Molecular confirmation of Spirometra mansoni (Cestoda: Diphyllobothriidae) in Javanese keelback water snake (Fowlea melanzosta) in Indonesia

Tapeworms of the genus <i>Spirometra</i> are important zoonotic parasites, yet their taxonomy remains unsettled and molecular species-level data from Indonesia are scarce. We examined plerocercoid larvae isolated from Javanese keelback water snakes (<i>Fowlea melanzosta</i>) collected in East Java, Indonesia. Infection prevalence in <i>F. melanzosta</i> was high (84 %), with 143 spargana recovered from subcutaneous tissues, musculatures, and the body cavities of 25 snakes. Morphological and histological features were consistent with <i>Spirometra</i>. Molecular analysis was used for accurate species-level identification. Partial mitochondrial cox1 sequences from five isolates were generated and analyzed phylogenetically. All sequences clustered unambiguously within the <i>S. mansoni</i> clade (PP = 0.99), alongside global reference isolates. Our analysis also reclassified a 2007 Indonesian isolate, previously assigned to <i>S. erinaceieuropaei</i>, as <i>S. mansoni</i>, retrospectively clarifying a misidentification. This study provides the first prospective molecular confirmation of <i>S. mansoni</i> in Indonesia, and underscores the role of semi-aquatic snakes in transmission cycles. These findings highlight the urgent need for expanded molecular surveillance and integrative taxonomy to clarify the epidemiology and zoonotic potential of <i>Spirometra</i> in the region.