Jerapas ThongpiyaDoonyapat Sa-nguanraksaNorasate SamarnthaiPatsharaporn T. SarasombathFaculty of Medicine Siriraj Hospital, Mahidol University2022-08-042022-08-042021-02-01Parasitology International. Vol.80, (2021)18730329138357692-s2.0-85092238428https://repository.li.mahidol.ac.th/handle/20.500.14594/77331Extralymphatic filariasis is an uncommon phenomenon that can be caused by several lymphatic filarial species, including zoonotic filaria of animal origins. In this study, we report a case of a 64-year-old Thai woman who presented with a lump in her left breast that was diagnosed with invasive ductal carcinoma. At the same time, a small nodule was found in her right breast, via imaging study, without any abnormal symptoms. A core needle biopsy of the right breast nodule revealed a filarial-like nematode compatible with the adult stage of Brugia sp. A molecular identification of the nematode partial mt 12rRNA gene and ITS1 suggested the causative species as closely related to Brugia pahangi, a zoonotic lymphatic filaria of animals such as cats and dogs. The sequence of the partial mt 12rRNA and ITS1 gene in this patient was 94% and 99% identical to the previously reported sequence of mt 12rRNA and ITS1 genes of B. pahangi. The sequence of ITS1 gene is 99% similar to B. pahangi microfilaria from infected dogs in Bangkok, which was highly suspected of having a zoonotic origin. As far as we know, this is the first case report of B. pahangi filariasis presented with a breast mass concomitantly found in a patient with invasive ductal carcinoma. This raised serious concern regarding the zoonotic transmission of filariasis from natural animal reservoirs.Mahidol UniversityImmunology and MicrobiologyMedicineArticleSCOPUS10.1016/j.parint.2020.102203