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Observations on Experimental and Field Infections of Pigs with Hyostrongylus Rubidus
Br. vet. J. (1970), 126,538
OBSERVATIONS ON EXPERIMENTAL AND FIELD INFECTIONS OF PIGS WITH HYOSTRONGYLUS RUBIDUS By A. BASKERVILLE AND
J.
G. Ross
Veterinary Research Laboratories, Stormont, Belfast
SUMMARY Forty young pigs were infected with 1000-45,000 larvae of Hyostrongylus rubidus and killed at intervals. The parasites developed within the gastric glands and formed nodules in the mucosa. The glands showed mucoid metaplasia and were surrounded by a lymphoid reaction. Sixty per cent of sows in an abattoir survey were infected with H . rubidus. INTRODU CT ION Hyostrongylus rubidus is a parasite which has received limited attention, but has been suggested as the cause of emaciation in sows (Clay, 1938; Nicholson &
Gordon, 1959; Connan, 1967; Larsen, 1967). Reports of the effects of anthelmintic treatment of sows infected with H. rubidus attribute pathogenicity to this parasite, but observations of experimental infections have produced widely differing conclusions (Porter, 1940; Kotlan, 1960; Shanks, 1965; Davidson & Sutherland, 1966; Davidson, Murray & Sutherland, 1967; Boch, Gerber & Horchner, 1968). The present investigation includes a survey of the incidence of the parasite in sows in Northern Ireland and experimental infections of young pigs. MATERIALS AND METHODS Survey. In total, 400 sows' stomachs were collected from two local abattoirs over a period of 24 months. The contents of each stomach were emptied and the mucosa washed and examined for gross lesions. Portions of mucosa were taken for histological examination. Total counts of the number of parasites present in the gastric contents and in trypsin digests of the mucosa were made, and the parasites examined and measured and the stage of development recorded. Experimental infections. A culture of H. rubidus was established by repeated passage in pigs of 3-8 weeks of age which were reared free from parasites. Forty parasite-free pigs were infected orally by stomach tube with single infections ranging from 1000 to 45,000 third stage infective larvae. The pigs were infected between 3 and 8 weeks of age, and were initially obtained by early weaning from anthelmintic-screened sows, but latterly minimal disease piglets obtained by Caesarean section and artificially reared were used. Normally entire litters were used and one-third of each litter was uninfected and maintained as a control on the effect of infection. The pigs were weighed
INCIDE NCE OF H. RUBID US I N PIeS
539
weekly and blood samples collected at intervals to follow changes in the constituents of blood and serum. The pigs were slaughtered by exsanguination under p entobarbitone sodium anaesthesia at intervals from I day to 14 weeks after infection. At post-mortem examination a total count of the number of parasites present in each stomach was carried out and observations of the size a nd stage of d evelopm ent of the parasite were made. Material for histology was fixed in formalin, and paraffin sections were stained by haematoxylin and eosin, periodic acid-Schiff, and Alcia n blue. RES ULTS
Survey Sixty per cent of the sows' stomachs examined were infected with H. rubidus a nd showed varying degrees of chronic gastritis. In heavily infected stomachs excess mucus was present and shallow ulcers were frequently observed. Immature fourth stage parasites were present in 15 per cent of the stomachs examined and in these the typical nodular lesion was observed. The m ean number of worms in the infected stomachs was 1235 with a range of IOO- 23,000. Examination of the stom achs from more than 2000 younger pigs submitted to the la boratory for routine post-mortem examination revealed the presence of H. rubidus infection on one occasion only. Experimental infections The percentage of larvae which became established following infec tion was very variable. The p ercentage ranged from I to 80 per cent with an average of about 15 per cent in infections ofless than 3000 infective third stage larvae, and below I p er cent in infec tions of more than 5000 third stage larvae. The rate and stages of development of the parasite were similar to previous descriptions (Alicata, 1935; Kotlan, 1949 ; Kendall, Thurley & Peirce, 1969) . No significant clinical disease was produced which was directly attributable to infection with H. rubidus. In a few of the piglets given infections of 5000 or more third stage larvae a d epressed weight gain and mild diarrhoea were observed between the second and third weeks following infec tion, but these piglets rapidly r ecovered and overtook the weight gains of control piglets. Histopathology Six days. The mucosa was covered with white raised nodules of 1- 3 mm. diameter (Fig. I). Nodules were most numerous in the fundic region, but were also present in the cardiac and pyloric zones. M any nodules had coalesced and the largest were often umbilicated. Coiled larvae were located in the basal parts of the gastric glands, which were dilated into cysts of up to 0·25 mm. diameter. The epithelium of the lacunae was columnar and of mucin-producing type in many areas, but in others was fl attened. A small qua ntity of cellular debris with a few neutrophils was present in the lumen of some glands. There was a moderate lymphoreticular reaction surrounding most of the infected glands, and this tissue contained numerous eosinophils and a few plasma cells.
540
BRITISH VETERINARY JOURNAL,
126,
10
Nine days. More nodules had coalesced forming small plaques. Cysts containing larvae were now up to 0'4 mm. diameter. Small numbers of neutrophils were invading the walls of many glands and there was marked mucoid metaplasia of the cells lining the gastric glands (Figs. 2 and 3). The lymphoid reaction had increased and involved neighbouring glands. Eosinophils were present locally in large numbers and were also diffusely scattered through the mucosa and submucosa. Twelve days. Nodules and plaques were still prominent. Microscopically there was marked oedema of the submucosa of all regions of the stomach and this layer was diffusely infiltrated by eosinophils. Glandular cysts up to 0'5 mm. in diameter and containing fifth stage parasites caused compression of adjacent glands. The lymphoid tissue around affected glands persisted at this stage. The epithelium lining affected glands was invariably intact and was predominantly of tall mucus-secreting type. There was a reduction in the number of parietal cells in the areas immediately surrounding the infected glands. Fifteen to twenty-one days. At the fifteenth day a few worms h ad emerged from the glandular cysts, and by the twenty-first day a large number lay in thick mucus on the surface of the mucosa. Nodules were no longer clearly defined. Histologically the glandular lacunae containing worms were irregular in shape and were lined by tall mucus-producing columnar cells. groups of which occasionally formed papillary outgrowths (Figs. 4 and 6). Superficial regions of the gastric glands were dilated and frequently emerging worms were seen protruding out of the neck onto the epithelial surface (Fig. 5). There was mucoid metaplasia of glands in the vicinity of cysts. Many empty cysts were present. These had a mucin-secreting epithelium and had often collapsed to form slit-like spaces. By day 18 the intense lymphoreticular reaction around infected glands had diminished and the lamina propria was diffusely infiltrated by small numbers of lymphocytes, plasma cells and eosinophils. At day 2 I the oedema of the submucosa was still present and moderate numbers of eosinophils were scattered in this region. Parietal cells were not detected in the areas immediately surrounding infected glands or vacated cysts. Chronic adult infection. The mucosa was covered with thick tenacious mucus and the tips of many of the rugae were hyperaemic. Frequently shallow ulcers were present. Worms were found in all regions of the stomach, but were most numerous in the fundic zone. There was necrosis of the superficial epithelium, and sloughed cells, together with small numbers of polymorphs, eosinophils and mucus, formed an exudate on the surface of the mucosa. Ulcers extended into the lamina propria and these were demarcated by an intense lymphoid reaction. Later stages of such lesions showed healing by fibrosis. Many stomachs of chronically infected sows had areas of fibrous scar formation throughout the mucosa. DISCUSSION
In the experimental investigations the percentage of larvae which became established was very low. The reason for this is not known, but the findings are
PLATE I
F ig.
I.
Gastric mucosa of pig 6 days after infection with H . rubidus. Some nodules have coalesced.
Fig. 2 . Gastric glands 9 days after infection. A coiled larva is present in one gland which is surround ed by a modera te lympho-reticular reaction. H & E , X 100.
Fig. 3. High power of gland in Fig. 2. T he gland is lined by columna r mucin-secreting cells. H & E , X 250. Baskerville and R oss, Br. vet.
J.
( 1970), 126, 10
PLATE II
Fig. 4. I S days after infection. There is an intense lym phoid reaction around the infected gastric gland . H & E , X I SO.
Fig. 5 . 18 days. Adult paras ites emerging from gas tric glands. H & E , x 100.
Fig. 6. 18 days. Greatly distended glands contain adult parasites. The lymphoid reaction has subsided but there is fibrosis of the lamina propria in the vicinity of the lacunae. H & E, X 100. Baskerville and Ross, Br. vet. J. ( 1970) ,
126, IO
INCIDENCE OF H. RUBID US IN PIGS
54 1
in agreement with those of Porter ( 1940) and Kendall et al. (1969). There was evidence of lower takes with higher infection levels as seen in infec tion of lambs with Trichostrongylus axei (Ross, Purcell & Todd, 1969a ) but not of a preferential loss of paTasites at any stage, although Porter suggested that a loss occurred after day 25. Davidson et al. (1967) recorded elevated gastric pH in hyostrongylosis, and the pathological changes in the gastric glands in the present study were suggestive of impairment of gastric function. Measurement of gastric pH was carried out and values of pH 2 to pH 6 were registered. Preliminary studies undertaken on a pig with a gastric cannula of a type previously used in calves (Phillipson & Innes, 1939; Ross et al., I 969b ) showed a similar and variable rang€: of pH both before and after infection. The pH of gastric fluid was apparently influenced by a number offactors, of which the presence and natUle offood wert important. Until the normal range and causes of fluctuations in the pH of the gastric fluid in the pig have been established its relationship to hyostrongylosis should be interpreted with caution. Significant clinical disease was not produced in young pigs by infection with H. rubidus in the present study or in the majOlity of previous investigations (Porter, 1940; Boch et al., 1968; Davidson et al., 1968; Kendall et al., 1969). Kotlan & Vajda (cited Kotlan, 1960) produced diarrhoea, emaciation, and even death following infection with 4000 to 27,000 larvae, but the d etails of this work have not been published. It is probable that other factors, such as the nutritional state of the animal, play an important role. Boch et al. (1968) showed that treatment of pigs with testosterone led to higher experimental infection levels. Connan (1967) d emonstrated that the excretion of eggs by the sow rises significantly during the suckling period, and it is possible that in sows, also, hormonal factors are involved in hyostrongylosis. Although the abattoir surveys indicated a high incidence of H. rubidus infection in sows the "thin-sow syndrome" is not a major problem in Northern Ireland. The absence of infection in the younger pigs submitted for routine post-mortem examination to this laboratory over a number of years probably reflects the intensive systems of pig husbandry in Northern Ireland. Current studies on Oesophagostomum spp . have indicated that O. den tatum is the principal species of Oesophagostomum in Northern Ireland and that this species does not produce significant disease in experimentally infected pigs (McCracken & Ross, in press). R eports of emaciation associated with parasitic gastritis in sows relate to mixed infections with H. rubidus and Oesophagostomum spp., and the ex ac t species of Oesophagostomum is not given. Schwartz (193 I) showed that O. quadrispinulatum produced more severe lesions than O. dentatum. There is clearly a n eed to clarify the precise parts played individually and collectively by Hyostrongy lus rubidus, Oesophagostomunn spp., and other gastrointestinal pathogens in unthriftincss in pigs. ACKNOWLEDGMENTS
We are indebted to the staff of the Parasitology and Pathology Departments for technical assistance.
542
BRITISH VETERINARY JOURNAL, 126, 10
REFERENCES
ALICATA, j. E. (1935). U.S. Dept. Agl'. T ech. Bull., 489 . BOCH, j., GERBER, H.-CH. & HORCHNER, F. (1968). B ert. Munch. tieriirz.tl. W schr., 81, 145. CLAY, A . L. (1938). Aust. vet. ] ., 14, 194. CONNAN, R . M . (1967). Vet. R ec ., 80, 424. DAVIDSON, j . B., MURRAY, M . & SUTHERLAND, I. H . (1967). Proc. 3rd Int. Conf. vet. Parasitol.,
P·9·
DAVIDSON, j. B., M URRAY, M. & SUTHERLAND, I. H . (1968) . Vet. R ec., 83, 582. DAVIDSON, j. B. & SUTHERLAND, I. H . (1966). Vet. R ec., 78, 702. KENDALL, S. B., THURLEY, D. C. & PEIRCE, M. A. (1969).]. compo Path ., 79, 87. KOTLAN, A. (1949). A cta vet. hung., I, 76. KOTLAN, A. (1960). Helminthologie, p . 470. Budapest: Hungarian Academy of Science. LARSEN, S . (1967). Acta vet. scand., 8, 347. MCCRACKEN, R. M. & Ross, j . G. (1970). In press. N ICOLSON, T. B. & GORDON, j. G. (1959) . Vet. R ec., 71, 133. PHILLIPSON, A. T. & INNES, j. R. M. (1939). Q . ]l. expo Physiol., 29, 333. PORTER, D . A. (1940). Proc. helminth. Soc. W ash. , 7, 20. Ross, j . G. , P URCELL, D . A. & TODD, j. R. ( 1969a). R es. vet. Sci., 10,46. Ross, J. G., PURCELL, D . A. & TODD, j. R . (1969b). R es. vet. Sci., 10, 142. SCHWARTZ, B. (193 1). Vet. Med., 26, 41 I. SHANKS, P . L. (1965). N.Z. vet. ]., 13,38. TAFFS, L. F. (1966). Vet. R ec., 79, 67 1. (Accepted f or publication 15 May 1970)
Observations s ur les infections experhnentales et naturelles des porcs par
Hyostrongylus rubidus (Baskerville et Ross) ResuIne. Quarante jeunes pores ont ete infectes avec 1000-45,000 larves de Hyostrongylus rubidus et sacrifies a intervalles. L es parasites se d eveioppaient a l'interieur des glandes gastriques et formaient d es nodules dans la muqueuse. Les glandes montraient d e la metaplasie mucolde et etaient entourees d'une reaction lympholde. Soixante pour cent d es truies au cours d 'une enquete dans un abattoir etaient infectees par H. rubidus. Beobachtungen tiber experiInentell und freie Infektionen von Schweinen Init
Hyostrongylus rubidus (Baskerville und Ros s ) ZusaInInenfass ung. Vierzig jungschweine wurden infiziert mit 1000-45,000 Larven von Hyostrongylus rubidus und in bestimmten Z eitintervallen geschlachtet. Die Parasiten hatten innerhalb d er gastrischen Driisen entwickeit und Knoten in d er Mucosa geformt. Die Driisen zeigten m u koide Metaplasie und waren von einer lymphoid en R eaktionsschicht umgeben . Sechzig Prozent der M u tterschweine waren, zufolge eines Schla ch thofberichtes, mit H. rubidus infiziert. Observaciones sobre infecciones experiInentales y de caInpo de cerdos con
Hyostrongylus rubidus (Baskerville y Ross) ResuInen. Se infectaron cuarenta cerdos j6venes con 1000- 45,000 larvas d e Hyostrongylus rubidus y se fueron sacrificando a intervalos. Los parisitos se desarrollaron dentro de las glandulas gastricas y formaron nodos en la mucosa. Las glandulas mostraron metaplasia mucoide y estuvieron rodeadas por u na reacci6n linfoide. Sesenta por ciento de las cerdas en u n estudio de un matadero estuvieron infectadas con H. rubidus.
OBSERVATIONS ON EXPERIMENTAL AND FIELD INFECTIONS OF PIGS WITH HYOSTRONGYLUS RUBIDUS By A. BASKERVILLE AND
J.
G. Ross
Veterinary Research Laboratories, Stormont, Belfast
SUMMARY Forty young pigs were infected with 1000-45,000 larvae of Hyostrongylus rubidus and killed at intervals. The parasites developed within the gastric glands and formed nodules in the mucosa. The glands showed mucoid metaplasia and were surrounded by a lymphoid reaction. Sixty per cent of sows in an abattoir survey were infected with H . rubidus. INTRODU CT ION Hyostrongylus rubidus is a parasite which has received limited attention, but has been suggested as the cause of emaciation in sows (Clay, 1938; Nicholson &
Gordon, 1959; Connan, 1967; Larsen, 1967). Reports of the effects of anthelmintic treatment of sows infected with H. rubidus attribute pathogenicity to this parasite, but observations of experimental infections have produced widely differing conclusions (Porter, 1940; Kotlan, 1960; Shanks, 1965; Davidson & Sutherland, 1966; Davidson, Murray & Sutherland, 1967; Boch, Gerber & Horchner, 1968). The present investigation includes a survey of the incidence of the parasite in sows in Northern Ireland and experimental infections of young pigs. MATERIALS AND METHODS Survey. In total, 400 sows' stomachs were collected from two local abattoirs over a period of 24 months. The contents of each stomach were emptied and the mucosa washed and examined for gross lesions. Portions of mucosa were taken for histological examination. Total counts of the number of parasites present in the gastric contents and in trypsin digests of the mucosa were made, and the parasites examined and measured and the stage of development recorded. Experimental infections. A culture of H. rubidus was established by repeated passage in pigs of 3-8 weeks of age which were reared free from parasites. Forty parasite-free pigs were infected orally by stomach tube with single infections ranging from 1000 to 45,000 third stage infective larvae. The pigs were infected between 3 and 8 weeks of age, and were initially obtained by early weaning from anthelmintic-screened sows, but latterly minimal disease piglets obtained by Caesarean section and artificially reared were used. Normally entire litters were used and one-third of each litter was uninfected and maintained as a control on the effect of infection. The pigs were weighed
INCIDE NCE OF H. RUBID US I N PIeS
539
weekly and blood samples collected at intervals to follow changes in the constituents of blood and serum. The pigs were slaughtered by exsanguination under p entobarbitone sodium anaesthesia at intervals from I day to 14 weeks after infection. At post-mortem examination a total count of the number of parasites present in each stomach was carried out and observations of the size a nd stage of d evelopm ent of the parasite were made. Material for histology was fixed in formalin, and paraffin sections were stained by haematoxylin and eosin, periodic acid-Schiff, and Alcia n blue. RES ULTS
Survey Sixty per cent of the sows' stomachs examined were infected with H. rubidus a nd showed varying degrees of chronic gastritis. In heavily infected stomachs excess mucus was present and shallow ulcers were frequently observed. Immature fourth stage parasites were present in 15 per cent of the stomachs examined and in these the typical nodular lesion was observed. The m ean number of worms in the infected stomachs was 1235 with a range of IOO- 23,000. Examination of the stom achs from more than 2000 younger pigs submitted to the la boratory for routine post-mortem examination revealed the presence of H. rubidus infection on one occasion only. Experimental infections The percentage of larvae which became established following infec tion was very variable. The p ercentage ranged from I to 80 per cent with an average of about 15 per cent in infections ofless than 3000 infective third stage larvae, and below I p er cent in infec tions of more than 5000 third stage larvae. The rate and stages of development of the parasite were similar to previous descriptions (Alicata, 1935; Kotlan, 1949 ; Kendall, Thurley & Peirce, 1969) . No significant clinical disease was produced which was directly attributable to infection with H. rubidus. In a few of the piglets given infections of 5000 or more third stage larvae a d epressed weight gain and mild diarrhoea were observed between the second and third weeks following infec tion, but these piglets rapidly r ecovered and overtook the weight gains of control piglets. Histopathology Six days. The mucosa was covered with white raised nodules of 1- 3 mm. diameter (Fig. I). Nodules were most numerous in the fundic region, but were also present in the cardiac and pyloric zones. M any nodules had coalesced and the largest were often umbilicated. Coiled larvae were located in the basal parts of the gastric glands, which were dilated into cysts of up to 0·25 mm. diameter. The epithelium of the lacunae was columnar and of mucin-producing type in many areas, but in others was fl attened. A small qua ntity of cellular debris with a few neutrophils was present in the lumen of some glands. There was a moderate lymphoreticular reaction surrounding most of the infected glands, and this tissue contained numerous eosinophils and a few plasma cells.
540
BRITISH VETERINARY JOURNAL,
126,
10
Nine days. More nodules had coalesced forming small plaques. Cysts containing larvae were now up to 0'4 mm. diameter. Small numbers of neutrophils were invading the walls of many glands and there was marked mucoid metaplasia of the cells lining the gastric glands (Figs. 2 and 3). The lymphoid reaction had increased and involved neighbouring glands. Eosinophils were present locally in large numbers and were also diffusely scattered through the mucosa and submucosa. Twelve days. Nodules and plaques were still prominent. Microscopically there was marked oedema of the submucosa of all regions of the stomach and this layer was diffusely infiltrated by eosinophils. Glandular cysts up to 0'5 mm. in diameter and containing fifth stage parasites caused compression of adjacent glands. The lymphoid tissue around affected glands persisted at this stage. The epithelium lining affected glands was invariably intact and was predominantly of tall mucus-secreting type. There was a reduction in the number of parietal cells in the areas immediately surrounding the infected glands. Fifteen to twenty-one days. At the fifteenth day a few worms h ad emerged from the glandular cysts, and by the twenty-first day a large number lay in thick mucus on the surface of the mucosa. Nodules were no longer clearly defined. Histologically the glandular lacunae containing worms were irregular in shape and were lined by tall mucus-producing columnar cells. groups of which occasionally formed papillary outgrowths (Figs. 4 and 6). Superficial regions of the gastric glands were dilated and frequently emerging worms were seen protruding out of the neck onto the epithelial surface (Fig. 5). There was mucoid metaplasia of glands in the vicinity of cysts. Many empty cysts were present. These had a mucin-secreting epithelium and had often collapsed to form slit-like spaces. By day 18 the intense lymphoreticular reaction around infected glands had diminished and the lamina propria was diffusely infiltrated by small numbers of lymphocytes, plasma cells and eosinophils. At day 2 I the oedema of the submucosa was still present and moderate numbers of eosinophils were scattered in this region. Parietal cells were not detected in the areas immediately surrounding infected glands or vacated cysts. Chronic adult infection. The mucosa was covered with thick tenacious mucus and the tips of many of the rugae were hyperaemic. Frequently shallow ulcers were present. Worms were found in all regions of the stomach, but were most numerous in the fundic zone. There was necrosis of the superficial epithelium, and sloughed cells, together with small numbers of polymorphs, eosinophils and mucus, formed an exudate on the surface of the mucosa. Ulcers extended into the lamina propria and these were demarcated by an intense lymphoid reaction. Later stages of such lesions showed healing by fibrosis. Many stomachs of chronically infected sows had areas of fibrous scar formation throughout the mucosa. DISCUSSION
In the experimental investigations the percentage of larvae which became established was very low. The reason for this is not known, but the findings are
PLATE I
F ig.
I.
Gastric mucosa of pig 6 days after infection with H . rubidus. Some nodules have coalesced.
Fig. 2 . Gastric glands 9 days after infection. A coiled larva is present in one gland which is surround ed by a modera te lympho-reticular reaction. H & E , X 100.
Fig. 3. High power of gland in Fig. 2. T he gland is lined by columna r mucin-secreting cells. H & E , X 250. Baskerville and R oss, Br. vet.
J.
( 1970), 126, 10
PLATE II
Fig. 4. I S days after infection. There is an intense lym phoid reaction around the infected gastric gland . H & E , X I SO.
Fig. 5 . 18 days. Adult paras ites emerging from gas tric glands. H & E , x 100.
Fig. 6. 18 days. Greatly distended glands contain adult parasites. The lymphoid reaction has subsided but there is fibrosis of the lamina propria in the vicinity of the lacunae. H & E, X 100. Baskerville and Ross, Br. vet. J. ( 1970) ,
126, IO
INCIDENCE OF H. RUBID US IN PIGS
54 1
in agreement with those of Porter ( 1940) and Kendall et al. (1969). There was evidence of lower takes with higher infection levels as seen in infec tion of lambs with Trichostrongylus axei (Ross, Purcell & Todd, 1969a ) but not of a preferential loss of paTasites at any stage, although Porter suggested that a loss occurred after day 25. Davidson et al. (1967) recorded elevated gastric pH in hyostrongylosis, and the pathological changes in the gastric glands in the present study were suggestive of impairment of gastric function. Measurement of gastric pH was carried out and values of pH 2 to pH 6 were registered. Preliminary studies undertaken on a pig with a gastric cannula of a type previously used in calves (Phillipson & Innes, 1939; Ross et al., I 969b ) showed a similar and variable rang€: of pH both before and after infection. The pH of gastric fluid was apparently influenced by a number offactors, of which the presence and natUle offood wert important. Until the normal range and causes of fluctuations in the pH of the gastric fluid in the pig have been established its relationship to hyostrongylosis should be interpreted with caution. Significant clinical disease was not produced in young pigs by infection with H. rubidus in the present study or in the majOlity of previous investigations (Porter, 1940; Boch et al., 1968; Davidson et al., 1968; Kendall et al., 1969). Kotlan & Vajda (cited Kotlan, 1960) produced diarrhoea, emaciation, and even death following infection with 4000 to 27,000 larvae, but the d etails of this work have not been published. It is probable that other factors, such as the nutritional state of the animal, play an important role. Boch et al. (1968) showed that treatment of pigs with testosterone led to higher experimental infection levels. Connan (1967) d emonstrated that the excretion of eggs by the sow rises significantly during the suckling period, and it is possible that in sows, also, hormonal factors are involved in hyostrongylosis. Although the abattoir surveys indicated a high incidence of H. rubidus infection in sows the "thin-sow syndrome" is not a major problem in Northern Ireland. The absence of infection in the younger pigs submitted for routine post-mortem examination to this laboratory over a number of years probably reflects the intensive systems of pig husbandry in Northern Ireland. Current studies on Oesophagostomum spp . have indicated that O. den tatum is the principal species of Oesophagostomum in Northern Ireland and that this species does not produce significant disease in experimentally infected pigs (McCracken & Ross, in press). R eports of emaciation associated with parasitic gastritis in sows relate to mixed infections with H. rubidus and Oesophagostomum spp., and the ex ac t species of Oesophagostomum is not given. Schwartz (193 I) showed that O. quadrispinulatum produced more severe lesions than O. dentatum. There is clearly a n eed to clarify the precise parts played individually and collectively by Hyostrongy lus rubidus, Oesophagostomunn spp., and other gastrointestinal pathogens in unthriftincss in pigs. ACKNOWLEDGMENTS
We are indebted to the staff of the Parasitology and Pathology Departments for technical assistance.
542
BRITISH VETERINARY JOURNAL, 126, 10
REFERENCES
ALICATA, j. E. (1935). U.S. Dept. Agl'. T ech. Bull., 489 . BOCH, j., GERBER, H.-CH. & HORCHNER, F. (1968). B ert. Munch. tieriirz.tl. W schr., 81, 145. CLAY, A . L. (1938). Aust. vet. ] ., 14, 194. CONNAN, R . M . (1967). Vet. R ec ., 80, 424. DAVIDSON, j . B., MURRAY, M . & SUTHERLAND, I. H . (1967). Proc. 3rd Int. Conf. vet. Parasitol.,
P·9·
DAVIDSON, j. B., M URRAY, M. & SUTHERLAND, I. H . (1968) . Vet. R ec., 83, 582. DAVIDSON, j. B. & SUTHERLAND, I. H . (1966). Vet. R ec., 78, 702. KENDALL, S. B., THURLEY, D. C. & PEIRCE, M. A. (1969).]. compo Path ., 79, 87. KOTLAN, A. (1949). A cta vet. hung., I, 76. KOTLAN, A. (1960). Helminthologie, p . 470. Budapest: Hungarian Academy of Science. LARSEN, S . (1967). Acta vet. scand., 8, 347. MCCRACKEN, R. M. & Ross, j . G. (1970). In press. N ICOLSON, T. B. & GORDON, j. G. (1959) . Vet. R ec., 71, 133. PHILLIPSON, A. T. & INNES, j. R. M. (1939). Q . ]l. expo Physiol., 29, 333. PORTER, D . A. (1940). Proc. helminth. Soc. W ash. , 7, 20. Ross, j . G. , P URCELL, D . A. & TODD, j. R. ( 1969a). R es. vet. Sci., 10,46. Ross, J. G., PURCELL, D . A. & TODD, j. R . (1969b). R es. vet. Sci., 10, 142. SCHWARTZ, B. (193 1). Vet. Med., 26, 41 I. SHANKS, P . L. (1965). N.Z. vet. ]., 13,38. TAFFS, L. F. (1966). Vet. R ec., 79, 67 1. (Accepted f or publication 15 May 1970)
Observations s ur les infections experhnentales et naturelles des porcs par
Hyostrongylus rubidus (Baskerville et Ross) ResuIne. Quarante jeunes pores ont ete infectes avec 1000-45,000 larves de Hyostrongylus rubidus et sacrifies a intervalles. L es parasites se d eveioppaient a l'interieur des glandes gastriques et formaient d es nodules dans la muqueuse. Les glandes montraient d e la metaplasie mucolde et etaient entourees d'une reaction lympholde. Soixante pour cent d es truies au cours d 'une enquete dans un abattoir etaient infectees par H. rubidus. Beobachtungen tiber experiInentell und freie Infektionen von Schweinen Init
Hyostrongylus rubidus (Baskerville und Ros s ) ZusaInInenfass ung. Vierzig jungschweine wurden infiziert mit 1000-45,000 Larven von Hyostrongylus rubidus und in bestimmten Z eitintervallen geschlachtet. Die Parasiten hatten innerhalb d er gastrischen Driisen entwickeit und Knoten in d er Mucosa geformt. Die Driisen zeigten m u koide Metaplasie und waren von einer lymphoid en R eaktionsschicht umgeben . Sechzig Prozent der M u tterschweine waren, zufolge eines Schla ch thofberichtes, mit H. rubidus infiziert. Observaciones sobre infecciones experiInentales y de caInpo de cerdos con
Hyostrongylus rubidus (Baskerville y Ross) ResuInen. Se infectaron cuarenta cerdos j6venes con 1000- 45,000 larvas d e Hyostrongylus rubidus y se fueron sacrificando a intervalos. Los parisitos se desarrollaron dentro de las glandulas gastricas y formaron nodos en la mucosa. Las glandulas mostraron metaplasia mucoide y estuvieron rodeadas por u na reacci6n linfoide. Sesenta por ciento de las cerdas en u n estudio de un matadero estuvieron infectadas con H. rubidus.