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PubMed1993

Demonstration of co-resistance of Haemonchus contortus to ivermectin and moxidectin.

Studies were conducted to determine whether organisms which are resistant to ivermectin are also resistant to moxidectin. The mechanisms of action of moxidectin and ivermectin were compared by measuring the changes in membrane conductance they induced in leg muscle fibres of the common shore crab (Pachygrapsus crassipes) by using standard micro-electrode techniques. Meriones unguiculatus (jirds) were infected with ivermectin-resistant or -susceptible strains of Haemonchus contortus, treated with moxidectin or ivermectin at a dose which routinely clears more than 98 per cent of the susceptible strain, and examined for parasite clearance. The results showed that moxidectin induced a rapid loss of membrane resistance in the muscle preparation, and that the effect was almost 50 per cent reversible with the chloride channel-blocker picrotoxinin; this pattern of activity is qualitatively similar to that of ivermectin. In the jird model, moxidectin achieved a clearance of only < or = 47.2 per cent against ivermectin-resistant H contortus at a dose which invariably clears > or = 98 per cent of an ivermectin-susceptible strain. These results indicate that moxidectin and ivermectin share a common mechanism of action, and that organisms that are resistant to ivermectin are also likely to be resistant to moxidectin.

Animals↗
PubMed1995

The persistence of the efficacy of injectable or oral moxidectin against Teladorsagia, Haemonchus and Trichostrongylus species in experimentally infected sheep.

The persistence of the efficacy of moxidectin was evaluated against experimental gastrointestinal nematode infections in 55 lambs randomly allocated to 11 equal groups and infected on day 0. Moxidectin 1 per cent injectable solution was administered at a dose rate of 0.2 mg moxidectin/kg bodyweight to five of the groups on days -42, -35, -28, -21 and -14; five other groups were treated with moxidectin 0.1 per cent oral drench at the same dose rate on days -35, -28, -21, -14 and -7, and the 11th group remained untreated as a control. The lambs were infected experimentally with 8000 Teladorsagia circumcincta, 2000 Haemonchus contortus and 10,000 Trichostrongylus colubriformis infective larvae and killed three weeks later. Both formulations of moxidectin showed excellent activity against T circumcincta and H contortus with almost 100 per cent efficacy against the abomasal parasites for up to 35 days after treatment. The efficacy of moxidectin 1 per cent injectable against T colubriformis was much higher (> 99 per cent) than that of the oral drench and it was highly effective up to 21 days after treatment, and gave a moderate reduction in worm burden for up to 35 days after treatment. No adverse reactions to moxidectin were observed in any of the animals.

Administration, Oral↗
PubMed2006

Use of Bacillus thuringiensis toxin as an alternative method of control against Haemonchus contortus.

The biocide activity of Bacillus thuringiensis (B. thuringiensis) IB-16 strain was evaluated against the blood-feeding nematode Haemonchus contortus (H. contortus) in vitro and in vivo assays. Twenty experimental jirds (Meriones unguiculatus) and 32 sheep were infected with H. contortus by oral route. Fourteen days post infection 10 jirds were treated with 0.2 mg per mL of IB-16 soluble toxin by intraperitoneal (i.p.) route and 8 sheep were treated with 0.5 mg of toxin per kg of body weight by intramuscular route 35 days after H. contortus infection. Same number of treated jirds and sheep were used as control. Fecal and blood samples were analyzed from experimental sheep to estimate the number of parasitic eggs, percentage of eosinophils, packed cell volume (PCV), and IgG title. All experimental jirds and 16 sheep (8 treated and 8 controls) were sacrificed at days 5, 7, and 30 after B. thuringiensis treatment. The percentage of nematode reduction was estimated from L(4) and H. contortus adults. The percentage of protection was 80.0 to jirds and 73.8 and 53.3 to sheep, sacrificed at days 7 and 30, respectively. Moreover, nonsignificant difference (P > or = 0.05) was detected from parasitic eggs, eosinophils, and PCV parameters. Significance level of IgG was observed only before H. contortus treatment with B. thuringiensis soluble toxin (P < or = 0.05) but nonsignificant difference was observed after treatment. These results showed that B. thuringiensis activity was similar to those observed by anthelmintic treatment and it could be used as an alternative biological method.

Analysis of Variance↗
PubMedDate not supplied

[Ecoepidemiology of Haemonchus contortus bahiensis, ecotype present in sheep of arid zones of Venezuela].

The frequency distribution of female Haemonchus contortus bahiensis Grisi, 1974 in sheep from Venezuelan arid zones is 15.32% for the type with vulvar flap, 51.6% for the vulvar-knob and 33.07% for smooth type. A Shannon-Weaver diversity index corresponding to 1.44 bits was calculated for these forms with similarities in the general size, egg-size and in the number of the longitudinal cuticular ridges. An aggregated kind of distribution in the host population according to the K parameter of a negative binomial distribution was recorded for male and female worms. A complicated interaction was observed between the abundance, aggregation and prevalence of this ecotype and the importance of these findings is discussed with regard to host-parasite relationships.

Animals↗
PubMedDate not supplied

In vitro activity of Brazilian strains of the predatory fungi Arthrobotrys spp. on free-living nematodes and infective larvae of Haemonchus placei.

In vitro tests were carried out to assess the activity of 26 Brazilian isolates of predatory fungi of the genus Arthrobotrys on a free-living nematode (Panagrellus sp.) and on infective larvae of Haemonchus placei, a parasitic gastrointestinal nematode of cattle. The results showed that the free-living nematode Panagrellus sp. was the most preyed upon, compared to H. placei, for all the fungal treatments. Also, variable predatory capacity was observed for different fungal isolates belonging to the same genus when applied to different nematode species.

Animals↗
PubMed2004

Ivermectin resistant and susceptible third-stage larvae of Haemonchus contortus: cholinesterase and phosphatase activities.

Cholinesterase and acid phosphatase (AP), but not alkaline phosphatase activities, were detected in cytosolic and membrane-bound fractions of ivermectin resistant and susceptible Haemonchus contortus infective-stage larvae. Some differences in acetylcholinesterase activity of cytosolic fractions and in the AP activity of these fractions as well as in the response to AP inhibitors by membrane-bound fractions were detected. Data are discussed.

Acid Phosphatase↗
PubMed2000

Characterization of acid phosphatase and phosphorylcholine hydrolase in adult Haemonchus contortus.

An acid phosphatase (AP) and a phosphorylcholine hydrolase (PCH) were detected in excretory-secretory (ESP) products from adult Haemonchus contortus. The AP had a pH optimum of 4.5 and was inhibited by tartaric acid and sodium fluoride, but not by o-phenanthroline. The AP hydrolyzed paranitrophenol (pnp)-phosphate and to a lesser extent pnp-phenyl-phosphonate but did not hydrolyze diester substrates. Purified AP consisted of heterodimers with relative molecular weight (Mr) of 41.9 and 48.7 kDa and had a native molecular weight of 98 kDa by size-exclusion chromatography (SEC). The PCH had a pH optimum of about 9.5 and was inhibited by EDTA and o-phenanthroline but not by the specific phospholipase inhibitor D609. The specific activity of PCH in the ESP was approximately 25-fold less than that of AP. PCH also hydrolyzed 5'-thymidine monophosphate-pnp at a rate about 40% lower than pnp-phosphorylcholine but did not hydrolyze 3'-thymidine monophosphate-pnp. Partial purification of PCH suggests an Mr of 50.2 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an Mr of 102 kDa by SEC. Both AP and PHC were secreted in vitro in a time-dependent manner and had their highest concentrations in the intestine. The results indicate that H. contortus adults secrete significant amounts of AP that might be a digestive enzyme. PCH is also an intestinal enzyme and is secreted in lesser amounts than AP. The PCH is probably not a phospholipase C but has some characteristics of a type I phosphodiesterase.

Acid Phosphatase↗
PubMed2000

Haemonchus contortus (Nematoda: Trichostrongylidae) is much more sensitive than Caenorhabditis elegans (Nematoda: Rhabditidae) to the ovicidal action of thiabendazole.

When eggs of the trichostrongylid nematode Haemonchus contortus were exposed to thiabendazole, the concentration required to prevent hatching in 90% of the eggs (MIC90) was found to be 0.1 microg/ml (using 1% dimethylsulfoxide [DMSO] as solvent). In contrast, eggs of the free-living rhabditid nematode Caenorhabditis elegans hatched at normal rates at a concentration 200 times higher, i.e., 20 microg/ml, and showed only a partial inhibitory effect at a concentration 1,200 times higher, i.e., 120 microg/ml (in 3% DMSO). Because solubility limitations precluded the testing of higher concentrations of thiabendazole, a more soluble derivative, 5-([1-methylethoxy]carbonylamino)-2-(4-thiazloyl)1H-++ +benzimidazolyliminoacetic acid N,N-diethylethanamine salt, was tested against C. elegans eggs. The MIC90 was found to be 400 microg/ml, and although the derivative was not tested against H. contortus eggs, this finding further suggests that C. elegans eggs have an exceptionally low degree of benzimidazole sensitivity.

Animals↗
PubMed2000

Oxidase activities in macrocyclic-resistant and -susceptible Haemonchus contortus.

The role of oxidative metabolism in resistance to macrocyclic lactones in Haemonchus contortus was examined by measuring activities toward 2 model cytochrome P450 substrates, aldrin and ethoxycoumarin, in a susceptible and a resistant isolate of the parasite. Microsomal preparations from larvae and adults of the 2 isolates showed no differences in levels of NADPH- or cumene hydroperoxide-supported aldrin epoxidase or ethoxycoumarin O-deethylase activities. Intact adult nematodes showed an ability to catalyze the epoxidation of significant amounts of aldrin, although the nature of the enzyme group responsible was unknown. This epoxidase activity was greater in adults of the susceptible isolate. It is apparent that oxidase activities toward the 2 substrates are not enhanced in the resistant isolate, suggesting that the observed resistance to macrocyclic lactones may not involve enhanced oxidative metabolism.

7-Alkoxycoumarin O-Dealkylase↗
PubMed2000

A developmentally regulated hyaluronidase of Haemonchus contortus.

The trichostrongylid nematode Haemonchus contortus released a hyaluronic acid-degrading enzyme during in vitro development from the third (L3) to fourth (L4) larval stage. The enzyme did not degrade chondroitin sulfate A. Enzyme activity was optimal between pH 4.0 and 6.0, and the enzyme was inhibited by high concentrations of NaCl; the divalent cations Cu2+, Zn2+, Ca2+, and Mn2+ were not inhibitory. The hyaluronidase had a molecular mass estimated at 57 kDa by sucrose density gradient centrifugation and at 111 kDa by substrate sodium dodecyl sulfate polyacrylamide gel electrophoresis (reducing and nonreducing conditions), suggesting the formation of a dimer during the electrophoretic separation conditions. The level of hyaluronidase released during in vitro development peaked between 24 and 48 hr in culture and then gradually decreased, with little or no activity present in the 168-hr culture fluid. The enzyme was not detected in culture fluid from 24-hr incubations of either the mid-L4 stage (obtained from sheep 7 days postinfection) or the adult stage (obtained from sheep 30-35 days postinfection). The temporal expression of the hyaluronidase suggested a role for this enzyme in the early stages of the L3-L4 developmental process.

Animals↗
PubMed2002

Localization of p-glycoprotein mRNA in the tissues of Haemonchus contortus adult worms and its relative abundance in drug-selected and susceptible strains.

Membrane transporter P-glycoproteins (Pgps) are present in a number of nematode species, including Haemonchus contortus. Allelic variation in some Pgp genes has been found to be associated with resistance to the anthelmintic ivermectin (IVM), although functional verification of a role for Pgps in IVM resistance has yet to be demonstrated. By in situ hybridization, the distribution of Pgp mRNA was visualized in transverse cryosections of adult H. contortus, using a digoxigenin-labeled cDNA probe encoding the ATP-binding region of an H. contortus Pgp. The probe sequence targeted a conserved ATP-binding region of Pgp-A (97.9% identity). It also shared 49.7-71.1% identity with 11 other Pgp sequences previously identified in H. contortus and may hybridize these sequences to give an overall measure of the total P-glycoprotein mRNA. Staining was predominately localized along the intestinal tract of the worms, with the most intense staining localized in the pharynx and anterior intestine. In the mid- and posterior intestinal regions, staining was restricted to the luminal side of the intestine. Some staining was also associated with the vas deferens and the lateral hypodermal chords anterior to the nerve ring. Using densitometry, the levels of Pgp mRNA in the pharynges of unselected and IVM- and moxidectin (MOX)-selected strains of male and female H. contortus were compared. No differences were detected between the levels of expression of Pgp in the susceptible strain versus the IVM- or MOX-selected strains. Evidence in the literature suggests that not all Pgp homologues are linked to chemical resistance phenotypes. It is thus possible that expression of I of the H. contortus Pgps is altered in IVM-resistant strains but that this phenomenon was undetectable in our experiments.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Performance of hair sheep composite breeds: resistance of lambs to Haemonchus contortus.

This study was designed to evaluate breed differences in resistance to Haemonchus contortus in lambs. A total of 181 ewe lambs representing crossbred Dorsets (DO) and Dorpers (DP; out of 1/2-Dorset, 1/4-Rambouillet, 1/4-Finnsheep ewes) and straight-bred Katahdins (KT) were evaluated over 3 yr. An additional 144 DO, DP, KT, and Barbados Blackbelly x St. Croix (HH) wethers were evaluated over 2 yr. Lambs were weaned at 60 to 90 d of age. After deworming at about 4 mo of age, ewe lambs received approximately 10,000 infective larvae and were evaluated for parasite resistance in drylot, whereas wethers were evaluated on pasture under conditions of natural infection. Each sex was analyzed separately. Egg counts per gram of feces (FEC), log-transformed FEC (LFEC), packed cell volumes (%), and body weights (kg) measured at 3, 4, 5, and 6 wk after deworming and reinfection were analyzed. Breed influenced all traits (P < 0.05) except BW in ewe lambs and PCV in wethers. Year and week influenced (P < 0.05) all traits. At most times, DP had the highest FEC, DO had the lowest PCV, and KT and HH had lower FEC and higher PCV than either DO or DP. Clearly, Dorper sheep were not more resistant to parasites than DO, but they were able to cope with infection better by maintaining similar or higher (P < 0.05) PCV and similar BW. Katahdin and HH were more resistant, with lower FEC (P < 0.05) than DO or DP. Breed differences were more apparent when infection levels were higher; DO and DP were less affected when infection levels were low and when animals were on a better plane of nutrition. Caribbean hair sheep originated in hot, humid regions of West Africa. They and the derivative Katahdin breed seem relatively resistant to parasitism. The Dorper, in contrast, was developed in more arid regions and exhibited little parasite resistance.

Animals↗
PubMed2004

Inheritance of fecal egg count and packed cell volume and their relationship with production traits in sheep infected with Haemonchus contortus.

This study describes responses to artificial infection with Haemonchus contortus in ewes and lambs of 50% Dorset, 25% Rambouillet, and 25% Finn-sheep ancestry and provides estimates of genetic parameters for measures of parasite resistance. One hundred ninety-eight ewes out of 64 sires, and 386 lambs out of 25 sires were evaluated in autumn and spring of 2 yr. Ewes were dewormed shortly after weaning their lambs and lambs were dewormed at about 120 d of age. One week after deworming, ewes and lambs were dosed with approximately 10,000 infective larvae of H. contortus. After infection, BW, fecal egg counts (FEC), and packed cell volume (PCV) were measured weekly for 7 wk in lambs kept in drylot and fortnightly for 11 wk in ewes on pasture. Summary traits were defined as initial PCV, mean BW across all times, and means for PCV (MPCV) and log-transformed FEC (MLFEC) at wk 3 to 7 after infection for lambs and wk 3 to 11 after infection for ewes. Ewes and lambs did not lose weight overall in any year or season, but there was no consistent effect of year or lambing season on mean LFEC or mean PCV during infection in either ewes or lambs. Yearling ewes were less resistant to infection than older ewes, with lower PCV (P < 0.05) and higher LFEC (P < 0.05). During infection, PCV was positively correlated with BW and negatively correlated with LFEC in both ewes and lambs. In lambs, heritabilities were 0.39 (P < 0.01) for PCV, 0.10 (P < 0.05) for LFEC across all measurement times, and 0.19 (P < 0.01) for three measures of LFEC taken at the peak of infection. Heritability estimates for ewes were 0.15 (P < 0.05) for PCV and 0.31 (P < 0.01) for LFEC. Repeatabilities for LFEC and PCV across measurement times were moderate in ewes and lambs. Correlations between dam and lamb records for MLFEC were generally low, suggesting different mechanisms of resistance in lambs and nonlactating ewes. Ewes with higher genetic merit for growth as lambs were less resistant to infection as adults, but genetic merit for fertility and prolificacy were not related to parasite resistance. Lambs with higher genetic merit for body weight were more resistant to infection. Selection for resistance to H. contortus is therefore possible and should not adversely affect growth of lambs and fertility of ewes in this production environment.

Age Factors↗
PubMed2002

Genetic parameters for resistance to Haemonchus contortus in Merino sheep in South Africa.

Resistance to natural infections of Haemonchus contortus (wireworm) was studied in Merino sheep. From February 1995 to July 1996 data were collected from the OTK Merino Stud on the farm Wildebeesfontein near Hendrina in Mpumalanga province. From March 1998 to January 2000 another Merino flock at Irene in Gauteng province was included in the study. In both cases, 50 randomly-chosen animals from each group of lambs weaned were sampled weekly for faecal egg count (FEC) until a mean of 2500 eggs per gram faeces (epg) was reached. At this stage, all lambs in the group were sampled for FEC, packed cell volume (PCV) and live mass in the case of the Wildebeesfontein flock. Animals were monitored from weaning to about 1 year of age. Data from 5 different groups of lambs (583 animals and 1722 records in total) with genetic links were accumulated and analysed. Variance components and resulting heritabilities for logFEC and PCV were estimated using a bivariate animal model with repeated records. The estimated heritabilities were 0.24 +/- 0.02 for logFEC and 0.14 +/- 0.02 for PCV. A strong negative correlation (-0.84 +/- 0.06) existed between the 2 traits. The genetic correlation between PCV and live mass for the Wildebeesfontein flock was low (0.28 +/- 0.09), while that between logFEC and live mass was negative, although not significantly different from zero (-0.13 +/- 0.09). These results suggest that FEC can be used as a selection criterion for resistance to H. contortus infections in Merino sheep.

Animals↗
PubMed2006

Characterization of HC58cDNA, a putative cysteine protease from the parasite Haemonchus contortus.

Because of the complexity of the cathepsin B-like (CBL) family, an information on the biological and biochemical characteristics of individual CBL genes is lacking. In this study, we investigated the degradative effects of the recombinant HC58 protein isolated from Haemonchus contortus parasites on protein substrates over a broad pH range in vitro. This protein, which hydrolyzed the synthetic peptide substrates Z-FR-AMC and Z-RR-AMC, had characteristics of the cysteine protease class of proteins. In the acidic pH range, the isolated protein actively degraded hemoglobin (Hb), the heavy chain of goat immunoglobulin G, and azocasein. By contrast, it degraded fibrinogen in the alkaline pH range. These activities were strongly inhibited in the presence of the cysteine protease inhibitor E-64. While the protein digested Hb, it did not induce the agglutination of erythrocytes from its natural host. These results suggest that the HC58 protein may play a role in the nutrition of this parasite.

Animals↗
PubMed1999

Characterization of a hemoglobin-like protein from adult Haemonchus contortus.

A hemoglobin-like protein was purified from supernatants of adult Haemonchus contortus extracts by high-pressure liquid chromatography. The purified protein had an M(r) of 33 kDa as determined by size-exclusion chromatography under non-denaturing conditions and an M(r) of 19 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting the hemoglobin may exist as a dimer. The sequences of 3 peptides resulting from proteolytic digest of the purified protein were determined and demonstrated greater than 50% identity to the globin from Trichostrongylus colubriformis. Adult H. contortus incubated overnight in [3H]leucine, incorporated radioactivity into a peak that coeluted with parasite hemoglobin, indicating the adults synthesize hemoglobin in vitro. The L3-stage lacked hemoglobin, but the L4-stage contained a hemoglobin with an M(r) of 19.6 kDa.

Amino Acid Sequence↗
PubMedDate not supplied

Cross-reactive antigens of Haemonchus contortus adult worms in Teladorsagia circumcincta infected goats.

The adult Haemonchus contortus somatic antigens responsible for cross-reactivity have been analysed using serum samples from goat kids infected and reinfected with Teladorsagia circumcincta. Goat kids infected with T. circumcincta had similar serum ELISA values against somatic antigens of H. contortus as goats infected with H. contortus itself. Immunoblotting confirmed this extensive cross-reactivity particularly in the molecular weight range 105-29 kDa. However, peptides with high (195, 152 and 119 kDa) or low (23 kDa) molecular weight were only faintly recognized by heterologous sera.

Animals↗
PubMed2000

Sensory neuroanatomy of a passively ingested nematode parasite, Haemonchus contortus: amphidial neurons of the first stage larva.

When infective larvae of Haemonchus contortus (a highly pathogenic, economically important, gastric parasite of ruminants) are ingested by grazing hosts, they are exposed to environmental changes in the rumen, which stimulate resumption of development. Presumably, resumption is controlled by sensory neurons in sensilla known as amphids. Neuronal function can be determined by ablation of specifically recognized neurons in hatchling larvae (L1) in which neuronal cell bodies are easily visualized using differential interference microscopy. Using three-dimensional reconstructions from electron micrographs of serial transverse sections, amphidial structure of the L1 is described. Each amphid of H. contortus is innervated by 12 neurons. The ciliated dendritic processes of 10 neurons lie in the amphidial channel. Three of these end in double processes, resulting in 13 sensory cilia in the channel. One process, that of the so-called finger cell, ends in a number of digitiform projections. Another specialized dendrite enters the amphidial channel, but leaves it to end within the sheath cell, a hollow, flask-shaped cell that forms the base of the amphidial channel. Although not flattened, this process is otherwise similar to the wing cells in Caenorhabditis elegans; we consider it AWC of this group. Two other neurons, ASA and ADB, appear to be homologs of wing cells AWA and AWB in C. elegans, although they end as ciliated processes in the amphidial channel, rather than as flattened endings seen in C. elegans. Each of the 12 amphidial neurons was traced to its cell body in the lateral ganglion, posterior to the worm's nerve ring. The positions of these bodies were similar to their counterparts in C. elegans; they were named accordingly. A map for identifying the amphidial cell bodies in the living L1 was prepared, so that laser microbeam ablation studies can be conducted. These will determine which neurons are involved in the infective process, as well as others important in establishing the host-parasite relationship.

Animals↗