Anthelmintic Treatment of Equids : Capabilities and Limitations Critical Tests of Nine Anthelmintic Agents on Ponies M

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ANTHELMINTIC TREATMENT OF EQUIDS : CAPABILITIES AND LIMITATIONS CRITICAL TESTS OF NINE ANTHELMINTIC AGENTS ON PONIES M. Pecheur

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M. Pecheur. ANTHELMINTIC TREATMENT OF EQUIDS : CAPABILITIES AND LIMITATIONS CRITICAL TESTS OF NINE ANTHELMINTIC AGENTS ON PONIES. Annales de Recherches Vétérinaires, INRA Editions, 1981, 12 (3), pp.303-316. hal-00901337

HAL Id: hal-00901337 https://hal.archives-ouvertes.fr/hal-00901337 Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ANTHELMINTIC TREATMENT OF EQUIDS : CAPABILITIES AND LIMITATIONS CRITICAL TESTS OF NINE ANTHELMINTIC AGENTS ON PONIES

M. PECHEUR

Faculty of Veterinary Medicine, 45, rue des V6t6rinaires, 1070 Brussels Service de Parasito%gie : Dir. Prof Dr. L. Pouplard

Résumé

POSSIBILITÉS ET LIMITES DU TRAITEMENT ANTIHELMINTHIQUE DES ÉQUIDÉS. TESTS CRITIQUES DE NEUF ANTIHELMINTHIQUES SUR PONEYS. - Il existe actuellement de très bons antihelminthiques permettant d’éliminer à plus de 90 % les nématodes gastro-intestinaux des équidés. Cette constatation provient de la comparaison par la méthode du test critique de 9 antihelminthiques testés chez le poney : les Embonate de Pyrantel 19 mg/kg, Oxfendazole 10 mg/kg, Mebendazole 10 mg/kg, Albendazole 5 mg/kg, Dichlorvos 40 mg/kg, Thiabendazole 44 mg/kg, Fenbendazole 7,5 mg/kg, Cambendazole 20 mg/kg, Parbendazole 7 mg/kg. Six à neuf poneys ont été traités avec chacun des produits. En tenant compte de l’activité totale vis-à-vis des différents helminthes, il n’y a pas de différence significative entre les 9 médicaments. A l’égard des Trichonematidae ou petits strongles, nématodes les plus nombreux et les plus cou- rants chez les équidés, l’analyse statistique permet de classer les neuf produits en trois groupes : le groupe 1 renfermant les plus efficaces : Oxfendazole et Pyrantel ; le groupe 2 : Thiabendazole, Mebendazole, Albendazole et Cambendazole ; le groupe 3 : Parbendazôle, Fenbendazole et Dichlorvos. Vis-à-vis des grands strongles ( Strongylus spp. les variations dans les résultats sont parfois considérables, les Pyrantel et Dichlorvos donnent les meilleurs résultats. Contre Oxyuris equi, les Mebendazole et Dichlorvos sont les produits à recommander ; contre Strongyloides westeri, le Cambendazole ; contre Parascaris equorum, le Pyrantel, le Cambendazole, le Dichlor- vos ; contre Gasterophilus equi, les Dichlorvos, Mebendazole + Trichlorfon, Pyrantel + Tri- chlorfon. Aucune action des 9 produits vis-à-vis de Tüchostrongylus axei, Anoplocephala sp. et Habronema sp. n’a été notée.

Anti-parasitic compounds are probably since then the list of new anthelmintic drugs among those which have undergone the most has considerably expanded, so that drugs are dramatic developments in recent years. Some currently available which are particularly effec- twenty years ago, phenothiazine was virtually tive. When we reviewed numerous publica- the only anthelmintic agent available. Its acti- tions dealing with activity of such drugs and vity was very limited, however, and it had a reporting efficiency rates often near 100 %, high toxicity level. Discovery of thiabendazole we wondered how parasites can still present a opened up a new era for parasite control, and problem. In fact, parasite control remains quite complicated, and it is important to be give an accurate picture of the effectiveness of aware of both capabilites and limitations of various anthelmintic compounds available on any anthelmintic treatment. the Belgian market, we used them in critical trial Results reported in literature do not always trials on ponies (Raynaud, 1972). Critical consists of eliminated worms in fae- agree with the activity spectrum announced in counting ces after treatment and non-eliminated worms insert leaflets that come with the drug pack- age. At times, these contradictions can be after necropsy. quite disturbing. It would take too long to analyse here reasons for such contradictions, but we should note that many efficiency trials Materials and Methods have been based on nematode egg counts in faeces before and after treatment. Such a Animals method, although it has some value, is fraught with many The number of eggs passed pitfalls. The ponies used in our study were from one an animal may vary by considerably depending to ten years old and came from various parts on time of season of the state infection, year, of this country where they had become natu- of of the host animal, genus and immunity rally infected. At least six of them were treated of nematodes involved, acti- species cyclical with each of the nine drugs tested, and a total of the and many other factors. vity parasite, of 69 animals were included in this study. Even if faecal tests remain negative for a Three before the drug, period of time after treatment, it may admit- days administering each was in an individual box tedly be due to real anthelmintic activity of a pony placed where could be easily collected. compound, but also to a mere inhibition of the droppings egg laying process in the parasite. On the other hand, re-emergence of reproductive Drugs forms after a certain time may just as well be The following drugs were used, and doses due to a resumption of the egg laying process were those recommended by manufacturers : as to a re-infection. 1. Pyrantel embonate (strongid-P’, Pfizer) : 19 Results of faecal counts should always be mg/kg (in paste form), to 9 ponies. subjected to stringent critical tests. In order to 2. Oxfendazole (SystameXR Wellcome) : 10 mg/kg (in liquid suspension), to 9 ponies. Results 3. Mebendazole (TelminR, Janssen Pharma- ceutical : 10 mg/kg (in past form), to 7 ponies. For each anthelmintic, the number of worms counted in faeces (worms eliminated) 4. Albendazole (Valbazen’, Smith Kline) : 5 and the number of worms counted after mg/kg (in liquid suspension), to 9 ponies. (worms not eliminated) are shown in 5. Dichlorvos Shell) : 40 slaughter (Equigard’ mg/kg (in table 1. Except for Parbendazole, activity of pellet form), to 6 ponies. each agent is mostly similar. 6. Thiabendazole 44 (MSD)R : mg/kg (in paste Trichonema spp. are the only nematodes to form), to 6 ponies. be evenly distributed in ponies, and be present 7. Fenbendazole (PanacurR, Hoechst) : 7.5 in large numbers. This is why a statistical mg/kg (in liquid suspension), to 7 ponies. analysis could be made for this group of para- 8. Cambendazole (Noviben’, MSD) : 20 sites. Tables 2, 2A, 2B, 2C, 2D show results mg/kg (paste form), to 8 ponies. obtained for this particular group. 9. Parbendazole (Helmatacl, SK Et F) : 7 Statistical analysis shows Oxfendazole to be mg/kg in two doses of 3.5 mg/kg each, two significanlty more active than Parbendazole (P days in succession (in powder form), to 8 < 0.0011, Dichlorvos (P < 0.01) and Camben- ponies. dazole and Fenbendazole (P < 0.1). On the other hand, Pyrantel embonate was significantly more active than Parbendazole Worms numeration (P < 0.01) and Dichlorvos (P < 0.1 Mebenda- After administration of the drug, faeces zole and Thiabendazole were significantly more active than Parbendazole (P < 0.05) and were individually collected every 24 hours for a Dichlorvos (P < 0.1).). period of 96 hours. Daily collections were dilu- ted in water so as to obtain a homogenous Cambendazole and Albendazole were si- mixture. An aliquot (1/10 in this case) was gnificantly more active than Parbendazole fixed in alcohol-glycerin. All ponies were (P < 0.05). slaughtered 4 days after completion of treat- Fenbendazole is more active than Parbenda- ment. Methods used for collection of digestive zole (P < 0.011, and no significant difference tract parasites have been described (Pecheur was noted between Parbendazole and Dichlor- et al., 1979). Quantities examined varied be- vos. tween 1/10 and 1/100 for faeces as well as for To sum up, based on their activity against stomach and contents. gut Trichonema spp., anthelmintic agents may be classed in three groups : Oxfendazole and embonate have the activity. A Parasite identification Pyrantel highest second group would include Cambendazole, Helminth identification was based mainly on Mebendazole, Thiabendazole and Albenda- Lichtenfels’ determination key (1975). Larvae zole. Finally, we would place Fenbendazole, in the third of Tiichonema spp. (L4) were not identified. Parbendazole and Dichlorvos group. Adult Trichonema with no buccal capsule were classed as undetermined adult Tricho- nema. Other nematodes larvae of Migrating Strongylus vulgaris, Apart from activity against Trichonema Strongylus equinus and edentatus Strongylus spp., it is difficult to compare accurately acti- were not looked for since the anthelmintic vity of the various anthelminintic drugs stu- doses used are not active normally against died for and of cer- these forms. here, presence population tain species vary widely from one animal to another. Statistical analysis Pyrantel embonate eliminated all 420 Strongylus vulgaris found in three ponies Data were analysed by one-way analysis of (respectively 100, 120 et 200). Three ponies variance. t-Test was used to compare means had Strongylus edentatus : one had 10 which of treatments. were all passed, another had 450 and passed

which were not eliminated (table 3A). 420, the third had 10 and failed to pass any Efficacy was 48 % in the two ponies which had (table 3A1. In one pony with Oxyuris equi, half pinworms (table 3B). the parasites present were passed (table 3B). In the Dichlorvos one had Oxfendazole failed to eliminate the 100 group, pony 100 Sirongylus vulgaris all of which were eli- Strongylus vulgaris in the only infected pony. minated (table 3A). Six ponies had pinworms, Out of 3 ponies with pinworms, 32 % were eli- and elimination rate reached 91 %. This was minated by this drug (tables 3A, 3B). the only group where Parascaris equorum was Rate of of Mebendazole efficacy against found : one pony had 200, and they were all Strongylus vulgaris was 100 % in two ponies, eliminated (table 3B). but 0 % in two others (table 3A). Four ponies To say that Thiabendazole was not active had pinworms, and 93 % were passed (table 3B). against large strongyles would be an exagge- ration, since animals treated with this drug Activity of Albendazole ranged from to had only a few of these : only two ponies had 100 % in 4 ponies with Strongylus vulgaris. 30 and 10 Strongylus respectively, and these One pony had 100 Strongylus edentatus were not eliminated (table 3A). One animal in this group had 1 060 L4 pinworms, of which mal passed all of the 200 Strongylus vulgaris only 150 were passed (table 3B1. with which it had been infected. One animal had If we consider the group treated with Fen- 300 Strongyloides westeri and 100 L4 pin- dazole, we note that 3 out of the 7 ponies had worms which proved resistant to treatment about one hundred Strongylus vulgaris ; (tables 3A, 3B). 2 of them all passed parasites, but the third Variations in showed a negative result (table 3A). The resultlt efficiency percentage was also negative in the one pony which had It should be noted that, as shown in table 4, Strongyloides westeri. Rate of activity in the wide individual variations exist in efficiency four animals which had pinworms averaged percentage for certain anthelmintics. 39 % (range 0-100 %) (table 3B). Two out of the 8 ponies treated with Cam- Time required to pass parasites bendazole has 200 in one Strongylus vulgaris : Fig. 1 shows time required to pass parasites. of them, effectiveness was rated at 100 %, Elimination of nematodes occurred 4 days while it was 0 % in the other Pin- (table 3A). after administration of the drug, and reached a worms infection showed a more consistent maximum between 24 and 48 hours for Thia- distribution in this group since five ponies bendazole, Pyrantel embonate, Fenbendazole, were infected, and activity of Cambendazole Parbendazole and Albendazole. Maximum eli- on the L4 form of these pinworms was only mination occurred between 48 and 72 hours 13.9 %. In contrast, in one pony with 11100 for Mebendazole, Oxfendazole and Dichlor- all were elimi- Strongyloiiles vvesteri, parasites vos. Pyrantel embonate caused the fastest eli- nated (table 3B). mination, with 24 % in the first 24 hours after Out of the 8 ponies treated with Parbenda- dosage, 52 % in the period between 24 and zole, only one had 10 Strongylus edentatus 48 hours, 21 % in the period between 48 and and two had 100 Strongylus vulgaris which 72 hours, and only 3 % in the period between were not eliminated. In contrast, a fourth ani- 72 and 96 hours. Stomach bots and 100 % against L, pinworms (Pecheur and Benakhla, 19811.). No bots are shown in the tables. Bot larvae With one 10 dose of were found in large numbers in stomach con- mg/kg Oxfendazole, and Reid noted a tents of all ponies except for animals treated Duncan (1978) good efficacy with Dichlorvos, Mebendazole plus Trichlor- of 99.8 % against Trichonema spp. in adult fon, and Pyrantel embonate plus Trichlorfon. and free L4 stages, and 97.6 % against Tricho- nema spp. L4 in mucosa. He reported 100 % activity against adult forms of Strongylus vulgaris and Strongylus edentatus, immature sta- Discussion ges of Strongylus edentatus in peritoneum, adult pinworms, Trichostrongylus axei, and Lyons et al. (1974) have obtained with one Parascaris equorum. Colglazier (1979) noted a 19.2 mg/kg dose of Pyrantel embonate 100 % similar response of large and small strongyles. efficacy against pinworms, both adult and L! Our results compare with those of Duncan and larvae ; 91 % against Strongylus vulgaris ; Reid (1978) with respect to adult Trichonema 89 % against Strongylus edentatus, and spp.. With respect to L4 larvae, they are lower, 42-92 % against Trichonema spp.. Troncy and and there was no elimination of Strongylus Hubert (1976) and Bussieras (1977) have obtai- vulgaris even though infection was on a low ned similar results. We made identical obser- level. Activity against L4 pinworms was only vations, apart from L4 pinworms against which 33 %. activity was low (50 % and Trichonema spp. McCurdy et al. (1976) using one 10 mg/kg against which activity was higher with 98 % dose of Mebendazole, reported an activity for adults and 83 % for free L4 larvae. In com- level between 98.4 % and 100 % against bination with Trichlorfon (30 mg/kg), Pyrantel Parascaris, Strongylus vulgaris, Strongylus embonate presents efficacy of 98 % against edentatus, Trichonema spp., and pinworms. stomach bots (Gasterophilus equfl (table 5) Using one 8.8 mg/kg dose, Colglazier et al. (1978) reached lower activity levels : 97-100 % worms ; of 99 % against Strongylus edenta- against large strongyles, 97 % against small tus and of 69 % against Tiichonema spp. L4. strongyles, 78 % against L4 of these strongy- We noted a similar degree of activity as Colgla- les, and 100 % against adult pinworms. They zier et al. (1978) against adult Tiichonema spp. noted an activity of only 63 % against Paras- Activity was lower against Strongylus vulgaris caris. Our trials confirmed the efficacy of the (79 %) and pinworms (48 %), but better drug against adult stages of Trichonema spp., against Tiichonema spp. L4 (88.2 %). a low level of activity against Tiichonema spp. Drudge and Sharp (personal communica- L4, while activity against L4 pinworms seemed tion from Shell B.C.) reported 100 % activity to us especially noteworthy (93 %1. of Dichlorvos at a dose rate of 43 mg/kg Colglazier et a/. (1978), using 5 mg/kg of against Strongylus vulgaris, Strongylus equi- Albendazole, reported an activity level of nus, Pascaris equorum, pinworms and bots ; 100 % against Strongylus vulgaris and 98.8-100 % against Trichonema spp. ; 98- Strongylus equinus, adult Trichonema spp., 100 % against bots and 78-100 % against Parascaris equorum, and adult and L4 pin- Strongylus edentatus. In other studies, Drudge and Lyons (1972) noted that one 43 ves, in combination with Trichlorfon, produce mg/kg dose was 100 % active against Paras- similar results. We noted in 7 ponies that com- caris equorum and adult pinworms, 95-100 % bination of Mebendazole and Trichlorfon was against Strongylus vulgaris, 78-100 % against 98 % active against bots (table 5). Our results Strongylus edentatus, and 89-100 % against proved better than those obtained by Muylle Trichonema spp., although with respect to the et aL (1979) (Pecheur and Benakhla, 1980). latter species activity was stronger against L4 than adults. Reineke (personal communication Lyons et a/. 11976) found Thiabendazole to from Shell B.C.) noted results similar to those be active against all Strongylus vulgaris and of Drudge and Lyons. On our part, we recor- adult pinworms, 95-99 % of Strongylus eden- ded results quite close to those above, apart tatus, and 40 % of Ascaris. By contrast, it from pinworm L4 larvae, for which activity appeared totally ineffective against Strongylo;- was 91 %. Here again, activity against L4 was des even with a 88 mg/kg dose. We noted a stronger than that against adult forms. Dich- good level of activity against adults and imma- lorvos is often regarded as the only anthelmin- tures Tiichonema spp., but a weak activity tic to be active against bot larvae. It should be against L4 pinworms , and against large noted, however, that Benzimidazole derivati- strongyles. Regarding Fenbendazole, a large number of adult forms of Trichonema spp. and only 33 % publications bear out its high level of activity. against immature forms. However, doses used vary widely. In trials using 5 mg/kg (Drudge et al., 1975 ; Colgla- zier et al., 1978), efficacy was 100 % against Conclusion Strongylus vulgaris, 99-100 % against Strongylus edentatus and Strongylus equinus, All currently available anthelmintic agents 92-100 % against adult forms of Tiichonema used on equids show a good level of activity spp., 78 % against immature forms of Tricho- and some have interesting properties, so that nema spp., 100 % against adult pinworms, choice of an anti-parasitic treatment will have and 43-100 % against immature pinworms. to be guided, on the one hand, by genus and Drudge et a/. (1978) reported 100 % activity species of infecting parasites (based on a fae- with one 10 mg/kg dose against Parascaris, cal examination), and on the other, on conve- Oxyuris, Strongylus vulgaris and Strongylus nience of a particular treatment. Also of edentatus. Duncan et al. (1978) are not as importance is the fact that results will be affec- optimistic. Using one 30 mg/kg dose of Fen- ted by the animal’s physical condition, by pre- bendazole, they reported 87 % activity against sence of unaffected, immature forms, and by Trichonema spp.4 L in mucosa and 98 % continuous re-infection. Dosages will there- against L5, 76 % against migrating Strongylus fore be required on a regular basis, and this is vulgaris L4 and 70 % against Strongylus eden- in turn poses the problem of parasite resis- tatus. Generally speaking, our results are tance to anthelmintic agents. Dewormers have mostly below usually reported levels. been divided into two groups for nematodes Colgiazier et al. (19781, Cairns and Holmden according to their mode of action, spectrum of (1977), and Lyons et aL (1971) have shown activity, and effectiveness against resistant that Cambendazole is 100 % active against populations : benzimidazoles and probenzimi- Strongylus vulgaris, 99 % active against dazoles were placed in group I, while Pyrantel Strongylus edentatus, 99 % against adult and Dichlorvos were placed in group II (Pri- forms of Trichonema spp., 77 % against Tri- chard et al., 1980). In order to prevent emer- chonema spp. L4, 100 % against adult forms gence of resistant strains and to control their of Parascaris equorum, and over 85 % against resistance, a twofold approach is required : (1) immature forms of Parascaris equorum, at decrease the frequency of anthelmintic dosa- least those in gut lumen. The results of our ges by resorting to prophylactic measures studies have not been so good, and they con- which lower the degree of pasture contamina- firm, among other things, the excellent activity tion, and (2) alternately use agents of groupI of the anthelmintic agent against Strongyloi= and group II at yearly intervals. des (table 3B1. Its activity against L4 pinworms and large strongyles has not been confirmed Accepted for publication, September 22nd, (table 3B). Colglazier et aL (1978) had noted 1981. 100 % activity against both adult and L4 forms of pinworms. We have found no data in literature on the Acknowledgements subject of controlled critical tests with Parben- dazole on horses. However, it seems that this We thank Prof. Hanset and Dr. Leroy for antiparasitic agent has a much lower activity their kind collaboration in statistical evaluation than other drugs. It averaged 83 % against of results.

Summary

A number of good anthelmintic drugs are currently available which eliminate gastrointestinal nematodes of equids with over 90 % success. This is shown by comparing results of critical tests conducted with 9 anthelmintic agents on ponies using the following dosages : 19 mg/kg for Pyrantel embonate, 10 mg/kg for Oxfendazole, 10 mg/kg for Mebendazole, 5 mg/kg for Alben- dazole, 40 mg/kg for Dichlorvos, 44 mg/kg for Thiabendazole, 7.5 mg/kg, for Fenbendazole, 20 mg/kg for Cambendazole and 7 mg/kg for Parbendazole. From 6 to 9 ponies were treated with each of these anthelmintic agents. Based on total activity of various parasites involved, there was no significant difference in activity of any of the nine agents. With respect to Tricho- nema spp., or small strongyles, which are most numerous and most common in equids, statistical analysis enabled all nine products to be classified into three groups as follows : group 1, with the most active being Oxfendazole and Pyrantel embonate ; group 2, including Thiabendazole, Mebendazole, Albendazole and Cambendazole ; group 3, with Parbendazole, Fenbendazole et Dichlorvos. Results with large strongyles sometimes vary quite significantly. Dichlorvos and Pyrantel embonate should be recommended against Strongylus spp. ; Mebendazole and Dichlorvos against pinworms ; Cambendazole against Strongyloi’cles westeri ; Pyrantel embonate, Cambendazole and Dichlorvos against Parascaris equorum ; and Dichlorvos, Mebendazole with Trichlorfon and Pyrantel embonate with Trichlorfon against bots. No activity against Trichostrongylus axei, Ano- plocephala spp. was noted with any of the nine agents tested.

References

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