Veterinary Parasitology, 12 (1983) 71--77 71 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

THE A C T I V I T Y O F C L O S A N T E L AS A N E Q U I N E A N T I P A R A S I T I C

A G E N T

JORGE GUERRERO*, BRUCE F. MICHAEL, MICHAEL W. ROHOVSKY and BARBARA P. CAMPBELL

Research Division, Pitman-Moore, Inc., P.O. Box 344, Washington Crossing, NJ 08560 (U.S.A.)

(Accepted for publication 23 September 1982)

ABSTRACT

Guerrero, J., Michael, B.F., Rohovsky, M.W. and Campbell, B.P., 1983. The activity of closantel as an equine antiparasitic agent. Ve t. Parasitol., 12:71--77.

Eighteen pony foals were experimentally infected with 500 third stage larvae of Strongylus vulgaris at 2 weeks, and at 2, 4, 6 and 8 months after birth. For the duration of the study, all foals were kept in the same pasture with their mothers to allow natural infection with other parasites by exposure to a contaminated environment. Twelve of the foals were utilized in groups of 3 and treated orally five times at two month intervals starting at one month of age with closantel at doses of 5, 10, 20 or 40 mg kg -1.

Ten months after birth the foals were necropsied to determine the parasitic burdens in the gastrointestinal tracts and the cranial mesenteric arteries. The results indicate a high antiparasitic activity of closantel against larval stages of Gasterophilus intestinalis and S. vulgaris, as well as against adult S. vulgaris, S. edentatus, Anoplocephala perfoliata and Triodontophorus spp., when used at doses of 20 or 40 mg kg -~.

INTRODUCTION

A m o n g the m a n y gas t ro in t e s t i na l paras i tes of equines , mig ra t ing larvae of S t rongy lus vulgaris are c o n s i d e r e d to be the g rea tes t p r o b l e m ( O g b o u r n e and Duncan , 1977) . These larvae cause severe p a t h o l o g i c a l d i s tu rbances in the crania l mesen t e r i c a r t e ry which m a y be r e spons ib le for 90% of equine col ic

(Kes te r , 1975) . M o d e r n a n t h e l m i n t i c s such as m e b e n d a z o l e and o the rs are h ighly ef fec t ive

agains t t he a d u l t stages o f S. vulgaris and are w i d e l y u t i l i zed to t r e a t and con. t ro l n e m a t o d e pa ras i t i c i n fec t ions in horses ( G u e r r e r o and Sharp , 1979) . However , p r e s e n t m e t h o d s fo r t r e a t m e n t or c o n t r o l o f migra t ing S. vulgaris larvae are l im i t ed t o mass ive or r e p e a t e d doses of t h i a b e n d a z o l e (Drudge and L y o n s , 1970) or , t h i a b e n d a z o l e (Georg ie e t al., 1980) , and are on ly ef fec t ive agains t ce r t a in ea r ly s tages of d e v e l o p m e n t of the paras i te .

*Author to whom correspondence should be addressed.

0304-4017/83/0000--0000/$03.00 © 1983 Elsevier Scientific Publishing Company

72

Closantel (N-(5-chloro-4(a (4-chlorophenyl)~-cyanomethyl)-2-methyl- phenyl)-2-hydroxy-3,5,diiodobenzamide), is a new salicylanilide anthel- mintic discovered by Janssen and Sipido (1977). It has been shown to be efficacious against several species of nematode (Van den Bossche et al., 1979), t rematode (Van den Bossche et al., 1979), and arthropod (Chaia et al., 1981a) parasites of cattle and sheep.

The present study was conducted to evaluate the activity of orally admin- istered closantel against migrating stages of S. vulgaris, and other common gastrointestinal parasites of equines.

MATERIALS AND METHODS

Animals

Eighteen mixed breed pony foals born on Pitman-Moore's Research farm were utilized in this study. During gestation the pregnant mares were con- fined in a fenced pasture. After parturition the foals and mares were main- tained together on the same pasture.

Parasitic infection

Infective third stage larvae (L3) of S. vulgaris were supplied by Drs. H.J. Drudge and E.T. Lyons {University of Kentucky). The foals were artificially infected by mouth with 500 L3 of S. vulgaris on Day 14 and 2, 4, 6 and 8 months after birth. The foals also acquired natural infections with equine parasites, including S. vulgaris, by constant exposure to a common environ- ment contaminated by the fecal material of the mares.

Drug

Closantel was utilized as a solution obtained from the Pharmacy Research Section of Pitman-Moore, Inc.

Experimental design

Eighteen foals received artificial and natural parasitic infections as de- scribed above. Twelve of these foals were randomly allocated into 4 groups of 3 and were treated orally at 1 month of age with closantel at doses of 5, 10, 20 or 40 mg kg -1. Closantel treatments were repeated in these foals at 3, 5, 7 and 9 months of age. Six remaining foals served as untreated controls.

A complete necropsy according to the procedure recommended in F.D.A.'s guidelines for the efficacy evaluation of equine anthelmintics (1979) was performed on each foal at 10 months of age. The identification of parasites encountered was based on Lichtenfeld's (1975) descriptions and taxonomical keys. Special at tention was paid to the larval populations of Gasterophilus

TA

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ses

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%

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Mea

n

% C

on

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M

ean

%

Co

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(mea

n)

effi

cacy

ef

fica

cy

effi

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ef

fica

cy

G.

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3

45

.8

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10

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P.

equ

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m

30.8

2

1.3

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ulga

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C.D

74

spp. and S. vulgaris. Eff icacy o f each dose level was ca lcula ted c o m p a r i n g parasi t ic bu rden fo r the t r ea t ed an imals to the parasi t ic burdens of the un- t r ea t ed cont ro ls .

RESULTS

A c o m p a r i s o n of the g roup means o f the parasi t ic bu rden at nec ropsy and the ca lcu la ted con t ro l l ed eff icacies are p r e sen t ed in Table I. All o f the foals t r ea t ed wi th c losante l a t 20 and 40 mg kg -1 were free of pa tho log ica l lesions in the i n t ima o f the cranial mesen te r i c a r t e ry and its ad jacen t b ranches (Fig. 1). One f i f th stage S. vulgaris larvae was f o u n d in the mesen te r i c a r te ry o f one an imal t r e a t ed wi th c losante l a t 40 mg kg -1 . No S. vulgaris larvae were f o u n d in the an imals t r ea t ed wi th c losantel a t 20 mg kg -1. All of the u n t r e a t e d con- trols had m a r k e d th i cken ing and d is tens ion o f the cranial mesen te r ic and ileo ceco colic ar ter ies , wi th large a c c u m u l a t i o n s o f f ibrin and S. vulgaris larvae (Fig. 2). A m e a n o f 28.7 larvae o f S . vulgaris was f o u n d in the u n t r e a t e d con t ro l ponies .

A t doses o f 5, 10, 20 and 40 mg kg -1, c losante l was 100% effec t ive against larvae o f G. intestinalis, Dose levels o f 20 and 40 mg kg -1 p rov ided 100%

Fig. 1. Cranial mesenteric artery of animal orally treated with closantel at doses o f 40 mg kg -1. Notice the absence of lesions in the arteries.

75

Fig. 2. Cranial mesenteric artery of untreated control animal. Notice the marked thickening and distension of the walls of the arteries.

efficacy against adult S. vulgaris, S. edentatus and Triodontophorus spp. A dose of 40 mg kg -~ of closantel was also 100% effective against Parascaris equorum and Anoplocephala perfoliata.

Oxyuris equi and small strongyles were consistently present in the treated and untreated groups.

DISCUSSION

By the experimental design utilized in this study, closantel confronted several stages of development of S. vulgaris larvae. At oral doses of 20 or 40 mg kg -~ , closantel was highly efficacious against 16 and 30 day old fourth stage larvae that originated from the experimental infections. Apparently closantel was also effective in controlling larvae that were acquired by natural infections originating from eggs eliminated by the mares. In some cases these larvae could have been 3 0 - 6 0 days old by the time of treatment.

Closantel's efficacy over different stages of development of S. vulgaris makes this compound unique among the chemotherapeut ic alternatives for t rea tment of this parasitic infection. The only other compounds which have previously been shown to eliminate S. vulgaris larvae completely are nitrami-

76

sole and avermectin Bla (Slocombe and McCraw, 1980), and ivermectin {Slocombe and McCraw, 1981). These compounds were only effective in the elimination of 7 day old larvae of S. vulgaris.

Closantel at even the lowest dose utilized, 5 mg kg -1, was also highly effi- cacious against G. intestinalis larvae. Previously closantel was shown to be efficacious against larval stages of Dermatobia hominis in cattle {Chaia et al., 1981a, 1981b), Hypoderma sp. and Oestrus bovis in sheep (Van den Bossche et al., 1979).

High anthelmintic efficacy (100%) against P. equorum and A. perfoliata was observed utilizing closantel at 40 mg kg -1, and against adult S. vulgaris, S. edentatus and Triodontophorus spp. at 20 and 40 mg kg -1. The efficacy against A. perfoliata was 100% in two of the three foals treated with closantel at 20 mg kg -~ . Partial activity against O. equi and poor activity against small strongyles was detected in closantel t reated ponies.

Closantel binds to blood plasma proteins and appears to be active against larval stages of parasites, especially of those species that feed on or are in contac t with blood or plasma. Recently Hall et al. {1981) observed high pro- phylactic activity against Haemonchus contortus in sheep for 60 days after t rea tment with closantel at doses of 10 mg kg -~. Sustained antiparasitic ac- tivity of closantel has previously been observed and utilized for the control of Ancylostoma caninum (Guerrero et al., 1982}, D. hominis (Chaia et al., 1981a, 1981b) and Boophilus microplus (L.M. Schmied, 1980, unpublished).

Utilizing Fasciola hepatica Van den Bossche et al. {1979) found that closantel causes disruption of phosphoryla t ion of mitochondria both in vitro and in vivo. A similar mechanism of activity may be responsible for the varied antiparasitic activity of closantel against some nematode and ar thropod spe- cies. The prophylact ic and lethal effect of closantel against common equine parasites, including migratory states of S. vulgaris and Gasterophilus spp., indicate the potent ia l usefulness of this antiparasitic compound in equine veterinary medicine.

REFERENCES

Chaia, G., Chiari, L., Da Silva, D.C. and Guerrero, J., 1981a. Pilot trials on the treatment of Dermatobia hominis infections in cattle with closantel. Am. J. Vet. Res., 32: 1240 -~ 1241.

Chaia, G., Chiari, L., Da Silva, D.C. and Guerrero, J., 1981b. Closantel (R 35120) no tramento da Dermatobia hominis (Lineu Jr., 1781). Pesq. Agrop. Bras., 16: 193--197.

Drudge, J.H. and Lyons, E.T., 1970. The chemotherapy of migrating strongyle larvae. In: J.T. Bryans and H. Gerber (Editors), Equine Infectious Diseases, Vol. II, S. Karger, Basel, pp. 310---322.

F.D.A., 1979. Guidelines for the Efficacy Evaluation of Equine Anthelmintics. Food and Drug Administration, Rockville, MD, 24 pp.

Georgie, J.R., Rendano, V.T., King, J.M., Bianchi, D.G. and Theodorides, V.J., 1980. Equine verminous arteritis; efficacy and speed of larvicidal activity as influenced by dosage of albendazole. Cornell Vet., 70:147 -~ 152.

Guerrero, J. and Sharp, M.L., 1979. Critical anthelmintic evaluation of mebendazole sus- pension in horses. Equine Pract., 1: 53--55.

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Guerrero, J., Page, M.R. and Schad, G.A., 1982. Closantel t reatment and prevention of re-establishment of patency of Ancylostoma caninum in dogs. J. Parasitol., 68: 616--619.

Hall, C.A., Kelly, J.D., Whitlock, H.V. and Ritchie, L., 1981. Prolonged anthelmintic effect of closantel and disophenol against a thiabendazole selected resistant strain of Haemonchus contortus in sheep. Res. Vet. Sci., 31: 104--106.

Janssen, M.A.C. and Sipido, V.K., 1977. Antiparasitic salicylanilide derivatives. United States Patent No. 4,005,218.

Kester, W.O., 1975. Strongylus vulgaris - the horse killer. Newsl. Am. Assoc. Equine Pract., July: 15--19.

Lichtenfeld, R., 1975. Helminths of domestic equids. Proc. Helminthol. Soc. Wash., 42: 1- -92.

Ogbourne, C.P. and Duncan, J.L., 1977. Strongylus vulgaris in the Horse: its Biology and Veterinary Importance. Commonwealth Institute of Helminthology Miscellaneous Publication. Vol. 4, 40 pp.

Schmied, L.M., 1980. Closanteh observaciones sobre su acci6n en Boophilus sp. Johnson & Johnson de Argentina, Buenos Aires, Argentina. Unpublished data, 12 pp.

Slocombe, J.O.D. and McCraw, B.M., 1980. Evaluation of pyrantel pamoate, nitramisole and avermectin B~a against migrating Strongylus vulgaris larvae. Can. J. Comp. Med., 44: 9 3 - 1 0 0 .

Slocombe, J.O.D. and McCraw, B.M., 1981. Controlled tests of ivermectin against mi- grating Strongylus vulgaris in ponies. Am. J. Vet. Res., 42: 1050--1051.

Van den Bossehe, H., Verhoeven, H., Vanparijs, O., Lauwers, H. and Thienpont, D., 1979. Closantel, a new antiparasitic hydrogen ionophore. Arch. Int. Physiol. Biochim., 87: 851--852.