Macrocyclic lactone resistance in Dirofilaria immitis

Microfilariae were isolated from a Katrina rescue dog that remained microfilariaemic despite successful adulticidal treatments and repeated treatment with high doses of macrocyclic lactones (MLs). The microfilariae were genotyped at two P-glycoprotein single nucleotide polymorphic sites which had been found to correlate with reduced sensitivity to MLs. The genetic polymorphism (GG-GG), previously found to be associated with insensitivity to MLs in vitro, was present at a frequency of 45.3% in microfilariae that survived repeated treatments with high doses of ML anthelmintics. The data show phenotypic and genotypic evidence of ML resistance in Dirofilaria immitis. (C) 2011 Elsevier B.V. All rights reserved.