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At least 127 records · Page 7Linked to original sources

PubMed1981

Resistance to reinfection with Haemonchus contortus in lactating and barren ewes following a single infection with larvae conditioned for inhibited development.

Ewes were infected in November 1977 with third stage larvae of Haemonchus contortus which were conditioned for inhibited development at +15 degrees C for 35 days. Worm counts in December and May and weekly faecal egg counts revealed that the high burdens of inhibited larvae present in December virtually disappeared during winter, while the faecal egg counts remained low. This happened whether the ewes were pregnant or not. Indications of a slight postpartum rise in faecal egg counts, however, were observed in May in three out of five lactating ewes. After experimental reinfection of seven barren ewes and five lactating ewes in May 1978 a considerable resistance to H. contortus was observed in the barren ewes, while the resistance to reinfection was negligible in the lactating ewes.

Animals↗

PubMed1978

Morphological, histochemical, and biochemical studies on the gut of Haemonchus contortus Rud., 1803).

A study has been made on the structure and chemical composition of the gut of Haemonchus contortus (Rud., 1803). The oesophagus has typically a triradiate, cuticle-lined lumen. The intestinal epithelium is provided with a well-developed brush border which contains periodic acid-Schiff-positive mucoproteins. The intestinal epithelium stores glycogen and lipids. It stains diffusely for phospholipids and general proteins and also for terminal-NH2 group. The presence of Fe2+ and Fe3+ containing pigments and activities of acid and alkaline phosphatases, glucose-6-phosphatase, and 5'-nucleotidase have been observed in the intestinal epithelium. Biochemically pH optimum for intestinal acid phosphatase has been found to be 4.8. The brush border shows positive reactions for acid phosphatase and glucose-6-phosphatase, and negative reactions for alkaline phosphatase and 5'-nucleotidase, and negative reactions for alkaline phosphatase and 5'-nucleotidase. The presence of enzymes in the brush border is related to extracellular digestion and absorption of nutrients.

Animals↗

PubMed1995

Actin isoforms in the parasitic nematode Haemonchus contortus.

Actin proteins in the parasitic nematode Haemonchus contortus were partially purified by a new method based on precipitation with podophyllotoxin and dimethylsulfoxide. Two-dimensional gel electrophoresis of partially purified actin proteins revealed differences in isoform composition between adults and third-stage larvae. The significance of this finding is possibly related to the existence of differential functional or developmental characteristics between these two life-cycle stages.

Actins↗

PubMed1995

Heat-shock and stress response of the parasitic nematode Haemonchus contortus.

Before and after a stress treatment, larval stages and adult worms of Haemonchus contortus were tested for the induction and expression of heat-shock proteins (HSPs) using immunoblot analysis with HSP70-and HSP65-specific monoclonal antibodies. Stress treatment or heat shock did not alter the signals obtained with these antibodies, but the amount of HSP70 differed between the successive stages. In addition, the different stages were metabolically labeled with [35S]-methionine during a temperature-shock or chemical treatment and proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The shocks resulted in an altered protein pattern. New was the de novo expression of a 20-kDa protein of adult worms after anthelmintic treatment.

Animals↗

PubMed1984

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Modulation of responsiveness by exposure to soluble larval antigen.

The in vitro transformation of lymphocytes in the presence of antigen was used to assay the response of lambs to antigens of Haemonchus contortus. Neither uninfected lambs nor lambs infected with H. contortus up to 9 weeks of age developed in vitro lymphocyte responsiveness to antigen. A slight and transient increase in reactivity was demonstrable in some of the infected lambs when these were reinfected with H. contortus at 26 weeks of age. This lack of responsiveness could be modulated through the exposure of lambs, early in neonatal life, to multiple parenteral injections of soluble third stage larval antigen of H. contortus. Thus, antigen specific responses were apparent in the lymphocytes from 21-week-old lambs if these were injected with antigen when 2 to 17 weeks of age. In particular, marked antigen specific reactivity developed in 19- or 24-week-old lambs if such lambs were injected with antigen on five occasions over the first 6 weeks of life and subsequently infected with H. contortus when 7 weeks old. This responsiveness was enhanced when the lambs were reinfected with H. contortus at 26 weeks of age.

Animals↗

PubMed1984

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Effect of infection in the ewe on the subsequent responsiveness of lambs.

Specific antigen-induced lymphocyte transformation in vitro and haemagglutinating antibody responses were absent from lambs infected with Haemonchus contortus. However, when lambs were injected with soluble third stage larval antigen of H. contortus, given on five occasions during the first 6 weeks of life, specific antigen-induced lymphocyte transformation and haemagglutinating antibodies were induced to the antigen. In particular, a periparturient increased susceptibility to infection and the resultant presence of heavy infections with H. contortus in ewes appeared to prime their lambs to respond and marked lymphocyte transformation was observed in antigen injected lambs born of heavily infected ewes. The enhancement of this response was associated with the colostral transfer of as yet unidentified factors. The superimposition of an infection with H. contortus in lambs which had been stimulated to respond to antigen, suppressed the in vitro responsiveness of their lymphocytes. Although individual variation was apparent, a direct correlation between the presence of in vitro antigen-induced lymphocyte transformation to third stage larval antigen and susceptibility to infection occurred.

Animals↗

PubMed1993

Systemic responses to challenge infection with Haemonchus contortus in immune Merino sheep.

Some systemic responses to single-dose infection with 10,000 Haemonchus contortus infective larvae were examined in sheep already shown to have protective immunity against the parasite. The major haematological finding was a neutrophil leukocytosis that occurred after the infections became patent but not during the pre-patent period. There was no definitive eosinophilia and no discernible change in the erythrocyte parameters. Systemic hyperthermia was not conclusively evident during the pre-patent period. Enzyme-linked-immunosorbent assays (ELISA) were used to measure the secondary anti-helminth antibody response in serum during the pre-patent period when the establishment of patent infection is resisted. These ELISAs employed preparations from adult worms to represent the parasitic stages of the worm, preparations from infective larvae to represent the pre-parasitic stages of the worm, and exsheathing fluid, which is the soluble material obtained when H. contortus larvae undergo ecdysis and transform from the pre-parasitic to the parasitic phase. Antibody responses to the three preparations differed qualitatively, indicating the presence of three different but perhaps overlapping sets of antigens. The three peaks in antibody against exsheathing fluid may reflect the pulses of antigen delivered to sheep as the parasite undergoes its three moults within the host.

Animals↗

PubMed1986

Effects of anthelmintics on Haemonchus contortus (Nematoda: Trichostrongylidae).

The review summarizes and evaluates recent information about the effects of anthelmintics on Haemonchus contortus. The topic is discussed under the headings effects of drugs on the absorptive surfaces, effects of drugs on metabolism, effects of drugs on the neuromuscular system, effects of drugs on developmental stages, anthelmintic efficacy, and resistant strains. Possible future lines of work are suggested in the conclusions.

Animals↗

PubMed1984

The effect of transfer factor treatment on two challenge infections of Haemonchus contortus in immuno-competent 7-month-old lambs.

A number of immuno-competent Blackface lambs were infected with 10,000 Haemonchus contortus third stage larvae and were later challenged with a second dose of 10,000 H. contortus third stage larvae. One group of lambs was treated with dialysed transfer factor prior to the second challenge dose. Histological changes in the abomasal wall, reductions in abomasal worm burdens at slaughter and faecal egg counts monitored throughout the experiment suggested the presence in some animals of an innate resistance, a "self curing" effect, an enhancement of this "self curing" effect in the transfer factor treated group and a response in one transfer factor treated animal comparable to "classical self cure".

Abomasum↗

PubMed1983

A comparison of the effects of dialysed and non-dialysed transfer factor preparations on Haemonchus contortus infections in young lambs.

Significant reductions in worm burdens were achieved in lambs treated with dialysed transfer factor and challenged with 10,000 Haemonchus contortus larvae, when compared with challenged control animals. Non-dialysed transfer factor, from the same leucocyte pool, produced no protection, but was successful in reducing worm burdens when given after a primary infection of 1,000 H. contortus larvae with subsequent challenge of 10,000 larvae. While the results confirmed the previously reported inconsistencies of transfer factor activity, the histological abomasal changes in all the dialysed and non-dialysed transfer factor treated groups, irrespective of measurable effects on worm burdens, were consistent and corresponded to immediate type hypersensitivity responses. The similarity of these responses with self cure in haemonchosis and the possibility of genetic factors influencing the quantitative expression of protection to the effects of transfer factor treatments is discussed.

Abomasum↗

PubMed1993

Efficacy of closantel against fenbendazole and levamisole resistant Haemonchus contortus in small ruminants.

Sheep infected with a fenbendazole resistant strain of Haemonchus contortus and goats with a levamisole resistant strain of the same parasite were used to evaluate the anthelmintic efficacy of closantel. Closantel at the rate of 10 mg/kg body weight was 100% effective against the 2 resistant strains of the parasite as indicated by faecal egg count and worm reduction. The efficacy of fenbendazole in sheep and of levamisole in goats was 56.68 and 76.90%, respectively.

Animals↗

PubMed1996

Development and survival of Haemonchus contortus and Trichostrongylus sp. on pasture in Cameroon.

The development and survival of Haemonchus contortus and Trichostrongylus sp. on pasture at Bamenda, Cameroon were studied by spreading faeces containing strongyle eggs from mixed infections on 12 experimental grass plots from April 1988 to March 1989. Development of eggs to infective larvae during the rainy season (April to October) took place within one week. The infective larvae of H. contortus survived for 11 +/- 2 weeks (with a range of 7 to 13 weeks) during this period while those of Trichostrongylus sp. survived for 9 +/- 2 weeks (with a range of 6 to 12 weeks). No larvae were recovered from eggs spread on pasture during the dry season, except in December when unseasonal rains fell within 9 days of spread of the faeces. Rainfall was identified as the most important climatic condition affecting the development and survival of infective larvae on pastures at Bamenda.

Animal Feed↗

PubMed1987

Development and survival of Haemonchus contortus larvae on pasture in Iraq.

The survival of Haemonchus contortus infective larvae on pasture and soil was studied over a period of 12 months in the Baghdad area. Infective larvae were found on herbage and soil at all times except in the summer months. During autumn and winter infective larvae in pasture survived for periods of up to 32 weeks. Little larval migration into soil was observed during this study and larvae did not survive for long in the faecal pellets during the summer.

Animals↗

PubMed1977

Development and survival of Haemonchus contortus larvae on pastures in Ibadan.

The development and survival of the eggs of Haemonchus contortus on pasture at Ibadan were studied by spreading faeces containing eggs on grass plots from October 1973 to October 1974. Development of the eggs to the infective larvae took place within one week in May, June, July, September and October. Larvae were not recovered in the other months. Their survival times were 28, 42, 42, 35, 63 and 49 days respectively in October 1973. May, June, July, September and October 1974. Rainfall was the most important epizootiological factor which influenced the development and survival of the infective larvae. Development of the eggs to the infective larvae took place when the mean daily rainfall for the first 7 days was 3 mm or more. The survival time of the larvae appeared to be prolonged when rain fell evenly throughout the periods the larvae were on pasture.

Animals↗

PubMed2004

cDNA cloning and expression patterns of a peroxiredoxin, a catalase and a glutathione peroxidase from Haemonchus contortus.

The range of antioxidant enzyme systems available to Haemonchus contortus for detoxification of hydrogen peroxide was investigated using cDNA cloning of candidate genes. PCR with primers based on conserved amino acid regions and spliced leader sequences was used to obtain full-length sequences for a 2-Cys peroxiredoxin, a catalase, and a selenium-independent glutathione peroxidase, indicating that H. contortus expresses a number of antioxidant systems with the potential to detoxify peroxide (nucleotide sequence data reported in this paper are available in the GenBank, EMBL and DDBJ databases under the accession numbers AY603335, AY603336 and AY603337). Quantitative PCR analysis comparing L3-stage larvae with adult worms showed significantly elevated peroxiredoxin levels in adults, equivalent catalase levels in the two stages, and significantly less glutathione peroxidase in adults, suggesting a significant role for peroxiredoxin in allowing the nematode to detoxify hydrogen peroxide encountered in the parasitic environment. Exposure of L4-stage worms to hydrogen peroxide in vitro (generated using glucose/glucose oxidase) caused no change in mRNA levels for each of the genes, though the exposed worms showed up to eightfold higher catalase activities. The lack of mRNA changes alongside increased catalase enzyme activity indicates that transcript level was not predictive of enzyme activity, suggesting that activity may be regulated in response to oxidative stress by a mechanism other than increased transcription.

Animals↗

PubMed2004

The failure of Haemonchus contortus excretory/secretory products to stimulate gastrin secretion in vitro.

Excretory/secretory (ES) products collected from exsheathed L3 or parasitic stages of Haemonchus contortus were tested in vitro for gastrin stimulatory properties using an ovine abomasal antral mucosal preparation. In addition, the motility of exsheathed L3 and parasites recovered on weeks 2, 6 and 8 post-infection was studied in water, saline, saline with glucose or ovine blood and in HBSS pH 2.5-7.4. Parasitic stages became immotile rapidly in water and HBSS pH 2.5, more slowly in HBSS pH 3.5, but nearly 100% remained motile for 48 h when blood was included in the medium. Exsheathed L3 motility was reduced only by water and HBSS pH 2.5, and then only in the second week of incubation. Gastrin secretion was not consistently increased by any of the parasite ES products tested in vitro, therefore, they probably do not stimulate the G cell directly to produce the hypergastrinaemia seen in parasitised sheep.

Abomasum↗

PubMed2005

Increased resistance to anthelmintics of Haemonchus contortus eggs associated with changes in membrane fluidity of eggshells during embryonation.

The embryonation of nematode eggs has been shown to increase their resistance to anthelmintics when parasites are submitted to egg hatch assays. Nevertheless, no mechanism has been suggested to explain this phenomenon. Earlier observations by other authors showed that the biochemical composition of eggshells is altered during the embryonation of eggs. The functional consequences of these changes have not been identified. We studied the changes in membrane environment (eggshells) of Haemonchus contortus eggs during the embryonation by fluidity measurements and their effects on nonspecific mechanisms of resistance to anthelmintics. We previously demonstrated that these mechanisms imply P-glycoproteins (Pgp) belonging to the multi-drug resistance (MDR) system and that the Pgp activity is very susceptible to their lipidic environment. The results obtained here show that the embryonation induced a significant and gradual increase in eggshell fluidity which was associated with an increased resistance to anthelmintics. Differences were observed between H. contortus isolates with various levels of resistance which might result from their specific biology and/or membrane composition. The membrane environment changes could act both on the solubilization of anthelmintics into the eggs and on the efflux of these lipophilic molecules by Pgp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Effects of excretory/secretory products of Haemonchus contortus on cell vacuolation.

Excretory/secretory (ES) products of the gastric nematode, Haemonchus contortus, have been implicated in the inhibition of gastric acid secretion which follows infection. Parietal cell vacuolation has been observed in abomasal sections from parasitised sheep, and ES prepared in vitro has been reported to cause vacuolation and to increase neutral red (NR) uptake in epithelial cell cultures. We have used the latter approach to examine, at the cellular level, the effects of ES prepared from L3 and adult nematodes. Both NR uptake and cellular vacuolation were increased following exposure to larval or adult ES products. ES preparations from adult worms induced more extensive vacuolation then those from L3 worms and, as with VacA treatment, adherent cells remained viable despite high levels of vacuolation. Whereas VacA-induced vacuolation resulted in NR uptake predominantly localised in vacuoles, this appeared not to be the case with ES-induced vacuolation, suggesting that different mechanisms might be involved. Both ES and VacA exposure was associated with an increased rate of cell detachment.

Abomasum↗