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PubMed1994

Multiple and multigeneric anthelmintic resistance on a sheep farm in Malaysia.

The anthelmintic efficacy of benzimidazoles, levamisole, closantel, ivermectin and moxidectin was evaluated on an institutional farm in Malaysia using faecal egg count reduction tests, controlled slaughter trials and an in vitro egg hatch assay. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles and ivermectin and of Trichostrongylus colubriformis against benzimidazoles and levaminsole on the same farm. Moxidectin was effective against the ivermectin resistant H. contortus.

Animal Husbandry↗
PubMed1994

Relative effect of temperature and moisture on the development of strongyle eggs to infective larvae in bovine pats in Argentina.

To determine the most efficient microclimatic factors in bovine faeces that could explain the rate of development of parasitic nematode species, experimental pats were deposited in three locations (sun, shade and laboratory) in central-west Argentina during summer, autumn and winter seasons. Faecal water content (FWC) and temperature inside the pats were recorded during the duration of the experimental periods. The mean temperature and minimal values of FWC explained 54% of the variability of the rate of development of Haemonchus (third-stage larvae per 100 eggs) and mean maximal temperature and minimal FWC values were the two main factors regulating Cooperia development (R2 = 0.42). Rainfall was the third factor. No microclimatic component explained the development of Ostertagia in our experiments.

Animals↗
PubMed1994

Ivermectin resistant Haemonchus contortus in Louisiana lambs.

Fifteen weaned crossbred (Suffolk x Louisiana Native) lambs were treated with albendazole (10 mg kg-1) to remove existing nematode infections. They were inoculated with Haemonchus contortus infective larvae from a residual population surviving treatment with the oral formulation of ivermectin (0.2 mg kg-1). One group of five lambs remained untreated, another group of five was treated with the injectable formulation of ivermectin (0.2 mg kg-1), and a third group of five was treated with the oral formulation of ivermectin (0.2 mg kg-1). Subsequent to the treatments, there was essentially no difference in mean fecal egg count or mean number of H. contortus recovered at necropsy between the three groups.

Albendazole↗
PubMed1994

Genetic resistance to parasitic disease: particularly of resistance in ruminants to gastrointestinal nematodes.

There is substantial variation among individuals in susceptibility to a wide variety of parasitic diseases and part of this variation in susceptibility is due to genetic factors. The challenge now is to determine the best methods of using the variation to improve our understanding of parasitic infection and to reduce the ravages of parasitic disease. Scientific and commercial applications will depend upon the type of genetic variation. Variation among breeds can be easily exploited by a policy of breed substitution. Variation within a breed can be exploited by selective breeding to improve resistance to infection or to disease, but more work is needed to develop selection indices which are acceptable to livestock breeders. Identifying genes which contribute to the variation in resistance provides a better understanding of the mechanisms of resistance but more work is needed to determine if such genes, alone or in combination, account for a sufficient proportion of the variation in resistance to allow marker assisted selection. A comparison of responses in susceptible and resistant stock provides a powerful tool to distinguish among protective, irrelevant and pathological responses. These themes have been illustrated by three studies of gastrointestinal nematode infections in ruminants.

Animals↗
PubMed1994

Control of haemonchosis in Malaysian goats with closantel.

The therapeutic and prophylactic effects of closantel on natural infections with Haemonchus contortus were studied in goats in Peninsular Malaysia. Closantel was highly effective against H. contortus, either at a subcutaneous (s.c.) injection of 5.0 mg kg-1 body weight (100%), or in an oral drench mixture with mebendazole at a dose of 10.0 mg kg-1 (99.2%), as indicated by faecal egg counts. H. contortus larvae were absent from faecal cultures for 5, 6 and 7 weeks following treatment with s.c. injections of closantel at doses of 2.5 mg kg-1, 5.0 mg kg-1 and 10.0 mg kg-1 respectively, and for 6 weeks after treatment with closantel at 10.0 mg kg-1, given orally. Through its sustained activity, closantel not only prevented reinfection with H. contortus but also caused a dramatic reduction in pasture contamination. The potential utility of closantel in the strategic control of haemonchosis in goats, and as an alternative treatment for benzimidazoles and levamisole resistant H. contortus strains, is discussed.

Administration, Oral↗
PubMed1995

Multiple anthelmintic resistance in Haemonchus contortus on a sheep farm in India.

Multiple resistance to benzimidazoles (fenbendazole, albendazole and mebendazole) in a strain of Haemonchus contortus in sheep was detected on a farm where fenbendazole resistance had already been identified. Following a faecal egg count reduction test, this was confirmed by both critical and controlled anthelmintic tests. Different groups of sheep infected naturally or given an experimental infection with the fenbendazole-resistant strain were treated with the recommended doses of various anthelmintics. Compared to the control group, percentage reductions in faecal egg counts of sheep treated with fenbendazole, albendazole, mebendazole, levamisole and morantel varied between 56% and 81% and worm counts between 71% and 86%. The results indicate the presence of multiple anthelmintic resistance in this strain of H. contortus on this farm. Sheep treated with ivermectin and closantel showed 100% reductions in faecal egg and worm counts, suggesting high efficacy of these drugs against the population of H. contortus on this farm.

Albendazole↗
PubMed1996

In vitro screening of Haemonchus contortus third stage larvae for ivermectin resistance.

The indiscriminate repeated use of ivermectin has resulted in the emergence of ivermectin resistant field strains of Haemonchus contortus in sheep in South Africa. There is a need for a rapid and cost effective in vitro test to detect such strains. Infective H contortus larvae known to be resistant to ivermectin, were incubated in vitro in a diluted concentration of the drug. Subsequently their ability to migrate was compared with that of larvae of isolates known to be susceptible to ivermectin. The criterion used to determine resistance was the ability of the larvae to migrate out of gelled agar after exposure to ivermectin using diluted propylene glycol as the control compound. The results obtained by this technique confirmed the results obtained with critical controlled tests; significant differences between the ivermectin sensitive and resistant isolates were demonstrated, thereby confirming that this in vitro technique may be used as a screening method to identify ivermectin resistant isolates of H. contortus.

Animals↗
PubMed1995

Dietary protein for young grazing sheep: interactions with gastrointestinal parasitism.

Effects of protein supplementation and of nematode control on production responses in young grazing sheep and on nematode population dynamics were assessed. Young Merino wether sheep (n = 270) were allocated to one of three supplementation (Su) treatments and one of three regimes of nematode control (drench, Dr) in a factorial design. Each of the nine treatments was replicated three times in a randomised complete block. Animals received no supplement (Su0) or were given supplements at a level equivalent to 200 g day-1, fed three times a week. The supplements contained 25% lucerne meal with either 75% sunflower meal (Su1) or 75% formaldehyde-treated sunflower meal (Su2). Nematode control regimes were: not drenched unless survival of individual animals was threatened (Dr0); drenched according to a strategic drenching programme (Dr1); treatment with a controlled-release albendazole capsule (Dr2). Infections with Haemonchus contortus were suppressed by use of closantel. Due to drought conditions and lack of pasture growth, lucerne hay was fed to all sheep from Week 14 onwards (350 g per head per day, fed twice a week). Supplementation reduced the need for 'survival drenching' in Dr0 sheep considerably. Live-weight gain was increased significantly by supplementation with Su1 or Su2 during the 36-week experiment. Undrenched animals given Su1 or Su2 tended to grow faster than unsupplemented animals in the Dr1 and Dr2 groups. Greasy wool production and fibre diameter were increased by supplementation and anthelmintic treatment. Faecal worm egg counts (FEC) in undrenched sheep were significantly lower for Su1 and Su2 sheep than for Su0 sheep. There were no effects of supplementation on FEC in Dr1 or Dr2 sheep. Worm burden was generally unaffected by supplementation, while the drenching treatments Dr1 and Dr2 reduced worm burden at Week 16 and to a lesser extent at Week 27. Trichostrongylus colubriformis was the predominant nematode species, with smaller numbers of Nematodirus spp., Trichostrongylus vitrinus, Trichostrongylus axei and Ostertagia circumcincta also present. It was concluded that supplementary feeding with protein meal substantially reduced production losses attributable to nematode infections in young grazing sheep. This appears to be due to an enhanced resilience of the host, rather than any major changes in development of protective immunity.

Animal Feed↗
PubMed1996

Comparison of methods for counting third stage larvae of gastrointestinal nematodes of small ruminants in tropical pastures.

The accuracy and the precision of a simple and reliable technique for the extraction and the counting of third stage larvae densities of gastro-intestinal strongyles of ruminants from pasture samples are assessed in tropical conditions, i.e. for pangola pastures and for the genera of Haemonchus and Trichostrongylus. To separate the larvae from herbage samples, water washings obtained by a centrifuge spin-dryer were put to sediment in disposable plastic bags. The extraction and counting of larvae from sediments were achieved by exhaustion of sediments with repeated sucrose/water interface procedures. The recovery rate of third stage infective larvae (L3) added to the sediment was 79.1% (+/- 9.49%). The accuracy, estimated as recovery rate of L3 added to herbage samples, was 76.5 (+/- 11.31%). The recovery by the sedimentation method was 3.5 times higher than that of a filtering method through a 20 microns sieve. The detection limit was estimated to be 130 L3 kg-1 dry matter. Precision, estimated as the residual standard deviation of duplicate assays, was 1857 L3 kg-1 dry matter (mean 9164 L3 kg-1 dry matter). Results obtained in routine epidemiological surveys of gastro-intestinal strongylosis of small ruminants in West Africa and in the West Indies demonstrated the usefulness of the technique.

Animal Feed↗
PubMed1996

Characterization of excretory-secretory products from larval stages of Haemonchus contortus cultured in vitro.

To determine biochemical changes associated with early parasite development, Haemonchus contortus larvae were cultured in vitro to the fourth stage (L4). Infective larvae developed from third to fourth stage in 48-96 h. Metabolic activity increased following stimulus of infective stages by CO2 secretion/excretion of significant amounts of protein into cultures and larval feeding did not occur until larvae had molted to the fourth stage. Larval feeding, as monitored by the ability of larvae to ingest fluorescein-labeled albumin, correlated with molting to the fourth stage and only fourth stage larvae were observed to feed. Fourth stage larvae secreted/excreted several enzymes into culture media including a metalloprotease, an acid phosphohydrolase, a cathepsin C-like enzyme, a phospholipase C-like enzyme and an N-acetyl-beta-D-glucosaminidase. Excretory-secretory (ES) products produced by L4 had antigenic homologies with parasite products produced during the second molt and with proteins and glycoproteins extracted from third and fourth stage larvae. ES products were recognized by sera from sheep infected with H. contortus. The enzymes identified here serve as markers for maturation to the fourth larval stage as well as the initiation of feeding and are likely to be involved in extracorporeal digestion. Further, they might serve as potential targets for immune or chemical control of trichostrongyle infections.

Acetylglucosaminidase↗
PubMed1996

Anthelmintic resistance in India.

Five sheep farms located in different geo-climatic regions were surveyed for resistance in gastrointestinal nematodes to albendazole, levamisole and ivermectin. Resistance to albendazole and levamisole was evident on all the farms. Albendazole reduced faecal egg counts by 0-73% and levamisole by 0-61%. No eggs were detected after treatment with ivermectin.

Albendazole↗
PubMed1996

Comparison of resistance of four genotypes of rams to experimental infection with Haemonchus contortus.

Fifty-five rams aged about 18-24 months weighing 30-42 kg were used in this study. Ten rams of each of four genotypes, S (Sumatra), H1 (50% Sumatra-50% Virgin Island), B1 (50% Sumatra-50% Barbados Blackbelly), E1 (50% Sumatra-50% Java Fat-tail), were infected orally with a newly isolated strain of Haemonchus contortus. Each animal received 2000 infective larvae 3 times week-1 for 3 weeks, with a total of 18,000 larvae. Fifteen rams belonging to Sumatra and its crosses with Virgin Island were used as uninfected controls. Peak egg counts were observed on Day 35 for genotype B1 and on Day 42 for genotype H1 and S. In genotype E1 a slow but consistent increase in EPG continued until Day 49 when the experiments terminated. Overall faecal egg counts at all sampling dates were not statistically different between genotypes (P > 0.05). There was a large variation in the EPG of individual rams within a genotype. The overall average EPG (geometric means) of individual rams within a genotype ranged from 3 to 1028 for B1, 4 to 261 for E1, 7 to 3119 for H1 and 9 to 506 for S. The analysis of packed cell volume (PCV) for four genotypes and controls from all sampling times showed significant differences (P < 0.05). The overall mean PCV was highest in S (31.1) and lowest in H1 (28.4). The ranking of four genotypes for PCV was S > E1 > B1 > H1. The decrease of PCV during the course of infection was highly significant for all genotypes of infected rams (B1, E1, H1, S) (P < 0.01). PCV of the control group did not exhibit much change during the course of the experimental period. Weight gain of infected rams was lower than those of uninfected controls (P < 0.5) but there was no significant difference between the four genotypes of infected rams. Individual variation within genotype in susceptibility to infections was generally more important than between genotype differences. Two major conclusions of the present study are: (1) The imported breeds with higher body weight, namely the Barbados Blackbelly and Virgin Island, may be used in cross breeding to increase the body size of local Sumatra sheep. (2) Based on the faecal egg counts it is possible to identify the animals for use in selective breeding programmes for higher resistance to H. contortus.

Analysis of Variance↗
PubMed1990

A membrane associated glutamate binding protein from Caenorhabditis elegans and Haemonchus contortus.

1. A glutamate binding protein has been identified in membrane preparations from the free living nematode, Caenorhabditis elegans, and from the parasitic nematode, Haemonchus contortus. 2. This putative glutamate receptor was solubilized with 30 mM octyl-B-glucoside and partially purified by anion exchange and gel filtration chromatography. 3. An 80-fold purification with recovery of 75% of the glutamate binding activity was achieved. 4. The soluble C. elegans binding protein displayed a Kd for glutamate of 0.1 microM, in close agreement with the findings for the membrane associated binding protein. 5. Quisqualate was capable of displacing glutamate from the soluble C. elegans receptor, again in agreement with previous findings for the membrane bound receptor. 6. The fact that a parasitic nematode, Haemonchus contortus, also possesses this putative glutamate receptor, strengthens the case for using C. elegans as a model system for the study of parasitic nematode neuromuscular physiology.

Animals↗
PubMed2005

Synthesis and anthelmintic properties of arylquinolines with activity against drug-resistant nematodes.

2,4-Disubstituted quinolines with additional substituents in positions 5-8 have been found to have anthelmintic properties. A number of 2,4-dimethoxy-6- or 8-arylquinolines have potent activity against the sheep nematode Haemonchus contortus, with LD99 values of the same order of magnitude as levamisole. These arylquinolines maintain their activity against levamisole-, ivermectin- and thiabendazole-resistant strains of H. contortus.

Animals↗
PubMed2006

Evaluation of a recombinant excretory secretory Haemonchus contortus protein for use in a diagnostic enzyme-linked immunosorbent assay.

The nematode Haemonchus contortus (H. contortus) is one of the most pathogenic and economically important parasites of sheep. A 24 kDa protein is one of the important components in H. contortus excretory/secretory (ES), which was shown to have important biological function. In our research, the cDNA of its open reading frame (ES24) was obtained and analyzed. Then the ES24 was sub-cloned into pET-30a expression vector. The recombinant vector that codes hexahistidyl peptide fusion protein (His-ES24) was transformed into Escherichia coli BL21 (DE3) strain. After induction, a high expression level of His-ES24 was found at 6h taking about 26% of the total bacterial protein analyzed by gel thin-layer scanning. The expressed His-ES24 was purified and then used in an enzyme-linked immunosorbent assay (ELISA) to detect specific antibodies in serum samples. The ELISA was able to differentiate between H. contortus-infected sheep serum and Fasciola hepatica-infected sheep serum or non-infected sheep serum. No cross-reaction was observed in sheep sera that have been experimentally infected with F. hepatica. A total of 153 field sheep serum samples conserved in our laboratory were examined using the His-ES24 ELISA, and 82 (53.6%) of them were found seropositive to H. contortus. Our results demonstrate that the prokaryotic-expressed His-ES24 might be a useful diagnostic reagent for epidemiological studies of H. contortus in sheep.

Animals↗
PubMed2004

Evaluation of Caenorhabditis elegans glycoproteins as protective immunogens against Haemonchus contortus challenge in sheep.

High levels of protection can be attained against Haemonchus contortus challenge infection in sheep using native antigens isolated from the gut of the adult parasite. However, vaccination with recombinant forms of these antigens, or components thereof, has disappointingly failed to generate similar levels of protection, suggesting that appropriate nematode glycosylation may be a prerequisite for protection. The free-living nematode, Caenorhabditis elegans is closely related to H. contortus and has been shown to share similar glycan moieties. In order to investigate the potentially protective role of these glycan moieties, a complex set of glycoproteins was isolated from C. elegans using ConA-lectin chromatography and their efficacy as immunogens against H. contortus challenge infection evaluated in sheep. Despite the generation of a high titre systemic IgG antibody response to the C. elegans glycoproteins and the ability of these antibodies to bind to the microvillar surface of the gut of H. contortus, no protection against challenge infection was observed. Serum antibodies to the C. elegans glycoproteins cross-reacted with the H. contortus host-protective antigen, H-gal-GP, by ELISA, although the level of cross-reactivity was not of a magnitude considered protective. Qualitative differences were also determined between the glycan epitopes of the C. elegans ConA-binding proteins and those of H-gal-GP, suggesting the presence of H. contortus-specific patterns of glycosylation.

Animals↗
PubMed2006

Prospects for exploring molecular developmental processes in Haemonchus contortus.

Haemonchus contortus of small ruminants is a parasitic nematode of major socio-economic importance world-wide. While there is considerable knowledge of the morphological changes which take place during the life cycle of H. contortus, very little is understood about the molecular and biochemical processes which govern developmental changes in the parasite. Recent technological advances and the imminent genomic sequence for H. contortus provide unique opportunities to investigate the molecular basis of such processes in parasitic nematodes. This article reviews molecular and biochemical aspects of development in H. contortus, reports on some recent progress on signal transduction molecules in this parasite and emphasises the opportunities that new technologies and the free-living nematode, Caenorhabditis elegans, offer for investigating developmental aspects in H. contortus and related strongylid nematodes, also in relation to developing novel approaches for control.

Animals↗