Z. Parasitenk. 47, 237--248 (¤975) © by Springer-Verlag 1975

The Location of Taenia pisiformis, Taenia ovis and Taenia hydatigena in the Gut of the Dog and hs Effect on Net Environmental Contamination with Ova B r i a n J. Coman a n d Michael D. l ~ i c k a r d University of Melbourne, Veterinary Clinieal Centre Beceived December 27, 1974

Summary. Autopsy of dogs 56 days after infection with either T. pisi/ormis, T. ovis or T. hydatigena showed that these worms could be found attached at any point along the length of the smM1 intestine, but were most commonly in the anterior half. The mean relaxed lengths of T. pisi/ormis, T. ovis and T. hydatigena were 107 cm, 156 cm and 177 cm respectively. Attached gravid proglottides contained a mean of 41000 eggs each in T. pisi/ormis, 31000 eggs in T. hydatigena and 95000 eggs in T. ovis, whereas proglottides free in the gut contained means of only 1370, 500 and 1400 eggs respectively; therefore, the majority of eggs were released into the gut before segments passed out into the faeces. I t was shown that eggs of all 3 species of worms hatched and activated in the sma]l intestine of the dog, especially in the anterior half. Eggs of T. pisi]ormis which had been passaged through the intestine of the dog and stored in the faeces for 5 days were poorly infective for rabbits compared with eggs only stored in faeces. It was concluded, therefore, that during taeniid infections of dogs the point of apolysis in the gut plays a significant role in determining environmental contamination with eggs. Puppies which had been ted 10000 T. ovis eggs daily for 6 weeks prior to infection with T. ovis cysticerci showed no difference in susceptibility to the infection when compared with untreated puppies.

Introduetion The results of i n v e s t i g a t i o n s on h a t c h i n g a n d a c t i v a t i o n of t a e n i i d eggs suggest t h a t t h e s t i m u l i i n v o l v e d are n o t specific to p a r t i c u l a r i n t e r m e d i a t e hosts (Silverman, 1954; Laws, 1968; S m y t h , 1969; B e v e r i d g e et al., 1975). I t is possible, therefore, t h a t t a e n i i d eggs m a y h a t c h a n d a c t i v a t e in t h e g u t of t h e i r definitive host; r e p o r t s of m e t a e e s t o d e s of Taenia solium in m a n (Slais, 1970) a n d Taenia pisi/ormis (Greve a n d Tyler, 1964; I v e n s et al., 1969) a n d Multiceps serialis (Voge a n d Berntzen, 1963) in dogs s u p p o r t this suggestion. T a e n i i d eggs are r a p i d l y e x p e l l e d from d e t a c h e d p r o g l o t t i d e s ( R i j p s t r a et al., 1961) so t h a t free segments in t h e faeces usua]ly c o n t a i n few eggs ( S w e a t m a n a n d P l u m m e r , 1957; F e a t h e r s t o n , 1969); h a t c h i n g of eggs released into t h e g u t could significantly reduce environm e n t a l c o n t a m i n a t i o n b y t h e definitive host. The degree of h a t c h i n g could v a r y w i d e l y along t h e l e n g t h of t h e intestine, a n d therefore t h e p o i n t of apolysis m a y be critical in d e t e r m i n i n g its extent. Dogs s u b j e c t e d to r e p e a t e d infections with T. pisi]ormis d e v e l o p i m m u n i t y m a n i f e s t e d b y a decrease in t h e n u m b e r of worms establishing, r e d u c e d g r o w t h of worms a n d a decline in f e c u n d i t y (unpublished data). T h e l i m i t e d c o n t a c t b e t w e e n a d u l t t a e n i i d s a n d t h e tissues of t h e i r hosts suggests l i t t l e o p p o r t u n i t y 1 Z. Parasitenk.

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B . J . Coman and M. D. l%ickard

for a n t i g e n i c s t i m u l a t i o n , b u t if h a t c h e d oncospheres p e n e t r a t e t h e mucosa t h e y m a y p l a y a role in i m m u n i s i n g t h e host a g a i n s t s u b s e q u e n t infection w i t h a d u l t worms. Beeause of t h e p o t e n t i a l significance of these factors in t h e epizootiology of cysticereosis in d o m e s t i c animals, t h e p r e s e n t i n v e s t i g a t i o n s on t h e f e c u n d i t y , l o c a t i o n in t h e g u t a n d h a t c h i n g of eggs of T. pisi/ormis, Taenia hydatigena a n d Taenia ovis, as well as t h e influence of oneospheres on i m m u n i t y to a d u l t cestodes, were u n d e r t a k e n . Materials and lVlethods Experimental Animals

Dogs. Dogs used in the experiments were of mixed breeds either bred in our colony or purchased at weaning. Initially they were reared on a diet of Puppy Chow (Harper and Co., Mulgrave, Victoria) and later were red Lucky Dog Pellets (I.G.Y. Veterinary Products, Marrackville, N.S.W.) ad lib; no animals had access to uncooked meat. Prior to experiments, pups were treated with piperazine citrate and bunamidine hydrochloride (Antoban and Scolaban-Burroughs Wellcome) to remove internal parasites. Rabbits. Six to 8 week old rabbits of a mixed strain were obtained Irom the Keith Turnbull l%esearch Station, Frankston, or New Zealand Whites were purchased from Tillside Rabbit Farm, Bargo, N.S.W. The rabbits were housed in wire-mesh cages and red entirely on a pelleted ration (RGP, Barastoc, Melbourne) to avoid accidental infection with T. pisi/ormis eggs. From time to time, small numbers of stock rabbits were killed and examined as a check for possible extraneous contamination with ova; no cysticerci were seen. Lambs. Lambs were obtained at birth before sucking and were reared under cestode free conditions. They were red a milk replacement ration (Denkavit-Barastoc, 1Vielboume) and later introduced to lucerne pellets and ewe and lamb cubes (Barastoc, Melbourne). A r t i f i c i a l I n f e c t i o n of H o s t s

De]initive Hosts. Dogs were i n f e c t e d b y m i x i n g cysticerci in a small q u a n t i t y of e a n n e d dog food. E a c h dog was g i v e n from 8-10 cystieerei; in t h e case of T. hydatigena, t h e large b l a d d e r was r u p t u r e d to f a c i l i t a t e i n c o r p o r a t i o n of t h e p a r a s i t e i n t o t h e dog food. Intermediate Hosts. F r e s h o v a of T. pisi•ormis, s u s p e n d e d in 1-5 ml of water, were red to e x p e r i m e n t a ] r a b b i t s using a s t o m a c h t u b e ; usually, r a b b i t s were g i v e n a dose of 2000 eggs. L a r g e n u m b e r s of cysticerci of T. ovis were o b t a i n e d b y m a i n t a i n i n g y o u n g l a m b s on a regime of 10 m g of d e x a m e t h a s o n e t r i m e t h y l a c e t a t e (Optieortenol, Ciba-Geigy) a n d 150 m g a m p i c i l l i n t r i h y d r a t e (Penbritin, B e e c h a m V e t e r i n a r y P r o d u c t s ) 3 t i m e s p e r w e e k from 2 weeks prior to oral i n o c u l a t i o n w i t h 2000 T. ovis eggs u n t i l s l a u g h t e r a n d eollection of eysticerci. F r e s h cysticerci of T. hydatigena were o b t a i n e d , as required, from t h e perit o n e a l c a v i t y of l a m b s s l a u g b t e r e d in a local a b a t t o i r .

Collection of T a e n i i d Eggs G r a v i d specimens of T. ovis, T. hydatigena a n d T. pisi/ormis were collected a f t e r a u t o p s y of e x p e r i m e n t a l l y i n f e c t e d dogs. The t e r m i n a l t e n p r o g l o t t i d e s from each worin were r e m o v e d , d i e e d in water, f i l t e r e d t h r o u g h a small sieve

Environmental Contamination with Taeniid Ow

239

(100 fzm aperture) and washed in several ehanges of sMine. They were stored at 4°C in antibiotic saline (Rickard and Outteridge, 1974) until used. Eggs were collected as soon as possible before use and were counted using a Neubauer Counting Chamber; the required number of eggs was obtained by appropriate dilution of the stock supply.

Experiments and Results 1. The Size, Location and Fecundity of T. pisi]ormis, T. ovis and T. hydatigena in Experimentally Infected Dogs

Experimental Method. Pure infections with T. pisi/ormis, T. hydatigena and T. ovis were established in three groups of live puppies; only four of the dogs infected with T. hydatigena survived to patency. Fifty-six days after feeding cysticerci, dogs were killed with a barbiturate overdose and the intestinM tract removed immediate]y, freed from the mesentery and its length measured. I t was cut open Mong its entire length and the distance from pyloric sphincter to scolices and terminal proglottides of cestodes was measured. The entire operation was carried out quickly since the worms contract rapid]y when exposed to the external environment. Worms were removed from the gut, washed in several changes of tapwater, relaxed in cold watet for 12 hours and then measured. Tapeworm fecundity was assessed by counting the eggs contained in the 2 terminal attached proglottides, in detached proglottides found free in the gut and eggs free in the contents of the ]arge bowel. The technique of collecting and counting eggs from proglottides was described earlier. The entire contents of the large bowel was removed and weighed, thoroughly mixed and a 2g sample taken for the egg counting using the technique of Whitlock (1948) with sodium nitrate (S.G. 1.33) as the flotation solution. Results. The positions of scolices and of terminal proglottides of T. pisi/ormis, T. ovis and T. hydatigena are shown in Figs. 1-3. Both T. pisi/ormis and T. ovis were attached at points along the anterior two-thirds of the small intestine. The positions of termina] proglottides overlapped those of scolices and, in a substantial number of worms, the strobila terminated in the anterior half of the small intestine. With T. hyäatigena, the range of positions was less marked; all were attached in the proximal half and a substantial number of worms terminated in t h a t region. Table 1 shows the relaxed lengths for each taeniid species; the figures are presented as a pooled sample encompassing all worms of the same species. Both T. ovis and T. hydatigena »vere substantially longer in average re]axed length than T. pisi•ormis. Nevertheless, there was considerable overlap in the length ranges for the three species. Details of fecündity of tapeworms and egg output by infected dogs are shown in Table 2. Dog 5 in the T. pisi/ormis group contained several worms which had recently partly destrobilated. For this reason, the pooled value for egg totals in rectal contents was based on the other four dogs only. The results demonstrate that freed proglottides release most of their eggs into the gut contents.

240

B, J. Coman and Yl. D. Rickard

,31I



12 I

. ~ Terminal proglottides

14

1~ ~o1

Scolices

,

~s

Total number of w o r m s : 51

,~

] / I /

'IlllIii II l 0

0

1

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

PYLORUS

CAECUM

LOCATION IN SMALL INTESTINE--(PERCENT OF TOTAL LENGTH)

Fig. 1. The positions of scolices and terminal proglottides of mature T. pisi~ormis in the small intestine of dogs 56 days after infection 12 11



10

%~ Terminal proglettides

Scolicea

Total number of worms=31

9 u~ 8

~a

11 0

0

5

t0

15 20 25 30 35 40 45 SO 55 6Q 65 70 75 80 85 90 95 100

PYLORUS

CAECUM

LOCATION ~N SMALL INTESTINE--(PERCENT OF TOTAL LENGTH)

Fig. 2. The positions of seoliees and terminal proglottides of mature T. ovls in the small intestine of dogs 56 days after infection

2. T h e H a t c h i n g of T a e n i i d O v a in t h e G u t of t h e D o g

Experimental Method. E i g h t e e n 14 m m d i a m e t e r diffusion c h a m b e r s (Millipore filter Corporation, U.S.A.) w i t h m e m b r a n e s of pore size 5 ~m, were c h a r g e d w i t h 100000 o v a each a n d sealed; six c h a m b e r s each were filled w i t h T. pisi]ormis, T. ovis Had T. hyclatigena eggs r e s p e c t i v e l y . A s h o r t l e n g t h of surgical silk was a t t a c h e d to each c h a m b e r for f i x a t i o n in t h e i n t e s t i n e .

Environmental Contamination with Taeniid Ova 20 19 18 17 16 15 14 B13



Total number of worms = 29 proglottides

,

~12 ~10 0 9

~8

Scoiices

,~~ Terminal

~

/

~~

I

m

~6

241

I,_, ~~~

5 4 3

5

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

PYLORUSLocÄTION IN SMALL INTEST]NE - -

(PERCENT OF TOTAL LENGTH )

CAE~CUM

Fig. 3. The positions of scolices and terminal proglottides oB mature T. hydatigena in the small intestine of dogs 56 days after infection Table 1. The relaxed lengths of Taenia pisi/ormis, T. ovis and T. hydatigena recovered 56 days after experimental infection of dogs Cestode

No. dogs Total No. worms

T. pisi/ormis T. ovis T. hydatigena

5 5 4

51 31 29

Range in length of worms (cm) 73-150 93-190 130-248

Mean length of gravid worms (cm =~S.D.) 107 ± 16.6 156:~ 19.8 177~: 32.0

C h a m b e r s were i m p l a n t e d v i a e n t e r o t o m y incision into t h e small intestines of 6 b a r b i t u r a t e a n a e s t h e t i s e d dogs a t positions shown in T a b l e 3, a n d a n c h o r e d b y t h e a t t a c h e d t h r e a d . A f t e r all incisions were elosed, dogs were m a i n t a i n e d u n d e r a n a e t h e s i a for 4 hours, k i l l e d b y b a r b i t u r a t e overdose a n d t h e c h a m b e r s reeovered. Contents of t h e c h a m b e r s were w a s h e d o u t into 10 ml of w a r m (37 ° C) eell culture m e d i u m (Medium 858, Commortwealth Serum L a b o r a t o r i e s , Melbourne) in a L e i g h t o n t u b e (Belco, U.S.A.). Es~imates of h a t c h i n g a n d a c t i v a t i o n were m a d e using an i n v e r t e d microscope m a i n t a i n e d a t a t e m p e r a t u r e of 37°C; 400 oncospheres were c o u n t e d in each sample. Controls were free eggs h a t c h e d a n d a e t i v a t e d using t h e t e c h n i q u e of R i e k a r d a n d Bell (1971), eggs c o n t a i n e d within diffusion c h a m b e r s s u b j e c t e d to t h e same a e t i v a t i o n procedure, a n d eggs m a i n t a i n e d in eell culture m e d i u m a t 37°C for 4 hours. Results. T h e h a t e h i n g a n d a c t i v a t i o n figures for eggs of each speeies of worin are shown in T a b l e 3. A s u b s t a n t i a l a m o u n t of h a t c h i n g oceurred in eaeh case, p a r t i c u l a r l y in those e h a m b e r s p l a c e d in t h e a n t e r i o r small intestine.

242

B . J . Coman and M. D. Rickard

Table 2. Egg production of T. ovis, T. hydatigena and T. pisi]ormis in experimentally infected dogs Species

Dog No.

No. gravid worms

Eggs per attached gravid proglottis

No. of shed proglottides

Eggs per shed proglottis

Total eggs in rectal contents

T. pisi/ormis

1 2 3 4 5

7 11 14 15 6

45000 19000 46000 53000 43000

8 7 3 6 10

5000 150 1200 100 400

21800 60000 nil 2000 575000 a

41000

7

1370

20 950

30300 32000 28000 34000

2 8 2 9

650 800 300 280

168000 33 000 115000 140000

31000

5.3

500

114000

55500 55500 108000 108 000 148000

nil 2 nil 2 12

-110 -300 3750

950 2 800 -53200 30000

95000

3.2

1400

17 400

Pooled ~¢Ieanvalues

T. hydatigena

1 2 3 4

8 8 6 7

Pooled Mean values

T. ovis

1 2 3 4 5

Pooled Mean vMues

5 3 11 6 6

a Destrobilated worms were present in this dog and the figure relating to egg counts in rectal contents is not included in the caleulation of pooled mean values.

3. The I n f e c t i v i t y of T. pisi]ormis Eggs after Exposure to I n t e s t i n a l Seeretions i n the Dog

Experimental Method. F o u r chambers c o n t a i n i n g 30000 T. pisi]ormis eggs each were placed at three points along t h e small i n t e s t i n e a n d i n the m i d large i n t e s t i n e of a b a r b i t u r a t e a n a e s t h e t i s e d dog as described above. After exposure i n the g u t for 4 hr. chambers were r e m o v e d a n d the c o n t e n t s washed into cell culture m e d i u m . Two control groups of eggs were used; 100000 u n t r e a t e d eggs in distilled w a t e r a n d 100000 eggs h a t e h e d a n d a c t i v a t e d in vitro a n d t h e n stored i n cell culture m e d i u m . Samples from each t r e a t m e n t were e x a m i n e d u n d e r the microscope a n d estimates of h a t c h i n g a n d a c t i v a t i o n made. A n e s t i m a t e d 4 000 eggs flora each t r e a t m e n t group were red via stomach t u b e to each of 6 groups of 7 rabbits. R a b b i t s were killed 5 weeks later a n d the n u m b e r of viable cysticerci i n each a n i m a l counted.

Results. The n u m b e r s of eysticerci recovered flora r a b b i t s a n d the observ~tions on h a t c h i n g of eggs are shown i n T a b l e 4. A l t h o u g h only a small proportion of eggs were observed to have h a t c h e d i n the diffusion chambers, m a n y eggs appeared damaged. I n f e c t i v i t y for r a b b i t s was lowest ~or eggs held i n e h a m b e r 2,

E n v i r o n m e n t a l C o n t a m i n a t i o n w i t h Taeniid Ova

243

Table 3. The e x t e n t of h a t c h i n g for taeniid eggs held w i t h i n diffusion e h a m b e r s in the g u t of the deg Species

Egg batch

Location in small intestine

Percentage of eggs hatching

Percentage of h a t c h e d embryos active

T. pisißrmis

DC 1 a DC 2 DC 3 DC 4 DC 5 Free egg control C h a m b e r control Eggs in M e d i u m 858

4% S.I. b 48% S.I. 73% S.I. 97% S.I. m i d large intestine ----

100 63 nil e nil c nil c 100 92 nil

6 8 ---1 16 --

T, ovi8

DC 1 DC 2 DC 3 DC 4 DC 5 Free egg control C h a m b e r control Eggs in Medium 858

5% S.I. 40% S.I. 68% S.L 97% S.I. m i d large intestine ----

42 2 2 nil c nil c 97 97 nil

13 nil nil --2 2 --

T. hydatigena

DC 1 DC 2 DC 3 DC 4 DC 5 F r e e egg control C h a m b e r control Eggs in m e d i u m 858

5% S.I. 47% S.I. 71% S.I. 97% S.L m i d large intestine ----

21 64 2 nil e nil e 97 48 nil

1 1l nil --2 2 --

a DC = diffusion chamber. b % S.I. refers to the site of t h e c h a m b e r in relation to the distance b e t w e e n p y l o r u s and ileoeaeeal valve. c Eggs w i t h i n ~hese diffusion chambers, a l t h o u g h no~ hatehed, often showed swelling, darkening a n d craeking of t h e e m b r y o p h o r e .

but in all cases infectivity of eggs exposed to gut secretions was significantly ]ower than for untreated ova. A number of oncospheres hatched and activated in vitro survived gastric passage in the rabbits and developed into cysticerci.

4. The Effect of Intestinal Passage and Subsequent Storage in Faeces upon the Infeetivity of Taenia pisi]ormis Eggs Experimental Method. Laparotomy was performed on ea•h of three anaesthetised dogs. Sections of the intestinal tract were exteriorised and a suspension of 40000 T. pisi]ormi8 eggs was injeeted into the intestinal lumen in one dog near the pylorie sphincter, in the second at a point 70 % of the distance from pylorus to iliocaee~l valve, and in the third dog at the mid large intestine. Fõllowing

244

B . J . Coman and M. D. l~ickard

Table 4. Hatching of T. pisi/ormis eggs contained in diffusion chambers implanted inte the gut of the dog and their subsequent infectivity for rabbits Group

Position of chamber in the gut

Percentage hatched eggs

:No. cysticerci recovered from rabbits (Mea~n ~= SD)

DC 1 DC 2 DC 3 DC 4 Activated Control Untreated Control

49% 73% 96% 50% ---

12 9 6 2 99 --

87± 63 21=]= 14 56:j: 44 78± 51 68 ~ 67 263 :~ 14~:

S.I.b S.I. S.I. L.I.c

a DC ~ diffusion chamber. b % S.L refers to the site of the chamber in relation to the distance between pylorus and ileocaecal valve. c % L.I. ~ position in large intestine. Table 5. Infectivity of T. pisi]ormis eggs for rabbits following inoculation into the gut of dogs, intestinal passage and subsequent storage in faces Site of inoculation of eggs into gut

:No. of cysticerci recevered from rabbits (Mean =E SD)

No. of Rabbits with cysticerci

Upper small intestine Posterior small intestine Large intestine Control ova stored in faeces

nil 1 387 ~= 218 853 =~416

nil 1 7 7

i n j e e t i o n of ova, the gut was replaced, the ineision s u t u r e d a n d the dogs allowed t o reeovor. The faeces of these dogs were collected over the n e x t four days a n d stored separately at 20°C i n a closed vessel m a i n t a i n e d a t a relative h u m i d i t y ol 76%. T o t a l storage t i m e r a n g e d from 3-7 days d e p e n d i n g on the date of collection. A control t r e a t m e n t i n v o l v e d seeding of ova into a q u a n t i t y of faeces collected from a dog k n o w n to be Iree of t a p e w o r m infection. These faeces were stored for 7 days u n d e r the same conditions as those for the e x p e r i m e n t a l dogs. Following storage, the faeces from each dog were b r o k e n u p i n water, passed t h r o u g h a series of sieves (apertures 700 ~m, 250 ~m a n d 150 ~m) a n d the filtrate allowed to settle. The s u p e r n a t a n t was d r a w n oft a n d the s e d i m e n t resuspended i n 70 m l water. T e n m l aliquots of these suspensions were given, via stomach t u b e , to 4 groups of 7 r a b b i t s each. l~abbits were killed after 5 weeks a n d the n u m b e r s of viable cysticerci counted. Results. The results (Table 5) showed t h a t eggs i n j e c t e d into the small i n t e s t i n e of dogs were no longer available to infect r a b b i t s after faecal passage a n d storage. The differenees b e t w e e n m e a n n u m b e r s of cysticerci developing from gut-passaged eggs a n d eggs only held i n faeces was m a r k e d .

Environmental Contamination with Taeniid Ova

20I

19 18 17 16 15 14 B 13 cr12 211 m]0 O9 cr 8

245

m Scolices -control dogs (50 worms) Sco[ices -dogs fed T.ovis eggs (48worms)

g7 z5 4 3 2 1 0

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 4 PYLORUS CAECLIM LOCATION IN SMALL INTESTINE-(PERCENTOF TOTAL LENGTH)

Fig. 4. The positions of scolices of T. ovis in the small intestine of normal puppies and puppies red 10000 T. ovis eggs daily for 6 weeks prior to infection with T. ovis cysticerci

Table 6. Comparison of T. ovis recovered from normal puppies and puppies red 10000 T. ovis eggs daily for 6 weeks prior to infeetion with T. ovis eystieerci Group

Normal controls Puppies red eggs

No. of worms recovered

Length of No. of worms proglot~ides (mean i SD cm) per worm (mean ~- SD)

Mean No. of eggs per gravid proglottis

of free proglo~tides in each dog

50 48

138.5~49.4 a 163.24-15.1 a

81520 97500

16.2 30.3

325.4=~61.1 b 365.9~=27.7 b

M@an ~o.

a, b Differences statistically not significant.

5. The Effeet of I~epeated Oral Dosing of P u p p i e s w i t h Eggs of T. ovi•, on S u b s e q u e n t I n f e e t i o n w i t h T. ovis Cystieerei E«perimental Method. Six 8 week old p u p p i e s were eaeh red 10000 eggs of T. ovis d a i l y for 6 weeks. A f u r t h e r group of 6 p u p p i e s of similar age a n d breeding were u n t r e a t e d eontrols. I m m e d i a t e l y after t h e l a s t dose of eggs, dogs in b o t h groups were fed 8 eystieerei of T. ovis eaeh. Six weeks l a t e r all dogs were killëd a n d worms within t h e m e x a m i n e d for position in t h e gut, length, a n d f e e u n d i t y as deseribed previously. Result•. T a b l e 6 shows t h e n u m b e r of worms reeovered, t h e i r l e n g t h a n d n u m b e r of segments, t h e i r f e e u n d i t y a n d t h e n u m b e r s of frëe p r o g l o t t i d e s f o u n d in t h e gut. The position oceupied b y the worms in t h e g u t of p u p p i e s is i l l u s t r a t e d in Fig. 4. The results i n d i e a t e d t h a t t h e sehedule of egg feeding nsed p r o d u e e d no significant effeet on a n y of t h e p a r a m e t e r s measured.

246

B.J. Com~n and M. D. I~ickard

Discussion The results of this study showed t h a t premature hatching of taeniid eggs occurs in the gut of the dog and t h a t the extent of this hatching depends largely on the position in the gut at which eggs are released. Premature hatching would effectively reduce the total number of intact ova passing from an infested dog and thereby decrease the extent of contamination of the external environment with ova. Although some eggs were retained in ripe proglottides passed in the faeces of dogs, eIearly, most are liberated into the intestinal contents. Rijpstra et al. (1961) noted t h a t a freshly detached proglottis of T. saginata expelled some 15000 eggs within a few minutes, the expulsion being linked directly to damage inflicted upon terminal anterior branches of the gravid uterus. These branches, referred to as the thysanus, are automatically ruptured during apolysis. Such a rapid expulsion process would explain the low egg numbers seen in detached proglottides lying in the dogs' gut. Similar low egg counts have been noted by Featherston (1969) for free proglottides of T. hydatigena in the faeces of infested dogs. The position of adult worms in the gut of the dog m a y influence the net fecundity of these worms measured in terms of the number of intact ova in the faeces of the dog. Since the degree of hatching is high in the anterior half of the small intestine, it follows t h a t eggs released from proglottides of worms occupying this portion of the gut will play a lesser part in environmental contamination t h a n those from worms positioned more posteriorly, where less hatching occurs. There were no clear preferences in location of attachment b y T. pisi/ormis, T. ovis or T. hydatigena although most worms were in the anterior half of the small intestine. I n contrast, Sutton (1974) found t h a t developing T. ovis were invari~bly located in the third quarter of the small intestine 28 to 35 days after infection. I t is possible t h a t migration of developing or adult worms occurs. Featherston (1969) presented evidence t h a t developing T. hydatigena undergo migration in the intestine of dogs, and the migration of adult HymenoIepis diminuta in rats has been reported b y BMley (i97t). Urdortunat,ely, the evidence for migration of cestodes in the definitive host has been based on sequential killing of groups of animals and the degree of host-induced variability is unknown. Our results indicate t h a t there is considerable variation in the location of individual worms within hosts and even greater variations between hosts; therefore both intrinsic " w o r m " factors and extrinsic " d o g " factors m a y govern the position occupied by adult worms. We have noticed t h a t in older dogs, with a history of several past taeniid infections, worms more often tend to be located in the posterior half of the small intestine (unpublished data). The immune status of the dog may, therefore, have some effect on intestinal location. Other extrinsic factors, such as breed and nutritional status of the host m a y also be involved. The considerable variation in relaxed length of worms had little bearing on the position occupied by terminal proglottides. Individual worms in the gut occupied a relatively small proportion of the total intestinal length. There are no previous studies of hatching of taeniid eggs during passage through t.he gut of the definitive host,, although Freeman (1962) found t h a t eggs of T. crassiceps would hatch when injected directly into the small intestine of a

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mouse. The hatehing requirements for taeniid ova are elearly not speeifie. Silverman (1954) noted that some ova of T. pisi[ormis would hateh in a solution of panereatin and Beveridge et al. (1975) obtained hatehing rates as high as 33 % for B. pisi]ormis eggs ineubated in a solution of bicarbonate and panereatin. Prolonged treatment in artifieal gastric juiee is apparëntly sufficient to eause hatching of some T. saginata ova (Rijpstra et al., 1961). The greater proportion of ova hatching in the anterior half of the small intestine indieated that the physico-ehemieM eonditions in that area are more suitable for hatehing than those existing in the posterior small intestine. The coneentration of bile salts, biearbonatë and pancreatie enzymes are likely to be greater in the proximal small intestine. Osmotie conditions and p I I in this area may also be more favourable for hatching than those existing in the posterior jejunum and ileum. The loss of the embryophore evidently renders the oncosphere very susceptible to unfavourable eonditions in the external environment. I t is unlikely that oncospheres passed in the faeees play any further role in the epidemiology of the parasite eoncerned. I-Iowever, frëshly hatehed oneospheres fed directly to rabbits survivëd gastrie passage and produced viable eystieerei. A proportion of hatehed oneospheres within the diffusion ehambers in the gut of dogs were visibly active. In natural infeetions, such embryos eould penetrate the mucosa and possibly play a part in the development of immunity to subsequent infection with adult worms. Wc were unable to demonstrate such an immunity in T. ovis infection with the dosing sehedule used, but further experiments must be done before drawing significant conclusions. Smyth (1969) has pointed out that adult speeimens of Echinococcus granulosus in the dog evoke no marked ce]lular reaetion but antibodies giving a strong serological reaction with adult worms can be detected in canine serum from infeeted dogs. In view of the consequences of premature hatching of eggs in dogs, the phenomenom of spontaneous destrobilisation may assume speeial significance in the epidemiology of cystieercosis. The spontaneous expulsion of ehains of proglottides in infested dogs has been reported by Sweatman and Plummer (1957) and Featherston (1969) for T. hydatigena and we have observed it on several occasions amongst dogs experimentally infested with T. ovis and T. pisi[ormis. When a chain of gravid proglottides detaehes from a worin, the anterior margin of all but the first proglottis are not ruptured and most of the eontained eggs are therelore protected from the hosts small intestinal seeretions. This results in high numbers of viable eggs passing out of the host to contaminate the environment.

Acknowledgement. We are grateful to Mr. G. Scott for technical assistanee and Professor J. H. Arundel for his encouragement. Finaneial support for this work was provided by the Australian Meat Researeh Committee and the University of Melbourne Veterinary Researeh Fund. Referenees Bailey, G.N.A. : Hymenole2ois diminuta: Circadian rhythm in movement and body length in the rat. Exp. Parasit. !9, 285-291 (1971) Beveridge, I., Riekard, M.D., Gregory, G. G., Munday, B.L. : Studies on Anoplotaenia dasyuri Beddard, 1911 (Cestoda: Taeniidae) a parasite of the Tasmanian Devil: Observations on the egg and metaeestode. Int. J. Parasit. ~, 251 -267 (1975)

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Featherston, D.W.: Taenia hydatigena: 1. Growth and development of adult stage in the dog. Exp. Parasit. 25,329-338 (1969) Freeman, R.S.: Studies on the biology of Taenia crassiceps (Zeder, 1800) Rudolphi, 1810 (Cestoda). Canad. J. Zool. 40,969-990 (1962) Greve, J.H., Tyler, D.E.: Cysticercus pisi]ormis (Cestoda: Taeniidae) in the liver of a dog. J. Parasit. 50, 712-716 (1964) Ivens, V., Conroy, J.D., Levine, N.D. : Taenia pisi]ormis cysticerci in a dog in Illinois. Amer. J. vet. Res. 80, 2017-2020 (1969) Laws, G.F. : The hatching of taeniid eggs. Exp. Parasit. 28, 1-10 (1968) Riekard, M.D., Bell, K . J . : Successful vaceination of lambs against infection with Taenia ovis using antigens produced during in vitro cultivation of the larval stages. Res. Ver. Sci. 12, 401-402 (1971) Rickard, M.D., Outteridge, P.M. : Antibody and cell-mediated immunity in rabbits infected with the larval stages of Taenia pisi/ormi«. Z. Parasitenk. 44, 187-201 (1974) Rijpstra, A.C., Smit, A.M., Swellengrebel, N.tI.: I-Iow and where to search for the ova of Taenia saginata. Trop. geogr. Med. 13, 160-166 (1961) Silverman, P. H. : Studies on the biology of some tapeworms of the genus Taenia. 1. Factors affecting hatching and aetivation of taeniid ova and some criteria of their viability. Arm. trop. Med. Parasit. 48, 207-215 (1954) Slais, J.: The morphology and pathogenicity of the bladder worms Cysticercus cellulosae and Cysticercus bovis. Academia, Prague 1970 Sutton, R. J. : Observations on experimental infections of dogs with Taenia ovis. Res. Ver. Sci. 17, 200-203 (1974) Smyth, J.D. : The physiology of cestodes. Edinburgh: Oliver and Boyd 1969 Sweatman, G.K., Plummer, P . J . G . : The biology and pathology of the tapeworm Taenia hydatigena in domestic and wild hosts. Canad. J. Zool. 35, 93-109 (1957) Voge, M., Berntzen, A. K. : Asexual multiplieation o~ larval tapeworms as the eause of fatal parasitic ascites in dogs. J. Parasit. 49, 983-988 (1963) Whitlock, H.V. : Some modifications of the Mc5~aster helminth egg-counting technique and apparatus. J. Coun. sci. ind. Res. Aust. 2], 177-180 (1948) Dr. M.D. Rickard Veterinary Clinical Centre University of Melbourne School of Veterinary Scienee Princes Itighway, Werribee Victoria 3030, Australia

The location of Taenia pisiformis, Taenia ovis and Taenia hydatigena in the gut of the dog and its effect on net environmental contamination with ova.

Autopsy of dogs 56 days after infection with either T. pisiformis, T. ovis or T. hydatigena showed that these worms could be found attached at any poi...
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