Control of Boophilus annulatus (Acari: Ixodidae) on cattle using injectable microspheres containing ivermectin.
ABSTRACT The efficacy of an injectable microsphere formulation of ivermectin for control of the cattle tick, Boophilus annulatus (Say), was tested on 2 groups of 6 Hereford heifers held on separate 7-ha, tick-infested, buffel grass pastures. Cattle in one pasture were injected subcutaneously in the neck with a controlled-release microsphere formulation of ivermectin at the rate of 2.4 mg AI/kg body weight; the other group was injected with carrier only. Beginning 4 wk after injection and continuing throughout the remainder of the test (16 wk), no engorged ticks (> or = 5.5 mm) were found on any of the treated cattle, whereas large numbers of engorged ticks were found on the untreated controls. During this period, a few ticks were recovered from untreated sentinel animals placed in the treatment pasture during 7-8 wk after treatment, but none were recovered from animals exposed from 11-12 wk or 14-15 wk. Large numbers of B. annulatus ticks were found on untreated sentinel cattle placed in the control pasture during these same periods. Although the cattle, pastures, and tick habitat were approximately equal, the treated cattle gained an average of 77 kg compared with an average of 42 kg for the control group. This technology offers a possible alternative to the current official program of dipping and vacating pastures for eradication of Boophilus sp. infestations from the quarantine zone in southern Texas. Larger scale testing is needed to determine the potential of the injectable microsphere formulation and to optimize its use in eradication or control strategies.
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ABSTRACT: The efficacy of eprinomectin in an extended-release injection (ERI) formulation was evaluated against infections with third-stage larvae or eggs of gastrointestinal and pulmonary nematodes in cattle under 120-day natural challenge conditions in a series of five studies conducted in the USA (three studies) and in Europe (two studies). For each study, 30 nematode-free (four studies) or 30 cattle harboring naturally acquired nematode infections (one study) were included. The cattle were of various breeds or crosses, weighed 107.5-273kg prior to treatment and aged approximately 4-11 months. For each study, animals were blocked based on pre-treatment bodyweight and then randomly allocated to treatment: ERI vehicle (control) at 1mL/50kg bodyweight or Eprinomectin 5% (w/v) ERI at 1mL/50kg bodyweight (1.0mg eprinomectin/kg) for a total of 15 and 15 animals in each group. Treatments were administered once on Day 0 by subcutaneous injection in front of the shoulder. In each study, all animals grazed one naturally contaminated pasture for 120 days. At regular intervals during the studies, fecal samples from all cattle were examined for nematode egg and larval counts. In four studies pairs of tracer cattle were used to monitor pasture infectivity at 28-day intervals before and/or during the grazing period. All calves were weighed before turnout onto pasture and at regular intervals until housing on Day 120. For parasite recovery, all study animals were humanely euthanized 27-30 days after removal from pasture. Cattle treated with Eprinomectin ERI had significantly (p<0.05) fewer strongylid eggs (≤1 egg per gram; egg count reduction≥94%) than the control cattle and zero lungworm larvae at each post-treatment time point. At euthanasia, cattle treated with Eprinomectin ERI had significantly (p<0.05) fewer of the following nematodes than the ERI vehicle-treated (control) cattle with overall reduction of nematode counts by >92%: Dictyocaulus viviparus (adults and fourth-stage larvae (L4), Bunostomum phlebotomum, Cooperia curticei, Cooperia oncophora, Cooperia punctata, Cooperia surnabada, Cooperia spp. inhibited L4, Haemonchus contortus, Haemonchus placei, Haemonchus spp. inhibited L4, Nematodirus helvetianus, Nematodirus spp. inhibited L4, Oesophagostomum radiatum, Oesophagostomum spp. inhibited L4, Ostertagia leptospicularis, Ostertagia lyrata, Ostertagia ostertagi, Ostertagia spp. inhibited L4, Trichostrongylus axei, Trichostrongylus colubriformis, Trichostrongylus spp. inhibited L4, Trichuris discolor, and Trichuris ovis. Over the 120-day grazing period, Eprinomectin ERI-treated cattle gained between 4.8kg and 31kg more weight than the controls. This weight gain advantage was significant (p<0.05) in three studies. All animals accepted the treatment well. No adverse reaction to treatment was observed in any animal in any study.Veterinary Parasitology 12/2012; · 2.38 Impact Factor
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ABSTRACT: The therapeutic and persistent efficacy of a single subcutaneous injection of a long-acting formulation of moxidectin at a concentration of 1 mg/kg body weight was determined against Rhipicephalus (Boophilus) microplus (Canestrini), along with the concentration-time blood sera profile in treated cattle. The therapeutic efficacy against ticks of all parasitic stages on cattle at the time of treatment was >99.9%, and the mean tick number, index of fecundity, engorgement weight, and egg mass weight of ticks recovered from treated animals were all significantly lower than ticks from untreated animals. The index of fecundity, engorgement weight of females, and egg mass weight of ticks recovered from treated animals infested at weekly (7-d) intervals between 14 and 63 d posttreatment were significantly lower than for ticks on untreated animals, whereas the number of ticks per animal recovered from treated cattle remained lower than that of untreated cattle for up to 49 d posttreatment. The percentage control remained >99% at weekly intervals between 14 and 49 d posttreatment, which is the minimum level of efficacy considered acceptable for use in the United States Cattle Fever Tick Eradication Program. The serum concentration of moxidectin in treated cattle increased to 25.6 ppb (parts per billion) within 1 d after treatment, and peaked at 47.3 ppb at 8 d posttreatment. Moxidectin sera levels remained above the estimated 100% threshold level for elimination of feeding ticks (5-8 ppb) for 44-53 d after treatment. The label claim of 50 d of prevention against reinfestation for the long-acting moxidectin formulation used in the study was supported by the efficacy and sera concentration data obtained. Based on these results, cattle could be treated at 63-d intervals with minimal risk of viable ticks detaching from treated animals. This treatment interval would be 4.5-fold longer than the presently required treatment interval of 14 d, thus leading to approximately 75% reduction in gathering and handling costs of cattle incurred by producers.Journal of Medical Entomology 03/2011; 48(2):314-21. · 1.86 Impact Factor
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ABSTRACT: Analysis of doramectin concentration in blood serum of pastured cattle injected repeatedly (12 treatments) at two different dosage rates and 28-day intervals throughout the year was used to predict the probability that cattle fever ticks could successfully feed to repletion during the interval between any two consecutive treatments. Treatment at ~270 μg/kg indicated that serum doramectin concentration dropped below the baseline concentration estimated for tick survival (8 ppb) in 7 of the 12 treatments. However, the longest period between any two treatments during which the doramectin concentration remained below the 8 ppb baseline level for successful tick feeding was 15 days, making it virtually impossible for any ticks to reach ovipositional status prior to a subsequent treatment. At a dosage rate of ~540 μg/kg, the concentration dropped below the baseline tick survival level (8 ppb) only once, following the initial treatment, and the duration during which the concentration remained below the baseline level prior to the subsequent treatment was only 6 days. Thus, at the high dosage rate results indicated, with absolute certainty, that no ticks could successfully feed to repletion between any two consecutive treatments. Based on the data obtained in the study it was concluded that analysis of doramectin concentration in serum of treated animals would be a reliable predictor for assessing the probability that ticks could successfully develop to repletion. More importantly, results demonstrated that the trial policy, instituted by the Cattle Fever Tick Eradication Program, of repeatedly treating cattle with doramectin injections at 25-28 day intervals for eliminating cattle fever ticks would produce little or no risk of any viable ticks developing to repletion and re-infesting the field between treatment applications.Experimental and Applied Acarology 02/2012; 56(4):365-74. · 1.85 Impact Factor