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

Abstract In the ecologically diverse metropolitan area of Seoul, raccoon dogs ( Nyctereutes procyonoides ) 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 Dirofilaria immitis in urban wildlife for veterinary and public health. Among 51 raccoon dogs examined, D. immitis 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 D. immitis across Asia and Europe, and haplotype analysis revealed low genetic diversity among Korean isolates. Wolbachia 16S ribosomal RNA sequences from raccoon dogs consistently grouped in supergroup C, confirming their association with D. immitis . These findings confirm natural infections of D. immitis and Wolbachia 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.