Submitted to: Agricultural Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 2001
Publication Date: N/A
Interpretive Summary: The Cattle Fever Tick Eradication Program (CFTEP) relies solely on the dipping of tick-infested cattle in the organophosphorus (OP) acaricide, coumaphos as the means of preventing the re-introduction of Boophilus ticks into the United States. Thus, the identification and development of alternative acaricides and treatment methods is critical to the continued success of the eradication effort. The effectiveness of the endectocide, ivermectin administered daily to cattle infested with all life stages of B. microplus was evaluated. Cattle were treated at dose rates of 25 and 50 mcg of ivermectin per kg of body weight for a period of 21 days. While both ivermectin treatment doses were highly effective (>99% control), the 50 mcg/kg/d dose was more effective than the 25 mcg/kg/d dose against all life stages of the tick. The presence of ivermectin in the blood of the cattle caused high mortality in the ticks, as well as producing dramatic adverse effects in the reproductive capability of the ticks that were able to survive and detach from the cattle. Based on the results of this study, the potential for use of ivermectin and other acaricides with similar chemistries is encouraging. The use of these types of acaricides applied by different delivery systems, such as long-term boluses or medicated feed systems has great promise for future applicability in the Boophilus eradication program.
Technical Abstract: The efficacy of oral ivermectin administered daily to cattle infested with all parasitic stages of Boophilus microplus (Canestrini) ticks was evaluated. Ivermectin capsules (one capsule per calf per day) were administered to two separate groups of cattle (n=3 per group) at a dose rate of either 25 or 50 mcg/kg for a period of 21 consecutive days. A third group of calves received a placebo capsule each day and served as a control. Although overall control achieved at both doses of ivermectin was >99% against all parasitic stages, the 50 mcg/kg/d dose was more effective (P<0.05) than the 25 mcg/kg/d dose against each parasitic stage of the tick. With the exception of egg hatch, all other measured parameters were lower (P<0.05) in the ivermectin treated groups than were observed in the untreated group. A dose related response (P<0.05), relative to the percentage reduction in female tick numbers and their reproductive performance was observed for ticks that were immature (nymphs and larvae) at the onset of ivermectin treatment. In contrast, egg mass weight was the only measured parameter of reproductive performance that was affected by dose for surviving females that were adults at the onset of ivermectin treatment. The potential applicability for treating tick-infested cattle with different delivery systems, such as daily oral treatments, boluses, and medicated feed systems that contain ivermectin or other macrocyclic lactone compounds is also discussed.