Repeated high doses of avermectins cause prolonged sterilisation, but do not kill, Onchocerca ochengiadult worms in African cattle

deC Bronsvoort, Barend M, Renz, Alfons, Tchakouté, Virginia, Tanya, Vincent N, Ekale, David and Trees, Alexander J
(2005) Repeated high doses of avermectins cause prolonged sterilisation, but do not kill, Onchocerca ochengiadult worms in African cattle. Filaria Journal, 4 (1).

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Background: Ivermectin (Mectizan™, Merck and CO. Inc.) is being widely used in the control of human onchocerciasis (Onchoverca volvulus) because of its potent effect on microfilariae. Human studies have suggested that, at the standard dose of 150 μg/kg an annual treatment schedule of ivermectin reversibly interferes with female worm fertility but is not macrofilaricidal. Because of the importance of determining whether ivermectin could be macrofilaricidal, the efficacy of high and prolonged doses of ivermectin and a related avermectin, doramectin, were investigated in cattle infected with O. ochengi. Methods: Drugs with potential macrofilaricidal activity, were screened for the treatment of human onchocerciasis, using natural infections of O. ochengi in African cattle. Three groups of 3 cows were either treated at monthly intervals (7 treatments) with ivermectin (Ivomec®, Merck and Co. Inc.) at 500 μg/kg or doramectin (Dectamax®, Pfizer) at 500 μg/ kg or not treated as controls. Intradermal nodules were removed at 6 monthly intervals and adult worms were examined for signs of drug activity. Results: There was no significant decline in nodule diameter, the motility of male and female worms, nor in male and female viability as determined by the ability to reduce tetrazolium, compared with controls, at any time up to 24 months from the start of treatments (mpt). Embryogenesis, however, was abrogated by treatment, which was seen as an accumulation of dead and dying intra-uterine microfilariae (mf) persisting for up to 18 mpt. Skin mf densities in treated animals had fallen to zero by

Item Type: Article
Additional Information: Published: 08 August 2005. 8 pages (page numbers not for citation purposes).
Uncontrolled Keywords: human onchocerciasis, Onchoverca volvulus, microfilariae, ivermectin, doramectin
Subjects: ?? SF ??
Divisions: Faculty of Health and Life Sciences > Institute of Infection, Veterinary and Ecological Sciences > School of Veterinary Science
Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 09 Nov 2009 12:35
Last Modified: 17 Dec 2022 01:41
DOI: 10.1186/1475-2883-4-8
Publisher's Statement : © 2005 deC Bronsvoort et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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