ABSTRACT
Since the introduction of broad-spectrum anthelmintics these drugs have been the major means of managed control of nematode parasites. Anthelmintics have been used particularly in livestock for the control of economically important parasites. Because of heavy reliance on these drugs and their widespread use, anthelmintic-resistant parasites have been selected and anthelmintic resistance has emerged as a problem amongst parasites of livestock. The same compounds have also been used to treat parasitic infections in human populations and there are fears that resistance will develop in these parasites too. Although resistance is defined formally below, a brief definition is: the ability of helminths to survive doses of drug that would normally remove them. Resistance is genetic, that is, resistant worms carry alleles for resistance which are inherited by the next generation.
