Authors

R Power¹; J Šlapeta‬¹;  ¹ The University of Sydney, Australia

Discussion

Canine heartworm disease is a potentially deadly cardiopulmonary disease caused by the mosquito-borne filarial nematode Dirofilaria immitis. In Australia, the administration of macrocyclic lactone (ML) drugs has successfully reduced the prevalence of canine heartworm infection. However, the recent re-emergence of canine heartworm in dogs from Queensland, Australia and the identification of ML-resistant isolates in the USA poses an important question of whether ML-resistance has emerged in this parasite in Australia. The aim of this study was to utilise phenotypic and genotypic approaches to examine the sensitivity to ML drugs in D. immitis in Australia. To do so, a total of 78 blood samples were collected from 45 dogs in Queensland and New South Wales, Australia across three years (2019 to 2022). We tested for the presence of D. immitis infection in these blood samples using a quantitative Modified Knott’s test, serology, and real-time PCR targeting D. immitis and its associated symbiont Wolbachia. A phenotype observed by utilising sequential quantification of microfilariae for 23/45 dogs was coupled with genetic testing of filtered microfilariae for Single Nucleotide Polymorphisms (SNPs) previously associated with ML-resistance in isolates from the USA. This presentation will reveal the results of these phenotypic and genotypic tests, and hence reveal the ML-sensitivity of the canine heartworms infecting these Australian dogs.