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PubMed1999

A comparison of the infectivity of cryopreserved versus unfrozen infective larvae of Haemonchus contortus, Trichostrongylus colubriformis and Trichostrongylus axei. Results of the Onderstepoort Veterinary Institute and collaborators from 1977 to the present.

The infectivity for sheep of cryopreserved infective larvae (L3) of various strains of Haemonchus contortus, Trichostrongylus colubriformis and Trichostrongylus axei is compared using previously published results of trials conducted at the Onderstepoort Veterinary Institute laboratories, and of collaborators. The means and ranges of development were similar for both frozen and unfrozen larvae of two of the three worm species reviewed. A mean of 33.4% (range, 12.7-63.0%) of cryopreserved H. contortus L3 developed, compared to a mean of 43.7% (range 2.4-78.7%) of unfrozen L3 of this worm species. The corresponding values for T. colubriformis were 33.0% (range 10.3-62.7%), and 33.5% (range 8.3-52.2%), respectively. In the case of T. axei, the development of the cryopreserved L3 (tested in only three trials) was markedly lower than that of unfrozen L3 in the single trial in which the latter was evaluated. It is concluded that development of cryopreserved L3 is probably similar to that of unfrozen L3 and that, for several reasons, maintaining nematode larvae in the frozen state in liquid nitrogen is a much superior method to that of one which entails cycling worm strains continually in their final hosts.

Animals↗
PubMed2000

Oral infectivity of cryopreserved Haemonchus contortus infective larvae that recovered relatively slowly when thawed after more than 15 years in liquid nitrogen.

Infective larvae (L3) of two different batches of anthelmintic-susceptible Haemonchus contortus, cryopreserved for 15,6 and 15,7 years in liquid nitrogen appeared dead when examined 10-20 min after thawing. However, having become motile later in the day, their viability was tested the next day in two separate groups of sheep. The mean development of 41,8% and 66,3% of the H. contortus compared favourably with previous trials with this strain, in which the L3 were injected into the abomasa of sheep after various periods of cryopreservation. It is speculated that the relatively slower recovery rates after thawing of the L3 used in this trial, when compared with those in previous trials in which one of the two batches of susceptible H. contortus was used after shorter periods of cryopreservation, may be an indication that these L3 were gradually approaching the limits of survival after almost 16 years in liquid nitrogen.

Animals↗
PubMed1975

The effect of ageing on the antigenicity of Haemonchus contortus larvae.

Viable Haemonchus contortus larvae used as a source of antigen in complement fixation tests showed a decrease in antigenic potency following storage for approximately two months at 5 degrees C. In contrast, larvae killed by freezing and stored at --15 degree C showed no such decline over a similar period. It is suggested that this loss of potency with ageing may be partly responsible for increased worm populations in sheep in spring.

Aging↗
PubMed1975

Age group interaction of Haemonchus contortus in premunized lambs.

Lambs premunized with a relatively less pathogenic (RLP) isolate of Haemonchus contortus were challenge exposed each day with 500 3rd-stage larvae (L3) of a normally pathogenic isolate of the same worm, starting on day 9 of the premunition-induced infection. In 6-month-old lambs, there was a fourfold decrease in egg production by the premunizing RLP isolate with challenge exposure compared with egg production in lambs given only the premunizing RLP isolate and not challenge exposed. Premunized lambs were able to carry larger worm burdens with less hemoglobin loss than were nonpremunized challenge-exposed control lambs. Although challenge exposure had affected parasitic egg production by the 9-day-old premunizing RLP worms, the same young infective isolates were able to survive and protect lambs against the additional parasitism.

Abomasum↗
PubMed1975

The use of disophenol in studies of the pathogenicity of the arrested fourth-stage larvae of Haemonchus contortus in the sheep.

Disphenol was administered to sheep infected with Haemonchus contortus in order to prevent the development of populations of adult worms, and studies were made of the pathogenicity of the arrested fourth-stage larvae which remained. The treated sheep showed elevated plasma pepsinogen and abomasal pH, predominantly negative dry-matter balance, and evidence of greater fluid loss, including plasma, into the gastro-intestinal tract. It was concluded that arrested larvae may cause damage to the abomasal mucosa.

Abomasum↗
PubMed2001

Potency of three Haemonchus contortus antigens in the diagnosis of ovine haemonchosis.

One hundred faecal specimens and corresponding blood samples were evaluated for Haemonchus contortus infection in sheep by ELISA utilizing somatic, circulating and coproantigens. Results proved that coproantigen was more potent than the others in diagnosis of sheep haemonchosis. SDS-polyacrylamide gel electrophoresis demonstrated that the three antigens are structurally related. Immunoblot analysis revealed that somatic antigen contained 6 polypeptides of molecular weights 234, 205, 178, 83, 48 and 14 kDa, while, coproantigen showed 4 immunogenic polypeptides of 234, 205, 85 and 45 kDa. In circulating antigen only 2 polypeptides of molecular weights 165 and 99 kDa were immunoreactive. The potency of coproantigen may be attributed partially to one polypeptide of molecular weight 45 kDa. This low molecular weight polypeptide was only expressed in coproantigen as an immunogen, probably increases the immunogenicity, and may have potential diagnostic and protective values.

Animals↗
PubMed2002

The parasitic hematophagous worm Haemonchus contortus inhibits human platelet aggregation and adhesion: partial purification of a platelet inhibitor.

Blood sucking parasites elaborate mechanisms to counteract the hemostatic system of their victim. Haemonchus contortus worms use several mechanisms directed against the normal platelet hemostatic function. Platelet adhesion onto collagen and fibrinogen, and the ristocetin-mediated interaction of von Willebrand Factor with glycoprotein (GP) Ib were inhibited by the protein extract of adult worms. Also platelet aggregation induced by collagen, thrombin, ADP, ristocetin or A23187 was inhibited. Although we obtained evidence for interference with fibrinogen binding to GPIIb/IIIa, the strongest inhibition was seen when the agonists collagen or thrombin were used. A small multisubunit inhibitor of collagen-induced platelet aggregation was partially purified using anion exchange chromatography, gel filtration and RP-HPLC. The inhibitor has a pI between 4 and 6.5, elutes with a molecular weight of 23,800 Da after gel filtration, and is part of the elaborate broad-spectrum antiplatelet activity that results in the potent synergistic anti-hemostatic cocktail produced by H. contortus.

Animals↗
PubMed1975

Trials with rafoxanide. 7. Efficacy against Fasciola hepatica, Haemonchus placei and Bunostomum phlebotomum in cattle.

Anthelmintic efficacy studies involving 49 cattle either naturally or artificially infested with Fasciola hepatica are described. Some of the animals were also artificially infested with Haemonchus placei and Bunostomum phlebotomum. At dosage rates of 3,75 and 5,0 mg/kg live mass rafoxanide was 64,6 and 92,6 per cent effective respectively against adult naturally acquired infestations of F. hepatica. At 7,5 and 10,0 mg/kg it was 37,9 and 55,7 per cent effective against 42 day old liver fluke. At 7,5 mg/kg it was 100, 87,4 and 94,6 per cent effective against mature F. hepatica, fourth stage H. placei and adult B. phlebotomum respectively.

Animals↗
PubMed2002

Freezing of sheep faeces invalidates Haemonchus contortus faecal egg counts by the McMaster technique.

Faecal pellets from a sheep that was artificially infected with a monoculture of Haemonchus contortus were collected over a 2-h period in the morning. In the laboratory the faeces were thoroughly mixed by hand and 48 by 1 g aliquots of the pellets were sealed in plastic bags, from which the air had gently been expressed. The faecal worm egg count of the sheep was about 14,000 g(-1). Varying numbers of the bags were either processed for faecal worm egg counting (FEC) by the McMaster technique on day 0, or were stored at one of the following temperatures: about 4 degrees C, -10 degrees C or -170 degrees C before processing. The faecal aliquots that were frozen were thawed at room temperature after having been frozen for either 2 h or 7 days, and processing of aliquots maintained at 4 degrees C proceeded shortly after the samples had been removed from the refrigerator. A dramatic reduction in egg numbers was found in all the aliquots that were frozen at -170 degrees C before faecal worm egg counts were done, as well as in those frozen for 7 days at about -10 degrees C. Numerous empty, or partially empty, egg shells were observed when performing the counts in faeces that had been frozen. In contrast, there was no significant reduction in the numbers of eggs in aliquots maintained for 7 days in a refrigerator at +/- 4 degrees C before examination, when compared with others examined shortly after collection of the faeces. Since H. contortus eggs in faeces are damaged by freezing, some methods that can be used for short term preservation are outlined. It is concluded that all nematode egg counts from cryopreserved faeces (whether in a freezer at -10 degrees C or in liquid nitrogen) should possibly be regarded as being inaccurate, unless the contrary can be demonstrated for different worm genera. However, exceptions are expected for the more rugged ova, such as those of the ascarids and Trichuris spp.

Animals↗
PubMed1976

Influence of potassium ion and osomtic pressure on development of Haemonchus contortus in vitro.

Development of infective larvae of Haemonchus contortus to the fourth stage in vitro was impaired if the concentration of potassium ion in the medium was 0.26 mM or less. At or below 0.015 mM, development was almost completely stopped. High concentrations of potassium, in solutions with a ratio of sodium to potassium from 150 down to 1.3, were all equally favorable for development, but solutions composed only of salts of potassium were unfavorable. Development was impaired by osmotic pressures below 200 mosm/kg or above 350 mosm/kg and ecdysis was arrested by high but not by low osmotic pressures.

Animals↗
PubMed1976

Effect of desiccation on the survival of infective Haemonchus contorus larvae under laboratory conditions.

When stored in water at 4 and 20 C, respectively, 42 and 36% of free 3rd-stage, infective larvae of Haemonchus contortus were alive after 256 days. When stored at -95 C, 73% of the free, desiccated larvae died during the 1st half hour and 80% during the 1st half day; thereafter no more died for 255 days, the duration of the experiment. Desiccation protected the larvae against death on storage at temperature below freezing, but it was harmful at temperatures above freezing. H. contortus larvae do not withstand a single episode of desiccation as well as Trichostrongylus colubrformis larvae.

Animals↗
PubMed1992

Histoenzymic effects of thiophenate and fenbendazole on the absorptive surfaces of Haemonchus contortus.

In vitro alterations induced by a 10 micrograms/ml and 50 micrograms/ml dose each of thiophenate and fenbendazole on the absorptive surfaces of Haemonchus contortus (Nematoda: Trichostrongylidae) were studied. The most significant changes were induced in the gut epithelium. Alkaline phosphatase and adenosine triphosphatase activities were decreased, succinic dehydrogenase activity was increased, while acid phosphatase and glucose-6-phosphatase were completely lost from the intestinal epithelium after treatment with either of the drugs. A stimulatory effect of these two anthelmintics was observe on lactic dehydrogenase and reduced nicotinamide adenine dinucleotide diaphorase distribution. Thiophenate caused an increase in the activities of glutamate dehydrogenase (GDH), glucose-6-phosphate dehydrogenase (G-6-PD) and nonspecific esterases and a decrease in reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-D) activity. Fenbendazole treatment led to the inhibition of GDH, while G-6-PD, NADPH-D, cytochrome oxidase, monoamine oxidase and nonspecific esterase activity remained unaltered in the epithelium.

Absorption↗
PubMed1992

Response to ivermectin treatment of parasitic stages of Haemonchus contortus resistant or susceptible to ivermectin.

Two groups of 33 helminth-naive lambs were infected with 5,000 L3 of an ivermectin-resistant or -susceptible strain of Haemonchus contortus (groups R and S). On days 6, 10, 16, and 21 postinfection, 5 animals from each group were chosen at random and orally treated with 0.2 mg/kg of ivermectin. On each occasion, 2 randomly selected lambs from each group were also killed to determine the number and stage of development of the worms present at the time of treatment. These necropsies revealed that by day 6 early and late fourth-stage larvae were present, whereas on day 10 the early fifth stage had been reached; by days 16 and 21 all worms had reached the adult stage. Necropsies on day 28 postinfection revealed that although animals treated at day 6 had 26.3% fewer worms than the controls, there was no significant difference (P greater than 0.05) between worm burdens from any of the animals infected with the R strain and treated at different times after infection when compared with the untreated controls. With ivermectin significant reductions were obtained in the worm burdens of the animals infected with the susceptible strain; these were reduced by 96% when treatment was given on day 6 against fourth-stage larvae and 98.9% when the drug was given on day 21 against adult stages. From these results it is clear that resistance to ivermectin in this strain of H. contortus is present as early as the fourth larval stage.

Animals↗
PubMed1992

Lymphocyte reactivity to antigens of Haemonchus contortus in antigen-inoculated and H contortus-naive lambs.

Lambs were inoculated during either fetal or early neonatal life with antigens of Haemonchus contortus (HcAg) third-stage larvae, or ovalbumin (OVA), or were left untreated. By the time lambs were 4 weeks old, blood lymphocytes from all of them responded to HcAg. This was evident in all lambs, regardless of the previous inoculation regimen, although higher response was seen in HcAg-inoculated lambs, compared with naive lambs. Only lambs inoculated with OVA had OVA-specific lymphocyte activity. In HcAg-naive lambs, the maximal HcAg lymphocyte response was observed between the ages of 5 and 25 weeks, with gradual decrease thereafter. In vitro detection of HcAg-reactive lymphocytes was affected by antigen concentration and presence of plasma. Plasma inhibited HcAg-reactive lymphocytes from all lambs at high in vitro antigen concentration and completely abrogated the response in H contortus antigen-naive lambs.

Animals↗
PubMed1992

Fibrinogen-degrading proteins from Haemonchus contortus used to vaccinate sheep.

Sixteen nonsibling sheep, approximately 12 months old, that were raised in a helminth-free environment, were used for 2 protection studies 6 months apart. Sheep were vaccinated weekly for 5 weeks by IM injection of fibrinogen-degrading proteins derived from the intestinal tract of adult Haemonchus contortus. Ten days after the last vaccination, sheep were given 2,500 infective H contortus larvae by intraruminal injection. Vaccinated sheep produced specific antibodies, and were protected from the worm challenge. Significant differences in mean fecal worm egg counts for 56 days after worm challenge, in mean numbers of H contortus worms, and female fecundity ratios at necropsy were detected in vaccinated sheep, compared with those in control sheep. These data suggest that the fibrinogen-degrading proteins have a protective role in vaccination of sheep against H contortus.

Abomasum↗
PubMed2004

Amphids: the neuronal ultrastructure of macrocyclic-lactone-resistant Haemonchus contortus.

The development of anthelmintic resistance by nematode parasites is a growing problem for veterinarians and producers. The intensive use of the macrocyclic lactones for the treatment of a variety of parasitic diseases has hastened the development of resistance to this family of parasiticides among sheep, goats and cattle. As a result, resistance to ivermectin, moxidectin and doramectin by Haemonchus contortus has been documented throughout the world. While the exact sites of action of the macrocyclic lactones remain incompletely known, a critical point of entry for these drugs may be the terminally exposed sensory major neurons located in the cephalic end of the worms. These neurons, called amphidial neurons, are located in a pair of channels, the amphids, on either side of the pharynx and are exposed to the external environment via pores at the anterior tip of the worm. Through these neurons, important chemical and thermal cues are gathered by the parasite. Examination of serial electron micrographs of ivermectin-susceptible and ivermectin-resistant H. contortus allows for comparison of neuronal structure, arrangement of neurons within the amphidial channel, and distance of the tip of the dendritic processes to the amphidial pore. The latter of these characteristics provides a useful means by which to compare the association between the neurons and the external environment of the worm. Comparison of parental laboratory strains of ivermectin-susceptible H. contortus with related selected, ivermectin-resistant strains and with a wild-type ivermectin-susceptible field strain of H. contortus from Louisiana reveals that the ivermectin-resistant worms examined have markedly shorter sensory cilia than their ivermectin-susceptible parental counterparts. Additionally, the amphidial neurons of ivermectin-resistant worms are characterized by generalized degeneration and loss of detail, whereas other neurons outside of the channels, such as the labial and cephalic neurons, are normal in structure. Similar degeneration was also observed in field strains of doramectin-resistant H. contortus collected from a New Jersey alpaca heard. These findings raise a number of questions regarding the relationship between amphidial structure and macrocyclic lactone resistance as well as the role of amphids as a means of entry for these molecules. While shortened amphidial sensilla are associated with ivermectin resistance, it remains unclear if such a structural modification facilitates survival of nematodes exposed to the macrocyclic lactones.

Animal Structures↗
PubMed1992

Controlled tests on activity of contemporary parasiticides on natural infections of helminths in lambs, with emphasis on strains of Haemonchus contortus isolated in 1955.

Ten controlled tests were done between 1972 and 1989, in lambs on pasture, evaluating activity of fenbendazole (FBZ; 5 mg/kg of body weight), oxfendazole (OFZ; 3.5 and 10 mg/kg), oxibendazole (OBZ; 10 mg/kg), pyrantel pamoate (PRT; 25 mg of base/kg), and thiabendazole (TBZ; 44 and 50 mg/kg) against natural infections of helminths, with emphasis on 2 strains (A and B) of Haemonchus contortus. Strain A was phenothiazine-susceptible and strain B was phenothiazine-resistant when isolated in 1955. For approximately 10 years prior to these tests, sheep infected with both strains had been treated periodically each year with several compounds, including thiabendazole, which was used many more times than the other drugs. For this study, 4 (FBZ, OFZ, OBZ, and PRT) of the 5 compounds were evaluated in either 1 or 2 controlled tests. The fifth compound, TBZ, was used for 5 tests. Strain A H contortus was resistant to TBZ for all years tested, but more susceptible to FBZ, OFZ, OBZ, and PRT. Overall, strain B was susceptible to TBZ (with a few exceptions), and also to FBZ, OFZ, OBZ (activity less on immature forms), and PRT. Other abomasal parasites (2 species of Ostertagia and 3 of Trichostrongylus) were found in low numbers, but removal overall was good for the compounds tested. Trichostrongylus axei, found in higher numbers than species of Ostertagia and other species of Trichostrongylus, were effectively removed by all compounds in most cases. Activities of TBZ and PRT were also evaluated against several species of intestinal helminths, most of which were found in low numbers. Cooperia curticei were inconsistently removed by TBZ, but activity of PRT was effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

[Use of FAMACHA Scoring System as a diagnostic aid for the registration of distinguishing marks in the breeding program for lambs exposed to an experimental Haemonchus contortus infection].

The control of gastro-intestinal nematodes in sheep has almost entirely been based on the use of anthelmintics and pasture management. Therefore anthelmintic resistance escalated in the past. One way of reducing this problem may be the limitation of anthelmintic treatment to those animals with clinical symptoms only. The FAMACHA Eye-colour-chart is based on the principle knowledge that the colour of mucous membranes are correlated with the anaemiae situation of an animal. To monitor anaemic animals they are identified and classified in a 1 to 5-color scale based on the colour of the conjunctiva, and anaemic animals can be selectively treated. It helps to reduce treatments and therefore the development of drug resistance. The objective of this study was to estimate the correlation between FAMACHA-scores, haematocrit values, faecal egg counts, plasma albumin level and worm burden following an experimental infection with Haemonchus contortus in lambs. The estimated correlations have been low. This proofs the limits of the FAMACHA system under a situation of low parasite pressure.

Anemia↗