Extralymphatic 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.

淋巴丝虫病是一种罕见的现象，可能是由几种淋巴丝虫物种引起的，包括动物来源的人畜共患的丝虫病。在这项研究中，我们报告了一例64岁的泰国妇女，其左乳房有一个肿块，被诊断为浸润性导管癌。同时，通过影像学检查发现她的右乳房有一个小结节，没有任何异常症状。右乳头结节的穿刺活检表明，丝状线虫与成年布鲁氏菌相容。线虫部分mt 12rRNA基因和ITS1的分子鉴定表明，该致病物种与布鲁吉亚·彭亨（Brugia pahangi）密切相关是动物（如猫和狗）的人畜共患的淋巴丝虫病。该患者的mt 12rRNA和ITS1基因的部分序列与先前报道的彭氏芽孢杆菌的mt 12rRNA和ITS1基因的序列分别有94％和99％的同一性。ITS1基因的序列与来自曼谷被感染狗的帕汉短芽孢杆菌微丝虫有99％的相似性，这被高度怀疑是人畜共患病起源。据我们所知，这是首例帕氏芽孢杆菌丝虫病，伴有浸润性导管癌患者伴有乳腺肿块。这引起了对天然动物水库中丝虫病人畜共患病传播的严重关注。