Testing for drug resistance in Dirofilaria immitis from dogs in Townsville, Australia

This study examined two cases of asymptomatic canine heartworm (Dirofilaria immitis) disease in dogs from Townsville, Australia. These dogs reportedly received 'rigorous' heartworm prevention for 12 months prior to diagnosis. We deployed currently available tools to assess the phenotypic and genotypic drug-resistance status of these two dogs. To do so, we performed the microfilariae suppression test using spot-on moxidectin (Advocate for dogs or Advantage Multi, 2.5 mg/kg). This phenotypic test was coupled with genetic testing of seven single nucleotide polymorphisms (SNPs) previously associated with resistance in D. immitis isolates from the USA. Tools utilised for genetic testing include Illumina amplicon next-generation sequencing and rhAmp SNP qPCR.