Migratory Soft-Tissue Swelling Owing to Subcutaneous Dirofilariasis

ABSTRACT. Dirofilariasis is an emerging zoonotic infection caused by filarial nematodes from the Dirofilaria genus, typically transmitted through mosquito bites. This case is unique because of the migratory nature of subcutaneous nodules, a presentation seldom associated with Dirofilaria infections. A 51-year-old Thai female presented with migratory subcutaneous nodules on her left arm. Initially misdiagnosed as cellulitis, she received empirical antibiotics, showing only partial improvement, and subsequently developed new nodules. A skin biopsy revealed nematode segments, and molecular identification confirmed Dirofilaria repens using polymerase chain reaction targeting the filarial mitochondrial 12s ribosomal RNA and internal transcribed spacer 1 genes. Treatment with a 3-week course of 400 mg oral albendazole resulted in complete resolution of the lesions. This case underscores the importance of molecular diagnostics when morphological identification is challenging as it enables accurate species identification, enhances disease management, and supports optimized treatment of unusual presentations of dirofilariasis.