Using population genetics to examine relationships of Dirofilaria immitis based on both macrocyclic lactone-resistance status and geography.

•Dirofilaria immitis isolates/strains were analyzed using 17 microsatellite markers.•Clustering based on macrocyclic lactone-resistance status or geography was not seen.•DAPC analysis was able to discriminate between susceptible and resistant samples.•No specific resistance-associated markers were detected.•Distinct passages of D. immitis strains displayed unexpectedly large. genetic distances.