MOSIS-LIKE DISEASE IN StflNB.

EPERYTHROZOON SUIS N. SP., THE ETIOLOGICAL AGENT OP ICTERO-ANEMIA OR AN ANAPLAS- MOSIS-LIKE DISEASE IN StflNB. by EARL JOHN SPLITTER D. V. U., Kansas State Cllege f Agriculture and Applied Science, 1943 A THESIS submitted in partial fulfillment f the requirements fr the degree MASTER OP SCIENCE Department f Pathlgy KANSAS STATE COLLEGE OP AGRICULTURE AND APPLIED SCIENCE 1950

li >U>9 Niell TABLE OP CONTENTS Page INTRODUCTION 1 MATERIAL AND METHODS 6 OBSERVATIONS ON FIELD CASES OF "ICTERO-ANEMIA" 9 Herd A 9 Herd B 11 Herd C 11 Herd D 13 MICROSCOPIC BLOOD EXAMINATION OF NORMAL SWINE 13 EXPERIMENTAL STUDIES 17 Experimental Prcedure 17 Differentiatin f Eperythrzn Species... 19 Mrphlgy 20 Eperythrzn aula 20 Eperythrzn parvum 22 Pathgenesis and Symptms 22 Mrbid Anatmy 26 Prevalence, Transmissin, and Relatin t Hg Chlera. 27 Chemtherapy, 29 DISCUSSION 32 SUMMARY 38 ACKNOWLEDGMENT 41 LITERATURE CITED 42

INTRODUCTIOH A disease entity characterized by generalized icterus and acute anemia has been recgnized fr a number f years in svine in the midwestern states. This spradic cnditin was first reprted by Kinsley (1932), and later that year by Dyle (1932). Since the initial descriptin f the disease articles have been written by Kinsley and Ray (1934), Dicke (1934), Quln (1938), Spencer (1940), Rbb (1943), and Campbell (1945). These Investigatrs have been in cmplete agreement in regard t symptms, grss pathlgy, clinical histry, and varius ther aspects cncerning the disease. It has appeared that this is a distinct disease entity f swine, and because f the similarity t bvine anaplasmsis it has been called "anaplasmsis-like disease" r "icter-anemia". The etilgy f the disease remained unknwn. The investigatins which are reprted in this thesis were begun fllwing the bservatin by the authr f an unreprted bld parasite in swine. The rganism was fund assciated with field cases f "icter-anemia" r "anaplasmsis-like disease". These studies were begun with the primary purpse f establishing whether r nt this parasite is in any way respnsible fr the disease with which it was fund assciated. Clinical and labratry data were gathered frm a number f field utbreaks f the "anaplasmsis-like" disease. The disease was reprduced in experimental swine, and the resulting symptms, disease prcess, and pathlgy were cmpared t thse f field cases in rder t establish prf f the etilgy f the disease.

Studies were undertaken t differentiate the rganism frm Eperythrzn species f ther animals, and frm anther Eperythrzn fund in these investigatins in swine. Experimental studies f the chemtherapy f the disease were als cnducted. Dr. David Weinman f the Tale University schl f Medicine; Dr. Rue Jensen, Clrad A. and M. Cllege; and Dr. '»;' 0. Neitz, Ondersteprt Labratry, Unin f suth Africa have cncurred in the identity f the tw species bserved as members f the genus Eperythrzn. The parasite which was bserved in field cases f "icter-anemia" was given the name Eperythrzn suls, and Eperythrzn parvum is the name given t the rganism fund during these experimental studies. At the time f this writing, E. suls has been fund assciated with a ttal f eight herd utbreaks f "icter-anemia". six f these ccurred in Iwa and tw in Kansas. Varius investigatrs in the past have reprted the presence f what appeared t be hemtrplc micr-rganisms assciated with the "anaplasmsis-like" disease f swine. Kinsley (1932) bserved a spherical bdy in the erythrcytes that resembled Anaplasma. Dyle (1932) described the structure he bserved as fllws: Bld smears stained with Oiemsa stain shwed the presence f bdies, evidently rganismal in nature, within the red cells. These bdies shwed cnsiderable variatin in mrphlgy. Sme were cccid, sme bacillifrm, while still thers were ring frmed. The ring frmed bdies ften shwed small chrmatin knts r masses at certain pints n their circumference. Sme f the erythrcytes were almst filled with these bdies, and many f the bdies were free frm the red cells. Dicke (1934) gives a similar accunt f an rganism he bserved in cases f "icter-anemia". The descriptins given by the tw

latter men are similar t the descriptin f E. suis, with certain variatins which will be nted later, fibb (1945) bserved similar structures assciated with "icter-anemia" and als in nrmal swine. He cncluded that the structures were actually artifacts having n cnnectin with this disease. Dyle (1945) stated that the red cell inclusins in typical "icter-anemia" are mre suggestive f Bartnella than they are f Anaplasma. Quin (1938) believed the disease t be transmitted by vectrs, and the causal agent t be a Pirplasma r Anaplasma. Kinsley and Ray (1934), Rbb (1943), and Dykstra and c-wrkers (1948) reprted failure in attempts t transmit the disease t nrmal swine. In a recent survey Harshfleld (1949) reprted ccurrences f this disease in ten states, fur f which bserved it in 1948. Breed (1950) describes an icter-anemic cnditin in yung pigs which he has attributed t imprper nutritin. He states that the bld cells cntain many bdies which may be mistaken fr bld parasites. Bld parasites f the genus Hperythrzn (E. cccides ) were first bserved by Schilling (1928) in aplenectmized mice. Bruynghe and Vassilaidis (1929) described E. dlspar f the vle. Adler and Ellenbgen (1934) reprted the presence f an Eperythr - zn in cattle in Palestine. They fund the rganism assciated with Thelleria annulata and Anaplasma. Neitx, Alexander, and Du Tit (1934) reprted a new species, E. vis, in African sheep. In classifying the genus, Eperythrzn, these wrkers were f the pinin that the rganism is clsely related t Bartnella, Grahamella, and Anaplasma. Their selectin f this classificatin

was based nt nly n mrphlgy, but als n symptms and curse f the disease prcess. A cmmn symptm resulting frm these rganisms is an anemia characterized by degenerative and regenerative changes in the bld. These changes ccur smetime after the appearance f the parasite, in a manner similar t that bserved in infectins with Anaplasma. Elit (1936) succeeded in transmitting E. cccldes with the luse, Plyplax serrata. Neitz (1937) described an acute, febrile anemia f sheep resulting frm experimental infectin with E. vis. He fund the pst mrtem lesins t be identical with thse f acute anaplasmsis. Neltz (1940) reprted bservatins n eperythrznsis f African cattle. The parasite appeared t be Identical t E. wenynl f Palestine cattle. Ltze and Tiengst (1941) first reprted the presence f E. wenynl in cattle in the United States, and fund it t be assciated with bvine anaplasmsis. Jensen (1943) fund the same rganism in mixed Infectins with anaplasmsis, and in calves unassciated with anaplasmsis in Luisiana. Jensen (1943) als fund E. vls t be an apparently cmmn bld parasite f native Luisiana sheep. His wrk crrbrated that f Neitz (1937) in demnstrating that the parasite is capable f prducing an acute, febrile anemia and icterus in susceptible, unperated sheep. Dykstra et al. (1948) reprted the presence f E. wenynl asaciated with bvine anaplasmsis in Kansas. Tyzzer and Weinman (1939) fund E. dispar t be a cmmn parasite f the vle, Micrtus pennsyl vanlcus, in the eastern United States. Tyzzer (1942) reprted a new species, E. varlans,

in the field muse, Permyacus maniculatua. Clark (1942) bserved an Eperythrzn in a cat in Suth Africa. The rganism was fund assciated with an acute and fatal anemia. N experimental wrk with this parasite was undertaken. In the therapy f Kperythrzn and Bartnella infectins, investigatrs fund varius arsenicala and arsenic -antimny cmpunds t exert a parasiticidal actin. Mayer, Br chard t, and Kikuth (1927) fund the rganic arsenicala nesalvarsan, atxyl, and tryparsamide t have high therapeutic value against Bartnella muris. Amak (1950) reprted that nesalvarsan and atxyl have a distinct prphylactic and therapeutic effect n B. muris. Kikuth (1932) reprted a new antimny-arsenic cmpund, std. 386B, t have a therapeutic index f 1:3,500 against B. muris. Kayer and Malams (1936) nted drug-fastness in B. muris frm repeated injectins f Increasing dses f nesalvarsan and std. 386B. Bruynghe and Vassiliadls (1929) were prmpted by the clse relatinship f Eperythrzn and Bartnella t investigate therapy f the frmer disease with nesalvarsan. This cmpund was fund t exert a specific actin n E. cccides. Sulfarsenal and tryparsamide were als fund t be effective. Tyzzer (1941) fund sulfarsphenamine t be effective against E. cccides. Neitz (1937) btained specific therapy f acute eperythrznsis f sheep with nesalvarsan and std. 386B. Nesalvarsan was administered intravenusly, and specific parasiticidal actin was btained in single dses varying frm 10 t 45 mg/kg. The larger dses cmpletely eliminated heavy bld infectins within 15 minutes. Dses less than 10 mg/kg were ineffective.

MATERIAL AND METHODS In the studies made n field utbreaks f "icter-anemia" in swine in Iwa, the authr received assistance frm Dr. R. L. Williamsn, lissex, Iwa. Clinical data and bld films frm animals in the Iwa utbreaks wer assembled by Dr. Williamsn, and frwarded t the Veterinary Research Labratry at Manhattan, Kansas. Pigs shwing clinical symptms and thse nrmal animals in the herds that were re-examined were ear-tagged t prvide prper means f identificatin. N attempts were made t cnduct bld cunts n the Iwa pigs ther than ne which was shipped t the labratry; hwever Tallquist readings f the hemglbin were made n animals shwing clinical symptms. In the herds under investigatin near Manhattan, Kansas, (herds C and D) bld films were btained frm all f the animals in bth grups. Daily bld examinatins were made n the animals shwing clinical symptms. In herd C hematlgical studies were made n alternate days n three pigs in rder t study the bld changes in subclinical cases. Tw f these pigs suffered a relatively heavy parasitic infectin, and the third a very mild degree f infectin. Bld examinatin f these three pigs was cntinued ver a perid f 12 days. All bld films btained in these studies were prepared fr micrscpic examinatin by staining with Gieisa stain. The bld picture as bserved in stained smears frm field cases was taken as a rugh measurement f the animals respnse t erythrcytic destructin. Althugh plychrmatphillic and varying numbers f

Hwell-Jlly bdies are nrmally present in swine f the age grups studied, the abnrmal increase in numbers f these immature cells can be bserved rather easily in clinical and subclinical cases f the "anaplasrasis-like disease" Bld samples fr labratry examinatin were btained frm the anterir vena cava. Bld smears were prepared immediately upn drawing the bld. Erythrcyte and leukcyte cunts, hemglbin determinatins, and packed erythrcyte vlumes were determined dally. The icteric index als was determined when icteric serum was evident* In acutely affected animals pipettes fr erythrcytic cunts were prepared at the time f btaining bld, t insure greater accuracy f results. In these animals a marked agglutinatin f erythrcytes ccurred in citrated r xalated bld, and prevented accurate enumeratin in samples s treated. Erythrcyte and leukcyte cunts were made using the imprved Neubauer hemcytmeter. hemglbin values were determined with a Klett-summersn phtelectric clrimeter. Packed erythrcyte vlume and bld sedimentatin were determined by the use f V/intrbe hematcrit tubes. The icteric index was determined by visual cmparisn with knwn standards. Intravenus injectins were made int the anterir vena cava. Cnsiderable care was taken, particularly with nearsphenamine, t depsit all f the substance within the vein. N untward effects were bserved frm repeated daily punctures f the vein r frm injectins made at this site. Thse cases that came t pst-mrtem revealed nly a slight amunt f hemrrhagic Infil-

8 tratin int the tissues surrunding the vein. Individual sterile needles were used in btaining bld samples t prevent accidental transmissin r Eprythrzn parasites. The nearsphenamine and sdium cacdylate used In these studies -were purchased at a lcal veterinary supply huse. Splenectmy peratins were perfrmed under intravenus anesthesia with sdium pentbarbital. The peratins were cnducted with ease, and n unusual surgical techniques were required. All susceptible swine, the calf, sheep, and mice were held under cnditins as nearly fly-free as pssible t prevent accidental transmissin f Kperythrzn frm knwn infected animals. Susceptible pigs were held in screened, fly-prf stalls at a distance f abut 50 yards frm infected pigs. An arbitrary means f indicating the degree f parasitic infectin was used in these studies, and is designated as fllws: Rare ne Kperythrzn structure in five t ten r mre micrscpic fields; Scarce - ne structure In ne t five micrscpic fields; Occasinal - apprximately 10 t 20 per cent f the erythrcytes cntaining at least ne r mre eperythrza; Frequent - apprximately 50 per cent f the erythrcytes cntaining ne r mre eperythrza; umerus - apprximately 80 t 90 per cent f erythrcytes cntaining ne r mre eperythrza; Very numerus - all erythrcytes infected and sme cmpletely cvered with parasites; Extremely numerus - all erythrcytes infected and many cmpletely cvered with parasites.

9 OBSERVATIONS ON FIELD CASKS OP "ICTJ^O-ANEMIA" Herd A This herd, lcated near Shenandah, Iwa, cnsisted f 77 pigs, a number f sws, and a bar. On May 9, 1949, the pigs were vaccinated with hg chlera serum and virus. Apprximately fur weeks later tw sws and tw pigs sickened and died. Pstmrtem examinatin f the dead pigs revealed a generalized icterus; thin, watery bld; a greatly enlarged, friable spleen; and an range-yellw disclratin f the gastr-intestlnal cntents. N lesins suggestive f hg chlera were bserved in these pigs, r in pigs that died later. Between June 1 and August 1, a ttal f 39 pigs died with this cnditin. Clinical symptms were identical t thse f the "icter-anemia" r "anaplasmsis-like" cnditin described in the literature. A sick pig frm this herd was shipped t a diagnstic labratry n July 13, 1949. The labratry reprt stated that lesins typical f the "anaplasmsis-llke" cnditin in swine were bserved. N bacterial grwth was fund n culturing the tissues. Micrscpic examinatin f bld mears disclsed the presence f many "anaplasmsis-like" bdies in the red cells. On July 23, 1949, tw sick pigs weighing apprximately 80 punds each were delivered t the Kansas State Cllege Veterinary Research Labratry. One pig died enrute, and a pst-mrtem examinatin revealed typical lesins f "icter-anemia". Examinatin f stained bld films frai the tw pigs disclsed the pres-

10 ence f a micr-rganism ( Kperythrzn suis ) very similar in appearance t Kperythrzn wenyni and s. via. Table 1 indicates the degree f parasitic infectin as pig 1 prgressed tward recvery. Bld films were btained frm fur additinal pigs frm this herd, tw f which were visibly affected and tw apparently nrmal. Subclinical anemia develped in bth nrmal pigs, and acute, icter-anemia was evidenced in the clinically affected animals. Bpery thr?, n parasites were bserved in all fur animals. The detailed results f these bld examinatins are given in Table 2. T determine the presence r absence f hg chlera virus, and t attempt transmissin f S. suis, fur cubic centimeters f citrated bld frm pig 1 was injected intravenusly int tw chlera -susceptible pigs. One pig was given 50 cc f anti-hgchlera serum subcutaneusly. Bth pigs remained nrmal after a perid f 45 days. Sperythrza appeared in bth animals, the resulting parasitic infectin being very mild with n clinical symptms evident. The s'tsceptibility f these pigs t Eperythrz n was nt prved prir t inculatin. It is, therefre, unknwn whether the animals were in a state f premunitin, r the infectin bserved was a recrudescence f a latent infectin r an actual transmissin. Bld films frm bth animals were negative prir t inculatin. E. sula was present in bth after twentyfur hurs. I third pig, nt inculated, Bhvtd eperythrza twenty-fur hurs after being cnfined in a pen with pig 1. A bld examinatin was nt btained prir t placing this animal in cntact with the sick pig. It is assumed the animal was al-

11 ready harbring E. aula. Herd B This herd, lcated near Shenandah, Iwa, cnsisted f 124 pigs in additin t the sws and bar. The pigs were vaccinated fr chlera by the simultaneus methd n May 7, 1949. On August 19, a pst-mrtem examinatin was made n a pig that had been sick abut ne week. Typical lesins f "icter-anemia" were bserved. Bld films were nt btained frm this animal. Smears were, hwever, btained frm tw additinal pigs shwing early clinical symptms, and five apparently nrmal pigs selected at randm. E. suis was fund in tw f the apparently nrmal pigs, and in bth animals shwing clinical symptms. As indicated in Table 2, an increased temperature and a subclinical anemia were present in ne f the apparently nrmal pigs which was harbring eperythrza. Herd C This grup f swine cnsisted f 17 pigs weighing apprximately 125 punds, and 2 brd sws. The pigs had nt been immunized t hg chlera. Examinatin f a sick pig (pig 12, Tables 1 and 2) frm this herd was made after the animal had been nticeably ill fr five days. Symptms and data btained n bld examinatin were typical f the "anaplasmsis-liice disease", icteric disclratin f the mucus membranes was nt evident, hwever. S. suis was bserved in smears frm this animal. Table 1 indicates the prgress tward recvery. A mild relapse develped in this

12 pig as Indicated in the data by a recrudescence f the parasitic infectin, fllwed by an increased bdy temperature and marked lwering f the erythrcytic cunt and hemglbin values. Examinatin f the remaining 16 pigs in the herd disclsed E. suls t be present in the fllwing degrees f infectin: three pigs were negative fr parasites; in six pigs the parasites were rare; in fur the parasites were scarce; and in ne pig each the rganisms were ccasinal, frequent, and numerus. Aa previusly stated, bld studies were made n the tw latter animals. A third pig, in which the parasites were scarce, was used as a cntrl. Data btained frm pig 10 in which the parasites were mst numerus are included in Table 1. The bld cunt in this pig at 9,390,000 per cu mm drpped t 6,820,000, the hemglbin drpping frm 15.1 t 12.2 grams per 100 cc f bld. Bld values returned t nearly nrmal fllwing the disappearance f the parasite. The erythrcyte cunt in the secnd pig at 8,410,000 per cu mm drpped t 6,130,000, the hemglbin drpping frm 14.9 t 12.2 grams per 100 cc f bld. Bld cunts in the cntrl pig at 8,490,000 drpped t a lw f 8,060,000 per cu mm; hemglbin values at 14.8 reached a lw f 14.3 grams per 100 cc f bld. Increased regenerative bld changes were evident in the tw frmer pigs, being mst marked in pig 10 which shwed the heaviest infectin f eperythrza. The bld picture remained unchanged in the cntrl. Temperatures f pig 10 ranged frm an initial high f 105.0 # P. dwn t 103.1 P. That f the secnd pig ranged frm an initial temperature f 103.8'dwn t 102. 6 P. Temperatures f the cntrl pig, initially at 102.4 P.,

13 varied a maximum f nly 0.4 f a degree during the entire curse f examinatin. Temperatures f several ther pigs selected each time at randm remained between 102.0'and 105. 5 F. Herd D This grup cnsisted f six chlera susceptible hgs lcated near Riley, Kansas. Five f the animals were apprximately ten mnths f age. A bar f unknwn age was intrduced int the herd n December 30, 1949. One f the riginal animals in the grup became ill n February 7, 1950, and was brught t the Veterinary Hspital fur days later. A diagnsis f acute, hemlytic anemia was made. Bld films examined by the authr revealed the presence f E. suis. The labratry data gathered in this case is given in Table 1. Bld films btained frm the five nrmal pigs revealed a mild parasitic infectin in tw. Hg lice were numerus n all six animals. MICROSCOPIC BLOOD EXAMINATION OF NORMAL SWINE A study was made f the bld f apparently nrmal swine t determine the number f animals that might be harbring Eperythrzn in visible numbers. Rbb (1945) fund ring-shaped structures bth in cases f "icter-anemia" and In nrmal swine. His descriptin f these structures suggested that he may have bserved Bperythrzn. Bld films were btained at a lcal livestck sales pavilin frm 25 apparently nrmal swine representing six separate herds. These pigs ranged in size frm 20 t 180

glbin Temp. t :! infectin : Hem- Degree : Eperythrzn : bld 14 Table 1. Bld values bserved during clinical and subclinical "icter -anemia n (acute eperythrznsis ). Date : 1949 : : 1 R.B.C. : 2!! f - < j : Anemic changes in film Pig 1 7-23 106.0 2,110,000 3.9 Numerus Frequent 25 103.8 3,620,000 7.2 Frequent Marked 27 103.0 6,080,000 10.1 Scarce Frequent 30 102.7 5,160,000 12.8 Scarce Nrmal 8-4 102.2 7,320,000 13.5 Negative Nrmal Pig 10 8-4 105.0 9,390,000 15.1 Numerus Nrmal 6 103.5 9,070,000 13.8 Numerus Nrmal 8 103.3 7,527,000 12.2 Frequent Frequent 10 104.6 6,820,000 12.5 Scarce Numerus 12 103.4 7,390,000 13.6 Negative Numerus 15 103.1 8,980,000 14.6 Negative Nearly nrmal Pig 12 8-2 103.1 2,220,000 2.6 Rare Numerus 3 102.5 3,120,000 4.5 Occasinal Numerus 4 103.0 3,730,000 7.7 Frequent Numerus 5 105.7 2,510,000 4.7 Occasinal Numerus 6 102.7 3,700,000 7.2 Rare Numerus 10 103.0 4,480,000 12.2 Negative Frequent 15 102.4 7,980,000 13.1 Negative Nearly nrmal 1950 Pig 13 2-11 103.6 3,210,000 7.7 Occasinal Frequent 14 102.2 2,580,000 6.9 Scarce Numerus 16 101.9 2,840,000 7.0 Rare Marked 18 101.4 4,990,000 11.4 Rare Numerus 20 101.0 4,460,000 10.4 Rare Frequent 1. Erythrcytes per cubic millimeter. 2. Expresseti in grams per 100 cc f bld.

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17 punds. N Eperythrzn parasites were bserved in any f the smears. The number f latent carriers was, f curse, nt determined by this methd. EXPERIMENTAL STUDIES Experimental Prcedure Field bservatins suggested that the pssibility f prducing acute, experimental eperythrznsis in nrmal swine is quite remte, since it was indicated that a majrity f swine may pass thrugh mild infectins with n ill effects. It is knwn in cnnectin with varius bld parasitic diseases, including the genus Eperythrzn, that the remval f the spleen increases the animal»s susceptibility t the disease. Marmrstn (1935) summarized the varius diseases in which the spleen plays an imprtant part in the immunity. Splenectmized swine were, therefre, used t study experimentally the effects f severe infectins f E. suls. It was fund that by this methd intense parasitic infectins culd be btained equalling thse that previusly had been bserved nly in field cases. Ten pigs varying in weight frm 45 t 125 punds were used in these experiments, pur were knwn t be carriers f E. suis prir t splnectmy; ne (pig 1, chlera immune) had recvered frm a natural field infectin f "icter^anemia"; tw (chlera susceptible) were injected with bld frm this pig, and develped a mild Eperythrzn infectin; a third pig (chlera sus-

18 eeptible) was fund t b harbring E. suia derived frm an apparently natural surce. All fur pigs develped acute eperythrznsis fllwing splenectmy. Six additinal pigs (chlera immune) f unknwn carrier status were splenectmized and bserved fr a perid f at least 30 days fllwing the peratin in rder t determine the presence r absence f latent infectin. It was demnstrated in these animals that the remval f the spleen alne resulted in n anemia r clinical symptms. Five f these pigs were negative fr E. suia fllwing splenectmy, and remained nrmal fr at least thirty days. One animal remained nrmal until experimentally infected with E. suis 82 days after being splenectmized. Experimental transmissin f Eperythrzn was accmplished in the susceptible pigs by intravenus injectin f citrated carier bld, pig 1 (the recvered field case) serving as the latent carrier f E. suis. k standard inculating dse f fur cubic centimeters f bld was used, stained bld film examinatins were made and temperatures taken at 48 hur intervals fllwing splenectmy t establish the presence r absence f latent infectin. The same bservatins were made daily fllwing inculatin f susceptible pigs in rder t determine mre accurately the perid f incubatin. Labratry determinatin f bld values was begun in each case upn the first bservatin f eperythrza, and cntinued daily thrughut the curse f the disease.

19 Differentiatin f Eperythrzn species The presence f tw separate Eperythrzn species in swine was indicated early in these experimental studies. Fllwing splenectmy, pigs f unknwn carrier status relapsed with an rganism differing in mrphlgy and pathgenicity frm the parasite previusly bserved in field cases f "icter-anemia 1 '. Crss inculatin experiments further established the individual species. tw rganisms as Pur splenectiaized pigs which had relapsed with E. pajrvum, nly, with r ill effects were injected with bld frm a knwn carrier f E. suis. E. suis appeared in all fur pigs after an incubatin perid f frm tw t five days. Acute eperythrznsis was evidenced in each animal, tw f which subsequently succumbed t the infectin. Cnversely, tw pigs that had recvered frm acute, clinical infectin with E. suis were infected with E. parvum. A mild infectin ccurred after incubatin perids f seven and ten days. One pig knwn t be susceptible t bth parasites mm infected with bth upn experimental inculatin. The tw swine species were differentiated frm E. wenynl and E. vis by inculatin f heavily infected bld int a susceptible calf and lamb. Bth animals remained negative fr 30 days. The susceptibility f each t its individual Eperythrzn species then was prved by injectin f knwn carrier bld. Cnversely, an Eperythrzn susceptible pig was injected intravenusly with fur cubic centimeters f heavily infected cattle and sheep bld which had been pled in equal amunts. The pig

20 remained free f parasites until experimentally infected with bth E. aula and K. parvum 58 days later. Differentiatin f the swine species frm E. cccldes and E. varlans was accmplished by intraperitneal injectin int mice with bld heavily infected with the swine parasites. One Swiss white muse and tw lcal white-fted deer mice f the species Permyscus maniculatus were used, the animals having been prved susceptible fllwing splenectmy. All three remained negative fr 30 days. Differentiatin frm E. dispar f the vle was nt undertaken. The failure t infect clsely related rdents wuld suggest that the Eperythrzn species f swine are nt clsely related t E. dispar. Mrphlgy Eperythrzn suis. As previusly stated this parasite is similar in appearance t ther species f Eperythrzn. The principal structure f this extracellular parasite is a delicate ring averaging frm 0.5 t 0.8 micrns in diameter, and is situated upn the erythrcyte r free in the plasma. Cccus, rd, and budding frms are als bserved. At the height f the parasitic attack there are present in gre^t numbers large ring and discid frms varying in size frm ne t tw and ne-half micrns. Many f the large ring frms are f distrted shapes, and 1. Identificatin by Dr. H. T. Gier, Department f zlgy, Kansas State Cllege.

V. *«*. & ṫ.. * - 21 * c.% i - 1 c < * L * 1 «A Fig. 1. hing frms f Eperythrzn aula lcated upn the erythrcytes. %» L? Pig. 2. Extracellular frms f Eperythrzn suis.

22 exhibit an irregular distributin f the chrmatin at varius pints n the ring. The discid frms are seen as flat, slid, chrmatin masses. Sme erythrcytes are given a vacule-like appearanc frm ring frms in which the central clear area f the structure appears t extend cmpletely thrugh the red cell. The parasites may be s numerus as t cver the erythrcytes cmpletely. Harked mrphlgical changes ccurred cnsistently in citrated r xalated bld. These changes tk place within ne minute after mixing with the anti-cagulant, and increased smewhat after further tine. While ring frms are the predminating structure in immediate smears, cccus and rd frms predminated in cltrated r xalated samples. The stained rganism frm samples s treated assumed an appearance similar t Bartnella. Sperythrzn parvum. This extra-cellular parasite is bserved primarily as small cccus frms and ccasinal ring structures. The rings average abut 0.5 micrns in diameter while the cccus frms are smewhat smaller. Accurate measurements f the ccci have nt been made. This parasite exhibits a tendency t accumulate in large numbers upn individual erythrcytes, even when very rare in the bld smear. Pathgenesis and Symptms Splenectmized pigs heavily infected with E. parvum evidenced n temperature rise r ther visible symptms. A mild reduc-

23 tin in bld cunt (abut tw millin cells per cu ran) with regenerative bld changes was bserved in tw pigs, while the bld values remained unchanged in three thers. One unperated pig exhibited a mild parasitic infectin fllwing inculatin. It appears that this rganism is relatively nn-pathgenic. A serius r fatal icter-anemia resulted in all experimental pigs in which initial parasitic attacks f E. suis were allwed t prceed vlthut treatment. Parasites culd be demnstrated in bld smears frm tw t five days fllwing the inculatin f susceptible animals r splenectmy f knwn carriers..'n extremely rapid rate f multiplicatin was bserved in mst cases. The time frm experimental inculatin r relapse frm splenectmy t the first appearance f clinical symptms varied frm six t ten days. Increased temperatures t 104.0* F. r 107. e F. were bserved when the parasites became numerus, and cntinued until spntaneus reductin f the parasites ensued r death ccurred. Clinical symptms became evident n the secnd r third day in which the parasites had been very numerus. Fever, depressin, and inappatence were the early symptms assciated with Intense parasitic infectins. Bld values began t fall at this pint, and nrmblasts appeared in stained smears. Red cell cunts drpped ne r tw millin cells per cu mm per day. A spntaneus reductin in the number f parasites usually ccurred during the develpment f acute anemia, and a crrespnding decline in temperature t nrmal r subnrmal ccurred. The animals were weak and gaunt,

24 and exhibited symptms f dyspnea n frced exercise, cnstipatin with bile stained feces, and anemic, icteric mucus membranes. lirythrcyte cunts reached a lw f frm ne t tw millin cells per cu mm, A lw cunt f 685,000 was bserved in ne animal immediately prir t death. Hemglbin values reduced t a minimum f tw t fur gr.^ms per 100 cc f bld, and packed erythrcyte vlumes fell t fur r seven per cent. An icteric index f frm 18 t 25 was bserved during acute bld destructin. "White cell cunts usually remained unchanged, hwever a marked leukcytsis was bserved in several cases. Immature erythrcytes appeared in increasing numbers as the a nemia develped, and were m3t numerus during the perid f cnvalescence. Spntaneus agglutinatin f the erythrcytes (bserved by Dyle, 1932 and Rbb, 1945 in "icter-anemia" ) was nted in all experimental cases, and was usually assciated with the perid f acute anemia. At this time bld sedimentatin rates were extremely rapid. Sedimentatin f 75 mm in ne minute cmplete t 85 mm in five minutes was bserved. Repeated parasitic attacks ccurred in splenectmized pigs, with each attack repeating the curse f the disease as described abve. After the secnd r third attack the parasitic invasins were usually f shrter duratin and f less intensity. The crrespnding symptms and bld damage als decreased. In these experiments fur animals died f acute eperythrznsis. Death ccurred in frm ne t five days fllwing the appearance f

25 SI a h TJ 1-0 s 3 toh C» 3 <cj J* > O csl p, g «ihh ^«q»ppi>!. 3*8 tt) G -P»Gh3 a P OK KP K EP y-t a H O «ft Pv -a - "a x» P HO ec ccca-d ah P 8-lH H G» 0 <0 «P. N 4J «a) <h S» H K a O a OvH«H ft-c a g O *d SO > *> «rt *4 J»< wt cc H U 1 Pi Pi Pi O mpi toft O P C 3 H g H O 0,5 +3 ft 8 CO «HP,+»CPi+>PiCO E»-Hft-HPi -P C P & +» *-> ft <HOBHWH«H O +> <S i (3 a 1 cm H (H ft t C H * H e 99 S5 «H +> «- r-4 0J ^ 8h m tf c (3 C +J Pi t-t «d H O O G 3S3 al H H ihhfh HH.Q *i <rt '0 -dooft H O «4 1 ggggl an? Pi 1 cr x m "a x> Pi Pi Pi Pi Pi Pi Pi OO Pt Pi B a ft i O O O O O O O OOP. 0h O O Pt. i 4 55 55 K 55 S3 55 S3 S Ji SBPi O «a a 09 3 a 8-i O c H i-l f-4 r-4. O N O ^» >» "H at <H G. p a rlbhiu -P fl fl P a P) 3 9 3 P > c 3?. 3 C O O C O E O H H O O EC BO.rl -H 3 i-jrh «4 P «3 Pi Pi Pi P, Cm 3 Q«0 M*i it O a >» p*d Pi Pi O* Pi fco Pi S p, g P»E P S-PS 0Pt 8w H Q H O fa 3 3 3 X3 K3 Pi O O O 3 O^ CO ft 55 «ffia> c p3c wc E OT««H O pa a *«> OH JC3 O 00 Cft U) CO CO GO to CM C- C~ t>) #-* O 5 < > 0) WW 01 CM CM H r* ft i-l rit-t O H [ * ** i 45 p g >» u ftp u r* H t-hoo ioo> H ri CO C* r-l r-to>c6»* 85»» ft fl 0J «-4H CMHCft > N lo ^ <«f lo T*tQ P E8h H r-ir4r4rt (3 O ««««fee P 3 > a«< Q OQOQO si OO OOO O OO O O O 8 5 Q 5 Q Q 5 O O OO O J* OOO O OOO ft TJ > Vt u «t «««* <k» >» >» * s Pi Q O OO O O O 5 05 CO lo CM OOO O OOO-H c B MS!> t- f- s CO t w «u jh ^«c r> «0 lo t- lo CM r4 (00 <0 > B >»»»»» «*» > «*» Pi O q Pi-H

in ii i ' 26 clinical syaptiis. Tw animals, died in initial, untreated parasitic attacks; ne animal died in the secnd attack, the first being successfully treated; and ne died in the furth parasitic recrudeaence, the three previus attacks being cntrlled by treatment, A ttal f 35 experimental, parasitic attacks f E. suis have been studied, Recvered animals prbably remain permanent carriers. Pig 1, vrtiieh had recvered frm a natural field Infectin, was prved by 3ubinculatins and finally by splenectmy t have retained i. suis a perid f thrse mnths. Bld examinatins made during the tw-mnth perid prir t splenectmy rere negative. Mrbid Anatmy The lesins bserved in all fur experimental cases that died f acute ept rythrzn3i2 were identical with thse described in field cases f "ictcr -anemia". Generalized icterus was present thrughut the bdy fat and tissues. The bld appeared thin and watery. The liver exhibited a yellwish-brwn clr, and the gall bladder cntained a thick, gelatinus bile. The heart and kidneys were pale and flabby, A few petechia were usually present n the mucsal surface f the bladder. The gastrintestinal cntents were deeply stained thrughut with a yellwrange bile. Hydr-pericardium and ascites were bserved in tw pigs, the fluid being a clear, yellw clr. Splenic lesins were, f curse, nt bserved in these studies. Bacterial examinatins f tissue were negative.

27 Micrscpically the principal changes were bserved in the liver. The severity f the lesins varied frm mildly retrgressive changes t a marked atrphy and necrsis f the central hepatic cells. Varying amunts f hemsiderin and sme lymphcytic infiltratin were present in all. Parenchymatus and fatty degenerative changes f the hepatic cells were present in all. One field case examined als shwed a severe central necrsis. Spencer (1940) described similar micrscpic lesins in field cases f "icter-anemia". The kidneys shwed relatively little change ther than parenchymatus degeneratin. N significant micrscpic lesins were bserved in any f the ther tissues examined. Eperythrgn parasites culd nt be distinguished in tissue sectins prepared with either hematxylin-esin r Oiemaa stains. Prevalence, Transmissin, and Relatin t Hg Chlera Field bservatins suggested that Kperythrzn infectin in swine is prbably quite cmmn. Additinal pprtunities were affrded in these experimental studies t determine the prevalence f E. suis and E. parvum in this lcality. Six f the experimental pigs btained fim a single herd had been expsed t sws and lder pigs in the herd fr a perid f frm June t August. As shwn by splenectmy fur were carriers f E. parvum, ne a carrier f bth E. parvum and E. suis, and ne pig was negative. The knwn susceptible pig was infected with bth species fllwing inculatin f pled bld btained

28 frm five pigs selected at randm at a lcal livestck sales pavilin. These five pigs represented five separate herds. The animals varied frm 40 t 200 punds in weight. Relatively little infrmatin is available as t the exact mdes f transmissin f Eperythrzn species. Slit (1936) succeeded in transmitting I. cccldes with the luse, Flyplax a errata. Jensen (1943) bserved rapid transmissin f E. wenynl when susceptible calves were expsed t carriers in the presence f large numbers f biting flies. Eperythrzn transmissin in swine is, in all prbability, effected by biting arthrpds. This is indicated als by the seasnal ccurrence f the majrity f cases f "icter-anemla" in swine. Quin (1958) and spencer (1940) nted that a rather significant number f cases f "icter-anemia" fllw in tw t six weeks after herd serum and virus vaccinatin fr hg chlera. An experiment was cnducted t determine the pssible transmissin f E. 8uls in hg chlera virus. Bld heavily infected with eperythrza was defibrinated, and phenlised t cntain 0.5 per cent phenl. A phenl slutin standardized by the Bureau f Animal Industry t a cntent f 5 per cent was used in securing the prper dilutin. The treated bld was held at a temperature f 37 P. fr 15 days. Pur cubic centimeters was then injected intravenusly int a susceptible, splenectmized pig. The pig remained negative fr 30 days, and then was infected with virulent carrier bld. Prm this experiment it appears unlikely that Eperythrzn transmissin ccurs thrugh the use f phenlized virus bld*

29 Mechanical transmissin frm carrier t susceptible pigs may, presumably, ccur by means f vaccinatin needles used in serum and virus injectins. It wuld appear, hwever, that mst cases f pst-vaccinal "icter-anemia" are the result f natural infectin ccurring cincidentally t the vaccinatin, rather than frm mechanical infectin at the time f immunizatin. This is indicated primarily by the ccurrence f such cases nly during seasns in which relatively rapid transmissin is t be expected frm insect vectrs. The disease has nt been reprted fllwing vaccinatin r ther surgical prcedures during the winter mnths. Lwered resistance f the animal during the hg chlera virus reactin, described by McBryde (1942), pssibly may allw the parasite t increase t pathgenic numbers in a larger number f pigs naturally infected during this perid. The effects f hg chlera virus reactin cincident t the fever and anemia f subclinical eperythrznsis are unknwn. If "breaks" can ccur under such cnditins, in all prbability, they are cnfined in mst cases t a relatively few animals in the herd. Campbell (1945) fund that "icter-anemia" may incur heavy lsses when cmplicating swine erysipelas r hg chlera. Chemtherapy The specific actin f arsenical cmpunds in Eperythrzn infectins, as demnstrated by Neitz (1937) and thers, prmpted investigatins f specific therapy against B. suls. The experimental chemtherapy f acute eperythrznsis f swine was cn-

30 ducted with nearsphenamine because f the availability f this drug. The detailed effects f varius intravenus dsages upn heavy infectins f E. aula are shwn in Table 4. Specific actin was btained in single intravenus injectin s at a dsage varying frm 15 mg/kg t 45 mg/kg, quicker actin being btained with the larger dses. Parasites were remved cmpletely frm the bld r reduced t nn-pathgenic numbers in frm 2 t 24 hurs fllwing initial therapeutic dses. Mst parasitic attacks were treated within 24 t 72 hurs after the animal had exhibited clinical symptms. Tw were treated prir t clinical symptms, and did nt develp visible evidence f the disease. The clinical cnditin and bdy temperatures returned t nrmal within 24 hurs fllwing effective therapeutic dses. Sme weakness remained in thse individuals in which bld values were cnsiderably lwered by delayed treatment. Bld destructin was halted almst immediately in mst cases by the remval f K. suis. Spntaneus relapses ccurred in nearly all f these splenectmized animals, and were usually re-treated with nearsphenamine. An increased resistance t repeated treatment was evidenced by E. suis in several animals. In pig 73 a marked resistance was develped fllwing an initial dse f 5 mg/kg, which temprarily reduced the number f parasites. In tw subsequent attacks single therapeutic dses had n effect, and additinal injectins were required t prduce actin. In ne case, pig 2, sdium cacdylate was injected intravenusly at a rate f 0.3 grain per pund f bdy weight. The

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32 parasites increased rather than decreased during the fllwing 72 hur perid. The infectin was cntrlled immediately with nearsphenamine. These experiments indicate that nearsphenamine and prbably ther drugs specific fr Kperythrzn shuld prve f value in field cases f acute eperythrznsis. It is bvius that such treatment will be f little r n value if delayed until spntaneus reductin f the parasites and severe bld damage have ccurred. It is nt expcted that severe, spntaneus attacks will re-ccur fllwing specific therapy f unperated swine; hwever such determinatin can be made nly by treatment f field cases. DISCUSSIOH The bservatin f a bld parasite assciated with the "anaplasinsis-like disease" f swine immediately suggested that the rganism might be the etilgical agent f the disease. Kinsley (1932), Dyle (1932), Dicke (1934), and Dyle (1945) als bserved similar parasites cnnected with the disease, but apparently made n attempts t identify the rganisms bserved. It has been recgnized, hwever, that this disease is typical f the cnditin prduced by bld prtza ( Anaplasma, Pirplasma, Bart - nella, and etc.). "Icter-anemia" is knwn t be a disease f spradic ccurrence. Hwever, these studies indicated that E. suls is a cmmn bld parasite f swine in this regin. It was evident, there-

33 fre, that the bservatin f the parasite in affected animals culd nt he cnsidered final prf that the rganism was respnsible fr the pathlgical prcesses bserved. Data was gathered frm field cases in a manner in which bservatins culd be made n the relatinship f the Eperythrzn infectin t the curse f the "anaplasmala-like disease". The experimental reprductin f acute eperythrznsia enabled a cmparisn t be made f the disease prcess and pathlgy knwn t be caused by E. suls with the diseaae prcess and pathlgy f field cases thught t be due t E. suis * In crrelating the parasitic infectin with the curse f the disease, the bservatin by Keitz and c-wrkera (1934) cncerning the curse f acute eperythrznais f sheep is f particular significance. They fund that the active multiplicatin f eperythrza cntinued up t the tire when the first aigns f anemia made their appearance in smears. Then the number suddenly decreaaed a that when the anemia waa mat marked, cmparatively few r n rganisms culd be seen. This characteristic disease curse was fund t be typical f acute, experimental infectins with E. sula (illustrated in detail in Table 3). In additin increased temperatures were fund t be directly related t the degree f parasitic infectin. High temperatures cincided with heavy infectins, and decreased as the parasites disappeared. In cmparing thia characteriatlc diaease curse f acute, experimental eperythrznais t the data btained in field cases f "icter-anemia" (Table 2), it will be nted that the

34 disease prcesses are identical. Data btained n pigs 1,4,6,7, 10, and 11 which apparently were bserved at r near the peak f parasitic infectin, illustrate the curse f acute eperythrznsis as described. Temperatures were increased early in the disease when the parasites were mst numerus, and usually decreased as the parasites disappeared..4, rapid decrease in the number f parasites was als crrelated with the develpment f an anemic bld picture, the parasites being few r absent during marked anemic changes in the smear. Additinal evidence f etilgy is indicated in the degree f parasitic infectin. Heavy perasitic attacks f E. suis in experimental animals apprximated the intensity f parasitic attacks bserved in field cuses f "icter-anemia". The symptms and curse f the disease fllwing attacks in these tw grups f animals were identical, liild parasitic attacks were bserved in bth experimental and field cases. These attacks resulted in subclinical r n symptms, stated in ther wrds, the develpment f a disease prcess in bth experimental and field cases depended directly upn the number f parasites present in the parasitic attack. Further indicatin that "icter-anemia" is identical t acute eperythrznsis is the identical pathlgy f each. Hwever, it is nt intended t imply that this can be cnsidered prf f etilgy alne, since varius bld parasites f animals prduce similar pathlgical changes. The basis fr establishing the parasite, E. suis, as the etilgical agent f "icter-anemia" then lies in the fact that

35 the disease was reprduced In experimental swine by the inculatin f infectius material frm field eases. The resulting symptms, disease curse, and pathlgy were Identical with the field cases. Prm the bservatins made In these studies and infrmatin available cncerning ther species f Eperythrzn, a number f puzzling aspects f the "anaplasmsis-like disease" f swine are apparent. Eperythrzn suia is a cmmn bld parasite f swine. The majrity f lder animals, in all prbability have been expsed and infected vjhen yung, and remain permanently immune, latent carriers. Clinical cases usually are encuntered, therefre nly In yung susceptible swine which are expsed t infectin frm carriers. A strictly seasnal ccurrence is indicative f insect transmissin, as wuld be expected with the available infrmatin cncerning the Eperythrzn species. The clinical cases ccur in an insignificant number f the animals actually infected. Depending upn the intensity and duratin f the parasitic attack, clinical, subclinical, r n symptms may appear. The majrity f animals are capable f suppressing the multiplicatin f the parasite, and as a result n bld damage r ther 111 effects are incurred. Because f this wide variatin in severity, it wuld seem that the clinical cnditin is mre cmmnly encuntered than generally recgnized, particularly in cases in which bld destructin has nt been excessive and prmpt recvery ccurs. Experimental cases that underg intense attacks f shrt duratin develp symptms lasting nly a day r tw

36 during this particular perid. Immediate imprvement ia evidenced upn the spntaneus reductin f the rganisms, and the animals are eating and active during the mild anemic stage. The inability f previus investigatrs t establish the etilgy f this disease may be attributed t a number f reasns. The failure t use splenectr-ized swine in transmissin attempts undubtedly has been the primary reasn. The failure f investigatrs t Identify bld parasites bserved in cnnectin with the disease has been anther. The characteristic reductin and disappearance f the parasite during the develpment f the acute anemic stage mst certainly adds t the difficulty in diagnsis. Needless t s?.iy, gd staining technique is essential fr the bservatin f the parasites. Heavy infectins may easily be verlked in slides stained in slightly excessive acid r alkaline slutins, r lightly stained with Wright* s stain. E. suie ia apparently the first species f this genus t be incriminated as prducing a clinical disease entity in naturally infected animals under field cnditins. As previusly stated, it has been determined that the severity f the disease depends upn the number f parasites present in the bld and the duratin f their presence. Hwever, these studies have nt explained why certain individual animals r grups f animals are unable t suppress the multiplicstin f the parasites while the majrity f animals successfully inhibit its grwth. In general terms the reasn may be advanced that these certain individuals pssess a lwered resistance t this parasite. There has been n evidence t indicate that the quantity f r-

37 ganisms intrduced materially influences the severity f the disease r that there Is a nticeable difference in the virulence f strains f E. suis. The factrs which perate t influence this susceptibility are unknwn* They may be inherent in certain individuals r derived frm external surces. Harshfield (1949) has reprted the bservatin that nutritinal anemia in yung pigs may be fllwed later by Mcter-anemla". Additinal investigatins will be required t determine what factrs are necessary t predispse nrmal, susceptible swine t acute eperythrznsia. The questin arises why acute eperythrznsis has nt been bserved in field cases in cattle and sheep, since it is apparent that these animals cmmnly harbr Kpcrythrsn. Kelts (1937) and Jensen (1943) demnstrated experimentally that K. vis may prduce an acute, febrile anemia in unperated sheep. Icterus was nt particularly prminent. It des nt seem imprbable that acute field infectins may ccasinally be bserved in individual sheep and the anemia attributed t gastr-intestinal parasites, imprper nutritin, r ther causes. There is n evidence at the present t indicate that clinical symptms f acute eperythrznsis may be bserved in nrmal, susceptible cattle. Kelt* (1940) bserved mild parasitic infectins when susceptible, unperated cattle were infected with E# wenyni. Heavy parasitic infectins in splenectmized calves «ay result in a mderate t severe anemia, accrding t Kelts (1940) and Jensen (1943). In the authr's bservatins K. suis, in heavy infectins,

38 has evidenced a much greater and a mre cnstant ability t bring abut clinical yyraptms and severe bld damage than either E. vls r E. vtenynl. In 21 acute parasitic attacks studied in splenactmiasd cattle and fur studied in unperated sheep the tw latter species f Sperjthrzn prduced variable degrees f aneaiia, and clinical symptms varying frm nne t severe. In the majrity f cases clinical symptms were absent, and the anemia mild. On the ther hand, equally intense infectins f E» suia invariably resulted in clinical symptms and severe bld damage in untreated swine. It is the authr's pinin that acute eperythrznsis is much mre likely t be encuntered in field cases in swine than in either sheep r cattle, because f the greater pathgenicity f E. suls in heavy Infectins. SUMMARY A bld parasite f the genus Eperythrzn was bserved in eight field utbreaks f the clinical entity f swine knwn as *icter-anenla n r "anaplasmsis-like disease". Animal inculatin studies established the rganism as a new species t which the name, Eperythrzn suis, was given. The disease was reprduced in susceptible, splenectmized swine by the Inculatin f infectius bld frm a field case. The resulting symptms, disease prcess, and pathlgy were identical t field cases. E. suis was fund assciated with a clinical r subclinical anemia in a ttal f 21 Individual field cases. The characteristic curse f the disease was nted in bth field and experimental cases. This cnsisted f a severe para-

39 sitic attack in which symptms f fever, depressin, and anrexia were present. Severe and rapid bld destructin quickly fllwed, and the parasites spntaneusly became reduced in numbers. The animals exhibited a lwered temperature, pale and icteric mucus membranes, marked weakness, and cnstipated bilestained feces at the nset f acute anemia. Repeated spntaneus relapses ccurred in splenectmized swine and repeated the curse f the disease as described. A ttal f 35 acute attacks f E. suis were studied in the experimental investigatins. It was fund that the severity f the disease is dependent upn the intensity and duratin f the parasitic attack. The disease culd nt be reprduced in unperated swine because f mild infectins which fllwed experimental inculatin. Mild parasitic infectins were als bserved in many f the animals in herds underging acute eprythrznsis. Parasitic infectins, which were equal in intensity t thse bserved in field cases f acute eperythrznsis ("icter-anemia"), were reprduced experimentally by the use f splenectmized swine. It was indicated that the majrity f yung swine in enztic areas underg infectin with E. suis, and usually are unaffected by the mild attack that results. All infected animals prbably remain permanent carriers. The exact mde f transmissin is unknwn, but Is presumed t be by insect vectrs. E. suis culd nt be transmitted in heavily infected bld which was subjected t the same cnditins as hg chlera virus bld. Specific therapy against E. suis was btained with nearsphenamine in single, intravenus dsages varying frm 15 t

. 40 45 mg/kg. An increased resistance t repeated treatment was evidenced by E. suis in several cases. Sdium cacdylate was ineffective at an intravenus dse f 0,3 grain per pund f bdy weight. An apparently nn-pathgenic bld parasite, designated as Kperythrzn parvum was bserved in the experimental studies, E. suis and E. parvum were bth fund t be cmmn parasites f swine in this lcality. It is cncluded that the disease f swine described in the literature as "icter-anemia" r "anaplasmsis-like disease" is the result f acute infectin with Eperythrzn suis. Shuld additinal agents be fund t prduce similar symptms and pathlgy, it will be necessary t differentiate these frm acute eperythrznsis

41 ACKNOWLEDGMENT Grateful acknwledgment is given t Dr. L. H. Rderick, Majr Instructr and Head f the Department f Pathlgy, fr his advice and assistance. The authr is als deeply indebted t Dr. E. L. Williamsn and his student assistant, Alex Hgg, Essex, Iwa, fr much f the field materials used in these studies.

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