infections in NI over the period 2007-2014 was retrieved from the database held by the Veterinary Sciences Division at Stormont. Positive diagnoses remained low throughout this period: the highest recorded figure was 3.1%, in 2007. Despite there being little-to-no justification for treating sheep for M. expansa on the basis of any likely benefit to the health or production of the animals, many farmers in NI do treat for tapeworm and often with ineffective products. This is of concern, in that it could lead to the inadvertent development of anthelmintic resistance in nematode and trematode parasites.

7.
Vet Parasitol ; 221: 93-103, 2016 May 15.
Article in English | MEDLINE | ID: mdl-27084479

ABSTRACT

The ultrastructure of the ovary of Fasciola hepatica collected from field-infected sheep, was compared with that of flukes from laboratory-infected rats harbouring the Oberon or the Cullompton fluke isolate. At the periphery of the ovarian tubules, in all flukes, interstitial tissue was identified that appears to provide physical support and facilitate the metabolism of the germinal-line cells. Oogonia undergo mitotic division to maintain the cell population and to produce oocytes. Early oocytes feature conspicuous synaptonemal complexes in the nucleoplasm, and these become less evident as the oocytes grow in size, move towards the core of the ovarian tubule, and synthesise osmiophilic bodies. The latter may represent cortical granules, and serve to block polyspermy. The identity of the synaptonemal complexes was confirmed by immunocytochemical labelling of synaptonemal proteins. The occurrence of synaptonemal complexes in the oocytes of all fluke types examined indicates that pairing of bivalent chromosomes, with the potential for genetic recombination and chiasmata formation, is a feature of the triploid aspermic parthenogenetic Cullompton flukes, as well as of the wild-type out-breeding field-derived and Oberon isolate flukes. In oocytes within shelled eggs in the proximal uterus of all flukes, condensed chromosomes align at meiotic metaphase plates. Following the reduction division, two equal pronuclei appear in each oocyte in the distal uterus. On the basis of these observations, a mechanism of facultative parthenogenesis for F. hepatica is proposed that accommodates the survival and clonal expansion of triploid aspermic isolates.


Subject(s)
Fasciola hepatica/physiology , Fasciola hepatica/ultrastructure , Animals , Fasciola hepatica/genetics , Female , Meiosis , Microscopy, Electron, Transmission , Oocytes/growth & development , Oocytes/ultrastructure , Ovary/ultrastructure , Parthenogenesis , Reproduction/physiology , Uterus/ultrastructure
8.
Vet Parasitol ; 215: 38-47, 2016 Jan 15.
Article in English | MEDLINE | ID: mdl-26790736

ABSTRACT

Lambs infected with the Cullompton isolate of Fasciola hepatica were treated orally or subcutaneously with 10mg/kg of closantel at 16 weeks post-infection. Adult flukes were recovered from the liver of individual animals at 12h, 24h, or 36h post-treatment. The flukes were processed for histological analysis. In general, degenerative changes in the reproductive and somatic tissues were progressive, and were most marked in flukes exposed to closantel in vivo for 36h. However, flukes from a 12h subcutaneously-treated lamb showed marked deterioration of the testis, possibly because a portion of the dose has been delivered intravenously. Fewer intact eggs were seen in the uterus of flukes exposed to closantel for longer times (whether administered subcutaneously or orally to the host). The most conspicuous closantel-induced effect in flukes from treated hosts was progressive damage to the tegumental syncytium. While the flukes from 24h-treated hosts showed relatively minor damage to limited areas of the syncytium, towards the posterior end, the flukes from 36h-treated hosts (and flukes from the lamb that putatively received intravenous dosage) had lost large areas of the surface syncytium from the posterior end and dorsal surface, although the syncytium over the anterior end and the anterior ventral surface was largely spared. In areas where the syncytium had sloughed, the underlying structures such as the vitelline follicles, gut profiles and testis profiles, showed marked degeneration and breakdown. Other changes included cell depletion and early stage apoptosis in the testis, ovary and vitelline follicles. This study establishes a model for histological changes in closantel-sensitive F. hepatica exposed to closantel in vivo. Histopathological studies could be complementary to the efficacy controlled test for for closantel resistance in fluke populations.


Subject(s)
Anthelmintics/therapeutic use , Fasciola hepatica , Fascioliasis/veterinary , Salicylanilides/therapeutic use , Sheep Diseases/drug therapy , Administration, Oral , Animals , Anthelmintics/administration & dosage , Injections, Subcutaneous , Salicylanilides/administration & dosage , Sheep , Sheep Diseases/parasitology
9.
Vet Parasitol ; 216: 72-83, 2016 Jan 30.
Article in English | MEDLINE | ID: mdl-26801598

ABSTRACT

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


Subject(s)
Animal Husbandry/trends , Anthelmintics/pharmacology , Benzimidazoles/pharmacology , Fascioliasis/veterinary , Sheep Diseases/prevention & control , Animal Husbandry/methods , Animals , Anthelmintics/administration & dosage , Anthelmintics/therapeutic use , Antigens, Helminth/analysis , Benzimidazoles/administration & dosage , Benzimidazoles/therapeutic use , Climate Change , Drug Resistance , Fasciola/drug effects , Fasciola/isolation & purification , Fascioliasis/drug therapy , Fascioliasis/epidemiology , Fascioliasis/prevention & control , Feces/chemistry , Feces/parasitology , Female , Northern Ireland/epidemiology , Parasite Egg Count/veterinary , Prevalence , Seasons , Sheep , Sheep Diseases/drug therapy , Sheep Diseases/epidemiology , Sheep Diseases/parasitology , Surveys and Questionnaires , Triclabendazole
10.
Vet Parasitol ; 212(3-4): 181-7, 2015 Sep 15.
Article in English | MEDLINE | ID: mdl-26234898

ABSTRACT

Chronic fasciolosis is often diagnosed by faecal egg counting (FEC), following concentration of the eggs in the sample by a zinc sulphate floatation method. However, concentration by a sedimentation technique gives improved sensitivity. Interpretation of FEC results for fasciolosis is complicated by factors such as the long pre-patent period and irregular egg shedding. Thus, FEC reduction tests (FECRT), when used alone, are not completely reliable for diagnosis of anthelmintic susceptibility or resistance in local fluke populations, especially when parasite burdens are small. A Fasciola hepatica coproantigen ELISA test has been introduced which more accurately reflects the presence of flukes in the host bile ducts in late pre-patent infections, and absence of flukes following successful chemotherapeutic intervention. The aim of the present study was to elucidate the specificity of the F. hepatica coproantigen ELISA technique, particularly regarding potential cross-reactivity with rumen fluke (paramphistome), gastrointestinal nematode and coccidian infections. The method involved parallel testing of a large battery of faecal samples from field-infected cattle and sheep using floatation and sedimentation FECs and coproantigen analysis. No evidence was found for significant false positivity in the F. hepatica coproantigen ELISA due to paramphistome, coccidian and/or gastrointestinal nematode co-infections. With sedimentation FECs less than 10 F. hepatica eggs per gram (epg), the likelihood of a positive coproantigen result for the sample progressively decreased. Diagnosis of fasciolosis should be based on consideration of both FEC and coproantigen ELISA findings, to ensure optimum sensitivity for pre-patent and low-level infections.


Subject(s)
Antigens, Helminth/chemistry , Cattle Diseases/parasitology , Enzyme-Linked Immunosorbent Assay/veterinary , Fasciola hepatica , Fascioliasis/veterinary , Sheep Diseases/parasitology , Animals , Cattle , Cattle Diseases/diagnosis , Coccidiosis/complications , Coccidiosis/veterinary , Coinfection , Fascioliasis/diagnosis , Feces/parasitology , Nematode Infections/complications , Nematode Infections/veterinary , Odds Ratio , Sensitivity and Specificity , Sheep , Sheep Diseases/diagnosis , Trematode Infections/complications , Trematode Infections/veterinary
11.
Vet Parasitol ; 211(3-4): 182-94, 2015 Jul 30.
Article in English | MEDLINE | ID: mdl-26093822

ABSTRACT

An in vivo study in the laboratory rat model has been carried out to monitor changes to the female reproductive system in 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 200mg/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 200mg/kg and flukes recovered 24, 48, 72 and 96 h pt. The flukes were processed for histological and transmission electron microscope (TEM) examination of the uterus, Mehlis' gland, ovary and vitellaria. After treatment with artemether, egg production had become abnormal by 72 h pt, with free vitelline cells and masses of shell protein material within the uterus; spermatozoa were absent. The Mehlis' gland and ovary retained a normal morphology over the 3-day period. A change in the cell population in the vitelline follicles was seen at 48 h pt, with a decline in the number of immature cells. This became more marked by 72 h and the follicles became progressively vacuolated over the 3-day period. At the TEM level, there were changes in the immature vitelline cells at 24h pt, as evidenced by a decrease in shell protein production and the presence of lipid droplets and abnormal mitochondria. Spaces in the follicles separated the cells from each other. The changes became progressively more severe with time, so that, by 72 h pt, the follicles were very disrupted, containing cells in the advanced stages of apoptotic breakdown. In extreme cases, the follicles were scarcely recognisable and had become filled with cellular debris. Fine structural changes to the vitelline cells induced by artesunate treatment were similar to those described for artemether, but generally occurred more quickly and were greater; this was particularly true of the swelling of the ger cisternae. Overall, the results have shown that artemisinin treatment has a severe impact on egg production by TCBZ-resistant flukes, an effect that is mediated by disruption of the vitelline cells.


Subject(s)
Artemisinins/pharmacology , Fasciola hepatica/drug effects , Genitalia, Female/drug effects , Animals , Antimalarials/chemistry , Antimalarials/pharmacology , Artemether , Artemisinins/chemistry , Artesunate , Female , Genitalia, Female/ultrastructure , Ovum/drug effects
12.
Vet Parasitol ; 207(1-2): 34-43, 2015 Jan 15.
Article in English | MEDLINE | ID: mdl-25529143

ABSTRACT

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


Subject(s)
Anthelmintics/pharmacology , Fasciola hepatica/drug effects , Fascioliasis/veterinary , Sheep Diseases/parasitology , Animals , Benzimidazoles/pharmacology , Drug Resistance/drug effects , Enzyme-Linked Immunosorbent Assay/veterinary , Fascioliasis/drug therapy , Fascioliasis/parasitology , Fascioliasis/pathology , Feces/parasitology , Female , In Situ Nick-End Labeling/veterinary , Nitroxinil/pharmacology , Northern Ireland , Parasite Egg Count/veterinary , Salicylanilides/pharmacology , Sheep , Sheep Diseases/drug therapy , Triclabendazole
13.
Vet Parasitol ; 195(1-2): 122-30, 2013 Jul 01.
Article in English | MEDLINE | ID: mdl-23398988

ABSTRACT

The prevalence of anthelmintic resistance in Northern Ireland sheep flocks was evaluated between July and October 2011. Sampling kits were sent to 172 flock owners and returns were received from 91. Within this survey population, 27 flock owners used benzimidazole products, 10 used levamisole products, 15 used avermectin products, 26 used milbemycin products and 4 flock owners used the amino acetonitrile derivative, Monepantel. The remaining 9 flock owners used combination drenches (broad spectrum wormer plus fasciolicide). However, 15 sets of samples were ineligible for faecal egg count reduction testing due to either too low an egg count or insufficient faecal volume. Treatment efficacy below 95%, indicating significant resistance, was detected in 81% (n=24) of flocks tested for benzimidazole resistance; in 14% (n=1) of flocks tested for levamisole resistance; and in 50% (n=7) and 62% (n=13) of flocks tested for avermectin and milbemycin resistance, respectively. Monepantel resistance was absent in all (n=3) flocks tested. Combination products (broad spectrum nematocide plus flukicide) containing levamisole were entirely effective, while treatment efficacy below 95% was detected in 60% (n=3) of flocks where the nematocide in the combination product was a benzimidazole. Where parasite identification based on coproculture was completed, Trichostrongylus was the dominant genus detected in all cases post-treatment, indicating the occurrence of anthelmintic-resistant Trichostrongylus spp. populations. Benzimidazole efficacy was highest in treating Trichostrongylus spp. (51%) and lowest when treating Teladorsagia spp. Levamisole was 100% effective in treating Cooperia, but ineffective (0%) in treating Trichostrongylus spp. Avermectin efficacy was highest when treating Haemonchus contortus (100%) and Teladorsagia spp. (73%), with a marginally lower efficacy against Trichostrongylus spp. (71%). Moxidectin efficacy was 33% against Trichostrongylus spp., 68% against Teladorsagia spp., 97% against Cooperia spp. and 100% against Haemonchus contortus infections.


Subject(s)
Anthelmintics/pharmacology , Gastrointestinal Diseases/veterinary , Sheep Diseases/parasitology , Trichostrongyloidea/drug effects , Trichostrongyloidiasis/veterinary , Aminoacetonitrile/analogs & derivatives , Aminoacetonitrile/pharmacology , Aminoacetonitrile/therapeutic use , Animals , Anthelmintics/therapeutic use , Antinematodal Agents/pharmacology , Antinematodal Agents/therapeutic use , Benzimidazoles/pharmacology , Benzimidazoles/therapeutic use , Drug Resistance , Feces/parasitology , Gastrointestinal Diseases/drug therapy , Gastrointestinal Diseases/epidemiology , Gastrointestinal Diseases/parasitology , Ivermectin/analogs & derivatives , Ivermectin/pharmacology , Ivermectin/therapeutic use , Levamisole/pharmacology , Levamisole/therapeutic use , Macrolides/pharmacology , Macrolides/therapeutic use , Northern Ireland/epidemiology , Parasite Egg Count/veterinary , Prevalence , Sheep , Sheep Diseases/drug therapy , Sheep Diseases/epidemiology , Sheep, Domestic , Treatment Outcome , Trichostrongyloidea/physiology , Trichostrongyloidiasis/drug therapy , Trichostrongyloidiasis/epidemiology , Trichostrongyloidiasis/parasitology
14.
Vet Parasitol ; 193(1-3): 179-84, 2013 Mar 31.
Article in English | MEDLINE | ID: mdl-23273780

ABSTRACT

Reports of anthelmintic resistance to multiple drugs in individual parasite species, and in multiple parasite species across virtually all livestock hosts, are increasingly common. A working group of UK researchers and practitioners devised a set of guidelines in 2003 (Sustainable Control of Parasites in Sheep, 'SCOPS') aimed at maintaining anthelmintic efficacy on farms. Over the years that followed, these guidelines were promoted through meetings, promotional literature and the agricultural press. Results from questionnaires conducted in Northern Ireland (NI) in 2005 (covering 1999-2004) and 2011 (covering 2008-2011) have provided an opportunity to examine the extent to which these campaigns have influenced parasite control on sheep farms. The percentage of flocks at risk of under-dosing through inaccurate weight estimation in NI has increased by 15.9% since 2005. The number of flocks at risk of under-dosing through non-calibrated equipment has increased by 14.3% since 2005. The size of the in refugia population may have potentially doubled, as indicated by an increased compliance with the recommendation (wherever possible) to leave a portion of the flock untreated. However, whether this is indeed the case cannot be explicitly determined without a measure of the impact of various factors, including host immunity, environment/climate, previous anthelmintic treatment and the species of parasite present.


Subject(s)
Anthelmintics/pharmacology , Sheep Diseases/parasitology , Animal Husbandry , Animals , Anthelmintics/administration & dosage , Data Collection , Drug Resistance , Northern Ireland/epidemiology , Sheep , Sheep Diseases/epidemiology , Sheep Diseases/prevention & control , Surveys and Questionnaires
15.
Vet Parasitol ; 192(1-3): 173-82, 2013 Feb 18.
Article in English | MEDLINE | ID: mdl-23228496

ABSTRACT

A questionnaire to obtain information on nematode control practices and sheep management was sent to over 1000 farmers in Northern Ireland. Replies were received from 305 flock owners, and data from 252 of them were analysed. Farms were divided into lowland and upland areas. Sizes of pasture and stocking rates on lowland and upland farms were 59.5 hectares, 6.99 sheep/hectare and 62.9 hectares and 10.01 sheep/hectare, respectively. Mean drenching rates for lambs and adults were 2.33 and 2.44, respectively, in lowland flocks and 2.73 and 2.71, respectively, in upland flocks. Between 2008 and 2011, the most frequently identified compounds in use were benzimidazoles and moxidectin in lowland flocks, and benzimidazoles and avermectins in upland flocks. Over the same period the most frequently identified commercial formulations were Tramazole(®), Panacur(®) and Allverm(®) (white drench), Levacide(®) (yellow drench), Oramec(®) (clear drench; avermectin), Cydectin(®) (clear drench; moxidectin) and Monepantel(®) (orange drench). Most respondents (56.35%) treated their lambs at weaning and the most common time to treat ewes was identified to be pre-mating (67.86% of respondents). The results of the questionnaire survey revealed that lowland annual drench frequency was 2.33 and 2.44 in lambs and ewes, respectively, although drench frequencies were higher in upland flocks: 2.73 and 2.71 for lambs and ewes, respectively. Annual drench rotation was practiced by 43.96% of flock owners, but whether this was true rotation or pseudo-rotation (i.e., substitution of one anthelmintic product by another product belonging to the same chemical group of anthelmintics) could not be explicitly determined.


Subject(s)
Anthelmintics/administration & dosage , Drug Resistance , Gastrointestinal Diseases/veterinary , Nematoda/drug effects , Nematode Infections/veterinary , Sheep Diseases/prevention & control , Animal Husbandry , Animals , Feces/parasitology , Female , Gastrointestinal Diseases/parasitology , Gastrointestinal Diseases/prevention & control , Male , Nematode Infections/parasitology , Nematode Infections/prevention & control , Northern Ireland , Parasite Egg Count/veterinary , Sheep , Sheep Diseases/parasitology , Surveys and Questionnaires
16.
Vet Parasitol ; 191(3-4): 240-51, 2013 Jan 31.
Article in English | MEDLINE | ID: mdl-23062689

ABSTRACT

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


Subject(s)
Anthelmintics/pharmacology , Benzimidazoles/pharmacology , DNA Breaks , Drug Resistance/drug effects , Endonucleases/metabolism , Fasciola hepatica/cytology , Fasciola hepatica/drug effects , Animals , Apoptosis , Fasciola hepatica/genetics , Female , Genitalia/cytology , Genitalia/drug effects , In Situ Nick-End Labeling , Male , Sheep , Triclabendazole
17.
Int J Parasitol ; 42(13-14): 1193-9, 2012 Dec.
Article in English | MEDLINE | ID: mdl-23131680

ABSTRACT

The liver flukes, Fasciola hepatica and Fasciola gigantica, are considered to be sister species and between them present a major threat worldwide to livestock production. In this study sequence data have been employed from informative regions of the nuclear and mitochondrial genomes of over 200 morphologically F. hepatica-like or F. gigantica-like flukes from Europe, sub-Saharan Africa and South Asia to assess genetic diversity. Evidence is presented for the existence of four well-separated clades: African gigantica-like flukes, Indian gigantica-like flukes, European hepatica-like flukes and African high-altitude hepatica-like flukes. Application of the Biological Species Concept to trematodes is problematic; however, the degree of separation between these groups was sufficient for them to be considered as distinct species using the four times rule for speciation.


Subject(s)
Fasciola/genetics , Fascioliasis/veterinary , Genetic Speciation , Genetic Variation , Africa South of the Sahara/epidemiology , Animals , Australia/epidemiology , Cattle , Cattle Diseases/epidemiology , Cattle Diseases/parasitology , DNA, Mitochondrial/genetics , Equidae , Europe/epidemiology , Fascioliasis/epidemiology , Fascioliasis/parasitology , Genome , India/epidemiology , Molecular Sequence Data , Phylogeny , RNA, Helminth/genetics , RNA, Ribosomal, 28S/genetics , Sheep , Sheep Diseases/epidemiology , Sheep Diseases/parasitology
18.
Vet Rec ; 171(20): 502, 2012 Nov 17.
Article in English | MEDLINE | ID: mdl-23077134

ABSTRACT

A commercial coproantigen ELISA test for fasciolosis, based on the use of MM3 monoclonal antibody for antigen capture, was investigated for possible cross-reactivity with Paramphistomum cervi, a trematode that commonly infects cattle and sheep grazing in fluke-infested pasture in Ireland. Histological sections of adult and immature Fasciola hepatica and P cervi were incubated with MM3 monoclonal antibody, and its binding to tissue-localised coproantigen was subsequently visualised by immunocytochemistry. In a related study, the soluble antigenic fractions derived from homogenates of P cervi adults and Taenia hydatigena metacestodes were tested for cross-reactivity with MM3 monoclonal antibody in an antigen-capture ELISA, using known F hepatica-positive and F hepatica-negative ovine faecal samples as natural controls. It was found that, while intense immunocytochemical labelling was located over the gastrodermis and gut contents of adult and immature F hepatica, sections of adult and immature P cervi were unlabelled. In the ELISA tests, the soluble fractions of F hepatica reacted strongly with MM3 monoclonal antibody, but those of P cervi and T hydatigena gave negative results. These findings support the specificity of the coproantigen ELISA test for fasciolosis in areas where paramphistomosis and cysticercosis are liable to occur singly or as coinfections with F hepatica.


Subject(s)
Antigens, Helminth/immunology , Enzyme-Linked Immunosorbent Assay/veterinary , Paramphistomatidae/immunology , Taeniasis/veterinary , Trematode Infections/veterinary , Animals , Antibodies, Helminth/analysis , Antibodies, Monoclonal/immunology , Cattle , Cattle Diseases/diagnosis , Cross Reactions , Enzyme-Linked Immunosorbent Assay/standards , Fascioliasis/diagnosis , Fascioliasis/epidemiology , Fascioliasis/veterinary , Feces/parasitology , Sensitivity and Specificity , Sheep , Sheep Diseases/diagnosis , Taenia/immunology , Taeniasis/diagnosis , Taeniasis/epidemiology , Trematode Infections/diagnosis , Trematode Infections/epidemiology
19.
Vet Parasitol ; 190(1-2): 167-77, 2012 Nov 23.
Article in English | MEDLINE | ID: mdl-22789298

ABSTRACT

While the influence of temperature and moisture on the free-living stages of gastrointestinal nematodes have been described in detail, and evidence for global climate change is mounting, there have been only a few attempts to relate altered incidence or seasonal patterns of disease to climate change. Studies of this type have been completed for England Scotland and Wales, but not for Northern Ireland (NI). Here we present an analysis of veterinary diagnostic data that relates three categories of gastrointestinal nematode infection in sheep to historical meteorological data for NI. The infections are: trichostrongylosis/teladorsagiosis (Teladorsagia/Trichostrongylus), strongyloidosis and nematodirosis. This study aims to provide a baseline for future climate change analyses and to provide basic information for the development of nematode control programmes. After identifying and evaluating possible sources of bias, climate change was found to be the most likely explanation for the observed patterns of change in parasite epidemiology, although other hypotheses could not be refuted. Seasonal rates of diagnosis showed a uniform year-round distribution for Teladorsagia and Trichostrongylus infections, suggesting consistent levels of larval survival throughout the year and extension of the traditionally expected seasonal transmission windows. Nematodirosis showed a higher level of autumn than Spring infection, suggesting that suitable conditions for egg and larval development occurred after the Spring infection period. Differences between regions within the Province were shown for strongyloidosis, with peaks of infection falling in the period September-November. For all three-infection categories (trichostrongylosis/teladorsagiosis, strongyloidosis and nematodirosis), significant differences in the rates of diagnosis, and in the seasonality of disease, were identified between regions.


Subject(s)
Gastroenteritis/veterinary , Nematodirus/isolation & purification , Sheep Diseases/epidemiology , Strongylida Infections/veterinary , Strongyloides/isolation & purification , Trichostrongyloidea/isolation & purification , Animals , Climate Change , Drug Resistance , Female , Gastroenteritis/diagnosis , Gastroenteritis/epidemiology , Gastroenteritis/parasitology , Geography , Northern Ireland/epidemiology , Parasite Egg Count/veterinary , Rain , Seasons , Sheep , Sheep Diseases/diagnosis , Sheep Diseases/parasitology , Strongylida Infections/diagnosis , Strongylida Infections/epidemiology , Strongylida Infections/parasitology , Strongyloidiasis/diagnosis , Strongyloidiasis/epidemiology , Strongyloidiasis/parasitology , Strongyloidiasis/veterinary , Temperature , Trichostrongylosis/diagnosis , Trichostrongylosis/epidemiology , Trichostrongylosis/parasitology , Trichostrongylosis/veterinary
20.
Vet Parasitol ; 187(1-2): 183-95, 2012 Jun 08.
Article in English | MEDLINE | ID: mdl-22285009

ABSTRACT

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.


Subject(s)
Anthelmintics/pharmacology , Benzimidazoles/pharmacology , Fasciola hepatica/drug effects , Fasciola hepatica/physiology , Ovulation/physiology , Animals , Anthelmintics/therapeutic use , Benzimidazoles/therapeutic use , Fasciola hepatica/ultrastructure , Fascioliasis/drug therapy , Fascioliasis/parasitology , Fascioliasis/veterinary , Female , Microscopy, Electron, Transmission , Ovary/drug effects , Ovary/ultrastructure , Sheep , Sheep Diseases/drug therapy , Sheep Diseases/parasitology , Time Factors
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