Ivermectin Controlled-release Capsule Research Articles

Prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (Chrysomya bezziana) infestation.

To determine the prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (OWS) myiases for potential use in screwworm containment and eradication programs. The longevity of protection provided by six insecticidal formulations (subcutaneous ivermectin, doramectin and abamectin, a topically applied aqueous formulation of spinosad, ivermectin controlled-release capsule and a dicyclanil spray-on formulation) was tested using implants of 1st-instar OWS larvae on Javanese thin-tail sheep. Therapeutic efficacy of four formulations (topical ivermectin, chlorfenvinphos/cypermethrin mixture, aerosol spinosad formulation and a formulation containing propetamphos and eucalyptus oil) was tested against 2- and 4-day-old OWS strikes. Both the ivermectin capsule and dicyclanil spray-on formulation gave 100% protection against screwworm implants for the full 12 weeks of the study. Ivermectin, doramectin and abamectin administered SC all gave 100% protection at 3 days post-treatment, but at 2 weeks the protection had become incomplete. Spinosad dipping did not give complete protection at any time. All four therapeutic treatments gave complete resolution of 2-day-old strikes and topical ivermectin, spinosad and chlorfenvinphos/cypermethrin, but not the propetamphos/eucalyptus oil formulation, gave complete resolution of all 4-day-old strikes. Dicyclanil spray-on and ivermectin capsule formulations, both registered for use in sheep, but not for cattle or other livestock species, gave much longer protection against screwworm implants than the currently recommended SC ivermectin. Pre-emptive action to facilitate rapid deployment of these formulations in the event of a screwworm incursion is urgently needed.

Association between nematode larvae and “low worm egg count diarrhoea” in sheep in Western Australia

Nine flocks of sheep with a high prevalence (>30%) of diarrhoea and severe breech faecal soiling were investigated over a three-year period to examine the causes of diarrhoea in sheep with low mean faecal worm egg counts (WEC). All nine flocks were located in the southwest of Western Australia in areas with a winter rainfall pattern (Mediterranean climate). There was no difference ( p = 0.304) in WEC of diarrhoeic sheep (loose faeces and severe breech faecal soiling) and “normal sheep” (pelleted faeces and mild or no breech faecal soiling). Teladorsagia ( Ostertagia) circumcincta and Trichostrongylus spp. were the nematodes most commonly identified by total worm counts and differentiation of larvae recovered from faeces and pasture. Larval stages of strongyle worms accounted for the largest proportion of total worm counts in both diarrhoeic and normal sheep. Adult worm burdens were small in most sheep. Diarrhoeic sheep had higher numbers of fourth stage larvae than normal sheep ( p = 0.046). There was no histopathological evidence of bacterial or viral causes of diarrhoea in any of the flocks or bacteriological evidence of bacterial infections associated with diarrhoea. Two flocks had marginal selenium glutathione peroxidase (selenium) levels. One flock was diagnosed with helminthosis based on rising WEC and high total worm counts. Larval hypersensitivity diarrhoea, nutritional factors or a combination of these two factors were the most likely causes of diarrhoea in the other eight flocks based on exclusion of other known causes of diarrhoea. Treatment with moxidectin and an ivermectin controlled-release capsule did not change faecal moisture content of treated sheep compared to untreated sheep three to five weeks after treatment. The findings suggest that the immune response to strongyle larvae may explain some cases of low WEC diarrhoea observed during winter–spring in immunocompetent mature sheep grazing in Mediterranean environments.

Effects of Psoroptes ovis infection and its control with an ivermectin controlled-release capsule on growing sheep : 1. Evaluation of weight gain, feed consumption and carcass value

To evaluate the prophylactic and therapeutic effects of an ivermectin controlled-release capsule (IVM-CRC) on the productivity of growing sheep infested with Psoroptes ovis 24 male and 24 female Merino landrace lambs, 5–6 months old and weighing 21.2–35.0 kg, were used. Sixteen replicates of three animals were formed based on sex and Day 0 body weight. Within each replicate animals were randomly allocated to one of three groups: untreated control; IVM-CRC on Day 0; IVM-CRC on Day 84. For treatment an IVM-CRC for sheep weighing 20–45 kg was used which is designed to deliver ivermectin at a minimum dose of 20 μg/kg per day for 100 days. The lambs were infested with 50–60 P. ovis mites each on Days 14 and 21. Mites in skin scrapings were counted on Days 70, 84, 98, 112 and 126. Body weight and feed consumption were measured every 2 weeks from Day 0 to 126. The animals were slaughtered on Day 127 and their carcasses evaluated. The IVM-CRC treatment on Day 0 prevented the establishment of P. ovis. All untreated lambs became infested. The lambs treated with an IVM-CRC on Day 84 became mite-free from Day 112 onwards. The lambs treated on Day 0 had significantly ( p<0.05) greater body weight gain from Day 0 to 84 (13.9 kg) and Day 0 to 126 (20.9 kg) than the untreated controls (9.6 and 12.8 kg, respectively) and the sheep treated on Day 84 (8.4 and 14.9 kg, respectively). Feed consumption (Days 0–126) for sheep treated with the IVM-CRC on Day 0 was higher than for sheep treated on Day 84 ( p<0.05) and for the untreated controls ( p<0.1). The carcasses of sheep treated with the IVM-CRC on Day 0 had significantly ( p<0.05) higher warm and cold weights, carcass yield, rib eye area and back fat thickness than the untreated control group and the sheep treated with the IVM-CRC on Day 84. The sheep treated with the ivermectin CRC on either Day 0 or 84 had significantly ( p<0.05) better muscle scores and lower muscle pH 1 h post-slaughter than the untreated controls. There was no significant ( p>0.1) difference between warm and cold carcass weights, carcass yield and rib eye area between sheep treated on Day 84 and untreated controls.

Effects of Psoroptes ovis infection and its control with an ivermectin controlled-release capsule on growing sheep : 2. Evaluation of wool production and leather value

To evaluate the prophylactic and therapeutic effects of an ivermectin controlled-release capsule (IVM-CRC) on the productivity of growing sheep infested with Psoroptes ovis 24 male and 24 female Merino landrace lambs, 5–6 months old and weighing 21.2–35.0 kg, were used. Sixteen replicates of three animals were formed based on sex and Day 0 body weight. Within each replicate animals were randomly allocated to one of three groups: untreated control; IVM-CRC on Day 0; IVM-CRC on Day 84. For treatment an IVM-CRC for sheep weighing 20–45 kg was used which is designed to deliver ivermectin at a minimum dose of 20 μg/kg/day for 100 days. The lambs were infested with 50–60 P. ovis mites each on days 14 and 21. The animals were shorn on Day 126. After slaughter on Day 127 the quality of the leather produced from their skins was evaluated. The IVM-CRC treatment on Day 0 prevented the establishment of P. ovis. All untreated lambs became infested. The lambs treated with an IVM-CRC on Day 84 became mite-free from Day 112 onwards. The lambs which were treated on Day 0 had significantly ( p<0.05) greater clean fleece weight (1.5 kg) and fleece yield (52.1%) than the untreated controls (0.9 kg and 34.1%, respectively) or than lambs treated on Day 84 (1.0 kg and 47.8%, respectively). Clean fleece weight and fleece yield were in the tendency ( p=0.055) or significantly ( p<0.001) greater, respectively, for lambs treated on Day 84 than for the untreated controls. The chrome tanned dried crust leather of all untreated controls and six of the 16 lambs treated on Day 84 showed grain surface defects such as discolourations, indurations and coarse, pitted grain. The useful (defect-free) leather size was significantly ( p<0.01) higher for the lambs treated on Day 0 (100%) than for the lambs treated on Day 84 (82.7%) and the untreated controls (7.8%). The physical testing revealed that the leather of sheep treated on Day 0 had significantly ( p<0.05) higher thickness, elongation break and tear resistance than the leather of both untreated controls and sheep treated on Day 84. There were no significant differences in the physical characteristics of the leather of the untreated controls and the sheep treated on Day 84.

Efficacy of an ivermectin controlled-release capsule against some rarer nematode parasites of sheep

A controlled trial was conducted to evaluate the efficacy of the intraruminal ivermectin controlled-release capsule (CRC) (IVOMEC ® Maximizer ™ CR Capsule for Sheep, Merial Ltd.) against induced incoming third-stage larvae and established adult infections with some rarer gastrointestinal nematode parasites of sheep. Twenty-one worm-free lambs were allocated by restricted randomisation based on body weight within sex to one of the following treatments: unmedicated control, ivermectin CRC given on Day 0 prior to induced infection, and ivermectin CRC given on Day 70 after establishment of induced infection. The ivermectin CRC delivers ivermectin at a minimum dose rate of 20 μg/kg/day for 100 days. Infections were induced by daily administration of third-stage larvae for five consecutive days. Nematodes were counted on Day 84, 14 days after treatment of established infection. The treatment with the ivermectin CRC prevented the establishment of Ostertagia leptospicularis, O. ostertagi, Bunostomum trigonocephalum, Cooperia oncophora, C. punctata, C. surnabada, Nematodirus helvetianus, N. roscidus and Strongyloides papillosus by >99% as compared with the untreated controls ( p < 0.01). The administration of the ivermectin CRC reduced established adult infections of O. ostertagi, B. trigonocephalum, C. oncophora, C. punctata, C. surnabada, N. roscidus and S. papillosus by >99% ( p < 0.01), and reduced established adult infections of O. leptospicularis and N. helvetianus by 96.5 and 98.4% ( p < 0.01), respectively.

Evaluation of the anthelmintic efficacy of an ivermectin controlled-release capsule in lambs under field conditions in Europe

Three field trials were conducted in Germany, Slovakia and UK to evaluate the anthelmintic efficacy and productivity responses attributable to treatment of lambs with an intra-ruminal controlled-release capsule which is designed to deliver ivermectin at 0.8 mg/day for 100 days to lambs weighing 20–40 kg at treatment. Sixty Merino Landrace, 60 Valaška or 52 Suffolk cross lambs weighing between 24.0 and 40.0 kg at the time of treatment were used. Lambs were either untreated (or subjected to salvage treatment) or they received an ivermectin controlled-release capsule. Faecal egg and larval counts of various nematodes, body weights and scores of the faecal soiling of the breech area (formation of dags) were determined before treatment and at 28, 56, 84, 98 and 112 days after treatment. Before treatment, faecal strongyle, Nematodirus and Trichuris egg counts and Dictyocaulus filaria larval counts were not significantly different ( P > 0.05 or P > 0.1) between groups, but at each point of time thereafter, egg and larval counts of the ivermectin controlled-capsule treated lambs were significantly reduced compared to the untreated controls. Lambs treated with the ivermectin controlled-release capsule gained significantly more weight (10.9, 11.1 or 11.1 kg, respectively) over the 112 days of the trials compared to untreated lambs (8.2, 9.7 or 5.5 kg, respectively). The mean scores of faecal soiling were not different at the start of the trials ( P > 0.05 or P > 0.1), but at the end of the trials, the ivermectin controlled-release capsule treated lambs had significantly lower scores of faecal soiling than the controls.

Efficacy of ivermectin in a controlled release formulation against Psoroptes ovis (hering, 1838) gervais, 1841 (acari: psoroptidae) on sheep

Three trials including 42 sheep were conducted in Brazil or Germany to evaluate the therapeutic (two trials) and prophylactic (one trial) efficacy of an ivermectin controlled release capsule (CRC) against Psoroptes ovis infestation. In one therapeutic trial naturally infested sheep were used while in the other trials infestations were experimentally induced. In each trial half of the animals were treated on Day 0 with one ivermectin controlled release capsule that delivers ivermectin at a rate of 1.6 mg/day for approximately 100 days, that is 20 mcg/kg/day to a 80 kg animal, while the other half remained untreated. In both therapeutic trials mites were counted in skin scrapings and their presence was recorded at predilection sites one day before treatment and at weekly intervals from Day 7 to Day 56. In the trial conducted to evaluate the prophylactic efficacy the sheep were experimentally infested with P. ovis 21 and 28 days post-treatment and mites were counted and recorded at predilection sites on Days 42, 49 and 56. The ivermectin controlled release capsule was completely effective in eliminating the P. ovis mites within 28 days of administration and it prevented the establishment of an infestation of P. ovis induced 21 and 28 days after administration.

Efficacy of ivermectin in a controlled-release capsule for the control of breech strike in sheep.

To investigate the efficacy of ivermectin in an intraruminal controlled-release capsule (CRC) against blowfly strike. Pen and field trials with controls. Pen studies: Two breech strike trials involving 60 Romney and 60 Merino sheep. One body strike trial using 100 Merino sheep. Field trials: Eight trials in New Zealand used 1000 Romney and Romney-cross sheep. Fifty Merino lambs in one trial in Australia. Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that delivered ivermectin at > or = 20 micrograms/kg/day for 100 days. In the breech strike trials, each animal was given an oral laxative 2 days before exposure to adult Lucilia cuprina. In the body-strike trial, the sheep sheep were kept wet to increase susceptibility prior to the release of blowflies. Field trials: Fifty or 200 sheep allocated to equal groups of nontreated or treated with the CRC and grazed at pasture exposed to natural blowfly challenge. Pen studies: Breech strikes developed in 24 of 60 controls but in none of 60 CRC-treated sheep. There was a 35% reduction in the number of CRC-treated sheep struck on the body. Field trials: The average number of breech strikes in CRC-treated sheep was reduced by 86% (P < 0.001). The number of body strikes in the treated groups was a reduced by 27% (P < 0.05). The ivermectin CRC is a useful aid in controlling breech strike, but provides only moderate reduction in the incidence of body strike.

Efficacy of an ivermectin controlled-release capsule against nematode and arthropod endoparasites in sheep

Five controlled trials were conducted in Germany or in the United Kingdom, using 74 female sheep of merino or Dorset horn breeds, to evaluate the efficacy of an ivermectin controlled-release...

Demonstration of the sustained anthelmintic activity of a controlled-release capsule formulation of ivermectin in ewes under field conditions in New Zealand

Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy of an intraruminal controlled-release capsule formulation of ivermectin. A total of 810 Coopworth, Perendale, Romney or Coopworth Romney ewes, weighing on average 42–70 kg, were used. Ewes were either untreated or treated shortly before lambing in late winter-early spring (eight trials) or in late spring (two trials) with an ivermectin controlled-release capsule which delivers ivermectin at 1.6 mg per day for 100 days (minimum dose rate 20𝛍g/kg/day). Bodyweights, faecal nematode egg counts and dag scores were determined before treatment and at about 2 and/or 4, 6 or 8, 10 or 12, 14 and 16 weeks after treatment. Ewes treated with the ivermectin controlled-release capsule gained on average I.I kg more than untreated sheep over the 16 weeks of the trials, but this difference was not significant (p > 0.10). Before treatment, faecal strongylid egg counts were equivalent (p > 0.10), but at each time point thereafter, egg counts in ivermectin controlled-release capsule treated sheep were significantly lower (p < 0.01 ; p < 0.05 at Week 2). Dag scores were not different at the start of the trial (p > 0.10), but at the end of the trial ivermectin controlled-release capsule treated ewes had significantly lower scores (p < 0.01 ) than untreated ewes. These findings indicated that treated animals shed significantly fewer nematode eggs and therefore pasture contamination with nematode eggs should be significantly reduced for at least 112 days. The control of dags should result in reduced direct losses due to the decreased value of dag wool, and indirect losses due to the cost of dagging sheep and the cost associated with the treatment and control of flystrike initiated by dags in the breech area.

Demonstration of the sustained anthelmintic efficacy of a controlled-release capsule formulation of ivermectin in weaner lambs under field conditions in New Zealand

Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy and production responses attributable to treatment of weaner lambs with an intra-ruminal controlled-release capsule formulation of ivermectin. A total of 800 Coopworth, Perendale and Romney lambs weighing on average 20.8–34.8 kg were used. Lambs were either untreated or treated shortly after weaning with an ivermectin controlled-release capsule which delivers ivermectin at 0.8 mg per day for 100 days (minimum dose rate 20 𝛍g/kg/day). Bodyweights, faecal nematode egg counts and dag scores (assessment of faecal soiling in the breech area) were determined before treatment and at about 4, 8, 12, 14 and 16 weeks after treatment. Sheep treated with the ivermectin capsule gained significantly more weight (11.6 kg) over the 16 weeks of the trials compared to untreated sheep (7.3 kg) (p < 0.01). Before treatment, faecal strongylid and Nematodirus spp. egg counts were equivalent (p > 0.10) but, at each time point thereafter, egg counts in ivermectin capsule-treated sheep were significantly lower (p < 0.01 or p < 0.05). Dag scores were not different at the start of the trial (p > 0.10), but at the end of the trial control sheep had significantly greater dags (p < 0.05) than sheep treated with the ivermectin capsule. These findings indicate that treated animals contributed significantly fewer nematode eggs to the contamination of pasture and therefore pasture contamination should be significantly reduced for at least 112 days. The productivity of the ivermectin capsule-treated sheep over the 16 weeks of the trials was also significantly increased compared to salvage-treated controls. Furthermore, the presence of dags, which predispose sheep to blowfly strike in the breech area and result in production losses due to the costs of dagging and downgrading of breech wool, were also significantly (p < 0.05) reduced in the ivermectin capsule-treated sheep.

Control of gastro-intestinal parasitism in sheep with ivermectin delivered via an intraruminal controlled-release capsule

The efficacy of ivermectin delivered by an intraruminal controlled-release capsule against gastro-intestinal nematodes of sheep was evaluated under controlled conditions. In seven Australian studies involving 170 Merino or Merino × Border Leicester sheep, intraruminal capsules developed for 20–40 kg or 40–80 kg sheep, and delivering 0.8 or 1.6 mg of ivermectin/day respectively for 100 days (minimum dose 20 μg/kg/day), were evaluated. Studies were designed to test the therapeutic efficacy against naturally acquired and induced infections treated at the adult and fourth larval stage, and the prophylactic efficacy against naturally acquired and induced infections with third stage infective larvae. The predominant pathogenic nematodes of sheep were represented. Two studies included known benzimidazole- and levamisole-resistant nematode strains. Sheep were necropsied for total nematode counts 21–8.5 days after treatment. The efficacy of the ivermectin controlled-release capsule was generally >99% against all nematode species tested, including those confirmed to be benzimidazole- and levamisole-resistant. High therapeutic activity was demonstrated against existing adult and fourth larval stage nematode infections at the time of treatment, and high prophylactic efficacy was shown against incoming third stage larvae of all species and strains tested.