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PubMed1984

Studies on Haemonchus contortus. XII. Effect of Trichostrongylus axei in Dorper lambs on natural pasture lightly infested with H. contortus.

Weaned Dorper lambs on natural pasture were predosed with 40 000 infective larvae (L3) of Trichostrongylus axei, irradiated (0,3 kGy) L3 of T. axei or closantel at 10 mg/kg either in September or November 1978 and were compared with Merino yearlings predosed with 40 000 L3 of T. axei in November 1977. The following summer (December-March) only 178,6 mm of rain fell and very few H. contortus were present on pastures. Artificial challenge with 20 000 L3 of Haemonchus contortus with the local strain from the University of Pretoria's experimental farm was given 6-7 months after predosing with T. axei. When compared with the controls, significant reductions occurred only in Group 11 (T. axei irradiated at 0,3 kGy on Day +63) (P = 0,025); Group 2 (T. axei on Day 0) (P = 0,003) and Group 4 (T. axei and closantel on Day 0) (P = 0,049). We concluded that predosing with T. axei was unsuccessful in Dorpers and Merinos artificially challenged 6-7 months later with H. contortus.

Animals↗
PubMed1984

Effect of cimetidine on abomasal pH and Haemonchus and Ostertagia species in sheep.

Cimetidine, a histamine H2-receptor blocking agent which reduces gastric acid flow in simple stomach animals was administered directly into the abomasum of sheep at 100 mg kg-1 twice daily for five consecutive days and again on the eighth day. The drug caused a significant increase in the pH values of the abomasal contents and was highly effective in reducing the adult population of Haemonchus contortus (100 per cent) and Ostertagia circumcincta (70 per cent) in the abomasum of sheep. The possibility of using cimetidine as a method of treating abomasal nematode parasitism is discussed.

Abomasum↗
PubMed1984

[Kinetics of the population of worms in various developmental stages, Haemonchus contortus in sheep after a single experimental infection] experimental infection].

This work was performed to study, in 147 month-old male lambs experimentally infected with 14000 Haemonchus contortus infective larvae and slaughtered at 6, 12, 18 and 24h and at 2, 6, 8, 11, 15 and 39 days post-infection (pi): 1, the importance, localisation and nature (with or without sheath) of the worms during the first 24 h pi; 2, the kinetics of the total worm population and of each evolutionary stages from the first to the 39th day pi: 3, the period of emergence of the fourth-stage larvae from the mucosae; 4, the topographic distribution of the different evolutionary stages of the parasite in the abomasum. During the first 24 h pi, the total worm population and that of the intramucosal larvae increase in lineary function to time (r = 0.98). After a maximum value, reached between 24 and 48 h pi, the total worm population decreases in lineary function to time (r = -0.94). Only 52% approximately of the larvae administered develop. One of the reasons is the fact that a proportion of 3rd stage larvae cannot leave their sheath during the rumino-omasal transit. Other limiting factors are discussed. The fourth-stage larvae appear in the mucosae 24 h pi. Their emergence from the mucosae starts between day 1 and 2 pi and increases in intensity from days 2 to 6 pi. The immature adults and the adults are encountered from days 6 and 14 pi respectively, and the prepatent period is on average 16 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Abomasum↗
PubMed1983

Morphology and histochemistry of the spicules and gubernaculum of Haemonchus contortus (Nematoda: Trichostrongylidae).

A study has been made of the morphological, histological and histochemical characteristics of spicules and gubernaculum in Haemonchus contortus (Rud., 1803). The correlation coefficients of body length and left and right spicule lengths, left and right spicule lengths, and the distance of barb from the distal end of left and right spicule ends have been found to be statistically significant while the correlation coefficient of body length and gubernaculum length has been found to be non-significant. The sclerotized part of each spicule is composed of three layers differing in density. The shaft of the spicule possesses dorsal and ventral wings which curve towards the corresponding wings of the other spicule. Gubernaculum is a wedge-shaped structure. The spicules and gubernaculum are mainly proteinaceous. The sclerotized part consists of mainly keratin and collagen. The presence of traces of acid phosphatase in the spicules may represent some metabolic activity. The protoplasmic part is composed of proteins, carbohydrates and lipids.

Animals↗
PubMed1983

Haemonchus contortus from the vaal ribbok, Pelea capreolus, and the bontebok, Damaliscus dorcas dorcas, in the Bontebok National Park.

During a survey of the parasites of antelope in the Bontebok National Park, Swellendam, Cape Province, specimens of Haemonchus contortus with exceptionally long spicules were recovered from 5 out of 8 bontebok, Damaliscus dorcas dorcas, and 3 out of 5 vaal ribbok, Pelea capreolus, but not from 4 springbok, Antidorcas marsupialis. Typically, H. contortus has spicules 0,466 +/- 0,085 mm long, but those recovered from vaal ribbok had spicules 0,581 +/- 0,02 mm long and were recovered in large numbers from this antelope only. This indicates that the nematode is probably a definitive parasite of vaal ribbok, and its occurrence in bontebok must be regarded as accidental.

Animals↗
PubMed1983

Stimulatory effects of prostaglandin F2 alpha on faecal egg production in Haemonchus contortus infected sheep.

The effect of prostaglandin F2 alpha on the pattern of faecal egg count was tested in 10- to 12-month-old sheep infected with 20,000 Haemonchus contortus larvae. Prostaglandin was infused intravenously 25, 50 and 75 days after infection for four hours at a rate of 5 micrograms/kg/minute and the egg counts in the faeces were determined daily for 110 days. Treatment on days 50 and 75 was followed by a significant rise in egg count lasting 19 and 12 days respectively. This observed rise seems to be related to a resumption of development of arrested larvae induced by prostaglandin treatment, and a hypothesis is proposed to explain its initiation.

Animals↗
PubMed1983

Radiolabeling of infective larvae of Haemonchus contortus (Nematoda: Trichostrongyloidea) with 75Se-methionine and their performance as tracers in sheep.

Haemonchus contortus infective larvae incorporated between 5 and 12 pCi/larva for each muCi of 75Se-methionine added per gram of fecal sediment. Thorough admixture of 75Se-methionine and fecal sediment was necessary to obtain approximately normal distribution and low variance of individual larval radioactivities. Ecdysis induced by treatment with 0.025% HClO in vitro resulted in loss of approximately 40% of the 75Se label of infective larvae. Loss of 75Se by parasitic larvae and adult H. contortus in vivo conformed to a two-component negative exponential function with half lives of 3.1 and 56 days acting on compartments representing 90% and 10%, respectively, of the 75Se label remaining after ecdysis. Labeled and unlabeled worms were readily distinguished by autoradiography 37 days after infection. No effect of gamma radiation arising from decay of 75Se in the range 130 to 1,300 pCi/larva could be measured in terms of survival or sex ratio of worms recovered at 17 days PI.

Animals↗
PubMed1984

Use of coproantibody measurement to assess the influence of diet on local immune responses of sheep vaccinated against Haemonchus contortus.

Local antibody responses to challenge with 10,000 normal Haemonchus contortus larvae were evaluated in vaccinated and control Blackface sheep fed either a high or low protein diet. Anti-parasite antibody activity was found in faecal extracts of both vaccinated and control animals after infection. The coproantibody levels showed some correlation with abomasal mucosa antibody levels and faecal antibody activity was mostly associated with IgA. The low protein diet reduced local antibody responses in vaccinated and control sheep. However despite lower antibody levels the efficacy of vaccination was not diminished in sheep fed a low protein diet.

Abomasum↗
PubMed1982

Glucose metabolism of Haemonchus contortus adults: effects of thiabendazole on susceptible versus resistant strain.

Analyses of the in vitro glucose metabolism of Haemonchus contortus adults have confirmed a complex series of end-products: ethanol, n-propanol, propionate, acetate, and CO2 as the major end-products of catabolism. No difference in end-product accumulation was seen between the cambendazole sensitive (BPL) and cambendazole resistant (CR) strains. Thiabendazole (5 mM) in vitro depressed ethanol, propanol, acetate, and propionate accumulation by approximately 42% in the BPL strain. However, in the resistant strain (CR), these end-product accumulations increased by 50% when the worms were exposed to drug in vitro and 80% when exposed in vivo. Resistance manifested by the CR strain appeared to be associated with the ability to increase its carbon flow in the presence of thiabendazole.

1-Propanol↗
PubMed1983

Development of benzimidazole resistance in a Haemonchus contortus strain in the Netherlands following fenbendazole treatment of ewes at parturition.

In contrast to observations in former years treatment of ewes after parturition with 5 to 7.5 mg/kg fenbendazole was not fully effective in removing Haemonchus contortus. Comparison of the H contortus populations in the lambs of these ewes and those of untreated ewes later in the year revealed that the treatment resulted in fenbendazole resistance and also in side resistance to other benzimidazoles. Though the faecal egg counts of the treated ewes were low, the prophylactic effect of the treatment on the population build up of H contortus in the lambs was very limited.

Animals↗
PubMed1983

Changes in resistance in mixed infections of susceptible and benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis passaged in sheep.

Benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis were each diluted with equal numbers of their respective susceptible genotypes and passaged in separate worm-free sheep. The progeny of the mixed susceptible and resistant infections were diluted with equal numbers of susceptible genotypes before passaging on two further consecutive occasions in worm-free sheep. In H contortus the amount of thiabendazole required to prevent a 50 per cent egg hatching (LC50) was reduced at each generation, but the reduction was significant (P less than 0.05) only at the third passage. In T colubriformis the LC50 for thiabendazole was reduced only at the first passage and thereafter remained constant. The reduction was not significant. In another experiment, the dilution with susceptible genotypes was made only at the first passage. Thereafter for two further generations the progeny produced from the mixed infection were passaged in worm-free sheep. In H contortus a reduced amount of thiabendazole was required to prevent a 50 per cent egg hatching at each generation, but did not reach a level of significance. The result for T colubriformis was identical to the continuous dilution experiment.

Animals↗
PubMed1980

Oxfendazole: anthelmintic activity in sheep artificially infected with nematodes. Results of trials against nine species including benzimidazole-resistant Haemonchus contortus.

In a series of 11 trials, in which 281 lambs were artificially infected with 9 species of nematodes, larval anthelmintic tests were carried out to assess the activity of a dose of 5 mg/kg oxfendazole against all 3 parasitic stages of each species. An efficacy of over 99,4% was obtained against all stages of Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus colubriformis, Nematodirus spathiger, Gaigeria pachyscelis, Chabertia ovina and Oesophagostomum columbianum with the exception of the third larval stage of O. Columbianum for which an efficacy of 93,5% was recorded. Against Dictyocaulus filaria efficacies against the fifth stages and adults, fourth larval and third larval stages were 99,8%, 92,0% and 37,5% respectively, and in two additional tests against the combined third and fourth larval stages, efficacies of 86,4% and 85,3% were recorded. Efficacy against Strongyloides papillosus was poor. In 2 supplementary experiments oxfendazole exhibited a 92,2--94,8% efficacy against adults of the Boshof benzimidazole-resistant strain of H. contortus, the highest activity so far recorded against the strain of any benzimidazole tested.

Animals↗
PubMed1982

Effect of anthelmintic treatment of ewes at parturition and lambs at weaning on the build up of Haemonchus contortus populations in lambs in the Netherlands.

In two groups of ewes and lambs, grazing pastures which were used respectively by calves and sheep in the previous year, infection with Haemonchus contortus was virtually prevented by a single treatment of the ewes with fenbendazole before turning out. In another group, grazing a pasture which was not grazed in the previous year, a delay of approximately eight weeks in the build up of high H contortus burdens in lambs was obtained by this treatment, compared with a group of untreated ewes grazing similar pasture. In two groups of lambs treated with fenbendazole at weaning and subsequently grazed on pastures which could be considered free or almost free of H contortus respectively, the build up of high pasture infectivity levels for H contortus also took at least six to eight weeks. It is suggested that treatment of ewes at parturition and lambs at weaning might delay the build up of high H contortus burdens in the lambs by less than the six to eight weeks observed in these experiments when such treatment is less than 100 per cent effective.

Animals↗
PubMed1982

Studies on Haemonchus contortus. VIII. Attempts to protect suckling lambs against infestation with H. contortus.

A group of 12 Merino lambs, 3,5 months of age, which were still suckling, were each dosed with 40 000 infective larvae of Trichostrongylus axei on Day 0. From Day +62-Day 64 each of these lambs and those of a 2nd group of 11 controls were dosed with 30 000 infective larvae of Haemonchus contortus, and all the lambs of both groups were killed on Day +90. Attempts to use T. axei to protect them against subsequent challenge with H. contortus were unsuccessful.

Animals↗
PubMed1982

The effect of predosing calves with Trichostrongylus axei on subsequent challenge with Haemonchus placei.

Twelve calves were dosed with 40 000 and a further 12 with 80 000 infective larvae of Trichostrongylus axei respectively. These 2 groups and a control group were subsequently dosed with 50 000 infective larvae of Haemonchus placei. Predosing with T. axei had no effect on the establishment of H. placei. It is postulated that the numbers of T. axei worms present were below the 'threshold' value necessary to protect the calves against challenge with H. placei.

Animals↗
PubMed1982

Comparison of changes in resistance of Haemonchus contortus eggs following withdrawal of thiabendazole selection.

Two strains of Haemonchus contortus with different levels of thiabendazole resistance were developed from the same parent strains by being subjected to different selection intensities. These two strains were each subdivided into two; one selected by thiabendazole in each generation, the other unselected for four generations. Levels of thiabendazole resistance were monitored in each generation by an in vitro egg hatch technique. During this time the unselected strain with the higher level of resistance maintained an LC50 similar to its selected control. The LC50 of the unselected strain with the lower level of resistance actually increased until at the end of the fourth generation it had an LC50 similar to the thiabendazole selected strains.

Animals↗
PubMed1980

Resistance of Haemonchus contortus to thiophanate.

The occurrence of a field strain of Haemonchus contortus which was resistant to thiophanate and susceptible to thiabendazole and levamisole is reported. The LD95 of thiophanate for the strain was found to be 156.1 mg/kg and its resistance factor was 6.7. In possessing specific thiophanate resistance it differed from previously reported thiophanate resistant strains of H contortus which have been benzimidazole resistant worms that have possessed cross resistance to thiophanate.

Animals↗
PubMed1981

Changes in response of a benzimidazole resistant strain of Haemonchus contortus from sheep after passing through calves.

A benzimidazole resistant strain of Haemonchus contortus was passaged through lambs only or from lambs to calves and back into lambs. Changes in response to thiabendazole were monitored by using an egg hatch test at each animal passage and by a controlled experiment on adult worms at the final passage in lambs. An increased level of resistance was shown for the isolate during its passage through calves by the egg hatch test, although this was not supported on the adult worms in sheep using a single dose rate of 66 mg/kg of thiabendazole.

Animals↗