Anthelmintic resistance: past, present and future

Anthelmintic resistance continues to increase in geographic range, in the n umber of species affected and the range of drugs involved. Several aspects of resistance have emerged as important issues. They include lack of geneti c reversion, presence of side resistance and lack of universality. Furtherm ore, resistant isolates recovered from the field may have different charact eristics to those selected in pen passage. Research into anthelmintic resis tance has not progressed far beyond the stage sf descriptive research. Some progress has been made in developing control strategies and in diagnosing resistance, especially in the development and adoption of in-vitro tests. H owever, these still need improvements in their ability to detect resistance to closantel and avermectin/milbemycin anthelmintics. Less progress into u nderstanding the basis of resistance has occurred. Research priorities incl ude improvement of diagnostic tests and the development of molecular tests, particularly for resistance to levamisole and the avermectin/milbemycins. Resistance itself, as a selectable marker for genetic transfection in paras ites, is a potential tool for investigating parasite biology. (C) 1998 Aust ralian Society for Parasitology. Published by Elsevier Science Ltd. All rig hts reserved.