Objective
To compare the efficacies of amitraz and fipronil for prevention of experimental and natural infestations of Rhipicephalus sanguineus.
Design
Prospective study.
Animals
30 dogs.
Procedure
In 3 trials, dogs were allocated to 3 groups of 10 each. In trial 1, dogs were experimentally infested on day -1, and on day 0 were fitted with an amitraz-impregnated collar, treated topically with fipronil, or not treated. Ticks were counted daily until day 7, when viability of ticks and their progeny was determined. In trial 2, dogs were treated on day 0 and experimentally infested on days 7, 8,10, and 13. Ticks were counted on days 8, 10, 13, and 18, and viability of ticks and their progeny was determined on day 18. In trial 3, dogs were exposed weekly to a tick-infested environment from day -3 to day 70. Dogs were treated on day 0, and ticks were counted and removed weekly from day 3 to day 77.
Results
Fipronil and amitraz were acaricidal and inhibited attachment and feeding. Amitraz had a significantly greater effect than fipronil on numbers of live, feeding ticks, egg hatchability, and larval viability, indicating partial ability to interrupt the tick life cycle. In field conditions, amitraz remained effective over the entire observation period.
Clinical Implications
Amitraz had stronger and more sustained effects against tick infestation than fipronil. (J Am Vet Med Assoc 1999;214:1799-1803)
