The anthelmintic efficacy of netobimin against naturally acquired gastrointestinal nematodes in sheep

The broad-spectrum anthelmintic efficacy of netobimin (SCH 32481, Schering Corporation) was evaluated using 30 cross-bred spring lambs with naturally acquired infections of gastrointestinal nematodes. Three groups of 10 animals each were allotted into either control (given a tap water drench as a placebo) or 7.5 and 20 mg kg-1 dosage groups (given the netobimin as an oral drench). Seven to fourteen days post-treatment, animals were necropsied and nematodes recovered by standard techniques. Examination of fecal samples taken on dates of necropsy showed median egg production was reduced in treated animals (61.98% with 7.5 mg kg-1 and 100% with 20 mg kg-1). The compound was highly effective in removal of adult nematodes representing a number of genera and species of trichostrongyloids at the 7.5 and 20 mg kg-1 dose levels (shown, respectively, below). These included Ostertagia spp., with O. circumcincta, O. trifurcata, O. ostertagi and Teladorsagia davtiani (96.20%; 100%), Trichostrongylus spp., with T. axei, T. vitrinus and T. colubriformis (100%; 98.72%), Nematodirus spp., with N. spathiger, N. filicollis and N. battus (100% both levels) and Haemonchus contortus (100% both levels). High efficacies against other species of nematodes (at both dose levels) were not statistically significant (Cooperia spp., Chabertia ovina and Oesophagostomum venulosum). At 20 mg kg-1, netobimin significantly reduced populations of early and late fourth stage larvae of Ostertagia spp. by 100%. The overall efficacy (all life stages included) was 90.16% at 7.5 mg kg-1 and 98.77% at 20 mg kg-1 dose levels. No adverse reactions or signs of toxicosis were observed.     

Activity of febantel on natural infections of gastrointestinal helminths in lambs in a controlled test

The efficacy of febantel paste formulation (6 and 12 mg/kg) against natural infections of gastrointestinal helminths in lambs (n = 33) in Kentucky was evaluated in a controlled test. For the test, 23 lambs were treated orally (17 at 6 mg/kg and 6 at 12 mg/kg) and 10 lambs were not treated. Removals at both dosages in treated lambs were 95% to 100% for species of immature and mature Haemonchus, Trichostrongylus, and Cooperia; and mature Ostertagia females, Nematodirus, and Strongyloides. For immature Nematodirus, removals were 92% and 77% at the dosages of 6 and 12 mg/kg, respectively. Only a few specimens (av less than 100) of some other species or stages were found in the nontreated group and removal of them (at both dosages) were 94% to 100% for Ostertagia (immature and males), Strongyloides (immature), Oesophagostomum (immature), and Moniezia (mature); and 61% (at 6 mg/kg) and 100% (at 12 mg/kg) for Capillaria (mature), 0% for Trichuris (mature, at both dosages), and 67% (at 6 mg/kg) and 100% (at 12 mg/kg) for Oesophagostomum (mature).     

Anthelmintic activity of ivermectin against immature gastrointestinal nematodes of sheep

Twenty-four lambs of mixed breeding with mixed experimental infections of Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, and T colubriformis were allotted to 4 groups. One group (control) was given the vehicle propylene glycol, and the others were given 100, 200, or 300 micrograms of ivermectin/kg of body weight by mouth. Twelve days after treatment, the sheep were necropsied. The compound was greater than 99% effective against immature stages of 4 nematode species at all dosages, except at the 100 micrograms/kg dosage, where efficacy was 96% against H contortus.     

Controlled trials of the anthelmintic oxfendazole in ewes and lambs naturally infected with gastrointestinal nematodes.

Oxfendazole doses at a rate of 5 mg per kg, before or after lambing, reduced nematode egg output to insignificant levels in ewes, most of which were not exposed to re-infection. Ewes treated with oxfendazole had a significantly lower egg output than those treated with levamisole, although the latter anthelmintic was also highly effective. In lambs, oxfendazole at a dose rate of 5 mg per kg, showed 100 per cent efficacy for Ostertagia circumcincta, O trifurcata, Teledorsagia davtiani, Trichostrongylus axei, T vitrinus, T colubriformis, Nematodirus battus, N filicollis, immature Nematodirus, Chabertia ovina, and 93 per cent efficacy for Trichuris spp. Levamisole showed similar efficacies but did not remove Trichuris.     

Oxfendazole--anthelmintic activity in Egyptian goats artificially infected with gastrointestinal nematodes.

The recently developed benzimidazole anthelmintic, oxfendazole, was tested against artificial nematode infestations in Egyptian goats using oral dosing at 4.5 and 2.8 mg/kg. A 100% clearance of mature and immature Haemonchus contortus, Trichostrongylus axei, Ostertagia circumcincta, Coopera curticei, Bunostomum trigonocephalum and Chabertia ovina was obtained at the 4.5 mg/kg level. Very high levels of clearance against the mature worms were obtained at 2.8 mg/kg but the drug was less effective against immature worms at the lower dose rate. PCV, hemoglobin concentration and total erythrocyte counts declined after infection but became significantly (P less than 0.001) raised in treated animal.     

Feasibility of genus-specific real-time PCR for the differentiation of larvae from gastrointestinal nematodes of naturally infected sheep

Results of real-time PCR analysis of coproculture third stage larvae (L3) using genus specific TaqMan minor groove binder probes were compared with the results of morphological differentiation of L3 after coprocultured and direct morphological worm differentiation from gastrointestinal samples of eight sheep with naturally acquired nematodes infections. Faecal egg counts prior to postmortem confirmed infections with trichostrongyles with a geometric mean count of 4828 eggs per gram for all sheep. Individual egg counts correlated positively with total worm counts (correlation coefficient 0.794). Five different nematode species and one genus were found in the abomasi and small intestines: Cooperia curticei, Haemonchus contortus, Nematodirus spp., Teladorsagia (Ostertagia) circumcincta, Trichostrongylus axei and Trichostrongylus colubriformis. Coproculture of faecal eggs yielded five of these, Cooperia spp., Haemonchus spp., Ostertagia/Teladorsagia spp. and Trichostrongylus spp. Comparison between morphological L3 and worm differentiation data showed high congruence (94%). The agreement between PCR analysis of L3 after coproculture and direct morphological worm differentiation was 84%. Thus, real-time PCR was found to be suitable as a speedy and reliable diagnostic tool for the assessment of gastrointestinal nematode infections of ruminants in the field.     

Efficacy of oxfendazole against natural infestations of nematodes and cestodes in sheep in Egypt.

Oxfendazole liquid suspension (Systamex; Wellcome) was administered orally at the dose of 4.5 mg per kg to 800 indigenous Egyptian sheep clinically affected with Dictyocaulus filaria, Moniezia expansa, Haemonchus contortus, Ostertagia circumcincta, Nematodirus spp, Trichostrongylus axei, Cooperia curticei, Trichuris ovis and Oesophagostomum spp. A 100 per cent clearance was recorded for all parasites with the exception of T ovis which were markedly reduced in number.     

Controlled test of anthelmintic activity of a macrocyclic lactone (compound F28249-alpha) in lambs

A controlled blind test was performed in 1984 to evaluate the anthelmintic activity of experimental formulations of compound F28249-alpha against gastrointestinal parasites in lambs in Kentucky. Twenty-five lambs were allotted to 5 groups of 5 lambs/group. The drug was administered SC to 2 groups (A, 0.2 mg/kg of body weight; B, 0.3 mg/kg) and orally to 2 groups (C, 0.2 mg/kg; D, 0.3 mg/kg). Group E received a placebo subcutaneously. Lambs were euthanatized 7 days after treatment for necropsy and identification and enumeration of worm parasites in the gastrointestinal tract. Group-E lambs harbored 7 genera (including 10 species) of nematodes and 1 genus of tapeworms. Worm collection data for group-A lambs indicated 97% to 100% of the mature Haemonchus, Ostertagia, Trichostrongylus, and Trichuris, and immature Haemonchus were removed; and 23% to 73% of the mature Cooperia, Nematodirus, and Strongyloides, and immature Nematodirus were removed. In group-B lambs, 94% to 100% of the mature Haemonchus, Nematodirus, Ostertagia, Trichostrongylus, and Trichuris, and immature Haemonchus were removed as were 70% to 84% of mature Strongyloides and immature Nematodirus, respectively, and 0% for mature Cooperia. The percentage of all nematodes removed in group C and D was 100%, except for Cooperia (95%) in group C and immature Nematodirus (93% and 95%), respectively. Toxicosis was not apparent. Small fibrotic or blood streaked lesions were observed at necropsy in muscle at the injection site of 2 lambs in group B and 1 lamb in group E.     

Effect of copper oxide wire particle treatment on establishment of major gastrointestinal nematodes in lambs

Eighty-four 10-week-old lambs were used to investigate the effect of copper oxide wire particle treatment on the establishment of major gastrointestinal nematodes. They were maintained on pasture previously treated to minimise larval contamination. Five grams of uniform sized copper oxide wire particles were given orally five days before infection with either 20,000 Trichostrongylus colubriformis larvae, 20,000 Ostertagia circumcincta larvae or 3000 Haemonchus contortus larvae given as three doses at three-day intervals. The animals were slaughtered 21 or 22 days after the last infective dose. Parasite burdens in the lambs treated with copper oxide wire particles were reduced by 96 per cent in the case of H contortus and by 56 per cent in the case of O circumcincta compared to burdens in controls. There was no significant effect of copper particles on the establishment of T colubriformis.     

Cryopreservation of some common nematodes of ruminants for up to 11,3 years

Infective larvae of selected batched of the following nematode species from sheep and cattle were examined for survival and infectivity (by injection into either the abomasum, the duodenum, or the jugular vein) after having been stored in liquid nitrogen for 103-136 months: Haemonchus contortus, Haemonchus placei, Ostertagia circumcincta, Ostertagia ostertagi, Marshallagia marshalli, Cooperia spp., Trichostrongylus axei, Trichostrongylus colubriformis, Trichostrongylus falculatus, Nematodirus spathiger, Nematodirus helvetianus, Oesophagostomum columbianum, Oesophagostomum radiatum, Chabertia ovina and Dictyocaulus filaria. Excluding D. filaria, a mean of 97.7% of the ovine and 96.0% of the bovine nematode larvae were alive when thawed. Compared with previous investigations in this series, little or no reduction occurred with time in either the survival or the viability of the nematodes from cattle, or in the survival of those from sheep. In contrast, the larvae developed poorly in sheep, possibly owing to parenteral treatment of the animals with ivermectin at a dosage of 0.4 mg kg-1, either 6 or 8 days before they were infected.     

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.     

Further tests of activity of levamisole on Ostertagia ostertagi in dairy calves with notes on overwinter survival of gastrointestinal helminths on pasture

Two controlled tests were conducted in 1981 and 1982 in dairy calves on the University of Kentucky research farm to determine activity of the bolus formulation of levamisole given at the dose rate of 8 mg/kg against naturally occurring infections of Ostertagia ostertagi. Removal efficacies of mature O ostertagi were 98% in the 1981 test (3 treated and 3 nontreated calves) and 94% in the 1982 test (7 treated and 8 nontreated calves). Against immature Ostertagia spp, removal efficacies were 100% and 65% for the 1st and 2nd tests, respectively. The calves were grazed on the same pasture as dairy calves in previous controlled tests in 1979 and 1980 where activity of levamisole against mature O ostertagi (data recently published) was much less than in the present tests. It does not appear that the poor performance in the early tests can be attributed to the drug resistance phenomenon. Data on overwinter survival (119 days) of free-living stages of gastrointestinal parasites on pasture were derived from the nontreated calves in the 1982 controlled test. The calves, raised helminth-free, were placed on the pasture on Apr 5, 1982. Helminths recovered at necropsy of the calves, besides O ostertagi, included Trichostrongylus axei, Nematodirus helvetianus, Nematodirus spp, Cooperia oncophora, Trichuris spp, and Moniezia spp. The lung-worm, Dictyocaulus viviparus, previously found in cattle on the farm, was not found in these calves.     

THE ANTHELMINTIC EFFICIENCY OF LAEVO-TETRAMISOLE HYDROCHLORIDE AGAINST NEMATODE PARASITES OF SHEEP AND CATTLE

Critical anthelmintic tests and controlled trials were used to assess the efficiency of laevo -tetramisole hydrochloride against nematode infections in sheep and cattle.
In sheep, oral dose rates of 5 mg/kg and above were 94 to 100% effective against adult Haemonchus contortus , intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbianum, O. venulosum and Chabertia ovina . A dose rate of 7.5 mg/kg was required for consistently high activity against Ostertagia spp, but activity against Trichostrongylus axei remained variable at this dose level. Efficiency against Trichuris ovis ranged from 76 to 100% at a dose rate of 10 mg/kg. The drug was 94 to 100% effective against 7-day old and 14-day old H. contortus , intestinal Trichostrongylus spp and O. colun bianum infections, and 83 to 89% effective against 14-day old Ostertagia spp and T. axei , at a dose rate of 5 mg/kg. Seven-day old Ostertagia spp larvae were highly resistant at a dose rate of 10 mg/kg, while activity against T. axei infections of the same age appeared variable at 5 and 10 mg/kg.
In cattle, subcutaneous treatment at dose rates of 1.5 mg/kg and above, and oral treatment at 7.5 mg/kg, were 93 to 100% effective against adult Haemonchus placei , intestinal Trichostrongylus spp, Nematodirus helvetianus, Cooperia spp and Oesophagostomum radiatum , and 84 to 98% effective against Ostertagia ostertagi . Against Trichostrongylus axei , a rate of 5 mg/kg subcutaneously was 83% effective, and a rate of 7.5 mg/kg orally 97% effective, while these dose rates gave 88 to 100% clearance of adult Dictyocaulus viviparous .     

Field observations on the epidemiology of abomasal parasites in young sheep during winter and spring.

A flock of spring born lambs was continuously exposed to natural parasite infection from birth until selected for slaughter in groups of two or three, at monthly intervals throughout winter and spring for abomasal worm counts. Meteorological data were recorded and regular estimates of infective pasture larval availability were made. Parasite population changes and inhibition patterns for Ostertagia spp, Haemonchus contortus and Trichostrongylus axei were recorded. Ostertagia spp were found to survive well both on the pasture and within the host, principally as arrested larvae. H contortus overwintered almost entirely in the host in the inhibited form and T axei overwintered mainly in the host, but in the adult stage.     

Studies on Haemonchus contortus. II. The effect of abomasal nematodes on subsequent challenge with H. contortus

Fifty-thousand infective larvae of Trichostrongylus axei dosed to 7-9-month-old Merinos protected them against a subsequent challenge with 50 000 infective larvae of Haemonchus contortus. Protection varied with the period between an initial dosage of T. axei and challenge with H. contortus as follows: After 90 days it was more than 80% effective in more than 80% of sheep; at 119 and 180 days there was still a significant reduction in the numbers of H. contortus recovered (P < 0,05 and P < 0,001, respectively). Prior infestation with either Ostertagia circumcincta or with Haemonchus placei was ineffective against challenge with H. contortus.     

Stocking rate effects on the worm burdens of Angora goats and Merino sheep

Worm egg counts of yearling Angora or Merino wethers grazing in mixed flocks at either 4/ha or 8/ha were observed over a 5 month period. Based on faecal egg counts infection levels in the sheep increased for the first 3 months and then decreased as the animals developed resistance. Egg counts in the goats did not decrease during the experiment. Post mortem worm counts indicated that there was a significant host species--stocking rate interaction on worm burdens of Haemonchus contortus adults and Ostertagia circumcincta adults and larvae. Goats had more H. contortus and O. circumcincta adults than sheep at the 8/ha stocking rate. At 4/ha goats had fewer O. circumcincta fourth stage larvae than sheep. There was no stocking rate effect on the numbers of Trichostrongylus axei or T. colubriformis. Sheep had more T. axei and fewer T. colubriformis than goats.     

The survival of nematodes and cestodes of sheep in the pasture during the winter in eastern Norway

Using 21 worm-free lambs in paddocks on old sheep pastures on 4 farms near Oslo, it was found that Nematodirus spp., Ostertagia spp. and Moniezia spp. were the only helminths which could survive the winter in the pasture in great numbers. A few Teladorsagia davtiani, Chabertia ovina, Trichuris ovis, Cooperia onchophora and Skrjabinema ovis survived the winter. Trichostrongylus axei, T. vitrinus and Oesophagostomum venulosnm showed a negligible ability to survive the winter in the pasture. The following species were never found to survive: Haemonchus contortus, Trichostrongylus colubriformis, Bunostomum trigonocephalum, Cooperia curticei and Strongyloides papillosus.     

Controlled dosage titration of febantel paste in naturally parasitized cattle

A controlled anthelmintic trial was conducted to determine the efficacy of febantel paste (45.5%) at dosages of 2.5, 5.0, 7.5, and 10.0 mg/kg in calves harboring natural gastrointestinal nematode infections. Dosages of 5.0, 7.5 and 10.0 mg of febantel/kg of body weight were greater than 96% effective in removing adults of Haemonchus contortus, Ostertagia spp, Cooperia spp, and Oesophagostomum radiatum. The 2.5 mg/kg dosage was considered suboptimal because of low efficacy against Ostertagia and Cooperia spp. Efficacies against Trichostronglylus axei, Trichuris spp, Bunostomum phlebotomum, and Stronglyloides papillosus were difficult to determine because fewer numbers of these nematodes were recovered. Efficacies of febantel paste against immature bovine parasites ranged from 83.62% to 97.72%.     

Removal of Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus spp. from goats, by morantel citrate, levamisole hydrochloride, fenbendazole, and oxfendazole

Young feral goats harbouring 3, 7 and 36 day old experimental infections of strains of gastrointestinal nematodes, known to be susceptible to anthelmintics in sheep, were dosed orally with commercially available anthelmintics at the manufacturers' recommended rates for sheep. The drugs and overall removals of Ostertagia circumcincta and Trichostrongylus spp. (T. colubriformis and T. vitrinus) respectively were: morantel citrate 69% and 68%; levamisole hydrochloride 55% and >99%; fenbendazole 98.5% and >99%; oxfendazole >99% and >99%. Results for Haemonchus contortus, while not inconsistent with high efficacy for all four drugs, must be interpreted with caution, in view of the erratic establishment of this worm in the controls.     

Seasonal changes in the abomasal nematodes of naturally infected ewes in Moulay-Bouazza (Morocco)

The nematode populations of 93 abomasa of ewes from Middle-Atlas (Morocco) were studied over a period of 3 years. The main species present were Ostertagia circumcincta, Marshallagia marshalli, Trichostrongylus axei and T. vitrinus; less frequent species were O. ostertagi and O. trifurcata. Two peaks of infection were recorded, 1 at the end of winter or the beginning of spring (February--March), and another in autumn (September). The first population peak consisted mostly of O. circumcincta and T. axei, and the second population peak, in autumn, had a high prevalence of M. marshalli and T. vitrinus.