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  • Title: Anthelmintic resistance in nematode parasites of sheep in Denmark with special emphasis on levamisole resistance in Ostertagia circumcincta.
    Author: Bjørn H, Monrad J, Nansen P.
    Journal: Acta Vet Scand; 1991; 32(2):145-54. PubMed ID: 1803927.
    Abstract:
    This study was undertaken to elucidate the presence of anthelmintic resistance in nematode parasites of sheep in Denmark. Twenty two flocks of sheep were selected for Faecal Egg Count Reduction (FECR) tests, based on a prior history of either the same anthelmintic, or anthelmintic class having been used 3 times or more over the previous 5 years. Evidence of anthelmintic resistance was detected in 7 flocks. Two flocks showed FECR of 88% and 94% after treatment with thiabendazole, FECR of another 2 were 90% and 94% following treatment with fenbendazole. Three flocks showed FECR of 73%, 89% and 94%, respectively following the use of levamisole. Ostertagia circumcincta was isolated from 1 of the latter flocks and subjected to an in vivo controlled slaughter assay. Following treatment with levamisole at the recommended dose rate of 7.5 mg/kg, FECR was 44.5% and worm counts were reduced by 67.7%. These results were further substantiated by an in vitro egg hatch paralysis assay and by measuring pepsinogen levels in treated and non-treated lambs. This is the first instance of anthelmintic resistance in sheep nematodes in Scandinavia. Formålet med denne undersøgelse var at belyse forekomst af ormemiddelresistens hos fårets indvoldsorm i Danmark. Toogtyve fårebesætninger udvalgtes til en feltundersøgelse over ormemiddelresistens under anvendelse af en fækal æg reduktions test (eng. Faecal Egg Count Reduction (FECR) Test). Kriterierne for udvælgelse af besætningerne var, at samme ormemiddel eller ormemidler hørende til samme virkningsgruppe havde været anvendt til mindst 3 årlige behandlinger over en 5-årig periode. Der fandtes indikation på ormemiddelresistens i 7 besætninger. Efter behandling med thiabendazol fandtes FECR i to besætninger til henholdsvis 88 % og 94 %, i andre 2 besætninger var FECR 90 % og 94 % efter behandling med fenbendazol og i 3 besætninger fandtes FECR til 73 %, 89 % og 94 % ved behandling med levamisol. Fra 1 af de sidstnævnte besætninger isoleredes en population af Ostertagia circumcincta, som underkastedes en in vivo kontrolleret undersøgelse over resistens mod levamisol. Ved behandling af denne population med levamisol (7.5 mg/kg) fandtes FECR til 44.5 % og en reduktion i ormebyrden på 67.7 %, mens både ægudskillelse og ormeantallet reduceredes med 100% i en tilsvarende anthelmintisk følsom population. Resultaterne understøttedes af en in vitro egg hatch paralysis test samt af målinger af serumpepsinogen. Dette er det første tilfælde af ormemiddelresistens hos fårets indvoldsorm i Skandinavien.
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