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PubMed1993

Isotype-specific antibody responses to Haemonchus contortus in genetically resistant sheep.

The kinetics of anti-Haemonchus antibody responses in serum and faecal extracts of pasture-reared, genetically resistant and random-bred sheep infected with Haemonchus contortus were examined using an isotype-specific ELISA. Anti-Haemonchus antibodies of IgA, IgG1, IgG2 and IgM isotypes were detected in serum and faecal extracts of both resistant and random-bred sheep after challenge infection. Serum IgG1 and IgA levels in resistant sheep were significantly higher than in random-bred sheep between 10 and 31 days after infection. However, there were no differences in IgG2 and IgM antibody responses between the two genotypes. Faecal antibody responses to H. contortus showed a clear genetic effect with resistant sheep exhibiting higher IgA levels throughout infection and higher IgG1 levels between 24 and 31 days after infection. Furthermore, serum IgG1 and IgA, and faecal IgA responses were negatively correlated with faecal egg counts in both genotypes on 17, 24 and 31 days after infection. Together, these results are taken to indicate that anti-parasite IgA and IgG1 antibodies may play an important role in genetically determined resistance of sheep to haemonchosis.

Analysis of Variance↗
PubMed1994

Protection studies with integral membrane fractions of Haemonchus contortus.

Techniques for targetting glycoproteins integral to the luminal membrane of the intestinal cells of Haemonchus contortus were used to isolate fractions of whole parasites with protective antigen potential. Sheep immunization trials with various candidate fractions revealed one which selectively bound to lectins with specificity for N-acetylgalactosamine and which reduced mean challenge worm burdens by up to 72% and mean faecal egg counts by up to 93%. The luminal surface of the intestines of the Haemonchus recovered from sheep immunized with this antigen were coated with host immunoglobulin, suggesting that the protective effect was due to antibodies interfering with the function of the gut. Further biochemical characterization of this fraction, which has been termed Haemonchus galactose-containing glycoprotein complex (H-gal-GP complex), showed that it could be distinguished from previously described protective antigens of this parasite and that it was only detectable in detergent extracts of the worms.

Acetylgalactosamine↗
PubMedDate not supplied

Presence of the LDNF glycan on the host-protective H-gal-GP fraction from Haemonchus contortus.

Immunization of sheep with the gut membrane-associated protein complex H-gal-GP of adult Haemonchus contortus induces high levels of protection against a homologous challenge infection. Protection is correlated with a systemic IgG response against the antigen. Analysis of the antibody response showed that the majority of the antigen-specific IgG was of the IgG2 isotype. A substantial proportion (74%) of this response was directed against the glycan component of H-gal-GP. The high immunogenicity of the H-gal-GP glycans may be due to the presence of the fucosylated LacdiNAc (LDNF) antigen. 2D electrophoresis, Western blotting and mass spectrometry analysis of H-gal-GP showed that this glycan epitope was specifically located on a metalloendopeptidase, MEP3. MEP3 is the most abundant protein in H-gal-GP and has been identified as one of the most likely protective components of the complex. Here, we present evidence that the LDNF glycan does not contribute to the protective capacity of H-gal-GP. Animals vaccinated with reduced and denatured H-gal-GP are not protected against subsequent infection, although the antibody response against the LDNF glycan is very similar to that of animals vaccinated with the native H-gal-GP. In addition, an alternative version of H-gal-GP, H-sialgal-GP, which is equally protective, but isolated by affinity chromatography on jacalin lectin rather than peanut lectin, contains a MEP3 component which has no detectable LDNF glycan.

Animals↗
PubMed2005

Protection induced by vaccinating sheep with a thiol-binding extract of Haemonchus contortus membranes is associated with its protease components.

Previous work has shown that a protein extract enriched for cysteine protease activity (TSBP) prepared from adult Haemonchus contortus using thiol sepharose affinity chromatography confers substantial protection against a single challenge infection. TSBP comprised proteases and other proteins. Here, TSBP were further fractionated using anion-exchange chromatography and fractions pooled on the basis of containing (1) protease activity, (2) a prominent non-protease peptide and (3) material which did not bind to the column. A protection trial showed that only the protease-enriched material conferred protective immunity and this was comparable to that observed in a TSBP-immunized positive control group. Immunization stimulated a marked IgG response with the IgG2 isotype predominating.

Animals↗
PubMed2006

Eosinophil interactions with Haemonchus contortus larvae in the ovine gastrointestinal tract.

Sheep were immunized by weekly oral infections with Haemonchus contortus for 9 weeks followed by anthelmintic treatment. They were challenged either 9 or 22 weeks later with PBS (sham controls) or one million exsheathed L3 surgically injected in the abomasum, and killed 24 h or 48 h later. Sheep challenged 9 weeks after immunization displayed varying degrees of tissue eosinophilia that showed a significant inverse relationship with the number of intra-epithelial mast cells (globule leucocytes). Close association of eosinophils with tissue larvae was observed mainly in the gastric pits (24 h) or on the mucosal surface (48 h). All L3-challenged sheep in this group had detectable globule leucocytes and tissue IL-4 mRNA, as measured by Southern blot RT-PCR. In contrast, sheep challenged 22 weeks after immunization had no detectable globule leucocytes or IL-4 mRNA and although they exhibited consistent tissue eosinophilia, eosinophils were not closely associated with tissue larvae. Scanning and transmission electron microscopy of sheep sensitized and rested for 9 weeks before challenge showed that L3 surrounded by eosinophils were at varying stages of damage and structural collapse. These studies strongly indicate that eosinophils can damage and probably kill gastrointestinal nematode larvae in vivo. In addition, they also suggest that effective killing by tissue eosinophils may depend on other microenvironmental factors such as intra-epithelial mast cells and IL-4.

Abomasum↗
PubMed2006

Further protection studies using recombinant forms of Haemonchus contortus cysteine proteinases.

Significant levels of protection against Haemonchus contortus have been achieved in sheep by vaccination with a cysteine proteinase-enriched fraction (TSBP) isolated from the gut of adult parasites. Protection is associated with three cathepsin B-like cysteine proteinases (hmcp 1, 4 & 6). Lambs vaccinated with these proteinases, expressed in bacteria as glutathione S-transferase fusion proteins, had significantly reduced (38%) worm burdens compared to challenge controls although, intriguingly, egg output was unaffected. Here, a repeat trial with similar results is reported and protection obtained compared to that induced by vaccination with the predicted mature forms of hmcp1, 4 and 6 expressed in bacteria as non-fusion proteins. Sheep immunized with a cocktail of these non-fusion proteins had reduced faecal egg counts of 27% (P = 0.17) and worm burdens of 29% (P = 0.01) compared to controls. High levels of host serum IgG were detected in GST-hmcp and non-fusion hmcp-immunized animals, although no correlation with protection could be determined. Sera from these groups bound to the microvillar surface of the gut of H. contortus.

Abomasum↗
PubMed1994

Access to the abomasum of sheep via a rumen fistula for follow-up studies during trichostrongylid infections.

A technique is described for the examination of the abomasum of adult sheep via a rumen fistula. The size of the fistula allowed a manual exploration of the rumen which was necessary to achieve an access to the abomasum. In four adult sheep, two of them infected with Haemonchus contortus, fibreoptic endoscopy was used to investigate the abomasal mucosa macroscopically as well as histopathologically and ultrastructurally by means of mucosal biopsy specimen. The acidity of the abomasal contents was measured directly by introducing an electrode into the abomasum or indirectly in abomasal fluid which was obtained via a stomach catheter through the rumen fistula. The measured values in all four sheep ranged between pH2 and 4. The fibreoptic examination of the abomasum did not influence the plasma pepsinogen and gastrin levels. The possibility of combining histological, serological and coprological data in follow-up studies on the pathophysiology of trichostrongylid infections in the abomasum of individual sheep seems to be useful for the investigation of primary and secondary infections and may contribute to a reduction of the number of experimental animals in such studies.

Abomasum↗
PubMed1998

Infection-induced protection against Haemonchus contortus in merino and manchego sheep. Relationship to serum antibody response.

Resistance to primary and secondary infections with Haemonchus contortus was studied in 10-month-old Manchego and Merino sheep. No notable interbreed differences were observed after primary infections in the parameters determined (prepatency period, faecal egg output, abomasal worm burden). Previously infected sheep (200 L-3/kg live weight (lw)) from both breeds showed notable protection after challenge (400 L-3/kg lw), evidenced by lower eggs/g faeces (epg) values and worm burdens. A protective response in the Manchego breed was associated with arrested development of fourth stage larvae in the abomasal mucosa, whereas in the Merino breed a more rapid expulsion mechanism seems to be involved. Serum antibody levels (IgG, IgA) were infective dose-dependent and protection from re-infection was not clearly related to the parasite-specific IgG response estimated by enzyme-linked immunosorbent assay (ELISA) and Western blotting.

Abomasum↗
PubMed1998

Haemonchus contortus: characterization and purification of excretory/secretory protease(s).

The activity of protease(s) has been examined separately in excretory/secretory (E/S) products from male and female Haemonchus contortus (Nematoda: Trichostrongylidae). The E/S proteolytic activity indicated the presence of preabsorptive digestion of host blood and/or tissues. Protease activity was optimum at 37 degrees C, pH 8.5 and 8.0 mg casein. These protease(s) were purified to 32.16- and 88.80-folds from male and female E/S products, respectively, by sequential purification with saturated ammonium sulphate followed by ion-exchange chromatography. The purification study revealed the presence of isomeric forms of protease(s) in the E/S products of H. contortus.

Abomasum↗
PubMed1978

The anthelmintic efficacy of non-benzimidazole anthelmintics against benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep.

The anthelmintic efficacy of 6 non-benzimidazole compounds and thiabendazole against standardised, benzimidazole resistant strains of H. contortus and T. colubriformis in sheep was determined using a controlled test. All compounds were administered intraruminally at their recommended therapeutic dose rates and 4 of the compounds were also assessed at half their recommended therapeutic dose rates. Levimisole at a dose of 6.4 mg/kg body weight, morantel at 4.4 mg/kg and 8.8 mg/kg, naphthalophos at 6.25 mg/kg and 12.5 mg/kg, rafoxanide at 7.5 mg/kg and phenothiazine at 530 mg/kg were 98% or more effective in removing adult infections of benzimidazole resistant H. contortus. Rafoxanide at 3.75 mg/kg, phenothiazine at 265 mg/kg and carbon tetrachloride at 0.05ml/kg were less effective, removing 80%, 73% and 72% respectively of the benzimidazole resistant H. contortus worm burdens. Against the benzimidazole resistant T. colubriformis levamisole at 6.4 mg/kg, and morantel at 4.4 mg/kg and 8.8 mg/kg removed 99%, 68% and 86% respectively of the adult infections. All other anthelmintics had little or no efficacy at the dose rates tested. Thiabendazole at 44 mg/kg had no significant effect against these strains of H. contortus and T. colubriformis. Several non-benzimidazole anthelmintics have shown high efficacy in this experiment and should be suitable for treating infections with benzimidazole resistant H. contortus. Of the anthelmintics tested, only levamisole and morantel show high efficacy against benzimidazole resistant T. colubriformis.

Animals↗
PubMed1978

Efficacy of oxfendazole against an ovine isolate of benzimidazole resistant Haemonchus contortus.

Eighteen parasite-free sheep were each infected with 6000 +/- 25 infective larvae of the AH-2, benzimidazole-resistant strain of Haemonchus contortus on each of experimental days -27, -15, -8 and -1. The sheep were subsequently randomized into 3 groups of 6 sheep each. Group 1 served as untreated controls; Groups 2 and 3 were treated orally with oxfendazole at dose levels of 5 mg/kg and 10 mg/kg body weight, respectively. At both dosage levels, oxfendazole was 100% effective against third, fourth, early fifth, and adult stages of the worms.

Animals↗
PubMed1979

The incidence of thiabendazole resistance in field populations of Haemonchus contortus on the northern tablelands of New South Wales.

A survey was undertaken to assess the incidence of thiabendazole resistance in field populations of H. contortus in sheep flocks on 40 farms distributed throughout the sheep grazing area of the northern tablelands of New South Wales. Treatment with thiabendazole at 66 mg/kg reduced H. contortus ova output by 96-100% in 18 flocks while in the remaining 22 there was a range of responses down to levels where the anthelmintic was without apparent effect. Factors which may contribute to the high incidence of anthelmintic resistance are discussed and the possibility of widespread resistance occurring in other sheep raising areas is considered.

Animals↗
PubMed1979

The role of inhibited larvae in the epidemiology of ovine haemonchosis.

Three paddocks were contaminated with Haemonchus contortus eggs from early spring to mid summer by yearling sheep. In Paddock 1, all contamination was derived from worms that had been previously inhibited in their development. The contamination in Paddock 2 was produced only by infections recently acquired from pasture, and in Paddock 3 contamination was attributable to both sources. When the yearling sheep were replaced in mid-summer by newly weaned lambs, severe outbreaks of haemonchosis occurred on all paddocks. It was concluded that inhibited H. contortus larvae are capable of producing sufficient eggs, when they resume development, to initiate an outbreak of haemonchosis in susceptible sheep.

Animals↗