USDA, ARS, SPA, Cattle Fever Tick Research Lab., Moore Air Base, Bldg. 6419, Edinburg, TX 78541, USA.
Vet Parasitol. 2010 Apr 19;169(1-2):149-56. doi: 10.1016/j.vetpar.2009.12.040. Epub 2010 Jan 7.
The concentration-time profile, therapeutic, and persistent efficacy of a single subcutaneous injection of cattle with a long-acting (LA) formulation of ivermectin at a concentration of 630microg/kg of body weight were determined against Rhipicephalus (Boophilus) microplus. Ivermectin sera concentration in treated cattle increased to 13.0ppb within 1d after treatment, and peaked at 26.2ppb at 11d post-treatment. Ivermectin sera levels remained above the threshold level for control of feeding ticks (>or=8ppb) for 42.6d after treatment. Therapeutic efficacy of ticks on treated animals was >99.9%, and tick number, index of fecundity, engorgement weight, and egg mass weight of ticks from treated animals remained dramatically less than ticks from untreated animals. Tick number and reproductive capacity of ticks infested on treated animals at 14 and 28d post-treatment were less than for ticks on untreated animals, whereas engorgement weight and egg mass weight of treated ticks remained lower than that of untreated ticks 49d post-treatment. However, the level of control against ticks infested at 14d after treatment (99.9%) was the only post-treatment infestation interval that provided the required 99% control necessary for use in the U.S. tick eradication program. The 14d post-treatment infestation was also the only interval at which infested ticks were exposed to ivermectin levels above the threshold level of 8ppb for the entire parasitic development period. Cattle would have to be treated at intervals of no more than 31d apart to ensure that no viable ticks could reach repletion and detach from the host. Although this treatment interval is >2-fold longer than the present treatment requirement (14d), it is dramatically less than the label claim for the LA ivermectin formulation of 75d of prevention against re-infestation.
单次皮下注射 630μg/kg 体重的长效（LA）伊维菌素对牛皮蝇蚴（Boophilus）微小亚种的浓度-时间曲线、治疗效果和持续效果进行了评估。治疗后第 1 天，牛血清伊维菌素浓度增加至 13.0ppb，第 11 天达到 26.2ppb。治疗后 42.6 天，牛血清伊维菌素水平仍高于控制采食的临界值（≥8ppb）。治疗动物的蜱虫治疗效果＞99.9%，并且治疗动物的蜱虫数量、繁殖指数、饱血重量和卵质量明显小于未治疗动物。治疗动物上的蜱虫在第 14 天和第 28 天的数量和繁殖能力均低于未治疗动物，而饱血的治疗蜱虫和未治疗蜱虫的体重在 49 天后仍低于未治疗蜱虫。然而，只有在治疗后 14 天（99.9%）的蜱虫感染间隔才能提供美国蜱虫根除计划所需的 99%的控制率。在整个寄生发育期间，只有在治疗后 14 天的感染间隔，蜱虫才会暴露于高于 8ppb 的伊维菌素水平。为了确保没有存活的蜱虫能够达到饱血状态并从宿主身上脱落，牛只需要每隔不超过 31 天进行一次治疗。尽管这一治疗间隔时间比目前的治疗要求（14 天）长了一倍以上，但比 LA 伊维菌素制剂标签上宣称的预防再感染的 75 天要短得多。
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