Observations on Strongyloides Papillosus Infection:

Brit. vet. J. (1963), 119,253

OBSERVATIONS ON STRONGYLOIDES PAPILLOSUS INFECTION: THE TREATMENT OF HEAVY NATURALLY ACQUIRED INFECTIONS OF SHEEP IN KENYA By M. C.

ROUND*

Veterinary Reseach Laboratory, Kabete, Kenya

Infections of ruminants with StrongJloides papillosus are usually light and overshadowed by infection with other gastrointestinal nematodes. It is probably for this reason that this parasite was formerly considered to be harmless. Over the past decade or so there has been an increasing awareness of its pathogenic potential and it is now realized that in sufficient numbers it can be highly pathogenic. Reports of deaths due to naturally acquired infections are few. Woodhouse (1948) reported the death of a calf and Turner & Wilson (1958) the deaths of three lambs. The pathogenic effects, and even deaths, in experimental infections of sheep with S. papillosus have been demonstrated by Woodhouse (1948), Turner (1955, 1959a), Garkavi (1956) and Turner, Shalkop & Wilson (1960). Similar experimental work on calves has been reported by Vegors (1954) , The findings of these workers may be briefly summarized. The prepatent period of the infection lasts a minimum of nine days. The numbers of adult worms resulting from percutaneous infection, the numbers of eggs per gram of faeces, and the ra,pidity of death are almost directly related to the number of infective larvae administered. Turner ( I 959a), working with sheep, found that the maximum egg production occurred 15 to 18 days after infection and that in non-fatal cases the disease ran its course in seven to eight weeks. Resistance to re-infection has been demonstrated by Roberts (1942) and Vegors (1954) in calves, and Turner (1959b) in sheep. Clinical signs of strongyloidiasis have been given as inappetence, lethargy, loss of weight or retardation of growth rate, weakness, slight to moderate anaemia, difficulty in r espiration, abnormal thirst, polyuria and abnormal stools. Ascites and hydrothorax are commonly found at autopsy. In the small intestine, particularly the duodenum, severe lesions may occur. Turner ( I959a) found lung lesions in one lamb which died 13 days after experimental infection. These lesions he thought to be secondary to the mechanical irritation and damage caused by the migrating larvae. None of Turner's other animals showed such lesions at the time of death and he concluded that the initial damage done by the migrating • Present address: Animal H ealth Trust, Equine Research Station, "Newmarket.

254

BRITISH VETERINARY JOURNAL, 119, 6

larvae had been repaired by this time. Turner, Shalkop & Wilson (1960) demonstrated the migration of larvae of S. papillosus through the lungs of sheep which were experimentally infected percutaneously. Damage caused by this migration was severe. The lesions were found only during the prepatent period, after which time they had disappeared. In addition to the direct pathogenic effects of S. papillosus, Beveridge (1934) has shown that the penetration of the skin of the feet of sheep by the infective larvae may be an important factor in the introduction of the causal organisms offootrot. Infections of sheep by S. papillosus in Kenya are common but are generally low-grade, and only occasionally are individual animals found to have high egg counts. During late 1961, very heavy and unseasonal rain occurred, flooding many parts of the country. This followed a long period of extremely dry weather when drought conditions prevailed. In the course of an experiment on the natural acquisition of helminth infections by sheep at Naivasha from 1960-62, a significant rise in the numbers of eggs of S. papillosus per gram of faeces was noted for the first time in December, 1961 and January, 1962. At the same time, faecal samples submitted for examination by stock owners showed that some individual sheep had high egg counts of S. papillosus. On two farms in the Naivasha district and one in the Nakuru area, high rates of mortality occurred in lambs with heavy infections of this parasite. The purpose of this communication is to report on the findings and anthelmintic treatment given. METHOD OF HELMINTHOLOGICAL EXAMINATION AND TREATMEN·T

Examination for helminth eggs was made by a slightly modified McMaster egg-counting technique, the results being expressed in numbers of eggs per gram of faeces (e. p.g.). Estimation of worm burdens was made on an actual count of numbers present in a sample of one twenty-fifth of the total sieved contents of the abomasum and small intestine, and on the total worms present in the caecum and large intestine. For the assessment of anthelmintic efficiency, faecal samples were collected immediately before dosing and then four days later. In Case 3, no further samples were taken. In Case 4, two further samples were taken at weekly intervals. Gracey & Kerr (1961) reported that no eggs of S. papillosus were detected in lambs after treatment with 2- (,B-methoxyethyl) pyridine (methyridine ; Promintic, I.C.I.) subcutaneously at a dose rate of 200 mg. Jkg. Initially, however, only small numbers of eggs of this parasite were present in the faeces. Since this information indicated some efficiency on the part of this drug, lambs from the farms in Cases 3 and 4 were treated with methyridine subcutaneously at a dose rate of 200 mg. Jkg. Levine & Szanto (1960) have reported the efficiency of the iodide, oxide and chloride salts of cadmium in the treatment of S. papillosus infections in sheep. Twelve lambs in Case 4 were treated with cadmium iodide at a dose rate of 67-99 mg. Jkg. per os. In all anthelmintic treatments the dose administered was calculated on a weight basis, all treated animals being weighed to the nearest pound body weight.

STRONGYLOIDES PAPILLOS US INFECTION IN SHEEP

255

CASE HISTORIES A N D RESULTS OF TREATMENT

Case 1 An experiment on the natural acquisition of helminth parasites by sheep was carried out a t the Government Experimental Station, Naivasha in the years 1960- 62. Two groups of lambs were used, one in 1960- 61 a nd the other in 1961 - 62. The m aximum individual egg count of S. papillosus during 1960- 61 was 1,900 e.p.g., the mean of all anim als throughout this period being under 200 e.p.g. Infections were low-grade but constan t in the m ajority of anima ls. The maximum individual egg count for this parasi te during the period 1961 - 62, u ntil November, 1961, was 400 e.p.g., with an overall m ean for all animals in the group of less than roo e.p.g. Throughout the greater part of the time the mean was under 50 e.p.g., the infections being low and sporadic. From November to D ecember, 1961, the egg count rose to a mean of a little over 1,500 e.p.g., the r ange for individuals being 0- 10,200 e.p.g. Foot disease occurred in the lambs at this time, although no such trouble was experienced with the previou s group. Fig. I shows the numbers of S. papillosus eggs per gram of fa eces during the two experimental periods, together with the rainfall recorded. 100l

1960 -1961

3 Inches of 2 lUinfall

soo

[PG.

2.000

Jan . Feb. Mar. 1961

Apr. May Jun. July 1960

10

9 1961 -1962

8

~500

7 Inches

01 HG.

6 rainlal.l

1000

500

oL,~,~~~~=+~~~~~~~--~O Apr. May Jun . July

Fig.

1.

Case

I.

Aug. Sop. Oct. 1961

Nov. Dec. Jan . Fob. Mar. 1962

Mean Strongyloides papillosus c.p .g. and rainfall during the ycars 1960 to 1962.

Case 2 A farm in the N aivasha area ha d had over 300 deaths of sheep during a twomonth period before the investigation, which was conducted in J anuary, 1962.

BRITISH VETERINARY JO UR NAL, 11 9,6

The majority of these d eaths were in lambs up to a year old. At the beginning of the deaths, bluetongue had been diagnosed, together with severe contagious footrot, cutaneous myiasis and pneumonia. Although some deaths were undoubtedly due to bluetongue, the high mortality r a te was not considered to be due to this disease alone. Examination of faeces from 24 five-month old lambs showed the presence oflarge numbers of eggs of S. J)apillosus, individual samples ranging from 0- 66,550 e.p .g., with an overall mean of 21,815 e.p.g. Coccidial oocysts were very numerous. "Strongyle" eggs were numerous, from 3003,900 e.p.g., with a mean of 2,004 e.p.g. The worm burden of one lamb available for autopsy was composed of approximately 24,000 S. papillosus and 3,000 Trichostrongylus spp. The lungs were pneumonic, but no helminths were found. Nine adult ewes were also sampled: the numbers of strongyle eggs ranged from 0- 3,000 e.p.g., with an overall mean of 822 e.p.g ., but only one animal had eggs of S. papillosus ( 100 e.p.g.). Fig. 2 gives the number of S. papillosus e.p.g. in the 24 la mbs sampled.

,--

10

@ 9

8

6 No. of animals

r--

G) 4

3

2r : ~. I

cfL

G) G) t---

0

@fCI5l 0 -10 11 - 20 21-30 3H O 41-5 0 51-6061-70

E P G (1'0005) Stro nqi :o.~es pcpillosus

Fig.

2.

Case

2.

I'(um cers:of (".r. g. S{1IIIDh id(s j aji//oms in 24IJa ml s.

Case 3 A second farm in the Naivash a a rea, adjacent to the Government Experimental Sta tion , had lost 1,500 sheep, m ainly lambs under a year old, out of a total of 15, 000, during the preceding three months. Bluetongue had again been responsible for some deaths, but even after the outbreak of this disease h ad been brought und er control deaths of lambs still continued . "Vhen the animals were examined in January, 1962, the clinical signs were suggestive of helminthiasis, with emaciation, lethargy and anaemia. Faecal samples from 36 three-monthold lambs were examined . Eggs of S. papillosus ranged from 0-100,850 e.p.g.,

STRONGYLOIDES PAPILLOSUS INFECTION IN SHEEP

257

with an overall mean of 12,654 e.p.g. Strongyle eggs were also present, individual samples ranging from 50-38,200 e.p.g., with a mean of 9,947 e.p.g. Coccidial oocysts were recorded as light to heavy. Treatment. Twenty-four three-month-old lambs were divided into two groups. One group was weighed and treated with methyridine (2 00 mg. /kg. subcutaneously) . Faecal samples were taken immediately before dosing and then again four days later. Methyridine brought about a complete disappearance of S. papillosus eggs from faeces. The untreated control group showed a corresponding increase of 62 '2 per cent in S. papillosus eggs. The results for strongyle eggs were a reduction of 94' I per cent in the treated group and a S- 5 per cent increase in the controls. Table I gives detailed results. TAB L E I CASE

3:

TH E EFF I C I ENCY OF M E THYRIDINE AT A DOSE RATE OF 200 MG./K G. SUBCU T ANEO USLY .

MEA N E.P. G . AND

%

I NC REA SE/DEC R EASE.

" Strollgyle"

- - -- ------ ---_.- - - -- - - --

Controls ( 12 ) La mbs Pre-treatment Post-treatmen t Increase (%)

Strongyloides

------

Methyridine ( 12 ) La mbs P re-treatment Post-treatment D ecrease (%)

1 2 , 595

o 1 00

7,675 8,100

5'5

Case 4 A farm in the Nakuru district had experienced many deaths of lambs over a period of four months immediately before the present investigation. Previous post-mortem examination had apparently revealed no specific disease condition. Because of the poverty of the carcases, however, helminthiasis had been suggested as the probable cause of deaths, but this h ad somewhat been ruled out as the owner h ad been treating the lambs with phenothiazine as a routine, at three-weekly intervals. Early in April, 1962, the owner submitted two d ead lambs and two moribund la mbs for helminthological examination. Faecal examination of the two dead lambs showed S. papillosus counts of 62 ,500 e.p. g. and 11,700 e.p.g. The strongyle counts were 300 and 150 e.p.g. A worm count of the lamb with the highest number of strongyloides eggs revealed a burden of 15,000 S. papillosus. Examination of the faeces of the two moribund lambs gave counts of S. papillosus as 39,250 and 12,050 e.p.g. No strongyle eggs were seen. Both of these lambs were treated subcutaneously with methyridine at a dose rate of 200 mg. /kg. This treatment brought about a reduction of virtually 100 per cent in S. papillosus eggs. The lamb which had the highest egg count died four days after trea tment. On post-mortem examination the small intestine was found to be severely inflamed. No worms were recovered. The other lamb

BRITISH VETERINARY JOURNAL, 119,6

made a complete recovery and was returned to its owner. The deaths on the farm were tentatively diagnosed as being due to strongyloidiasis and a visit was made with a view to carrying out an anthelmintic trial. Treatment. Thirty-six six-month-old lambs were selected and divided into three equal groups. These lambs were in very poor condition and weighed from 19-40 lb. The 12 poorest lambs were treated with methyridine as in Case 3. The second group was treated with cadmium iodide at a dose rate of 67-99 mg. Jkg., per os. The third group served as a control. Weights of all animals and faeces samples were taken immediately before treatment and then after four days, followed by two more samples and weights at weekly intervals. A further group of 58 lambs in somewhat better condition was also treated with methyridine. Only the weights of this group were taken. Table II gives the details of the egg counts of S. papillosus and Fig. 3 shows the percentage gain or loss in weight during the experiment. The weights of each group are given in Table III. The methyridine group showed a reduction of 97.6 per cent in S. papillosus 10

9

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II

Methyrid", treated 12 Melhyridine treated 58 Cadmium iodide treated 12 Controls 12

18

Days after treatment

Fig. 3. Case 4. Percentage gain or loss in pounds of the four groups. (See also Table III.)

eggs on the first post-treatment date. On the second post-treatment sample the count had risen to a mean of 250 e.p.g. This increase was solely due to one lamb which had a count of 3,000 e.p.g. It died the following day. A second animal of this group died on the third post-treatment sampling date. Counts of 150 e.p.g. of S. papillosus and 1,650 e.p.g. of strongyles were recorded. The worm count was composed of 75 Cooperia punctata, I, I 13 Haemonchus contortus and 475 S. papillosus. The cadmium iodide-treated group showed a reduction of 82·6 per cent of S. papillosus eggs after treatment and thereafter remained low. In the control group 39·5 per cent reduction occurred. On the second posttreatment sampling date, one animal had died and no sample was available

STRONGYLOIDES PAPILLOSUS I:\FECTIOK 1:'-1 SHEEP

259

for examination. On the last post-treatment sampling d a te the egg count had risen again and this was due to one la mb which had 8,050 e.p.g. This lamb died and on post-mortem examination was found to be infected with 2,025 S. papillosus. In all three groups, the strongyle egg counts increased between the second and third post-treatment sampling dates . The range in individual animals was 50- 5,100 e.p.g. These counts remained low until the last sampling da te, when the m ethyridine-treated group and the control group rose to overall means of 1,829 and 1,127 e. p.g. respectively, the cadmium iodidetreated group having a mean of 487 e.p.g . Six of the methyridine-treated group, which at the beginning of the experiment h ad been in very poor condition, had been kept in a small paddock known to be well contaminated with helminth eggs and larvae. The remainder of the flock had been moved to fresh pasture after treatment. Four lambs of this group contributed 15,250 e.p.g. out of a total of 20,150. Since the strongyle egg counts in Case 4 were so low at the time of treatment the efficiency of treatment cannot be judged. The cadmium iodide-treated and the control groups both showed small losses in weight on the first sampling date after treatment. The control group at the end of the experiment had only gained 0'28 lb. The cadmium iodide group had gained an average of 2 '09 lb. , the group of 12 m ethyridine-treated lambs 2 '50 lb. and the 58 lambs treated with methyridine gained an average of 3'47 lb. TABLE II CASE

4:

PRE-TREATMENT AND POST-TREATMENT S. papillosus MEAN E.P.G. AND EFFICIENCY OF METHYRIDINE AT A DOSE RATE OF 200 M G./ K G . SUB CU TANEO USLY, AND CADMIUM IODIDE, 67-99 MG./KG" per os.

Methyridine Cadmium iodide Controls anima ls) ( I 2 a nimals) ( I 2 animals)

(I 2

Pre-treatment Post-treatment I % reduction Post-treatment 2 Post-treatment 3

875 2I

121 21

97 '6

82 '6

25 0 ' 14

13 21

879 53 2 39 'S 42 7 764t

• Due solely to one ani m al with 3,000 e.p,g.

t Due mainly to one animal wi th 8,050 e,p,g, TABLE III CASE

4:

MEAN WEIGHTS ( IN LB. ) OF LAMBS I N THE FOUR GRO U PS T HR OUG HO UT THE PERIOD OF THE EXPERIMENT , ( N U MBER S I N BRACKETS I NDICATE THE G AIN S OR LOSSES AS PERCENTA G E S OF THE ORIGINAL WEIGHTS,

I.E. 100%. ) Days after treatment

0 4 II

18 M ean actual gain :

c

Controls

Methyridine

Methyridine

(12 animals)

(58 animals)

Cadmium iodide ( 12 animals)

(12 animals)

29'41 (100) 30'16 (102 '55) 32'09 (109 ' 1 I ) 31'9 1(108'5°)

39'41 (100) 4°'34 (102'3 6 ) 42 '4 8 ( 107 '79) 42 ,88 ( 108 ,80)

3 I ,83 (100) 31 '58 ( 99'21 ) 33 '58 (105'5 0 ) 33 '9 2 (106'57)

33'°8 (100) 32'8 1 ( 99'18) 33'9 0 (102'48 ) 33 '36 (10°'85)

2'5 0

3'47

2'09

0 '28

BRITISH VET ERE"';ARY JOURNAL, 119,6

DISCUSSIO N

The occurrence of heavy infections of lambs in Kenya with Strongyloides papillosus is of great interest. Resistance to reinfection by this parasite has been demonstrated by Roberts (1942), Vegors (1954) and Turner (1959b). Under normal conditions, it may be presumed that a small number of infective larvae, insufficient to cause ill effects, are continuously penetrating the host's skin and stimulating the immune mechanism. Thus only a small burden will result. The year 1960 was not as dryas 1961 and the survival of larvae on pasture was sufficient to ensure a fairly constant though low-grade infection in the majority of lambs. Until October, 1961 was a year of drought and the lambs in the experiment of that year had lower and more sporadic individual infections than did the lambs in 1960. Fuelleborn (1914) has shown that strongyloides larvae are very susceptible to desiccation. The susceptibility of larvae of S. papillosus to desiccation has been demonstrated by Turner & Wilson (1961). The very wet conditions experienced in Kenya during October to December of 1961 would have greatly favoured the survival of these larvae on pasture. The high egg counts in the lambs during this period were presumably due to the non-availability of sufficient numbers of infective larvae earlier in the year to stimulate the immune mechanism, followed by ideal conditions for their survival, resulting in heavy infections in susceptible animals. Of the nine adult ewes examined in Case 2, and six ewes and six hoggets in Case 4, only one animal in each case had eggs of S. papillosus. This can be explained on the basis that they had acquired a resistance earlier in life and in times when a small population of infective larvae was present, and in the wet period of 1961 when large numbers of these larvae were available on pasture, the animals were immune to infection. Temperatures in the Naivasha area are probably adequate throughout year the for larval development and survival. The main factor necessary for their survival would thus appear to be sufficient moisture. In the first three cases reported here, the effects of heavy burdens of S. papillosus were obscured by other diseases. Lambs in Case 1 and Case 2 had footrot in addition to S. papillosus infections and also fairly heavy burdens of strongyles. The strongyloides burdens in Case 1 were comparatively low when compared with Cases 2, 3 and 4 and no deaths occurred in these lambs. Cases 2 and 3 had, in addition to heavy helminth infections, outbreaks of bluetongue, and in Case 2 there was also cutaneous myiasis and severe lung infections. No direct or clear-cut effects can therefore be attributed to the strongyloides infections in Cases I, 2 and 3. The high egg counts of S. papillosus in Case 4 and the relative absence of strongyles, the clinical picture of helminthiasis and the absence of any other recognizable disease strongly suggest that the deaths which had occurred were due to this parasite. This is further supported by the increase in condition and weight gain of the treated animals, as compared with the controls. The pathogenicity of S. papillosus has been clearly demonstrated experimentally by several workers. Many of the individual egg counts of this parasite

STRONGYLOIDES PAPILLOSUS INFECTION IN SHEEP

261

in cases reported here were of the same order as those found in fatal experimental infections. It is suggested that although no clear-cut evidence can be given in Cases 2 and 3, such heavy burdens were pathologically significant and had a contributory effect on the high rate of mortality in lambs in these cases. The farm in Case 2 is situated 8,000 feet above sea level in a very exposed position on the edge of the Kinangop plateau. Severe generalized lung infections were found in the lambs. It is thought probable that the migration of large numbers of infective larvae of S. papillosus through the lungs of these lambs predisposed them to secondary invasion by other organisms. The farms in Cases I, 3 and 4 are situated at approximately 6,000 feet in less exposed positions and with higher night temperatures. No lung diseases were found. Turner (I 959a) and Turner et al. (1960) found that damage caused by the migrating larvae is usually quickly repaired. Turner ( I959a) found one experimental lamb with badly affected lungs and was of the opinion that this was due to a secondary infection by other organisms. Beveridge (1934) suggested that the penetration of the skin of the feet of sheep by the infective larvae of S. papillosus may provide a portal of entry for the causal organisms of footrot. He did not suggest that this parasite was the only factor but that any trauma may do the same. He pointed out the occurrence of footrot at times most favourable for the development of the larvae of S. papillosus. The larvae will not cause footrot in the absence of the causal organism. The lambs in Cases I and 2 had been or were severely affected with footrot during the period of high egg counts of S. papillosus. Adult sheep were also badly affected. The fact that these latter animals had footrot but negligible strongyloides burdens does not invalidate the theory. Damage to the feet causing a portal of entry for the causal organism would occur before the infective larvae could experience the immune mechanism of the host. Methyridine was selected for trial since the work of Gracey & Kerr (196 I ) suggested that it acted efficiently on S. papillosus and also because it has been shown to bring about rapid recovery in acute cases of helminthiasis where other anthelmintics have failed. The findings of the two small trials reported here show a very high efficiency of methyridine against S. papillosus. The cadmium salts have been shown to be effective under experimental conditions by Levine & Szanto (1960). Because of their insolubility in water, they have to be administered in a dry state in capsules, and since doses of 100 mg./kg. or more may cause scouring and loss of weight, an accurate dose must be given. This is a great disadvantage because of the difficulty of preparing and administering an accurate dose under field conditions. The efficiency of cadmium iodide was not found to be as high as that of methyridine and the initial loss of weight of lambs in Case 4, although small, is undesirable. SUMMARY

Th~ literature on the pathogenicity of Strongyloides papillosus infections in ruminants is reviewed and the main clinical and pathological effects are

BRITISH VETERINARY JOURNAL, 119,6

briefly summarized. The occurrence of heavy infections of sheep with this parasite in Kenya during and following extremely wet conditions is reported. The possible reasons for this are discussed. Two small trials using methyridine indicate that this drug is highly efficient in its effect on S. papillosus. Cadmium iodide was also found to be effective. ACKNOWLEDGEMENT

The author wishes to thank the Director of Veterinary Services, Kenya for permission to publish this paper. REFERENCES

J., 10,43.

BEVERIDGE, W. I. B. (1934). Aust. vet. FUELLEBORN, F. (1914), Arch. SchiJfs-u.

Tropenhyg., 18,26. 'GARKAVI, B. L. (1956). Veterinaria, 33, 37. ·GRACEY, J. F. & KERR, J. A. M. (1961). Vet. Rec., 73, 171. LEVINE, N. D. & SZANTO, J. (1960). Amer. J. vet. Res., 21, 84· ROBERTS, F. H. S. (1942). Aust. vet. J., 18, 19. 'TURNER, J. N. (1955). Proc. helminth. Soc. Wash., 22, 132. TURNER, J. H. (1959a). Amer. J. vet. Res., 20, 102. 'TURNER, J. H. (1959b). J. Parasit., 45, 76. 'TURNER, j. H., SHALKOP, W. T. & WILSON, G . I. (1960). Amer. J. vet. Res., 21, 536. 'TURNER, j. H. & WILSON, G. I. (1958). Vet. Med., 53, 242. TURNER,j. H., & WILSON, G.I. (1961).J. Parasit., 47, 30. VEGORS, H. H. (1954). Amer. J. vet. Res., 15,429. WOODHOUSE, C. A. (1948). J . Amer. vet. Med. Ass., 113,354. (Receivedfor publication, 9 December, 1962)