Fasciola hepatica: the effect of the sodium ionophore monensin on the adult tegument

The effect on the tegument of adult Fasciola hepatica of incubation in the sodium ionophore monensin, the Na+/K+-ATPase inhibitor ouabain and ouabain pretreatment followed by monensin has been determined in vitro by scanning and transmission electron microscopy (SEM, TEM). With monensin incubation alone (1 x 10(-6) M), a flattening of the tegument with some loss of spines on the ventral surface is evident from 0.5 h onwards. Internally, the subtegumental musculature becomes grossly swollen, although there is no swelling of the infoldings of the basal plasma membrane of the tegument, even after 24 h incubation. Ouabain incubation (1 x 10(-3) M) induces folding of the apical surface of the tegument from 0.5 h onwards, and this is accompanied by the formation of blebs and microvilli. Brief (0.5 h) exposure to ouabain (1 x 10(-3) M) followed by monensin treatment (1 x 10(-4) M, 3 h) leads to gross "vacuolation" of the tegument, but this is not due to swelling of the basal infoldings. The other main feature of ouabain-pretreated flukes is the projection of basal lamina-like material into the tegumental syncytium. Monensin treatment alone (1 x 10(-6) M) results in the Golgi complexes of the tegumental cells becoming very diffuse from 1.5 h onwards, and relatively few secretory bodies are present in the cytoplasm. After 0.5 h incubation in ouabain (1 x 10(-3) M), the Golgi complexes of the tegumental cells are indistinct, although numerous secretory bodies are still present. The classical monensin-induced swelling of the Golgi cisternae is observed in the tegumental cells only when monensin treatment (1 x 10(-4) M, 3 h) was preceded by brief (0.5 h) exposure to ouabain (1 x 10(-3) M). The results are discussed in relation to the postulated osmoregulatory role of the tegument and the role of sodium pumps in membrane function in the fluke.

Environmental stress and parasitic infections: I. The effects of Gramoxone and Hexadrin on embryo and hatching of Fasciola gigantica miracidia

The effect of two chemical compounds commonly used in agriculture, Gramoxone (a herbicide) and Hexadrin (an insecticide) on embryonic development and hatching of Fasciola gigantica miracidia were experimentally assessed. These two pesticides were introduced in varying quantities into petri dishes containing unembryonated eggs of the trematode for a period of 30 days. LC50 (lethal concentration for 50% hatching) values were determined for them. For gramoxone it was 2 ppm and for Hexadrin it was 2.5 ppm. Results also show that at 4 ppm and 5.5 ppm the pesticides achieve 99.0% mortality of eggs. At sublethal concentrations they cause prolongation of embryonic processes and inhibition of hatching of miracidia.

Flukicidal action of closantel against immature and mature Fasciola hepatica in experimentally infected rats and sheep

The relative importance of peak level- and residual level-related flukicidal activity of closantel against immature and mature Fasciola hepatica was evaluated in a comparative efficacy trial using two animal species with a different plasma elimination pattern, that is, the rat and the sheep with an elimination half-life of less than one week and of two to three weeks, respectively. The rats were dosed orally with closantel at 20 mg kg-1 at two, four, six, eight and 10 weeks; the sheep at 10 mg kg-1 at eight, 10 and 12 weeks after artificial infection. Necropsy was performed either one week after treatment or 12 weeks after infection. Efficacy rates and the length of the recovered flukes were evaluated. It was demonstrated that the flukicidal effect of closantel is directly related to its peak plasma levels and less to its residual plasma concentrations. In the rat, a high efficacy (P less than 0.001) could be demonstrated against immature stages of four weeks or older. The two-week immature stages were less markedly affected. No significant differences in efficacy and size of the flukes were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection. In the sheep, the efficacy against six-week and eight-week-old immature stages varied between 70.3 and 76.8 per cent and between 92.8 and 96.5 per cent, respectively. As in the rats, no marked differences in efficacy were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Fasciola hepatica: perturbation of secretory activity in the vitelline cells by the sodium ionophore monensin

The effect of the sodium ionophore monensin on the vitelline cells of Fasciola hepatica has been determined both in vitro and in vivo by means of transmission electron microscopy. In intact flukes in vitro, vacuolation of the Golgi complex of the intermediate, shell protein secreting vitelline cells is evident after 1.5 hr incubation in monensin (1 X 10(-6) M). The vacuolation becomes progressively greater with time, eventually spreading to the late stem cells and mature cells. In addition, there is a block in the normal migration of the shell protein globules to the periphery, the shell globule clusters becoming very loosely packed and empty, and distended single globules accumulate in the perinuclear region of the cell. Disruption of the nurse cell cytoplasm is apparent from 6 hr onwards, giving the follicle a less compact appearance. Morphological changes induced by higher concentrations of monensin (up to 1 X 10(-4) M) followed a similar time course and pattern to that described for 1 X 10(-6) M) followed a similar time course and pattern to that described for 1 X 10(-6) M. In tissue-slice material (1 X 10(-6) M) these effects of monensin are evident more rapidly, and to a far greater extent: the condition of the vitelline cells in slices after only 1.5 hr resembles that reached in intact flukes after more than a 12-hr incubation. Incubation in ouabain, an inhibitor of Na+/K+-ATPase activity, has little effect on vitelline morphology over a 6-hr period (1 X 10(-3) M), although brief (0.5 hr) exposure to ouabain followed by monensin treatment (1 X 10(-4) M, 3 hr) does lead to gross vacuolation of the intermediate cells, the condition resembling that in tissue-slice material. In contrast, in vivo treatment of infected laboratory rats (1 X 5 mg/kg) only leads to a transient effect on the ultrastructure of the intermediate vitelline and nurse cells. The specific perturbation of the Golgi complex and secretory traffic in the vitelline cells of F. hepatica by monensin follows the classic pattern observed in other cell types.

Comparative efficacy of triclabendazole, nitroxynil and rafoxanide against immature and mature Fasciola hepatica in naturally infected cattle

In two trials the fasciolicidal activities of triclabendazole, nitroxynil and rafoxanide were assessed in cattle naturally infected with predominantly immature stages of Fasciola hepatica. Tablets containing 900 mg triclabendazole were administered orally at a dose rate of 12 mg/kg bodyweight. Rafoxanide and nitroxynil were used at a dose rate of 10 mg/kg, rafoxanide being given orally and nitroxynil by subcutaneous injection. Based on faecal egg counts nine weeks after treatment the efficacies were calculated to be 100 per cent for triclabendazole and 95.0 per cent for nitroxynil in the first trial and 98.4 per cent for triclabendazole and 52.9 per cent for rafoxanide 15 weeks after treatment in the second trial. In the first trial five animals from each of the three groups were slaughtered and their fluke burdens counted. Compared with the untreated control group the reductions in the fluke burdens were 96.9 per cent in triclabendazole treated cattle and 76.4 per cent in the nitroxynil treated group.

Diamphenethide--a reassessment of its pharmacological action

At a concentration of 1 x 10(-4) M (28.84 micrograms/ml), with a solvent concentration of 1.0% (v/v) ethanol, the deacetylated (amine) metabolite of diamphenethide (DAMD) causes an initial stimulation of activity, followed by suppression, leading to a paralysis within 3 h. These changes are accompanied by an increase in muscle tone of more than 200 mg. However, ethanol alone at a concentration of 1.0% (v/v) causes an initial stimulation of activity and increase in muscle tone (approximately 550 mg). If the concentration of DAMD is kept at 1 x 10(-4) M (28.84 micrograms/ml) but the solvent concentration reduced [e.g., 0.05% (v/v) dimethyl sulphoxide], then only a suppression of motility and flaccid paralysis are observed. This response is also seen at the lower concentration of 10 micrograms/ml, which corresponds to the maximum blood levels of DAMD in vivo. The sodium ionophore monensin induces a suppression of motility, leading to a rapid flaccid paralysis (in approximately 1.5 h at 1 x 10(-7) M, and within a few minutes at higher concentrations). Ouabain, an inhibitor of Na+/K+-ATPase activity, also causes a suppression of motility, but this is accompanied by an increase in muscle tone, leading to a spastic paralysis (in approximately 2.5 h at 1 x 10(-3) M, and 3.5 h at 1 x 10(-4) M). Pretreatment with ouabain (1 x 10(-3) M for 15 min) followed by monensin (1 x 10(-5) M) reverses the original effect of monensin by inducing a rapid spastic paralysis (in approximately 50 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of a fenbendazole-triclabendazole combination against Fasciola hepatica and gastrointestinal nematodes in sheep

A fenbendazole and triclabendazole combination was tested against experimentally induced 6-and 14-week-old infections of Fasciola hepatica and naturally acquired infections of gastrointestinal nematodes in sheep. Forty-eight sheep were divided randomly into six treatment groups of eight animals each. At 7.5 and 10.0 mg kg-1 body weight (BW) (3.75 and 5.0 mg kg-1 BW of each drug), the drug combination was 98.3 and 99.7% effective against 6-week-old F. hepatica infections, and 100 and 99.9% effective against 14-week-old infections. At the same drug dosages, the drug combination was effective against naturally acquired adult Ostertagia spp. (97.3-100%) and adult Nematodirus spp. (90.3-99.9%). No adverse effects associated with treatment were noted.

Efficacy and safety of albendazole against experimentally induced Fasciola hepatica infections in goats

Forty 8-week-old goats were allocated to five groups of equal size to determine the optimal dosage of albendazole against experimentally induced 14-week-old Fasciola hepatica infections. Albendazole suspension given orally at 5.0, 7.5, 10.0 and 15 mg kg-1 of body weight was 73.3, 88.2, 88.3 and 95.9% effective, respectively, when compared to untreated controls. Mean number of F. hepatica in the untreated control goats was 75.4. No signs of toxicity were observed. When albendazole was given to eight, 8-week-old goats orally at 75 mg kg-1 (five times the optimal dosage), no signs of toxicity were observed.

The anthelmintic efficacy of netobimin against experimental infections of Fasciola hepatica in sheep

Netobimin (coded SCH 32481, Schering Corporation), a new broad-spectrum anthelmintic having both fasciolicidal and nematocidal properties was evaluated for efficacy against mature Fasciola hepatica infections in sheep. The trial was conducted with 30 cross-bred spring lambs, each experimentally infected with 250 F. hepatica metacercariae. A single treatment of netobimin was administered at 17 weeks post-infection (PI) by oral drench at 7.5 or 20 mg kg-1 body weight while 10 animals remained as untreated controls. At necropsy (either 1 or 2 weeks post-treatment), the mean number of adult flukes recovered from the control, 7.5 and 20 mg kg-1 groups were 94.7, 35.9 and 8.8, respectively. The resulting efficacies were 62% (P less than or equal to 0.05) and 90.7% (P less than or equal to 0.01), respectively. No clinical signs of fascioliasis were noted in any sheep during the trial. No signs of toxicosis nor any adverse reactions to the drug were observed.

Fasciola hepatica in vitro: increased susceptibility to fasciolicides in a defined serum-free medium

The cidal properties of some phenolic, halogenated diphenyl, salicylanilide, benzimidazole and diaminophenoxyalkane anthelmintics, against 6-week-old worms of Fasciola hepatica were assessed in vitro. In a conventional fluke culture medium containing RPMI 1640, supplemented with serum with or without rabbit erythrocytes or pink-ghosts, only the halogenated diphenyl and salicylanilide compounds showed activity at concentrations equal to or less than 100 microM. However, when basal, serum and cell-free RPMI 1640 was used, all compounds other than diamphenethide were highly active, their minimum lethal concentrations being some 25-125 times lower under these conditions. The inclusion of rabbit liver microsomes in the basal culture medium resulted in diamphenethide exhibiting cidal activity equivalent to that seen when its free-amine active metabolite was assayed. The possibility that the activity of many of these compounds was masked in vitro because of their serum binding properties is discussed. Recommendations are made that in vitro screens for new fasciolicides should be carried out in serum-free medium and that additional replicates containing mammalian liver microsomes and liver cytosolic extracts be included as means for the metabolic activation of certain otherwise undetectable prodrugs.

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

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

Inhibition of malate dehydrogenase enzymes by benzimidazole anthelmintics

Determinations were made of the inhibitory activities of four benzimidazole anthelmintics (Albendazole, Parbendazole, Mebendazole and Thiabendazole) on purified extracts of cytoplasmic and mitochondrial malate dehydrogenase obtained from Ascaris suum, Fasciola hepatica and Moniezia expansa. The highest percentage inhibitions were exhibited by Mebendazole. The results confirm that cytoplasmic MDH and mitochondrial MDH regulator enzymes of glycogen synthesis are the sites of mebendazole inhibitory activity, but the activity sites of the other anthelmintics in the study remain unclear.

An evaluation of the efficacy of monensin against Fasciola hepatica in the albino rat

The in vivo efficacy of monensin against Fasciola hepatica was determined in the albino rat. The results were variable, with monensin generally showing greater activity against juvenile (two-week-old) than adult (12-week-old) flukes. Significant (p less than 0.005) reductions in worm burdens were obtained only following treatment of adult flukes with 2 X 10 mg/kg monensin (52.9% efficacy), and of juvenile flukes with 1 X 10 mg/kg (42.4% efficacy) and 2 X 10 mg/kg (56.23% efficacy). Monensin administered in the diet (200 ppm) had a negligible effect on juvenile and adult fluke burdens. Prophylactic treatment of rats with monensin (100 ppm) produced a 45.5% efficacy, but this was not statistically significant. At doses of 1 X 5 mg/kg and 2 X 2.5 mg/kg, monensin had little effect on egg output by F. hepatica. No clear relationship was established between egg output and worm burden, and so faecal egg counting was not a reliable indicator of fluke burdens in the rat.

Fasciola hepatica: action in vitro of triclabendazole on immature and adult stages

Under in vitro conditions in a balanced salt solution, triclabendazole was found to accumulate in significant amounts in both immature (3 week old) and adult Fasciola hepatica. A viable parasite was needed to concentrate the drug, but a high percentage of the compound was also bound by the dead worm. The drug could penetrate into liver flukes even when the oral route had been closed off by ligation, indicating that the drug can be taken up by transtegumentary absorption. A 24 hr exposure to triclabendazole, at 10-25 microM concentrations, was found to result in a strong inhibition of the parasite's motility. This effect was paralleled by dramatic changes in the worm's resting tegumental membrane potential. The onset of these actions was found to develop very slowly, and high drug levels had to accumulate within the parasite to initiate its immobilization. In addition to drug concentration and incubation time, physiological alterations observed were also dependent on other culture conditions, such as the presence or absence of serum albumin and the drug tissue/medium ratio. Biochemical examinations showed that triclabendazole significantly stimulated glucose derived acetate and propionate formation by adult liver flukes. Adenosine triphosphate levels were not changed even in the presence of high triclabendazole concentrations (25 microM). Likewise, the activities of various membrane associated adenosine triphosphatases were not altered by the drug. However, the ability of the drug to inhibit colchicine binding to microtubular protein purified from adult liver flukes suggested an interference of the drug with microtubular structure and function.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction between the deacetylated (amine) metabolite of diamphenethide (DAMD) and cytochemically demonstrable Na+/K+-ATPase activity in the tegument of Fasciola hepatica

The relative effects on tegumental Na+/K+-ATPase activity in Fasciola hepatica of the deacetylated (amine) metabolite of diamphenethide (DAMD) (10 micrograms/ml, 18 h) and the Na+/K+-ATPase inhibitor ouabain (0.1 mM, 0.5 h) have been assessed cytochemically. In the normal tegument, Na+/K+-ATPase activity is particularly concentrated along the invaginations of the apical plasma membrane and the infoldings of the basal plasma membrane. Ouabain pretreatment significantly reduces the overall level of Na+/K+-ATPase activity, but does not induce swelling of the basal infolds. In contrast, DAMD does not significantly reduce either the level or distribution of Na+/K+-ATPase activity, but does cause a pronounced swelling of the basal infolds. The results are discussed in relation to the postulated action of diamphenethide as an inhibitor of Na+/K+-ATPase activity.

Fasciola hepatica: tegumental surface alterations following treatment in vitro with the deacetylated (amine) metabolite of diamphenethide

The effect of the deacetylated (amine) metabolite of diamphenethide (10 micrograms/ml) on the tegumental surface of Fasciola hepatica over a 24 h period in vitro has been determined by scanning electron microscopy. Blebbing begins around the oral sucker after 3 h and then passes backwards along the body, reaching the ventral sucker and midbody by 6 h, and finally the posterior end of the body (by 12 h). Initially, the blebs are small, the tegument surrounding the spines is swollen and the tegument generally has a smooth, swollen appearance. This submerges the spines below the body surface. At higher magnification the surface is seen to bear microvillous-like projections in addition to the blebs and surface pitting is deeper than normal. Later on, the blebs increase in size and burst, causing lesions and loss of spines. Lesions begin to appear on the oral cone and ventral sucker after 6 h, in the midbody by 12 h and on the dorsal surface of the posterior region after 24 h. By this time the damage is extensive: around the oral and ventral suckers, and over large areas of the oral cone and midbody region the tegument has been stripped off to expose the basal lamina beneath. The dorsal surface of the fluke is consistently more severely affected than the ventral surface.

Effects of cholinergic drugs on longitudinal muscle contractions of Fasciola hepatica

Acetylcholine, cholinergic agonists and acetylcholinesterase inhibitors significantly decrease the amplitude and frequency of spontaneous longitudinal muscle contractions in Fasciola hepatica. In order of their effects on the inhibition of muscle contractions, the cholinergic agonists can be ranked as nicotine greater than carbachol greater than acetylcholine. High calcium ion concentration also causes a significant inhibition of contractions. Atropine, a cholinergic antagonist that acts on muscarinic receptors, significantly increases the amplitude and frequency of spontaneous contractions and completely reverses the effects of cholinomimetic drugs, including nicotine. In adult F. hepatica, the levels of acetylcholine and its precursor choline are 3.14 +/- 0.55 and 13.75 +/- 3.72 pmol/mg wet weight, respectively. The activities of choline acetyltransferase, specific acetylcholinesterase and the nonspecific cholinesterase are 1.25 +/- 0.19, 238.0 +/- 13.0, and 83.0 +/- 33.0 nmol/hr/mg protein, respectively.

Fasciola hepatica: tegumental changes induced in vitro by the deacetylated (amine) metabolite of diamphenethide

The effect of the deacetylated (amine) metabolite of diamphenethide (10 mugm/ml) on the tegument of Fasciola hepatica over a 24 hr period in vitro has been determined by means of transmission electron microscopy. In the tegumental syncytium, there is an initial accumulation of T2 secretory bodies at the apical surface (after 6 hr), together with increased exocytosis of secretory bodies and blebbing of the surface membrane. After 9 hr, the two surfaces of the fluke show different tegumental responses to drug treatment with a marked swelling of the basal infolds in the dorsal tegument, while the ventral tegument remains normal. By 18 hr, the swelling in the dorsal tegument is very severe, the entire basal region becoming edematous. In some areas, the tegument becomes detached to expose the basal lamina. The ventral tegument retains a fairly normal morphology, although there is a slight swelling of the basal infolds. The edema spreads internally to the cell bodies, beginning after 9 hr on the dorsal side of the fluke and 18 hr on the ventral side. By 18 hr, the flooding on the dorsal side is very severe and the cells attenuated, retaining few contacts with the surrounding parenchyma. From 9 hr onwards, there are progressive changes in cell structure, including a decrease in amount of granular endoplasmic reticulum and extent of its ribosomal covering, a decrease in numbers of secretory bodies, a swelling of the trans-most Golgi cisternae and disruption of the release of secretory bodies, and a swelling and disorganization of the mitochondria. The results are discussed in relation to the postulated activity of the deacetylated (amine) metabolite of diamphenethide as a Na+ ionophore.

Anthelmintic activity of triclabendazole

Triclabendazole was tested in vitro and in vivo against a range of helminths. Although in vitro activity was found against Hymenolepis diminuta (0.5 microgram/ml), Fasciola hepatica (2.5 micrograms/ml), Taenia crassiceps and Schistosoma mansoni (50 micrograms/ml), in vivo activity was only found against F. hepatica, a single oral dose of 40 mg/kg killing 99% of adult flukes in the rat. This spectrum of activity suggests a mechanism of action unlike that of other benzimidazole anthelmintics.

The behavior of juvenile Fasciola hepatica

The behavioral repertoire of the infective stage of Fasciola hepatica was qualitatively characterized. During activation, a primary activity was the emptying of the ceca by peristaltic-like contractions. Emergence behavior comprised coordinated patterns of body movement and sucker activity specifically directed at disruption of the ventral plug. The stimulus specificity of the emergence response for glycine-conjugated cholic acid and the log dose-effect relationship of this response with glycocholic acid suggested a receptor-mediated sensory recognition. Extracts from the duodenum (departure organ) and the liver (arrival site) significantly affected the rate of locomotion and the orientation of the migratory stage. The evidence for orientation in the migrating stages is unequivocal, but the mechanisms by which they orient are unclear.