Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Haemonchiasis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 55 records · Page 3Linked to original sources
PubMed1997

Epidemiology of gastro-intestinal nematodes of sheep in wet tropical conditions in Malaysia.

A study on the seasonal variations in the population structure of Haemonchus contortus and Trichostronglyus colubriformis was conducted for a period of 12 months in a typical large scale sheep farm on improved pasture in Peninsular Malaysia which has a wet tropical climate. Successive groups of helminth-free tracer lambs were grazed for 4 weeks together with naturally infected sheep and were necropised for worm counts 2 weeks after their removal from the pasture. The monthly populations of H. contortus fluctuated slightly except in May and August during which more worms were found in the tracer animals. The numbers of T. colubriformis were comparatively high from October to December 1992 and again in March 1993, low during April and June 1992. Small numbers of hypobiotic larvae of H. contortus were detected in the tracer animals. Development and survival of infective larvae of H. contortus and T. colubriformis on pasture were investigated by spreading faeces containing eggs on grass plots in October 1993, February and May 1994. Development of the eggs to the infective larvae occurred within one week and their survival times were 7 weeks in the 3 experiments. The potential for control by rotational grazing is discussed.

Animals↗
PubMed2000

Immunisation of lambs with drug-abbreviated Haemonchus contortus infections: protection against homologous and heterologous challenge.

Haemonchus contortus is known as a prolific parasite, producing high numbers of eggs. It could therefore be used as a cheap source of larvae for immunisation of lambs. The value of immunisation would be improved if the immunity produced gave protection against not only homologous but also heterologous infections. Because antibody cross-reactivity between Haemonchus and Ostertagia has been well established, we wanted to know whether drug-abbreviated infections of H. contortus would stimulate production of antibodies that would cross-react with Trichostrongylus colubriformis. The results obtained from these trials indicated that H. contortus drug-abbreviated infections produced significant immunity against not only Haemonchus but also O. circumcincta. Immunisation increased the level of immunoglobulin E (IgE) and IgE-specific antibodies against T. colubriformis, but the differences between experimental and control animals were not statistically significant. Significantly higher levels of IgG-specific antibodies against T. colubriformis were observed.

Animals↗
PubMed2002

Analysis and partial reversal of multidrug resistance to anthelmintics due to P-glycoprotein in Haemonchus contortus eggs using Lens culinaris lectin.

Our previous work has shown that drug efflux pumps close to MDR1 P-glycoprotein (Pgp) can regulate anthelmintic efflux in nematodes in a way similar to that of the mutidrug resistance system (MDR) in vertebrate cancer cells. In the present study, the role of the glycosylation of Pgp was studied using a lectin specific for the alpha-mannosyl residues ( Lens culinaris agglutinin, LCA). Highly significant reversion (up to 50%) in the resistance to thiabendazole of eggs pre-treated with the lectin was obtained. Flow cytometric examinations were performed using FITC-labelled lectin. The results demonstrated that: (1) the number of Pgp sites was higher in resistant H aemonchus contortus, (2) resistance can also be associated with a decreased affinity of LCA for these sites, (3) eggs stained with LCA were also stained with specific MDR1 monoclonal antibodies. The implication of the glycosylation of Pgp in the activity and/or degradation of these pumps in eukaryotic cells is discussed.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

The influence of parasitism on the pharmacokinetics of moxidectin in lambs.

Most pharmacokinetic studies on anthelmintic drugs have been performed on non-parasitized animals. However, it seems likely that the parasite burden could influence the deposition of such drugs. The pharmacokinetics of moxidectin administered orally and by subcutaneous injection was compared in lambs exposed to nematode infection and in parasite naive lambs. Plasma samples were analyzed for moxidectin over 40 days post-treatment. The main pharmacokinetic parameters calculated demonstrated a significant change in drug deposition in infected lambs when compared to controls. The area under the plasma concentration-time curve was decreased 54% and 46% by infection in the subcutaneous and oral groups, respectively. There was also a major decrease in the mean residence time in parasitized lambs. In parallel, the clearance of the drug was increased by infection. Thus, parasite infection dramatically influences the disposition of moxidectin in lambs. These results may contribute to determining a therapeutic strategy adapted to heavily infested animals.

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

Excretory/secretory products of sheep abomasal nematode parasites cause vacuolation and increased neutral red uptake by HeLa cells.

Excretory/secretory (ES) products of Ostertagia (Teladorsagia) circumcincta and Haemonchus contortus have been implicated in the inhibition of gastric acid secretion and vacuolation, and the loss of parietal cells associated with abomasal parasitism. Vacuolation of epithelial (HeLa) cells caused by adult O. circumcincta or L3 O. circumcincta or H. contortus ES products have been examined by differential interference contrast microscopy and by the neutral red uptake assay. ES products caused visible vacuolation of HeLa cells, and this effect was enhanced by 8 mM NH4Cl. Some parasite ES products caused a marked detachment of cells from the coverslip. At lower concentrations of ES products, neutral red uptake was usually increased above the control, but at higher concentrations of ES products, uptake was often decreased, probably because of cell detachment. Although generally consistent with direct observations of HeLa cell vacuolation by parasite chemicals, neutral red uptake was not a satisfactory quantitative assay.

Abomasum↗
PubMed2005

Cyclohexadepsipeptides (CHDPs) with improved anthelmintical efficacy against the gastrointestinal nematode (Haemonchus contortus) in sheep.

Besides 24-membered cyclooctadepsipeptides (CODPs) with the most prominent member of this class emodepside, the structurally related 18-membered cyclohexadepsipeptides (CHDPs) were of interest with regard to their efficacy against the nematode H. contortus in sheep.The CHDPs prepared by a simple total synthesis represent enniatin derivatives with strong in vivo activity against H. contortus in sheep. The correlation between the nature of the CHDP major conformers and their anthelmintic activities was studied in detail. All CHDPs with strong in vivo activity exists in deuterochloroform solution as conformers with restricted flexibility which was found by 2D-NMR spectroscopic analysis. This reduced flexibility of the major conformer can be exemplified by CHDPs containing e.g.: (i) an unsymmetrically folded conformation with no cis-amide bound, (ii) an internal hydrogen bond or (iii) one cis-amide bond, respectively.The strong in vivo anthelmintic activity against H. contortus in sheep indicates that the stereochemistry in 2-position of CHDPs is less important for their high inding affinity. It may be assumed that the identified inflexible region of the major conformers might mimic the active conformation of these CHDPs, which could be helpful for rational design of anthelmintics with less complicated structures.

Animals↗
PubMed1997

Identification of Haemonchus species in domestic ruminants based on morphometrics of spicules.

An easy and rapid tool for the individual identification of Haemonchus species in domestic ruminants might be very useful in the study of natural populations, especially when two (or three) species are sympatric. Techniques based on cytology, cuticular-ridge patterns, sublateral hypodermic chords, or molecular biology allow species identification but are either expensive or time-consuming. Therefore, a discriminant function combining three measures of male spicules was established from experimental infections with H. contortus in both sheep and goats and with H. placei in zebu. The discriminant function was evaluated on individual worms and on average values obtained in natural and experimental populations throughout the world. It was compared with a previously established function. The use of our function permitted better species identification for all Haemonchus species of ruminants, including H. longistipes from camels and H. similis from cattle.

Analysis of Variance↗
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↗
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↗
PubMed1990

Resistance to benzimidazoles in Haemonchus contortus of sheep in Tanzania.

This study was undertaken to establish whether resistance to benzimidazole anthelmintics was present in gastrointestinal nematodes of sheep and goats at the university farm of Sokoine University of Agriculture, Morogoro, Tanzania. Groups of lambs were treated with albendazole at 3.8 mg/kg (recommended dose rate), 5.6 mg/kg and 10.0 mg/kg and a fourth group was untreated. Seven days after treatment, faecal egg count reductions (FECR) were found to be 94.3%, 97.6% and 99.3% and 14 days after treatment FECR of the same groups were 83.0%, 81.3% and 99.6%, respectively. Larval cultures indicated that only H. contortus were present in post-treatment samples. This strain of H. contortus, (DASP) and another strain of H. contortus (MKATA), considered susceptible to anthelmintics, were used in an experimental in vivo study and for an in vitro egg hatch assay. Treatment with fenbendazole at the recommended dose of groups of lambs infected with either strains showed no reduction in the DASP strain and a 70.5% reduction in the MKATA strain. The in vitro egg hatch assay established a significant difference (p less than 0.05) in hatchability of eggs of the two strains. The development of the high level of resistance to fenbendazole in the DASP strain is related to the history of anthelmintic usage and management of sheep and goats at the university farm.

Albendazole↗
PubMedDate not supplied

Changes in liveweight gain, blood constituents and worm egg output in goats artificially infected with a sheep-derived strain of Haemonchus contortus.

Two groups of goats were dosed with 10,000 and 20,000 sheep-derived strain (SDS) larvae of Haemonchus contortus respectively. Over a period of 42 days goats dosed with 20,000 larvae lost more weight than those dosed with 10,000 larvae. Infected goats showed anaemia from about 2 weeks after infection as well as reduced levels of total serum proteins and albumins.

Animals↗
PubMedDate not supplied

Infection of goats with Haemonchus contortus and Trichostrongylus colubriformis: histopathology and pH changes.

Two groups of goats were experimentally infected with Haemonchus contortus and Trichostrongylus colubriformis, and killed at various days after infection (DAI). The percentage of worms that established in the abomasum and the small intestine was low. At necropsy, abomasums from infected goats had thickened walls and oedematous folds. At 7 DAI there was an initial infiltration of eosinophils and some neutrophils which tend to increase with age of infection. The mean pH of the abomasum in goats infected with H. contortus was 5.43 (range 5.3-5.7), while that of the control goats was 3.30 (range 2.8-3.7).

Abomasum↗