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 pari- etal 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 vis- cera, 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 .............................

Load more