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PubMed1990

Seasonally inhibited development of cyathostomine nematodes in Shetland ponies in The Netherlands.

Two groups of three yearling Shetland ponies were used in 1988 to study the epidemiological significance of inhibited development of the Cyathostomine nematodes. In Group 1, acquisition of infections was prevented throughout the grazing season whereas in Group 2 strongylid infections were acquired from the beginning of July until the end of September. Worm counts showed that the Cyathostomine nematode populations of Group 1 ponies mainly consisted of adult worms and those of Group 2 ponies of inhibited early third stage larvae (L3). These results indicate that a large proportion of Cyathostomine larvae which establish between the beginning of July and the end of September inhibit their development. The results also suggest that the pool of inhibited larvae which has overwintered in young ponies will be depleted in autumn.

Animals↗
PubMed1990

Phenothiazine in the origin of benzimidazole resistance in population-B equine strongyles.

Clinical trials on a central Kentucky Thoroughbred Farm (B) during 1960-1961 involved nine test treatments of mares, yearlings and weanlings (n = 124), and compared efficacies of phenothiazine (PTZ), piperazine (PPZ), mixtures of PTZ + PPZ and thiabendazole (TBZ) for (1) percent reduction and (2) complete clearance or graded reduction of strongyle egg per gram (epg) counts. Three grades of PTZ (N.F. green, micronized purified and 2-3 microns purified) at the dose rate of 55 mg kg-1 were ineffective in six tests; reduction of strongyle epg count were low grade (26%) and complete clearance was found in only 1 of 32 horses. Piperazine alone at 88 mg base kg-1 was efficacious in two tests; epg counts were effectively reduced (98%), but complete clearance was found in only 2 of 10 horses. Several mixtures of PTZ + PPZ with various dosages of PTZ (27.5-55 mg kg-1) plus PPZ base (88 mg kg-1) were quite effective in six tests, as epg counts were reduced by 96% and complete clearance occurred in 25 of 38 horses. Four trials with TBZ at dose rates between 13 and 44 mg kg-1 in 1961 reduced epg counts by 98%, but cleared only 15 of 36 horses. These data indicated: (1) a large segment of the Farm B small strongyle population was resistant to PTZ at the outset of these observations in 1960; (2) TBZ-resistant individuals were also present in this population when TBZ was first used in 1961. During the ensuing 4-year study (1962-1965) on Farm B mares (n = 15 per year) and yearlings (n = 15-17 per year), biweekly epg and larvae per gram (lpg) counts were carried out to compare the efficacy of three treatment programs: (1) monthly doses of TBZ at 26 mg kg-1; (2) monthly doses of TBZ at 13 mg kg-1; (3) bimonthly doses of a mixture of PTZ + PPZ and carbon disulfide (CS2) at dose rates of 27.5 + 88 and 78 mg kg-1, respectively, or a mixture of PTZ + PPZ + trichlorfon (TCF) at dose rates of 27.5 + 88 + 40 mg kg-1, respectively. Emergence of a TBZ-resistant segment of the small strongyle infections was evaluated by three criteria: (1) annual mean strongyle epg counts; (2) efficacy of individual treatments for epg reductions (%); (3) complete clearance or graded reductions of strongyle epg counts.4+ PTZ-resistant small strongyles. Initial use of TBZ in 1961 produced effective epg reductions, but complete clearance data revealed the presence of TBZ-resistant small strongyles at the outset...

Animals↗
PubMed1991

Identification of thiabendazole-resistant cyathostome species in Louisiana.

A critical trial was performed with five ponies 6-9 months of age and raised on a horse farm with demonstrated benzimidazole-resistant cyathostomes. Eleven species of cyathostomes were recovered, seven of which had resistance to thiabendazole. Degrees of resistance varied among ponies and from species to species. Resistant species were Cyathostomum coronatum, Cyathostomum catinatum, Cylicostephanus minutus, Cylicostephanus calicatus, Cylicostephanus longibursatus, Cylicostephanus goldi and Cylicocylus nassatus. This is the first study identifying resistant cyathostome species in the Gulf Coast region of the USA and, although no new resistant species were found, results differed somewhat from those of other authors in that none of the cyathostome populations that have been studied contain the same complement of resistant species.

Animals↗
PubMed1991

Periparturient rise in faecal nematode egg counts in west African dwarf sheep in southern Ghana in the absence of arrested strongyle larvae.

The nematode egg output of two groups of ewes, a pregnant test group (2-3 years of age) mated between March and April and a non-pregnant control group (5-6 years of age) was followed. The worm burdens acquired by worm-free 'tracer' lambs were also followed on the same pasture from March 1988 to February 1989. There was a significant difference (P less than 0.05) in the magnitude of the egg output in the test group compared with the control group. In the test ewes, an initial rise in egg production occurred 2 weeks after lambing and was maintained for five consecutive months. Necropsy worm counts from the 'tracer' lambs revealed that pasture larval levels were directly related to the levels of rainfall. Adult nematodes (Trichostrongylus colubriformis, Trichostrongylus axei, Haemonchus contortus, Oesophagostomum venulosum and Trichuris ovis), and some Moniezia expansa were present in almost all the lambs throughout the year, with the exception of January and February 1989. The absence of immature larvae in these lambs indicates that arrested development is not a feature of the life cycle of these species in Southern Ghana. The occurrence of a periparturient rise of nematode eggs in West African Dwarf ewes, a year-round breeder, means that susceptible lambs could be open to infection throughout the year. Control should, therefore, be conducted by treating ewes after lambing and restricting the breeding season to particular periods of the year.

Animals↗
PubMed1991

Effect of parasitism with Nematodirus battus on the pharmacokinetics of levamisole, ivermectin and netobimin.

The pharmacokinetics of levamisole, ivermectin and netobimin administered orally and by subcutaneous injection were compared in lambs exposed to a moderate challenge with Nematodirus battus and in parasite naive lambs. There were no significant differences (P greater than 0.05) in the bioavailability of any of the anthelmintics tested between parasitized and non-parasitized animals. Levamisole reduced nematode faecal egg output by more than 99% when administered by either route. Ivermectin was also highly effective (greater than 99%). Orally administered netobimin reduced egg output by more than 98% seven days after administration. However egg output was only reduced by 89% 21 days after administration, suggesting poor activity against the early parasitic stages of N. battus. Netobimin was not effective against N. battus when administered by the subcutaneous route and this was probably because very low plasma concentrations of its active albendazole metabolites were achieved.

Administration, Oral↗
PubMed1991

Effect of treatment with netobimin on milk production of sheep.

In the Basque country lambing takes place during winter, followed by milking until late spring or summer, so it was considered that this would be the most profitable period for deworming, when there was an increased production pressure on ewes with depressed immune status owing to the peri-parturient relaxation of immunity. The drug employed was netobimin, and the trial was carried out in 22 commercial flocks, in each of which ewes were allocated to one of three similar groups. One group was left as a non-treated control (T0), the second was dosed 15 days before parturition (T1), and the remaining group dosed both at 15 days before and 15 days after lambing (T2). Mean total milk production in the T2 group increased by 8.8 and 6.3% in the second and third month post-partum, respectively, compared with that of the controls (T0), while over the standard lactation period of 120 days the T2 group showed a significant (8.9%) increase in production compared with the controls. The T1 group did not significantly differ from T0. The market value of the increase in milk production was calculated to be approximately 700% of the cost of treatment with netobimin.

Animals↗
PubMed1992

The effect of ivermectin treatment against inhibited early third stage, late third stage and fourth stage larvae and adult stages of the cyathostomes in Shetland ponies and spontaneous expulsion of these helminths.

A controlled and critical test on the efficacy of ivermectin against larval and adult stages of the cyathostomes was carried out in six yearling castrated male Shetland ponies. The ponies grazed together as one group from 3 May to 4 October 1990, after which they were housed. Three ponies were treated with ivermectin on 29 October while the others served as controls. The shedding of helminths in the faeces was followed in all ponies until necropsy on 14 November. Comparison of worm counts of both groups before and after necropsy showed no evidence for an effect of ivermectin against inhibited early third stage larvae (EL3) and mucosal late third stage (LL3) and fourth stage larvae (L4). However, a high, but not 100%, efficacy was observed against adults and lumenal L4. A remarkable observation was the high incidence of spontaneous expulsion of L4 and adult populations of some species in two of the untreated ponies.

Animals↗
PubMed1992

The development of naturally acquired cyathostome infection in ponies.

Groups of animals of different ages and experience of previous parasite exposure were allowed to graze a single pasture for 5 weeks in autumn (7 October to 11 November). There was evidence that previous exposure modified cyathostome development, as acquired burdens in foals which had previously grazed were smaller and developed more slowly than those of helminth-naive animals of the same age. The burdens acquired by yearling and adult ponies were of a similar size to those of the previously grazed foals, but the incidence of arrested development was higher in the younger groups of foals and yearlings when compared with adults. Further evidence of an effect of age on cyathostome development was that the level of faecal egg output of the adult ponies was lower than in the groups of young animals.

Age Factors↗
PubMed1996

Non-surgical transplantation of Oesophagostomum dentatum to recipient pigs via rectal intubation.

This experimental was designed to evaluate a new transplantation method, which employs a non-invasive rather than a surgical technique for transplanting Oesophagostomum dentatum worms to recipient pigs. Four groups of pigs were used. Group A (four pigs) served as a donor group, and these pigs were each inoculated with 6000 L3 of O. dentatum. Groups B, C, and D (five pigs each) served as helminth naive recipient pigs. On Day 28 post inoculation, the donor pigs were slaughtered, and the worms recovered by an agar-gel technique. Within 3-4 h after slaughter of the donor animals, a mean of 357 worms (male/female = 1.0) were transferred to each of the sedated recipient pigs via a PVC tube inserted approximately 50 cm up into the rectum and colon descendens. The infection was then monitored by weekly faecal egg counts and by killing the recipient pigs at Week 1 (group B), Week 2 (group C), and Week 3 (group D) post transplantation. The majority of the recovered worms were found in the proximal third of the colon, i.e., the normal predilection site of O. dentatum. The mean worm recovery for groups B and D was 85%, whereas from group C it was only 23%. The faecal egg counts were positive throughout the experiment, although low in group C at the time of slaughter 2 weeks post transplantation. The male/female ratios changed from an initial 1.0 to 1.5 group C, whereas there was little or no change in groups B and D. The reason for the deviating results in group C are obscure. This method is less traumatic to animals when compared with surgical transfer techniques, is rapid to perform, and will allow studies on a larger scale.

Animals↗
PubMed1996

Use of two in vitro methods for the detection of benzimidazole resistance in equine small strongyles (Cyathostoma spp.).

Ten stables were included in a study to evaluate two in vitro methods for the detection of anthelmintic resistance in cyathostomes by comparing a faecal egg count reduction test (FECRT) to a larval development assay (LDA) and an egg hatch assay (EHA). The LDA was used in seven stables and EHA in the last three. On the basis of FECR values, resistance to benzimidazoles was detected in eight of the ten small strongyle populations. Resistance to pyrantel pamoate and ivermectin was not detected. The mean concentrations that inhibited hatching in 50% of the eggs (EC50), using thiabendazole (TBZ) in an EHA, were 1.02 microM in resistant populations and 0.37 microM in susceptible or suspected resistant ones. In the LDA, TBZ concentrations preventing 50% development by first/second stage larvae to the third larval stage (LC50) were 3.8 times lower than EC50 values in resistant worm populations. Mean LC50 for morantel, levamisol, ivermectin monosaccharide and avermectin-B2 in small strongyle populations susceptible to pyrantel and ivermectin was 8.0 microM, 0.99 microM, 15.6 nM and 2.93 nM, respectively. Data on pyrantel and ivermectin resistant populations could not be obtained as no resistant populations were detected. This study concludes that in vitro tests may be useful as a supplement to FECRT for the detection of benzimidazole resistance in cyathostomes, even if reference populations to be used as controls in the assays were not available. It is suggested that EC50 values for TBZ > 0.6 microM in LDA and > 0.5 microM in EHA strongly indicate benzimidazole resistance in equine small strongyles.

Animals↗
PubMed1996

Efficacies of different doses of ivermectin against male, female and L4 Oesophagostomum dentatum in pigs.

Efficacies of ivermectin against larval stages and adult males and females of Oesophagostomum dentatum were investigated in two slaughter assays. In Experiment A, 20 pigs were each infected with 6000 third-stage larvae on Day 0 and Day 24. Pigs were ivermectin treated on Day 28 at dose rates of 0, 75, 150, and 300 micrograms kg-1 bodyweight (bw) and slaughtered 6 days after treatment. In Experiment B, 20 pigs each received 6000 third-stage larvae and were treated 35 days after infection at dose rates of 0, 150, 300 and 600 micrograms kg-1 bw. Pigs were slaughtered 14 days after treatment. In Experiment A, the adult worm burden was reduced by 69.1% at a dose rate of 300 micrograms kg-1 bw and the larval burden was reduced by 68.7 and 90.9% at 150 and 300 micrograms kg-1 bw, respectively. In Experiment B, the adult worm burden was reduced by 88.8, 96.2 and 99.6% at dose rates of 150, 300 and 600 micrograms kg-1 bw, respectively. In the control group of Experiment A, the mean proportion of females among adults worms was 57.6%, but this decreased to 19.7% after ivermectin treatment at 300 micrograms kg-1 bw. In Experiment B, at 300 micrograms kg-1 bw, this proportion was reduced from 46.0% to 0.8%. The fecundity of female worms was reduced at dose rates of 150 and 300 micrograms kg-1 bw in Experiment A, but not in Experiment B. It is concluded that in O. dentatum, ivermectin not only reduces the egg output of female worms, but also is more effective against female than male worms.

Animals↗
PubMed1986

Phosphorylcholine bearing components of some helminthic parasites: localization to parasite lipoproteins.

Extracts of various helminthic parasites were studied to determine the molecular carrier of the hapten phosphorylcholine (Pc). Physicochemical studies showed that the carrier was heterogeneous with regard to apparent molecular weight (70,000-greater than 10(6) daltons). Ultracentrifugal analysis of Ascaris suum and Nippostrongylus brasiliensis showed that Pc was associated with low (LDL), high (HDL) and a heterogeneous group of very high density (VHDL) lipoproteins. The majority of Pc was found in the most dense VHDL (d greater than 1.25 g ml-1). The apparent molecular weight and particle diameter of A. suum HDL was 751,000 daltons and 16.2 nm, respectively. The apparent molecular weights and particle diameters of A. suum VHDL ranged from 469,000 to 677,000 daltons and 13.6 to 15.5 nm, respectively. The electrophoretic mobilities of A. suum LDL and HDL were beta and gamma, respectively. A suum VHDL was electrophoretically heterogeneous. It is probable that Pc is associated with the phospholipid phosphatidylcholine.

Animals↗
PubMed2005

Isolation and characterisation of a beta tubulin isotype 2 gene from two species of cyathostomin.

This study describes the isolation and characterisation of beta tubulin isotype 2 cDNA sequences from two common species of cyathostomin, Cylicocyclus nassatus and Cyathostomum catinatum. The full-length cDNAs for these species were 1709 and 1753 bp in length, respectively, including 1350 bp of sequence inferred to encode 450 amino acids of peptide sequence. They had greatest identity with previously characterised isotype 2 sequences from Trichostrongylus colubriformis, Cooperia oncophora and Haemonchus contortus (96% for C. nassatus and 95% for C. catinatum), and grouped together with these sequences in phylogenetic analysis. Both cyathostomin beta tubulin isotype 2 sequences contained the isotype-specific carboxyl terminal region described previously in other nematode species. Alignment with beta tubulin isotype 1 proteins from other trichostrongyloids, indicated 95 and 94% identity for the isotype 2 sequences of C. nassatus and C. catinatum, respectively. This comparison revealed 14 isotype-specific amino acid substitutions. Also, 2605 bp of beta tubulin isotype 2 genomic DNA sequence were isolated from C. nassatus. Comparison with the previously published isotype 1 gene of C. nassatus indicated differences in genomic organisation between the two isotypes. Reverse transcriptase (RT)-polymerase chain reaction analysis revealed constitutive temporal expression of beta tubulin isotype 1, whilst isotype 2 appeared to be developmentally expressed, with transcripts detected only in RNA derived from adult parasites.

Animals↗
PubMed2005

Effect of moxidectin selection on the genetic variation within Cylicocyclus nassatus based on amplified fragment length polymorphism (AFLP).

Cyathostomins are among the most important intestinal nematodes of horses, yet, the literature on the molecular genetics of these worms is scarce. In this study, the technique of amplified fragment length polymorphism (AFLP) was applied to study the genetic diversity as well as to determine the effect of moxidectin selection on the population genetic diversity for Cylicocyclus nassatus, one of the most common cyathostomin species. Genomic DNAs from 30 individual male worms were used from each of two populations: an avermectin-milbemycin (AM)-naive population (Population-S) and a population derived from Population-S following 21 treatments with moxidectin (Population-Mox). Three selective primer pairs were used for each worm, yielding a total of 229 AFLP markers. Calculation of average pair wise Jaccard indices revealed a high degree of genetic variation within both populations using all three primer combinations. In addition, selection by moxidectin during a 3-year period caused a significant decrease in the level of genetic diversity as evidenced by analysis of AFLP markers for two primer combinations but not for the third. A dendrogram of relationships among individuals based on AFLP markers did not show a clear classification of individuals in separate groups. It was concluded that a high degree of genetic intrapopulation variation exists in C. nassatus and that moxidectin selection has a significant effect on the genetic composition of C. nassatus.

Animals↗
PubMed2006

Cloning and characterization of genes encoding alpha and beta subunits of glutamate-gated chloride channel protein in Cylicocyclus nassatus.

The invertebrate glutamate-gated chloride channels (GluCls) are receptor molecules and targets for the avermectin-milbemycin (AM) group of anthelmintics. Mutations in GluCls are associated with ivermectin resistance in the soil dwelling nematode Caenorhabditis elegans and the parasitic nematode Cooperia oncophora. In this study, full-length cDNAs encoding alpha and beta subunits of GluCl were cloned and sequenced in Cylicocyclus nassatus, a common and important cyathostomin nematode parasite of horses. Both genes possess the sequence characteristics typical of GluCls, and phylogenetic analysis confirms that these genes are evolutionarily closely related to GluCls of other nematodes and flies. Complete coding sequences of C. nassatus GluCl-alpha and GluCl-beta were subcloned into pTL1 mammalian expression vector, and proteins were expressed in COS-7 cells. Ivermectin-binding characteristics were determined by incubating COS-7 cell membranes expressing C. nassatus GluCl-alpha and GluCl-beta proteins with [(3)H]ivermectin. In competitive binding experiments, fitting the data to a one site competition model, C. nassatus GluCl-alpha was found to bind [(3)H]ivermectin with a high amount of displaceable binding (IC(50)=208 pM). Compared to the mock-transfected COS-7 cells, the means of [(3)H]ivermectin binding were significantly different for C. nassatus GluCl-alpha and the Haemonchus contortus GluCl (HcGluCla) (p=0.018 and 0.023, respectively) but not for C. nassatus GluCl-beta (p=0.370). This is the first report of orthologs of GluCl genes and in vitro expression of an ivermectin-binding protein in a cyathostomin species. These data suggest the likelihood of a similar mechanism of action of AM drugs in these parasites, and suggest that mechanisms of resistance may also be similar.

Amino Acid Sequence↗