The effect of route of administration on the anthelmintic efficacy of benzimidazole anthelmintics in sheep infected with strains of Haemonchus contortus and Trichostrongylus colubriformis resistant or susceptible to thiabendazole

Observations of erratic anthelmintic activity of fenbendazole against known standardised thiabendazole-resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep were investigated. Fenbendazole at a dose rate of 10 mg/kg body weight was administered by oral, intra-ruminal or intra-abomasal routes, and was most effective against both resistant strains following intra-ruminal administration. In addition thiabendazole, oxibendazole, fenbendazole, parbendazole and mebendazole plus two unrelated compounds, levamisole and morantel tartrate, were used at one and a half times their suggested or recommended therapeutic dose rate against thiabendazole-resistant strains of H contortus and T colubriformis in sheep; each drug being administered by the intra-ruminal or intra-abomasal routes. Fenbendazole was more effective against both strains following intra-ruminal administration. Parbendazole was more effective against the resistant strain of T colubriformis following intra-ruminal administration. At the dose rate chosen for the other benzimidazoles used against these resistant strains, there was no difference in anthelmintic efficacy due to route of administration. Levamisole was highly effective against both resistant strains, irrespective of the route of administration. In the groups treated with morantel tartrate, the results obtained were difficult to interpret due to mortalities and a highly variable response in the surviving sheep. Fenbendazole, thiabendazole and mebendazole when used at their suggested or recommended therapeutic dose rate in sheep, were highly effective against known thiabendazole-susceptible strains of H contortus and T colubriformis following both intra-ruminal or intra-abomasal administration.

Comparative studies on the evaluation of the effect of new anthelminthics on various intestinal helminthiasis in Iran. Effects of anthelminthics on intestinal helminthiasis

The effect of pyrantel pamoate, levamisole, mebendazole, thiabendazole and bephenium hydroxynaphthoate on various intestinal helminths were evaluated among the inhabitants of four villages in the Dezful area southwest of Iran. A total number of 328 persons, all infected simultaneously with Ascaris and hookworm (Ancylostoma duodenale) and 49.2% with Trichostrongylus spp., were randomly divided into six groups. One group was kept as the control and the other five were each treated with one compound. Follow-up examinations showed that all of the drugs used were highly effective on Ascaris, and the differences in the cure rate were not statistically significant except for bephenium hydroxynaphthoate which showed a lower cure rate. For hookworm, cure rates of 100, 90, and 85% were observed with levamisole, pyrantel pamoate and bephenium hydroxynaphthoate, respectively. Cure rates observed with mebendazole and thiabendazole were 35 and 51%, respectively. For Trichostrongylus, the highest cure rate was achieved with levamisole, followed by thiabendazole and mebendazole. While the percentage of people showing side-effects was rather low for all drugs, thiabendazole and bephenium hydroxynaphthoate produced a higher, and levamisole a lower, percentage of side effects.

The anthelmintic efficacy of fenbendazole against thiabendazole-resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep

The anthelmintic efficacy of fenbendazole (methyl 5-(phenylthio)-2-benzimidazole carbamate) was tested in sheep against standardised strains of Hcaemonchus contortus and Trichostrongylus colubriformis, known to be resistant to thiabendazole (LD90 for thiabendazole against H ontortus was 200 mg/kg bodyweight and against T colubriformis was 150 mg/kg). Fenbendazole at dose rates of 5, 10 and 20 mg/kg per os reduced total worm counts in H contortus infected sheep by 66, 90 and 100 per cent respectively, with similar reductions recorded for worm egg outputs. For the thiabendazole resistant strain of T colubriformis, fenbendazole reduced total worm counts in infected sheep by 4, 44 (40-48), 79 (75-83), 96 and 100 per cent at dose rates of 5, 10, 20, 40 and 80 mg/kg per os. Significant suppression of worm-egg production by thiabendazole resistant T colubriformis was obtained with fenbendazole at dose levels of 5 mg/kg and above. The implications of these results are discussed in the light of the increasing occurrence of strains of trichostrongylid nematodes resistant to currently available benzimidazole anthelmintics.

The anthelmintic efficacy of fenbendazole against a mixed nematode infection in sheep

Fenbendazole (methyl-5-(phenylthio)-2-benzimidazole carbamate) at dose rates of 5 mg/kg and above was 100 per cent effective in eliminating a naturally acquired Dictyocaulus filaria infection in sheep. The drug was 100 per cent effective in eliminating concurrent infections of adult Trichostrongylus axei, Haemonchus contortus, Haemonchus placei, Ostertagia circumcincta, Ostertagia ostertagii, Cooperia oncophora, Cooperia mcmasterii, Nematodirus spathiger, Neumatodirus filcollis, Oesophagostomum venulosum and Chabertia ovina. Fenbendazole was 93 per cent and 97 per cent effective at doses of 5 and 10 mg/kg respectively in removing infection with adult T colubriformis, and post-treatment worm-egg production was completely suppressed in surviving female worms. No adverse side-effects were observed in treated sheep at either of the two dose rates used.

Controlled test of anthelmintic activity of levamisole administered to calves via drinking water, subcutaneous injection, or alfalfa pellet premix

A controlled test of the activity of 3 formulations of levamisole, at the dose level of approximately 8 mg/kg, against naturally occurring infections of gastrointestinal parasites and lungworms was made in 24 calves allotted to 4 groups of 6 calves each. Levamisole was administered to group I calves in the drinking water, to group II calves by subcutaneous injection, and to Group III calves by feeding alfalfa pellets mixed in corn silage; group IV calves were nontreated controls. Group I calves consumed the medicated water between 4 hours and 20 minutes and 9 hours and 40 minutes; group III calves consumed the medicated feed within 2 hours and 15 minutes. For calves of group I, II, and III, removals of 4th-stage Ostertagia sp were 64, 23, and 0%; of mature Ostertagia ostertagi, 90, 93, and 83%; and of mature Trichostrongylus axei, 92, 99, and 92%, respectively. For all 3 treated groups of calves, removal was 100% for 4th-stage Cooperia sp and for mature Trichostrongylus colubriformis, Cooperia oncophora, Cooperia punctata, and Oesophagostomum radiatum. Removals of Dictyocaulus vivipara were 90, 90, and 94% for calves of groups I, II, and III, respectively. There was no evidence of toxicosis. At necropsy, 2 calves in group II had small areas of edema at the sites of injection of levamisole.

Studies of the responses of basophil and eosinophil leucocytes and mast cells to the nematode Trichostrongylus colubriformis. I. Observations during the expulsion of first and second infections by guinea-pigs

During expulsion by guniea-pigs of both first and second infections with the intestinal nematode parasite Trichostrongylus colubriformis, increased numbers of basophils and eosinophils were present in the bone marrow and blood. In addition, increased numbers of basophils, mast cells and eosinophils, many possessing reduced numbers of cytoplasmic granules, accumulated at the sites of infection. Blood eosinophil counts, however, did not show significant changes during the early part of a first infection.

The effect of fenbendazole on nematode parasites in experimentally infected lambs

Fenbendazole given orally to experimentally infected lambs at a dose rate of 5 mg per kg was found to be 100 per cent effective against three and 10-day larave and also against 20-day adults of H contortus, O circumcincta, N battus and T colubriformis. The same dose was also 100 per cent effective against 10-day, 17-day larvae and 27-day adult D filaria.