A diagnostic algorithm for evaluating cases of potential macrocyclic lactone-resistant heartworm

Background: the emergence of macrocyclic lactone resistance in canine heartworm poses a substantial threat to what is currently the only effective,fda-approved available method of prevention. further study of the biotypes is necessary to understand the mechanism of resistance and evaluate novel prevention options. identifying cases of drug-resistant infection remains problematic,however,especially when poor compliance and insufficient testing are concerns. furthermore,a definitive demonstration of resistance requires experimental infection and treatment,which is prohibitively costly. methods: with the aim of identifying likely cases of macrocyclic lactone-resistant heartworm and preventing their continued spread,we describe an algorithm for determining the likelihood of drug resistance and appropriate treatment strategies for each case. results: this algorithm relies on the microfilarial suppression test (mfst),which has been used previously as an efficient and discrete measure of suspected resistance. by standardizing this method in a format that is readily available to practitioners,it could become possible to preliminarily survey the emergence and spread of resistance. conclusion: heartworm isolates identified through this method can be used in research to better understand macrocyclic lactone resistance so prevention strategies can be adapted. © 2017 the author(s).