Resistance of Fasciola hepatica against triclabendazole in cattle and sheep in The Netherlands

In the winter of 1998/1999, sheep on a farm in the province of North Hollan d, The Netherlands, died from subacute and chronic liver fluke disease desp ite four previous treatments with triclabendazole (TCBZ), Faecal examinatio ns of sheep and cattle on the farm showed high number of liver fluke eggs. In a randomised clinical trial, the fluke egg output was monitored weekly f or 3 weeks in sheep which were treated with TCBZ or with closantel; in dair y cows treated with TCBZ or with clorsulon; and in heifers treated with TCB Z or clorsulon. The results showed a significant reduction of 99.7, 98.1 an d 99.2%, respectively, in fluke egg output at 21 days in all non-TCBZ treat ed animals. TCBZ treatment produced percentage decreases of 15.3, 4.3 and 3 6.6%, respectively. These results are highly indicative of the presence of TCBZ-resistant Fasciola hepatica in sheep and cattle on this farm. (C) 2000 Elsevier Science B.V. All rights reserved.