Strongylus Edentatus: Development and Lesions from Ten Weeks Postinfection to Patency

Strongylus edentatus: Development and Lesions from Ten Weeks Postinfection to Patency

B. M. McCraw and J. 0. D. Slocombe*

ABSTRACT dont les voies genitales contenaient des oeufs, dans le contenu du caecum et du colon. Meme Pony foals inoculated with infective Strongy- si plusieurs larves migrent dans des endroits lus edentatus larvae were examined at necropsy eloignes de l'organisme, il semble que seules from ten to 72 weeks postinfection. At ten celles qui atteignent la base du caecum reus- weeks postinfection larvae were visible retro- sissent 'a atteindre la forme adulte, dans le peritoneally in the liver and flanks and were caecum et le colon. Au bout de 36 semaines, recovered from the ligaments of the liver. on trouva des larves dans le foie et, jusqu'a The fourth molt was detected at 16 weeks cette periode, on n'en retrouva aucune dans postinfection and larvae were also recovered la cavite peritoneale. On ne recouvra pas de from the wall of the cecum at this time. By 40 larves dans le parenchyme pulmonaire. Tout weeks adult S. edentatus containing eggs au long de l'experience, l'epiploon presenta were found in the contents of the cecum and souvent des adherences et des dommages ar- colon. While many larvae migrate to remote chitecturaux. On nota aussi, sous l'intima des parts of the body, it is likely that only those principales veines du caecum et du colon, des that attain the base of the cecum are success- amas d'eosinophiles necrotiques qui encer- ful in establishing in the cecum and colon as claient des sillons migratoires et des larves. adult forms. By 36 weeks postinfection no Au bout de 16 a 20 semaines, le foie etait larvae were found in the liver and up to this rugueux et sa capsule, epaissie; les flancs de. time none were found in the peritoneal cavity. meurerent oedemateux, jusqu'a 36 semaines Larvae were not recovered from the paren- apres l'administration des larves. chyma of the lungs. Adhesions and disruption of omental architecture were frequent changes observed throughout infection. Casts of necrotic eosinophils enclosing tracks and larvae were observed beneath the intima of major INTRODUCTION veins of the cecum and colon. The liver was rough and the capsule thickened at 16 and 20 weeks postinfection and the flanks remained edematous until 36 weeks postinfection. Although Strongylus edentatus is very common in horses, much of its later development is still only vaguely understood. It is often recorded from the flanks, especially RESUME, the right flank, as well as from other regions of the body (2, 4, 7). Whether larvae Cette experience visait 'a administrer des in areas of the body far removed from the larves infectantes du nematode Strongylus cecum and colon ever return to these struc- edentatus 'a des jeunes poneys et 'a effectuer tures to complete development seems ques- la necropsie de ces animaux, de dix a 72 se- tionable. Hemorrhagic lesions in the flanks maines plus tard. Au bout de dix semaines, associated with S. edentatus are well known on pouvait deceler des larves dans le foie et to the pathologist. From necropsies Rooney les flancs, ainsi que dans les ligaments du (7) concluded that strongyle larvae invade foie. Au bout de 16 semaines, on decela le in greatest numbers through the terminal quatrieme stade larvaire et on recouvra des portion of the jejunum and ileum and that larves dans la paroi du caecum. Au bout de this correlates well with the predilection 40 semaines, on recouvra des femelles adultes, of the ileum to segmental ileus. Indeed, Rooney (7) believes that the most common cause of segmental ileus in the horse is the *Department of Pathology, University of Guelph, Guelph, Ontario NIG 2W1. inflammation associated with Strongylus Submitted August 12, 1977. spp. migrations.

340 Can. J. comp. Med. Experimental studies by Wetzel (14) ligaments. Seven larvae were removed from established that S. edentatus reached ma- beneath the visceral surface of the dia- turity in 11 months, and later Wetzel and phragm. They were easily seen in the Kersten (16) found that the molt to the flanks and perirenal fat but were absent fourth stage occurred in the liver between from the parenchyma of the kidneys. None 11 and 18 dagys postinfection (PI). Pre- were recovered from 87 ml of brown-col- viously, we recorded the development and ored peritoneal fluid. pathogenesis of this nematode to the end Two larvae were found immediately be- of the eighth week PI (5). The results of neath the pleura of the dorsal surfaces of experimental infections from ten to 72 the lungs and one was within the dorsal weeks PI are now presented. mediastinum. None were recovered from the parenchyma of the lung. Like the observations at six and eight weeks postinfection (5) adhesions involving the greater omentum, cecum and colon were present. In the greater omentum, MATERIALS AND METHODS nodules up to 6 mm in diameter and containing larvae were found to be eosinophilic granulomas like those described previously in this structure (10). Other nodules simi- The methods used for culturing infective lar to those observed at four and six weeks larvae, rearing of ponies from birth, infec- postinfection (5) were abundant on the tion of ponies, monitoring blood parameters serosal surface of the right ventral colon; and clinical signs as well as the procedures they were found to a lesser extent on the at necropsy were the same as those out- lateral surface of the cecum. Mural throm- lined in our earlier study (5). The experi- bi, 2 to 4 mm long by 2 mm wide were ob- mental design is given in Table I. Most served in the medial and lateral cecal veins pony foals were inoculated with 15000 ± and in the ventral colic vein (= colic branch 6% infective S. edentatus larvae. All pho- of the ileocolic vein NAV 1968). Six were tographs of gross specimens were taken at present on the intima of the medial cecal the time of necropsy. vein within a length of 25 mm. Close to and along most of the length of the ventral colic artery (= colic branch of the ileocolic artery, NAV 1968 and vein were granulomas each with a central core of necrotic eosinophils. No granulomas were in the RESULTS' wall of the artery but they were present in the adventitia of the vein. Tracks were most prevalent on the parietal surface of the liver, but unlike those TEN WEEKS POSTINFECTION seen previously (5) many were now hemorrhagic. The visceral surface of the liver All larvae found at this time were fourth was rough but the capsule was not thick- stage and were recovered mainly from the ened. Extensive retroperitoneal hemorrha- greater omentum, liver, flanks and peri- gic areas immediately beneath the perirenal fat. Recoveries of measured larvae toneum were present in the right and left are summarized in Table II. Larvae were flanks (Fig. 1). There were no lesions in visible in the omentum and readily dis- the parenchyma of the kidneys. sected from a few small nodules in this Several gray nodules, 3 to 6 mm in dia- structure. They were also observed retro- meter and containing fourth stage larvae peritoneally on both surfaces of the liver were located on the lateral surface of the and in the falciform ligament. One was diaphragmatic regions of both lungs. No dissected from the round ligament as well lesions were found in the parenchyma of as from the left triangular and hepatorenal the lung.

'As far as possible descriptions of pathological changes 12 WEEKS POSTINFECTION are in the following order: general observations of viscera, changes in the cecum and colon, etc. and associated vessels, liver, flanks and other organs or structures. At 12 weeks PI all S. edentatus larvae Volume 42 - July, 1978 341 TABLE I. Experimental Strongylus edentatus. Age of Ponies at Infection, Number of Infective Larvae given and Duration of Infection No. of Age at Infective Duration of Pony No. Infection Larvae Infection 1...... 34 days 15000 10 weeks 2...... 40 days 15000 12 weeks 3...... 40 days 15000 12 weeks 4...... 34 days 15000 13 weeks, 4 days 5...... 36 days 15000 16 weeks 6...... 58 days 15000 20 weeks 7...... 50 days 15000 27 weeks 8...... 52 days 15000 36 weeks 9...... 30 days 5000 36 weeks 10...... 29 days 5000 40 weeks 11...... 107 days 5000 59 weeks 12 ...... 54 days 15000 72 weeks

TABLE II. Summary of Recoveries of S. edentatus Fourth Stage Larvae from Various Organs or Structures at Ten Weeks Postinfection No. of Mean Range Organ or Structure Larvae Length mm mm

Greater omentum ...... 14 3.6 3.0 - 4.3 Liver ...... 113 4.3 2.1 - 6.0 Right flank ...... 62 4.7 3.3 - 7.0 Left flank ...... 25 Perirenal fata Right kidney ...... 32 4,3 3.3 - 6.5 Left kidney ...... 22 4.9 3.5 - 7.5 aLarvae in perirenal fat were nearly twice the diameter of those in the liver or flanks

TABLE III. Summary of Recoveries of S. edentatus Fourth Stage Larvae From Various Organs or Structures at Twelve Weeks Postinfection No. of Mean Range Organ or Structure Larvae Length mm mm Diaphragm ...... 25 3.6 3.3 - 5.0 Greater omentum ...... 3 5.3 4.8 - 5.5 Liver ...... 79 5.5 3.1 - 14.2 Ligaments Hepatorenal ...... 1 9.5 0 Right triangular ...... 4 7.5 7.0 - 8.0 Right flank ...... 69 6.0 3.3 - 12.4 Perirenal fat Right kidney ...... 17 5.7 3.3 - 12.1 Left kidney ...... 25 5.7 3.5 - 12.3 aLarvae were abundant in the left flank but were not measured

were still fourth stage and widely dispersed nodule containing two larvae was present (Table III). Numerous larvae were now in the fascia near the inguinal region on seen in the hepatorenal ligament of both the medial side of the right leg of pony 2. ponies examined at this time. In pony 2 One fourth stage S. edentatus was located they were widely distributed under the on the right ventricle beneath the epicar- serosa on the abdominal surface of the dium of this pony. muscular portion of the diaphragm. In the Of the two ponies, in one (pony 2) the flanks, most larvae were embedded in the abdominal viscera were severely disturbed. fat next to muscle in the region of the The entire right colon was twisted over the last three or four ribs. Many were recov- left dorsal and ventral colon. The greater ered from the perirenal fat. A hemorrhagic omentum was adherent to the apex of the 342 Can. J. comp. Med. Fig. 1. Extensive hemorrhagic areas immediately beneath the peritoneum of the right flank. Pony 1, ten weeks postinfection.

Fig. 2. Disturbance of the abdominal viscera with congested greater omentum adherent to the apex of the cecum. The entire right colon is twisted over the left dorsal and ventral colon. Pony 2, 12 weeks postinfection. Volume 42 -July, 1978 343 Fig. 3. Numerous buff-colored casts (arrows) 1 to 3 mm Fig. 4. Section of two casts, similar to those in Fig. 3, long immediately beneath the intima of the medial cecal from an area immediately beneath the serosa of the vein. Pony 2, 12 weeks postinfection. medial surface of the cecum. Casts are accumulations of necrotic eosinophils containing tracks, some with remnants of larvae (arrows). Pony 2, 12 weeks postinfection. H and E stain. X75. cecum (Fig. 2) and both were firmly at- tached to the right body wall. Extensive adhesions involving the greater omentum diameter were also found in the lateral and and visceral surface of the right lobe of medial cecal veins. No lesions were ob- the liver were also noted. There was wide- served on or beneath the intima of the spread congestion of the blood vessels of cecal or the ventral colic arteries. the omentum. The parietal surface of the liver had a Beneath the serosa on the medial surface mottled appearance and the capsule on both of the cecum were many small twisted casts surfaces was thick, especially along the which were buff-colored, granular, and ventral border (Fig. 5). The capsule meas- measured 1 to 3 mm long. A few were also ured up to 1.4 mm and beneath the serosa present on the omentum near its adherence were large amounts of collagen in which to the cecum. These casts were also readily were islands of mononuclear cells and hepa- dissected from lymph nodes on the lateral tocytes. Immediately beneath the serosa it surface of the cecum, as well as from was frequently quite vascular. White foci beneath the intima of the lateral and medial and dark red tracks up to 15 mm long were cecal veins (Fig. 3). In section these casts numerous on the parietal surface of the were massive accumulations of necrotic liver. A few casts were also present be- eosinophils riddled with tracks, some with neath the serosa. Lesions were similar but remnants of larvae (Fig. 4). The tracks less numerous on the visceral surface of averaged 62 ,um in diameter. Although in the liver of these ponies. There were several section these large eosinophilic granulomas areas of strong fibrous adhesions between were often closely associated with veins, the tendinous portion of the diaphragm and none were found in the walls of arteries. liver. Several mural thrombi, up to 1 mm in The abdominal surface of the diaphragm 344 Can. J. comp. Med. Fig. 5. Thickened capsule of the diaphragmatic surface of the liver. Pony 2, 12 weeks postinfection. of pony 3 was rough and covered with many present on the greater omentum which was nodules containing remnants of larvae. The adherent to the ventral body wall and right flanks of both ponies were slightly edema- ventral colon. Nodules, 6 to 10 mm in dia- tous with focal hemorrhagic areas contain- meter were numerous on the cecum and ing living larvae. right ventral colon, as well as in the con- Along the lateral surface of the lungs nective tissue between the ventral and dor- of both ponies were a series of granulomas sal colon. Casts, like those seen at 12 weeks 5 to 15 mm in diameter. Several were also PI, were found beneath the intima of the present on the medial surface of each lung. medial cecal and ventral colic veins. The They usually contained tracks, all in the corresponding arteries were normal. 60 to 67 ,um range. Isolated accumulations Both surfaces of the liver were rough of casts, identical to those on the cecum and the capsule was thick like that seen were also seen beneath the pleura on the at 12 weeks PI. A few foci were present lateral surface of the diaphragmatic region and tracks were poorly defined. No lesions of the lungs. They were absent in the paren- were found in the ligaments of the liver. chyma. The liver was adherent to the tendinous portion of the diaphragm. The flanks were slightly edematous. Tortuous casts, 15 to 13 WEEKS, 4 DAYS POSTINFECTION 20 mm long were widely distributed but not abundant beneath the pleura on lateral sur- Many larvae were recovered from the faces of the lung. greater omentum, liver, flanks and perirenal fat. All were fourth stage and were similar in size to those at 12 weeks PI. 16 WEEKS POSTINFECTION Many larvae were visible in the omentum and were also observed beneath the serosa For the first time fifth stage larvae were at the base of the cecum. No larvae were recovered (Table IV). They were found in found in the ligaments of the liver. the flanks, perirenal fat and near the base Numerous nodules (granulomas) were of the cecum as well as in the extension of

Volume 42 - July, 1978 345 TABLE IV. Summary of Recoveries of S. edentatus Larvae from Various Organs or Structures at Sixteen Weeks Postinfection No. of Mean Range Organ or Structure Stage Larvae Length mm mm Liver ...... 4th 31 4.3 3.0 - 6.0 Hepatorenal ligament ...... 4th 1 9.0 0 Pancreas ...... 4th 2 7.4 6.5 - 8.3 Right flanka ...... 4th 32 10.4 7.1 - 15.1 5th (Male) 11 9.4 8.2 - 12.0 5th (Female) 7 10.3 9.0 - 14.0 Perirenal fat Right kidney ...... 4th 15 7.6 5.0 - 10.8 5th (Male) 8 10.9 9.8 - 13.0 5th (Female) 8 11.9 10.0 - 15.0 Left kidney ...... 4th 3 7.6 5.5 - 10.2 5th (Male) 3 10.5 8.0 - 13.5 5th (Female) 0 -Larvae were abundant in the left flank but were not measured the hepatorenal ligament. Although the heavily fibrosed as were the right triangu- pancreas was normal grossly, two fourth lar, falciform and round ligaments. Two stage larvae were recovered from the paren- small hemorrhagic nodules, about 3 mm chyma. No larvae were observed in the in diameter were present in each of the peritoneal cavity. hepatorenal and right triangular ligaments. Again, adhesions of the greater omentum were extensive, involving the diaphragm, right and middle lobes of the liver as well as the upper small intestine. How- ever, the reaction of the intestine was less severe than at 12 weeks PI. An extensive chain of confluent nodules and lymph nodes, up to 25 mm in diameter, was present along the medial and lateral surfaces of the cecum. A large gelatinous mass was found at the base of the cecum. Several sections of larvae were observed in this mass, the largest measuring 730 ,Am in diameter. The larvae were surrounded by an extensive zone of hemorrhage and contained erythrocytes and neutrophils in their intestines (Fig. 6). Numerous small (1 to 3 mm) hemorrhages were present in the mesentery of the small intestine. The surface of the liver was exceeding- ly rough, much more so than at 12 weeks PI, and the capsule was very thick, especially on the visceral surface where it measured up to 2 mm (Fig. 7). Long fibrous tags were present, particularly on the border of the left lobe and on the visceral surface of the right lobe (Fig. 7). The composition of the capsule was like that at 12 weeks PI with dilated capillaries and lymphatics (Fig. 8). Only a very few foci were evident, but tracks were still the discrete abundant although they lacked Fig. 6. Section of two S. edentatus larvae at the base appearance of those at six or eight weeks of the cecum and surrounded by a zone of hemorrhage. The larvae contained erythrocytes and neutrophils in postinfection (5). The tracks were white. the intestines. Pony 5, 16 weeks postinfection. H and E The hepatorenal ligament was thick and stain. X75. 346 Can. J. comp. Med. Fig. 7. Extreme thickening with fibrous tass of the capsule on the visceral surface of the liver. Pony 5, 16 weeks postinfection.

Both flanks were edematous owing to ex- found in 35 ml of red-brown peritoneal tensive accumulations of gelatinous fluid fluid. Few were seen when the flanks were retroperitoneally and between the internal first exposed and most removed were fourth and external oblique muscles. Beneath the stage. Over 50 larvae were recovered from peritoneal surface were loosely arranged perirenal fat of which relatively few were strands of collagen with an abundance of fifth stage. Two fourth stage S. edentatus edema fluid between them. Plasma cells were observed in the fascia on the proxi. were widely distributed often accumulating mal medial side of the left hind limb. around capillaries and larvae were often Granulomas on the lateral and medial seen in sections. The diaphragm was slight- surfaces of the right ventral colon as well ly rough on the abdominal surface. as adhesions between the greater omentum Except for one nodule on the lateral sur- and various viscera were still prominent face of the right lung, this organ was nor- features. The omentum was now severely mal as were the remaining organs. The congested and twisted into strands. Lymph nodule contained a larva possibly undergo- nodes along the right ventral colon were ing a molt to the fifth stage. large (up to 25 mm in diameter) and were often contiguous. Two small mural thrombi, 1.2 mm in diameter, were found in the 20 WEEKS POSTINFECTION ventral colic and medial cecal veins. The endothelium of the lateral cecal artery was Both fourth and fifth stage larvae were distended and swollen, and the edema also recovered at 20 weeks PI. However, only extended into the tunica media (Figs. 9 seven larvae, all fourth stage, were recov- and 10). There was also extensive destruc- ered from the liver. In addition, only one tion of the internal elastic membrane and fourth stage larva was found from each of erythrocytes were observed beneath the the round, right triangular and hepatorenal endothelium. A similar edema was seen ligaments. All larvae removed from nodules in the endothelium of the lateral cecal vein on the pleural and visceral surfaces of the and in arterioles. diaphragm were dead. No larvae were The liver was similar to that at 16 weeks

Volume 42 - July, 1978 347 Fig. 8. Section of the thickened capsule of the visceral Fig. 9. Swollen and distended endothelium of the lateral surface of the liver showing loosely arranged collagen cecal artery (arrows). Pony 6, 20 weeks postinfection. and dilated capillaries and lymphatics. Pony 5, 16 H and E stain. X75. weeks postinfection. H and E stain. X120. postinfection. The largest larva seen in of both lungs were numerous gray nodules. sections was 605 ,um in diameter. Portal Over 50 were counted on the left lung and lymph nodes were much enlarged. Three more were present on the right. About 12 granulomas 2 to 3 mm in size, were present red nodules were also located on the left in the falciform ligament. lung (Fig. 13). Both types were 5 to 8 The abdominal surface of the diaphragm mm in size. In section, all were granulomas was generally rough. In addition, ten no- like those seen at ten and 12 weeks. dules 8 to 9 mm in size were present (Fig. 11), and from two, fourth stage larvae were dissected. The remaining nodules had 27 WEEKS POSTINFECTION hard granular cores. Eight similar nodules were present on the pleural surface of the A summary of larvae recovered and meas- diaphragm. Both flanks were thickened but ured is given in Table V. Fifth stage larvae there was little gelatinous material present, comprised 89.5% of all S. edentatus meas- in contrast to the findings at 16 weeks PI. ured and nearly 55% of these were females. Near the ventral surface of the pancreas The remainder were fourth stage. Many close to the posterior border was a hemor- fifth stage S. edentatus had blood in the rhagic area about 8 mm in greatest dimen- buccal cavity. Only one larva, in the fourth sion. This was found to contain tracks con- stage, was recovered from the liver but sisting of necrotic debris and eosinophils larvae were observed in the right triangu- surrounded by a thick zone-of loosely ar- lar and hepatorenal ligaments. They were ranged collagen (Fig. 12). also numerous retroperitoneally immediate- Along the lateral surface close to the ly posterior to the hepatorenal ligament. ventral border of the diaphragmatic regions None were found in the left triangular 348 Can. J. comp. Med. depth of 10 or 12 mm. Near the midventral line a hemorrhagic area, about 55 mm in greatest dimension was present. The lungs were normal.

36 WEEKS POSTINFECTION Widespread distribution of S. edentatus characterized the infection at this time (Table VI). Larvae were observed in hemorrhagic areas within the fascia on the medial side of the left thigh, retroperitoneally along the midventral abdomen, on either side of the lumbar region of the vertebral column, subserosal in the bladder, within the mesentery near the origin of coeliac and cranial mesenteric arteries and even along the path of the umbilical arteries. However, no larvae were recovered from the liver. In pony 8 three normal larvae were present in the greater omentum and numerous S. edentatus, many of which were over 20 mm long, were observed in the flanks. Larvae tended to con- centrate along the ventral border of the ribs. Three living pre-adults were dissected from the pancreas of pony 9. One was contained in a fibrous capsule 1 cm in diameter. The other two were in the parenchyma with no gross reaction around them. Fig. 10. Swollen and distended endothelium of the lateral cecal artery. Extensive portions of the internal elastic One female S. edentatus 30 cm long was membrane are destroyed (arrows). Pony 6, 20 weeks found in the contents of the ventral colon. postinfection. H and E stain. X300. Well-defined esophageal glands were present in fifth stage larvae. ligament. Numerous stout fifth stage lar- In pony 8 worm-like casts were present vae were observed or exposed in the flanks. in the greater omentum which was adherent They were also seen near the psoas muscles to the cecum and right ventral colon. The and retroperitoneally deep in the pelvic colon had a few soft nodules 8 to 10 mm in cavity. Many fifth stage larvae were lo- diameter, but numerous nodules containing cated in the perirenal fat of both kidneys worm-remnants and casts lined the medial (Fig. 14). For the first time, S. edentatus, surface of the cecum. Casts were also pres- a pre-adult male 19 mm long, was recovered ent in the wall and beneath the intima of from the right ventral colon. medial cecal vein. In pony 9, except for Although adhesions of the greater omen- two red nodules at the base of the cecum, tum and viscera were again observed, the this structure and the colon were essen- colon and cecum were essentially normal tially normal. except for slightly enlarged lymph nodes The liver of pony 9 was normal except on the right ventral colon. Six mural throm- for four white foci, and that of pony 8 bi were found in the ventral colic vein. had only faint tracks on the visceral sur- There was only slight evidence of tracks in face. The capsule of the latter was slightly the liver. Only five white foci were found thickened. and these were on the parietal surface of At the line of attachment of the dia- the liver. phragm to the flanks several cyst-like struc- Numerous raised rough areas were pres- tures approximately 10 mm in diameter ent on the abdominal surface of the dia- were present in pony 8. Each was filled phragm. The greatest changes were ob- with a yellow fluid and contained a larve served in the flanks which contained retro- measuring 18 to 22 mm long.. peritoneally clear gelatinous material to a The flanks were very thick and con- Volume 42 - July. 1978 349 Fig. 11. Nodules, two of which contained fourth stage S. edentatus larvae, on the abdominal surface of the diaphragm. Pony 6, 20 weeks postinfection. tained beneath the peritoneum considerable necropsy, were found in the peritoneal fat and gelatinous material now yellow in cavity. color but otherwise similar to 27 weeks PI. A few nodules and six diffuse hemor- This retroperitoneal fatty and gelatinous rhagic areas were present on the medial layer was up to 30 mm thick. Numerous side of the cecum. Another large (15 cm) hemorrhagic areas (many with larvae) 10 hemorrhagic area and a series of nodules to 25 mm in diameter were generally dis- were observed on the lateral side of the tributed over the peritoneum of the flanks. cecum. Cecal nodes were only slightly enlarged. A series of nodules and six larger 40 WEEKS POSTINFECTION (15 cm) hemorrhagic areas lined the medial side of the right ventral colon. Al- though a few casts were found in the cecum A few S. edentatus were found in the and colon, the cecal and colic arteries and contents of the cecum and colon but most veins were devoid of lesions or larvae. The were recovered from the intestinal wall dorsal colon was normal. Several nodules near the junction of the cecum and colon were visible on the mucosal surface of the (Table VII). A pre-adult female 20 mm 15). long was dissected from a hemorrhagic area cecum (Fig. at the base of the cecum. Other females The greater omentum was disrupted into from both the walls and contents of the strands and contained many nodules (gra- cecum and colon contained eggs. No S. nulomas) 5 to 6 mm in diameter. No foci edentatus were recovered from the liver. or tracks were o-bserved in the liver. The Numerous pre-adults were removed from peritoneal surface of the flanks was cov- the flanks and perirenal fat. Several worms, ered with diffuse hemorrhagic areas from probably dislodged from the flank during which pre-adult S. edentatus were easily 350 Can. J. comp. Med. was withdrawn from each pony and a 24 mm pre-adult female S. edentatus was found in the peritoneal cavity of pony 11. The greater omentum of both ponies was congested, twisted into strands and adherent to the liver. There were no foci and there was little or no evidence of tracks in the livers of these ponies. A few casts were evident under the capsule of the diaphragmatic surface of the right lobe of the liver of pony 12. Lesions (and larvae) were absent in the ligaments of the liver. The flanks of pony 11 were normal but approximately 30 casts were observed along the ventral border of the ribs. A few casts were seen in the perirenal fat of both kidneys of pony 12. About ten nodules lined the ventral border of the cardiac and diaphragmatic regions of each lung of this pony. The remaining organs were normal.

CLINICAL SIGNS Except possibly for pony 4, no clinical signs attributable to S. edentatus were observed following infection. The rectal tem- perature of pony 4 increased to 40.22°C on day 55 PI and varied from 39.44 to 40.56°C for ten days thereafter. Although Fig. 12. Track near the ventral surface of the pancreas containing numerous eosinophils, necrotic debris and total circulating eosinophil counts consist- surrounded by a zone of loosely arranged collagen. Pony ently increased around the time of the 6, 20 weeks postinfection. H and E stain. X75. molt to the fourth stage there were generally no spectacular changes about the time exposed (Fig. 16). All other organs were of the molt to the fifth stage. normal.

59 AND 72 WEEKS POSTINFECTION One 35 mm female S. edentatus containing eggs was recovered from the cecal DISCUSSION contents and one pre-adult was found in the contents of the ventral colon of pony 11. No S. edentatus were found in the contents of the cecum or colon of pony 12. It was observed previously (5) that fol- In pony 11 (59 weeks PI) petechial lowing infection third stage S. edentatus hemorrhages were generally distributed on larvae soon penetrated the wall of the in- the serosa of the cecum and ventral colon. testine, mainly the cecum and right ventral A few were present on the dorsal colon as colon. Larvae reached the liver via the well as on the jejunum and ileum. A large portal system before the end of the second number of casts were present under the day of infection. The molt to the fourth serosa on the medial side of the cecum of stage occurred in the liver about 15 days pony 12 (72 weeks PI) but the colon was PI. Up to 15 days only white foci were normal. No lesions were found in or close observed in the liver, but by 30 days PI to the walls of the arteries or veins of the tortuous tracks were present indicating cecum and colon of either pony. Slightly active migration of larvae. This migratory over 25 ml of cloudy brown peritoneal fluid activity continued and as early as the sixth Volume 42 - July, 1978 351 Fig. 13. Red nodules on the surface of the lung (arrows). Pony 6, 20 weeks postinfection.

TABLE V. Summary of Recoveries of S. edentatus Larvae from Various Organs and Structures at 27 Weeks Postinfection No. of Mean Range Organ or Structure Stage Larvae Length mm mm Ligaments Hepatorenal ...... 5th (Male) 1 12 0 5th (Female) 3 13 12 - 14 Right triangular ...... 4th 2 6 0 Right flank ...... 5th (Male) 58 19.2 11 - 25 5th (Female) 76 22.2 12 - 31 Perirenal fat Right kidney ...... 4th 23 5th (Male) 52 18.6 11 - 24 5th (Female) 43 23.2 14 - 32 Left kidney ...... 4th 8 5th (Male) 16 19.4 15 - 23 5th (Female) 33 25.8 19 - 31 week after infection S. edentatus had pleura of the lungs, as well as being re- gained entry into the hepatorenal ligament. covered from the round, left triangular and At eight weeks several more larvae were hepatorenal ligaments. The molt from the recovered from this ligament. fourth to the fifth stage was first detected In the present study, it was found that at 16 weeks PI and this coincided with the by ten weeks the migratory activity of recovery of larvae from the extension of the fourth stage S. edentatus had extended hepatorenal ligament (to the base of the considerably. Larvae were now visible retro- cecum) as well as from a gelatinous mass peritoneally in the liver and flanks, in the in the wall of the cecum near its base. As falciform ligament and even beneath the early as 36 weeks a female pre-adult was 352 Can. J. comp. Med. Fig. 14. Pre-adult S. edentatus in the perirenal fat of Fig. 15. Nodules visible from the mucosal surface of the left kidney (arrows). Pony 7, 27 weeks postinfection. the cecum (arrows). Pony 10, 40 weeks postinfection. recovered from the contents of the ventral into these structures. At 40 weeks PI the colon, and four weeks later S. edentatus largest nematodes were found in the wall containing eggs were found in the contents or contents of the cecum and colon (Table of both the cecum and colon. From a study VII) suggesting that these sites provide of the development of natural infections, the most favorable environment for growth Russell (8) first found eggs of S. edentatus and development of S. edentatus. in foals at 40 weeks of age, but they were At 36 weeks PI no S. edentatus were generally observed in foals between 50 and recovered from the liver, and it is there- 55 weeks old. Wetzel (14) recorded a pre- fore probable that few or no living larvae patent period of 46 weeks and Poynter (6) remained there by that time. This finding gave an average age of 45.9 weeks for the also coincides with the widespread distri- first appearance of S. edentatus eggs in bution of this nematode that evidently foals. reaches its height about 36 weeks PI (Ta- While during development many S. eden- ble VI). tatus migrate to remote parts of the body, No S. edentatus were found in the peri- it is likely that only the larvae which toneal cavity until 40 weeks PI and these escape from the liver and attain the base may have been dislodged during necropsy. of the cecum are successful in establishing At least during the first 36 weeks of de- in the cecum and colon as adult forms. velopment S. edentatus is generally unable Moreover, the distance from the right lobe to penetrate serosal, peritoneal or mesen- of the liver to the base of the cecum teric surfaces and migrates entirely beneath through the hepatorenal ligament is short these layers. in equids, thus providing a direct route to S. edentatus is well known for its wide the large bowel. There was no evidence that distribution in the equine host. In the S. edentatus in regions far removed from present study, larvae and pre-adults were the cecum and colon are able to gain entry occasionally found in the pancreas, usually Volume 42 - July, 1978 353 Fig. 16. Diffuse hemorrhagic areas on the left flank from which pre-adult S. edentatus were easily exposed. Pony 10, 40 weeks postinfection. near the surface and most often without a found no lesions in the lung. Larvae are reaction around them. At 20 weeks PI the evidently equally abundant in both flanks pancreas of one pony contained hemorrhagic and worms tend to accumulate in perirenal tracks, and that of another at 36 weeks PI fat. However, they were not found in the contained a pre-adult within a fibrous cap- kidney parenchyma. sule. It is possible that a reaction only oc- Adhesions, disruption of omental archi- curs in the pancreas if S. edentatus molts tecture and variable disturbance of the ab- there. S. equinus normally migrates from dominal viscera were changes frequently the liver through the peritoneal cavity to found throughout the period of infection the pancreas where the fourth molt occurs with S. edentatus. The greater omentum of (13). Smith (11) recorded several cases of older horses is often twisted into strands S. edentatus in the testes of ponies. Most (9) and may well be the result of previous of the affected testes were intra-abdominal infection with migratory strongyles. As and he considered that migration occurred observed previously (5), nodules (granu- under the peritoneum covering the sper- lomas) were present on the surface of the matic cord. Such a retroperitoneal migration cecum and right ventral colon, and these would be consistent with the present find- persisted until 40 weeks PI. Casts of ne- ings. crotic eosinophils enclosing tracks were ob- On several occasions granulomas contain- served variably until 72 weeks PI in the ing larvae or remnants of larvae were ob- cecum and colon. These tracks often con- served beneath the pleura. They were not tained remnants of larvae which were al- found in the parenchyma of the lungs. S. ways small indicating death of larvae with- edentatus probably reached the lungs via in a few weeks of infection (5). Similar the hiatus esophagus of the diaphragm or casts were also found up to 36 weeks PI possibly via the abdominal wall. Years ago, beneath the intima of the cecal and colic Wetzel and Enigk (15) concluded that no veins and occasionally in the adventitia of migration of S. edentatus to the lung via veins, but they were never closely asso- the circulatory system occurred, and they ciated with arteries. Aberrant S. edentatus 354 Can. J. comp. Med. TABLE VI. Summary of Recoveries of S. edentatus from Various Organs or Structures at 36 Weeks Postinfection (Pony 8) No. of Mean Range Organ or Structure Stage Larvae Length mm mm Hepatorenal ligament ...... 5th (Male) 2 15 0 5th (Female) 2 26 21 - 31 Cecum wall at- Base of cecum...... 5th (Male) 14 20.5 15 - 25 5th (Female) 8 32.3 28 - 38 Right flanka...... 4th 1 15 0 5th (Male) 41 20.6 17 - 25 5th (Female) 24.2 20 - 29 Left flank...... 4th 10.5 6 - 15 5th (Male) 41 20.9 15 - 23 5th (Female) 61 27.2 21 - 32 Midventral abdomen- Fascia under skin...... 4th 1 10 0 5th (Male) 2 16 10 - 22 5th (Female) 2 26.5 24 - 29 Perirenal fat Right kidney...... 4th 1 10 0 5th (Male) 45 18.4 15 - 22 5th (Female) 58 23.2 20 - 30 Left kidney...... 4th 2 10 9 - 11 5th (Male) 63 24.2 22 - 26 5th (Female) 58 30.4 20 - 38 Serosa of bladder...... 5th (Female) 1 25 0 Right thigh - Fascia on medial surface ...... 4th 1 13 0 5th (Male) 1 22 0 5th (Female) 2 26.5 24 - 29 -The number of S. edentatus in the flanks was estimated to be five times that recovered.

TABLE VII. Summary of Recoveries of S. edentatus from Various Organs or Structures at 40 Weeks Postinfection Pre-adults No. of Mean Range Organ or Structure and Adults Larvae Length mm mm Cecum wall ...... Male 3 31 30 - 33 Female 6 37.8 22 - 48

Cecum contents ...... Male 2 28 26 - 30 Female 1 43 0

Colon wall ...... Male 12 29.9 26 - 32 Female 12 40.8 28 - 45

Colon contents ...... Male 3 32 30 - 36 Female 1 42 0

Right flanka ...... Male 11 18 14.5 - 21 Female 42 25.8 19.5 - 30 Left flank ...... Male 20 20.2 16 - 24 Female 34 28.3 21 - 34 Perirenal fat Right kidney ...... Male 19 17.2 15 - 22 Female 24 24.5 18 - 31

Left kidney ...... Male 8 18.1 16 - 21 Female 21 25.8 18 - 30

Peritoneal cavity ...... Male 3 23.7 23 - 25 Female 10 35.4 31 - 41 -An additional 50 worms were estimated to be present in each of the flanks Volume 42 - July, 1978 355 larvae may penetrate the intima of veins financial support of the Ontario Ministry soon after infection (5). Mural thrombi of Agriculture and Food is also gratefully were present in the veins of several ponies acknowledged. The authors wish to thank and were noted previously (5). Changes Mr. E. W. Eaton for his invaluable tech- similar to the swollen endothelium found nical assistance. in the lateral cecal artery and vein at 20 weeks PI have been recorded in the pulmonary arteries of cats infected with REFERENCES Aelurostro'ngylus abstrusus (1, 3, 12). Swelling and proliferation of intimal cells 1. DUBEY, J. P., J. K. A. BEVERLEY and W. A. J. CRANE. Lung changes and Aelurostrongylus ab- which contained eosinophils were noted by strusus infestation in English cats. Vet. Rec. 83: both Hamilton (3) and Stockdale (12). 191-194. 1968. 2. GLAGE, F. Beitrage zur Kenntnis der Pallisaden- Although at 16 and 20 weeks PI the wurmkrankheiten der Filllen und der Pferde. Zschr. surface of the liver was rough and the cap- Infektionkr., Haustiere. 1: 341-375. 1906. 3. HAMILTON, J. M. The influence of infestation by sule thickened, by 36 weeks the surface Aelurostrongylus abstrusus on the pulmonary vas- was near-normal to normal. Only faint culature of the cat. Br. vet. J. 126: 202-208. 1970. tracks were evident, and four weeks later 4. MARTIN, 0. Beitrage zur Kenntnis der Verbreitung und Entwicklund des Sklerostomum edentatum Loos. no foci or tracks were present. The disap- Arch. Wiss. Prakt. Tier. 37: 106-151. 1910. pearance of lesions on the surface of and 5. McCRAW, B. M. and J. 0. D. SLOCOMBE. Early development of and pathology associated with within the liver coincided with the inability Strongylus edentatus. Can. J. comp. Med. 38: 124- to recover S. edentatus from the liver be- 138. 1974. re- 6. POYNTER, D. Some observations on the nematode ginning at 36 weeks PI, indicating that parasites of horses. In Proceedings of the Second pair is relatively rapid after the nematodes International Conference on Equine Infectious Dis- eases, Paris (1969). Vol. 2, pp. 269-289. Basel, leave the liver. Switzerland: S. Karger. 1970. Hemorrhagic tracts in the flanks ap- 7. ROONEY, J. R. Autopsy of the Horse. Baltimore: peared at 10 weeks PI and this change was The Williams and Wilkins Co. 1970. 8. RUSSELL, Ann F. The development of helmin- followed by slight edema at 12 weeks. Ede- thiasis in thoroughbred foals. J. comp. Path. 58: ma of the flanks became more pronounced 107-127. 1948. related to 9. SISSON, S. and J. D. GROSSMAN. The Anatomy by 16 weeks and was possibly of the Domestic Animals. 4th Edition. Philadelphia the fourth molt which occurred about this and London: W. B. Saunders Company. 1964. time. The flanks remained edematous until 10. SLOCOMBE, J. 0. D. and B. M. McCRAW. Sup- pression of the pathogenic effects of Strongylus 36 weeks PI but by 59 and 72 weeks were edentatus larvae with thiabendazole. Can. J. comp. normal except for a few casts. There was Med. 39: 256-260. 1975. 11. SMITH, J. A. The occurrence of larvae of Strongy- thus a well-defined tendency for repair in lus edentatus in the testicles of stallions. Vet. Rec. most organs and structures. 93: 604-606. 1973. 12. STOCKDALE, P. H. G. The pathogenesis of the lesions elicited by Aelurostrongylus abstrusus during its prepatent period. Pathologia vet. 7: 102-115. 1970. 13. WETZEL, R. Zur Entwicklund des grossen Palisa- denwurmes (Strongylus equinus) im Pferd. Arch. Wiss. Prakt. Tier. 76: 81-118. 1940. 14. WETZEL, R. Die Entwicklungsdauer (Prepatent- periode) von Strongylus edentatus im Pferde. Dt. ACKNOWLEDGMENTS tierirztl. Wschr. 59: 129-130. 1952. 15. WETZEL, R. und K. ENIGK. Wandern die Larven der Palisadenwurmer (Strongylus spec.) der Pferde durch die Lungen'? Arch. Wiss. Prakt. Tier. 73: 83-93. 1938. 16. WETZEL, R. und W. KERSTEN. Die Leberphase This study was supported by a grant der Entwicklund von Strongylus edentatus. Wien. from the Ontario Racing Commission. The tierarztl. Mschr. 43: 664-673. 1956.

356 Can. J. comp. Med.