The Development of Ascaris
suum
in Calves
B. M. McCraw*
ABSTRACT To determine the development of Ascaris suum after a primary and a secondary infection, 18 calves were inoculated with 2,000,000 infective eggs and examined from 18 hours to 13 days postinfection. At 18 hours larvae were recovered from the wall of the abomasum, duodenum and jejunum. They were found in small intestine lymph nodes on the third day, in the liver at five days and were most abundant in the lungs on days 7 and 9. The pattern of recovery of larvae from the lung between days 5 and 13 postinfection was similar after a primary or a secondary infection. Slower growth of larvae following a secondary infection was the only evidence of resistance to A. suum. There were no pathological changes observed in the alimentary canal. White foci were found on the surface of the liver as early as the third day. The rapid decline in the number of A. suum in the lungs after the ninth day was considered to be related to immobilization or death of larvae soon after the reaction to them commences.
RESUME Afin d'etudier le developpement d'Ascaris suum ai la suite d'une premiere ou d'une deuxieme infestation, I'auteur administra 2,000,000 d'oeufs infectants a 18 veaux et il proceda a differents examens, entre 13 heures et 18 jours apres ces infestations. Au bout de 18 heures, il recouvra des larves de la paroi de la caillette, du duodenum et de jejunum. Au bout de trois
*Department of Pathology, University of Guelph, Guelph, Ontario. Submitted December 5, 1974.
354
jours, il en retrouva dans les ganglions lymphatiques de l'intestin grele; au bout de cinq jours, elles avaient atteint le foie et, du septieme au neuvieme jour, les poumons en contenaient le plus grand nombre. La recolte de larves des poumons, du cinquieme au 13e jour, s 'avera semblable, dans le cas de la premiere comme de la deuxieme infestation. Le developpement moins rapide des larves, apres la deuxiieme infestation, s'avera le seul indice d'une resistance a l'egard de A. suum. L'auteur ne decela pas de lesions dans le tractus digestif; il observa cependant des petits nodules blanchatres sur le foie, des le troisieme jour apres l'infestation. II considera la diminution rapide du nombre d'ascaris dans les poumons a partir du neuvieme jour, comme etant reliee 'a l'immobilisation ou 'a la mort des larves, tot apres le debut de la reaction a leur endroit.
INTRODUCTION In earlier studies with Ascaris suum (1, 4) infected calves were examined at necropsy around the 13th day postinfection when clinical signs were generally most severe. No attempt was made to follow the migration of A. suum to determine when this nematode was most abundant in various organs or structures. It was observed, however, that when calves died following infection they did so at seven or nine days postinfection and large numbers of larvae were found in the lungs (4). Whether this abundance of larvae is related to the severity of infection leading to the death of calves or occurs normally at this time is not known. The purpose of this study was to investigate the development of A. suum in calves after a single infection and to determine as well the growth and behavior of this worm following a secondary infection.
Can. J. comp. Med.
TABLE I. Infection of Calves with Ascaris suum Eggs: Group A, - Primary Infection at Four Weeks of Age; Group B, - Primary Infection at Four Weeks of Age Followed by a Secondary Infection at Seven Weeks of Age Group A: Primary Infection" Time: Infection Calf No. to Necropsy 1 18 hours 2 2 days 3 3 days 4 3 days
5 days 7 days 9 days 11 days 13 days
5
6 7 8 9
Group B: Secondary Infectiona Time: Secondary Calf No. Infection to Necropsy 10 5 days 11 5 days 12 7 days 13 7 days 14 9 days 15 i1 days 16 11 days 17 13 days 18 13 days
s2,000,000 infective eggs
MATERIALS AND METHODS
RESULTS
Two groups of calves were infected with A. suum. Groups A and B were each inoculated at four weeks of age with 2,000,000 infective eggs and Group B was given a secondary infection of 2,000,000 eggs at seven weeks (Table I). Inoculation was by stomach tube with eggs harvested and cultured as in earlier studies (1). Both groups were examined at necropsy at selected times after single or secondary infection (Table I). Up to the third day postinfection the entire abomasum and one foot segments of the small and large intestine were examined for larvae as outlined previously (6). Every fourth segment of the small intestine and every third of the large intestine was examined. The entire lung by lobes (apical, cardiac, diaphragmatic) was placed in heated (42°C) saline Baermann preparations and suspended by fibreglass screens. Examination was carried out after four and 18 hours. Thoroughly washed mesenteric lymph nodes were treated in a similar way to lung. Random samples of 25 % of the liver by weight were placed in heated saline Baermann preparations. Finely chopped liver was suspended by one layer of gauze over fibreglass screening and examined four and 18 hours later. Generally no more than 50 gm samples of larger structures were placed in a Baermann apparatus. From days 5 to 11 postinfection between 20 and 25 larvae recovered from the lung were measured from photographic prints using a planometer. Tissues were fixed in 10% formalin, sections were cut at 5 p. intervals and stained with hematoxylin and eosin.
At 18 hours postinfection one second stage A. suum larva was recovered from the wall of the abomasum and duodenum and two were recovered from the wall of the jejunum. Eight larvae were found in the lymph nodes associated with the small intestine on the third day after infectioni. Only at five days were larvae recovered from the liver and they were mostly third stage by this time. Larvae were also first detected in lung at five days and highest recoveries were on the seventh followed by ninth day postinfection (Table II). When A. suum were most abundant in the lung the mean number of larvae per gram (from combined primary and secondary infections) was 2.72. There were no significant differences between lo,bes. The pattern of recovery of larvae from the lung was similar after both a primary and secondary infection (Table II). However, the growth of larvae was slower in calves following a secondary infection (Fig. 1). In addition, the number of A. suum recovered from the lungs of calves after a primary infection was greater (5826 larvae) than that recovered following a secondary infection
Vol. 39 -July, 1975
(4746 larvae)1. There were no pathological changes observed in the esophagus, abomasum, small intestine, cecum or colon. Small white foci. 2 to 3 mm in diameter were present on both surfaces of the liver at three days post'Calculation for secondary infection based on the total of the mean daily recoveries from days 5 to 13.
355
infection. They were numerous at five days but by seven days they were difficult to find, only two or three foci being observed in one of three livers. Mesenteric lymph nodes were generally not enlarged until the seventh day. The earliest changes in the lungs were seen at nine days and these were characterized by a slight edema and emphysema. Thereafter, the changes were similar to previous observations (4).
TABLE II. Mean Recoveries of Ascaris suum Larvae from the Lungs of Calves"
Days
Postinfection 5 7 9 11 13 Total
Left
Right
Lung
Lung
230 1524 770 205 11
309 1446 725 305 16
Total 539 2970 1495 510 27
2740
2801
5541
-Combined data from primary and secondary infections
DISCUSSION The route of migration of A. suum in calves evidently does not vary from that in other foreign hosts (3, 7, 8). Larvae reached the lungs of calves mainly by the portal system with some possibly migrating via the lymphatic system. The large number of larvae found at seven and nine days postinfection (Table II) corresponds with previous findings that if death follows a single inoculation it occurs at this time in the bovine host (4). Moreover, in calves that die under field conditions recoveries from the lungs are high (5) although under experimental conditions both the size of the inoculating dose resulting in death and the number of larvae recovered varied widely (4). Dead larvae have not been recovered from the trachea of calves in experimental infec__ Primary -__. Secondary
1300 z110
0
a 900
w
/,'
ui
/-
4 700 i
/ / /
500
U.
0
/
---I
X 300
z
IU 100 -i 0
1
2
3
DAYS
4
5
6
7
8
9 10 11 12
POSTINFECTION
Fig. 1. Growth of Ascaris suum larvae in calves following a primary and secondary infection. (Day 5, P < .001; day 7, P
suum
in Calves
B. M. McCraw*
ABSTRACT To determine the development of Ascaris suum after a primary and a secondary infection, 18 calves were inoculated with 2,000,000 infective eggs and examined from 18 hours to 13 days postinfection. At 18 hours larvae were recovered from the wall of the abomasum, duodenum and jejunum. They were found in small intestine lymph nodes on the third day, in the liver at five days and were most abundant in the lungs on days 7 and 9. The pattern of recovery of larvae from the lung between days 5 and 13 postinfection was similar after a primary or a secondary infection. Slower growth of larvae following a secondary infection was the only evidence of resistance to A. suum. There were no pathological changes observed in the alimentary canal. White foci were found on the surface of the liver as early as the third day. The rapid decline in the number of A. suum in the lungs after the ninth day was considered to be related to immobilization or death of larvae soon after the reaction to them commences.
RESUME Afin d'etudier le developpement d'Ascaris suum ai la suite d'une premiere ou d'une deuxieme infestation, I'auteur administra 2,000,000 d'oeufs infectants a 18 veaux et il proceda a differents examens, entre 13 heures et 18 jours apres ces infestations. Au bout de 18 heures, il recouvra des larves de la paroi de la caillette, du duodenum et de jejunum. Au bout de trois
*Department of Pathology, University of Guelph, Guelph, Ontario. Submitted December 5, 1974.
354
jours, il en retrouva dans les ganglions lymphatiques de l'intestin grele; au bout de cinq jours, elles avaient atteint le foie et, du septieme au neuvieme jour, les poumons en contenaient le plus grand nombre. La recolte de larves des poumons, du cinquieme au 13e jour, s 'avera semblable, dans le cas de la premiere comme de la deuxieme infestation. Le developpement moins rapide des larves, apres la deuxiieme infestation, s'avera le seul indice d'une resistance a l'egard de A. suum. L'auteur ne decela pas de lesions dans le tractus digestif; il observa cependant des petits nodules blanchatres sur le foie, des le troisieme jour apres l'infestation. II considera la diminution rapide du nombre d'ascaris dans les poumons a partir du neuvieme jour, comme etant reliee 'a l'immobilisation ou 'a la mort des larves, tot apres le debut de la reaction a leur endroit.
INTRODUCTION In earlier studies with Ascaris suum (1, 4) infected calves were examined at necropsy around the 13th day postinfection when clinical signs were generally most severe. No attempt was made to follow the migration of A. suum to determine when this nematode was most abundant in various organs or structures. It was observed, however, that when calves died following infection they did so at seven or nine days postinfection and large numbers of larvae were found in the lungs (4). Whether this abundance of larvae is related to the severity of infection leading to the death of calves or occurs normally at this time is not known. The purpose of this study was to investigate the development of A. suum in calves after a single infection and to determine as well the growth and behavior of this worm following a secondary infection.
Can. J. comp. Med.
TABLE I. Infection of Calves with Ascaris suum Eggs: Group A, - Primary Infection at Four Weeks of Age; Group B, - Primary Infection at Four Weeks of Age Followed by a Secondary Infection at Seven Weeks of Age Group A: Primary Infection" Time: Infection Calf No. to Necropsy 1 18 hours 2 2 days 3 3 days 4 3 days
5 days 7 days 9 days 11 days 13 days
5
6 7 8 9
Group B: Secondary Infectiona Time: Secondary Calf No. Infection to Necropsy 10 5 days 11 5 days 12 7 days 13 7 days 14 9 days 15 i1 days 16 11 days 17 13 days 18 13 days
s2,000,000 infective eggs
MATERIALS AND METHODS
RESULTS
Two groups of calves were infected with A. suum. Groups A and B were each inoculated at four weeks of age with 2,000,000 infective eggs and Group B was given a secondary infection of 2,000,000 eggs at seven weeks (Table I). Inoculation was by stomach tube with eggs harvested and cultured as in earlier studies (1). Both groups were examined at necropsy at selected times after single or secondary infection (Table I). Up to the third day postinfection the entire abomasum and one foot segments of the small and large intestine were examined for larvae as outlined previously (6). Every fourth segment of the small intestine and every third of the large intestine was examined. The entire lung by lobes (apical, cardiac, diaphragmatic) was placed in heated (42°C) saline Baermann preparations and suspended by fibreglass screens. Examination was carried out after four and 18 hours. Thoroughly washed mesenteric lymph nodes were treated in a similar way to lung. Random samples of 25 % of the liver by weight were placed in heated saline Baermann preparations. Finely chopped liver was suspended by one layer of gauze over fibreglass screening and examined four and 18 hours later. Generally no more than 50 gm samples of larger structures were placed in a Baermann apparatus. From days 5 to 11 postinfection between 20 and 25 larvae recovered from the lung were measured from photographic prints using a planometer. Tissues were fixed in 10% formalin, sections were cut at 5 p. intervals and stained with hematoxylin and eosin.
At 18 hours postinfection one second stage A. suum larva was recovered from the wall of the abomasum and duodenum and two were recovered from the wall of the jejunum. Eight larvae were found in the lymph nodes associated with the small intestine on the third day after infectioni. Only at five days were larvae recovered from the liver and they were mostly third stage by this time. Larvae were also first detected in lung at five days and highest recoveries were on the seventh followed by ninth day postinfection (Table II). When A. suum were most abundant in the lung the mean number of larvae per gram (from combined primary and secondary infections) was 2.72. There were no significant differences between lo,bes. The pattern of recovery of larvae from the lung was similar after both a primary and secondary infection (Table II). However, the growth of larvae was slower in calves following a secondary infection (Fig. 1). In addition, the number of A. suum recovered from the lungs of calves after a primary infection was greater (5826 larvae) than that recovered following a secondary infection
Vol. 39 -July, 1975
(4746 larvae)1. There were no pathological changes observed in the esophagus, abomasum, small intestine, cecum or colon. Small white foci. 2 to 3 mm in diameter were present on both surfaces of the liver at three days post'Calculation for secondary infection based on the total of the mean daily recoveries from days 5 to 13.
355
infection. They were numerous at five days but by seven days they were difficult to find, only two or three foci being observed in one of three livers. Mesenteric lymph nodes were generally not enlarged until the seventh day. The earliest changes in the lungs were seen at nine days and these were characterized by a slight edema and emphysema. Thereafter, the changes were similar to previous observations (4).
TABLE II. Mean Recoveries of Ascaris suum Larvae from the Lungs of Calves"
Days
Postinfection 5 7 9 11 13 Total
Left
Right
Lung
Lung
230 1524 770 205 11
309 1446 725 305 16
Total 539 2970 1495 510 27
2740
2801
5541
-Combined data from primary and secondary infections
DISCUSSION The route of migration of A. suum in calves evidently does not vary from that in other foreign hosts (3, 7, 8). Larvae reached the lungs of calves mainly by the portal system with some possibly migrating via the lymphatic system. The large number of larvae found at seven and nine days postinfection (Table II) corresponds with previous findings that if death follows a single inoculation it occurs at this time in the bovine host (4). Moreover, in calves that die under field conditions recoveries from the lungs are high (5) although under experimental conditions both the size of the inoculating dose resulting in death and the number of larvae recovered varied widely (4). Dead larvae have not been recovered from the trachea of calves in experimental infec__ Primary -__. Secondary
1300 z110
0
a 900
w
/,'
ui
/-
4 700 i
/ / /
500
U.
0
/
---I
X 300
z
IU 100 -i 0
1
2
3
DAYS
4
5
6
7
8
9 10 11 12
POSTINFECTION
Fig. 1. Growth of Ascaris suum larvae in calves following a primary and secondary infection. (Day 5, P < .001; day 7, P
