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Efficacy of ivermectin in reducing gastrointestinal nematode fecal egg counts in goats in Burundi
ELSEVIER
Preventive Veterinary Medicine 23 (1995) 173-178
Efficacy of iverrnectin in reducing gastrointestinal nematode fecal egg counts in goats in Burundi M. Dacasto*, U. Cocuzza Dipartitnento di Patologia Animale, Settore di Farmacologia e Tossicologia, I-10126 Torino, Italy
UniversitLi di Torino, via Niua 52,
Accepted 22 October 1994
Abstract Cross-bred investigations
goats in Burundi infested with gastrointestinal nematodes were submitted to fecal and injected subcutaneously with ivermectin. In Experiment 1, goats were treated with
200 /Lg kg- ’ bw ivermectin. In Experiment 2, animals were administered twice that dose. In Experiment 3, goats suspected to be resistant to other anthelmintics were treated with 200 pg kg-’ bw ivermectin. In Experiment 4, two doses of the same strength were injected with an interval of 7 days. Results demonstrate that 200 pg kg-’ bw ivermectin is effective for the control of gastrointestinal nematodes of goats in Burundi; this dosage is also effective against nematodes suspected to be resistant to other anthelmintics. The administration of 400 pg kg- ’ bw did not induce greater or more prolonged effectiveness percentages. The supposed decrease of ivermectin’s residual activity on Day 28 might be avoided by administering two doses with an interval of 7 days. No adverse effects were observed in treated animals. Keywords: Burundi; Efficacy; Gastrointestinal parasites; Goat; Iverrnectin
1. Introduction
In tropical areas of Africa goats are of great economic importance, as they represent one of the most important sources of animal food-stuffs (Singh et al., 1983). Data from the Minis&e de 1’Agriculture et de 1’Elevage indicate that there are 779 000 goats in Burundi (U. Cocuzza, personal communication, 1991). Parasitic diseases, particularly gastrointestinal nematode infections of Huemonchus, Trichostrongylus, Cooperia and Oesophagostomum, are considered to be a major health problem in these goats (Horchner et al., 1981; Museru, 1989). Gastrointestinal infestation prevalence may range * Corresponding author.Tel: + 39.11.650.21.55. Fax: + 39.1 I .65.026.87 0167-5877/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
SSDIO167-5877(94)00441-2
174
hf. Dacasto, U. Cocuzza /Preventive
Veterinary Medicine 23 (1995) 173-l 78
between 67% and 97% and control programs use anthelmintics such as tetramisole and oxyclozanide (Museru, 1989). Ivermectin (Ivomec, Merck Sharp & Dohme) is a semisynthetic avermectin used worldwide in the control of parasitic disorders in domestic animals (Dacasto, 1993). Limited studies have assessed the effectiveness of ivermectin injected subcutaneously into goats and the results are often contradictory (Carmichael et al., 1987; Njanja et al., 1987; Pearson and Rutherford, 1988; Benz et al., 1989; Badger and Mckenna, 1990; Craig and Miller, 1990; Sudhan et al., 1990; Zamri-Saad et al., 1990; Shastri, 1991). Also, anthelmintic resistance to other antiparasitic drugs has been reported in goats (Prichard et al., 1980; Hall et al., 1981; Njanja et al., 1987). The aim of this study was to evaluate the effectiveness of subcutaneous administration of ivermectin to Burundi goats in the reduction of fecal egg counts of gastrointestinal nematodes.
2. Materials and methods The trial involved a total of 108 cross-bred East Africa dwarf goats ( 19 males and 89 females) of different ages, belonging to small flocks and reared in the region of Buyogoma, in the district of Karuzi. In every flock (except those of Experiment 4)) goats were divided into three groups on the basis of a stratified-on-age analysis as follows: (A) animals less than 10 months old; (B) animals between 10 and 24 months old; (C) animals more than 2 years old. Each member of these different age groups was submitted to a routine faecal egg count and randomly assigned to either the control or the treatment group. In every flock, this selection was made in order to have, whenever it was possible, about the same number of treated and control animals. All treatments were done by subcutaneous (SubQ) injection, and controls were always untreated. Four experiments were performed. In Experiment 1 (it = 39)) 23 goats received 200 pg kg - ’ body weight (bw) ivermectin. In Experiment 2 (n = 3 1) , 17 goats were treated with 400 pg kg - ’ bw. In Experiment 3 (n = 24)) 12 goats were treated with 200 pg kg-’ bw ivermectin. Goats belonging to this flock still had considerable numbers of eggs per gram of feces (EPG) , although they had been treated 25 days earlier with an oxyclozanide-tetramisole drug (Nilzan, Coopers) ; anthelmintic resistance to Nilzan was suspected in this flock. In Experiment 4, two doses of ivermectin (200 pg kg - ’ bw) were subcutaneously administered to eight adult goats from a total of 14 (all belonging to the same flock) with an interval of 7 days. This protocol had been used successfully in the treatment of ovine and goat mange (Roncalli and Sutherland, 1986; Wasfi and Hashim, 1986). After the administration of the anthelmintic, the animals were put back onto pasture. All goats were observed by a veterinarian of the CISV organization (Comunita Impegno Servizio Volontariato) hourly after treatment for 4 h, and then weekly, for any adverse reactions. In this respect and on the basis of the literature, the following parameters were taken into account: changes in animal behavior (CNS depression, ataxia) , allergic reactions or alterations at the injection site (e.g. reddening, swelling, itch or local pain). Fecal samples collected from the rectum were taken on Days 0, 7, 14, 21 and 28. Nematode EPG counts were determined by a modified McMaster technique (Thienpont et al., 1979). EPG counts
M. Dacasto, II. Cocuua / Preventive Veterinary Medicine 23 (1995) 173-I 78 Table 1 Subcutaneous
ivermectin
in goats in Burundi: geometric
Group
mean egg per gram (EPG) counts
Days
Experiment 1: 200 pg kgA( 24 months old) Controls (n = 6) Treated (n=7) Efficacy (%)
’ BW
Experiment 2: 400 pg kg-’ A ( < 10 months old) Controls (n = 4) Treated (n=4) Efficacy (o/o) B (10-24 months old) Controls (n = 6) Treated (n = 9) Efficacy (%) C ( > 24 months old) Controls (n=4) Treated (n = 7) Efficacy (%)
BW
0
7
14
21
28
1292 1031 _
2243 4* 99.8
2485 67* 97.3
2692 38* 98.5
3881 78* 98.0
951 1276 _
1293 0* > 99.9
1182 0* > 99.9
1364 3* 99.8
1456 11* 99.2
550 578 _
743 0* > 99.9
873 0* > 99.9
888 0* > 99.9
1539 o* > 99.9
1125 1341
1341 o* > 99.9
2593 0* > 99.9
2107 0* > 99.9
2696 o* >99.9
873 1903
1202 o* > 99.9
1574 o* > 99.9
1163 0* > 99.9
2083 67* 96.8
949 1579 _
1002 0* > 99.9
1137 0* > 99.9
1360 0* > 99.9
2709 19* 99.3
Experiment 3: 200 pg kg- -’ BW once (flocks recently submitted to anthelminthic Coopers) (A ( < 10 months old) 507 599 Controls (n=4) 1049 769 0* Treated (n=4) 0* > 99.9 > 99.9 Efficacy (%) B ( 1O-24 months old) 991 1038 Controls (n=4) 1741 1092 o* Treated (n-4) 0* > 99.9 Efficacy (%) > 99.9 C ( > 24 months old) Controls (n = 4) 161 332 339 385 0* Treated (n=4) 0* Efficacy (%) _ > 99.9 > 99.9 Experiment 4: pg 200 kg-’ Controls (n = 6) Treated (n=8) Efficacy (%) *Significantly
175
BW twice 7 days apart (1 flock containing 963 1346 1347 o* > 99.9
different from control group mean (P < 0.06).
therapy with Nilzan,
2799 0* > 99.9
3049 198* 93.5
3449 o* > 99.9
3653 202* 94.4
1130 0* > 99.9
1143 147* 87.1
only adult goats) 1402 1591 o* o* > 99.9 > 99.9
2049 o* > 99.9
176
M. Dacasro. U. Cocuua /Preventive Veterinary Medicine 23 (1995) 173-l 78
were converted to their geometric means and percent effectiveness relative to the control group. Statistical analyses were performed by the Mann-Whitney U test, with the level of significance set at P < 0.06 (Glantz, 1988).
3. Results No adverse effects were ever observed in goats treated with ivermectin, other than a transient and acceptable pain reaction at the injection site. In Experiment 1, all ivermectin-treated goats showed significant (P< 0.06) reductions in nematode EPG counts compared with controls, and there was > 97% reduction in EPG (Table 1) . Similar results were seen in each of the other trials (Experiments 2-4, see Table 1).
4. Discussion Throughout all the experiments ivermectin was well tolerated and no adverse reactions (except for the transient pain reaction at the injection site) were recorded, confirming the safety of the drug when administered at appropriate doses and also at up to ten times the highest dose rate (Pulliam and Preston, 1989). Our results indicate that ivermectin, injected subcutaneously at a dose rate of 200 pg kg-’ bw, is highly effective against gastrointestinal nematodes of goats in Burundi, and agree with those previously observed in goats and other ruminants (Campbell and Benz, 1984; Dakkak et al., 1986; Njanja et al., 1987; Benz et al., 1989; Gupta et al., 1990; Hoyt et al., 1992). The subcutaneous administration of twice the ivermectin therapeutic dosage (Experiment 2) does not induce higher or more prolonged effectiveness percentages. Ivermectin reduced high EPG counts (650 and 2615 on Days 0 and 28, respectively) found in goats treated 25 days earlier with an oxyclozanide-tetramisole association. The poor effectiveness shown by these other anthelmintics might be indicative of an anthelmintic-resistance phenomenon (Hall et al., 1981; Barragry, 1992). Ivermectin’s residual activity is estimated to persist for up to 21 days (Barragry, 1992; Zajac et al., 1992); in this respect the SubQ administration of two doses of ivermectin, 7 days apart (200 pg kg- ’ bw; Experiment 4)) might be useful in the control of larval stages which had survived to the first treatment, and in eliminating eggs after 14-22 days, as observed in Trials 1,2 and 3 after 28 days (Mendoza Ruiz et al., 1991; Hoyt et al., 1992).
5. Conclusion In conclusion, ivermectin at a dose rate of 200 pg kg-’ bw SubQ is effective for the control of gastrointestinal nematode infections of goats in Burundi; this dosage is also effective in the treatment of nematodes suspected to be resistant to other anthelmintics. The administration of 400 pg kg- ’ bw did not induce greater or more prolonged effectiveness
M. Dacasto, II. Cocuua /Preventive
percentages animals.
(within
our 28-day follow-up).
Veterinary Medicine 23 (199.5) 173-178
177
No adverse effects were observed in treated
Acknowledgements This study was partly supported by a grant from Centro Piemontese di Studi Africani, Torino, Italy. We also acknowledge CISV for the logistic support in Burundi. References Badger, S.B. and McKenna, P.B., 1990. Resistance to ivermectin in a field strain of Ostertagia spp. in goats, N. Z. Vet. J., 38: 72-74. Barragry, T.B., 1992. Therapy of parasitic infestations. Irish Vet. J., 14: 9-22. Benz, G.W., Roncahi, R.A. and Gross, S.J., 1989. Use of ivermectin in cattle, sheep, goats, and swine. In: W.C. Campbell (Editor). lvermectin and Abamectin. Springer, New York, pp. 215-229. Campbell, W.C. and Benz, G.W., 1984. Ivermectin: A review of efficacy and safety. J. Vet. Pharmacol. Therap., 7: I-16. Carmichael, I., Visser, R., Schneider, D. and SOB, M., 1987. Haemonchus contortus resistance to ivermectin. J. S. Afr. Vet. Med. Assoc., 58: 93-94. Craig, T.M. and Miller, D.K., 1990. Resistance by Haemonchus contortus to ivermectin in angora goats. Vet. Rec., 126: 580. Dacasto, M., 1993. lvermectina. Caratteristiche farmaco-tossicologiche. Summa, 10: 17-23. Dakkak, A., Robin, B. and Kachani, M., 1986. Efficacy of ivermectin in the ewe. Rev. Med. Vet. (Toulouse), 137: 781-787. Glantz, S.A., 1988. Statistica per Discipline Biomediche. McGraw-Hill, Milan, 347 pp. Gupta. S.C., Bakshi, S.B., Kumar, S. and Singh, J., 1990. Efficacy of ivermectin against naturally acquired nematode infections of sheep. Indian Vet. J., 67: 673-674. Hall, CA., Ritchie. L. and McDonell, P.A., 1981. Investigations for anthehuintic resistance in gastrointestinal nematodes from goats. Res. Vet. Sci., 31: 116-l 19. Horchner, F., Schlichting, H., Merker, M., WinkIer, G. and Muller, I., 198 I. La repartition des hehnintes chez les vaux au Burundi, Ann. Sot. Belge Med. Trop., 61: 413-419. Hoyt, P.G., French, D.D., Miller, J.E., Williams, J.C., Hackett, G.E., Jr., Kearney, M.T. and Hoyt, M.J., 1992. Evaluation of ivermectin against experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats. Vet. Parasitol., 42: 257-263. Mendoza Ruiz, M.A., Quiroz Romero, H. and Ducoing Watty, A., 1991. Reinfestacibn de nematodos gastroentericos en cabras tratadas con ivermectina. Vet. Mexico, 22: 305-309. Museru, B., 1989. Epid6mioIogie des maladies des Petits Ruminants en milieu rural: cas des helminthoses gastrointestinales des chevres et des moutons en commune de Giheta, province de Gitega. Burundi. In: lnstitut pour la Recherche Agro-Zootechnique, Gitega, pp. l-33. Njanja, J.C., Wescott, R.B. and Ruvuna, F., 1987. Comparison of ivermectin and thiabendazole for treatment of naturally occurring nematode infections of goats in Kenya. Vet. Parasitol., 23: 205-209. Pearson, A.B. and Rutherford. D.M., 1988. lvermectin injection less effective in goats than oral treatment. Surveillance, 15: 22. P&hard, R.K., Hall, C.A., Kelly, J.D., Marti. I.C.A. and Donald, A.D.. 1980. The problems of anthelmintic resistance in nematodes. Aust. Vet. J., 56: 239-25 1. Pulliam, J.D. and Preston, J.M., 1989. Safety of ivermectin in target animals. In: W.C. Campbell (Editor). Ivermectin and Abamectin. Springer, New York, pp. 149-161. Roncalli, R.A. and Sutherland, I.H., 1986. The use of injectable ivermectin against Psoroptes ouis (Acarina: Psoroptidae) in sheep. In: Proc. 31st Annu. Meet. American Association of Veterinary Parasitology, p. 10. Shastri, U.V., 1991. Efficacy of ivermectin (MSD) against lice infestations in cattle, buffaloes, goats and dogs. Indian Vet. J., 68: 191.
178
M. Dacasto, U. Cocuua / Preventive Veterinary Medicine 23 (1995) 173-l 78
Singh, B.B., Welu, M. and Baderha, B., 1983. Epidemiologic et controle des helminthoses gastro-intestinales des caprins de la region de Kabare au Kivu (Z&e). Rev. Elevage Med. Vet. Pays Trop., 36: 151-156. Sudhan, N.A., Prasad, K.D., Ansari, M.Z. and Sahai, B.N., 1990. A note on the trial of ivermectin against mange infestations in goats. Indian Vet. J., 67: 675-676. Thienpont, D., Rochette, F. and van Parijs, O.F.J., 1979. Janssen Research (Editor), Diagnosis of Hehninthiasis through Coprological Examination. Beerse, Belgium. Wasfi, IA. and Hashim, N.H., 1986. Ivermectin treatment of sarcoptic and psoroptic mange in sheep and goats. World Anim. Rev., 59: 29-33. Zajac, A.M., Thatcher, C.D., Brock, R.A., Umberger, S.H. and Notter, D.R., 1992. Comparison of ivermectin formulations in an ovine parasite control programme. Vet. Rec., 130: 353-354. Zamri-Saad, M., Kamal Hizat, A. and Kamil, W.M., 1990. Effect of ivermectin on sarcoptic mange of goats. Trop. Anim. Health Prod., 22: 144-145.
Preventive Veterinary Medicine 23 (1995) 173-178
Efficacy of iverrnectin in reducing gastrointestinal nematode fecal egg counts in goats in Burundi M. Dacasto*, U. Cocuzza Dipartitnento di Patologia Animale, Settore di Farmacologia e Tossicologia, I-10126 Torino, Italy
UniversitLi di Torino, via Niua 52,
Accepted 22 October 1994
Abstract Cross-bred investigations
goats in Burundi infested with gastrointestinal nematodes were submitted to fecal and injected subcutaneously with ivermectin. In Experiment 1, goats were treated with
200 /Lg kg- ’ bw ivermectin. In Experiment 2, animals were administered twice that dose. In Experiment 3, goats suspected to be resistant to other anthelmintics were treated with 200 pg kg-’ bw ivermectin. In Experiment 4, two doses of the same strength were injected with an interval of 7 days. Results demonstrate that 200 pg kg-’ bw ivermectin is effective for the control of gastrointestinal nematodes of goats in Burundi; this dosage is also effective against nematodes suspected to be resistant to other anthelmintics. The administration of 400 pg kg- ’ bw did not induce greater or more prolonged effectiveness percentages. The supposed decrease of ivermectin’s residual activity on Day 28 might be avoided by administering two doses with an interval of 7 days. No adverse effects were observed in treated animals. Keywords: Burundi; Efficacy; Gastrointestinal parasites; Goat; Iverrnectin
1. Introduction
In tropical areas of Africa goats are of great economic importance, as they represent one of the most important sources of animal food-stuffs (Singh et al., 1983). Data from the Minis&e de 1’Agriculture et de 1’Elevage indicate that there are 779 000 goats in Burundi (U. Cocuzza, personal communication, 1991). Parasitic diseases, particularly gastrointestinal nematode infections of Huemonchus, Trichostrongylus, Cooperia and Oesophagostomum, are considered to be a major health problem in these goats (Horchner et al., 1981; Museru, 1989). Gastrointestinal infestation prevalence may range * Corresponding author.Tel: + 39.11.650.21.55. Fax: + 39.1 I .65.026.87 0167-5877/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
SSDIO167-5877(94)00441-2
174
hf. Dacasto, U. Cocuzza /Preventive
Veterinary Medicine 23 (1995) 173-l 78
between 67% and 97% and control programs use anthelmintics such as tetramisole and oxyclozanide (Museru, 1989). Ivermectin (Ivomec, Merck Sharp & Dohme) is a semisynthetic avermectin used worldwide in the control of parasitic disorders in domestic animals (Dacasto, 1993). Limited studies have assessed the effectiveness of ivermectin injected subcutaneously into goats and the results are often contradictory (Carmichael et al., 1987; Njanja et al., 1987; Pearson and Rutherford, 1988; Benz et al., 1989; Badger and Mckenna, 1990; Craig and Miller, 1990; Sudhan et al., 1990; Zamri-Saad et al., 1990; Shastri, 1991). Also, anthelmintic resistance to other antiparasitic drugs has been reported in goats (Prichard et al., 1980; Hall et al., 1981; Njanja et al., 1987). The aim of this study was to evaluate the effectiveness of subcutaneous administration of ivermectin to Burundi goats in the reduction of fecal egg counts of gastrointestinal nematodes.
2. Materials and methods The trial involved a total of 108 cross-bred East Africa dwarf goats ( 19 males and 89 females) of different ages, belonging to small flocks and reared in the region of Buyogoma, in the district of Karuzi. In every flock (except those of Experiment 4)) goats were divided into three groups on the basis of a stratified-on-age analysis as follows: (A) animals less than 10 months old; (B) animals between 10 and 24 months old; (C) animals more than 2 years old. Each member of these different age groups was submitted to a routine faecal egg count and randomly assigned to either the control or the treatment group. In every flock, this selection was made in order to have, whenever it was possible, about the same number of treated and control animals. All treatments were done by subcutaneous (SubQ) injection, and controls were always untreated. Four experiments were performed. In Experiment 1 (it = 39)) 23 goats received 200 pg kg - ’ body weight (bw) ivermectin. In Experiment 2 (n = 3 1) , 17 goats were treated with 400 pg kg - ’ bw. In Experiment 3 (n = 24)) 12 goats were treated with 200 pg kg-’ bw ivermectin. Goats belonging to this flock still had considerable numbers of eggs per gram of feces (EPG) , although they had been treated 25 days earlier with an oxyclozanide-tetramisole drug (Nilzan, Coopers) ; anthelmintic resistance to Nilzan was suspected in this flock. In Experiment 4, two doses of ivermectin (200 pg kg - ’ bw) were subcutaneously administered to eight adult goats from a total of 14 (all belonging to the same flock) with an interval of 7 days. This protocol had been used successfully in the treatment of ovine and goat mange (Roncalli and Sutherland, 1986; Wasfi and Hashim, 1986). After the administration of the anthelmintic, the animals were put back onto pasture. All goats were observed by a veterinarian of the CISV organization (Comunita Impegno Servizio Volontariato) hourly after treatment for 4 h, and then weekly, for any adverse reactions. In this respect and on the basis of the literature, the following parameters were taken into account: changes in animal behavior (CNS depression, ataxia) , allergic reactions or alterations at the injection site (e.g. reddening, swelling, itch or local pain). Fecal samples collected from the rectum were taken on Days 0, 7, 14, 21 and 28. Nematode EPG counts were determined by a modified McMaster technique (Thienpont et al., 1979). EPG counts
M. Dacasto, II. Cocuua / Preventive Veterinary Medicine 23 (1995) 173-I 78 Table 1 Subcutaneous
ivermectin
in goats in Burundi: geometric
Group
mean egg per gram (EPG) counts
Days
Experiment 1: 200 pg kgA(
’ BW
Experiment 2: 400 pg kg-’ A ( < 10 months old) Controls (n = 4) Treated (n=4) Efficacy (o/o) B (10-24 months old) Controls (n = 6) Treated (n = 9) Efficacy (%) C ( > 24 months old) Controls (n=4) Treated (n = 7) Efficacy (%)
BW
0
7
14
21
28
1292 1031 _
2243 4* 99.8
2485 67* 97.3
2692 38* 98.5
3881 78* 98.0
951 1276 _
1293 0* > 99.9
1182 0* > 99.9
1364 3* 99.8
1456 11* 99.2
550 578 _
743 0* > 99.9
873 0* > 99.9
888 0* > 99.9
1539 o* > 99.9
1125 1341
1341 o* > 99.9
2593 0* > 99.9
2107 0* > 99.9
2696 o* >99.9
873 1903
1202 o* > 99.9
1574 o* > 99.9
1163 0* > 99.9
2083 67* 96.8
949 1579 _
1002 0* > 99.9
1137 0* > 99.9
1360 0* > 99.9
2709 19* 99.3
Experiment 3: 200 pg kg- -’ BW once (flocks recently submitted to anthelminthic Coopers) (A ( < 10 months old) 507 599 Controls (n=4) 1049 769 0* Treated (n=4) 0* > 99.9 > 99.9 Efficacy (%) B ( 1O-24 months old) 991 1038 Controls (n=4) 1741 1092 o* Treated (n-4) 0* > 99.9 Efficacy (%) > 99.9 C ( > 24 months old) Controls (n = 4) 161 332 339 385 0* Treated (n=4) 0* Efficacy (%) _ > 99.9 > 99.9 Experiment 4: pg 200 kg-’ Controls (n = 6) Treated (n=8) Efficacy (%) *Significantly
175
BW twice 7 days apart (1 flock containing 963 1346 1347 o* > 99.9
different from control group mean (P < 0.06).
therapy with Nilzan,
2799 0* > 99.9
3049 198* 93.5
3449 o* > 99.9
3653 202* 94.4
1130 0* > 99.9
1143 147* 87.1
only adult goats) 1402 1591 o* o* > 99.9 > 99.9
2049 o* > 99.9
176
M. Dacasro. U. Cocuua /Preventive Veterinary Medicine 23 (1995) 173-l 78
were converted to their geometric means and percent effectiveness relative to the control group. Statistical analyses were performed by the Mann-Whitney U test, with the level of significance set at P < 0.06 (Glantz, 1988).
3. Results No adverse effects were ever observed in goats treated with ivermectin, other than a transient and acceptable pain reaction at the injection site. In Experiment 1, all ivermectin-treated goats showed significant (P< 0.06) reductions in nematode EPG counts compared with controls, and there was > 97% reduction in EPG (Table 1) . Similar results were seen in each of the other trials (Experiments 2-4, see Table 1).
4. Discussion Throughout all the experiments ivermectin was well tolerated and no adverse reactions (except for the transient pain reaction at the injection site) were recorded, confirming the safety of the drug when administered at appropriate doses and also at up to ten times the highest dose rate (Pulliam and Preston, 1989). Our results indicate that ivermectin, injected subcutaneously at a dose rate of 200 pg kg-’ bw, is highly effective against gastrointestinal nematodes of goats in Burundi, and agree with those previously observed in goats and other ruminants (Campbell and Benz, 1984; Dakkak et al., 1986; Njanja et al., 1987; Benz et al., 1989; Gupta et al., 1990; Hoyt et al., 1992). The subcutaneous administration of twice the ivermectin therapeutic dosage (Experiment 2) does not induce higher or more prolonged effectiveness percentages. Ivermectin reduced high EPG counts (650 and 2615 on Days 0 and 28, respectively) found in goats treated 25 days earlier with an oxyclozanide-tetramisole association. The poor effectiveness shown by these other anthelmintics might be indicative of an anthelmintic-resistance phenomenon (Hall et al., 1981; Barragry, 1992). Ivermectin’s residual activity is estimated to persist for up to 21 days (Barragry, 1992; Zajac et al., 1992); in this respect the SubQ administration of two doses of ivermectin, 7 days apart (200 pg kg- ’ bw; Experiment 4)) might be useful in the control of larval stages which had survived to the first treatment, and in eliminating eggs after 14-22 days, as observed in Trials 1,2 and 3 after 28 days (Mendoza Ruiz et al., 1991; Hoyt et al., 1992).
5. Conclusion In conclusion, ivermectin at a dose rate of 200 pg kg-’ bw SubQ is effective for the control of gastrointestinal nematode infections of goats in Burundi; this dosage is also effective in the treatment of nematodes suspected to be resistant to other anthelmintics. The administration of 400 pg kg- ’ bw did not induce greater or more prolonged effectiveness
M. Dacasto, II. Cocuua /Preventive
percentages animals.
(within
our 28-day follow-up).
Veterinary Medicine 23 (199.5) 173-178
177
No adverse effects were observed in treated
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