A group of Merino sheep, aged 6-7 months was infested orally with 50 000 infective larvae of Trichostrongylus axei. This group and a control group were challenged 90-92 days later with 50 000 infective larvae of Haemonchus contorus. Previous infestation with T. axei caused a reduction of more than 80% in the worm burdens of H. contorus in more than 80% of the sheep.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi.
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Reinecke, R.K.

The articles have been scanned in colour with a HP Scanjet 5590; 300dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.A group of Merino sheep, aged 6-7 months was infested orally with 50 000 infective larvae of Trichostrongylus axei. This group and a control group were challenged 90-92 days later with 50 000 infective larvae of Haemonchus contorus. Previous infestation with T. axei caused a reduction of more than 80% in the worm burdens of H. contorus in more than 80% of the sheep

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Onderstepoort J. vet. Res. 41 (4), 213-216 (1974) STUDIES ON HAEMONCHUS CONTORTUS. I. THE INFLUENCE OF PREVIOUS EXPOSURE TO TRICHOSTRONGYLUS AXEl ON INFESTATION WITH H. CONTORTUS* R. K. REINECKE, Department of Parasitology, Faculty of Veterinary Science, University of Pretoria ABSTRACT REINECKE, R. K. Studies on Haemonchus contortus l. The influence of previous exposure to Trichostrongylus axei on infestation with H . cantor/us. Onderstepoort J. vet. Res. 41 (4) , 213- 216 (1974) . A group of Merino sheep, aged 6- 7 months was infested orally with 50 000 infective larvae of Trichostrongylus axei. This group and a control group were challenged 90- 92 days later with 50 000 infective larvae of Haemonchus contortus. Previous infestation with T. axei caused a reduction of more than 80 % in the worm burdens of H. contort us in more than 80 % of the sheep. INTRODUCTION There is some experimental evidence of inter-generic cross-reactions between abomasal helminths (Turner, Kates & Wilson, 1962; Durie, 1962; Reinecke, 1966). This has been confirmed in the field by Muller (1968), who noted: "that where T. axei was predominant the depression of H. contortus was notable, while the numbers of Ostertagia circumcincta were affected to a lesser extent". The present experiment is an attempt to determine whether initial infestation ofT. axei confers protection to a subsequent challenge with H. contortus. TABLE I Experimental design No. of infective larvae dosed to each sheep Day I Group A Controls Group B 0 . .. - 12 500 La* of T. axei + 2 ... . - 12 500 La of T. axei + 10 .. - 12 500 La of T. axei + 13 .. - 12 500 La ofT. axei --- - -------- --------------Total. - 50 000 ==-----+ 30 .. - Sheep 22 died + 90 .. 16 000 La of H. contortus 16 000 La of H. contortus + 91.. 16 000 La of H. contortus 16 000 La of H. contortus + 92 .. 18 000 La of H. contortus 18 000 La of H. contortus Total. 50 000 50 000 =---= + 98 .. Sheep 68 died. . . . . . . . . . -+ 114 - Sheep 62 slaughtered + 118 - Sheep 9 died + 126 I 0 sheep slaughtered .. . . 2 sheep slaughtered + 127 - 7 sheep slaughtered *La- third stage larvae MATERIALS AND METHODS Sheep Twenty-three S month-old Merino wethers and ewes obtained from Vrede, Orange Free State were stabled under worm-free conditions and treated on 2 occasions with broad-spectrum anthelmintics prior to the commencement of the experiment. Infective larva The larvae used in this trial were harvested from the faeces of sheep with mono-specific infestations of T. axei and H. contort us. *This project was subsidised by a research grant from the Department of Agricultural Technical Services, Republic of South Africa Received 12 August 1974- Editor 213 Experimental design This is summarized in Table 1. Sheep were divided as follows: Group A (Controls) Eleven worm-free sheep were dosed from Day + 90 to Day + 92 with a total of SO 000 infective larvae of H. contortus. Group B Each of the 12 sheep in this group received a total of SO 000 infective larvae of T. axei divided into 4 equal doses administered from Day 0 to Day + 13 (Table 1 ). The sheep in this group and the controls were challenged simultaneously on Days + 90 to 92 with a total of SO 000 infective larvae of H. contortus. Emergency slaughter had to be performed on Sheep 62 which fractured a tibia on Day + 114. Worm recovery At autopsy worms were recovered from 3 separate specimens: the ingesta of the abomasum and duode-num ; the digested abomasal and duodenal wall; the ingesta of the first 7 m of the jejunum. Specimens were heated to 60 oc to kill the worms, formalin was added to fix them and the specimens were sieved on to Endecott sieves (apertures 37 ,urn) and examined as described by Reinecke (1973). Total counts were carried out on all the H. contortus recovered from the sheep in Group Bas well as those of Sheep 2S and 28 in Group A (Table 2). The latter figures were essential for estimation of the lower limit (L L) of the controls. Elsewhere worm burdens were estimated from aliquots using the methods of Clark, Tucker & Turton ( 1971 ). La rval stages of H. contortus were identified according to the descriptions of Veglia (191S). RESULTS The number of worms recovered is recorded m Table 2. Group A: Controls On Day + 98 Sheep 68 died of bluetongue 8 days after it had received the last dose of infective larvae of H. contort us and this explains wh y 4th stage larvae were dominant in it. The survivors were killed on Day + 126 when the youngest worm was 34 days old. The relatively large numbers of 4th stage larvae in these sheep cannot be explained. The sheep were suscep-tible, worm burdens in all of them varying from 1S6 to 9 3S8 (Table 2) . STUDIES ON HAEMONCHUS CONTORTUS TABLE 2 Worms recovered postmortem Sheep No. L, 5 H . cantor/us T . axei Adult Total Adult Total Group A Controls 10 ......... . . ... 2 539 441 4 468 7 448 - -15 . .... ......... 1 681 331 4 998 7 010 - -17 ........... . .. 2 216 850 3 780 6 846 - -25* .... ... .. .... 837 327 2 741 3 905 - -28* ... .. .. ... .. . l 206 1 365 3 161 5 732 - -37 ...... . .... . .. I 365 150 4 555 6 070 - -45 ...... ... .. .. . 1 148 207 196 I 551 - -64 ...... .. . .. . .. 8 173 506 679 9 358 - -68 ..... . . ..... . . 14 893 0 1 14 894 - -71 ... ........... 73 0 83 156 1 1 77 .... .......... 1 419 484 5 227 7 130 60 60 --------------- ------Group B Dosed with T. axei 90 days before challenge 2 ........ . ...... 6 9 3 . . ...... . ...... 0 5 9 ..... ... . ...... 0 0 16 ........ .. ... . 0 2 19 ....... . . . . . . . 0 18 21 . .. ........ . . . 0 5 39 . . . . . ......... 0 7 52 .. . .. . ........ 0 5 62 . .... .... . . . . . 0 0 73 ........... .. . 0 3 78 .............. 1 1 *Total worm counts were carried out Group B: Dosed with T. axei prior to challenge One sheep died from T. axei infestation on Day + 30 and emergency slaughter had to be performed on Sheep 62 which fractured a tibia on Day + 114. Sheep 9 and 62 had no H. contortus while the numbers in the remainder varied from 11 to 594 (Tables 2 and 3). Adult worms were dominant and in only 2 animals were 4th stage larvae found: 6 in sheep 2 and 1 in Sheep 78. The number ofT. axei, however, varied from 14 315 to 41 880. The death of Sheep 9 was probably due to thi s species despite the fact that its worm burden fell within the range of T. axei recovered from the group. Statistical analysis The results were analysed by the non-parametric method of Groeneveld & Reinecke ( 1969) to determine the influence of previous exposure to T. axei on infestation with H. contortus. The worm burdens of H. contortus in both groups are ranked numerically in Table 3. The first step is to estimate the lower limit (LL) of the median of the controls . This lies between the 3rd (Sheep 25) and 4th (Sheep 28) lowest number of worms in this group (Groeneveld & Reinecke, 1969, Table 9). These numbers are essential for an accurate estimation of the influence of T. axei and the numbers listed in Tables 2 and 3 are totals of all 3 specimens of the respective sheep. Using Tables 9 and I 0 from Groeneveld & Reinecke (1969) the LL of the controls can be calculated as being: N c Probability K' K" 11 0 , 90 0 , I 0 0 , 90 LL = 3905 (0 ' 10) + 5732 (0' 90) = 5549' 3 Eighty % reduction o n the LL of the controls ts therefore : LL (0 ,02)= 5 549, 3 (0,2) = I 109 , 86 579 34 0 20 134 11 37 38 0 275 9 - --------------- - - ----594 16 842 16 842 39 26 965 26 965 0 40 340 40 340 22 14 840 14 840 152 41 880 41 880 16 23 175 23 175 44 14 315 14 315 43 27 060 27 060 0 27 800 27 800 278 18 670 18 670 11 36 300 36 300 TABLE 3 Level of reduction of H. contort us burden estimated by the non-parametric method H . cantor/us Group A Controls 156 1 551 *3 905 *5 732 6 070 6 846 7 010 7 130 7 448 9 358 14 894 3 905 x 0 , 1= 390 , 5 5 732 x 0 ,9 = 5158,8 LL = 5549 ,3 5 549 ,3 x 0 , 2= 1 109, 86 *Total worm counts were carried out I Group B 0 0 11 16 22 39 43 44 152 278 594 0/11 exceed I 109 None of the treated animals had worm burdens exceeding I 109. Therefore infestation with T. axei apparently caused more than 80 % reduction in H. contort us in more than 80 % of the infested popula-tion. DISCUSS ION The present experiment has shown that " infesta-tion" with 50 000 infective larvae of T. axei dosed orally over a period of 13 days can protect sheep from a subsequent challenge of /-/. contortus 90 to 92 days later. It was not the object of this investigation to deter-mine the mechanism responsible for the protection that was induced . Self-cure does not appear to have taken place because the sensitizing dose of T. axei was not affected. It is therefore not clear whether a hypersensitivity reaction was involved. Jt is known that large worm burdens of T. axei cause a rise in 214 ,_ abomasal pH (Ross, Purcell & Todd, 1969) and Christie (1970) has suggested that a change in aboma-sal conditions, as exemplified by a rise in pH due to H. contortus infection, is directly responsible for preventing a massive challenge of this worm from overwhelming the host. The major defect of this method of "vaccination" is that 50 000 infective larvae of T. axei were lethal in 2 out of 11 sheep (18, 1 %) within the experimental period of 127 days. To apply this method of control in practice it would be essential not only to reduce the dose of infective larvae of T. axei to non-pathogenic levels but also the frequency of their administration to 1 or, at the most, 2 doses. ACKNOWLEDGEMENTS The Director, Veterinary Research Institute, Onder-stepoort is thanked for the facilities to carry out these trials and The Dean, Faculty of Veterinary Science for allowing the time to do this work. Mrs. Helga Seaman, Miss Elizabeth Lategan and Mr N. J. Meintjies are thanked for their valuable technical assistance. P. K. REfNECKE REFERENCES CHRISTIE, M. G., 1970. The fate of very large doses of Haemonchus conrorrus and their eflect on conditions in the ovine abomasum. J. camp. Path. , 80, 89- 100. CLARK, C. J. , TUCKER, A. M. & TURTON, J. A., 1971. Sampling technique for esti mating round-worm burdens of sheep and cattle. Expl Parasir., 30, 181 - 186. DURIE, P. H. 1962. Parasitic gastro-enteritis of cattle: seasonal fluctuations in populations of strongyle larvae on a calf pasture and their significance in infection of the grazing animal. Ausr. J. agric. Res. , 13 , 767- 777. GROENEVELD, H. T. & REINECKE, R. K., 1969. A stat is-tical method for comparing wo rm burdens in two groups of sheep. Ondersrepoorr J. ver. Res., 36, 285- 298. MULLER, G. L. , 1968 . The epizootiology of helminth infes-tation in sheep in the South-Western district of the Cape. Ondersrepoorr J. vet . Res., 35, 159- 194. RElNECKE, R . K. , 1966. The value of uniform worm burdens in the larval anthelmintic test. Jl S. Aji-. l'el . 111ed. Ass. , 37, 133- 142. REINECKE, R. K., 1973 The larval anthelmintic test in ruminants. Tech . Coiii/IIUII. Dep. agric. tech. Serv. S. A/r., No. 106. ROSS, J. G., PURCELL, D. A. & TODD, J. R. , 1969. Experi-mental infections of lambs with Trichostrongylus axei; investigations using abomasal cannulae. Res. vet. Sci., 10, 133- 141. TURNER , J. H. , KATES, K. C. & WILSON, G. 1. , 1962. The interaction of concurrent infection s of the abomasal nema-todes, Haemonchus conrorrus, Osrerragia circu111cincra and Trichostrongylus axei (Trichostrongylidae) in lambs. Proc. helminth. Soc. Wash. , 29, 210- 216. VEGUA, F., 1915. The anatomy and life-history of the Haemonc/rus conlortus (Rud.) Rep. Pel. Res. Un. S. Aji·., 3/4, 347- 500. Printed by and obtainable from The Government Printer, Private Bag X85, Pretoria , 000 I 215 

Studies on Haemonchus contortus. I. The influence of previous exposure to Trichostrongylus axei on infestation with H. contortus

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Studies on Haemonchus contortus. I. The influence of previous exposure to Trichostrongylus axei on infestation with H. contortus

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