THE EFFICACY OF IVERMECTIN AGAINST LABORATORY STRAINS OF HELIGMOSOMOIDES-POLYGYRUS (NEMATODA)

A susceptible strain of Heligmosomoides polygyrus was selected for 15 generations with increasing doses of ivermectin (0-6 mg/kg). A passage strain was developed, parallel with the ivermectin-selected strain, t o control for changes due to rapid passage from mouse to mouse. The LD (50)s of the 8th and 15th generations of the ivermectin-selected strai n were 1.5 times that of the susceptible strain. The LD50 of the passa ge strain at generations 8 and 15 remained similar to that of the susc eptible strain. Ivermectin efficacy was lower against the L4 stage tha n against the adult stage in the susceptible strain, the ivermectin-se lected strain and the passage strain at generation 8. (C) 1997 Austral ian Society for Parasitology. Published by Elsevier Science Ltd.