The problem of escalating resistance of Haemonchus contortus to the modern anthelmintics in South Africa

Show simple item record Malan, F.S. Gerber, H.M. Alves, Regina M.R.
dc.contributor.editor Verwoerd, Daniel Wynand
dc.contributor.upauthor Van Wyk, J.A. (Jan Aucamp) 2014-09-29T06:32:53Z 2014-09-29T06:32:53Z 2014 1989
dc.description The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format. en
dc.description.abstract During the past decade in South Africa there has been a continual increase in sheep of strains of gastrointestinal helminths resistant to the modern anthelmintics. Five strains of Haemonchus contortus are described in this paper. Despite the fact that 2 of the 5 strains were tested for susceptibility only to ivermectin, a total of 10 instances of resistance were found. Four of the 5 strains were resistant to ivermectin, 2 to closantel, 2 to rafoxanide and 2 to the benzimidazoles. One of these strains was concurrently resistant to 3 different anthelmintic groups, namely, the ivermectins, the benzimidazoles and the salicylanilides. Resistance to ivermectin developed in 2 strains of H. contortus after a history of only 3 treatments with this compound in one instance and 11 treatments in the other. In the latter case drenching with ivermectin was well interspersed with that of other anthelmintics. This rapid development of resistance suggests that there may be cross-resistance between ivermectin and another anthelmintic group. Two of the ivermectin resistant strains were recovered from separate properties in the south-western Cape Province, where Ostertagia circumcincta, which is usually the dominant parasite in this region, was virtually eliminated by the anthelmintic treatment. On each of these properties it was apparently replaced by a resistant strain of H. contortus. A serious threat to control is the dissemination of worm strains with multiple resistance to anthelmintics. The strain of H. contortus resistant to 3 anthelmintic groups has already been widely dispersed, as the farmer concerned suddenly decided to give up farming with sheep and to sell his flock. en
dc.description.librarian lmchunu2014 en
dc.description.librarian mn2014
dc.identifier.citation Van Wyk, JA, Malan, FS, Gerber, HM & Alves, RMR 1989, 'The problem of escalating resistance of Haemonchus contortus to the modern anthelmintics in South Africa', Onderstepoort Journal of Veterinary Research, vol. 56, no. 1, pp. 41 - 49. en
dc.identifier.issn 0330-2465
dc.language.iso en en
dc.publisher Published by the Government Printer, Pretoria. en
dc.rights © ARC-Onderstepoort (original). © University of Pretoria. Dept of Library Services (digital). en
dc.subject Veterinary medicine en
dc.subject.lcsh Veterinary medicine -- South Africa
dc.title The problem of escalating resistance of Haemonchus contortus to the modern anthelmintics in South Africa en
dc.type Article en

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