Epidemiological survey of <i>Dirofilaria immitis</i> and its <i>Wolbachia</i> endosymbiont in wild raccoon dogs in Seoul, Korea, with emphasis on lung tissue-based detection

In the ecologically diverse metropolitan area of Seoul, raccoon dogs (<i>Nyctereutes procyonoides</i>) coexist with humans and domestic animals, creating opportunities for vector-borne parasite transmission. Climate-driven shifts in mosquito populations may further enhance these risks, highlighting the need to monitor <i>Dirofilaria immitis</i> in urban wildlife for veterinary and public health. Among 51 raccoon dogs examined, <i>D. immitis</i> was identified in the pulmonary arteries and right ventricle of 13 animals (25.5%) by necropsy, with worm burdens ranging from 2 to 9. Lung tissue PCR revealed 4 additional subclinical infections, resulting in a final confirmed prevalence of 17 positives (33.3%). In contrast, whole-blood PCR detected only 11 positives (21.6%), all confirmed by necropsy, indicating higher sensitivity of lung tissue PCR. Phylogenetic analysis of cytochrome c oxidase subunit 1 sequences showed all isolates clustered with reference <i>D. immitis</i> across Asia and Europe, and haplotype analysis revealed low genetic diversity among Korean isolates. <i>Wolbachia</i> 16S ribosomal RNA sequences from raccoon dogs consistently grouped in supergroup C, confirming their association with <i>D. immitis</i>. These findings confirm natural infections of <i>D. immitis</i> and <i>Wolbachia</i> in wild raccoon dogs and highlight their potential role as urban wildlife reservoirs, while lung tissue-based molecular detection offers synergistic advantages for detecting subclinical infections and improving estimates of heartworm occurrence.