Diagnosis of proliferative sparganosis caused by Spirometra decipiens complex 2 ( Spirometra sp. 3) in a domestic cat in the United States

Sparganosis, a zoonotic infection caused by the plerocercoid (sparganum) larval stage of Spirometra spp., is rarely reported in domestic cats. Sparganosis is typically seen as subcutaneous or visceral granulomatous lesions and has been associated with Spirometra mansonoides in North America. A proliferative form of sparganosis, with tissue invasion and widespread dissemination, has always been associated with Sparganum proliferum. However, emerging molecular evidence challenges this distinction. Here, we report a confirmed case of proliferative sparganosis in a domestic cat caused by Spirometra decipiens complex 2 (also referred to as Spirometra sp. 3). The cat had widespread lesions in multiple tissues, with gross and histologic lesions resembling those attributed to S. proliferum. Molecular identification of larval cestode DNA demonstrated a 99% match to S. decipiens, confirming its role in severe disseminated disease. Our case broadens the understanding of the pathogenic capacity of S. decipiens (Spirometra sp. 3) in felids and emphasizes the critical role of molecular detection for accurate species identification. To our knowledge, proliferative sparganosis attributable to Spirometra sp. 3 has not been reported previously in domestic cats. Given the zoonotic potential of sparganosis, our findings have important implications for both veterinary care and public health surveillance.