The narrow-spectrum anthelmintic oxantel is a potent agonist of a novel acetylcholine receptor subtype in whipworms

In the absence of efficient alternative strategies, the control of parasitic nematodes, impacting human and animal health, mainly relies on the use of broad-spectrum anthelmintic compounds. Unfortunately, most of these drugs have a limited single-dose efficacy against infections caused by the whipworm, Trichuris. These infections are of both human and veterinary importance. However, in contrast to a wide range of parasitic nematode species, the narrow-spectrum anthelmintic oxantel has a high efficacy on Trichuris spp. Despite this knowledge, the molecular target(s) of oxantel within Trichuris is still unknown. In the distantly related pig roundworm, Ascaris suum, oxantel has a small, but significant effect on the recombinant homomeric Nicotine-sensitive ionotropic acetylcholine receptor (N-AChR) made up of five ACR-16 subunits. Therefore, we hypothesized that in whipworms, a putative homolog of an ACR-16 subunit, can form a functional oxantel-sensitive receptor. Using the pig whipworm T. suis as a model, we identified and cloned a novel ACR-16-like subunit and successfully expressed the corresponding homomeric channel in Xenopus laevis oocytes. Electrophysiological experiments revealed this receptor to have distinctive pharmacological properties with oxantel acting as a full agonist, hence we refer to the receptor as an O-AChR subtype. Pyrantel activated this novel O-AChR subtype moderately, whereas classic nicotinic agonists surprisingly resulted in only minor responses. We observed that the expression of the ACR-16-like subunit in the free-living nematode Caenorhabditis elegans conferred an increased sensitivity to oxantel of recombinant worms. We demonstrated that the novel Tsu-ACR-16-like receptor is indeed a target for oxantel, although other receptors may be involved. These finding brings new insight into the understanding of the high sensitivity of whipworms to oxantel, and highlights the importance of the discovery of additional distinct receptor subunit types within Trichuris that can be used as screening tools to evaluate the effect of new synthetic or natural anthelmintic compounds.

The human whipworm, Trichuris trichiura, is an intestinal parasitic nematode infecting approximately 289.6 million people globally, primarily children living in developing countries. Chronic T. trichiura infection may cause dysentery, growth stunting and decreased cognitive performance. Whipworm infections are notoriously difficult to control with most available anthelmintics, including those commonly used in mass drug administration programs. Recent randomised controlled trials with whipworm-infected humans, have reported superior efficacies of oxantel, a classic, narrow-spectrum anthelmintic, developed for the treatment of Trichuris infections. Despite this knowledge, the molecular target(s) of oxantel within the whipworm has not been identified. In this study, we used the whipworm from pigs as a model and identified a receptor, which was explored using the Xenopus oocyte expression system. We demonstrated that this receptor is highly responsive to oxantel, and therefore a major target of oxantel within Trichuris. In addition, we discovered that this receptor-type is distinctive and only present in the ancient group of parasitic nematodes, Clade I, which also includes the important zoonotic parasite Trichinella. Our findings, explain the specific mode of action of oxantel and open the way for additional characterization of similar receptor subtypes in other medically or veterinary important parasitic nematodes of Clade I.

Field evaluation of the efficacy and the safety of a combination of oxantel/pyrantel/praziquantel in the treatment of naturally acquired gastrointestinal nematode and/or cestode infestations in dogs in Europe

In five multicentre field trials, the efficacy and safety of a combination of oxantel/pyrantel/praziquantel (Dolpac), Vetoquinol SA) in the treatment of naturally acquired gastrointestinal nematode and/or cestode infestation in dogs was evaluated in northern and southern Europe. Forty-eight investigators from France, Belgium, Germany, Italy and Spain enrolled 329 dogs to be treated with the tested combination; 235 of these dogs complied with the inclusion criteria of the protocol and had a tested helminth identified on Day 0. A pooled analysis was performed on each of the following helminth species: Toxocara canis, Ancylostoma caninum, Toxascaris leonina, Trichuris vulpis, Uncinaria stenocephala, Taenia spp. and Dipylidium caninum, which were isolated on Day 0. The main efficacy criterion was the egg per gram (epg) percent reduction of the nematodes and the absence of proglottids and or eggs for the cestodes. After treatment, dogs were examined on Day 7, Day 14 and Day 21. The efficacy of the combination against Toxocara canis was 99.1%, 98.8% and 98.9% on Day 7, Day 14 and Day 21, respectively. At the same occasions the efficacy was, respectively, 99.2%, 99.2% and 99.3% against Ancylostoma caninum, 97.3%, 97.2% and 98.4% against Trichuris vulpis, 98.4%, 98.8% and 98.8% against Uncinaria stenocephala, 98.9%, 99.5% and 99.9% against Toxascaris leonina, 97.1%, 100% and 100% against Dipylidium caninum and 100% against Taenia spp.

Immuno-epidemiology of Ascaris lumbricoides infection in a high transmission community: antibody responses and their impact on current and future infection intensity

The role of the humoral immune system in human infection with Ascaris lumbricoides remains unclear. This study documents an epidemiological investigation in a highly endemic community in Vietnam, whereby serum antibody levels were assessed before treatment and after a 6-month reinfection period. These data were examined by correlation with infection status using an age-structured approach in an attempt to help shed light on the role of the humoral immune response. The first part of this study characterized levels of all serum antibody isotypes from the community in response to antigens of both adult and larval A. lumbricoides. Data were assessed in terms of their relation to host age and infection intensity with the aim to provide a broadly detailed account of immune responses to the parasite. In the second part, antibody responses to both life-stages of A. lumbricoides in serum samples collected before anthelmintic chemotherapy were analysed in relation to intensity of re-infection with the parasite 6 months following treatment. The results suggest that antibody responses may not confer protection from current infection or re-infection with A. lumbricoides and may not serve as reliable indicators of future infection intensity. Our results thereby lend support to the theory that immunity to A. lumbricoides may not be based on the humoral immune system.

Mutation of the feh-1 gene, the Caenorhabditis elegans orthologue of mammalian Fe65, decreases the expression of two acetylcholinesterase genes

The molecular adaptor Fe65 is one of the cytosolic ligands of the Alzheimer's beta-amyloid precursor protein (APP), and this complex is believed to play important roles in mammalian cells. Upon cleavage of APP by specific processing activities, the complex between Fe65 and the APP intracellular domain (AICD) translocates to the nucleus. Experimental evidence suggests that the Fe65-AICD complex regulates gene transcription. In Caenorhabditis elegans the orthologue of the Fe65 gene, feh-1, regulates pharyngeal activity. In fact, the rate of pharyngeal contraction is increased following transient or stable suppression of the feh-1 gene expression. Here we show that the increased contraction rate of the pharynx in feh-1 mutant worms is associated to decreased acetylcholinesterase activity. The decreased activity is accompanied by reduced expression of ace-1 and ace-2 transcripts, coding for the two major acetylcholinesterase activities in the nematode. These results indicate a target of the regulatory mechanisms based on the Fe65-APP complex that could be relevant for the pathogenesis of Alzheimer's disease.

Oxantel is an N-type (methyridine and nicotine) agonist not an L-type (levamisole and pyrantel) agonist: classification of cholinergic anthelmintics in Ascaris

Three pharmacological subtypes of cholinergic receptors have been distinguished in Ascaris suum using a muscle contraction assay and classical pharmacological techniques. The receptor subtypes are: a B-subtype (sensitive to bephenium); an L-subtype (sensitive to levamisole and pyrantel); and an N-subtype (sensitive to nicotine and methyridine). Oxantel is a cholinergic anthelmintic that was first introduced for the treatment of whipworm, Trichuris, infections in children. Here, we compare the subtype selectivity of oxantel with thenium and other cholinergic anthelmintics. We used the A. suum assay to derive pA(2) values for the agonists: oxantel, thenium, bephenium, levamisole, pyrantel, nicotine and methyridine with the antagonists: paraherquamide, 2-desoxyparaherquamide and methyllycaconitine. pA(2) values, rather than pK(B) values, were determined for all agonists when it was found that Schild slopes for some agonists were significantly less than 1.0. The pA(2) of oxantel was 6.58+/-0.25 for paraherquamide; 5.39+/-0.28 for 2-desoxyparaherquamide; 7.01+/-0.19 for methyllycaconitine. Comparison of pA(2) values using cluster analysis showed that oxantel was grouped with nicotine and methyridine, the N-subtype agonists. Thenium had pA(2)s of 7.84+/-0.41 for paraherquamide; 5.52+/-0.50 for 2-desoxyparaherquamide; 6.33+/-0.19 for methyllycaconitine. Cluster analysis placed thenium between the L-subtype agonists and the B-subtype agonist. The therapeutic significance of classification of cholinergic anthelmintics is discussed. Combination of oxantel and pyrantel would have therapeutic advantages, covering N- and L-subtypes, and so increasing spectrum of action and reducing the potential for development of resistance. Our results predict that oxantel may remain effective in some nematode isolates that have become levamisole- and pyrantel-resistant.

Evaluation of the efficacy of pyrantel-oxantel for the treatment of soil-transmitted nematode infections

A randomized controlled trial comparing the efficacy of pyrantel-oxantel (10 mg/kg) with mebendazole (500 mg) was performed on 1329 schoolchildren aged 6-9 years on Pemba Island in September-October 2000 to evaluate alternative single-dose drugs for regular treatment of intestinal nematode infections. Both mebendazole and pyrantel-oxantel were very effective in eliminating Ascaris lumbricoides infection, inducing cure rates of more than 96% and reducing the mean egg counts by more than 95%. Both drugs had a moderate efficacy against Trichuris trichiura infection, but pyrantel-oxantel had a higher cure rate (31.5% vs. 23.3%, P < 0.01), though the reductions in egg counts did not differ significantly and were more than 80%. Pyrantel-oxantel and mebendazole had a similar, poor efficacy in curing hookworm infections and had a moderate effect in reducing the egg counts by 67% and 68%, respectively. Pyrantel-oxantel (10 mg/kg) offers a valuable alternative to mebendazole as a single-dose treatment for the control of intestinal nematode infections in children in endemic areas of sub-Saharan Africa, due to its comparable efficacy, its low cost and its suitability for use in young children.

Anthelmintic actions on homomer-forming nicotinic acetylcholine receptor subunits: chicken alpha7 and ACR-16 from the nematode Caenorhabditis elegans

Two homomer-forming nicotinic acetylcholine receptor subunits with 47% identity in their amino acid sequences were employed to compare the actions of cholinergic anthelmintics and ivermectin on expressed vertebrate and nematode nicotinic receptors of known molecular composition. Voltage-clamp electrophysiology was used to study recombinant nicotinic receptors expressed in Xenopus laevis oocytes following nuclear injection of cDNA encoding either chicken alpha7 or Caenorhabditis elegans ACR-16 (Ce21) subunits. Butamisole, morantel and metyridine were without agonist actions on either alpha7 or ACR-16 nicotinic receptors in the range 10nM-1mM. However, butamisole (pIC(50)=4.9 for both alpha7 and ACR-16) and morantel (pIC(50)=5.6 for alpha7 and 5.7 for ACR-16) antagonized responses of both alpha7 and ACR-16 receptors to acetylcholine. Metyridine (1mM) did not affect responses to acetylcholine of either receptor. Oxantel was without agonist actions on ACR-16, but was an acetylcholine antagonist (pIC(50)=5.4). In contrast, it was found to have low efficacy agonist action (pEC(50)=4.4) on alpha7 at concentrations in the range 10-300microM. In agreement with a previous study, ivermectin (30microM), an agonist of L-glutamate-gated chloride channels, enhanced the amplitude of responses to acetylcholine of alpha7 nicotinic receptors. However, this same concentration of ivermectin (30microM) did not potentiate the acetylcholine-induced responses of ACR-16, but rather resulted in a slight attenuation. We conclude that oxantel and ivermectin have identified new pharmacological differences between the chicken alpha7 nicotinic receptor and its C. elegans homologue ACR-16.

Fumarate metabolism and the microaerophily of Campylobacter species

(1) The role of fumarate metabolism in the microaerophily of the Campylobacter genus and the effects of therapeutic agents against it were investigated. (2) NMR spectroscopy was employed to determine the properties of Campylobacter fumarase (Fum) and fumarate reductase (Frd). Radiotracer analysis was used to determine the production of carbon dioxide by Campylobacter cells. Standard microbiological techniques were used to measure the effects of environmental conditions and inhibitors on bacterial growth. (3) All Campylobacter species tested showed both Fum and Frd activities. Frd activity was observed with or without the addition of an exogenous electron donor in the particulate fractions obtained from lysates. Fumarate was oxidized to carbon dioxide via the acetyl-CoA cleavage pathway. The genes encoding proteins involved in fumarate metabolism were identified in the Campylobacter jejuni genome. Cells grew better in atmospheres with 5 and 10% oxygen levels. Fum activity was the same in cultures grown under different oxygen tensions and did not vary with the age of cultures. Frd activity was higher in cultures which grew at faster rates and decreased with the age of cultures. Four Frd inhibitors showed bactericidal effects against Campylobacter spp. with different potencies. The relative strengths of inhibition of the compounds followed the same order as the bactericidal effects. (4) The results suggested that Frd and Fum are constitutive and play a fundamental role in these microaerophiles which show characteristics of anaerobic metabolism, and that the Frd inhibitors tested would not be of therapeutic use.

The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs

The pharmacokinetic disposition of pyrantel after intravenous (i.v.) and oral (p.o.) administration as the citrate and p.o. administration as the pamoate salt was determined in pigs. Following i.v. administration pyrantel was quickly cleared from the bloodstream, exhibiting a terminal half-life of 1.75 +/- 0.19 h and a residence time (MRT) of 2.54 +/- 0.27 h. After p.o. administration as the citrate salt, the absorption time (MAT) of pyrantel was 2.38 +/- 0.25 h and although significant quantities of pyrantel were absorbed (mean bioavailability of 41%) the rapid clearance resulted in a MRT of only 4.92 +/- 0.36 h. By comparison, the significantly extended MAT of the less soluble pamoate salt resulted in reduced circulating concentrations and a significantly lower mean bioavailability of 16%. The poor efficacy of pyrantel citrate against nematodes inhabiting the large intestine of pigs is therefore suggested to result from insufficient quantities of drug passaging to the site of infection. When tested against pyrantel-resistant adult Oesophagostomum dentatum the mean efficacy of pyrantel citrate was only 23%, whereas the efficacy of the lesser absorbed pyrantel pamoate was 75%. These results indicate that for maximum activity pyrantel should be administered to pigs as the pamoate salt.

In vitro characterization of anthelmintic susceptibility of field isolates of the pig nodular worm Oesophagostomum spp., susceptible or resistant to various anthelmintics

A larval development assay (LDA) and an egg hatch paralysis assay (EHPA) were used to measure the sensitivity to anthelmintics of eggs and larvae of nodular worms (Oesophagostomum spp.) in pigs. The tests were carried out using in vivo defined resistant and susceptible isolates of Oesophagostomum dentatum, O. quadrispinulatum and Oesophagostomum spp. For measurement of pyrantel/morantel and levamisole sensitivity the LDA was found able to distinguish between susceptible or resistant isolates of Oesophagostomum. The EHPA was able to detect levamisole resistance, but the test failed to show differences in response to pyrantel between pyrantel susceptible and resistant lines. The possible routine application of LDA and EHPA in the diagnosis of anthelmintic resistance in Oesophagostomum spp. is discussed.

Fumarate reductase: a target for therapeutic intervention against Helicobacter pylori

The potential of fumarate reductase as a therapeutic target against the human pathogen Helicobacter pylori was investigated by studying the cytotoxicity of morantel, oxantel, and thiabendazole, known to inhibit the enzyme in parasitic worms. Nuclear magnetic resonance spectroscopy was employed to investigate the effects of the inhibitors on the fumarate reductase activity of laboratory-adapted and wild-type bacterial strains. Production of succinate from fumarate in H. pylori cells was inhibited by morantel, oxantel, and thiabendazole. Cell growth and viability techniques were used to examine the bacteriostatic and bactericidal effects of the three anthelmintics. Each of the antiparasites arrested growth and produced cell death in liquid cultures, although the minimal inhibitory and bactericidal concentrations of these compounds are such that they would not be of therapeutic use. The strength of the effects as measured by minimal inhibitory and bactericidal concentrations was oxantel > thiabendazole > morantel. The findings suggested that fumarate reductase is an essential component of the metabolism of H. pylori and as such constitutes a possible target for therapeutic intervention in the treatment of the bacterium.

Oxantel-activated single channel currents in the muscle membrane of Ascaris suum

The patch clamp technique was used to investigate the action of the anthelmintic drug, oxantel, on nicotinic acetylcholine receptor (nAChR) currents recorded from vesicles of the somatic muscle cells of the nematode parasite Ascaris suum. The amplitudes of the currents were analysed at different membrane potentials to determine the single channel conductance. Also the open and closed durations were measured to determine the kinetic properties of the activated channel. Oxantel activated single nAChR currents throughout a concentration range 10-100 microM, these currents were not observed with oxantel-free pipette solutions. The mean open time of the activated channels at a membrane potential of -75 mV and a concentration of 10 microM was 1.34 ms. At higher concentrations the open times were shorter and voltage sensitive, decreasing in duration on hyperpolarization, thus suggesting open channel block. The kinetics were analysed using a simple channel block model. The forward block rate, K + B, increased with increasing oxantel concentration but showed little increase as the membrane was hyperpolarized. K + B was 2.41 x 10(7) M-1 s-1 at -50 mV and 2.64 x 10(7) M-1 s-1 at -100 mV. The unblocking rate constant, K-B, did exhibit voltage sensitivity being 443.6 s-1 at -50 mV and 86.8 s-1 at -100 mV. Thus the blocking dissociation constant KB (= K-B/K + B) was 18.5 microM at -50 mV and 3.3 microM at -100 mV. The simple channel block scheme was found to be insufficient to explain fully the observations made; reasons for this are discussed.

Evaluation of the efficacy and safety of two formulations of pyrantel pamoate in cats

The efficacy of paste and granule formulations of pyrantel pamoate against concurrent infections of Toxocara cati and Ancylostoma tubaeforme in cats was examined in a controlled trial. Three groups of 8 cats received either no medication (controls) or pyrantel pamoate in paste or granule formulations at a dosage of 20 mg/kg of body weight. After administration of the paste formulation, fecal egg counts of A tubaeforme and T cati were decreased by 98.6 and 96.4%, respectively, and 100% of hookworms and 93.5% of ascarids were removed from the intestine. After administration of the granule formulation, fecal egg counts of A tubaeforme and T cati were decreased by 99.4 and 78.2%, respectively, and 100% of adult hookworms and 88.9% of ascarids were removed. All reductions of egg counts and worm numbers were significant (P less than 0.01). The clinical safety of pyrantel pamoate was evaluated in 4- to 6-week-old kittens. Three groups of 10 kittens received either no medication (controls) or pyrantel pamoate in paste or granule formulations at the rate of 100 mg/kg for 3 consecutive days. Adverse effects were not observed in young kittens following administration of the high dose of pyrantel pamoate.

Evaluation of pyrantel-tartrate abbreviated Ascaris suum infections for the development of resistance in young pigs against migrating larvae

Crossbred young pigs were used to test whether abbreviated infections with eggs of Ascaris suum can stimulate the acquisition of resistance to challenge. Weanling pigs from an Ascaris-free colony were kept free of A. suum until they were divided into groups at the age of 7-8 weeks. The experimental animals received pyrantel tartrate during the period when they were being exposed to increasing numbers of infective A. suum eggs and challenged 10 days after the last infective dose. Liver milk-spot counts and larval recoveries from the lungs indicated that the strongest resistance was acquired by the animals that received the drug continuously for 6 weeks while being exposed to six weekly infective egg doses. The data do not suggest any drug-related suppression of the resistance response to A. suum infection.

Field efficacy of ivermectin, fenbendazole and pyrantel embonate paste anthelmintics in horses

Three anthelmintic pastes were compared in terms of their ability to suppress the output of parasite eggs in the faeces of 108 grazing horses at four sites in Britain; the horses were treated once with either ivermectin, fenbendazole or pyrantel. At each site, the horses grazed together throughout the trials which took place during the summers of 1985 and 1986. The median periods before parasite eggs reappeared in faeces were 70 days for ivermectin, 14 days for fenbendazole and 39 days for pyrantel embonate. Geometric mean faecal egg counts in the groups treated with ivermectin and pyrantel were significantly less (P less than 0.05) than in the fenbendazole group on days 21, 28, 35 and 42 after treatment. On days 49, 56, 63 and 70 the mean egg counts in the ivermectin group were significantly lower (P less than 0.05) than those in either of the other groups. The results indicated that in order to ensure minimal contamination of pastures, grazing horses treated with ivermectin paste would have required a second treatment approximately 10 weeks after the first, and to achieve similar control with fenbendazole or pyrantel embonate, a second treatment would have been required after approximately two weeks and six weeks, respectively.

[Experience with the use of nemocide (pyrantel pamoate) in nematodiases]

The clinical efficacy of and tolerance to the nemocide pyranthel pamoate produced by "IPCA" (India) and applied to nematodiasis treatment have been investigated. A high efficacy of the drug (94.4-100%) for ascariasis, enterobiasis and ancylostomiasis treatment has been established. The drug is well tolerated by adults and induces slight short-term alterations of hepatic functional activity in 5-10-year-old children.

Response of adult Necator americanus to some known anthelminthics in hamsters

Adult Necator americanus infection in laboratory hamsters (the hamster-hookworm model) was examined as an anthelminthic screening system. Three reference anthelminthics--pyrantel (PYTL), mebendazole (MBZ) and ivermectin (IVRN)--were used to assess the sensitivity of adult N. americanus and also to investigate the value of the hamster-hookworm model for predicting clinical results. Serial drug dosages were used, and the ED50 was determined from the resulting cure rates. In addition, percentage worm reductions were calculated by reference to the worm burdens in control groups. The results showed that the hamster-hookworm model was able to differentiate anthelminthics on their efficacy. Absolute activity (100% worm reduction) followed treatment with 8 mg kg-1 MBZ, 38-40 mg kg-1 PYTL and 18 mg kg-1 IVRN. Based on ED50 data of PYTL and MBZ, adult N. americanus appeared to be two to five times more sensitive than pre-adult stages. However, with IVRN the reverse appeared true. MBZ appeared to be most active and PYTL least active in terms of curing infected animals, but there were no obvious differences between the rates of worm reductions following single or multiple doses of anthelminthics. It is considered that the hamster-hookworm model will prove of value in identifying and characterizing possible new anthelminthics.

Determination of the efficacy of pyrantel pamoate at the therapeutic dose rate against the tapeworm Anoplocephala perfoliata in equids using a modification of the critical test method

A total of 59 equids (54 horses and five Shetland ponies) were treated with pyrantel pamoate once, at the dose rate of approximately 6.6 mg base kg-1, during the period November 1985-January 1988. The drug was administered as a paste formulation (51 equids) intraorally or as a suspension formulation by stomach tube (eight equids). The purpose of treatment was to evaluate the activity of pyrantel pamoate (at the therapeutic dose rate) for removal of the tapeworm, Anoplocephala perfoliata, by a modified (24-h) critical test. The presence or absence of tapeworms was not determined for the equids before treatment. Twenty-three (39%) of the 59 treated equids were found to be infected with A. perfoliata (from one to 180 specimens per infected equid) at necropsy. Removals varied from 67 to 100% (average 88%) for the 18 infected equids treated with the paste formulation. For the five infected equids treated with the suspension, removals were 58-100% (average 75%). The combined average removal of A. perfoliata for both formulations was 87%. Two abnormal (triradiate) specimens of A. perfoliata were recovered; one from each of two different equids.

Effect of fenbendazole and pyrantel tartrate on the induction of protective immunity in pigs naturally or experimentally infected with Ascaris suum

An experiment was conducted with 96 weanling pigs (avg initial wt 18.5 kg) divided into six treatment with two replicates of eight pigs each. Pigs in Treatments 1, 2 and 3 were penned in outside pens with dirt lots that previously were contaminated with A. suum ova to induce a natural ascaris infection. Pigs in Treatments 4, 5 and 6 were penned in an open-front building with solid concrete floors and were experimentally infected with 2,000 embryonated A. suum. ova on d 1, 15 and 29 of the experiment. Pigs in Treatments 1 and 4 were medicated with fenbendazole (FBZ, 3 mg/[kg BW.d]) for three consecutive days during three consecutive time periods. Pigs in Treatments 2 and 5 were medicated with pyrantel tartrate (PT, 106 mg/kg feed) for 28 d. Pigs in Treatments 3 and 6 served as infected, unmedicated controls. All pigs were challenged with 100 A. suum eggs 7 d after termination of the final FBZ treatment. All pigs were killed 66 d after challenge and worms were recovered. Fenbendazole treatment resulted in greater (P less than .07) average daily gain than PT treatment in pigs penned outside. Among inside pigs, FBZ treatment resulted in better (P less than .02) feed utilization than in controls. The FBZ and PT treatments reduced (P less than .03) the total number of A. suum, the length and weight of female ascarids and the length of male ascarids compared with controls. A natural continual infection with A. suum was less effective than experimental infection in inducing protective immunity in pigs.

Periodic deworming with pyrantel in an industrial township

Between June 1986 and September 1987 a population of 100 families was dewormed every 3 months (quarter) by using a single dose of pyrantel. Stool samples were examined by Kato's thick smear method; height (m), weight (kg), hemoglobin concentration (g/dl) and clinical morbidity were recorded before each deworming treatment. Clinical morbidity was recorded in another 100 control families who did not receive anthelmlntics. There were 477 and 490 individuals in the study and the control families respectively. In the study group the prevalence of roundworm was reduced from 10.3% to to 0% and that of hookworm infection was reduced from 2.9% to 0% after 2 quarters. At the end of the 4th quarter the mean hemoglobin rose by 0.1 g/dl (P less than 0.01) and the mean BMI increased by 0.37 (P less than 0.01). There was a significant reduction in the clinical morbidity in the study group compared with the control group (P less than 0.05). There were no side effects reported to pyrantel treatment. Thus quarterly treatment with pyrantel was found to be effective in keeping roundworm and hookworm prevalence at 0% in an industrial township.

A collaborative study: high-pressure liquid chromatographic determination of carbadox and pyrantel tartrate in animal feeds

Carbadox (CBX), an antibacterial agent, and pyrantel tartrate (PT), an anthelmintic, are formulated either separately or together in swine feeds. The official Association of Official Analytical Chemists (AOAC) spectrophotometric methods for both drugs are long, nonspecific, and require standard addition techniques. Results by this technique are positively biased. A simple, direct, specific, high-pressure liquid chromatographic (HPLC) method to determine either one or both drugs simultaneously with apparent accuracy and precision is developed. Drugs are released from feed matrices by water, extracted with dimethylformamide (DMF), cleaned up on alumina, and quantitated by direct comparison to standards using a Whatman Partisil 10 ODS-3 column and a mobile solvent containing 23.5 +/- 1.5% DMF in phosphate buffer (pH 2.0). Fourteen laboratories participated in a collaborative study of this method for determination of CBX and PT in animal feeds.

High-performance liquid chromatographic determination of oxantel and pyrantel pamoate

A method is described for the determination of oxantel and pyrantel pamoate in proprietary broad spectrum anthelmintic tablets. Quantitation is performed by using an octyl Spherisorb column with a mobile phase consisting of acetonitrile and water modified with butylamine. Carbaryl-(1-naphthyl methylcarbamate) is used as internal standard.

An investigation of hookworm infection and reinfection following mass anthelmintic treatment in the south Indian fishing community of Vairavankuppam

Hookworm infections, as assessed by counting worms expelled following anthelmintic treatment and by egg output, were found to be of low prevalence and intensity in a South Indian fishing community. The initial overall prevalence of infection in the community was 43%, and the average burden was estimated at 2.2 hookworms per person. The age profiles of prevalence and intensity differed between males and females, with the latter harbouring significantly higher levels of infection. Children of both sexes under 10 years of age rarely harboured hookworms. Treatment with pyrantel pamoate was estimated to be 91% effective in clearing hookworm infections. Egg counts made on stools collected during an 11-month period of reinfection indicated that female patients became reinfected soon after treatment, while little hookworm egg excretion was observed in males during the observation period following treatment. Females acquired a significantly higher number of worms during the reinfection period compared with males, although the average burden in females reached only 28% of the initial, pre-treatment level. The hookworm population consisted of predominantly Necator americanus, and less than 10% of Ancylostoma duodenale. The parasites were highly aggregated within the host population with 10% of the community harbouring over 65% of the total hookworms. Low values of the negative binomial aggregation parameter, k, (indicating extreme over-dispersion) were recorded in groups stratified by age and sex. Highly significant positive correlations were observed between the initial (pre-treatment) and reinfection worm burdens of female (but not of male) patients. It is suggested that occupational practices related to walking through areas contaminated with hookworm larvae play an important role in generating the observed patterns of infection within this community.

The importance of host age and sex to patterns of reinfection with Ascaris lumbricoides following mass anthelmintic treatment in a South Indian fishing community

Analysis of egg and worm counts of Ascaris recorded at various intervals following a mass anthelmintic treatment programme in a South Indian fishing community is presented. Three indices of infection in the community are compared, namely the prevalence and intensity of egg output (at 2, 6 and 11 months following treatment) and the number of worms expelled following an 11 month period of reinfection. Detailed examination of these measurements revealed significant associations with patient sex and age. The age-prevalence profile of Ascaris infection changed little over time (except immediately following treatment) with the peak prevalence found in the 5-9 year age group. Although 85% of both males and females harboured Ascaris initially, the prevalence following 11 months reinfection was decreased, due to a significantly lower proportion of males being reinfected. By the 11th month of reinfection, the age-intensity profiles of egg output were similar to those observed at initial treatment in the older age groups (10 years and above) and in male children (less than 10 years). However, a dramatic increase in the egg output of female children, greatly exceeding the initial mean, was observed within a 6 month period of reinfection. The intensity of egg output did not accurately reflect the abundance of Ascaris recovered via drug-induced expulsion following an 11 month period of reinfection. Although the egg output attained preintervention levels, the average worm intensity reached only half the initial value. The trends in the sex- and age-intensity profiles were consistent at the two sampling dates and showed similar patterns to the egg output curves. The relevance of the results to helminth control and the monitoring of reinfection is discussed.

Efficacy of four anthelmintics against benzimidazole-resistant cyathostomes of horses

In order to confirm benzimidazole resistance as recommended at a workshop of the Commission of the European Communities the isolate 'E' of cyathostome strongyles originating from a stud where benzimidazole resistance had been demonstrated by egg hatch tests and by egg count reduction tests was investigated in two series of critical tests. Each of 11 foals reared strongyle-free was infected with 130,000 third stage cyathostome larvae. One animal remained untreated, two pairs of foals were treated with paste formulations of the (pro)benzimidazoles cambendazole (20 mg/kg bodyweight) or febantel (6 mg/kg bodyweight) and two groups of three foals were given pastes containing the non-benzimidazole drugs pyrantel pamoate (19 mg/kg bodyweight) or ivermectin (0.2 mg/kg bodyweight) either at 101 days (trial 1) or at 59 to 62 days (trial 2) after infection. Strongyles were counted in faecal samples collected daily between treatment and post mortem examination five or seven days later and worm burdens were counted in the intestinal contents and mucosal digests. Nine species of the cyathostome subfamily were found in the infected foals. The numbers of luminal stages were reduced by only 3.1 and 20.2 (mean 7.9) per cent by cambendazole and by 13.6 and 32.8 (mean 21.3) per cent by febantel in the individual animals. However, pyrantel pamoate (93.6 to 98.2, mean 96.3 per cent reduction) and ivermectin (100 per cent reduction) were highly effective. These trials provide the first report of benzimidazole resistant Cylicostephanus poculatus anywhere in the world and demonstrate (pro)benzimidazole resistance in seven other species for the first time in Europe.

Control of Toxocara canis in puppies: a comparison of screening techniques and evaluation of a dosing programme

Conventional chemoprophylaxis of canine toxocariasis is based upon the treatment of young puppies. It is proposed that physiological considerations and the complexity of the host-parasite relationship in the case of Toxocara canis demand that anthelmintic evaluation should properly be conducted in such animals rather than in adolescent or adult dogs. A screening model using the critical trial technique in early weaned pups gave variable results even with compounds known to be of high efficacy in older dogs. Circumstantial evidence suggested that this inconsistency may be related to the rate of passage of ingesta through such young animals. More satisfactory results were obtained by pairing unweaned naturally infected puppies by weight and sex and treating one of each pair with the test compound. Natural in utero and transmammary infection was found to give fairly consistent worm-burdens within each litter and a good indication of efficacy could therefore be estimated by comparing post mortem worm-counts. On this basis, the apparent efficacies of pyrantel pamoate (5 mg kg-1) and piperazine (100 mg kg-1) were found to be 83.5 and 82.5%, respectively. This method was extended to evaluate a prophylactic programme in which anthelmintic therapy was given to pups when aged 10, 20 and 30 days. Intestinal T. canis populations were reduced, at 35 days of age, by between 94.2% and 98.0%. This programme increased overall weight gains between 10 and 30 days of age by 18% (P less than 0.05) although there was great variation between litters. The biggest response was observed in male pups between 20 and 30 days old.

The epidemiology and control of intestinal helminths in the Pulicat Lake region of Southern India. I. Study design and pre- and post-treatment observations on Ascaris lumbricoides infection

The study design of a project to investigate the epidemiology, population dynamics and control of intestinal nematode infections in fishing village communities in Southern India is described. The paper focuses on Ascaris lumbricoides infection and describes changes in prevalence and intensity (worm burdens) with host age, the aggregated frequency distributions of parasite numbers per person, a density-dependent relationship between parasite fecundity and worm burden and rates of reinfection following chemotherapeutic treatment. The age-intensity of infection profile is convex in form, where maximum worm burdens are attained in children in the age range five to nine years. On the basis of juvenile to adult worm ratioos, the life expectancy of Ascaris in man is estimated to be of the order of one year. Rates of reacquisition of worms after chemotherapy are shown to be dependent on host age. Wormy individuals with heavy infections are shown to be predisposed to this state such that they reacquire heavier than average worm burdens following treatment.

[Experiences with a paste used as an anthelmintic in cats]

When the anthelmintic Banminth 'Katze' was administered twice to ninety-two cats, the owners were questioned on the method by which the animals took this paste. Minor, if any, problems were observed in 94.5 per cent of the cats. Major problems occurred in 5.5 per cent of the animals. Significantly more adult than young cats had difficulties in taking the paste.

[Viability of Ascaris lumbricoides ova after human treatment with specific drugs. I--Levamisole and pyrantel pamoate]

Com o objetivo de testar a viabilidade do ciclo biológico, 15 pacientes (masculinos, de quatro a 14 anos) com Ascaris lumbricoides, foram selecionados ao acaso. Após tratamento clássico com sais básicos de levamisole (7 pacientes) e de pamoato de pirantel (8), os ovos retirados das fêmeas expelidas ficaram incubados por 18 dias em de H2SO4 N/10. A seguir foram administrados per os a grupos de 5 camundongos por pacientes. Decorridos 8 dias da infecção, os animais foram sacrificados para pesquisas microscópica de larvas nos fragmentos pulmonares. Dos 75 animais, somente 1, pertencente ao grupo de tratados com levamisole, não apresentou larvas nos fragmentos pulmonares. Concluiu-se que as drogas, nas doses utilizadas, não possuem ação deletéria sobre os ovos de A. lumbricoides, mas promovem a eliminação de material infectivo, com possibilidade de incrementar a poluição onde vivem comunidades sem adequadas condições de saneamento básico.

Epidemiological approach to the control of horse strongyles

An investigation of the spring rise in strongyle egg output of grazing horses on two commercial horse farms in northern USA in 1981 and 1982 revealed two distinct spring and summer rises in faecal egg counts, with peaks in May and August/September. There was a marked rise in the concentration of infective larvae on pasture two to four weeks after the peaks in egg output, so that grazing horses were at serious risk from June onwards and pasture larval counts on one farm did not fall to low levels until June of the following year. The spring and summer rises in faecal egg counts appeared to be seasonal in nature, to be derived largely from worms developing from previously ingested larvae, rather than from newly ingested larvae, and to be unrelated to the date of foaling. An epidemiological approach to strongyle control based on prophylactic treatments in the spring successfully eliminated the spring rise in egg output but was inadequate to control the summer rise or subsequent escalation of pasture infectivity in September. It was, nevertheless, superior to a conventional treatment programme at eight week intervals, using the same drug, pyrantel pamoate. Prophylactic spring/summer treatments proved to be much more effective. Both pyrantel pamoate at four week intervals and ivermectin at eight week intervals kept faecal egg counts at low levels during spring and summer. As few as two ivermectin treatments (11 May, 6 July) resulted in a sixfold reduction in pasture larval counts on 9 November and 3 January for the treated group (8872, 8416 stage three larvae [L3]/kg) compared to the control group (52,824, 50,984 L3/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

A study of the effectiveness of mebendazole and pyrantel pamoate as a combination anthelmintic in Papua New Guinean children

A mixture of 150 mg mebendazole and 30mg pyrantel pamoate was given on 3 consecutive or near-consecutive days to 70 children infected with one or more of Necator americanus, Ascaris lumbricoides, Strongyloides stercoralis, S. fuelleborni-like and Trichuris trichiura. This treatment had an efficacy of 95 per cent for N. americanus infections, 100 per cent for A. lumbricoides, 57 per cent for Strongyloides spp., and 75 per cent for T. trichiura. The results indicate that the treatment given is effective against the infections of N. americanus and A. lumbricoides but is only partially effective for Strongyloides and T. trichiura infections.

Incidence of helminthic infections and comparative study of pyrantel pamoate with levamisole and mebendazole in hospital patients at Barisal, Bangladesh

A study was carried out to find out the incidence of helminthic infections in hospitalized patients at Sher-e-Bangla Medical College, Barisal and to determine the comparative efficacy of pyrantel pamoate, levamisole, and mebendazole. It was observed that 76.2 per cent of total hospitalized patients were infected with intestinal helminths. Polyparasitism (52.6 per cent) was more frequent than single infection (21.8 per cent). Amongst these, 47.5 per cent was suffering from Asearis lumbricoides (AL), 42.5 per cent from Hookworm (H.W) and 65.8 per cent from trichuris trichura (TT). Out of 255 cases examined separately, 40 per cent was suffering from Enterobious vermicularis (EV) infection. The comparative study showed that mebendazole produced egg negative stool in 90.9 per cent of AL, 95.6 per cent of HW and 86.8 per cent of TT after eight days of treatment. On the other hand, pyrantel pamoate cured AL in 93.3 per cent, HW in 78.5 per cent and TT in 34.2 per cent eases. Levamisole cured 75 per cent AL, 4.1 per cent H.W. and 22.2 per cent TT within the same period.

Studies on chemotherapy of parasitic helminths (XVIII). Mechanism of spastically paralyzing action of pyrantel in Angiostrongylus cantonensis

Pyrantel tartrate caused spastic paralysis through stimulating nicotinic cholinoceptors in Angiostrongylus cantonensis.

Successful treatment of Capillaria hepatica infection in an acutely ill adult

A man with massive Capillaria hepatica infection survived after treatment with prednisone, disophenol, and pyrantel tartrate. He remained well during an 8-year follow-up.

Studies on chemotherapy of parasitic helminths (XVII). Effects of pyrantel on the motility of various parasitic helminths and isolated host tissues

Pyrantel tartrate caused spastic paralysis in various parasitic nematodes, but not in cestodes and trematodes.

High pressure liquid chromatographic determination of carbadox and pyrantel tartrate in swine feed and supplements

A rapid yet reliable procedure for the simultaneous extraction and assay of carbadox and pyrantel tartrate is described. The feed is extracted with water-acetonitrile-methanol and cleaned up on a short alumina column. The eluant is separated by high pressure liquid chromatography and the compounds are detected at different wavelengths. The drugs of interest are well resolved in all feeds studied. The procedure has also been applied to a wide range of feeds which contained either one of the drugs or both in combination. No significant interferences were observed. Spiked sample recoveries were 97% for carbadox and 101% for pyrantel tartrate. Ruggedness test coefficients of variation were 2.0% for carbadox and 2.1% for pyrantel tartrate.

[Thin-layer chromatographic determination of pyrantel in cow's milk and blood serum after oral administration of Banminth]

After oral administration of the anthelmintic Banminth to cows the effective agent pyrantel appeared unchanged in blood serum and milk. After a therapeutic dose of 12,1 mg pyrantel tartrate/kg body weight, a maximum level of 8-9 micrograms/l could be found in milk 0-24 h after the application; the highest concentration of 22 micrograms/l in blood serum appeared after 10 h and the half-life time of elimination was ca. 15 h. Pyrantel determination in milk and blood serum was performed by quantitative thin layer chromatography. Positive results could be verified by HPLC.