Controlled evaluation of fenbendazole as a bovine anthelmintic

Calves experimentally infected with Haemonchus, Ostertagia, and Cooperia, and to lesser degrees with Trichostrongylus, Oesophagostomum, Nematodirus, and Bunostomum were used in a controlled experiment to record the anthelmintic efficacy of a benzimidazole compound methyl 5-(phenylthio)-2-benzimidazolecarbamate at dosage levels of 3.5, 5, and 7.5 mg/kg bodyweight. With the 3 dosages, reductions of Haemonchus were 96.7, 99.2, and 99.8%; of Ostertagia, 97.2, 97.2, and 99.5%; and of Cooperia, 99.9, 99.9, and 99.9%. Pronounced reductions were also recorded for Trichostrongylus, Nematodirus, Oesophagostomum, Trichuris, and Capillaria, but these populations were too numerically small or too unevenly distributed within the control groups to be given much emphasis. The experimental parasitic populations which developed in the 10 control calves amounted to 91, 763 worms (total).

Efficacy of p-Toluoyl chloride phenylhydrazone against gastrointestinal helminths in ovines

A new anthelmintic candidate, p-toluoyl chloride phenlylhydrazone, was administered to lambs in a paste formulation. The efficacy of this drug was determined at dose rates of 20, 30, 40, and 50 mg of active ingredient per kilogram of body weight. Helminths expelled by these dosages included Haemonchus contortus, Ostertagia circumcicta, Trichostrongylus colubriformis, T. axei, Nematodirus filicollis, Cooperia curticei, Strongyloides papillosus, Oesophagostomum columbianum, Bunostomum trigoncephalum, Chabertia ovina, Moniezia expansa, and M. benedeni.

The efficacy of thiabendazole against the arrested larvae of some Trichostrongylidae and Chabertia ovina in sheep

The activity of thiabendazole at 100 mg/kg was tested against the arrested larvae of Ostertagia spp, Haemonchus contortus, Trichostrongylus axei, Nematodirus spp and Chabertia ovina in natural infections, in 10-month-old lambs. The result, assessed by means of worm counts, showed the treatment to be very effective.

The resistance of a field strain of Haemonchus contortus to five benzimidazole anthelmintics in current use

Using artificially infected sheep, the response of a laboratory strain of Haemonchus contortus, which had not been subjected to anthelmintics for three years, was compared with that exhibited by a parbendazole resistant field strain following treatment with each of seven anthelmintics, the laboratory strain proved fully susceptable to thiabendazole, parbendazole, cambendazole, mebendazole, fenbandazole, levamisole and haloxon, in contrast to the field strain which showed a moderate to marked resistance to all five benzimidazoles, but was fully susceptible to levamisole and haloxon.

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.

Laboratory investigations in sheep with a new anthelmintic

The efficacy of fenbendazole against the following gastrointestinal nematodes was tested in experimentally infected lambs: O circumcincta, H contortus, T colubriformis and N filicollis. As low a dose as 0.5 mg per kg reduced the egg output of a patent infection with H contortus and T colubriformis by 85 per cent to 100 per cent. A dose of 3.5 mg per kg has a 100 per cent effect on three or 10-day-old stages of H contortus and one of more than 99 per cent or 100 per cent T colubriformis. The same dose reduces seven-day-old stages of O circumcincta and N filicollis by more than 94 per cent or 100 per cent, while 10 mg per kg produces a 100 per cent elimination of seven-day-old stages of O circumcincta. In field trials and efficacy of more than 99 per cent was determined after oral dosage with 5.0 mg per kg against Ostertagia, Haemonchus, Trichostrongylus, Cooperia, Nematodirus and Chabertia. Fenbendazole has a wide therapeutic-toxic dose ratio. Discoloration of the wool does not occur. Fenbendazole can be administered as a drench or with the feed.

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.

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.

[Experimental investigations on the effectiveness of fenbendazole in parasitic helminths of the stomach, intestines and lung of cattle (author's transl)]

Helminth-free bulls were injected artificially with Ostertagia ostertagi (120 000 L3), Cooperia oncophora (240000 L3), Haemonchus spec. (1 000 L3) and/or Dictyocaulus viviparus (60 L3/kg) orally or intraruminally. The animals were treated with fenbendazole during the prepatent period or after having reached maturity. The effect of 5 mg fenbendazole/kg p.o. on 3-d, 10-d- and adult stages of Ostertagia ostertagi, Haemonchus spec. and Cooperia oncophora ranges between less than 94% and 100%. Particularly noticeable was the effect on 10-d-old Ostertagia ostertagi with less than 94%. 5 mg/kg fenbendazole orally removed nearly 100% of 6-d-, 13-d-, and adult stages of Dictyocaulus viviparus. Fenbendazole may be administered as a drench or as medicated feed. The safety of the compound permits the administration of excessively high doses without clinical signs.

The effect of natural worm loss on the estimate of anthelmintic activity in an anthelmintic test with Haemonchus contortus

An anthelmintic test was carried out in lambs against fourth-stage larvae of Haemonchus contortus to determine whether a natural loss of worms from either untreated control animals or from animals treated with anthelmintic affected the estimated activity of the anthelmintic.

Thirty-two lambs were each infected with 1500 larvae of H. contortus on 4 consecutive days and divided into 4 groups of 8 animals. Two groups of lambs were treated with anthelmintic on day 7, the first group being slaughtered on day 9 and the second on day 29. An untreated control group was slaughtered 7 days after infection and a second control group was killed 29 days after infection.

The numbers of worms recovered indicated that in the untreated control lambs there was an estimated daily loss of about 7% of the parasite population between the first day of infection and day 29, and in the lambs given anthelmintic an estimated daily loss of about 2% of the worm population was indicated between days 9 and 29. If the rate of worm loss is not the same in the untreated control hosts and in the treated animals, the estimate of anthelmintic efficacy will vary according to the time of autopsy. To minimize the possibility of an incorrect result occurring in an anthelmintic trial due to a natural loss of worms, it is recommended that the untreated control and the treated lambs are slaughtered on the same day, and that the autopsy is carried out as soon as possible after anthelmintic therapy.