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Abstract
This survey was conducted in the southern Brazilian state of Rio Grande do Sul and
involved 182 farms located in 26 counties. In addition to the three major broad-spectrum
anthelmintic groups (viz. benzimidazole, levamisole and ivermectin) the combination
benzimidazole and levamisole and the H. contortus specific anthelmintic, closantel,
were tested by the faecal egg count reduction method for the prevalence of anthelmintic
resistance. Resistance was found to be 90%, 84%, 13%, 73% and 20%, respectively. This
is a crisis situation. Immediate, drastic action needs to be implemented, otherwise
the sheep industry in this region (approx. 10 million head) will soon face a lack
of any effective anthelmintics with the inevitable consequences of major restructuring
or abandonment.