The establishment and development of Trichostrongylus colubriformis in goats

Veterinary Parasitology, 35 (1990) 195-200 Elsevier Science Publishers B.V., A m s t e r d a m - - P r i n t e d in T h e Netherlands

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The E s t a b l i s h m e n t and D e v e l o p m e n t of Trichostrongylus colubriformis in Goats W A H A B A. R A H M A N 1 a n d G.H. C O L L I N S 2

1School of Biological Sciences, University Sains Malaysia, Minden, 11800 Penang (Malaysia) 2Department of Veterinary Pathology, University of Sydney, N.S. W. 2006 (Australia) (Accepted for publication 25 September 1989)

ABSTRACT R a h m a n , W.A. a n d Collins, G.H., 1990. T h e establishment and development of Trichostrongylus colubriformis in goats. Vet. Parasitol., 35: 195-200. Twelve goats were inoculated with 20 000 infective larvae of Trichostrongylus colubriformis a n d two were killed on each of Days 4, 7, 11, 14, 18 a n d 21 after inoculation (DAI). T h e n u m b e r of worms t h a t established, a n d the site of development were recorded. Most of the worms established within the first 3 m of the small intestine. T h e r e was little relocation or loss of nematodes after establishment. T h e worms started to migrate from the mucosa to the lumen 11 days after infection. At 4 DAI, 637o of the worms were still at the late L3 stage; the remainder of the worm population had completed the t h i r d moult to the L4 stage. T h e population at 11 DAI comprised largely young adults. W h e n 21 DAI was reached, about 57% of the female worms h a d eggs in their uteri.

INTRODUCTION

The development of Trichostrongylus colubriformis in goats has been briefly described by Fitzsimmons (1966) but only for the first 10 days after infection. Fitzsimmons et al. (1968) reported that T. colubriformis had a pre-patent period of 19 days in adult goats. The present study was carried out with the aim of extending the findings of Fitzsimmons (1966) and Fitzsimmons et al. (1968) and comparing the development of T. colubriformis in goats with that in sheep, as described by other workers. M A T E R I A L S AND M E T H O D S

Newly born goats were obtained from farms near Sydney, Australia. The majority were Saanens or Nubians, whilst a few were Toggenburgs or British

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Alpines. All goats were reared worm-free, on wire mesh floors, indoors, until the age of 2-3 months. The goats were fed a milk replacer (Denkavit: Daken Corporation Pty. Ltd., New South Wales, Australia) first by bottle, later ad libitum; chaffed lucerne was introduced into the diet from 3 weeks of age.

Infective larvae Infective larvae of T. colubriformis were obtained from the McMaster laboratory, CSIRO, Sydney from a strain ( M c M a s t e r susceptible) which had been regularly passed through sheep for several years. The larvae were less than 1 week old when used and had been stored at 4 °C. Larvae were checked for motility before used.

Experimental procedure Twelve goats were fasted for 12 h and 20 00O infective larvae were administered directly into the rumen using a stomach tube. Two goats were killed by barbiturate overdose on each of Days 4, 7, 11, 14, 18 and 21 days after inoculation (DAI).

Recovery of worms At necropsy, the abomasum and the small intestine were removed. The abomasum was cut open; the contents and the washings from the mucosa were collected into containers containing 10% formalin. The abomasum was then cut into smaller pieces and digested in an aqueous solution of 1.0% pepsin with hydrochloric acid at 37 °C for 45 min. The digested tissues were washed in a sieve (mesh size 0.0625 mm). Large pieces of tissue were discarded and the sieved material was preserved in 10% formalin. The results from goats killed at 4 DAI showed that worms were present in the proximal 600 cm of the small intestine. Therefore, in subsequent necropsies, i.e. 7, 11, 14, 18 and 21 DAI, only the first 6 X 1-m segments were examined. Worm counts were performed on 3 X 5% aliquots of the contents and of the digested material from each metre segment. Where worm counts were low, all of the contents were examined. After counting, all worms from each goat were combined and 100 unselected worms were identified according to their stage in the life cycle (Monnig, 1926; Douvres, 1957). RESULTS No goats died during the course of the experiment, but diarrhoea and illthrift occurred in some goats.

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Establishment and development o[ worms The total number of larvae that established and developed was low in all goats (Table 1). Few worms were recovered from the abomasum and it was noted that most of these established in the pyloric rather than the middle or fundic thirds of the abomasum. The proportion of the total that were found in the abomasum at 18 and 21 DAI was higher than that at 4, 7, 11 and 14 DAI (Table 1 ). Table 2 shows the total number of worms found in sequential metre-long segments of the small intestine. Most of the worms established within the first 3 m. At 4 and 7 DAI, all the worms were recorded from the mucosa and none from the lumen (Table 3). Worms were found in the lumen from 11 DAI; at 14, 18 and 21 DAI, the majority were in the lumen.

Development of T. colubriformis in goats At 4 DAI, 63% of the worms were still at the late L3 stage; the remainder of the worm population had completed the third moult to the L4 stage. The population at 11 DAI comprised largely young adults, although about 18% of the total worm population were still at the late L4 stage. At 14 DAI, about 9% of the female worms were observed to have eggs in their uteri, with the majority still immature. At 18 DAI, about 17% of the female population had eggs in TABLE 1 Total number of worms found in the abomasum and small intestine (S.I.) of goats after infection with 20 000 infective larvae of T. colubriformis at various times after infection DAI

4 7 11 14 18 21

Goat

1 2 1 2 1 2 1 2 1 2 1 2

Number of worms

Total

Abomasum ( % of total estab. )

S.I. ( % of total estab. )

38 22 0 79 65 38 48 13 227 317 365 165

2677 7914 4387 8685 5478 2033 8418 3262 6678 7113 8320 2122

(1.4) (0.3) (0) (0.9) (1.2) (1.8) (0.6) (0.4) (3.4) (4.3) (4.2) (7.8)

(98.6) (99.7) (100) (99.1) (98.8) (98.2) (99.4) (99.6) (96.6) (95.7) (95.8) (92.8)

Percent established Individual goat

2715 7936 4387 8764 5543 2071 8466 3275 6905 7430 8685 2287

13.6 39.7 21.9 43.8 27.7 10.4 43.3 16.4 34.5 37.2 43.4 11.9

Mean

26.7 32.9 19.1 29.9 35.9 27.7

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TABLE 2 Total number of worms found in sequential metre-long segments of small intestine in goats at various intervals after infection with 20 000 infective larvae of T. colubri[ormis DAI

Goat

Number of worms in each segment (% of total estab.) 1

4 7 11 14 18 21

1 2 1 2 1 2 1 2 1 2 1 2

2

1282 3871 1877 3871 1303 1248 1278 1154 1734 2397 4833 581

(47.9) (48.9) (42.8) (48.9) (23.8) (61.4) (15.2) (35.4) (26.0) (33.7) (58.1) (27.4)

964 1892 768 1892 1015 465 1507 701 1775 1152 1614 658

3

(10.9) (23.9) (17.9) (23.9) (18.5) (22.9) (17.9) (21.5) (26.6) (16.2) (19.4) (31.0)

293 890 1317 890 1544 205 3129 339 1041 1615 876 492

4

(10.9) (11.2) (30.0) (11.2) (28.2) (10.1) (37.2) (10.4) (15.6) (22.7) (10.5) (23.2)

118 1005 362 1005 927 71 1145 487 1536 1714 571 261

5

(4.4) (12.7) (8.3) (12.7) (16.9) (2.5) (13.6) (14.9) (23.0) (24.0) (6.9) (12.3)

17 175 45 175 608 44 867 375 483 149 332 130

6

(0.6) (2.2) (1.1) (2.2) (11.1) (2.2) (10.3) (11.5) (7.2) (2.1) (4.0) (6.1)

3 81 0 81 81 0 492 206 109 86 94 0

(0.1) (1.0) (0) (1.0) (1.5) (0) (5.8) (6.3) (1.6) (1.2) (1.1) (0)

TABLE 3 Number of worms recovered from the mucosa and lumen of the small intestine of goats after infection with 20 000 infective larvae of T. colubriformis DAI

4 7 11 14 18 21

Goat

1 2 1 2 1 2 1 2 1 2 1 2

Number of worms recovered

Total

Mucosa ( % of total )

Lumen ( % of total )

2677 7419 4387 8685 3835 1333 3190 1594 850 2177 892 489

0 0 0 0 1643 700 5228 1668 5828 4936 7428 1633

(100) (100) (100) (100) (70.0) (65.6) (37.9) (48.9) (12.7) (30.6) (10.7) (23.0)

(0) (0) (0) (0) (30.0) (34.4) (62.1) (51.1) (87.3) (69.4) (89.3) (77.0)

2677 7419 4387 8685 5478 2033 8418 3262 6678 7113 8320 2122

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their uteri; when 21 DAI was reached, about 57% of the females had eggs in their uteri. DISCUSSION There was a large variation in the percentage of T. colubriformis larvae that were able to establish in individual goats. In general, the establishment rates in the goats were lower than those reported for the same species in sheep by Andrews (1939) and Barker (1975); both of them reported establishment rates of more than 60%. It is possible that, as the larvae used for infecting the goats were obtained from a strain which has always been maintained in sheep, they may have been less successful in establishing in goats. The possibility that there are differences in infectivity between sheep-derived and goat-derived strains needs further investigation. Although T. colubriformis were recovered from both the abomasum and the small intestine, the latter was the preferred site of establishment. The largest numbers of worms were always found within the first 3 m of the small intestine as has been similarly reported for species of Trichostrongylus in sheep and rabbits (Tetley, 1937; Davey, 1938; Barker, 1974). It is likely that T. colubriformis larvae, having been stimulated to exsheath in the abomasum (Rogers and Sommerville, 1957; Sommerville, 1963 ) establish in the next section of the gastrointestinal tract they encounter; as suggested by Davey (1938), the first few metres of the small intestine is the most favoured site as compared with the more distal parts. The cause of the increase in the numbers of worms in the abomasum at 18 and 21 DAI is unknown. It is possible that as adult worms mature, they become more active and that some migrate back into the pyloric abomasum. The pattern of distribution of T. colubriformis in the gastrointestinal tract of goats corresponds in general with that found in sheep (Tetley, 1937; Davey, 1938; Barker, 1974). Sommerville (1963) using various Trichostrongylus spp. in sheep and rabbits and Bull (1953) using T. retortaeformis in rabbits reported a similar pattern of distribution. This contrasts with guinea pigs where populations of T. colubriformis are gradually redistributed into the caudal intestine, probably in association with the development of immunity (Connan, 1966). This study showed that T. colubriformis stays in the mucosa until about 11 DAI, and that the immature adults emerge and mature in the lumen. Although at 18 DAI 17% of the females already had eggs in their uteri, it was not until 20 DAI when eggs were first detected in the faeces. However, the minimal time to reach patency could have been as early as 13 DAI, because at 14 DAI some female worms already contained eggs.

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ACKNOWLEDGEMENTS

The authors wish to thank Mr. David Griffith and Ms. Sally Pope from the Department of Veterinary Pathology, University of Sydney, Australia for their able technical assistance. The Australian Development Assistance Bureau (ADAB) is kindly acknowledged for providing a grant for the above research. REFERENCES Andrews, J.S., 1939. Experimental trichostrongylosis in sheep and goats. J. Agric. Res., 58: 761770. Barker, I.J., 1974. The relationship and abnormal mucosal microtophography with distribution of T. colubriformis in the small intestine of lambs. Int. J. Parasitol., 4: 153-163. Barker, I.J., 1975. Location and distribution of T. colubriformis in the small intestine of sheep during the prepatent period, and the development of villous atrophy. J. Comp. Pathol., 85:417 426. Bull, P.C., 1953. Distribution of the nematode T. retaetor[ormis (Zeder, 1800) in the wild rabbit Cryctolagus cuniculus (L.). N.Z.J. Sci. Technol., 34:449 456. Connan, R.M., 1966. Experiments with T. colubri[ormis (Giles, 1982) in the guinea pig. 1. The effect of the host response on the distribution of the parasites in the gut. Parasitology, 30:278 295. Davey, P.G., 1938. Studies on the physiology of the nematodes of the alimentary canal of sheep. Parasitology, 30: 278-295. Douvres, F.W., 1957. The morphogenesis of the parasitic stages of T. axei and T. eoIubriformis, nematode parasites of cattle. Proc. Helminthol. Soc. Wash., 24: 4-14. Fitzsimmons, W.M., 1966. Growth and development of parasitic stages of 7'. eolubriformis in the goat. Vet. Rec., 78: 221-222. Fitzsimons, W.M., Harness, E. and Sellwood, S.S., 1968. The experimental T. eolubriformis infection in adult goats. Res. Vet. Sci., 7: 101-111. Monnig, H.O., 1926. The life-histories of T. instabilis and T. rugatus of sheep in South Africa. Report of the Director of Veterinary Education and Research, Department of Agriculture, Union of South Africa, Vols. 11 and 12: 231-251. Rogers, W.P. and Sommerville, R.I., 1957. Physiology and exsheathment in nematodes and its relation of parasitism. Nature (London), 179: 619-621. Sommerville, R.I., 1963. Distribution of some parasitic nematodes in the alimentary tract of sheep, cattle and rabbits. J. Parasitol., 49: 593-599. Tetley, J.H., 1937. The distribution of nematodes in the small intestine of sheep. N. Z. J. Sci. Technol., 18: 805-817.