Birds As a Factor in the Control of a Stomach Worm of Swine

38O BirdControl ofStomach Worm of Swine. rAuk[July BIRDS AS A FACTOR IN THE CONTROL OF A STOMACH WORM OF SWINE. • BY r•Lo•sr• B. caxM. Introduction. A GROUPof roundwormparasites known as spirurlds,the name being derived from the superfamilyname Spiruroidea,occur as adultsin a wide variety of hosts,including mammals, reptiles and birds. Theseparasites have an indirectlife history,that is one in which there is involved an intermediate host. This intermediate host is usually a small arthropod, such as an entomostracanor insect; encystedin the body tissuesof the arthropod, the larval form of the parasitedevelops to a stagewhich is infectivefor the final host. Birdswhich feed on arthropodsin largenumbers, such as water birds which eat entomostracans and insectivorous birds which eat insects, are therefore liable to infection with such parasitesand it is not surprisingthat a great variety of adult roundwormsof this groupis found to occurin suchbirds. However, the arthropodswhich are eaten by birds may be infestedwith roundwormlarvae which as adults parasitizea group of animals other than birds, such as mammals. The fate of such larval parasiteswhich are thus introducedinto the wronghost has beenstudied by earlier workers,notably the French parasitologist Seurat, who found that the larvae migrate into the tissuesof such a host and again encyst. The presentinvestigation resulted from the discoverymade by H. L. Stoddard several years ago that the LoggerheadShrikes (Lanius ludovicianusludovicianus) in northern Florida, chiefly in Leon County, and in southernGeorgia, chiefly in Grady County, were infestedwith large numbersof roundwormsencysted in the walls of the digestivetract. Theseparasites were identifiedby the writer as splruridlarvae and the infestationas a caseOf aberrant parasitismsuch as that mentionedabove, the larvae being in a • Read before the Forty-seventh Stated Meeting of the American Ornithologists ' Union at Philadelphia, Pa., October 24, 1929 voiwx] riraCorol 4 atomhWorn 4 aw/e. 381 host other than the correct final host and thereforeincapable of further development.As the larval formsof theseparasites have been little studied, identification was thought impossiblefrom morphologicalexamination, but an opportunitywas later presented for a moreextensive investigation of the life historyof the parasite by meansof feedingexperiments. Findingsof presentinvestigation.--During a two monthsperiod, May and June, 1928, twenty-oneLoggerhead Shrikes from Leon County, Florida, were examinedby the writer and eachbird was found to be infestedwith large numbersof the encystedlarval parasites. The roundwormswere located in the walls of the digestivetract, nearits outersurface, and alsoin the mesenteries. All parts of the digestivetract werefound to be parasitized,from the upperend of the esophagus,near the mouth, to the lowerend of the intestine. As regardsthe stomach,the wall of the pro- ventriculuswas more heavily infestedthat that of the gizzard. However, the concentrationof the infestationwas observedto be alwaysat the posteriorend of the digestivetract, in the rectumand its mesenteries;here the larger numberof larvae and the thinner wallsof the tract greatlyfacilitated the findingof the parasites. Therewas no visibleevidence of damageto the wall of the digestive tract from thesemaSsive invasions of small roundworms;due to the fact that onehundred per cent of the Shrikesof that vicinityappear- ed to be infested,judging from a considerablenumber of examina- tionsmade by H. L. Stoddardduring a periodof five years,and from the twenty-oneexaminations made by the presentwriter, no com- parisonwas possibleof an infestedwith a non-infestedbird, to judgeof clinicalor pathologicalresults of the parasitism. Desiring,as a 'first step in the unravellingof the life history of thisparasite, to discoverthe arthropodintermediate host which was responsiblefor the infectionof the Shrikes,the writer wasstruck by the fact that the stomachcontents of the birdsin a largepercentage of casesshowed the brightly coloredparts of the dung beetle, Phanaeusearnilex, and attentionwas accordinglydirected toward this beetle as a possibility. Examination of specimensof P. earnilexin the samevicinity revealed the fact that practicallyone hundredper cent were heavily parasitizedwith the samelarval roundwormas was found in the Shrikes. A seconddung beetle, 382 caA, BirdControl ofStomach Worm ofSwine. [•lky Canthonlaevis, was alsofound to be infested,although to a lesser degree. Examinationof birdsother than the Shrike,which would probably feed on thesebeetles, resulted in the findingof similarnatural infestationsof the larval roundwormin three ScreechOwls (Otus asiaasia) and one Red-tailedHawk (Buteaborealis borealis) taken in Grady County, Georgia. In an attempt to determinethe final hostof the parasite,feeding experimentswere undertaken;larvae derivedfrom Shrikesand also thosefrom the arthropodhosts, were fed to a seriesof experiment animals, representingbirds, mammals and reptiles, with the followingresults: ReSncystmentof larvaederived from the Shrikewas experimentally producedin the digestivetracts of oneTurkey, two Chickens, two Red-tailed Hawks, one skunk,one oppossum,two rats, three mice and one black snake. ReSncystmentof larvaederived from the dungbeetle (Phanaeus carnifex),was experimentally produced in the digestivetracts of one ScreechOwl, three Turkeys, three Bobwhites,three Chickens, one Pigeon,one skunk, one opossum,one mouse,two rats, one rabbit and one guineapig. In theseexperiments check animals held as controlsin eachcase werenegative with referenceto infestationwith the parasiteexcept in the casesof the Owls,Hawks, rats, and snake,in which the check animalswere also parasitized. It is possible,therefore, that the findingsin theseanimals, after experimentalfeeding, represented an experimentalinfestation superimposed on a natural infestation. The reSncystmentof the spiruridlarvae in eachof theseexperi- ment animalsindicated that the final host of the parasitewas not includedin the series. As the resultof an observationmade during the collectionof the dungbeetles, namely that in pasturesin which there was a choiceof manure from cattle, horsesand swine, the beetlesshowed a decidedpreference for that from swine, it was concludedthat swinewere probably the final hostof the parasite. Accordinglythree young pigs were fed respectivelyas followswith the results as shown: Six specimensof the beetle(Phanaeus carnifex), with the finding at necropsytwo monthslater of approximately1700 specimensof Vol. 1930XL¾II] J CRAM,Bird Control ofStomach Worm of Swine. 383 the roundworm(Physocephalus sexalatus), in the stomachof the pig. About one-halfthe lengthof the intestinalwall of a Loggerhead Shrike,with the findingat necropsy80 dayslater of approximately 800 specimensof the roundworm(Physocephalus sexalatus), in the stomachof the pig. Six specimensof the beetle(Canthon laevis), with the findingat necropsy51/• months later of 12 specimensof Physocephalus sexalatusin the stomachof the pig. This feeding•xperiment, in contrastto the formerseries which wascarried out at Beachton,Georgia, was conducted at the experiment station at Beltsville, Maryland, the beetles and Shrike viscerahaving been brought from Florida; the pigswere raised on concretefloors and two of the lot of five pigswere held as check animals,these showing at necropsyan absenceof the stomach wormswhich were present in the experimentallyfed pigs. D/scuss/on.--Theidentity of the larval roundwormsfound in casesof aberrantparasitism encysted in the wallsof the digestive tractsof LoggerheadShrikes, Screech Owls and Red-tailedHawks in southernGeorgia and northern Florida was thus establishedex- perimentallyas Physocephalus sexalatus, which in its adult formis a stomachworm of swine. The arthropodintermediate hosts of the roundworm,from which the birds derive the infestation, were foundto be the dungbeetles, Phanaeus carnifex and Canthonlaevis. It was experimentallyestablished that the parasite would also encystin Chickens,Turkeys, Bobwhitesand Pigeons,as well as in certain mammals and reptiles. However, due to the food habitsof the Shrike,that is, habitsinvolving a largeconsumption of these beetles,and the abundanceof these birds in the area involved,the Shrikeis probablythe mostimportant of the accidental hostsof this parasitein that locality. The practicalsignificance of thesefindings is easilyseen. Swine beingraised in suchan area are protectedfrom infectionwith this roundwormto the extentto whichthe arthropodintermediate hosts are consumedby birds and other animalswhich serve as accidental hosts. It wasshown that sixspecimens of the dungbeetle (Phana- eu,earnilex) were capable of infectinga pigwith approximately 1700 specimensof this stomachworm. The numbersof theseparasites 384 CRA,Bird Control ofStomach Worm of Swine. [July[Auk which are prevented from completing their normal life cycle, becauseof the ingestionof the beetlesby Shrikesand otherbirds of similar food habits, is thereforeevidently enormous,and birds in this manner undoubtedlyare an important factor in limiting the degree of infestatlon of swine with this parasite. A definite correlationmay be suspectedbetween these two factorsand it is probablethat a decreasein suchbirds would result in an increase in this stomachworm of swine,in a givenarea suchas that consider- ed. While swinewould becomeinfested by eating theseaccidental secondaryhosts, and doubtlessdo in somecases, it seemslikely that this would happenonly rarely and that

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