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Schistosoma mattheei in the ox: Distribution of the parasite in the host
Veterinary Parasitology, 3 (1977) 305--315 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
305
SCHISTOSOMA MATTHEEI IN THE OX: DISTRIBUTION OF THE PARASITE IN THE HOST
J.A. LAWRENCE
Veterinary Research Laboratory, Department of Veterinary Services, Salisbury (Rhodesia), P.O. Box 8101, Causeway (Rhodesia) (Received 23 November 1976)
ABSTRACT Lawrence, J.A., 1977. Schistosoma mattheei in the ox: distribution of the parasite in the host. Vet. Parasitol., 3: 305--315. Nineteen Friesian steers infested with between 5 000 and 45 000 cercariae of
Schistosoma mattheei were slaughtered at intervals between 7 and 107 weeks postinfestation. The distribution of parasites was assessed directly after their recovery from blood vessels and indirectly from the distribution of their eggs. The predilection sites were the small intestine and proximal large intestine. During the period of acute clinical illness 8--9 weeks after infestation there appeared to be a relative shift of parasites to the distal large intestine. Commencing at about 18 weeks post-infestation there was a partial shift from the intestine to the stomachs and bladder. During the later stages of infestation there was a relative increase in egg deposition in the liver which was not associated with a shift of parasites.
INTRODUCTION
During recent years Schistosoma mattheei (Veglia and Le Roux, 1929) has caused a number of outbreaks of clinical schistosomiasis in cattle in southern Africa (Lawrence and Condy, 1970; Reinecke, 1970; Van Wyk et al., 1974). Following these outbreaks a comprehensive investigation was undertaken (Lawrence, 1976) which included observations on the distribution of the parasite within its host. The only direct information published previously is that of Van Wyk et al. (1974), who found in naturally infested cattle that 74--96% of the parasites were present in the mesentery, with 0.8--2.8% in the liver and 0.8--23.0% in the lungs. Saeed et al. (1969) found in experimentally infested animals that the concentration of eggs was higher in the small intestine than the large intestine and was lowest in the liver. Eggs have been found widely distributed in other organs. McCully and Kruger (1969) recorded their presence in the rumen, reticulum and omasum of an experimentally infested ox and in the pancreas, mesenteric lymph nodes and urinary bladder of naturally infested cattle. In addition to these sites, Hussein (1971) found eggs in
306 the abomasum and the portal and pancreatic lymph nodes of experimentally infested calves, Condy (1960) f o u n d them in the ovary, fallopian tube and uterus of naturally infested cows and Van Wyk et al. (1974) found them in the gall bladder and ureters of heavily infested animals. In this paper observations on the distribution of parasites and their eggs in experimentally infested cattle are presented and changes in distribution which occur as infestation progresses are recorded. Some of these observations have been published previously in summary (Lawrence, 1974}. MATERIALS AND METHODS Investigations were carried out in Friesian steers infested experimentally with between 5 000 and 45 000 cercariae of S. mattheei as described previously (Lawrence, 1977). The animals were held on either a low plane of nutrition, supplying little more than maintenance, or a high plane providing a mass gain of 0.7--0.9 kg/day. At varying intervals between 7 and 107 weeks post-infestation 19 animals were killed and worms recovered from the mesenteric and gastric radicles and the intrahepatic branches of the portal vein, the internal iliac veins draining the bladder and the pulmonary arteries, using a modification of the perfusion technique of McCully and Kruger (1969). The concentration of eggs in liver, lung and intestine at various levels was determined after digestion in 5% potassium hydroxide. In other organs the presence of eggs was recorded at histological examination. RESULTS All infested calves developed clinical schistosomiasis characterised by diarrhoea or dysentery, anorexia and loss of condition, commencing 7--8 weeks post-infestation. The severity and duration of illness were proportional to the level of infestation and those animals allowed to survive recovered spontaneously.
Distribution o f parasites The number of parasites present at slaughter varied with the number of cercariae administered and the time elapsed since infestation, parasites being eliminated as infestation progressed. The distribution of parasites in 12 animals in which all five sites were perfused is shown in Table I. The intestine was the predilection site for the parasite, but significant numbers were found in the stomachs and liver.
Ratio o f sexes Mean ratio of male to female worms at the different sites, and overall, in 18 animals is shown in Table II. In the mesentery and stomachs there was a
307 TABLE I Percentage distribution of Schistosoma mattheei in 12 calves
Site
Mean (%)
Standard deviation
Range
Mesentery Stomachs Bladder Liver Lung
83.3 8.0 0.2 6.9 1.6
3.92 4.72 ----
0.0--0.8 2.0--14.8 0.0--5.0
TABLE II Ratio of male to female Schistosoma mattheei in 18 calves Site Mesentery Stomachs (13 calves) Bladder (11 calves) Liver Lung (16 calves) Overall
Mean ratio (males : females)
Standard deviation
Range
1.26
0.160
--
1.20
0.226
--
0.97 35.89
0.177 --
-0.9--204.0
6.49 1.50
-0.296
0.7--32.2 --
c o n s i s t e n t slight excess o f m a l e s o v e r females, while in t h e liver a n d lung t h e r e was a m a r k e d excess. Changes in d i s t r i b u t i o n Significant c h a n g e s in t h e d i s t r i b u t i o n o f parasites within t h e b o d y occ u r r e d w i t h t i m e . T h e s e c h a n g e s c a n be u n d e r s t o o d m o s t clearly if t h e s c h i s t o s o m e p o p u l a t i o n is r e g a r d e d as b e i n g m a d e u p o f t w o c o m p o n e n t s , t h e o n e consisting o f e q u a l n u m b e r s o f m a l e s a n d females, t h e m a j o r i t y o f w h i c h is p a i r e d a t t h e t i m e o f c o l l e c t i o n a n d is f o u n d in t h e m e s e n t e r y a n d s t o m a c h s , t h e o t h e r consisting o f surplus m e m b e r s o f o n e o r o t h e r sex, usually males, m o s t n u m e r o u s in m e s e n t e r y , liver a n d lungs. T h e r e was a significant r e d u c t i o n o f single parasites in t h e liver as infestat i o n progressed. T h e n u m b e r o f single parasites in 17 calves e x a m i n e d b e t w e e n 8 a n d 79 w e e k s p o s t - i n f e s t a t i o n , e x p r e s s e d as a p e r c e n t a g e o f t h e n u m b e r o f infesting cercariae (%R), is p l o t t e d against t i m e in w e e k s (t) in Fig.1 a n d t h e regression c a l c u l a t e d f r o m 15 p o i n t s , e x c l u d i n g t w o at 0.0%, is %R = 16e -°'°673t.
308 10 ¸
"~ --
" ~
"/,R= 1 5 , O e
-0'0673
t
o
~-
O-
,;
2'0
•
i=
3'0
Weeks
~o
5'o
6b
7'0
I
80
Post-Infestation
Fig. 1. Single parasites recovered from the liver expressed as a percentage of infesting cercariae.
The correlation between log e %R and t is highly significant (r = - 0 . 8 5 9 , P < 0.001). The percentage of infesting cercariae recovered as single parasites from the other four sites, mean 3.48%, showed no change with time. The change in distribution of paired parasites was most clearly seen in a group of seven animals infested with 20 000 cercariae (Table III). Between 8 and 18 weeks there appeared to be a shift of paired parasites from the mesentery to the stomachs, and to a lesser extent to the bladder and lungs. In No. 917 recovery from the stomachs was incomplete because of rupture of the gastric vein during perfusion. From 42 weeks onwards the relative distribution between mesentery and stomachs remained constant, while the number of parasites in bladder, liver and lungs dwindled to nothing. Support for these observations was provided by data from four other heavily infested animals. Two steers infested at 23--24 months of age had only 2.4% and 0.9% of paired parasites in the stomachs at 7 and 9 weeks respectively after infestation, while two calves slaughtered 26 and 33 weeks after infestation had 10.5% and 8.1% respectively in this site. The shift of parasites to the stomachs also occurred in animals with a lower level of infestation, but at a later stage. In three calves infested with 10 000 cercariae the number of parasites in the stomachs doubled between 31 weeks and 52 weeks (Table IV). Very few parasites were seen in the veins of the stomachs at 16--20 weeks in three other lightly infested animals, but an actual count was n o t attempted. The timing of the shift of parasites to the stomachs also appeared to be affected by the plane of nutrition. In two calves infested with 15 000 cercariae and slaughtered 17 weeks later there was clear evidence of a shift in the animal on the high plane of nutrition but not in the one on the low plane, although numbers of worms in the stomachs were not determined.
Distribution o f eggs Intestine The concentration of eggs in the intestine varied with the site, the number of cercariae administered and the time elapsed since infestation, and ranged
8 15 18 19 42 79 107
914 915 918 917 922 934 929
9 9 8 6 3 1
710 704 390 054 050 184 492
97.0 94.9 78.3 91.1 85.7 86.8 84.2
200 442 2 090 360* 376 136 92
Number
Number
Percent
Stomachs
Mesentery
2.0 4.3 19.5 5.4 10.6 10.0 15.8
Percent 2 12 68 22 14 8 0
Number
Bladder
0.0 0.1 0.6 0.3 0.4 0.6 0
Percent 48 18 76 174 72 28 0
Number
Liver
Weeks postinfestation
31 52 52
Calf No.
919 892 898
3 246 1 924 1 192
96.4 87.9 84.5
76 148 140
Number
Number
Percent
Stomachs
Mesentery
2.3 6.8 9.9
Percent 0 6 0
Number
Bladder
0 0.3 0
Percent
32 110 64
Number
Liver
D i s t r i b u t i o n o f paired S c h i s t o s o m a m a t t h e e i in calves a f t e r i n f e s t a t i o n w i t h 10 0 0 0 cercariae
T A B L E IV
* I n c o m p l e t e recovery.
Weeks postinfestation
Calf No.
D i s t r i b u t i o n o f paired S c h i s t o s o m a m a t t h e e i in calves a f t e r i n f e s t a t i o n w i t h 20 0 0 0 cercariae
T A B L E III
1.0 5.0 4.5
Percent
0.5 0.2 0.7 2.6 2.0 2.1 0
Percent
12 0 16
Number
Lung
46 54 88 36 46 8 0
Number
Lung
0.4 0 1.1
Percent
0.5 0.5 0.8 0.5 1.3 0.6 0
Percent 006 230 712 646 558 364 584
3 366 2 188 1 412
Total number
10 10 10 6 3 1
Total number
~O
310 up to a m a x i m u m of 15 640 eggs/g. As infestation progressed parasites were eliminated and the egg o u t p u t of those remaining was reduced. Analysis of variance was carried out on data from 18 calves for evidence of significant differences in concentration of eggs between calves and between the following segments of the intestine: proximal d u o d e n u m ; small intestine -- first quarter, second quarter, third quarter and fourth quarter; terminal ileum; caecum; proximal colon; distal colon and rectum. There was a highly significant variation between both calves and segments (P < 0.001), but no significant variation between proximal d u o d e n u m and the four quarters of the small intestine, nor between terminal ileum, caecum and proximal colon (P > 0.05). Egg counts for these segments were pooled and counts were calculated for four sites; small intestine (mean of all levels except terminal ileum); ileo-caeco-colon (mean of terminal ileum, caecum and proximal colon); distal colon and rectum. TABLE V Proportional concentration of eggs of Schistosoma mattheei at four sites in the intestine: m e a n of 18 calves Site
Mean
Range
Small intestine* Ileo-caeco-colon÷ Distal colon
1.00 1.76 0.46 0.75
-0.50--4.44 0.04--1.95 0--2.05
Rectum
*All levels e x c e p t terminal ileum. *Terminal ileum, c a e c u m and proximal colon. Calculation of the mean proportional concentration of eggs in ileo-caecocolon, distal colon and rectum relative to that in the small intestine revealed t h a t the ileo-caeco-colon had the highest relative concentration and the distal colon the lowest {Table V). Of 18 animals examined only two showed egg counts in the distal colon higher than those in the ileo-caeco-colon, and t h e y were the only animals slaughtered at the height of clinical illness, 8--9 weeks post-infestation. Liver
Eggs were detected in tissue digests in all but one of 18 calves examined between 8 and 107 weeks and counts ranged from 30--2 990 eggs/g. In contrast to the intestine, in which total eggs fell sharply as infestation progressed, the egg c o u n t in the liver remained unchanged at a mean of 165 eggs/infesting cercaria. In the early weeks of infestation this constituted an insignificant proportion of the total eggs in the body but by 80 weeks it represented more than 50% of the total eggs, indicating a substantial change in distribution.
311
Lungs Eggs were detected in tissue digests in nine of 13 calves examined between 8 and 33 weeks post-infestation and in none of five examined thereafter. Egg loads never exceeded 200 eggs/g. Eggs in other organs Eggs were detected in a number of other organs by histological examination (Table VI). The incidence of 63% in the abomasum may be an under-estimate, as macroscopic lesions were recorded in this organ in some animals in which eggs were n o t detected histologically. The relationship between the incidence of eggs in mesenteric lymph node and bladder and the duration and level of infestation is shown in Fig.2. Eggs were detected only between 17 and 31 weeks post-infestation in the mesenteric lymph nodes, and from 18 weeks onwards in the bladder. T A B L E VI
Incidence of eggs of Schistosoma mattheei in organs other than intestine, liver and lung Organ
Number of animals examined
Eggs present
Percent
Rumen Reticulum Omasum Abomasum Pancreas Mesenteric lymph node Bladder Kidney Spleen Heart Brain
11 11 9 16 18 18 18 18 18 18 3
8 8 3 10 10 5 6 0 0 0 0
73 73 33 63 56 28 33 0 0 0 0
+ eggs present
-
eggs absent
+
o
~o
ib
3'0
;o
Mesenter=C
s; Lymph
6;
7~
80
7'0
80
Node
4cercc~r lae /kg
+
>90 c e f f : ~ I Q"
o
J'o
+
2'0
+
3'o
Weeks
÷
4~
s~
6'o
Post-Infestation
Bladder
Fig. 2. Incidence of eggs in mesenteric lymph node and bladder.
312
DISCUSSION
This study confirms the findings of Van Wyk et al. (1974) t h a t the mesentery is the predilection site for S. mattheei in the ox. The small intestine, because of its greater size, is the major site for oviposition, although the ileocaeco-colic region is apparently a more favourable site. Distal colon and rectum are relatively unfavourable. The relative concentration of eggs in the different portions of the intestine appears to vary during the early months of patency. In one animal examined at 7 weeks post-infestation, before the onset of clinical illness, the concentration of eggs in the distal large intestine was low. In two animals examined at 8--9 weeks egg counts in the distal large intestine, especially the distal colon, were high and this was associated with the presence of severe haemorrhagic enteritis. In animals examined at a later stage, when the enteritis had subsided but while egg counts in the small intestine and proximal colon were still high, the concentration of eggs in the distal colon was low. The data suggested t h a t there was a partial shift of parasites to the distal large intestine during the acute clinical illness. It is postulated that this was a result of diarrhoea and intestinal haemorrhage caused by the severe reaction which occurs in the mucosa of the proximal large intestine in the early stages of heavy egg laying. The contents of the distal intestine become altered and it is possible t h a t a change in the composition of blood in the veins draining the region may attract schistosomes to it. As the animal recovers, the lesions in the proximal intestine abate, the intestinal contents return to normal and the region reverts to its usual status as a relatively unfavourable habitat. The abomasum and the forestomachs, with the possible exception of the omasum, are c o m m o n l y parasitised and may harbour an appreciable proportion of the parasite population. There was clear evidence of a shift of parasites from mesentery to stomachs in the experimental calves which was influenced by duration and level of infestation and possibly by plane of nutrition. This suggests that it was mediated in some way by the immune response of the host, a heavy infestation provoking a more intense reaction and a low plane of nutrition possibly inhibiting the cell-mediated immune response (Geefhuysen et al., 1971). This situation appears to differ from that recorded with other schistosomes. It is generally considered that schistosomes have predilection sites in the body and that in light infestations they concentrate in them. As numbers of parasites increase the limit to the number which these sites can accommodate is reached and the surplus overflow to less favourable sites, as seen with S. spindale in the goat (Fairley and Mackie, 1930) and S. bovis in the ox (Carta, 1951). With the reduction in parasite numbers as infestation progresses one would expect the survivors to concentrate once more in the predilection sites, although this has n o t been demonstrated directly. In the ox with S. mattheei the predilection site, the intestine, harbours over 95% of the paired parasites at patency, and the move away to the stomachs and other sites is delayed for
313 several weeks. This suggests that the predilection site becomes less favourable, possibly as a result of the development of lesions in the intestinal veins (Lawrence, 1978), encouraging the parasites to seek other accommodation. The stimulus for migration appears to be short-lived and once it has occurred the distribution of parasites remains constant. This suggests that, having been colonised, the alternative sites begin to lose their attraction and all the sites become equally favourable, with the parasites distributed in proportion to the capacity of the veins in the various organs. Male parasites in the stomachs are significantly longer than those in the mesentery in some animals at the time of the shift, and this observation supports the hypothesis that the stomachs may provide a more favourable habitat at this time (Lawrence, 1977). Lesions in the bladder caused by eggs have been recorded by Alves (1953), Condy (1960), McCully and Kruger (1969) and Van Wyk et al. (1974), b u t it is clear that the organ harbours few parasites. In this study eggs were detected consistently in the bladder from 18 weeks onwards in calves with a high level of infestation, indicating that the shift from the mesentery included a migration of parasites to the bladder and that, once there, they remained. The bladder was involved in only one calf with a low level of infestation, less than 90 cercariae/kg, suggesting that the organ was n o t involved in the shift from the mesentery when population pressure was less intense. This finding supports the opinion of Pitchford (1963) that there is a correlation between heavy infestation and the occurrence of bladder lesions in the ox. There is evidence that the bladder becomes involved at an earlier stage in lightly infested animals exposed to reinfestation than after primary infestation (Lawrence, 1976). An increasing tendency for the parasites to establish in the bladder after repeated reinfestation would explain the observation that the incidence of bladder lesions in slaughter cattle increases with age. In a survey of 867 animals at the Salisbury abattoir no bladder lesions were found in y o u n g animals with two or less permanent incisors, while the incidence increased steadily to 16.8% in mature animals, with eight permanent incisors (Lawrence, 1976). The pancreas was a reasonably c o m m o n site of egg laying at all stages of infestation. The mesenteric lymph nodes, however, were parasitised for only a short time, mainly between 17 and 19 weeks post-infestation, suggesting that they provided a habitat for parasites shifting from the veins of the intestine, b u t only for a limited period. The liver harboured a large proportion of the unpaired parasites in the early weeks after infestation. It was evident that many of the surplus males which arrived in the liver during their migration from the lungs to the mesentery remained there and were eliminated, and they were frequently reduced in length (Lawrence, 1977). Some, however, were able to migrate, without pairing, to the mesentery and elsewhere. Egg counts in the liver were relatively low during the early period of high egg o u t p u t by the parasites, but as infestation progressed there was an appar-
314
ent shift of egg-laying from intestine to liver. This was n o t caused by a shift of parasites, and it was apparent from morphological studies that those females which were present in the liver were usually not active in laying eggs {Lawrence, 1977). The eggs in the liver were probably laid by worms living in the mesenteric and gastric veins and were carried there passively in the portal blood. The relative increase was presumably caused by a larger proportion of eggs failing to lodge in the intestinal venules and being carried to the liver. A similar p h e n o m e n o n has been seen with S. mansoni and S. ]aponicum in rhesus m o n k e y s (Cheever and Powers, 1972; Cheever et al., 1974). It may be related to inflammatory changes in the intestinal veins, or to a reduction in size (Lawrence, 1977) and general activity of the females in the mesentery, preventing them from penetrating into the distal venules for oviposition. CONCLUSION
The small intestine and the proximal large intestine are the predilection sites for S. mattheei in the ox, b u t the parasite may also be found widely distributed in the lungs and abdominal organs. The parasite has the ability to vary its habitat in response to certain stimuli as the duration of infestation progresses. One such stimulus appears to be a change in the nature of the intestinal contents at the time of acute clinical illness, causing a relative shift to the distal large intestine. Another may be an immunologically induced reaction to the parasites in the intestinal veins, causing a shift away from the intestine to other organs. ACKNOWLEDGEMENTS
I am pleased to acknowledge the support and assistance in this study of the successive Assistant Directors of Veterinary Services (Research), Drs. G.J. Christie and A. Wilson, and numerous members of staff of the Veterinary Research Laboratory. I am grateful to Dr. R. Swanepoel for his advice on the preparation of this paper. The Director of Veterinary Services has given permission for publication.
REFERENCES Alves, W., 1953. Urinary bilharziasis in an ox in Southern Rhodesia. Trans. R. Soc. Trop. Med. Hyg., 47: 272. CarLa, A., 1951. Le alterazione dell 'intestino e dei linfonodi regionali nella bilharziosi dei hovini. Riv. Parassitol., 12: 169--183. Cheever, A.W. and Powers, K.G., 1972. Schistosoma mansoni infection in rhesus monkeys: comparison of the course of heavy and light infections. Bull. WHO, 46: 301--309. Cheever, A,W., Erickson, D.G., Sadun, E.H. and Von Lichtenberg, F., 1974. Schistosoma japonicum infection in monkeys and baboons: parasitological and pathological findings. Am. J. Trop. Med. Hyg., 23: 51--64.
315
Condy, J.B., 1960. Bovine schistosomiasis in Southern Rhodesia. Cent. Aft. J. Med., 6: 381--384. Fairley, N.H. and Mackie, F.P., 1930. Studies in Schistosoma spindale. Part III. The experimental pathology in the goat with special reference to verminous phlebitis. Indian Med. Res. Mem., No. 17, pp. 17--51. Geefhuysen, J., Rosen, E.U., Katz, J., Ipp, T. and Metz, J., 1971. Impaired cellular immunity in kwashiorkor with improvement after therapy. Br. Med. J., 4 : 527--529. Hussein, M.F., 1971. The pathology of experimental schistosomiasis in calves. Res. Vet. Sci., 12: 246--252. Lawrence, J.A., 1974. Schistosoma mattheei in cattle: variations in parasite distribution. In: Proc. Third Int. Congr. Parasitol., Miinchen, 1974, Vol. 2. p. 832, Facta Publication, Vienna. Lawrence, J.A., 1976. Schistosoma mattheei in the Ox. Thesis, University of Rhodesia, Salisbury, 308 pp., mimeo. Lawrence, J.A., 1977. Schistosoma mattheei in the ox: observations on the parasite. Vet. Parasitol., 3: 291--303. Lawrence, J.A., 1978. The pathology of Schistosoma mattheei infestation in the ox. 2. Lesions attributable to the adult parasites. J. Comp. Path., in press. Lawrence, J.A. and Condy, J.B., 1970. The developing problem of schistosomiasis in domestic stock in Rhodesia. Cent. Aft. J. Med., 16 (Suppl. to No. 7): 19--22. McCully, R.M. and Kruger, S.P., 1969. Observations on bilharziasis of domestic ruminants in South Africa. Onderstepoort J. Vet. Res., 36: 129--162. Pitchford, R.J., 1963. Some brief notes on schistosomes occurring in animals. J.S. Aft. Vet. Med. Assoc., 34: 613--618. Reinecke, R.K., 1970. The epizootiology of an outbreak of bilharziasis in Zululand. Cent. Afr. J. Med., 16: (Suppl. to No. 7): 10--12. Saeed, A.A., Nelson, G.S. and Hussein, M.F., 1969. Experimental infection of calves with Schistosoma mansoni. Trans. R. Soc. Trop. Med. Hyg., 63: 456--458. Van Wyk, J.A., Bartsch, R.C., Van Rensburg, L.J., Heitmann, L.P. and Goosen, P.J., 1974. Studies on schistosomiasis. 6. A field outbreak of bilharzia in cattle. Onderstepoort J. Vet. Res., 41: 39--49. Veglia, F. and Le Roux, P.L., 1929. On the morphology of a schistosome (Schistosoma mattheei, sp. nov.) from the sheep in the Cape Province. In 15th Annu. Rep. Dir. Vet. Serv., Union of S. Africa, pp. 335--346, Government Printer, Pretoria.
305
SCHISTOSOMA MATTHEEI IN THE OX: DISTRIBUTION OF THE PARASITE IN THE HOST
J.A. LAWRENCE
Veterinary Research Laboratory, Department of Veterinary Services, Salisbury (Rhodesia), P.O. Box 8101, Causeway (Rhodesia) (Received 23 November 1976)
ABSTRACT Lawrence, J.A., 1977. Schistosoma mattheei in the ox: distribution of the parasite in the host. Vet. Parasitol., 3: 305--315. Nineteen Friesian steers infested with between 5 000 and 45 000 cercariae of
Schistosoma mattheei were slaughtered at intervals between 7 and 107 weeks postinfestation. The distribution of parasites was assessed directly after their recovery from blood vessels and indirectly from the distribution of their eggs. The predilection sites were the small intestine and proximal large intestine. During the period of acute clinical illness 8--9 weeks after infestation there appeared to be a relative shift of parasites to the distal large intestine. Commencing at about 18 weeks post-infestation there was a partial shift from the intestine to the stomachs and bladder. During the later stages of infestation there was a relative increase in egg deposition in the liver which was not associated with a shift of parasites.
INTRODUCTION
During recent years Schistosoma mattheei (Veglia and Le Roux, 1929) has caused a number of outbreaks of clinical schistosomiasis in cattle in southern Africa (Lawrence and Condy, 1970; Reinecke, 1970; Van Wyk et al., 1974). Following these outbreaks a comprehensive investigation was undertaken (Lawrence, 1976) which included observations on the distribution of the parasite within its host. The only direct information published previously is that of Van Wyk et al. (1974), who found in naturally infested cattle that 74--96% of the parasites were present in the mesentery, with 0.8--2.8% in the liver and 0.8--23.0% in the lungs. Saeed et al. (1969) found in experimentally infested animals that the concentration of eggs was higher in the small intestine than the large intestine and was lowest in the liver. Eggs have been found widely distributed in other organs. McCully and Kruger (1969) recorded their presence in the rumen, reticulum and omasum of an experimentally infested ox and in the pancreas, mesenteric lymph nodes and urinary bladder of naturally infested cattle. In addition to these sites, Hussein (1971) found eggs in
306 the abomasum and the portal and pancreatic lymph nodes of experimentally infested calves, Condy (1960) f o u n d them in the ovary, fallopian tube and uterus of naturally infested cows and Van Wyk et al. (1974) found them in the gall bladder and ureters of heavily infested animals. In this paper observations on the distribution of parasites and their eggs in experimentally infested cattle are presented and changes in distribution which occur as infestation progresses are recorded. Some of these observations have been published previously in summary (Lawrence, 1974}. MATERIALS AND METHODS Investigations were carried out in Friesian steers infested experimentally with between 5 000 and 45 000 cercariae of S. mattheei as described previously (Lawrence, 1977). The animals were held on either a low plane of nutrition, supplying little more than maintenance, or a high plane providing a mass gain of 0.7--0.9 kg/day. At varying intervals between 7 and 107 weeks post-infestation 19 animals were killed and worms recovered from the mesenteric and gastric radicles and the intrahepatic branches of the portal vein, the internal iliac veins draining the bladder and the pulmonary arteries, using a modification of the perfusion technique of McCully and Kruger (1969). The concentration of eggs in liver, lung and intestine at various levels was determined after digestion in 5% potassium hydroxide. In other organs the presence of eggs was recorded at histological examination. RESULTS All infested calves developed clinical schistosomiasis characterised by diarrhoea or dysentery, anorexia and loss of condition, commencing 7--8 weeks post-infestation. The severity and duration of illness were proportional to the level of infestation and those animals allowed to survive recovered spontaneously.
Distribution o f parasites The number of parasites present at slaughter varied with the number of cercariae administered and the time elapsed since infestation, parasites being eliminated as infestation progressed. The distribution of parasites in 12 animals in which all five sites were perfused is shown in Table I. The intestine was the predilection site for the parasite, but significant numbers were found in the stomachs and liver.
Ratio o f sexes Mean ratio of male to female worms at the different sites, and overall, in 18 animals is shown in Table II. In the mesentery and stomachs there was a
307 TABLE I Percentage distribution of Schistosoma mattheei in 12 calves
Site
Mean (%)
Standard deviation
Range
Mesentery Stomachs Bladder Liver Lung
83.3 8.0 0.2 6.9 1.6
3.92 4.72 ----
0.0--0.8 2.0--14.8 0.0--5.0
TABLE II Ratio of male to female Schistosoma mattheei in 18 calves Site Mesentery Stomachs (13 calves) Bladder (11 calves) Liver Lung (16 calves) Overall
Mean ratio (males : females)
Standard deviation
Range
1.26
0.160
--
1.20
0.226
--
0.97 35.89
0.177 --
-0.9--204.0
6.49 1.50
-0.296
0.7--32.2 --
c o n s i s t e n t slight excess o f m a l e s o v e r females, while in t h e liver a n d lung t h e r e was a m a r k e d excess. Changes in d i s t r i b u t i o n Significant c h a n g e s in t h e d i s t r i b u t i o n o f parasites within t h e b o d y occ u r r e d w i t h t i m e . T h e s e c h a n g e s c a n be u n d e r s t o o d m o s t clearly if t h e s c h i s t o s o m e p o p u l a t i o n is r e g a r d e d as b e i n g m a d e u p o f t w o c o m p o n e n t s , t h e o n e consisting o f e q u a l n u m b e r s o f m a l e s a n d females, t h e m a j o r i t y o f w h i c h is p a i r e d a t t h e t i m e o f c o l l e c t i o n a n d is f o u n d in t h e m e s e n t e r y a n d s t o m a c h s , t h e o t h e r consisting o f surplus m e m b e r s o f o n e o r o t h e r sex, usually males, m o s t n u m e r o u s in m e s e n t e r y , liver a n d lungs. T h e r e was a significant r e d u c t i o n o f single parasites in t h e liver as infestat i o n progressed. T h e n u m b e r o f single parasites in 17 calves e x a m i n e d b e t w e e n 8 a n d 79 w e e k s p o s t - i n f e s t a t i o n , e x p r e s s e d as a p e r c e n t a g e o f t h e n u m b e r o f infesting cercariae (%R), is p l o t t e d against t i m e in w e e k s (t) in Fig.1 a n d t h e regression c a l c u l a t e d f r o m 15 p o i n t s , e x c l u d i n g t w o at 0.0%, is %R = 16e -°'°673t.
308 10 ¸
"~ --
" ~
"/,R= 1 5 , O e
-0'0673
t
o
~-
O-
,;
2'0
•
i=
3'0
Weeks
~o
5'o
6b
7'0
I
80
Post-Infestation
Fig. 1. Single parasites recovered from the liver expressed as a percentage of infesting cercariae.
The correlation between log e %R and t is highly significant (r = - 0 . 8 5 9 , P < 0.001). The percentage of infesting cercariae recovered as single parasites from the other four sites, mean 3.48%, showed no change with time. The change in distribution of paired parasites was most clearly seen in a group of seven animals infested with 20 000 cercariae (Table III). Between 8 and 18 weeks there appeared to be a shift of paired parasites from the mesentery to the stomachs, and to a lesser extent to the bladder and lungs. In No. 917 recovery from the stomachs was incomplete because of rupture of the gastric vein during perfusion. From 42 weeks onwards the relative distribution between mesentery and stomachs remained constant, while the number of parasites in bladder, liver and lungs dwindled to nothing. Support for these observations was provided by data from four other heavily infested animals. Two steers infested at 23--24 months of age had only 2.4% and 0.9% of paired parasites in the stomachs at 7 and 9 weeks respectively after infestation, while two calves slaughtered 26 and 33 weeks after infestation had 10.5% and 8.1% respectively in this site. The shift of parasites to the stomachs also occurred in animals with a lower level of infestation, but at a later stage. In three calves infested with 10 000 cercariae the number of parasites in the stomachs doubled between 31 weeks and 52 weeks (Table IV). Very few parasites were seen in the veins of the stomachs at 16--20 weeks in three other lightly infested animals, but an actual count was n o t attempted. The timing of the shift of parasites to the stomachs also appeared to be affected by the plane of nutrition. In two calves infested with 15 000 cercariae and slaughtered 17 weeks later there was clear evidence of a shift in the animal on the high plane of nutrition but not in the one on the low plane, although numbers of worms in the stomachs were not determined.
Distribution o f eggs Intestine The concentration of eggs in the intestine varied with the site, the number of cercariae administered and the time elapsed since infestation, and ranged
8 15 18 19 42 79 107
914 915 918 917 922 934 929
9 9 8 6 3 1
710 704 390 054 050 184 492
97.0 94.9 78.3 91.1 85.7 86.8 84.2
200 442 2 090 360* 376 136 92
Number
Number
Percent
Stomachs
Mesentery
2.0 4.3 19.5 5.4 10.6 10.0 15.8
Percent 2 12 68 22 14 8 0
Number
Bladder
0.0 0.1 0.6 0.3 0.4 0.6 0
Percent 48 18 76 174 72 28 0
Number
Liver
Weeks postinfestation
31 52 52
Calf No.
919 892 898
3 246 1 924 1 192
96.4 87.9 84.5
76 148 140
Number
Number
Percent
Stomachs
Mesentery
2.3 6.8 9.9
Percent 0 6 0
Number
Bladder
0 0.3 0
Percent
32 110 64
Number
Liver
D i s t r i b u t i o n o f paired S c h i s t o s o m a m a t t h e e i in calves a f t e r i n f e s t a t i o n w i t h 10 0 0 0 cercariae
T A B L E IV
* I n c o m p l e t e recovery.
Weeks postinfestation
Calf No.
D i s t r i b u t i o n o f paired S c h i s t o s o m a m a t t h e e i in calves a f t e r i n f e s t a t i o n w i t h 20 0 0 0 cercariae
T A B L E III
1.0 5.0 4.5
Percent
0.5 0.2 0.7 2.6 2.0 2.1 0
Percent
12 0 16
Number
Lung
46 54 88 36 46 8 0
Number
Lung
0.4 0 1.1
Percent
0.5 0.5 0.8 0.5 1.3 0.6 0
Percent 006 230 712 646 558 364 584
3 366 2 188 1 412
Total number
10 10 10 6 3 1
Total number
~O
310 up to a m a x i m u m of 15 640 eggs/g. As infestation progressed parasites were eliminated and the egg o u t p u t of those remaining was reduced. Analysis of variance was carried out on data from 18 calves for evidence of significant differences in concentration of eggs between calves and between the following segments of the intestine: proximal d u o d e n u m ; small intestine -- first quarter, second quarter, third quarter and fourth quarter; terminal ileum; caecum; proximal colon; distal colon and rectum. There was a highly significant variation between both calves and segments (P < 0.001), but no significant variation between proximal d u o d e n u m and the four quarters of the small intestine, nor between terminal ileum, caecum and proximal colon (P > 0.05). Egg counts for these segments were pooled and counts were calculated for four sites; small intestine (mean of all levels except terminal ileum); ileo-caeco-colon (mean of terminal ileum, caecum and proximal colon); distal colon and rectum. TABLE V Proportional concentration of eggs of Schistosoma mattheei at four sites in the intestine: m e a n of 18 calves Site
Mean
Range
Small intestine* Ileo-caeco-colon÷ Distal colon
1.00 1.76 0.46 0.75
-0.50--4.44 0.04--1.95 0--2.05
Rectum
*All levels e x c e p t terminal ileum. *Terminal ileum, c a e c u m and proximal colon. Calculation of the mean proportional concentration of eggs in ileo-caecocolon, distal colon and rectum relative to that in the small intestine revealed t h a t the ileo-caeco-colon had the highest relative concentration and the distal colon the lowest {Table V). Of 18 animals examined only two showed egg counts in the distal colon higher than those in the ileo-caeco-colon, and t h e y were the only animals slaughtered at the height of clinical illness, 8--9 weeks post-infestation. Liver
Eggs were detected in tissue digests in all but one of 18 calves examined between 8 and 107 weeks and counts ranged from 30--2 990 eggs/g. In contrast to the intestine, in which total eggs fell sharply as infestation progressed, the egg c o u n t in the liver remained unchanged at a mean of 165 eggs/infesting cercaria. In the early weeks of infestation this constituted an insignificant proportion of the total eggs in the body but by 80 weeks it represented more than 50% of the total eggs, indicating a substantial change in distribution.
311
Lungs Eggs were detected in tissue digests in nine of 13 calves examined between 8 and 33 weeks post-infestation and in none of five examined thereafter. Egg loads never exceeded 200 eggs/g. Eggs in other organs Eggs were detected in a number of other organs by histological examination (Table VI). The incidence of 63% in the abomasum may be an under-estimate, as macroscopic lesions were recorded in this organ in some animals in which eggs were n o t detected histologically. The relationship between the incidence of eggs in mesenteric lymph node and bladder and the duration and level of infestation is shown in Fig.2. Eggs were detected only between 17 and 31 weeks post-infestation in the mesenteric lymph nodes, and from 18 weeks onwards in the bladder. T A B L E VI
Incidence of eggs of Schistosoma mattheei in organs other than intestine, liver and lung Organ
Number of animals examined
Eggs present
Percent
Rumen Reticulum Omasum Abomasum Pancreas Mesenteric lymph node Bladder Kidney Spleen Heart Brain
11 11 9 16 18 18 18 18 18 18 3
8 8 3 10 10 5 6 0 0 0 0
73 73 33 63 56 28 33 0 0 0 0
+ eggs present
-
eggs absent
+
o
~o
ib
3'0
;o
Mesenter=C
s; Lymph
6;
7~
80
7'0
80
Node
4cercc~r lae /kg
+
>90 c e f f : ~ I Q"
o
J'o
+
2'0
+
3'o
Weeks
÷
4~
s~
6'o
Post-Infestation
Bladder
Fig. 2. Incidence of eggs in mesenteric lymph node and bladder.
312
DISCUSSION
This study confirms the findings of Van Wyk et al. (1974) t h a t the mesentery is the predilection site for S. mattheei in the ox. The small intestine, because of its greater size, is the major site for oviposition, although the ileocaeco-colic region is apparently a more favourable site. Distal colon and rectum are relatively unfavourable. The relative concentration of eggs in the different portions of the intestine appears to vary during the early months of patency. In one animal examined at 7 weeks post-infestation, before the onset of clinical illness, the concentration of eggs in the distal large intestine was low. In two animals examined at 8--9 weeks egg counts in the distal large intestine, especially the distal colon, were high and this was associated with the presence of severe haemorrhagic enteritis. In animals examined at a later stage, when the enteritis had subsided but while egg counts in the small intestine and proximal colon were still high, the concentration of eggs in the distal colon was low. The data suggested t h a t there was a partial shift of parasites to the distal large intestine during the acute clinical illness. It is postulated that this was a result of diarrhoea and intestinal haemorrhage caused by the severe reaction which occurs in the mucosa of the proximal large intestine in the early stages of heavy egg laying. The contents of the distal intestine become altered and it is possible t h a t a change in the composition of blood in the veins draining the region may attract schistosomes to it. As the animal recovers, the lesions in the proximal intestine abate, the intestinal contents return to normal and the region reverts to its usual status as a relatively unfavourable habitat. The abomasum and the forestomachs, with the possible exception of the omasum, are c o m m o n l y parasitised and may harbour an appreciable proportion of the parasite population. There was clear evidence of a shift of parasites from mesentery to stomachs in the experimental calves which was influenced by duration and level of infestation and possibly by plane of nutrition. This suggests that it was mediated in some way by the immune response of the host, a heavy infestation provoking a more intense reaction and a low plane of nutrition possibly inhibiting the cell-mediated immune response (Geefhuysen et al., 1971). This situation appears to differ from that recorded with other schistosomes. It is generally considered that schistosomes have predilection sites in the body and that in light infestations they concentrate in them. As numbers of parasites increase the limit to the number which these sites can accommodate is reached and the surplus overflow to less favourable sites, as seen with S. spindale in the goat (Fairley and Mackie, 1930) and S. bovis in the ox (Carta, 1951). With the reduction in parasite numbers as infestation progresses one would expect the survivors to concentrate once more in the predilection sites, although this has n o t been demonstrated directly. In the ox with S. mattheei the predilection site, the intestine, harbours over 95% of the paired parasites at patency, and the move away to the stomachs and other sites is delayed for
313 several weeks. This suggests that the predilection site becomes less favourable, possibly as a result of the development of lesions in the intestinal veins (Lawrence, 1978), encouraging the parasites to seek other accommodation. The stimulus for migration appears to be short-lived and once it has occurred the distribution of parasites remains constant. This suggests that, having been colonised, the alternative sites begin to lose their attraction and all the sites become equally favourable, with the parasites distributed in proportion to the capacity of the veins in the various organs. Male parasites in the stomachs are significantly longer than those in the mesentery in some animals at the time of the shift, and this observation supports the hypothesis that the stomachs may provide a more favourable habitat at this time (Lawrence, 1977). Lesions in the bladder caused by eggs have been recorded by Alves (1953), Condy (1960), McCully and Kruger (1969) and Van Wyk et al. (1974), b u t it is clear that the organ harbours few parasites. In this study eggs were detected consistently in the bladder from 18 weeks onwards in calves with a high level of infestation, indicating that the shift from the mesentery included a migration of parasites to the bladder and that, once there, they remained. The bladder was involved in only one calf with a low level of infestation, less than 90 cercariae/kg, suggesting that the organ was n o t involved in the shift from the mesentery when population pressure was less intense. This finding supports the opinion of Pitchford (1963) that there is a correlation between heavy infestation and the occurrence of bladder lesions in the ox. There is evidence that the bladder becomes involved at an earlier stage in lightly infested animals exposed to reinfestation than after primary infestation (Lawrence, 1976). An increasing tendency for the parasites to establish in the bladder after repeated reinfestation would explain the observation that the incidence of bladder lesions in slaughter cattle increases with age. In a survey of 867 animals at the Salisbury abattoir no bladder lesions were found in y o u n g animals with two or less permanent incisors, while the incidence increased steadily to 16.8% in mature animals, with eight permanent incisors (Lawrence, 1976). The pancreas was a reasonably c o m m o n site of egg laying at all stages of infestation. The mesenteric lymph nodes, however, were parasitised for only a short time, mainly between 17 and 19 weeks post-infestation, suggesting that they provided a habitat for parasites shifting from the veins of the intestine, b u t only for a limited period. The liver harboured a large proportion of the unpaired parasites in the early weeks after infestation. It was evident that many of the surplus males which arrived in the liver during their migration from the lungs to the mesentery remained there and were eliminated, and they were frequently reduced in length (Lawrence, 1977). Some, however, were able to migrate, without pairing, to the mesentery and elsewhere. Egg counts in the liver were relatively low during the early period of high egg o u t p u t by the parasites, but as infestation progressed there was an appar-
314
ent shift of egg-laying from intestine to liver. This was n o t caused by a shift of parasites, and it was apparent from morphological studies that those females which were present in the liver were usually not active in laying eggs {Lawrence, 1977). The eggs in the liver were probably laid by worms living in the mesenteric and gastric veins and were carried there passively in the portal blood. The relative increase was presumably caused by a larger proportion of eggs failing to lodge in the intestinal venules and being carried to the liver. A similar p h e n o m e n o n has been seen with S. mansoni and S. ]aponicum in rhesus m o n k e y s (Cheever and Powers, 1972; Cheever et al., 1974). It may be related to inflammatory changes in the intestinal veins, or to a reduction in size (Lawrence, 1977) and general activity of the females in the mesentery, preventing them from penetrating into the distal venules for oviposition. CONCLUSION
The small intestine and the proximal large intestine are the predilection sites for S. mattheei in the ox, b u t the parasite may also be found widely distributed in the lungs and abdominal organs. The parasite has the ability to vary its habitat in response to certain stimuli as the duration of infestation progresses. One such stimulus appears to be a change in the nature of the intestinal contents at the time of acute clinical illness, causing a relative shift to the distal large intestine. Another may be an immunologically induced reaction to the parasites in the intestinal veins, causing a shift away from the intestine to other organs. ACKNOWLEDGEMENTS
I am pleased to acknowledge the support and assistance in this study of the successive Assistant Directors of Veterinary Services (Research), Drs. G.J. Christie and A. Wilson, and numerous members of staff of the Veterinary Research Laboratory. I am grateful to Dr. R. Swanepoel for his advice on the preparation of this paper. The Director of Veterinary Services has given permission for publication.
REFERENCES Alves, W., 1953. Urinary bilharziasis in an ox in Southern Rhodesia. Trans. R. Soc. Trop. Med. Hyg., 47: 272. CarLa, A., 1951. Le alterazione dell 'intestino e dei linfonodi regionali nella bilharziosi dei hovini. Riv. Parassitol., 12: 169--183. Cheever, A.W. and Powers, K.G., 1972. Schistosoma mansoni infection in rhesus monkeys: comparison of the course of heavy and light infections. Bull. WHO, 46: 301--309. Cheever, A,W., Erickson, D.G., Sadun, E.H. and Von Lichtenberg, F., 1974. Schistosoma japonicum infection in monkeys and baboons: parasitological and pathological findings. Am. J. Trop. Med. Hyg., 23: 51--64.
315
Condy, J.B., 1960. Bovine schistosomiasis in Southern Rhodesia. Cent. Aft. J. Med., 6: 381--384. Fairley, N.H. and Mackie, F.P., 1930. Studies in Schistosoma spindale. Part III. The experimental pathology in the goat with special reference to verminous phlebitis. Indian Med. Res. Mem., No. 17, pp. 17--51. Geefhuysen, J., Rosen, E.U., Katz, J., Ipp, T. and Metz, J., 1971. Impaired cellular immunity in kwashiorkor with improvement after therapy. Br. Med. J., 4 : 527--529. Hussein, M.F., 1971. The pathology of experimental schistosomiasis in calves. Res. Vet. Sci., 12: 246--252. Lawrence, J.A., 1974. Schistosoma mattheei in cattle: variations in parasite distribution. In: Proc. Third Int. Congr. Parasitol., Miinchen, 1974, Vol. 2. p. 832, Facta Publication, Vienna. Lawrence, J.A., 1976. Schistosoma mattheei in the Ox. Thesis, University of Rhodesia, Salisbury, 308 pp., mimeo. Lawrence, J.A., 1977. Schistosoma mattheei in the ox: observations on the parasite. Vet. Parasitol., 3: 291--303. Lawrence, J.A., 1978. The pathology of Schistosoma mattheei infestation in the ox. 2. Lesions attributable to the adult parasites. J. Comp. Path., in press. Lawrence, J.A. and Condy, J.B., 1970. The developing problem of schistosomiasis in domestic stock in Rhodesia. Cent. Aft. J. Med., 16 (Suppl. to No. 7): 19--22. McCully, R.M. and Kruger, S.P., 1969. Observations on bilharziasis of domestic ruminants in South Africa. Onderstepoort J. Vet. Res., 36: 129--162. Pitchford, R.J., 1963. Some brief notes on schistosomes occurring in animals. J.S. Aft. Vet. Med. Assoc., 34: 613--618. Reinecke, R.K., 1970. The epizootiology of an outbreak of bilharziasis in Zululand. Cent. Afr. J. Med., 16: (Suppl. to No. 7): 10--12. Saeed, A.A., Nelson, G.S. and Hussein, M.F., 1969. Experimental infection of calves with Schistosoma mansoni. Trans. R. Soc. Trop. Med. Hyg., 63: 456--458. Van Wyk, J.A., Bartsch, R.C., Van Rensburg, L.J., Heitmann, L.P. and Goosen, P.J., 1974. Studies on schistosomiasis. 6. A field outbreak of bilharzia in cattle. Onderstepoort J. Vet. Res., 41: 39--49. Veglia, F. and Le Roux, P.L., 1929. On the morphology of a schistosome (Schistosoma mattheei, sp. nov.) from the sheep in the Cape Province. In 15th Annu. Rep. Dir. Vet. Serv., Union of S. Africa, pp. 335--346, Government Printer, Pretoria.