Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, USA.
Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA; Grupo de Parasitología Veterinaria, Universidad Nacional de Colombia, Colombia.
Vet Parasitol. 2020 Jun;282:109100. doi: 10.1016/j.vetpar.2020.109100. Epub 2020 May 5.
Dirofilaria immitis is the globally distributed agent of heartworm disease. Infection in canines causes debilitating disease that can be fatal if left untreated. Macrocyclic lactones can prevent heartworm disease in dogs, cats and ferrets by killing larvae before they develop into adult worms in the pulmonary artery. However, administration of prophylactic drugs to wild canids to prevent D. immitis infection is not feasible. Furthermore, a vaccine against heartworm is currently unavailable and drug resistant D. immitis have been identified, highlighting the need for new strategies to prevent parasite transmission. We recently established a method to block development of emerging third-stage larvae (eL3) from the mosquito Aedes aegypti by over-activating the Toll pathway, one of the major innate immune signaling pathways in mosquitoes. Our previous study used a drug-sensitive strain of D. immitis and it remains unknown if the strategy is effective against different D. immitis genotypes and, more importantly, if it would work against drug-resistant genotypes. The purpose of this study was to determine whether Toll pathway activation is capable of blocking eL3 development of D. immitis strains that are resistant to macrocyclic lactones. We infected mosquitoes with two independent strains of D. immitis previously confirmed as being resistant to macrocyclic lactones, and then activated Toll signaling by RNAi-mediated silencing of the pathway inhibitor, IκB/Cactus, and quantitatively measured eL3 development. Similar to the drug-sensitive strain, eL3 were strongly reduced by Toll activation in both drug-resistant strains. Furthermore, similar to the drug-sensitive strain, the reduction of eL3 in both drug-resistant strains suggests a defect in larval invasion of, or development in, the Malpighian tubules - the organ in the mosquito to which microfilariae migrate after ingestion and where the larvae undergo several developmental molts. In summary, Toll pathway activation blocks the development of three distinct D. immitis genotypes, including two different drug-resistant genotypes. If this strategy can be applied to heartworm vectors in the field, it may help reduce the spread of disease and is not predicted to favor the spread of drug resistance.
犬恶丝虫是一种分布广泛的全球寄生虫，可导致犬类患心丝虫病，使犬类虚弱，如不治疗可能致命。大环内酯类药物可以通过杀死幼虫来预防犬、猫和雪貂的心丝虫病，这些幼虫在肺动脉中发育成成虫。然而，给野生犬类使用预防性药物来预防犬恶丝虫感染是不可行的。此外，目前还没有针对心丝虫的疫苗，并且已经发现了耐药的犬恶丝虫，这突显了需要新的策略来防止寄生虫传播。我们最近建立了一种方法，可以通过过度激活 Toll 途径来阻止埃及伊蚊中新兴的第三期幼虫 (eL3) 的发育，Toll 途径是蚊子主要的先天免疫信号通路之一。我们之前的研究使用了对药物敏感的犬恶丝虫菌株，并且尚不清楚该策略是否对不同的犬恶丝虫基因型有效，更重要的是，它是否对耐药基因型有效。本研究的目的是确定 Toll 途径的激活是否能够阻止对大环内酯类药物耐药的犬恶丝虫菌株的 eL3 发育。我们用两种先前证实对大环内酯类药物耐药的独立犬恶丝虫菌株感染蚊子，然后通过 RNAi 介导的途径抑制剂 IκB/Cactus 沉默来激活 Toll 信号，并定量测量 eL3 的发育。与药物敏感菌株相似，在两种耐药菌株中，Toll 激活强烈减少了 eL3 的发育。此外，与药物敏感菌株相似，两种耐药菌株中 eL3 的减少表明幼虫在入侵或在马尔皮基小管中发育过程中存在缺陷，马尔皮基小管是蚊子中微丝蚴摄入后迁移并在其中经历几次发育蜕皮的器官。总之，Toll 途径的激活阻止了三种不同的犬恶丝虫基因型的发育，包括两种不同的耐药基因型。如果这种策略可以应用于心丝虫的传播媒介，它可能有助于减少疾病的传播，并且预计不会助长耐药性的传播。
