SEARCH · PubMed Health

Results for “Haemonchus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed2005

Molecular and biochemical characterization of a protein cyclophilin from the nematode Haemonchus contortus( P ).

We have cloned, sequenced and expressed a gene of Haemonchus contortus that encodes a protein (termed HcCYP) consisting of a cyclophilin domain and an RNA recognition motif (RRM). An antiserum raised against the recombinant protein showed that HcCYP was present in the insoluble fraction (mostly nuclear) of the parasite homogenate. The recombinant protein possessed the typical cis-trans peptidyl-prolyl isomerase activity of cyclophilins and this activity was inhibited by the immunosuppressant cyclosporin A. The N-terminal portion of the molecule, carrying the RRM, was able to bind to nucleic acids, whereas the C-terminal portion did not have any binding activity. The possible function of HcCYP in the parasite is discussed on the basis of information available on similar proteins in other organisms.

Amino Acid Motifs↗

PubMed2005

Immunolocalisation of an ABC transporter, P-glycoprotein, in the eggshells and cuticles of free-living and parasitic stages of Haemonchus contortus.

Recent data have suggested that P-glycoprotein (Pgp), working as membrane efflux "pumps", plays a major role in the transport of anthelmintic drugs in parasitic nematodes of ruminants. Flow cytometry analyses has shown that active Pgp is probably present in the external layers of Haemonchus contortus eggshells, following staining with the mouse monoclonal anti-human MDR1 antibody UIC2, which binds to Pgp in its active conformation. We evaluated the presence and distribution of this protein in the envelopes (eggshells and cuticles) of H. contortus and compared the various stages (eggs, L1-L2 larvae, L3 larvae, adult male and female worms). Electrophoresis revealed a 170-kDa band, corresponding to the molecular weight of Pgp in all stages. Indirect immunofluorescence staining with UIC2 showed Pgp to be located in the external layer of eggshells or cuticles. Transmission electron microscopy was used to localise Pgp more accurately in the three layers of the eggshells and cuticles. The conformation and biological functions of this protein, which we did not expect to find in such structures, remain to be determined.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Isolation and characterization of class II myosin genes from Haemonchus contortus.

In this study, cDNAs encoding myosin from the parasitic nematode Haemonchus contortus were isolated and characterized. Several exhibited a considerable degree of sequence variation at the nucleotide and limited divergence at the amino acid levels within the various functional domains. The results suggest that the cDNAs isolated represented a single myosin heavy chain, which, by comparison with a number of other myosins, is inferred to represent a homologue of a muscle myosin (CeMHCA) of the free-living nematode Caenorhabditis elegans. The findings could have implications for investigating cytoskeletal dynamics and/or signalling pathways.

Amino Acid Sequence↗

PubMed2007

Real-time PCR for quantifying Haemonchus contortus eggs and potential limiting factors.

The purpose of this study was to evaluate the practicality of using real-time PCR for quantifying feces-derived trichostrongyle eggs. Haemonchus contortus eggs were used to evaluate fecal contaminants, time after egg embryonation, and the presence of competing and non-competing DNAs as factors that might interfere with generating reproducible results during simplex and multiplex quantitative real-time PCR (QPCR). Real-time PCR results showed linear quantifiable amplification with DNA from five to 75 eggs. However, threshold cycle (C (T)) values obtained by amplification of DNA from egg numbers between 75 and 1,000 did not differ significantly. Inhibitors of QPCR were effectively removed during DNA extraction as exemplified by the absence of any improvement in C (T) values with bovine serum albumin or phytase treatments. Changes from egg embryonation could only be detected during the first 6 h. Noncompetitive DNA did not appear to impact amplification; however, in a multiplex reaction a competing trichostrongyle such as Cooperia oncophora can hinder amplification of H. contortus DNA, when present at tenfold greater amounts. This study demonstrates the usefulness of QPCR for amplification and quantification of trichostrongyle eggs, and identifies potential limitations, which may be addressed through multiplex assays or the addition of a standard: exogenous DNA target.

Animals↗

PubMed1996

Carbohydrate epitopes on Haemonchus contortus antigens.

Extracts of infective larvae and adults of the trichostrongylid Haemonchus contortus were studied for the presence of carbohydrate moieties. Several different lectin-binding sites were demonstrated in both stages using a panel of nine lectins. The carbohydrate specificity of the lectins used strongly suggests that alpha-D-mannose, alpha-D-glucose, and D-N-acetylglucosamine are the most important carbohydrate epitopes present on H. contortus proteins. Thus, N-linked oligosaccharides form the major part of the carbohydrate moieties on these glycoproteins. Treatment with sodium periodate was performed to investigate the immunoreactivity towards the carbohydrate moieties. This treatment resulted in a reduction in the immunoreactivity of these antigens as demonstrated by enzyme-linked immunosorbent assay (ELISA) and immunoblotting, suggesting that a substantial part of the host immune response against H. contortus is directed against the carbohydrate epitopes on the parasite antigens.

Animals↗

PubMed1997

Proteolytic enzymes of infective larvae and adults of Trichostrongylus colubriformis and Haemonchus contortus.

The aim of this study was to acquire preliminary characterisation of the proteolytic enzymes of Trichostrongylus colubriformis and Haemonchus contortus so as to obtain a better understanding of the parasites' defence mechanisms against the host immune response. The proteinase band-pattern activity obtained using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed nine bands in T. colubriformis and H. contortus L3 larvae and four bands in adult T. colubriformis at alkaline pH. Similar testing of adult H. contortus at acidic pH gave four bands. Within the same species the same proteinase may occur in both larvae and adults. Some enzymes of similar molecular weight occurred in both species, but their relative activities differed. The majority of proteinases of T. colubriformis and H. contortus larvae and adult forms are generally of high molecular weight (35-200 kDa). Because proteinase of T. colubriformis and H. contortus have been difficult to classify on the basis of their enzymatic activity, we suggest they may be proteasomes.

Animals↗

PubMed1997

Reduced egg counts in mixed infections with Oestrus ovis and Haemonchus contortus: influence of eosinophils?

In all, 2 groups of lambs were infected either with Oestrus ovis first-instar larvae or with 10,000 third-stage larvae (L3) of Haemonchus contortus. Another group of lambs was infected with both parasites. Fecal nematode egg counts, plasma pepsinogen concentrations, specific O. ovis enzyme-linked immunosorbent assay (ELISA) antibodies, and blood eosinophil counts were monitored and compared to with the values recorded for a control group of uninfected lambs. There was no significant difference between the burden of H. contortus found in mixed and single infections. However, the nematode egg production was significantly depressed in mixed infections. O. ovis affects the population of H. contortus at least by decreasing the parasite egg output. This effect may be mediated through the increase in eosinophil production stimulated by the presence of O. ovis.

Animals↗

PubMed1998

Repeated infections with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats: comparison of resistant and susceptible animals.

A total of 70 strongyle-free French Alpine dairy goats were exposed to a combination of sequential and challenge infections with Haemonchus contortus and Trichostrongylus colubriformis third-stage larvae. The sequential infection consisted of three inoculations at 50-day intervals, each infection being abbreviated by anthelmintic treatment at 40 days postinoculation. The challenge infection, composed of the same nematode strains, was undertaken 2 months later, when goats were at their 1st month of lactation. Fecal egg counts (FECs), packed cell volumes (PCVs), pepsinogen concentrations, inorganic phosphate concentrations, and peripheral eosinophil numbers were measured at 30-40 days after each inoculation. Goats were defined as being resistant or susceptible according to their level of nematode egg output following the first inoculation. Significant differences in FECs were recorded between the two groups throughout the further inoculations and the challenge infection. The reliability of FECs was supported by the high repeatability values found within and between infections. With regard to blood constituents, only PCVs related to H. contortus infection showed values that differed significantly between the two groups, resistant goats having higher PCVs after the first and the third inoculations than did susceptible animals. However, this difference was not detectable after the challenge infection. The milk production yield for the current lactation was significantly lower in the resistant goats. Moreover, resistant animals exhibited constantly greater body condition scores as compared with susceptible animals. These results indicate that the individual responsiveness of dairy goats to experimental nematode infection can be estimated on the basis of FECs and PCVs (for H. contortus) and is negatively related to the level of milk production of the animals.

Analysis of Variance↗

PubMed1998

Superoxide dismutase and total antioxidant status of larvae and adults of Trichostrongylus colubriformis, Haemonchus contortus and Ostertagia circumcincta.

Superoxide dismutase (SOD), a cytosolic enzyme that is specific for scavenging superoxide radicals, is involved in protective mechanism(s) in tissue injury following oxidative processes and phagocytosis. The presence of SOD activity in larval and adult Trichostrongylus colubriformis, Haemonchus contortus and Ostertagia circumcincta was examined using a xanthine-xanthine oxidase assay and by polyacrylamide gel electrophoresis (PAGE) and non-denaturing sodium dodecyl sulfate (SDS)-PAGE followed by specific enzyme staining. Total antioxidant status was determined using the Randox Laboratories kit. The infective larval stages (L3) of the three species contained 8-10 times more activity than the corresponding adults. SOD activity from adult parasites was sensitive to KCN and SDS and may therefore belong to a Cu/Zn and Mn class of enzymes. SOD from the larvae was sensitive only to KCN, suggesting that it may belong to a Cu/Zn class of enzymes. Insignificant interspecies variation was observed when SOD isozyme profiles of larvae were compared. PAGE showed at least five bands of SOD activity with molecular weights of between 18 and 205 kDa. Examination of total antioxidant status showed that non-enzymatic antioxidant potential was also present, but only in the infective larvae. The level of antioxidants in the three genera of larvae studied was similar and amounted to about 0.33-1.07 microM/mg of protein.

Animals↗

PubMed1999

Flow cytometry analysis of drug transport mechanisms in Haemonchus contortus susceptible or resistant to anthelmintics.

The role of membrane drug-transport mechanisms in resistance to anthelmintics was examined using a flow cytometry method. This method was adapted from assays developed for the study of similar mechanisms in tumor cells. Rhodamine 123, a P-glycoprotein transport probe, associated with the reversal agent verapamil gave a significantly higher level of green fluorescence in Haemonchus contortus-resistant eggs as compared with that of susceptible eggs. In the same way, verapamilbodipy, a new fluorescent probe for the detection of multidrug resistance in cells, showed a significantly higher degree of binding to resistant eggs. The results confirm those obtained with biological drug assays using both anthelmintics and verapamil and provide a quantitative and effective methodology for the functional study of multidrug resistance in nematodes.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

Unexpected increased thiabendazole tolerance in Haemonchus contortus resistant to anthelmintics by modulation of glutathione activity.

The effect of several modulators of the synthesis or activity of glutathione (GSH) on the susceptibility of Haemonchus contortus eggs susceptible or resistant to anthelmintics was investigated using in vitro egg-hatch assays. Diethylmaleate, D,L-buthionine-[S,R]-sulfoximine, and patulin induced an unexpected decrease in the susceptibility of resistant eggs to thiabendazole, which was chosen as a reference for resistance to benzimidazole compounds. The results demonstrate that the level of GSH or SH analog plays an important role in the toxicity of thiabendazole to nematode eggs. Comparison with changes observed in the cytotoxicity of antitumor or antiprotozoal drugs after GSH modulation suggests that in H. contortus eggs this increased thiabendazole tolerance might depend on different factors, whether associated or not, including the ability of thiabendazole to conjugate with parasitic GSH or analog, the potential toxicity of such conjugates, their cellular distribution, and their role in the expression of glutathione S-transferase activities, and, perhaps, in the regulation of apoptosis.

Animals↗

PubMed1999

Analysis of helminth genetic data: comparative examples with Haemonchus contortus isozymes using exact tests or resampling procedures.

Population genetic data on helminths are scarce and it is important to fine tune analyses of these data, the interpretation of which is based on between-(Fst) and within-(Fis) population variability. Several computer programs are available and confidence intervals of each index are based on different procedures. These programs (Genetix, Diploid, Genepop) were compared with a classical program (Biosys-1) using a large set of Haemonchus contortus isozyme data. The results were identical for all softwares for large differences when natural populations were studied (Fst > 0.25 and Fis > 0.15 or <-0.15). When small Fst were investigated in laboratory-reared populations, the significance of differences was often related to the software used. As a rule of thumb, it is suggested that at least two out of three software packages (based on different calculation procedures) should give similar results before differences are validated.

Animals↗

PubMed1999

Effects of the multidrug-resistance-reversing agents verapamil and CL 347,099 on the efficacy of ivermectin or moxidectin against unselected and drug-selected strains of Haemonchus contortus in jirds (Meriones unguiculatus).

The development of anthelmintic resistance is making parasite control in small ruminants problematic. Following the discovery that the drug transporter P-glycoprotein may be involved in macrocyclic lactone resistance in Haemonchus contortus, we determined the effect of two multidrug-resistance modulators, verapamil and CL347,099, on the efficacy of ivermectin and moxidectin against unselected and drug-selected strains of H. contortus. CL347,099 is an analog of verapamil that has multidrug-resistance properties but weaker calcium-channel-blocking activity than the parent drug. The combinations of verapamil with either ivermectin or moxidectin significantly reduced worm counts of the selected strains as compared with the untreated controls, whereas ivermectin or moxidectin alone did not significantly reduce worm counts as compared with the untreated controls. The CL347,099 plus moxidectin combination was significantly more efficacious than moxidectin alone against the ivermectin-selected strain. The drug-combination regimes were without adverse effect on the jirds. However, higher levels of verapamil (> or =40 mg/kg) produced some toxicity.

Animals↗

PubMed2001

In vitro metabolism of moxidectin in Haemonchus contortus adult stages.

We studied the implication of cytochrome P450 enzymes in the in vitro metabolism of moxidectin (MXD) in homogenates of Haemonchus contortus adult stages (susceptible isolate, Weybridge, UK). After homogenisation in a phosphate buffer, 2 ml of homogenates (equivalent to 1 g of nematodes) were incubated with 5 microg [14C] MXD at 37 degrees C for 24 h. MXD and its metabolites were separated by HPLC with radiodetection on-line. Only one metabolite was detected and its production was inhibited by carbon monoxide. This result demonstrates that the cytochrome P450 system is implicated in the metabolisation of MXD in H. contortus susceptible to milbemycin. Furthermore, this metabolite did not match those previously described in vertebrates.

Animals↗

PubMed1991

Specific interaction of benzimidazole anthelmintics with tubulin from developing stages of thiabendazole-susceptible and -resistant Haemonchus contortus.

The low- and high-affinity binding of tritiated benzimidazole anthelmintics (mebendazole and oxibendazole) to tubulin-containing supernatants derived from unembryonated eggs, third stage larvae or adult worms of thiabendazole-susceptible and -resistant strains of Haemonchus contortus were examined and compared. The displacement of these radioligands by unlabelled benzimidazoles (mebendazole, fenbendazole, thiabendazole and oxibendazole) also was examined. The binding affinity, K alpha, and maximum binding, Bmax, for the high-affinity binding were calculated by non-linear least-square iterative curve fitting using a computer programme (LIGAND) based on the exact mathematical model of ligand-receptor interactions. The K alpha was of the same order of magnitude (x 10(7) M-1) for the susceptible and resistant eggs, larvae and worms. Resistance was associated with a loss of high-affinity binding. There was a 2- to 5-fold loss of Bmax by the resistant strain. The eggs showed greater high-affinity binding per milligram of protein than the larvae which, in turn, showed greater high-affinity binding than the adult worms. It was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis that the tubulin content per milligram of protein decreased from egg, through larvae to adult worm. Cross-displacement studies indicated that different benzimidazole drugs interacted with the same receptor (tubulin) and that a rank order of affinity of the benzimidazole drugs could be inferred.

Animals↗

PubMed1994

Haemonchus contortus: the role of two beta-tubulin gene subfamilies in the resistance to benzimidazole anthelmintics.

The role of beta-tubulin genes in benzimidazole (BZ) resistance was investigated using one susceptible (S) and two resistant (Rt and Rc) strains of Haemonchus contortus. The Rt strain was isolated from the field on the basis of thiabendazole resistance. The Rc strain was derived from the S strain by treatment with cambendazole. cDNAs, derived from the S strain, encoding two isoforms of beta-tubulin (beta 12-16 and beta 8-9), alpha-tubulin and phosphofructokinase (Pfk) were used as probes for Southern hybridization analysis of genomic DNA digested by restriction enzymes. Genomic DNA was isolated from a pool of worms or single worms. The restriction-enzyme fragment length polymorphism (RFLP) differences among these strains depended on the enzyme and the probe used. When digested with Stu I or Hpa I, and probed under stringent conditions with beta 8-9 or beta 12-16, fewer fragments were seen in the Rt and Rc strains than in the S strain. Different hybridizing fragments were found in different individuals. The frequency of individuals bearing certain fragments hybridizing to beta 12-16 or beta 8-9 in the susceptible population was reduced significantly in the resistant populations. Some differences in RFLP between these strains were observed when probed with alpha-tubulin or Pfk, but the changes were not consistent with fragments being lost from the resistant strains as observed for beta-tubulin probes. These changes in RFLP pattern correlate with changes in the binding profiles of BZs and isoelectric isoform patterns reported previously for these strains. The data confirm that reduced heterogeneity within the population is associated with BZ resistance. Our results show that both the beta 8-9 and the beta 12-16 subfamilies of beta-tubulin are affected to a similar extent by this reduction in heterogeneity in a resistant population.

Animals↗

PubMed1990

Haemonchus contortus: evidence that the 3A3 collagen gene is a member of an evolutionarily conserved family of nematode cuticle collagens.

Rabbit antisera were raised against an 18 amino acid-long peptide that corresponds to the predicted sequence of the carboxy-terminal, nontriple helical region of the Haemonchus contortus 3A3 collagen gene. This sequence is highly conserved and diagnostic for members of the col-l collagen family, which includes the 3A3 gene. We find that these antisera react predominantly with multiple, high molecular weight (greater than 68 kDa) proteins on Western blots of whole worm extracts. The number and molecular weights of the reacting proteins vary depending upon the developmental stage of the worms analyzed. All of the reacting proteins are collagenase sensitive. The reacting collagens copurify with cuticles and are released from cuticles by reducing agents. In indirect immunofluorescence assays the antisera react only with the broken edges of isolated cuticles, suggesting that the antisera are reacting with an internal cuticle layer. This layer appears to be circular and to extend throughout the length of the worm. The antisera react on Western blots with multiple, high molecular weight collagens of eight other nematodes examined, representing two classes and several orders. These data provide additional support for the notion that the 3A3 collagen gene, and other members of the col-l collagen family, encode cuticle collagens. Collagens with this peptide sequence, presumably other members of the col-l collagen family, appear to be widely distributed in the phylum Nematoda.

Amino Acid Sequence↗

PubMed1990

Haemonchus contortus: a simple procedure for purifying surface proteins from third- and fourth-stage larvae.

Surface proteins were solubilized from exsheathed third (XL3)- and fourth (L4)-stage larvae of Haemonchus contortus by a one-step extraction procedure involving brief heat treatment of the worms in the presence of buffer and 100 mM sodium chloride. Surface proteins also could be preferentially extracted from XL3s, but not from L4s, by heating the worms briefly in 1% sodium dodecyl sulfate. The major proteins extracted by these procedures were similar in molecular weight to those detected by surface-labeling live worms with 125Iodine. Both extraction procedures solubilized a single, major protein with an apparent molecular weight of 68-97 kDa from XL3s. In contrast, extraction of L4s with 100 mM sodium chloride yielded four major proteins with relative molecular weights of 27, 29, 78, and 200 kDa. Antibodies raised in rabbits to surface proteins prepared by the sodium chloride procedure reacted with the surfaces of live worms in indirect immunofluorescence assays. The anti-XL3 surface protein serum was stage specific in immunofluorescence experiments using live worms and in immunoprecipitation experiments using 125Iodine-labeled XL3 and L4 surface proteins. The overall amino acid composition of the surface proteins is hydrophilic. Twenty-six percent of the amino acid residues of the XL3 surface proteins, which consist predominantly of the 68-97 kDa species, are glutamate or glutamine.

Amino Acids↗