A diagram illustrating the experimental design is given in Figure 1. Feb. & Mar./65 4 calves 15 lambs

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1 DEVELOPMENT OF ROSS IMMUNITY IN LAMBS BY EXPOSURE TO BOVINE GASTROINTESTINAL PARASITES H. J. Smith* and R. McG. Archibaldt INTRODUTION TIE ROLE that cross immunity might play in the control of parasitism has only recently been investigated. Vegors et al in 1963 (12) indicated that the ovine lungworm, Dictyocaulus filaria, stimulated immunity in calves to challenge with the bovine species, D. viviparus. More recently, Parfitt and Sinclair (6) also showed that calves which were infected with D. filaria were more resistant to a challenge infection of D. viviparus than previously uninfected animals. In 1966, Demski (1) showed that calves could also be sensitied to D. viviparus by intravenous injections of the freeliving nematode, Rhabditis axei. Louch in 1962 (4) found that infection with Nippostrongylus muris protected rats to some extent against subsequent infection with Trichinella spiralis. As for the role of cross immunity in the control of parasites inhabiting the gastrointestinal tract, Stewart (1) in 1955 showed that Haemonchus contortus larvae will cause "self-cure" of infestations with other abomasal parasites such as Ostertagia circumcincta and Trichostrongylus axei and that intake of larvae of the latter two species will cause "self-cure" of infections with H. contortus or with T. colubriformis. Downey in 1962 (2) showed that there was establishment of fewer Osteragia spp. and H. contortus in lambs previously infected with T. axei than in the case of lambs not previously so infected. Herlich (3) in 1965, working with ooperia oncophora and. pectinata, showed that those calves and lambs which acquired immunity to homologous challenge had a strong immunity to heterologous challenge. In 1963, the authors showed that lambs exposed to bovine gastrointestinal parasites did not develop clinical signs of disease (7). The numbers of ooperia that did establish in lambs were very much smaller than those in susceptible calves on the same pasture. Since lambs exposed to bovine parasites failed to develop apparent signs of disease, an experiment was undertaken in 1965 to determine if lambs *Animal Pathology Division, Health of Animals Branch, anada Department of Agriculture, Atlantic Area Branch Laboratory, P.. Box 141, Sackville, New Brunswick. fdeceased. AN. VET. JOUR., vol. 1, no. 11, November, 1969 exposed to bovine parasites developed resistance to subsequent exposure to ovine species. The results of this investigation are given in this report. MATERLALS AND METHODS A diagram illustrating the experimental design is given in Figure 1. Feb. & Mar./65 4 calves 15 lambs IGroup A IGroup B I 9 lambs 6 lambs June 23/65 4' Infected cattle pasture Parasite-free pastui July 22-25/65]r 4 necropsies Aug. 24/65 Aug. 24/65 3 necropsies KInfected sheep pasture Oct. 6/65 6 necropsies 6 necropsies FIGURE 1. Diagram illustrating the experimental design. Fifteen newly born lambs were obtained in February and March, 1965, and reared under parasite-free conditions as described previously (8). The lambs were randomly divided into two groups, A and B, of 9 and 6 animals, respectively. Four parasite-free calves were also reared under similar parasite-free conditions. On June 23 both the group A lambs and the calves were placed on a pasture which had been graed the previous year by calves heavily 286 1N r 1r Ire

2 GASTROINTESTINAL PARASITES infected with Ostertagia ostertagi, ooperia oncophora and Nematodirus helvetianus, while the group B lambs were put on a parasite-free pasture. Fecal examinations were performed weekly on all group A lambs and the calves, while only sporadic checks were made on the group B lambs. The calves either died or were killed 28 to 32 days after entering the pasture and the gastrointestinal tracts were placed in 1% formalin for later parasitological examination. Sixty-two days after going out to pasture, three group A lambs were also killed for parasitological examinations. The 12 remaining lambs of groups A and B were then transferred to a pasture on which six parasitied sheep had graed for the previous 74 days. Until all 12 lambs were killed and examined for parasites 43 days later, fecal examinations were performed weekly on all animals; the simple flotation method was used until the lambs started passing eggs regularly, at which time the McMaster technique was employed. Parasitological examinations were carried out by Swales' technique (11). The data were analyed by the Student t-test and the Mann-Whitney U-test. OBSERVATIONS AND RESULTS For a period of about a month starting the third week on the infected cattle pasture, the group A lambs sporadically passed small numbers of worm eggs. Nematodirus eggs were recovered from five, while gastrointestinal helminth (G.I.H.) eggs (presumed to be ooperia eggs) were found in eight of the nine lambs. Worm eggs were never recovered from lamb 97. On the other hand, very high counts were recorded from all calves. At slaughter, egg counts ranged from 75 to 3,45 eggs per gram (e.p.g.) of feces. Nematodirus egg counts never rose above 25 e.p.g. During this period the group B lambs on the parasite-free pasture had negative fecal counts. All group A lambs had negative fecal examinations by the time they were transferred to the sheep pasture. Lamb 15 was passing a few Nematodirus eggs but it was one of the three lambs slaughtered. Fecal examinations remained negative for all A and B lambs until the third week on the sheep pasture, when small numbers of eggs were observed. Average fecal egg counts for both groups increased initially but dropped off quite sharply for the group A lambs after a few days, while the group B average counts rose steadily (Figure 2). The species and number of parasites recovered from the four calves and three group A lambs which were exposed only to the infected 287 OgRu 5 /47 /5 2 as IAI.f((AyJ) FIGURE 2. Average egg counts of lambs sensitied by cattle parasites (group A) and previously unexposed controls (group B) when exposed to sheep parasites. cattle pasture are given in Table I.. oncophora and N. helvetianus infections were established in the lambs but not. ostertagi, while infections with all three species were established in the calves. The species and number of parasites recovered from the group A lambs that were exposed to both cattle and sheep parasites and from the group B lambs that were exposed to sheep parasites only are given in Table II. The A lambs on the average had less Ostertagia spp.. curticei, N. spathiger and Bunostomum trigonocephalum than the B lambs but a greater number of Trichostrongylus spp. The mean differences in the numbers of. curticei, N. spathiger and B. trigocephalum found in the two groups were statistically significant. The differences observed for Ostertagia spp. and Trichostrongylus spp. in the two groups were not statistically significant. The group A lambs lost their burdens of bovine parasites rather rapidly as all six animals of this group which graed the sheep pasture for 43 days had few, if any, bovine parasites when compared to those killed coming off the cattle pasture six weeks previously (Tables I and II). DISUSSION In consideration of the initial rise in worm egg counts and the considerable number of several species of worms still present at slaugh- A

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4 GASTROINTESTINAL PARASITES ter, it is apparent that previous exposure of lambs to large numbers of cattle parasites does not completely prevent the initial establishment of sheep parasites in lambs. However, the immune response of these lambs to the newly established ovine species appears to change rapidly as manifested by the exponential-like decrease in egg counts and the statistically significant lower average numbers of ooperia, Nematodirus and Bunostomum present at slaughter. It is interesting to note that Demski (1) reported somewhat similar findings in calves that had been sensitied to D. viviparus by the free-living nematode, R. axei. Both sensitied and control calves developed patent Dictyocaulus infections but in the former larval counts soon diminished and at slaughter a smaller number of lungworms were recovered. Michel (5), working with Ostertagia in calves, has shown that resistance may be manifested in several ways, such as an inhibition of development, stunting of adult worms, inhibition of ovulation or resistance to establishment of newly acquired worms. These are different and separate one from another and may appear at different stages in the infection, affect different developmental stages of the parasite and are separate both in effects and their causation. It would appear that the resistance observed in the sensitied lambs of this study developed for the most part only after the establishment of infection. There is little doubt, as demonstrated by Demski (1), Downey (2) and Stewart (1), that cross-reactions (presumably due to common antigens) do occur between different genera of parasites. Herlich (3), working with the cattle parasites,. oncophora and. pectinata, has shown experimentally that lambs which do acquire immunity to homologous challenge have a strong immunity to heterologous challenge. However, it was not always possible to develop immunity in lambs, which emphasies the individual variability of the host response. It is not known if the resistance or crossimmunity observed in this experiment will provide any protection to lambs in the face of a heavy challenge with sheep parasites, since the challenge in this study was light. However, even though exposure to cattle parasites does not prevent the establishment of sheep parasites in lambs, the findings suggest that the subsequent development of resistance in these animals is more rapid than in control lambs. As a result, the course of the infection may be lambs of this study confirms an earlier observation (7) that this species apparently has a high host specificity. However, it is interesting to note that N. helvetianus infections were established in a number of the lambs in this study based on fecal counts and recovery of worms in one lamb. It would appear that resistance develops rapidly and that the Nematodirus burden is soon shed. SUMMARY Previous exposure to the cattle parasites, Ostertagia ostertagi, ooperia oncophora and Nematodirus helvetianus for 62 days did not prevent establishment of sheep parasites in lambs, but a rapid drop in worm egg output soon occurred and significantly lower average numbers of ooperia curticei, Nematodirus spathiger and Bunostomum trigonocephalum were found in the sensitied animals than in the previously non-exposed lambs when both groups were examined 43 days after exposure to ovine parasites. ross resistance was not demonstrated for Ostertagia and Trichostrongylus species. RESUMEI Le fait de les mettre en contact pendant 62 jours avec les parasites bovins Ostertagia ostertagi, ooperia oncophora et Nematodirus helvetianus n'empecha pas des agneaux de s'infester de parasites du mouton. On observa cependant, che les animaux exposes 43 jours auparavant, une diminution rapide dans le nombre d'aeufs disperses et remarquablement moins de ooperia curticei, Nematodirus spathiger et Bunostomum trigonocephalum. On ne put mettre en evidence aucun resistance croisee pour les especes Ostertagia et Trichostrongylus. AKNOWLEDGMENTS The technical assistance of Mr. K. E. Snowdon is greatly appreciated. The author also wishes to express his appreciation to Mr. David Higham, Mount Allison University, for assistance with the statistical analysis. REFERENES 1. DEMSKI, G. Uber eine Verstarkung der Widerstandskraft gegen parasitare Infektionen. I. Sensibilesierung mit Rhabditis axei (obbold. 1884) gegen Infektionen des Rinderlungenenwurmes Dictyocaulus viviparus (Block, 1782). Arch. exp. VetMed. 2: DOWNEY, N. E. The establishment of Ostertagia spp. in lambs previously infected with modified and, consequently, the effects on the host as well. Trichostrongylus axei. Vet. Rec. 74: The failure of. ostertagi to establish in the

5 3. HERLIH, HARRY. Immunity and cross immunity to ooperia oncophora and ooperia pectinata in calves and lambs. Am. J. vet. Res. 26: LOUH,. D. Increased resistance to Trichinella spiralis in the laboratory rat following infection with Nippostrongylus muris. J. Parasit. 48: MIHEL, J. F. The phenomena of host resistance and the course of infection of Ostertagia ostertagi in calves. Parasitology 53: PARFirr, J. W. and I. J. SINcLAIm. ross resistance to Dictyocaulus viviparus produced by Dictyocaulus filaria infections in calves. Res. vet. Sci. 8: SmITH, H. J. and R. McG. ARHIBALD. ross transmission of bovine parasites to sheep. an. vet. J. 6: ANADIAN VETERINARY JOURNAL 8. SMrr, H. J. and R. McG. ARHIBALD. The overwinter survival of gastrointestinal parasites in the Maritime Provinces. an. vet. J. 6: SMITH, H. J. and R. McG. ARHIBALD. The effects of age and previous infection on the development of gastrointestinal parasitism in cattle. an. J. comp. Med. 32: STEWART, D. F. 'Self-cure' in nematode infestations of sheep. Nature, Lond. 176: SWALES, W.. The helminth parasites and parasitic diseases of sheep in anada. I. A survey and some preliminary studies on existing problems. an. J. Res. 18: VEGORS, H. H., J. T. LUKER and F. W. DouvREs. Sheep lungworm larvae as a vaccine against cattle lungworm. J. Anim. Sci. 22: ABSTRATS Moulton, J. and oggins, L. (1968). Synthesis and cytopathogenesis of African swine fever virus in porcine cell cultures-am. J. vet. Res. 29, (Sch. Vet. Med., Univ. alifornia, Davis 95616). Porcine buffy coat (B) cells infected with the virus showed chromosomal, nucleolar, and cytoplasmic degeneration and developed intracytoplasmic inclusion bodies beginning 12 hours after infection. ytolysis began 2 hours after infection and was widespread at 4 hours. Similar cytological and cytochemical changes were observed in porcine kidney "2a" cells infected with cell culture-attenuated strains of the virus, but the time sequence of changes was extended. Viral synthesis in B cells was partially inhibited by some oxyuridine compounds. Viral DNA was synthesied between the 6th and 7th hours, and infective virus between the 1th and 11th hours after infection. Reprinted from "The Veterinary Bulletin", Vol. 38, No. 8, August, Adler, H. E. and DaMassa, A. J. (1968). Effect of dextrose in medium for the preparation of Mycoplasma gallisepticum plate antigens.-appl. Microbiol. 16, (Dep. Epidem. Preventive Med., Univ. alifornia, Davis, 95616). Antigens were prepared from organisms propagated in media with and without a glucose supplement. The antigens prepared from organisms grown in medium enriched with glucose were less sensitive than the others in slide agglutination tests. Reprinted from "The Veterinary Bulletin", Vol. 38, No. 1, October, Hungerford, T. G. (1968). A clinical note on avian cholera. The effect of age on the susceptibility of fowls.-aust. vet. J. 44, (P.O. Box 331, Penrith, N.S.W.). Vaccination of 9, fowls with infectious laryngotracheitis vaccine contaminated with virulent Pasteurella multocida resulted in violent reactions in the cloaca of young birds up to 16 weeks old, but there was no mortality and no recurrence of the disease. In older birds so vaccinated, there was heavy mortality from cholera, but no recurrence among the survivors or in-contacts. Reprinted from Vol. 38, No. 1, "The Veterinary October, Bulletin", 29