Efficacy of four commercially available heartworm preventive products against the JYD-34 laboratory strain of Dirofilaria immitis

Blagburn, Byron L.; Arther, R. G.; Dillon, A. Ray; Butler, Jamie M.; Bowles, Joy; Simson, Cristiano von; Zolynas, Robert

doi:10.1186/s13071-016-1476-7

Cited by 48 publications

(52 citation statements)

References 12 publications

(16 reference statements)

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“…Since 2005, a lack of efficacy of MLs to prevent heartworm infection has been reported in the USA, suggesting the possibility that heartworm is developing resistance to ML-preventatives [ 21 ]. Studies since have been focused on identification of potential molecular changes that could be associated with ML lack of efficacy [ 22 – 25 ]. Comparisons of ML-resistant and susceptible D. immitis have identified possible single nucleotide polymorphisms (SNPs) such as the GG-GG genotype in the P-glycoprotein (P-gp) with ivermectin-resistance [ 22 , 23 , 26 ].…”

Section: Introductionmentioning

confidence: 99%

Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

et al. 2016

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BackgroundHeartworm (Dirofilaria immitis) in dogs is considered endemic in Australia, but the clinical heartworm disease caused by the heartworm is rare and prevalence is low. The mainstream prevention of the heartworm is based on macrocyclic lactone (ML) administration. The aim of this study was to confirm endemism of the heartworm under current Australian conditions using a cohort of recent microfilaria-positive dogs which were on variable heartworm prevention.MethodsA hotspot of canine heartworm antigen-positive and microfilaria-positive dogs has been detected recently in Queensland, Australia. Blood samples from 39 dogs from Queensland and two dogs from New South Wales were investigated for canine filarioids. Rapid antigen diagnostic tests capable of detection of D. immitis and real-time PCR for quantification and differentiation between D. immitis from Acanthocheilonema reconditum with quantification of microfilariae in canine blood samples, together with D. immitis specific real-time PCR assay, were applied to microfilaria-positive dogs. The P-glycoprotein genotype was determined to test whether Australian-sourced heartworm shared the same genetic markers as those suspected of ML-resistance in North America.ResultsOnly D. immitis was detected in the samples from Queensland and New South Wales, Australia. Using high resolution melt real-time PCR and D. immitis specific real-time PCR, the calculated microfilaria concentration ranged from 1 to 44,957 microfilariae/ml and from 7 to 60,526 microfilariae/ml, respectively. DNA sequencing of the PCR products confirmed D. immitis. Fifteen of the examined dogs were on putative, rigorous ML prevention. For the remaining dogs, compliance with heartworm prevention was unknown or reported as inconsistent. Wild-type genotype AA-GG of the P-glycoprotein locus of D. immitis sequence has been obtained for three blood samples. Due to the incomplete history, any suggestion of a loss of efficacy of MLs must be treated as ‘remotely possible’. In the immediate future, records of preventative administration and annual antigen testing would be required to determine any problems with the efficacy of preventatives.ConclusionsThe prevalence of canine heartworm in Australia remains poorly understood. It is generally assumed to be low by veterinary practitioners. The localised increase in the study area confirms endemism of canine heartworm and a requirement for ongoing vigilance through annual heartworm testing to better understand the changing distribution of canine heartworm, client compliance, as well as to detect any change in ML-susceptibility.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1821-x) contains supplementary material, which is available to authorized users.

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Section: Introductionmentioning

confidence: 99%

Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

et al. 2016

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“…The JYD-34 isolate was validated in April 2011 with dogs testing positive for both MF and adult heartworm antigen. The JYD-34 strain was later found to be resistant to ML drugs [ 19 ]. In contrast, the ZoeMo strain was established by Zoetis (Kalamazoo, MI) from a blood sample collected from the same source dog, but approximately 17 months later on 4 December 2012.…”

Section: Methods and Resultsmentioning

confidence: 99%

A statistical approach for evaluating the effectiveness of heartworm preventive drugs: what does 100% efficacy really mean?

2017

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BackgroundInitial studies of heartworm preventive drugs all yielded an observed efficacy of 100% with a single dose, and based on these data the US Food and Drug Administration (FDA) required all products to meet this standard for approval. Those initial studies, however, were based on just a few strains of parasites, and therefore were not representative of the full assortment of circulating biotypes. This issue has come to light in recent years, where it has become common for studies to yield less than 100% efficacy. This has changed the landscape for the testing of new products because heartworm efficacy studies lack the statistical power to conclude that finding zero worms is different from finding a few worms.MethodsTo address this issue, we developed a novel statistical model, based on a hierarchical modeling and parametric bootstrap approach that provides new insights to assess multiple sources of variability encountered in heartworm drug efficacy studies. Using the newly established metrics we performed both data simulations and analyzed actual experimental data.ResultsOur results suggest that an important source of modeling variability arises from variability in the parasite establishment rate between dogs; not accounting for this can overestimate the efficacy in more than 40% of cases. We provide strong evidence that ZoeMo-2012 and JYD-34, which both were established from the same source dog, have differing levels of susceptibility to moxidectin. In addition, we provide strong evidence that the differences in efficacy seen in two published studies using the MP3 strain were not due to randomness, and thus must be biological in nature.ConclusionOur results demonstrate how statistical modeling can improve the interpretation of data from heartworm efficacy studies by providing a means to identify the true efficacy range based on the observed data. Importantly, these new insights should help to inform regulators on how to move forward in establishing new statistically and scientifically valid requirements for efficacy in the registration of new heartworm preventative products. Furthermore, our results provide strong evidence that heartworm ‘strains’ can change their susceptibility phenotype over short periods of time, providing further evidence that a wide diversity of susceptibility phenotypes exists among naturally circulating biotypes of D. immitis.

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“…Recently, microfilariae (MF) collected from a small number of LOE isolates, after development in mosquitoes to L3 larvae, were used to infect new host dogs and the isolates confirmed to be resistant to ML prophylaxis in controlled efficacy studies in dogs challenged with the L3 larvae [ 4 , 5 ]. D. immitis JYD-34 was originally isolated from the field and taken into the laboratory by TRS Labs Inc. (Athens, Georgia, USA) where it was subsequently found to have less than 100% susceptibility to 3 ML-based preventives [ 5 , 6 ]. For claims for prevention of heartworm disease, evidence of 100% efficacy is required by the US Food and Drug Administration ( https://www.fda.gov/ucm/groups/fdagov-public/@fdagov-av-gen/documents/document/ucm052652.pdf ).…”

Section: Introductionmentioning

confidence: 99%

Dirofilaria immitis JYD-34 isolate: whole genome analysis

et al. 2017

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BackgroundMacrocyclic lactone (ML) anthelmintics are used for chemoprophylaxis for heartworm infection in dogs and cats. Cases of dogs becoming infected with heartworms, despite apparent compliance to recommended chemoprophylaxis with approved preventives, has led to such cases being considered as suspected lack of efficacy (LOE). Recently, microfilariae collected from a small number of LOE isolates were used as a source of infection of new host dogs and confirmed to have reduced susceptibility to ML in controlled efficacy studies using L3 challenge in dogs. A specific Dirofilaria immitis laboratory isolate named JYD-34 has also been confirmed to have less than 100% susceptibility to ML-based preventives. For preventive claims against heartworm disease, evidence of 100% efficacy is required by FDA-CVM. It was therefore of interest to determine whether JYD-34 has a genetic profile similar to other documented LOE and confirmed reduced susceptibility isolates or has a genetic profile similar to known ML-susceptible isolates.MethodsIn this study, the 90Mbp whole genome of the JYD-34 strain was sequenced. This genome was compared using bioinformatics tools to pooled whole genomes of four well-characterized susceptible D. immitis populations, one susceptible Missouri laboratory isolate, as well as the pooled whole genomes of four LOE D. immitis populations. Fixation indexes (FST), which allow the genetic structure of each population (isolate) to be compared at the level of single nucleotide polymorphisms (SNP) across the genome, have been calculated. Forty-one previously reported SNP, that appeared to differentiate between susceptible and LOE and confirmed reduced susceptibility isolates, were also investigated in the JYD-34 isolate.ResultsThe FST analysis, and the analysis of the 41 SNP that appeared to differentiate reduced susceptibility from fully susceptible isolates, confirmed that the JYD-34 isolate has a genome similar to previously investigated LOE isolates, and isolates confirmed to have reduced susceptibility, and to be dissimilar to the susceptible isolates.ConclusionsThese results provide additional evidence for the link between genotype and the reduced susceptibility phenotype observed in such isolates as JYD-34. Further work on other isolates showing reduced susceptibility to ML is required to demonstrate the value of genetic analysis in predicting the response to ML chemoprophylaxis. The authors suggest that genetic analysis may be useful in helping to interpret the results of in vivo efficacy testing of ML heartworm preventives against D. immitis isolates.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2437-5) contains supplementary material, which is available to authorized users.

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Efficacy of four commercially available heartworm preventive products against the JYD-34 laboratory strain of Dirofilaria immitis

Cited by 48 publications

References 12 publications

Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

A statistical approach for evaluating the effectiveness of heartworm preventive drugs: what does 100% efficacy really mean?

Dirofilaria immitis JYD-34 isolate: whole genome analysis

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