EVALUATION OF ANTHELMINTIC FISHMEAL POLYMER BAITS FOR

THE CONTROL OF BAYLISASCARIS PROCYONIS IN FREE-RANGING

RACCOONS (PROCYON LOTOR)

Timothy J. Smyser,1,5 Shylo R. Johnson,2 Melissa D. Stallard,1 Ashley K. McGrew,3

L. Kristen Page,4 Nikki Crider,2 Lora R. Ballweber,3 Robert K. Swihart,1 andKurt C. VerCauteren2

1 Department of Forestry and Natural Resources, Purdue University, 715 W State Street, West Lafayette, Indiana 47907,USA2 USDA/APHIS/WS/National Wildlife Research Center, 4101 LaPorte Avenue, Fort Collins, Colorado 80521, USA3 College of Veterinary Medicine and Biomedical Sciences, Colorado State University, 200 W Lake Street, Fort Collins,Colorado 80523, USA4 Biology Department, Wheaton College, 501 College Avenue, Wheaton, Illinois 60187, USA5 Corresponding author (email: tjsmyser@purdue.edu)

ABSTRACT: Baylisascaris procyonis is a common gastrointestinal parasite of raccoons (Procyonlotor) and is a zoonotic helminth with the potential to cause severe or fatal infection. Raccoonsthrive in human-dominated landscapes, and the fecal-oral transmission pathway and lack ofeffective treatment make B. procyonis a serious threat to public health. The distribution ofmedicinal baits has emerged as a socially acceptable and cost-effective method for managingdisease in free-ranging wildlife. We assessed the suitability of a mass-producible anthelmintic baitfor B. procyonis mitigation by evaluating the willingness of free-ranging raccoons to consumeanthelmintic baits and determining whether bait consumption successfully cleared B. procyonisinfections from raccoons. Anthelmintic baits were modified from standard fishmeal polymer baits,the food attractant commonly used in oral rabies vaccine baits, with the introduction of 220 mg ofpyrantel pamoate into the fishmeal mixture. We captured 16 naturally infected raccoons,presented one anthelmintic bait, and monitored B. procyonis infection over 90 d by screeningfeces for eggs. Treatment cleared B. procyonis infections for nine of 12 raccoons that consumed.10 g of the 15 g bait. We used remote cameras to monitor in situ patterns of bait consumption foranthelmintic baits relative to standard baits. Both anthelmintic and standard baits were rapidlyconsumed, with no differences in the rate of consumption between bait types. However, after baitcontact, raccoons demonstrated a greater willingness to consume standard baits while ignoringanthelmintic baits more frequently (P50.06). Initial trials of anthelmintic baits show promise,although refinement in both dose and palatability is needed. At mass production scales, theaddition of pyrantel pamoate to fishmeal polymer baits would be inexpensive, potentially makinganthelmintic baits a viable management option when coupled with an oral rabies vaccine or usedindependently for B. procyonis mitigation.

Key words: Anthelmintic, baiting, Baylisascaris procyonis, Procyon lotor, raccoon, zoonosis.

INTRODUCTION

Baylisascaris procyonis is a helminthiczoonosis that can cause severe or fatalinfection (Sorvillo et al. 2002; Gavin et al.2005). As a common gastrointestinal para-site of raccoons (Procyon lotor), the threatposed by B. procyonis to human healthextends throughout the distribution of thiswidespread generalist omnivore, includingthe raccoon’s natural (Central and NorthAmerica) and introduced (Europe) range(Gavin et al. 2005; Bauer 2013; Page 2013).Mature female B. procyonis are prolific eggproducers, with eggs disseminated into the

environment through raccoon feces (Pageet al. 1998, 1999; Kazacos 2001). Rac-coons preferentially defecate at specificmicrosites (latrines) typically associatedwith the base of large trees, horizontalsubstrates (e.g., roofs or fallen logs), ornear denning areas (Page et al. 1998;Bauer 2013). Millions of eggs may accu-mulate at latrines and on surroundingsubstrates, which serve as foci for in-fection of human and paratenic hosts. Weuse paratenic to describe the role ofa broad array of small mammals and birdsin the lifecycle of B. procyonis, given that

DOI: 10.7589/2014-09-236 Journal of Wildlife Diseases, 51(3), 2015, pp. 640–650# Wildlife Disease Association 2015

640

B. procyonis likely undergoes develop-ment to third-stage larvae while in the egg,like other Ascaridinae (Sprent 1992) andcan directly infect the definitive raccoonhost through the ingestion of these infectiveeggs (D. Bowman pers. comm.; Page et al.1999; Kazacos 2001). Eggs are resilient inthe environment and, in appropriate sub-strates, remain viable for many years(Kazacos 2001). Therefore, latrines mayserve as a source of environmental contam-ination even in the absence of apparentraccoon feces. Following the incidentalingestion of larvated eggs, the eggs hatchand larvae begin aggressive somatic migra-tion with human disease attributable to theinvasion of the viscera, eye, or centralnervous system (Sorvillo et al. 2002).

Raccoons are synanthropic, readilyadapting to human-dominated landscapes.Densities in agricultural, suburban, andurban landscapes often exceed those innatural habitats (Page et al. 2001; Hadi-dian et al. 2010). The ability of raccoons tothrive in human-dominated landscapes,the fecal-oral transmission pathway, andlack of effective treatment options makeB. procyonis a serious public health threat.Since B. procyonis was described asa causative agent of human disease (Huffet al. 1984), at least 30 severe or fatalinfections have been reported (Gavin et al.2005; Haider et al. 2012; Hernandez et al.2013). Furthermore, the severity of thisthreat appears to be increasing with thegeographic expansion of B. procyonis andrecent increases in severe infection (Bliz-zard et al. 2010; Chavez et al. 2012;Hernandez et al. 2013; Pipas et al. 2014).

The distribution of vaccine-laden ormedicinal baits is often used to managesome zoonotic diseases among free-rang-ing wildlife, and such disease-managementefforts may be appropriate for B. procyo-nis mitigation. Oral rabies vaccination(ORV) has been used to eliminate rabiesfrom numerous wildlife, including red fox(Vulpes vulpes) populations in Westernand Central Europe and Ontario, Canada(MacInnes et al. 2001; Freuling et al.

2013) and coyote (Canis latrans) popula-tions in south Texas (Sidwa et al. 2005).Most notably, widespread annual distribu-tion of ORV baits is the primary tool in anactive management program that seeks toprevent the expansion of the raccoonrabies variant enzootic region beyond theeastern US (Slate et al. 2009). Additional-ly, medicinal anthelmintic baits have beenused in numerous landscape-scale fieldtrials in Europe and Japan to controlEchinococcus multilocularis, a commonzoonotic helminth of red foxes and thecausative agent of human alveolar echino-coccosis (Tsukada et al. 2002; Hegglinet al. 2003; Hegglin and Deplazes 2013).Using baits to treat free-ranging wildlifefor localized control of a parasitic agentposes unique challenges relative toprotecting susceptible individuals withvaccine-laden baits. Unlike vaccines, con-sumption of an anthelmintic bait conveysno protective immunity because hostsremain susceptible to reinfection; further-more, in the complex life cycle of a parasitesuch as E. multilocularis, environmentscontaminated with infective eggs or meta-cestode stages within intermediate hostpopulations serve as disease reservoirs thatare unaffected by anthelmintic baiting(Hegglin and Deplazes 2013). Therefore,repeated baiting is needed to obtainmanagement objectives.

Building on established methods ofusing anthelmintic baits to manage para-sitic zoonoses and the development of baitdelivery systems attractive to raccoons,preliminary experiments have extendedthe application of anthelmintic baits tomanage B. procyonis infection in free-ranging raccoons (LoGiudice 1995; Pageet al. 2011; Smyser et al. 2013). Field trialsemployed a fishmeal polymer attractant(Bait-Tek, Orange, Texas, USA) that wasdeveloped for delivery of an oral rabiesvaccine (RABORAL V-RGH fishmealblock; Merial, Duluth, Georgia, USA)and was readily accepted by raccoonsrelative to other bait types (Hanlon et al.1989). Baits were modified from ORV

SMYSER ET AL.—ANTHELMINTIC BAITS FOR BAYLISASCARIS PROCYONIS 641

baits in that the hollow chamber of theattractant was filled with a dose (90 mg[base]) of the general anthelmintic pyr-antel pamoate mixed with marshmallowcream and sealed within the chamber withmelted paraffin wax (Page et al. 2011;Smyser et al. 2013). The monthly distri-bution of anthelmintic baits successfullyreduced levels of environmental contam-ination as measured by the prevalence ofB. procyonis eggs in raccoon feces foundat latrines (Page et al. 2011; Smyser et al.2013). Furthermore, Page et al. (2011)observed reduced B. procyonis infectionof paratenic hosts (white-footed mice[Peromyscus leucopus]) within treatedareas, suggesting that repeated bait distri-bution disrupted pathogen transmissiondynamics. The multiple components ofthese baits (fishmeal attractant, anthelmin-tic, marshmallow cream, paraffin wax)make them expensive and labor intensiveto assemble, limiting their suitability forbroad-scale management applications. Byintegrating an anthelmintic directly intothe fishmeal attractant, a bait could beproduced that is cost effective and suitablefor mass production. However, questionsremain as to whether the bait manufactur-ing process would compromise the efficacyof the drug (Johnston et al. 2005) and if theintroduction of a drug into the fishmealattractant would reduce the willingness ofraccoons to consume the bait (Hanlonet al. 1989). We evaluated the suitabilityof an anthelmintic fishmeal polymer bait(anthelmintic bait) for B. procyonis miti-gation by examining 1) whether theconsumption of an anthelmintic baitwould successfully clear B. procyonis in-fection in naturally infected raccoons and2) the willingness of free-ranging raccoonsto consume anthelmintic baits relative tostandard fishmeal polymer baits.

MATERIALS AND METHODS

Anthelmintic fishmeal polymer baits

Anthelmintic baits were modified fromstandard fishmeal polymer baits (Bait-Tek)

with the introduction of pyrantel pamoatedirectly into the fishmeal matrix. Pyrantelpamoate was effective for clearing B. procyo-nis infections in naturally infected raccoonswhen delivered at 20 mg/kg (Kazacos 1986;Bauer and Gey 1995). Pyrantel pamoate hasa wide margin of therapeutic safety, making itan appropriate drug for introduction into theenvironment. Anthelmintic baits were pro-duced for this experiment by Bait-Tek usingstandard production protocols with a modifiedbait composition in which pyrantel pamoate(Sigma-Aldrich Corporation, St. Louis, Mis-souri, USA; 4.3% by weight) was added to thestandard bait mixture (fishmeal, binder agent,and fish oil). We designed baits to delivera therapeutic dose for raccoons in the 95thpercentile by weight (11 kg; S. D. Gehrt pers.comm.). Accordingly, each 15-g anthelminticbait delivered 220 mg of pyrantel (base).

Captive trials

We used live traps (Tomahawk Live Trap,Hazelhurst, Wisconsin, USA) baited withcommercial cat food to collect 21 adultraccoons from Larimer County, Colorado,over a 4-wk period starting in June 2013;individuals ,5 kg or actively lactating werereleased at the capture location. We anesthe-tized captured raccoons with ketamine/xyla-zine (10 mg/kg ketamine and 2 mg/kg xylazine,intramuscularly [Fowler 2009]). Upon induc-tion, animals were weighed and implantedwith a passive integrated transponder tag (AvidIdentification Systems, Norco, California,USA), and blood samples were collected. Wetransported raccoons to animal care facilitiesat the National Wildlife Research Center, FortCollins, Colorado, where they were placed inindividual pens (33332.5 m) with a den boxand enrichment structures.

Following release into pens, we collectedthe first fecal sample available to assess B.procyonis infection at the time of collection.For 16 of the 21 raccoons used in the trial, wepresented one anthelmintic bait immediatelyafter the first fecal collection. If fecal collec-tion occurred on the same day as capture, theanthelmintic bait was the only source of foodavailable during the first night in captivity. Ifthe animal did not defecate within 24 h ofcollection, we provided a daily food ration (180g, Mazuri Omnivore, PMI Nutrition Interna-tional, Brentwood, Missouri, USA) until fecalcollection occurred. Once feces were collectedfrom these individuals, one anthelmintic baitwas provided with the daily food ration,although the food ration was removed at theend of the day, leaving only the anthelmintic

642 JOURNAL OF WILDLIFE DISEASES, VOL. 51, NO. 3, JULY 2015

bait overnight. We maintained this pattern offood and bait availability for five nights or untilthe bait was consumed; after five nights anyuneaten portion of the bait was removed. Inresponse to the reluctance of some of the first16 raccoons used in the trial to consume ananthelmintic bait directly, we crumbled andmixed an anthelmintic bait with 155.9 g ofmoist cat food for the final five raccoons addedto the captive population after these animalshad been held in captivity up to 20 d. Weremoved any remaining cat food after 24 h andevaluated how much of the cat food/baitmixture had been consumed.

To determine whether bait consumptioneffectively cleared B. procyonis infections, weperformed fecal flotation (Foreyt 2001) onsamples collected before treatment (describedearlier) and 7, 14, 28, 60, and 90 d afterpresentation of an anthelmintic bait. Sampleswere individually collected and stored frozenuntil they were screened for B. procyonis eggs.Because freezing negatively affects the abilityof parasite elements to float (Foreyt 1986; VanWyk and Van Wyk 2002), we also examinedthe sediment that remained on the bottom ofthe tube for eggs following centrifugation.Additionally, we visually examined fecal sam-ples collected 1–4 d after anthelmintic baitconsumption for passed nematodes. If eggswere present on day 14 after bait consump-tion, we provided an additional bait mixed incat food, as described above, within 6 wk ofthe initial presentation of the anthelminticbait. If infection persisted through two doseswith anthelmintic baits, raccoons were de-wormed with liquid pyrantel pamoate (20 mg/kg) mixed in cat food. Activities associatedwith these captive trials were approved by theUSDA National Wildlife Research CenterInstitutional Animal Care and Use Committeeunder protocol QA-2111.

Field trials

To evaluate palatability of anthelminticbaits, we conducted field trials using remotecameras to monitor patterns of bait consump-tion for anthelmintic baits relative to standardfishmeal polymer baits. Trials were conductedin three disjunct mature hardwood forestpatches in Tippecanoe County, Indiana, be-tween 19 September and 7 November 2013.Each forest patch was adjacent to row cropagriculture with exurban development nearbyand had water available in ponds or creeks.For each trial, we tethered either an anthel-mintic or standard bait to a tree so that animalinteractions with the bait could be capturedby a remote camera. Specifically, we looped

a 1.6-mm wire rope through the emptychamber of the bait and attached the wirerope to the tree so that the bait was 15 cmabove the forest floor (Fig. 1). We then affixeda motion-activated, camera (PC900, RECO-NYX Inc., Holmen, Wisconsin, USA) to anadjacent tree with the camera programmed tocapture images continuously through theduration of the detected motion (approximate-ly two images per second). Additionally, weprogrammed cameras to capture a time-lapseimage every 30 min; this allowed us to identifythe time the bait was consumed if the camerafailed to detect the bait removal. We estab-lished camera stations in a grid with 100-mspacing throughout the forest patches, alter-nating bait type (anthelmintic versus standard)between adjacent stations. Bait densities of100/km2 were realistic for management appli-cations, similar to densities in raccoon rabiesORV baiting (75 or 150 baits/km2; Slate et al.2009). We maintained six to nine cameras at

FIGURE 1. Experimental setup used to monitorvia remote camera in situ bait consumption forstandard fish meal polymer baits and experimentalanthelmintic baits (220 mg pyrantel pamoate [base]added to standard bait mixture of fishmeal, fish oil,and binding agent) in three disjunct forest patches inTippecanoe County, Indiana, USA, in 2013.

SMYSER ET AL.—ANTHELMINTIC BAITS FOR BAYLISASCARIS PROCYONIS 643

a time, moving camera stations through thegrid after each trial. Trials began at sunset onday 1 for all cameras deployed simultaneously.We used imagery and associated time stampsto identify the outcome of bait contact(consume or ignore), the species contactingthe bait, and the time the interactionsoccurred. We calculated Kaplan-Meier esti-mates to evaluate differences between baittypes in the time to consumption and con-ducted a test of equal proportions to evaluatedwhether the proportion of baits consumed byraccoons as opposed to nontarget speciesdiffered by bait type. Characterizing the out-come of raccoon visits to a bait as eitherconsume (1) or ignore (0), we used logisticregression to evaluate the influence of baittype on the probability that a raccoon con-sumed the bait. All of these analyses wereconducted in R (R Development Core Team2014). All in situ assessments of bait consump-tion conformed to Purdue University AnimalCare and Use Committee policies (Protocol1211000761).

RESULTS

Captive trials (Table 1)

Of the 21 raccoons in the captive trial,16 had patent infections, actively sheddingB. procyonis eggs at the time of capture.Of the 16 raccoons that were presented ananthelmintic bait directly, the willingnessto consume a bait varied among individ-uals, with five consuming the entire bait,four consuming .10 g but less than theentire bait, five consuming a small portionof the bait (1.26–3.78 g), and two con-suming ,1 g. Of the subsequent fiveraccoons that were presented a crumbledbait mixed with moist cat food, threeconsumed the entire mixture, whereas twoconsumed only a small portion andtherefore received a reduced pyranteldose.

Of the 16 infected raccoons, 10 con-sumed .10 g of an anthelmintic bait(directly n57, mixed with cat food n53).Of these 10 individuals, seven were nolonger shedding eggs when re-evaluated 7d postbait consumption, nor were eggsdetected during the 90-d monitoringperiod. Two of the three raccoons withpersistent infections were presented with

a second anthelmintic bait. Of these tworaccoons, B. procyonis infection wascleared in one, as indicated by lack ofeggs in the feces. The second continued toshed eggs after the consumption ofa second bait; a third treatment withliquid pyrantel pamoate also failed toeliminate B. procyonis. Of the six infectedraccoons that consumed only a portion ofthe first bait, four were no longer sheddingeggs when evaluated at 14 d. For theremaining two raccoons, infections werecleared with the complete consumption ofa second anthelmintic bait mixed in catfood. Two of the four raccoons that ceasedshedding eggs 14 d after partial baitconsumption resumed egg shedding laterin the trial (eggs detected at 28 d for oneraccoon and 60 and 90 d for the second);however, these individuals were not trea-ted a second time within the context ofthis study.

Of the 16 raccoons collected with patentinfections, adult B. procyonis were ob-served in feces of 13 raccoons shortly afterinitial bait consumption (8/10 with com-plete bait consumption; 5/6 with partialbait consumption). Of the five individualsfor which infection persisted after theconsumption of either a complete (n53)or partial (n52) bait, nematodes wereobserved in the feces of three. Nonematodes were detected in the feces ofthe five raccoons that were not sheddingeggs at the time of capture.

Field trials

We conducted 70 bait trials (36 anthel-mintic, 34 standard baits) from which thetime to bait consumption could be de-termined for 60 baits (32 anthelmintic, 28standard baits; four anthelmintic and twostandard baits were still present whencameras were serviced and thereforecensored for survival analysis), and thespecies consuming the bait was identifiedfor 51 trials (27 anthelmintic, 24 standardbaits; cameras failed to detect motionassociated with bait removal of fiveanthelmintic and eight standard baits).

644 JOURNAL OF WILDLIFE DISEASES, VOL. 51, NO. 3, JULY 2015

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SMYSER ET AL.—ANTHELMINTIC BAITS FOR BAYLISASCARIS PROCYONIS 645

Both bait types were consumed rapidly insitu (Fig. 2) with 44% (15/36 anthelmintic;14/30 standard) consumed in the firstnight, 70% by the end of the second night(25/36 anthelmintic; 21/30 standard), and80% by the end of the third (28/36anthelmintic; 25/30 standard). There wasno difference in the rate of bait consump-tion between the two bait types (x250.40,df51, P50.50). Of the trials in which wecould identify the species consuming thebait, raccoons consumed 10 of 27 (37%)anthelmintic baits and 12 of 24 (50%)standard baits. Differences in the pro-portion of baits consumed by raccoonswere not statistically significant (x250.42,df51, P50.52). Raccoons approachedanthelmintic baits on 39 occasions andconsumed 10 of these baits, whereasraccoons contacted standard baits on 21occasions and consumed 12 baits. Baittype was a significant predictor of theoutcome of bait contact by raccoons(P50.02, odds ratio53.89 for standardvs. anthelmintic), indicating that, uponencounter, raccoons were more willing toconsume standard baits than anthelminticbaits. Virginia opossums (Didelphis vir-giniana) were the only nontarget speciesthat consumed baits (consuming 17 an-thelmintic in 24 encounters and 12

standard in 12 encounters). We observedbait contact by flying squirrels (Glaucomysvolans) and white-footed mice on multipleoccasions; however, these small-bodiedanimals were unable to remove baits fromtethers.

DISCUSSION

Anthelmintic fishmeal polymer baitswere moderately effective for eliminatingB. procyonis infections in naturally in-fected raccoons. Infections were eliminat-ed in nine of 12 raccoons when individualsconsumed .10 g (of 15 g) of a bait,resulting in realized dose rates of 18.9–48.0 mg/kg. Of those individuals withpersistent infections, the presence of adultB. procyonis in feces suggests that parasitenumbers were reduced, although noteliminated, with bait consumption. Bauerand Gey (1995) found that one dose ofpyrantel delivered in food at 20 mg/kgcleared 100% of B. procyonis infection incaptive raccoons. Additional work is need-ed to determine why infection persistedamong some individuals after bait con-sumption. Tetracycline is often incorpo-rated into fishmeal polymer ORV baits asa biomarker. High-performance liquidchromatography analyses of bait contents

FIGURE 2. Proportion of standard (solid line) fishmeal polymer baits and experimental anthelmintic(dashed line) baits (220 mg pyrantel pamoate [base] added to standard bait mixture of fishmeal, fish oil, andbinding agent) remaining during bait consumption trials conducted in three disjunct forest patches inTippecanoe County, Indiana, USA, with bait consumption monitored by remote cameras. Baits that remainedunconsumed at the conclusion of the trial period were right censored for analysis and are indicated with +.

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have demonstrated that baits delivera lower effective dose of tetracycline thanintended because of degradation duringthe bait manufacturing process and por-tions of the dose being functionally un-available by binding with polymer in thebait formulation (Johnston et al. 2005).Similar processes may have limited theeffective dose of pyrantel delivered inbaits and contributed to the failure todeworm three of 12 individuals. However,therapeutic use of anthelmintics oftenrequires multiple doses to clear infection(Overgaauw 1997), and it is recommendedthat raccoons taken into captivity receivemultiple treatments to ensure completeelimination of B. procyonis (Kazacos2001). Management applications of an-thelmintic baits for B. procyonis mitiga-tion will require repeated bait distributionbecause of the potential for raccoons to bereinfected from environmental reservoirs(Hegglin and Deplazes 2008; Page et al.2011; Smyser et al. 2013). Therefore,should initial bait contact result in re-duction, but not elimination, of B. pro-cyonis infections, raccoons likely wouldreceive additional treatments with sub-sequent bait distribution.

The range of realized dosages in ourstudy illustrates one of the challenges ofusing medicinal baits to manage diseaseamong free-ranging wildlife. Our intent inanthelmintic bait development was todeliver a minimum pyrantel dose of20 mg/kg. A failure of some individualsto consume an entire bait, thereby re-ceiving a dose below recommended ther-apeutic levels, may have contributed to thepersistence of infection in some individu-als. Furthermore, pyrantel is intended tobe consumed as a single dose. However,some raccoons consumed one bait overmultiple days (S.R.J. unpubl. data); it ispossible that these individuals did notconsume a sufficient amount of bait at onetime to obtain a therapeutic dose. Imagescollected during our in situ trials providedno evidence of similar behavior amongfree-ranging raccoons; among the 22

anthelmintic and standard baits consumedby raccoons, we did not observe raccoonsdiscarding a partially eaten bait. While thisbehavior may occur in the wild, thereluctance to consume baits and theconsumption of only portions of baitsobserved in captive trials were likelyexacerbated by the stress associated withtransfer from the wild to the captivefacility immediately before the initiationof bait trials.

We could not determine whether thefailure to clear B. procyonis infection fromsome raccoons may have been attributableto the presence of nematodes with geno-types resistant to pyrantel. Given that free-ranging raccoons would not have beentreated previously with pyrantel, we wouldnot expect anthelmintic-resistant B. pro-cyonis to have a selective advantage oversusceptible nematodes in the generalpopulation. Thus, this hypothesis for thecause of persistent infections seems un-likely. However, anthelmintic resistanceamong gastrointestinal helminths of do-mestic animals is a major challenge inveterinary medicine (Kaplan 2004; Wol-stenholme et al. 2004), and similar chal-lenges could arise with the broad-scaledistribution of anthelmintic baits forB. procyonis control. Among domesticanimals, emergence of anthelmintic re-sistance appears to be associated with a lackof refugia for anthelmintic-susceptibleparasites and administration of dosagesbelow therapeutic levels (Falzon et al.2014). Anthelmintic bait distribution forB. procyonis control would maintain abun-dant refugia for susceptible nematodes.Even if broadly adopted, we would expectbaiting to be restricted to urban andsuburban landscapes, where the risk ofhuman exposure is greatest. Therefore,B. procyonis infecting raccoons in outlyingrural habitats would represent a largerefugium with the potential to continuallyintroduce susceptible parasites via rac-coon immigration. Moreover, egg andlarval stages in the environment or para-tenic hosts are unaffected by raccoon

SMYSER ET AL.—ANTHELMINTIC BAITS FOR BAYLISASCARIS PROCYONIS 647

treatment and serve as refugia. Finally,baits were developed to deliver a thera-peutic dose for raccoons in the 95thpercentile by weight. In managementapplications, the density of distributedbaits would exceed raccoon densities, thuscreating potential for raccoons to con-sume multiple baits, and would reducethe risk of under-dosing large raccoons.Collectively, multiple factors should hin-der the emergence of anthelmintic re-sistance in B. procyonis.

Despite consumption of anthelminticand standard baits in situ at similar rates,we observed a consistent preference byraccoons for standard baits. A greaterproportion of standard baits was con-sumed by raccoons (50% standard vs.37% anthelmintic) and, when encoun-tered in the landscape, raccoons con-sumed standard baits more frequentlythan anthelmintic baits (26% [10/39]anthelmintic vs. 57% [12/21] standard).In contrast, opossums seldom failed toconsume a bait of either type onceencountered (81% [29/36]). Of the sevenencounters in which opossums failed toconsume a bait, imagery suggested opos-sums attempted and failed to remove thebait from the tether on three occasionsrather than simply ignoring the baits. Insum, nontarget opossums were less dis-criminating between bait types than sym-patric raccoons. Bait consumption byopossums can limit bait availability forraccoons (Olson and Werner 1999; Olsonet al. 2000; Smyser et al. 2010, 2013).Therefore, if raccoons are more reluctantto consume anthelmintic baits, then opos-sums, as less selective foragers, could havean even greater effect on reducing baitavailability for raccoons relative to stan-dard baits. Additional work is needed toevaluate whether pyrantel pamoate inanthelmintic baits can be masked byincreasing fish oil content or introducingmolasses or other flavor enhancers toimprove palatability (Hanlon et al. 1989).

Initial trials of a mass-producible an-thelmintic bait for the control of

B. procyonis in free-ranging raccoonsappear promising. The small batch ofanthelmintic baits used in this trial cost$0.50/bait, a savings of $0.10/bait over themultiple-ingredient baits (fishmeal attrac-tant, anthelmintic, marshmallow cream,paraffin wax) used previously in field trials(Page et al. 2011; Smyser et al. 2013). Atmass production scales, the introductionof pyrantel pamoate to fishmeal polymerbaits could add as little as $0.05 to thecost of standard baits. Furthermore, byintegrating pyrantel pamoate into thefishmeal matrix, the chamber of the baitremains available to deliver vaccine, me-dicinal, or contraceptive products. Anthel-mintic baits could be coupled with an oralrabies vaccine to manage two zoonoticdiseases with one bait if the addition ofpyrantel does not reduce vaccine efficacyor bait palatability (Roberts and Aubert1995). Continued work is needed todevelop appropriate strategies to mitigatethe risk posed by B. procyonis to humanhealth. With refinement in dose andpalatability, we believe anthelmintic baitscould contribute to this goal.

ACKNOWLEDGMENTS

We thank T. Rigg for help with datacollection on captive raccoons, M. Freiburgerand L. Estrada for assistance with remotecamera deployment and imagery assessment,and M. Smith for assistance with bait de-velopment. This research was funded byPurdue University, Indiana Department ofNatural Resources (SWG T7R12 and T7R10),USDA National Rabies Management Pro-gram, and the Wheaton College FacultyAchievement Award.

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Submitted for publication 23 September 2014.Accepted 10 January 2015.

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