Motility in the L3 stage is a poor phenotype for detecting and measuring resistance to avermectin/milbemycin drugs in gastrointestinal nematodes of livestock

Publication date: Available online 18 December 2017 Source:International Journal for Parasitology: Drugs and Drug Resistance Author(s): Melissa M. George, Lorraine Lopez-Soberal, Bob E. Storey, Sue B. Howell, Ray M. Kaplan Motility is a commonly used in vitro phenotype for assessing anthelmintic activity of candidate compounds, and for detecting anthelmintic resistance in nematodes. Third-stage larvae (L3) of parasitic nematodes are commonly used in motility-based assays because L3 are simple to obtain and can remain viable in storage for extended periods. To improve the measurement of motility of microscopic stages of nematodes, our laboratory developed the Worminator, which quantitatively measures motility of parasites. Using the Worminator, we compared the dose-response characteristics of several avermectin/milbemycin (AM) compounds using L3 from both AM-susceptible and AM-resistant Cooperia spp. (abamectin, doramectin, eprinomectin, ivermectin, moxidectin) and Haemonchus contortus (eprinomectin, ivermectin, moxidectin). Concentrations tested with the Worminator ranged from 0.156 to 40 μM. Differences in EC50 between AM-susceptible and AM-resistant isolates of Cooperia spp. and Haemonchus contortus were small, with resistance ratios ranging from 1.00 to 1.34 for Cooperia spp., 0.99 to 1.65 for Haemonchus contortus. Larval migration inhibition assays were conducted using the same isolates and were equally ineffective for detection of resistance with resistance rat...
Source: International Journal for Parasitology: Drugs and Drug Resistance - Category: Parasitology Source Type: research