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Muscleworms, Parelaphostrongylus andersoni(Nematoda: Protostrongylidae), Discovered inColumbia White-Tailed Deer from Oregon andWashington: Implications for Biogeography andHost AssociationsIngrid M. AsmundssonAnimal Parasitic Disease Laboratory, Agricultural Research Service, United States Department of Agriculture

Jack A. MortensonVeterinary Services, United States Department of Agriculture

Eric P. HobergAnimal Parasitic Disease Laboratory, Agricultural Research Service, United States Department of Agriculture,geocolonizer@gmail.com

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Asmundsson, Ingrid M.; Mortenson, Jack A.; and Hoberg, Eric P., "Muscleworms, Parelaphostrongylus andersoni (Nematoda:Protostrongylidae), Discovered in Columbia White-Tailed Deer from Oregon and Washington: Implications for Biogeography andHost Associations" (2008). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 815.http://digitalcommons.unl.edu/parasitologyfacpubs/815

MUSCLEWORMS, PARELAPHOSTRONGYLUS ANDERSONI

(NEMATODA: PROTOSTRONGYLIDAE), DISCOVERED IN COLUMBIA

WHITE-TAILED DEER FROM OREGON AND WASHINGTON:

IMPLICATIONS FOR BIOGEOGRAPHY AND HOST ASSOCIATIONS

Ingrid M. Asmundsson,1 Jack A. Mortenson,2 and Eric P. Hoberg1,3

1 United States National Parasite Collection and Animal Parasitic Disease Laboratory, United States Department ofAgriculture, Agricultural Research Service, BARC East No. 1180, 10300 Baltimore Avenue, Beltsville, Maryland 20705,USA2 United States Department of Agriculture, Veterinary Services, 530 Center Street NE, Suite 335, Salem, Oregon 97301,USA3 Corresponding author (email: eric.holberg@ars.usda.gov)

ABSTRACT: Parelaphostrongylus andersoni is considered a characteristic nematode infectingwhite-tailed deer (Odocoileus virginianus). Host and geographic distribution for this parasite,however, remain poorly defined in the region of western North America. Fecal samples collectedfrom Columbia white-tailed deer (O. v. leucurus) in a restricted range endemic to Oregon andWashington, USA, were examined for dorsal-spined larvae characteristic of many protostrongylidnematodes. Multilocus DNA sequence data (internal transcribed spacer 2 and cytochrome coxidase subunit 1) established the identity and a new record for P. andersoni in a subspecies ofwhite-tailed deer previously unrecognized as hosts. Populations of P. andersoni are nowrecognized along the basin of the lower Columbia River in Oregon and Washington and fromsouth-central Oregon on the North Umpqua River. Current data indicate a potentially broad zoneof sympatry for P. andersoni and Parelaphostrongylus odocoilei in the western region of NorthAmerica, although these elaphostrongylines seem to be segregated, respectively, in white-taileddeer or in black-tailed and mule deer (Odocoileus hemionus) at temperate latitudes. Thegeographic range for P. andersoni in white-tailed deer is extended substantially to the west of thecurrently defined limit in North America, and we confirm an apparently extensive range for thiselpahostrongyline. These observations are explored in the broader context of host and geographicassociations for P. andersoni and related elaphostrongylines in North American cervids.

Key words: Columbia white-tailed deer, COI, ITS-2, muscleworm, Odocoileus virginianusleucurus, Parelaphostrongylus andersoni.

INTRODUCTION

The nematode muscleworm, Parela-phostrongylus andersoni Prestwood 1972,is an elaphostrongyline parasite occurringin white-tailed deer (Odocoileus virginia-nus), barrenground caribou (Rangifer tar-andus groenlandicus and R. t. grantii), andwoodland caribou (R. t. caribou) fromNorth America (Prestwood et al., 1974;Anderson and Prestwood, 1981; Lankester,2001). Although considered a characteristicnematode infecting cervids from the Ne-arctic, aspects of the host and geographicdistribution remain poorly or incompletelydefined for this species, as well as con-geners including the meningeal worm,Parelaphostrongylus tenuis (Dougherty,1945), and the mule deer muscleworm,Parelaphostrongylus odocoilei (Hobmaier

and Hobmaier, 1934). Data for P. ander-soni are particularly sparse for the region ofwestern North America (Lankester, 2001).

Numerous accounts document an ap-parently disjunct, patchy, but extensiverange for P. andersoni from the southeast-ern United States to the Canadian Sub-arctic and Alaska, USA (Fig. 1). Infectedwhite-tailed deer have been identifiedfrom the southeastern United States (Prest-wood et al., 1974; Anderson and Prest-wood, 1981), New Jersey (Pursglove,1977), Michigan (Pybus et al., 1990),northeastern Wyoming (Edwards, 1995),and southeastern and south-central BritishColumbia, Canada (Pybus and Samuel,1981; Lankester, 2001). This parasite isunknown in natural infections of black-tailed or mule deer (subspecies of Odocoi-leus hemionus), moose (Alces alces), or

Journal of Wildlife Diseases, 44(1), 2008, pp. 16–27# Wildlife Disease Association 2008

16

potential wild caprine hosts (Kutz et al.,2001, 2007; Jenkins et al., 2005; Mortensonet al., 2006). In both barrenground andwoodland caribou, P. andersoni is regardedto be geographically widespread, excludingthe Arctic islands of Canada, althoughrelatively few records have documentedthe actual distribution (summarized inLankester, 2001; Kutz et al., 2007).

Until recently, confirmation of theoccurrence and distribution of P. ander-soni and other species of Parelaphostron-gylus was dependent on the collection andidentification of adult worms recoveredfrom carcasses of various ungulate hosts(Lankester, 2001). The first larval stage ofmany protostrongylid species is character-ized by the presence of a dorsal spine onthe tail (Boev, 1975). Such dorsal spinedlarvae (DSLs) recovered from feces can-

not be reliably identified based on mor-phology, and polymorphism among larvaeof some species has been noted (Hoberget al., 2005). The advent of molecular-based methods has altered our approachto survey and inventory for protostrongylidand other nematodes in ungulates (e.g.,Hoberg et al., 2001). Sequence data fromindividual DSL assessing both nuclear andmitochondrial loci are now used as epide-miologic probes to explore identity, distri-bution, and phylogeography based ongeographically extensive and site intensivesampling (e.g., Jenkins et al., 2005; Mor-tenson et al., 2006; Kutz et al., 2007;Hoberg et al., unpubl. data). Unequivocalmolecular-diagnostic protocols are alsoavailable for elaphostrongylines, but theyhave not yet been extended to all proto-strongylids that produce DSLs in North

FIGURE 1. Map showing approximation of the known distribution of Parelaphostrongylus andersoni (inpart based on Lankester, 2001). A prior report of P. andersoni in Arkansas as cited by Anderson andPrestwood (1981) and Lankaster (2001) seems to be in error, because Prestwood et al. (1974) to whom thisrecord was attributed did not find this elaphostrongyline in this locality.

ASMUNDSSON ET AL.—P. ANDERSONI IN WESTERN NORTH AMERICA 17

American ungulates (e.g., Huby-Chiltonet al., 2006).

Thirty-eight subspecies of white-taileddeer are widely distributed from NorthAmerica, across the Panamanian Isthmus,into northwestern South America (Smith,1991). This suggests the potential fora broad geographic range for P. andersonilargely congruent to that of O. virginianus.Sampling for protostrongylids in species ofOdocoileus in the western region of NorthAmerica has been limited (e.g., Mortensonet al., 2006), and the area encompassingthe ‘‘doughnut-hole’’ extending acrosseastern California, Oregon, Washington,and the Great Basin remains to beexplored. Our study serves to continuethe exploration of this region by examiningelaphostrongyline parasites among popu-lations of Columbia white-tailed deer(Odocoileus virginianus leucurus; CWTD)using molecular-based survey.

As the western-most subspecies,CWTD was historically distributed in thelowlands of southwestern Washington andmuch of Oregon west of the CascadeMountains (Douglas, 1829; Nash, 1877;Smith, 1985). Currently, CWTD are re-stricted to two isolated populations, onepopulation in southern Oregon along theNorth Umpqua River (Douglas County)and the other population along the lowerColumbia River, in both Oregon andWashington, the latter now defined bythe Julia Butler Hansen Refuge. In themid-nineteenth century, the range of theCWTD was reduced coincidental withEuro-American settlement of the PacificNorthwest (Livingston, 1987). In the earlytwentieth century, this subspecies wasthought to be extinct (Jewett, 1914; Taylorand Show, 1929; Bailey, 1936; Cowan,1936). Surveys of CWTD by Scheffer(1940), however, estimated the populationto consist of 500–700 animals along thelower Columbia River. These low num-bers resulted in their subsequent listing asone of the first endangered mammalianspecies recognized by the federal govern-ment (Gavin, 1979). With recovery

through the 1980s (Smith, 1985), popula-tions of CWTD were estimated at 3,000animals in the north on the ColumbiaRiver and 6,000 individuals in southernOregon when the subspecies was delistedby the Department of Interior in 2003 (FRDoc. 03-17756). Parasitologic informationpreviously available for CWTD has beenlimited to notes on the occurrence ofpulmonary nematodes, with one caseidentified as Dictyocaulus viviparus(Bloch, 1782) (Scheffer, 1940; Gavin etal., 1984); however, this record may be inerror because these lungworms in westerncervids are attributable to Dictyocauluseckerti Skrjabin, 1931 (Hoberg andAbrams, unpubl. data). During recentprecipitous declines in the northern pop-ulation of CWTD, a health survey wasinitiated that reported the occurrence ofDSLs and a presumptive, but uncon-firmed, identification of P. andersoni(Creekmore and Glaser, 1999).

In the current study, we address thepaucity of definitive information about thehost and geographic associations for spe-cies of Parelaphostrongylus through fecal-based sampling of endemic white-taileddeer in Oregon and Washington. Disjunctpopulations of CWTD were sampled forDSLs, one population on the lowerColumbia River and the other populationon the North Umpqua River. We furtherdiscuss the biogeography and history of P.andersoni and related species in cervidhosts from North America.

MATERIALS AND METHODS

Fecal specimens

Fecal samples were collected from 31 adultCWTD across the range occupied by thissubspecies in Oregon and Washington. On theJulia Butler Hansen Refuge at Puget Island,Washington, USA, and on the south bank ofthe Columbia River in Oregon on 25–26March 2006, 21 fecal samples were collectedin the process of handling animals duringa relocation project (Table 1). Activities werecovered under the following jurisdiction: 1)Federal Fish and Wildlife permit (TE702631-18, subpermit WNWR-6) was issued by the

18 JOURNAL OF WILDLIFE DISEASES, VOL. 44, NO. 1, JANUARY 2008

US Fish and Wildlife Service; and 2) OregonScientific Taking Permit (065-06) was issuedby the Oregon Department of Fish andWildlife for the collection of the deer on thelower Columbia River. Washington state didnot require a permit due to involvement ofWashington Department of Fish and Wildlifepersonnel. In Douglas County, along theNorth Umpqua River, fresh fecal sampleswere collected from the ground after defeca-tion by 10 identified CWTD, including eightadult females and single male and femalefawn; in this area, CWTD are sympatric withColumbia black-tailed deer (CBTD), Odocoi-leus. hemionus columbianus, and thus it wasnecessary to identify the source of fecalsamples.

Fecal specimens were extracted for recoveryof first-stage protostrongylid larvae usinga modified Beaker-Baermann technique (For-rester and Lankester, 1997; Jenkins et al.,2005); numbers of larvae per gram of feceswere not quantified. Dorsal-spined larvae ofputative elaphostrongyline nematodes weresorted and individual specimens were trans-ferred by micropipette to single cryo-vials withmolecular grade water for further processing.Voucher specimens were preserved in 70%ethanol and deposited in the US NationalParasite Collection, USDA, Beltsville, Mary-land (USNPC; Table 2).

Comparative specimens

Two isolates of P. tenius recovered fromfecal samples in white-tailed deer collected onor near Gibson Island, Maryland, USA, wereused for comparisons using cytochrome coxidase subunit 1 (COI; Table 2). Two isolatesof P. odocoilei from coastal Oregon werecollected from CBTD (OR-8244 and OR-8408 in Mortenson et al., 2006), and a thirdisolate was collected from a Dall’s sheep Ovisdalli at Katherine Creek, Mackenzie Moun-tains, Northwest Territories, Canada (Ta-

ble 2). These three isolates of P. odocoileiwere used for COI comparison.

DNA extractions and polymerase chain reaction(PCR) amplification

Individual DSLs were assessed via multi-locus sequencing of nuclear ribosomal (in-ternal transcribed spacer 2 [ITS-2]) andmitochondrial (COI) DNA. The DNA wasextracted from single DSL (two each from 12CWTD hosts from the lower Columbia River;three each from three CWTD and one froma forth CWTD from Douglas County) usinga DNeasy Tissue Kit (QIAGEN, Valencia,California, USA) and eluted twice with 100 mlof AE buffer provided in kit. The PCRamplification (DNA Engine PTC-200, MJResearch, Watertown, Massachusetts, USA)used 4 pmol of each of NC1 and NC2 primersfor ITS-2 (Gasser et al., 1993) or primersPtCOI-F (GGTTGGAGAGTTCTAATCA-TAAAGA) and PtCOI-R (CCCAAACATAG-TAGCCAACCA) for COI, 0.2 U of PlatinumTaq DNA Polymerase High Fidelity (Invitro-gen, Carlsbad, California, USA), 4 nmol eachof dNTP mix (Sigma-Aldrich, St. Louis,Missouri, USA), and 2 ml of template in 20-mlreaction (94 C for 2 min, 353 [94 C for20 sec, 50 C for 30 sec, 68 C for 40 sec], 68 Cfor 7 min).

Cloning and sequencing

Due to difficulty sequencing through a poly-A region, PCR products of ITS-2 were clonedusing a TA Cloning Kit (Invitrogen) into OneShot chemically competent cells (Invitrogen).Colonies containing the insert were PCRamplified directly by first transferring cellsinto 50 ml of molecular grade water andheating to 90 C for 10 min, and then using2 ml of that as template with M13 forward andreverse primers supplied in the TA CloningKit (4 pmol each). The PCR conditions wereas described above. PCR products for COI

TABLE 1. Locality data for fecal samples from Columbia white-tailed deer.

Host collection location (moved to) No. of deer % prevalence

Puget Island, Washington, USA 7 43(Fisher Island) 7 43

South bank of Columbia River, Oregon, USA 15 60(Lord Island) 9 44(Crimms Island) 1 0(Gull Island) 4 100(not moved) 1 100

Douglas County, Oregon, USA 10 50

ASMUNDSSON ET AL.—P. ANDERSONI IN WESTERN NORTH AMERICA 19

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20 JOURNAL OF WILDLIFE DISEASES, VOL. 44, NO. 1, JANUARY 2008

were sequenced directly. BigDye Terminatorv3.1 chemistries and an ABI Prism 3730xlDNA Analyzer were used for sequencing(Applied Biosystems, Foster City, California,USA).

Data analysis

Sequence chromatograms were edited usingSequencher version 4.6 (Gene Codes, AnnArbor, Michigan, USA). Identification ofDSLs based on ITS-2 used a BLAST search,and definitive differentiation was done inreference to fixed nucleotide polymorphismpreviously documented among the threespecies of Parelaphostrongylus according toJenkins et al. (2005). Edited COI sequenceswere aligned in Vector NTI (Invitrogen). Thealignment was edited by eye using GeneDoc(Nicholas and Nicholas, 1997) and convertedto nexus format in ClustalX (Thompson et al.,1994). Inference of phylogenetic relationshipof COI haplotypes was reconstructed inPAUP* 4.0b10 (Swofford, 2001) by means ofthe neighbor joining uncorrected ‘‘P’’ distancemethod. All novel sequences from the presentstudy were deposited in GenBank (Table 2).

RESULTS

Specimens of DSLs were found in fecalsamples in deer from both the northernand southern populations of CWTD (Ta-ble 1). Twelve of the 21 fecal samplesfrom the northern population containedDSLs as follows: three of seven (43%)deer from Puget Island, within the lowerColumbia River; and nine of 14 (60%)deer from the south bank of the ColumbiaRiver. Five of 10 fecal samples from thesouthern population contained DSLs, andparasites were demonstrated at eachlocality within the sampling region; allhosts were adults except for one malefawn.

A 504–511-base pair (bp) fragment ofITS-2 sequence was amplified indepen-dently from 33 DSLs in 17 CWTD.Twenty-two DSLs from the northernpopulation of CWTD on the ColumbiaRiver were sequenced: two larvae from 10hosts, and a single larva from two hosts.Eleven DSLs from the southern popula-tion of CWTD on the North UmpquaRiver were sequenced: three each from

two hosts, two from two other hosts, anda single DSL from the fifth host. All 33sequences were identified as being con-sistent with P. andersoni (four extractionsfailed to yield usable sequence).

After assessment and initial identifica-tion based on the ITS-2 data, COI wasamplified and sequenced from 22 of the37 DSLs in CWTD (13 from the northernpopulation and nine from the southernpopulation) and further compared withsequences from P. tenuis and P. odocoilei(Table 2). The 22 amplicons were 773–863 bp. The 728 bp shared by all isolatesof P. andersoni represented six haplotypes,none of which differed in pairwise com-parisons by more than 8 bp (1%). Addi-tionally, 517–521 bp were aligned forcomparison with the other species ofParelaphostrongylus. Phylogenetic recon-struction revealed reciprocal monophylyrelative to sequences representing othercongeneric species.

Multilocus data establish a new recordfor P. andersoni in disjunct populations ofa subspecies of O. virginianus previouslyunrecognized as hosts. These new recordssubstantially extend the known geographicrange for P. andersoni to the basin of thelower Columbia River in Oregon andWashington and to the North UmpquaRiver in south-central Oregon.

DISCUSSION

Host and geographic range

A new host and geographic record isestablished for P. andersoni in the north-ern and southern populations of CWTDfrom Oregon and Washington. Despitea high level of nucleotide conservationwithin ITS-2 sequences of this genus,P. odocoilei, P. tenuis, and P. andersonican be differentiated based on severalfixed nucleotide polymorphisms (Jenkinset al., 2005); a phylogenetically basedcomparison of COI data from DSLs inCWTD to sequences from P. tenuis and P.odocoilei further supports this identifica-tion. Thus, we substantially extend the

ASMUNDSSON ET AL.—P. ANDERSONI IN WESTERN NORTH AMERICA 21

known geographic distribution of thiselaphostrongyline in white-tailed deer tonear the Pacific coast of North America(Fig. 1). Furthermore, this confirms theprior presumptive identification of P.andersoni in fecal samples from five of20 CWTD at Tenasillahe Island on theJulia Butler Hansen Refuge (Creekmoreand Glaser, 1999).

Discovery of P. andersoni in CWTD atdisjunct localities in far western NorthAmerica alters our understanding of geo-graphic range, but it does not yet resolvethe issue for continuity versus isolation orheterogenous distributions for parasitepopulations (Fig. 1). Based on geograph-ically dispersed records for this parasite inO. virginianus across North America,occurrence of P. andersoni in the PacificNorthwest certainly is not completelyunexpected (e.g., Mortenson et al.,2006). Limited records for this parasitemay reflect inadequate or incompletesampling (Lankester, 2001), difficulty indemonstrating the presence of adult para-sites during necropsy (Lankester andHauta, 1989), inability to reliably differ-entiate DSLs of congeners and otherprotostrongylids in fecal samples (e.g.,Jenkins et al., 2005), or an actual disjunctor heterogenous geographic range drivenby historical and environmental factors.

Parelaphostrongylus andersoni hasbeen widely recorded in the southeasternUnited States (Prestwood et al., 1974).Intensive sampling in this region (121 deerin 11 states) by technically proficientparasitologists may provide an explanation,opposed to being indicative of a higherregional prevalence for the parasite. Lan-kester (2001) suggested that the apparentdisjunct distribution for P. andersoni inO. virginianus reflected the incompletenature and difficulty of sampling for thiscryptic parasite in the musculature.

Alternatively, a limited distribution mayresult from competitive interactions withP. tenuis in zones of contact for theseelaphostrongylines in North America(Lankester and Hauta, 1989; Lankester,

2001). The absence of P. andersoni in deerfrom some eastern localities suggests thiselaphostrongyline may be effectively re-placed by P. tenuis on a cline extendingnorthward in eastern North America, butthe western limit for the latter has notbeen clearly documented outside of south-ern Canada (Lankester, 2001). It has beenpostulated that the presence of P. tenuis,which is not known to occur in thesoutheastern United States, suppresses oreliminates infections of P. andersoni bycross-immunity or another mechanism(Lankester and Hauta, 1989; Lankester,2001). Interestingly, the few recordsdocumenting natural mixed infections inO. virginianus are from the mid- to southAtlantic region of coastal North America.For example, 10 deer examined at thePeaslee Wildlife Management Area inNew Jersey revealed both P. andersoniand P. tenuis (Pursglove, 1977), but it wasnot clear whether infections were concur-rent in single hosts. Additionally, two of 52white-tailed deer from North Carolinawere found to be infected with bothspecies (Prestwood et al., 1974). A con-comitant experimental infection has alsobeen demonstrated in a white-tailed deerfawn (Pybus et al., 1990).

Putative isolated or focal populations forP. andersoni in Dakota white-tailed deer(Odocoileus virginianus dakotensis) fromnortheastern Wyoming and the northwestwhite-tailed deer (Odocoileus virginianusochrourus) from southeastern British Co-lumbia are apparently beyond the westernlimit of the distribution known for P.tenuis. Notably P. tenuis, but notP. andersoni, has been discovered inwhite-tailed deer (Odocoileus virginianustruei) from Costa Rica (Carreno et al.,2001). Additional field data seem tosupport the contention that sympatry islimited for P. andersoni and P. tenuis.Necropsy of 42 white-tailed deer failed tofind P. andersoni in central Maine (Bo-gaczyn, 1992), where P. tenuis is known tooccur. In a study involving 10 white-taileddeer in Oklahoma, USA, nine were found

22 JOURNAL OF WILDLIFE DISEASES, VOL. 44, NO. 1, JANUARY 2008

to be infected with P. tenuis and none withP. andersoni (Pursglove, 1977).

A western distribution for P. andersoniwould suggest the potential for sympatrywith P. odocoilei in some habitats andlocalities (Fig. 1). Throughout the distri-bution of CWTD, dispersion and habitatuse overlapping with CBTD, which rangewest of the Cascade and Sierra NevadaMountains, has been well documented(Smith, 1987). The southern population ofCWTD is sympatric with black-tailed deeralong the North Umpqua River, whereasthe northern population along the lowerColumbia River is parapatric. Parelaphos-trongylus andersoni and P. tenuis are notknown to naturally infect black-tailed deeror mule deer within the host’s naturalrange, and P. odocoilei has not been foundin white-tailed deer (summarized in Lan-kester, 2001), despite evidence of hybrid-ization of the two host species (Hughesand Carr, 1993). Preliminary evidence thatsegregation may be maintained for speciesof Parelaphostrongylus among species ofOdocoileus is suggested by the occurrenceof P. odocoilei in coastal populations ofCBTD in relative parapatry to CWTDwhere P. andersoni was demonstratedin the current study (Mortenson et al.,2006). Continued sampling, however, isnecessary to define the distribution ofParelaphostrongylus in the doughnut holeencompassing eastern Oregon and Wash-ington and the Great Basin extending toWyoming in the east and British Columbiain the north.

Potential limitations on completion ofthe life cycle for P. andersoni due toabiotic environmental factors determininglarval development or the distribution ofgastropod intermediate hosts could alsohave an influence on overall geographicdistribution. There is a paucity of data,however, for climatologic or biotic factorsserving as controls on the potential fortransmission for elaphostrongylines andother protostrongylids (Lankester, 2001;Kutz et al., 2002). Known intermediatehosts, including slugs of the genus Dero-

ceros, are abundant and widespread inNorth America, and they indicate thepotential for transmission, although suchmay be influenced by seasonality, micro-climate, density of gastropods, and thedistribution of cervids (Lankester, 2001;Jenkins et al., 2006). Lankester (2001) hadsuggested that the broad distribution forP. andersoni, which encompasses a rangeof often extreme habitats from the south-eastern United States into the Arctic, wasevidence of considerable environmentaltolerance for these nematodes.

Collections documented from thenorthern population in the current studywere taken during the translocation ofanimals within the Julia Butler HansenRefuge along the Columbia River. Thus,the sources for animals and their historyare known, and it is clear that P. andersonihas been disseminated with these move-ments of infected hosts (Table 1). Al-though the muscleworm is likely to bedistributed throughout this refuge inCWTD, the role of host relocation asa determinant of parasite introduction andestablishment is clearly demonstrated.Such has been a concern with respect tothe distribution of the congener P. tenuisand the relationship to emergence ofdisease attributable to this parasite innew localities and hosts (e.g., Samuel etal., 1992; Lankester, 2001). This serves toemphasize the pervasive nature of anthro-pogenic events, particularly conservation-based or management-based decisions fortranslocation that may influence the over-all distribution of parasites and pathogens.These observations constitute a strongjustification for development of baselinesand archival collections for biodiversity todocument faunal perturbation (e.g., Ho-berg et al., 2001, 2003).

Molecular-based survey

Dorsal-spined larvae of P. andersoni,which are easily recovered from freshfeces, are morphologically indistinguish-able from those produced by congeners, aswell as other protostrongylids such as

ASMUNDSSON ET AL.—P. ANDERSONI IN WESTERN NORTH AMERICA 23

Varestrongylus alpenae (Dikmans, 1935)and Muellerius capillaris (Mueller, 1889)that occur in North American cervids andcaprines (e.g., Boev, 1975; Jenkins et al.,2005; Kutz et al., 2007). Before the adventof molecular markers for these nematodes,adult worms had been required to confirmthe identity of species infecting each host.Adult P. andersoni are found in or aroundthe blood vessels of the musculatureassociated with the hindquarters of thehost (Lankester, 2001). Therefore, to doc-ument an infection, a labor-intensive nec-ropsy was involved, which no doubt hasvastly limited the number of geographicrecords for this and other elaphostrongy-line parasites. Molecular analyses of DSLsare necessary to establish the true range ofthis parasite in white-tailed deer acrossrespective subspecies and their ranges.

Before the application of geographicallyextensive and site-intensive sampling inconjunction with molecular-based protocols(Jenkins et al., 2005), the ranges describedfor other elaphostrongylines, such as P.odocoilei, were considered to be heteroge-nous and disjunct (Kutz et al., 2001;Lankester, 2001). Fecal-based surveys inconjunction with population level geneticanalysis will be a powerful tool for timelyassessment of geographic range; rapidlychanging patterns of distribution, such asthose anticipated with habitat perturbationand global climate change; and for eluci-dating the complex coevolutionary historyamong these parasites and their hosts.

Establishing a broader context forParelaphostrongylus and cervid hosts

Parelaphostrongylus is endemic to theNearctic and seems to have coevolvedwith species of Odocoileus (Platt, 1984;Carreno and Lankester, 1994). Occur-rence of P. tenuis in Costa Rica at thenorthern limits of the Neotropical regionis attributed to range expansion for hostsand parasites from North America (Car-reno et al., 2001). Furthermore, species ofParelaphostrongylus are currently un-known in species of Odocoileini (among

Mazama, Ozotoceros, and Blastocerus) orRangiferini (among Hippocamelus andPudu) endemic to South America, poten-tially consistent with a restricted historyfor these elaphostrongylines in NewWorld cervids in the Northern Hemi-sphere (e.g., Carreno and Lankester,1994).

Historical bottlenecks for deer popula-tions, with local extirpation, may haveinfluenced contemporary patterns for oc-currence and population structure relativeto past distributions among species ofParelaphostrongylus. Such may accountin part for heterogenous distributions thatare apparent for P. andersoni, particularlyin the western region of North America,and along the Atlantic coastal plain(Fig. 1). For example, Columbia white-tailed deer underwent a sharp decline innumbers during the 1800s when theColumbia River population was estimatedto be approximately 500–700 animals(Scheffer, 1940). The population has sinceincreased to numbers supportable byavailable habitat, and it is consideredstable, although a precipitous decline inthe northern population was documentedin 1996 (Creekmore and Galser, 1999).Presumably, the northern population hasbeen physically and genetically isolatedfrom the southern population of CWTD inDouglas County, Oregon. Additionally,the Columbia River population seems tohave been continuously isolated fromother white-tails (O. v. ochrourus) ineastern Oregon and Washington by.300 km. Phylogeographic analyses canresolve how this history of isolation hasinfluenced populations of P. andersoni inCWTD and how such are related to thosepopulations distributed to the east in bothO. v. ochrourus and O. v. dakotensis.

Results of the current study confirma geographically extensive range for P.andersoni in white-tailed deer. A putativesister-species association with P. odocoileisuggests that the distribution of thiselaphostrongyline is limited to the Nearc-tic and that occurrence in caribou (sub-

24 JOURNAL OF WILDLIFE DISEASES, VOL. 44, NO. 1, JANUARY 2008

species of R. tarandus) is attributable tohost switching during the Pleistocene(Carreno and Lankester, 1994). If caribouwere hosts for P. andersoni before the lastglaciation, genetic partitioning would bepredicted between lineages that survivedin the eastern Beringian refugium andsouth of the Laurentide and Cordillera icesheets. In contrast, host switching fromdeer may have occurred during the finalstage of the Wisconsin south of theLaurentide ice in the precursor of R. t.caribou, with secondary geographic ex-pansion and colonization of R. t. groen-landicus and R. t. grantii during theHolocene. The latter would be consistentwith phylogeography for subspecies ofRangifer across the Holarctic (Flagstadand Røed, 2003) and represents a frame-work or testable hypothesis for exploringthe history of P. andersoni among cervidhosts in the Nearctic.

Whether the current parasite distribu-tion can be explained by a single host-switching event or results from multipleorigins from independent colonizationevents can be tested by examining thepartitioning of genetic diversity across theentire range for P. andersoni in deer andcaribou. Analyses of haplotype diversitycan contribute to understanding the bio-geography of this species. In addition,a comparison of haplotype diversity of P.andersoni among populations of CWTDand other white-tailed deer would beinformative about true levels of isolationbetween these host populations sincedeclines and range retraction by CWTDduring the postsettlement period.

ACKNOWLEDGMENTS

We thank A. Abrams of the USNPC forassistance in sampling DSLs from deer. Also,we gratefully acknowledge Oregon Depart-ment of Fish and Wildlife biologists D.VandeBergh and T. Lum for assistance inobtaining samples.

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Received for publication 22 December 2006.

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