Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, New South Wales 2006, Australia.
Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, New South Wales 2006, Australia; Sydney Infectious Diseases Institute, The University of Sydney, New South Wales 2006, Australia.
Vet J. 2024 Oct;307:106209. doi: 10.1016/j.tvjl.2024.106209. Epub 2024 Aug 2.
Macrocyclic lactone (ML) anthelmintics are currently the only class of drugs available for canine heartworm prevention. Recent reports of Dirofilaria immitis infection occurring in dogs reportedly receiving 'rigorous' prevention in Queensland, Australia, coupled with the confirmation of ML-resistant isolates in the USA, has led to speculation about the potential emergence of ML-resistance in Australia. In this study, we describe two cases (Dog 1 and 2) of asymptomatic canine heartworm disease in Townsville, Australia, that were reportedly receiving 'rigorous' heartworm prevention according to the owners' claims. We aimed to deploy currently available tools to assess the phenotypic and genotypic ML-resistance status of these two dogs. For phenotypic testing, we performed an in-vivo 7-day microfilariae suppression test using a dose of spot-on moxidectin (Advocate™ for Dogs, 100 g/L imidacloprid + 25 g/L moxidectin). This formulation is marketed as Advantage Multi® for Dogs in the USA, which claims a D. immitis microfilaricidal effect. For genetic testing, an Illumina amplicon metabarcoding approach was used to target single nucleotide polymorphisms (SNPs) previously associated with ML-resistance in D. immitis from the USA. Dog 1 and Dog 2 demonstrated <10 % and <40 % reductions in circulating microfilariae seven days after moxidectin treatment, respectively. These phenotypes were not corroborated by genetic SNP testing, as both dogs were classified as susceptible across all examined markers. To streamline testing of D. immitis SNPs, we developed a rhAmp™ SNP qPCR approach for rapidly genotyping suspect cases of ML-resistant infections at the two major loci (L15709_A and L30575). These findings illustrate a phenomenon shown in some heartworm cases outside the USA, whereby infected dogs are failing to see marked reductions in microfilaraemia after ML treatment but possess an ML-susceptible genotype.
大环内酯类驱虫药（ML）驱虫药目前是唯一可用于犬心丝虫预防的药物。最近有报道称，在澳大利亚昆士兰州，据称接受过“严格”预防措施的犬感染了犬恶丝虫，但这与美国确认存在 ML 耐药分离株有关，这引发了人们对澳大利亚可能出现 ML 耐药性的猜测。在这项研究中，我们描述了两例（狗 1 和 2）在澳大利亚汤斯维尔无症状犬心丝虫病病例，据称根据主人的说法，这两只狗接受了“严格”的心丝虫预防。我们旨在利用现有的工具来评估这两只狗的表型和基因型 ML 耐药状态。为了进行表型检测，我们使用了剂量为滴剂莫昔克丁（Advocate™ for Dogs，100g/L 吡虫啉+25g/L 莫昔克丁）进行了为期 7 天的体内微丝蚴抑制试验。这种配方在美国以 Advantage Multi® for Dogs 销售，声称具有 D. immitis 微丝蚴杀灭作用。为了进行基因检测，我们使用了靶向美国先前与 ML 耐药相关的单核苷酸多态性（SNP）的 Illumina 扩增子代谢组学方法。莫昔克丁治疗后 7 天，狗 1 和狗 2 的循环微丝蚴分别减少了<10%和<40%。这些表型与基因 SNP 检测不一致，因为两只狗在所有检查的标记物中均被归类为敏感型。为了简化 D. immitis SNP 的检测，我们开发了一种 rhAmp™ SNP qPCR 方法，用于快速对两种主要基因座（L15709_A 和 L30575）的可疑 ML 耐药感染病例进行基因分型。这些发现说明了在美国以外的一些心丝虫病例中出现的一种现象，即感染的狗在接受 ML 治疗后微丝蚴血症没有明显减少，但具有 ML 敏感的基因型。
