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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↗
PubMed1983

Interaction of dichlorvos-crotoxyphos insecticide with phenothiazine anthelmintic in sheep with or without Haemonchus and Trichostrongylus infections.

The temporal interaction of an emulsifiable mixture of 2.3% dichlorvos and 10% crotoxyphos with phenothiazine anthelmintic was studied in 8 groups of 5 lambs each, free from or parasitized with Haemonchus and Trichostrongylus spp. Each lamb in 1 of 3 parasitized groups and 1 of 3 nonparasitized groups was treated with phenothiazine orally (12.5 g initially and 4 days later with 6.25 g every 3 days for 9 treatments) and/or the mixture of dichlorvos and crotoxyphos dermally (1,550 ml of 0.25% emulsion sprayed every 2 weeks for 3 applications). Two groups served as controls. Onset of clinical signs of toxicosis, lethality, and erythrocyte acetylcholinesterase (EACE) activity were monitored. After each dichlorvos-crotoxyphos mixture spray, clinical signs of toxicosis were seen within 40 minutes in parasitized and nonparasitized lambs regardless of concurrent phenothiazine treatment. Phenothiazine alone was not toxic and did not inhibit EACE activity. The EACE activities of dichlorvos-crotoxyphos mixture-sprayed lambs were significantly (P less than 0.05) depressed regardless of parasitism or concurrent phenothiazine treatments. The severity of inhibition increased with each dichlorvos-crotoxyphos mixture spray, but EACE activity recovered within 48 hours after each spray although base-line values were never attained. There was no apparent potentiation of the toxic effects of the dichlorvos-crotoxyphos mixture by phenothiazine.

Animals↗
PubMed1982

Slight resistance to the residual effect of closantel in a field strain of Haemonchus contortus which showed an increased resistance after one selection in the laboratory.

On the strength of a complaint of suspected resistance to closantel, a field strain of Haemonchus contortus was isolated from sheep on a farm near Pretoria and tested for resistance to the remedy, both without exposure to closantel in the laboratory (designated the "unselected" substrain of the parasite) and after a single selection with closantel (called the "selected" substrain). For comparative purpose a few sheep were treated with rafoxanide to ascertain whether the efficacy of this drug was unchanged. While the unselected substrain appeared to show only slight increased resistance to the residual effect of closantel drenched at a dosage rate of 5 mg/kg, there was a dramatic increase in resistance after one selection. The residual efficacy (determined by the modified NPM test of Groeneveld & Reinecke, 1969, as outlined by Reinecke, 1973), 13-14 days after treatment with closantel was reduced from the registered claim of the remedy in South Africa of greater than 80% effective in greater than 80% of the treated flock to "ineffective", or less than 50% effective in less than 50% of the treated flock. Furthermore, there also appeared to be a slight increase in the resistance of this substrain to rafoxanide, as its efficacy was reduced from 99-100% to about 92%. This sharp reduction in efficacy after a single selection with closantel seemed to indicate that the slight increase in resistance of the unselected substrain was probably due not to possible variation in the repeatability of the trail method but to repeated treatment with closantel on the farm.

Animals↗
PubMed1981

Effects of two consecutive experimental Haemonchus contortus infections on abomasal pepsin and electrolytes and serum pepsinogen and electrolytes of sheep.

Pepsinogen, sodium, potassium and chloride concentrations in blood, and pepsin, pH and ionic concentrations in abomasal contents were measured in 4 lambs each fitted with a permanent abomasal cannula infected with 25 000 H. contortus larvae at intervals of 39 days. No significant change in blood sodium, potassium and chloride concentrations occurred after infections while the pepsinogen level increased rapidly to reaching a maximum (600% of control) 7-8 days after infection. This increase was associated with a rise in abomasal pepsin secretion, the pepsin concentration in the contents rising from 7210 to 9220 mU of tyrosine during the same period. This period was characterized by a significant (P less than 0.01) increase in abomasal pH and Na+ concentration whereas the K+ and Cl- concentrations were significantly (P less than 0.01) reduced. The second infection was associated with similar abomasal ionic changes but of shorter duration. It is likely that the second infection transiently stimulated the egg-aying of the adult worms of the first infection. Twenty one days after the re-infection the number of adult worms remaining was very low (139 +/- 41) and is considered as an effect of the "self-cure" phenomenon.

Abomasum↗
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↗
PubMed1983

[Observations on the effect of some measures for preventing gastrointestinal helminth infections in sheep].

Prophylactic anthelmintic treatment of ewes about parturition has only a negligible effects on the most important species of helminths when the ewes and their lambs are not grazed on clean pasture. Haemonchus contortus infections were completely prevented in some cases but usually severe infections occurred. As the build-up of these heavy infections in lambs was slightly delayed in comparison with that in the lambs of untreated ewes, treatment about parturition should still be regarded as useful. Treatment of lambs at the time of weaning combined with moving the animals to a clean pasture is a useful though not entirely effective preventive measure. Particularly when the lambs continue to stay on the farm, they have to be moved to clean pasture and/or treated with anthelmintics more frequently.

Animals↗
PubMed1981

Investigations for anthelmintic resistance in gastrointestinal nematodes from goats.

Field results from a commercial goat herd, based on egg counts and larval differentiation, suggested that anthelmintic resistance was present to albendazole, fenbendazole, levamisole, morantel, naphthalophos and phenothiazine. When the isolate was tested in sheep, using levamisole or oxfendazole, a possible resistance was shown for Trichostrongylus sp but no resistance was demonstrated in Haemonchus or Ostertagia spp. Ivermectin at a dose rate of 100 micrograms/kg was more than 98 per cent efficient in removing the adults of each of the three species of nematode. The phenomenon relating to the influence of the host on anthelmintic resistance is discussed.

Animals↗
PubMed1982

Changes in the flow and composition of gastric lymph in sheep given a primary infection of 10,000 Haemonchus contortus.

Some aspects of the local immune response to a primary infection with 10,000 Haemonchus contortus were studied in five sheep by monitoring changes in the flow and composition of gastric lymph continuously sampled for up to 34 days from the start of infection. Increases in lymph flow rates were recorded in four animals at varying times after the start of infection. These were usually associated with an increase in the protein content of the lymph and were considered to be a consequence of inflammatory reactions in the abomasum. Apart from a small increase in lymphocyte traffic no changes which could be attributed to a local immune responses were observed in the lymph. It is suggested that the chronic nature of infections like haemonchosis is possibly because the worms can parasitise the gut without stimulating a vigorous local immune response.

Albumins↗
PubMed1982

Studies on Haemonchus contortus. VI. Attempts to stimulate immunity to abomasal trichostrongylids in Merino sheep.

Two doses of infective larvae of 20 000 Trichostrongylus axei, dosed to Merino lambs at an interval of 14 days and subsequently challenged with Ostertagia circumcincta, caused a significant reduction (P less than 0.01) in the establishment of 5th and adult stages of the latter. T. axei was unable to protect Merino sheep against homologous challenge nor was Haemonchus contortus a successful vaccine against challenge with the same species. The vaccinated group showed a reduction (P less than 0,025) only in 5th and adult H. contortus, but not in the total worm burdens.

Animals↗
PubMed1982

Studies on haemonchus contortus. VII. The effect of treatment of Trichostrongylus axei prior to challenge with H. contortus.

Four-month-old worm-free Merino lambs were dosed with 20 000 infective larvae of Trichostrongylus axei on Day 0 and again on Day +14. On Day +83 they were treated with mebendazole at 15 mg/kg. All lambs in this group and a further group of 11 worm-free Merino control lambs were challenged with 50 000 infective larvae of Haemonchus contortus dosed from Day +90-Day +92. At necropsy 27 and 28 days later there was no significant difference between the worm burdens of the 2 groups. T. axei must be present in the abomasum to protect sheep from challenge with H. contortus.

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

The anthelmintic efficacy of Artemisia herba-alba against Haemonchus contortus infection in goats.

The anthelmintic activity of the powdered shoots of Artemisia herba-alba was investigated in experimental haemonchosis in six Nubian goats which had been infected with single doses of 800 to 1,000 infective Haemonchus larvae. The clinical signs of caprine haemonchosis included inappetence, dullness and soft faeces and were correlated with the pathological findings. None of these changes were observed in four of the six goats following the treatment with 2, 10 or 30 g of Artemisia shoots. This successful therapy was supported by the absence of eggs in the faeces, of adult worms in the abomasum at necropsy and of significant lesions in the tissues of the goats and return of the concentrations of serum ammonia, sodium, potassium, total protein and creatinine and of the activity of aspartate aminotransferase (GOT) to normal. In two goats, treated with either 10 or 30 g of Artemisia shoots, egg production was not completely suppressed and a few adult Haemonchus worms were found in the abomasum.

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↗
PubMed1982

Quantitative studies of ovine haemonchosis. 2. Relationship between total worm counts of Haemonchus contortus, haemoglobin values and bodyweight.

The relationships between Haemonchus contortus burdens, haemoglobin levels and bodyweight, were examined in 50 commercial Merino sheep, 9-18 months of age, in south-east Queensland where haemonchosis was endemic. Worm counts and haemoglobin levels were predictable (P less than 0.001, r = 0.68) from the equations log worm count = B.wt. X 0.06942 + log worm count X (-2.18896) + 12.51557. Bodyweight was not predictable from either worm counts or haemoglobin levels. Although bodyweight was represented in both equations, it was only a small and insignificant contributor. When haemoglobin levels became moderately depressed (less than 10.5 g%) or severely depressed (less than 8.0 g%), then the number of worms associated with these haemoglobin levels varied with the bodyweight of the sheep. For sheep up to 20 kg, 10.5 g% Hb was associated with 112 worms and 8 g% with 355 worms. However, 355 worms caused only moderate depression of Hb levels in sheep over 50 kg, and 1259 worms were required to cause severe depression (less than 8.0 g%) in sheep over 50 kg. Three sheep were found to be severely anaemic in the presence of less than 100 worms. It was postulated that additional factors of time and nutrition may have affected these sheep. The sheep were of low bodyweight, in poor condition (low fat score) and were subject to high stocking rates on long grass pastures and high rainfall in autumn. Other internal parasite species present were Nematodirus spp. and Trichostrongylus spp. However, their numbers were low (57 and 218 worms, respectively) and did not contribute to anaemia. The correlation between H. contortus and Nematodirus spp. was found to be negative but non-significant (r = -0.26, P less than 0.01), while the correlation between H. contortus and Trichostrongylus spp. was positive and significant (r = 0.38, P less than 0.01).

Abomasum↗