Drought and flock isolation may enhance the development of anthelmintic resistance in nematodes

A survey of anthelmintic resistant nematodes was conducted in sheep and goa t flocks in Greece using in vivo and in vitro tests. Faecal egg count reduc tion tests in Macedonia were all greater than 99% indicating very high sens itivity of the nematodes to anthelmintics. In vitro tests showed benzimidaz ole resistant Teladorsagia circumcincta in 17 out of 106 flocks on small is lands. On the mainland there were only three cases of benzimidazole resista nce out of 310 flocks and animals had recently been introduced to the flock s. Flocks on the islands are isolated and there are higher temperatures tha n on the more mountainous mainland, where flocks tend to intermingle. It is concluded that drought and isolation are likely to be the major factors ac counting for the development of anthelmintic resistance in nematodes in the island flocks. (C) 2001 Elsevier Science B.V. All rights reserved.