M. Franc, F. Beugnet, and S. Vermot Efficacy of Fipronil–( S)-Methoprene on Fleas, Flea Egg Collection, and Flea Egg Development Following Transplantation of Gravid Fleas onto Treated Cats* M. Franc, Pr, DVM, PhD, DEVPC a F. Beugnet, DVM, MSc, PhD, DEVPC b S. Vermot a al’UMR181 Physiopathologie et Toxicologie Experimentales, b Merial SAS INRA, ENVT 29 Av Tony Garnier Ecole Nationale Vétérinaire 69007 Lyon, France 23 chemin des Capelles 31076 Toulouse Cedex, France CLINICAL RELEVANCE The goal of this study was to assess the insect growth regulator activity of the com - bination product fipronil–( S)-methoprene under a severe challenge model. Gravid fleas were allowed to feed on untreated donor cats for 48 hours before being trans - planted onto untreated control cats and treated cats (treated once on day 0); 24 hours later, adult fleas were collected from all cats and counted to assess the 24- hour kill efficacy against the transplanted fleas, and flea eggs were collected and in - cubated to assess viability. The process was repeated weekly for 11 weeks. The 24- hour efficacy against transplanted adult fleas in the treated group was about 100% for the first 3 weeks and gradually declined to 93.4% by week 6. Egg production numbers were reduced on the treated cats compared with controls, with geometric mean egg counts on treated cats reduced from 76.9% to 96.3% during the initial 6 weeks of the study. The combination product was 100% ovicidal through day 56 and was still about 98% effective against eggs at the end of the study (day 76). I INTRODUCTION of the flea life cycle. Most flea control products It has long been acknowledged that an inte - that offer integrated control combine an adul - grated approach provides the best direct con - ticide with an insect growth regulator (IGR) .4 trol of flea infestations on domestic animals. 1–3 IGRs affect eggs and subsequent juvenile de - Such an approach not only targets activity velopment. They can affect eggs while they are against adult fleas but also affects other stages still inside the adult flea or by direct penetra - *This research was funded by Merial Limited, Duluth, tion of eggs when they come in contact with Georgia. treated skin and hair. 5,6 Environmental infesta - 285 Veterinary Therapeutics • Vol. 8, No. 4, Winter 2007 tion by multiple life stages necessitates several felt that this scenario offered the most severe treatments at regular intervals to resolve an ex - challenge possible. isting flea problem. 2,6,7 However, combining an adulticide with an IGR may help speed the rate I MATERIALS AND METHODS of control. 8 These same combinations rarely al - Nineteen shorthaired cats were included in low the opportunity to critically assess IGR ac - this trial. Nine cats were selected to be used tivity alone because the adulticide typically only as flea-donor cats , providing engorged, eliminates or negatively affects fleas before any gravid fleas that had the opportunity to feed for eggs are produced throughout most of the 48 hours. The remaining 10 cats were random - monthly treatment interval. ly allocated, first by sex and then by body Essentially all naturally occurring infestations weight and receptivity to flea infestations , to involve fleas that are newly emerged from co - form two groups of five cats each. By random coons in the environment. When these newly draw, Group 1 was selected as the control group emerged fleas come in contact with animals and Group 2 as the treatment group. Each of treated with the combination of fipronil –( S)- the five cats in Group 2 was treated once on day The goal of this study was to assess the insect growth regulator activity of the combination product fipronil–( S)-methoprene under a severe challenge model. methoprene, there is little chance they will sur - 0 with a single dose of the commercially avail - vive long enough to produce any significant able combination of fipronil–( S)-methoprene numbers of eggs during the normal monthly (Frontline Combo [Frontline Plus in the Unit - treatment interval .4,9 Thus, a typical weekly post - ed States], Merial ). Per the manufacturer’s in - treatment challenge or infestation study design structions, the 0.5-ml dose (9.8% fipronil would not readily offer the opportunity for crit - [7.5–13 mg/kg] and 11.8% ( S)- methoprene ical assessment of the IGR activity of the ( S)- [10–20 mg/kg]) was applied directly to the skin methoprene component in a combination prod - on the dorsal aspect of the base of the neck just uct. Therefore , a different infestation model was anterior to the shoulder blades. deemed necessary for accurate assessment of Throughout the study, cats were maintained IGR activity. Although relocation of actively re - in individual stainless steel cages with trays be - producing female fleas from one host to another neath each cage to collect flea eggs . The cats is possible, 10 it is understood that this is likely were managed similarly and with due regard for rare in a natural setting. However, to fully assess their safety and well-being. They were handled the ovicidal activity of an adulticide –IGR com - in compliance with and with the approvals of bination product , it was decided that the transfer the National Veterinary School of Toulouse of actively reproducing fleas from untreated to (France) Institutional Animal Care and Use treated cats would allow production of sufficient Committee (IACUC) and any applicable local numbers of eggs for analysis of the product ’s ovi - regulations, as well as requirements of any local cidal activity. Because the primary goal of this IACUC, which may have exceeded the univer - study was to critically assess the IGR activity, we sity IACUC. Cats were acclimated to their en - 286 M. Franc, F. Beugnet, and S. Vermot vironment 14 days before treatment. All cats re - TABLE 1. Geometric Mean 24-Hour ceived food and drinking water ad libitum . Flea Counts from Treated and Control Pretrial experiments confirmed the success Cats and Percent Efficacy Following of the transplant methodology of this protocol Transplantation of Fleas Previously and helped to determine the appropriate quan - Fed for 48 Hours tity of fleas necessary to achieve the targeted in - festation rate of 50 fleas /cat. On day –1 and Geometric Mean Counts then approximately weekly throughout the 11 - Study Fipronil– week study, each of the nine cats in the dedi - Day (S)-Methoprene Control % Efficacy cated donor group was infested with 200 unfed 1 0.25 33.93 99.30 a fleas. Forty-eight hours later, the fleas were a carefully combed off the donor cats, assessed 7 0.00 35.86 100 for mobility and viability, and then pooled to - 14 0.00 37.87 100 a gether. Healthy -appearing fleas with normal 21 0.32 39.85 99.20 a mobility were collected from the pool in lots of 28 1.35 39.69 96.60 a at least 50 fleas (approximately 50% female a and 50% male), and each lot was transferred to 35 2.44 36.12 93.30 individual cats in Groups 1 and 2 on days 1, 7, 42 2.59 39.27 93.40 a 14, 21, 28, 35, 42, 49, 56, 62, 69, and 76. 49 4.43 35.15 87.40 b Twenty-four hours after each infestation, 56 16.78 37.39 55.10 b cats from Groups 1 and 2 were combed to col - lect fleas. To perform flea counts, two techni - 62 16.63 35.76 53.50 cians simultaneously combed each cat to col - 69 25.67 35.86 28.40 lect fleas. All cats were combed for 7 to 12 76 35.47 39.43 10.10 minutes; however, if no fleas had been ob - aDenotes value is statistically significant ( P < .0001). tained after 7 minutes, combing was discon - bDenotes value is statistically significant ( P < .02). tinued at that time. If either technician discov - ered fleas, combing continued until no fleas were found for a period of 1 minute (e.g. , if no trays were counted. For each egg count day, fleas were obtained between 10 and 11 min - geometric mean flea egg counts were deter - utes, combing was discontinued at 11 min - mined for eggs collected using the transforma - utes). For each flea count day, geometric mean tion to the natural logarithm of (count + 1). flea counts were calculated using the transfor - After egg counts were recorded, eggs from mation to the natural logarithm of (count + 1). each cage were placed in individual vials con - Comparisons of treatment means were per - taining sand and nutritive medium. The vials formed using t-tests for means with poolable were individually identified by date and cat variances or for means with unequal variances, number and placed in an incubation unit that as appropriate. Variances were then compared maintained temperature at 27 °C and relative using the maximum F-test ; if variances were humidity at 75% to 80%. found to be unequal , degrees of freedom were After 1 month of incubation, any emerged estimated using Satterthwaite’s approximation. fleas in each individual vial were counted. As At the same time flea comb counts were per - with adult efficacy assessment, for each count formed, flea eggs retrieved from the collecting day, geometric mean counts of emerging fleas 287 Veterinary Therapeutics • Vol. 8, No. 4, Winter 2007 Frontline Combo (Frontline Plus) Reduced Flea Emergence by 100% through Day 56 100 2,000 n o i t a t 90 1,800 s e % Reduction in Flea Development f n I ) from Eggs Produced by Gravid Fleas 80 1,600 g n % on Treated Cats vs.