A field trial of the effectiveness of 65% permetrin spot-on and 9.7% fipronil spot-on against ticks (Ixodes ricinus) on dogs

Malmgren Lena DVM, PhD (1), Nilsson Börje DVM (2), Bonnett Brenda BSc, DVM, PhD (3)

(1) Schering-Plough Animal Health, Sweden;
(2) Milostab M, Strängnäs, Sweden
(3) Dept. of Population Medicine, Ontario, Veterinary College, University of Guelph, Canada

Email: lena.malmgren@spcorp.com

The knowledge about tick-born diseases in dogs has increased over the last years, which has dramatically heightened the public’s concern about ticks and diseases they transmit. The most important tick-born diseases in dogs in northern Europe and North America are Lyme disease (Borreliosis) and Ehrlichiosis.

To minimise the potential risk of tick-borne diseases, an effective control to prevent the ticks from biting is essential. On the Swedish market there are three drug formulations available for prevention against ticks in dogs, Exspot® vet. spot-on (65.0% permethrin, 744 mg/ml), Frontline® vet. spot-on (fipronil, 100 mg/ml) and Frontline® vet. Spray (2.5 mg/ml).The objective of this blind randomised field trial was to compare the effectiveness of 65% permethrin spot-on and 9.7% fipronil spot-on against the tick species Ixodes ricinus over a 3-month period with repeated treatments at monthly intervals.

Thirty-six dogs were used in the study and they were housed at three different sites. The dogs at each site were randomly assigned into 2 groups, I and II. Group I was treated with permethrin spot-on and group II was treated with fipronil spot-on. The dogs were treated 3 times at monthly intervals. Each dog were examined carefully daily and the number of biting ticks found on the dog was recorded. Most statistical analysis was performed, using the Statistical Analysis System (SAS Institute Inc. SAS User’s Guide, SAS Institute Inc., Cary, N.C.).

For the entire 12 week treatment period, 53% (10/19) dogs treated with permethrin never had ticks whereas only 18% (3/17) dogs treated with fipronil had no ticks.  Permethrin treated dogs were approximately 3 times as likely to have no ticks compared to fipronil treated dogs (Relative Risk, p=0.04).  Over the 12 weeks period, 10 permethrin treated dogs had 0 ticks, 4 dogs had 1 tick and 5 had more than 1 tick. Among fipronil treated dogs, the distribution of 0, 1 or >1 tick, was 3, 3, and 11 dogs, respectively. Overall permethrin was significantly better in reducing the number of ticks on infested dogs. On average, permethrin treated dogs had 1.1 ticks, whereas fipronil treated dogs had 2.8 ticks (p=0.02). None of the dogs in the study showed any signs of side effects due to treatment.

In conclusion, over a 3 months treatment period permethrin (Exspot® vet.) spot-on showed a better effectiveness compared with fipronil (Frontline® vet.) spot-on in reducing both the number of ticks on the dogs and the probability of having any tick.

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