Efficacy of Eprinomectin and Doramectin Against Amblyomma Americanum (Acari: Ixodidae) on Cattle

VETERINARY ENTOMOLOGY Efﬁcacy of Eprinomectin and Doramectin Against Amblyomma americanum (Acari: Ixodidae) on Cattle

1 K. H. LOHMEYER, J. A. MILLER, J. M. POUND, AND D. D. OEHLER

USDAÐARS, Knipling-Bushland U.S. Livestock Insects Research Laboratory, 2700 Fredericksburg Road, Kerrville, TX 78028

J. Econ. Entomol. 102(2): 809Ð814 (2009) ABSTRACT Steers were treated with doramectin or eprinomectin by daily oral capsule for 28 consecutive days. The level of doramectin in the serum of steers treated at 200 ␮g/kg/d reached a maximum of 104.0 Ϯ 22.1 ppb at day 21 and declined from 93.3 Ϯ 20.5 ppb on the Þnal day of treatment to below detectable by day 56. Steers treated at 50 ␮g/kg/d reached a maximum level of doramectin in the serum of 24.7 Ϯ 1.2 ppb on day 21 and declined from 24.7 Ϯ 0.6 ppb on the Þnal day of treatment to less than detectable on day 42. Both doramectin dosages provided 100% control of estimated larvae (EL) of Amblyomma americanum (L.) (Acari: Ixodidae) throughout the 28-d treatment period. Daily oral treatment with eprinomectin at a dosage of 200 ␮g/kg for 28 consecutive days produced a maximum concentration in the serum of 41.6 Ϯ 11.0 ppb at day 14. On the Þnal day of eprinomectin treatment, the serum concentration was 38.3 Ϯ 5.9 ppb. Seven days later at day 35, eprinomectin was not detectable in the serum. For steers treated at 50 ␮g/kg/d for 28 consecutive days, the serum level of eprinomectin reached a maximum of 10.0 Ϯ 3.0 ppb on day 28 and was undetectable on day 35. Both eprinomectin dosages provided complete control of EL of A. americanum during the 28-d treatment period. Because eprinomectin is efÞcacious against A. americanum at lower serum levels in cattle and is eliminated from the serum at a more rapid rate than either doramectin or ivermectin, it provides advantages for use in applications such as the medicated bait for control of ticks on white-tailed deer and could have potential for use in the Cattle Fever Tick Eradication Program.

KEY WORDS oral treatment, macrocyclic lactones, acaricidal activity

The avermectins, a class of endectocides that includes Pound et al. (1996) developed technology for the ivermectin (Campbell 1989), doramectin (Vercruysse delivery of ivermectin by using medicated-corn, Zea 1993), moxidectin (Webb et al. 1991, Scholl et al. 1992, mays L., for the control of lone star ticks, Amblyomma Miller et al. 1994), and eprinomectin (Shoop et al. americanum (L.) (Acari: Ixodidae). The medicated- 1996), have proven to be an important class of com- bait technology was subsequently used in conjunction pounds for control and management of arthropod with the Cattle Fever Tick Eradication Program pests of livestock because of their chemistry, mode of (CFTEP) to eliminate Boophilus spp. from large in- action, and broad spectrum of activity and efÞcacy at fested ranches in Webb County, TX (George 1996). extremely low dosages. Ivermectin, the Þrst of this Miller et al. (1999) demonstrated that injectable, bio- class to be introduced, provides control of a variety of absorbable microspheres could be used to deliver iver- both endo- and ectoparasites, including ticks (Drum- mectin over an extended period (Ͼ12 wk) and mond 1985, Lasota and Dybas 1991). Numerous stud- thereby eliminate Boophilus annulatus (Say) (Acari: ies have shown that ivermectin can control a variety Ixodidae) from treated cattle and the infested pasture. of tick species (Drummond et al. 1981; Nolan et al. Other potential uses for these technologies include 1981; Lancaster et al. 1982; Miller et al. 1983, 1998; the control of ticks that transmit diseases to animals Pegram and Lemche 1985; Cramer et al. 1988; Soll et and humans. al. 1989, 1990; Taylor and Kenny 1990; Davey et al. The CFTEP relies solely on the use of coumaphos, 2001). an organophosphorous acaricide, in its systematic dipping of cattle. Presently, there are two major concerns associated with the reliance on this single organophosphorous acaricide: 1) whether the man- This article represents the results of research only. Mention of a ufacturer will continue to support the label for this proprietary product does not constitute an endorsement or a recom- mendation by USDA for its use. limited use and 2) whether widespread occurrence 1 Corresponding author, e-mail: [email protected]. of organophosphate resistance in tick populations in 810 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 102, no. 2

Mexico will render the compound ineffective. trol of EL was calculated using AbbotÕs formula (Ab- There is a critical need to develop alternative acar- bott 1925). icides and treatment methods that might have po- Treatment Procedures. The efÞcacy of two differ- tential for use in the CFTEP and more speciÞcally ent oral doses of eprinomectin and doramectin was against resistant ticks. The objective of this study evaluated in the study. Before initiation of the daily was to determine the efÞcacy of doramectin and oral treatments, each calf was weighed individually so eprinomectin against adult lone star ticks on cattle that the appropriate treatment dose could be calcu- and thus provide additional compounds useful for lated. Formulation of each treatment dose for each the control of ticks on cattle, white-tailed deer, and calf was conducted by loading the appropriate volume other wild ungulates. of the pour-on formulation of the drug (either Dec- tomax Antiparasitic 0.5% Pour-on, (PhiÞzer Animal Health, Exton, PA; or Eprinex Pour-on for Beef and Materials and Methods Dairy Cattle, Merial, Duluth, GA) based on the individual weight of each calf, into a 30-cc gelatin capsule This study was conducted at the USDA, Agricultural with enough whole wheat ßour to absorb the liquid Research Service, Knipling-Bushland U.S. Livestock formulation. The formulated capsules were placed in Insects Research Laboratory, Kerrville, TX, as part of prescription bottles marked for use on each individual a research program to develop more effective methods calf. A sufÞcient number of capsules were made so that of controlling ticks on cattle. Although two separate each calf within each of the three groups of cattle tests were conducted, one test with doramectin and could be treated for a period of 28 consecutive days. one test with eprinomectin, the protocols were simi- A standard balling gun was used to administer a single lar. In conducting the research described in this re- individual capsule to each calf at the appropriate dose port, we adhered to the Guide for the Care and Use of for a period of 28 consecutive days after initiation of Laboratory Animals, as promulgated by the Institu- the oral treatments. Care was taken to place the cap- tional Animal Use and Care Committee of the sule far enough into the throat of the calf to prevent Knipling-Bushland U.S. Livestock Insects Research regurgitation. Laboratory. One group of three steers received a daily oral Experimental Design. Nine Hereford steers weigh- dose of 50 ␮g of the drug per kg body weight per day. ing Ϸ200 kg each were randomly separated into three A second group of three steers received a dose of 200 equal groups. Throughout the study each calf was ␮g/kg/d, and the third group of three steers re- stanchioned in an enclosed barn. Steers were feed ceived a placebo containing only the whole wheat alfalfa cubes twice daily at an approximate rate of 1% ßour and served as an untreated control group. of body weight at each feeding. Water was provided Blood Sample Procedures. Immediately before ini- ad libitum. Lone star tick bioassays were conducted to determine efÞcacy of the treatment against feeding tiation of the daily oral treatments (day 0), blood adults as described by Gladney and Drummond samples were collected from the jugular vein of each (1970). Stockinet sleeves were glued onto each animal calf. For the treatment with doramectin, samples were at least 24 h before infestations. At each infestation, 15 also drawn at 3- to 4-day intervals through day 56. For pair of Þeld-collected lone star tick adults were placed the eprinomectin treatment, blood samples were in a stockinet sleeve on each animal. Infestations were taken on days 3 and 7 and weekly thereafter through begun on the day of treatment and at weekly intervals day 35. Whole blood samples were collected in 13-ml for 8 wk. The ticks were examined periodically to SST Vacutainer tubes (BD Biosciences, Franklin determine percentage of attachment and to collect Lakes, NJ). After the blood samples were allowed to engorged females. Engorged females were collected, clot for1hatroom temperature, they were centri- individually weighed, and placed in a coded 25- by fuged at 2,500 rpm for 30 min to separate the serum. 95-mm (8-dram) shell vial with a screen stopper. The serum (5 ml) was then poured into a plastic These vials were held in an incubator at 27 Ϯ 2ЊC, 85% holding vial, labeled, sealed, and frozen at Ϫ20ЊC for RH, and a photoperiod of 12:12 (L:D) h and allowed later analysis. Serum samples were analyzed for the to oviposit for 28 d. After oviposition was complete drug concentration using by a high-performance liq- females were discarded, and the eggs produced by uid chromatography technique described by Oehler each female were weighed and returned to the incu- and Miller (1989) that enables quantiÞcation of as bator. After 4 wk, the percentage egg hatch of each little as 2 ppb in 5 ml of serum. sample group was visually estimated by comparing the Data Analysis. Data on the efÞcacy of the treatment proportion of larvae to the proportion of unhatched as measured by the EL values were analyzed using eggs within the vial. analysis of variance (ANOVA) of repeated mea- The number of engorging females, the weight of surements (SAS Institute 2004). Because many ob- each female, the weight of the egg mass produced and servations indicated no engorging female ticks and the estimated hatch of eggs from each steer in each of hence no EL values, all data were transformed to ϩ the three groups of animals was used to determine log10 (count 1) for the ANOVA. AbbottÕs formula estimated larvae (EL) as described by Drummond et (Abbott 1925) was applied to the geometric means al. (1972) (EL ϭ grams of eggs ϫ estimated percent- EL to determine overall control because of the age of hatch ϫ 20,000). Corrected percentage of con- treatment. April 2009 LOHMEYER ET AL.: EPRINOMECTIN AND DORAMECTIN FOR LONE STAR TICK CONTROL 811

Fig. 1. Mean Ϯ SE concentration of doramectin in serum of three steers as a result of the oral treatment at dosages of 200 or 50 ␮g/kg/d.

Results and Discussion 100, 38.8, and 16.3% control of El for those infestations on day 42, 49 and 56. For both treatments, the observed Doramectin Trial. As a result of the daily oral treatment with 200 ␮g/kg/d treatment for 28 consecutive level of control is consistent with the decline in the level days, the concentration of doramectin in the serum of of acaricide in the serum. A repeated measures ANOVA Ϯ indicated a signiÞcant difference (F ϭ 103.15; df ϭ 2, 6; the treated cattle reached a maximum of 104.0 22.1 P Ͻ ppb at day 21 and steadily declined from 93.3 Ϯ 20.5 0.001) in EL between the untreated steers and those ppb on the Þnal day of treatment (day 28) to below treated with doramectin. However, there was no signif- P Ͼ detectable on day 56 (Fig. 1). For those steers treated icant difference ( 0.05) in EL between the two at 50 ␮g/kg/d, the serum level of doramectin reached treatments at any infestation time. a maximum of 24.7 Ϯ 1.2 ppb on day 21 and declined Eprinomectin Trial. The daily oral treatment at a from 24.7 Ϯ 0.6 ppb on the Þnal day of treatment to less dosage of 200 ␮g/kg/d treatment for 28 consecutive than detectable on day 42 (Fig. 1). days produced a maximum concentration of epri- Although the daily oral treatments were terminated nomectin in the serum of 41.6 Ϯ 11.0 ppb at 2 wk on day 28, both the 50 and 200 ␮g/kg/d dosing pro- posttreatment and declined from 38.3 Ϯ 5.9 ppb on the vided 100% control of EL for ticks placed on the steers Þnal day of treatment (day 28) to below detectable on each week through the day 35 (Fig. 2). The 50 ␮g/ day 35 (Fig. 3). For those steers treated at 50 ␮g/kg/d, kg/d treatment showed a reduction in EL of 81.7, 0, the serum level of eprinomectin reached a maximum and 12.9% for those infestations on day 42, 49, and 56, of 10.0 Ϯ 3.0 ppb on day 28 and declined to less than respectively. The 200 ␮g/kg/d treatment resulted in detectable on day 35 (Fig. 3).

Fig. 2. Percentage of control of estimated larvae from A. americanum on steers treated orally with doramectin at 200 or 50 ␮g/kg/d. 812 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 102, no. 2

Fig. 3. Mean Ϯ SE concentration of eprinomectin in serum of three steers as a result of the oral treatment at dosages of 200 or 50 ␮g/kg/d.

The corrected percentage of control of EL for each and 18 ppb in the serum of cattle treated by daily oral day of infestation on the treated steers treated orally capsule at dosages 200 and 50 ␮g/kg, respectively. with eprinomectin for 28 d is shown in Fig. 4. None of Thus, the serum levels of doramectin, Ϸ100 ppb and the adult lone star ticks placed on cattle during the 25 ppb for steers treated with 200 and 50 ␮g/kg/d, treatment period fed to repletion for either treatment respectively, are somewhat greater than for ivermec- level and as a result both treatments completely in- tin. In contrast, the serum levels of eprinomectin, 42 hibited reproduction. For the infestation applied on and 10 ppb for steers treated with 200 and 50 ␮g/kg/d, the Þnal day of treatment (day 28), on those animals respectively, are lower than that observed for both treated with 50 ␮g/kg/d, 83% control of EL was ob- ivermectin and doramectin. More importantly, epri- served. The 200 ␮g/kg/d dose provided 100% control nomectin is eliminated much more rapidly than either of EL for those ticks placed on cattle on day 28. Both doramectin or ivermectin. Because eprinomectin is treatment levels showed 40% control of EL for infes- efÞcacious against lone star ticks at lower levels in the tations on day 35 despite undetectable levels of aca- serum of cattle and is eliminated from the serum at a ricide in the serum on that day. A repeated measures more rapid rate than either doramectin or ivermectin, ANOVA indicated a signiÞcant difference (F ϭ 243.43; it provides an advantage for use in applications such as df ϭ 2, 6; P Ͻ 0.001) in EL between the untreated the medicated bait for control of ticks on white-tailed steers and those treated with the eprinomectin. As deer where quick withdrawal times are necessary be- with the doramectin treatments, there was no signif- cause of hunting (Pound et al. 2004). Because previous icant difference (P Ͼ 0.05) in EL between the two laboratory and Þeld trials have proven the efÞcacy of treatments at any infestation time. avermectins for controlling B. microplus on pastured In a similarly conducted trial, Miller and Oehler and stanchioned cattle, it is likely that comparable (1996) reported maximum ivermectin levels of Ϸ75 treatments with eprinomectin could provide control

Fig. 4. Percentage of control of estimated larvae from A. americanum on steers treated orally with eprinomectin at 200 or 50 ␮g/kg/d. April 2009 LOHMEYER ET AL.: EPRINOMECTIN AND DORAMECTIN FOR LONE STAR TICK CONTROL 813 of the B. microplus as well and may be useful in the tions of the cattle tick Boophilus microplus (Acarina: Ix- Cattle Fever Tick Eradication Program (Campbell et odidae). Vet. Parasitol. 87: 237Ð241. al. 1983, Cramer et al. 1988, Gonzales et al. 1993, Lancaster, J. L., R. L. Kilgore, and J. S. Simco. 1982. EfÞcacy Remington et al. 1997, Caproni et al. 1998, Gugliel- of low level daily doses of ivermectin in calves against mone et al. 2000, Davey et al. 2001, Davey and George three species of ticks. Southwest. Entomol. 7: 116Ð118. 2002). Lasota, J. A., and R. A. Dybas. 1991. Avermectins, a novel class of compounds: implications for use in arthropod pest control. Annu. Rev. Entomol. 36: 91Ð117. Acknowledgments Miller, J. A., and D. D. Oehler. 1996. 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