The biology of Hyostrongylus rubidus

J. COMP.

PATH.

1970. VOL.

80.

601

HYOSTRONGYLUSRUBZDUS

THEBIOLOGYOF III.

EFFECT

OF

HOST

AGE

ON

A PRIMARY

INFECTION

BY

D. J.

J. D. J.

BURDEN, Central

Veterinary

Laboratory,

HARDING hfinistry

and S. B. of Agriculture.

KENDALL

Weybridge

INTRODUCTION

Hyostrongylosis appears to be of most economic importance in the adult sow where, it has been claimed, the disease manifests itself in such ways as loss of body condition particularly during lactation, pallor of the skin and mucous membranes, grinding of the teeth etc. (Davidson, Murray and Sutherland, 1968). It has also been implicated in the thin sow syndrome (Maclean, 1968). Both Connan (1967) and Davidson et al. (1968) found in clinically affected sows large numbers of immature parasites which they believed had been retarded in their development. The present paper reports an attempt to determine whether there is an age resistance to a primary infection in pigs. MATERIALS

AND

METHODS

The materials and methods used are essentially those described in the first paper of this series (Kendall, Thurley and Peirce, 1969). Pigs from a caesarean-derived, barrier-maintained herd were used which has never had experience of H. rubidus, in as much as regular faecesexamination (at least fortnightly throughout the lives of all animals) has never revealed H. rubidus eggs. The study was conducted in three parts, according to the availability of pigs. For the main part of the experiment (Exp. 1) eighteen pigs were used, grouped according to age as follows, group I, 6 x 8 weeks old; group II, 6 x 174 weeks old; group III, 3 x 11 month castrates and 3 x 14-3 year old sows. Within a two day period all the pigs were infected, each with 4,000 infective H. rubidus larvae, which were administered by stomach tube with the pigs under anaesthesia produced by the inhalation of “Trilene except that the large pigs of group III were tranquilised beforehand with intramuscular injections of Azaperonet. Twenty two days after infection three pigs from each group were killed by captive bolt gun stunning and exsanguination and their stomachsexamined for worms and for pathological changes.By this time the remaining pigs were all producing worm eggs in their faeces and this output was then followed daily for each pig until the 76th dav after infection when they were killed. Their stomachs were examined as before (Exp. I. Table 1.) For the secondexperiment two two and a half year old sowsand one four year old boar were infected as before with 4,000 infective larvae of H. rubidus. By the third week of the infection all three pigs were producing worm eggsin their faecesand they were killed and examined for worms on the 28th day (Exp. 2, Table 1.) + On clinical trial t Trichloroethylene,

from Messrs. I.C.I.

Janssen

Pharmaceutics,

Beerse,

Belgium.

602

BIOLOGY

OF

Hyostrongylus

rubidus

Five pigs were used in the third experiment and their ages were between eight weeks and four years. Again each pig was infected with 4,000 infective larvae and the egg output of each was followed daily from patency until the 34th day after infection when they were killed. Their stomachs were examined for worms as before (Exp. 3, Table 1). TABLE NUMBERS

Pigs infected

Pk .No.

I

--II

1

---_-

III

-

* Pathologically

examined

1

OF WORMS

\vith

RECOVERED

4000 larvae

:l,p

sex

0

590

1

688

8 8 ~--~--

:: 76

17; weeks >. >> .. %, ..

417* 166 416 171* 187 418

11 months I yr, 6 mths. 11 months 1 yr. 5 mths. 3 yrs. 1 mth. 11 months

121

6

287 220

4 years yrs. 22 yrs. 6 mths. ---__8 weeks I year

146 160 104

years 224 years 4 years

c

(not availahle

Nos. adults ._-_-~

22

659* 658 662 663* 661 663

22 22 22 76 76 76

6 0 3

__~.

Nos. larvae __-.--

s$

8 weeks )I 3, ,I .> 3.

material

Lmgth infection days 22 22

:z* 695 689* 683 691

149 123

each

: d __ :

22 22 22 76 76 76 -.-- ..-. 28 28 28

Q for recovery

949 450

1: 1 0

506 340

2; ~~---~.-~

942 293

13 28

693 85

8 134

1094 408

532 692 724

1870 921 1164

2” 257 86 46

824 819 1100 1174 96

34 c

-

--

of worms).

RESULTS

Numbers of Worms Recovered Table 1 shows the numbers of larvae, mainly late fourth stage, and adult Hyostrongylus recovered from the pigs at postmortem examination. The numbers represent the pooled totals of the initial saline extraction and subsequent peptic digestion. As males and females occurred in practically equal numbers in all animals the sexesare combined. The results of the first experiment show that there is no appreciable decrease in worm populations during the fifty-four days after patency. This supports previous findings that a single Hyostrongylus infection is long lived. The worm recoveries,

D. J.

URDBEN

et

al.

603

shown in Table 1, are not markedly different in the three groups, with a total recovery of about 10 to 20 per cent. of the infecting dose. However, a few more larvae were found in the group III pigs than in the younger groups. The results from the second experiment are interesting in that they do not correlate with the group III results of the first experiment. They show a greatly increased percentage recovery in the order of about 50 per cent. of the infecting dose and an increased proportion of larvae. These results could have been caused by the fact that a different culture of larvae was used for the infecting doses, although in previous experiments all larvae have behaved in a similar manner even after storage for several months. In a worm population there is probably a wide range of developmental rates and it is possible that as these pigs were killed only 28 days after infection the larvae found represent those that were not developing quite as fast as the rest. The results from the third experiment tend to take a halfway position between those of experiments 1 and 2. The numbers of larvae and adults recovered from the younger animals are of the same order as those recovered from groups I and II of experiment 1. In the older animals, however, the proportion of larvae is greater than in comparable animals of experiment 1 but rather less than those of experiment 2. Worm

Eggs in the Faeces

As has been observed previously, the worm egg output was not large and in this instance seemed to fluctuate about a mean of 20 to 30 e.p.g. All three groups began egg production at about the 20th day after infection and no real differences were noted in the subsequent pattern of egg output. Pathology

At no time during the experiment was there evidence of clinical disease. Stomachs from pigs of each group in the first experiment were examined for pathological change at 22 and 76 days after infection. On both occasions the histological picture was similar in all three groups. At 22 days much eosinophil infiltration was apparent towards the cardiofundic junction whilst in the fundic region the reaction was patchy, consisting sometimes of eosinophil infiltration external to the muscularis, sometimes on both sides and sometimes of streaks and patches of mixed eosinophils and lymphocytes between the glands. This reaction was moderately marked at the cardiofundic junction and very marked at the fundopyloric junction. The reaction in the pyloric region was similar to that in the fundus, but more marked. At 76 days the stomachs from groups I and II showed little abnormality whilst the group III stomach showed infiltration of lymphocytes, histiocytes and eosinophils in the fundic and pyloric mucosa. DISCUSSION

For some time it has been accepted that “one of the most important factors influencing the composition of the parasite fauna of any host is that animals age”’ (Dogiel 1962). I n g eneral, young animals carry more parasites, but it is important H

604

BIOLOGY

OF

Hyostrongylus

rubidus

to distinguish between resistance arising from increasing age and resistance arising from the greater opportunity in the older animal of having experienced an immunizing infection. Sandground (1929) dealt with this subject at some length and pointed out the importance of distinguishing carefully between acquired and age resistance. He suggested that the former tended to be highly specific, the latter non-specific; the closer the genetic relationship between two hosts the closer will the conditions be in these hosts when young. As they grow older the physiological disparity between them begins to increase and an age resistance may be elicited, particularly in those hosts to which the parasite is not fully adapted. It is clear that evidence of true resistance must be obtained from carefully controlled experiments of which not very many have been reported in the literature. Bailey (1949), in experimental infections of calves with Cooperia punctata, found no evidence of a protective age resistance developing, at least in the first twelve months. Gordon (1953) showed that 7 out of 10 sheep aged between 3 to 4 years that had been kept worm-free all their lives died when given a single dose of 50,000 or 100,000 T-colubriformis larvae. At the same time nine-month-old lambs that had been previously infected were far more resistant. Fitzsimmons (1966) produced acute disease in worm-free goat kids of 15 to 17 weeks, dosed with 200,000 larvae of T. colubriformis, and similar results have been obtained with goats three years of age (Fitzsimmons, Harness and Selwood, 1968). There are a few positive indications of age resistance per se. Thus, although Tetley (1935) could find no evidence of age resistance to mixed infections of Nematodirus fillicollis and N. spathiger in lambs, Seghetti and Senger (1958) demonstrated that lambs more than three months old have a marked resistance to N. spathiger. Later work by Gibson (1959) indicated that with Nematodirus both age resistance and acquired immunity play a part. Spedding (1954) reported that age resistance as reflected by increased live weight gains was fully operative in one year old lambs infected with T. axei. Gibson (1962) demonstrated that lambs infected for the first time at 13 weeks of age showed a resistance, in that although a high proportion of worms became established, the majority were inhibited and those that reached maturity were gradually eliminated. As previous work (Gibson, 1959) had shown that lambs 8 weeks old were completely susceptible, this age resistance must develop some time between 8 and 13 weeks of age. In the present study no age resistance as such was observed. Certainly no valid differences were seen between the results of the three groups in the first experiment. In the second and third, however, the development in the older animals seemed to take a slightly different course. Although the total number of adult worms that established themselves was no less than in younger pigs, and in fact was higher in some cases, the proportion of late fourth’stage larvae found tended to be greater. In the pigs of experiment 2 that were examined seven days after patency of the worms, the percentage of larvae recovered was of the order of 50 per cent. of the adult worm recovery. Unfortunately, in this experiment no young pigs were available for comparison. AS our cultures of larvae as stated previously, have always reacted similarly even after long periods of storage, we feel that these results can be accepted with caution. Recoveries from pigs of experiment 3 which were killed

D. J. BURDEN

et

605

d.

13 days after patency showed a similar adult population, but the larval population had decreased a little. This might indicate that in these older animals a large proportion of the population had a retarded rate of development, although they were not completely inhibited and do eventually mature. SUMMARY

Groups of pigs with ages between 2 months and four years that had been kept free from Hyostrongylus rubidus all their lives, were given a primary infecting dose of 4,000 H. rubidus third stage larvae. The animals were killed at various times after the patency of the worm infection and their stomachs examined either for pathological changes or for the numbers and state of development of the worms. No evidence for age resistance was found, but there was a little evidence to suggest that in older animals the rate of development of a proportion of the population was slower. The pathological picture was similar in all the pigs examined. ACKNOWLEDGMENTS

We are grateful to Mr. J. A. Small and Mr. G. Snell for technical assistance. REFERENCES

Bailey W. S. (1949). Amer. j. vet. Res., 10, 119. Connan, R. M. (1967). Vet. Rec., 80, 424. Davidson, J. B., Murray, M., and Sutherland, I. H. (1968). Ibid., 83, 582. Dogiel, V. A. (1962). 3rd Edition. Oliver and Boyd; Edinburgh. Fitzsimmons, W. M. (1966). Res. vef. Sci., 7, 101. Fitzsimmons, W. M., Harness, E., and Sellwood, S. A. (1968). Ibid., 9, 237. (Gibson, T. E. (1959). Brif vet. J., 115, 120; (1962). 1. Helminth., 26, 43. Gordon, H. (1953). Ausf. vet. J., 26, 14. Kendall, S. B., Thurley, D. C., and Peirce, M. A. (1969). J. camp. Path., 79, 87. Maclean, C. W. (1968). Vet. Rec., 83, 308. Sandground, J. H. (1929). Parasitology, 21, 227. Seghetti, L., and Senger, C. M. (1958). Amer. j. vet. Res., 19, 642. Spedding, C. R. W. (1954). Emp. J. exp. Agric., 22, 55. Tetley, J. H. (1935). J. Helminfh., X3,41. [Received for publication,

February

23rd, 19701