Abstract
BackgroundThe 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.MethodsWith 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.ResultsThis 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.ConclusionHeartworm isolates identified through this method can be used in research to better understand macrocyclic lactone resistance so prevention strategies can be adapted.
Highlights
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
The only FDA-approved available method of preventing the development of adult heartworms (Dirofilaria immitis) in dogs and cats is the compliant administration of products containing macrocyclic lactone (ML) drugs [1]
Methods it is possible that new data might be produced that contradict this assertion, current evidence suggests that the microfilarial suppression test (MFST) is the most practical and accurate method for determining whether a heartworm case is ML-resistant
Summary
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. The only FDA-approved available method of preventing the development of adult heartworms (Dirofilaria immitis) in dogs and cats is the compliant administration of products containing macrocyclic lactone (ML) drugs [1]. These products are extremely effective against third-stage larvae (L3) and up to 30-day-old fourth-stage larvae, with a label efficacy of 100%. In Atkins et al [5], the authors examined 319 lack of efficacy (LOE) cases from the Mississippi Delta region of the United States using the Window of Infection tool (http://www.heartwormedu.com/).
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