|Hunter Iii, James|
Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1997
Publication Date: N/A
Citation: Interpretive Summary: The Fever Tick Eradication Program relies almost exclusively on the use of one chemical agent, coumaphos, to eliminate fever tick infestations. However, during the past 15 years, acaricide resistance in Mexico has cast a shadow on the continued use of coumaphos as an effective treatment agent. A new material, fipronil, was evaluated to determine initial and residual effectiveness against fever ticks on cattle at three different concentrations. Initial effectiveness indicated that the control was related to the concentration applied. At 0.25 and 0.5% active ingredient (AI) the control achieved (86.2 and 94.3%, respectively) did not meet eradication program standards. However, at 1.0% AI the control was very high (99.7%). Results of the residual effectiveness of fipronil were also dose related. At 0.25% AI the protection against larval reinfestation was less than one week, whereas at 0.5% AI no ticks were able to successfully reinfest animals for four weeks after treatment. Again, the 1.0% AI concentration produced the longest protection against larval reinfestation, providing 100% protection for eight weeks after treatment. Thus, fipronil at the 1.0% AI concentration has potential for use in the eradication program as an alternative to presently used chemicals and should also be effective against pesticide resistant populations.
Technical Abstract: The therapeutic and persistent efficacy of three concentrations (0.25, 0.5, or 1.0% active ingredient) of a pour-on formulation of fipronil was determined against Boophilus microplus on cattle. With each increase in concentration the therapeutic efficacy of fipronil resulted in a corresponding decrease in the numbers, fecundity, and fertility of engorged females that survived. The overall therapeutic control achieved at 0.25 and 0.5% AI was 86.2 and 94.3%, respectively, while the control at the 1.0% AI concentration was 99.7%. The persistent efficacy of fipronil was also dose related. The 0.25% AI treatment failed to provide complete protection (100%) against larval reinfestation for even one week after treatment. In contrast, at 0.5% AI the control remained at 100% for the first four weeks after treatment. However, the 1.0% AI treatment afforded the longest residual activity, providing virtually 100% protection against larval reinfestation for eight weeks after treatment. Based on results, neither the 0.25 or 0.5% AI concentration met the standards required for use in an eradication program. However, the 1.0% AI concentration produced therapeutic efficacy that has potential for use in the eradication program, as well as providing virtually complete protection against larval reinfestation for eight weeks.