Co-infection of Dipetalonema species (Nematoda: Onchocercidae) in a captive squirrel monkey (Saimiri sciureus) from China: first molecular characterization of Dipetalonema freitasi

Infection of <i>Dipetalonema</i> species in Neotropical primates has been documented extensively. However, there is limited information on the molecular characterization of the genus <i>Dipetalonema</i>, specifically regarding the identification of co-infections. In this study, we report the co-infection of <i>Dipetalonema gracile</i> and <i>D</i>. <i>freitasi</i> in a captive squirrel monkey (<i>Saimiri sciureus</i>) from a zoo in China and provide the first molecular characterization of <i>D. freitasi</i>. Morphological analysis identified thirteen adult worms, consisting of nine <i>D. gracile</i> and four <i>D. freitasi</i>. Phylogenetic analyses based on concatenated sequences of two nuclear (18S ribosomal RNA and 28S ribosomal RNA) and two mitochondrial (cytochrome <i>c</i> oxidase subunit I and 12S ribosomal RNA) genes revealed that species of <i>Dipetalonema</i> sensu stricto form a monophyletic clade, divided into two highly supported subclades (DipA and DipB). The DipA clade includes <i>D. robini</i>, <i>D. gracile</i>, and <i>D. graciliformis</i> and is characterized by a sinuous vagina vera, whereas the DipB clade comprises <i>D. yatesi</i>, <i>D. freitasi</i>, and <i>D. caudispina</i> and exhibits a simple vagina vera. Evolutionary changes in the left spicule morphology suggest ancestral and derived states. This integrative approach enhances the understanding of <i>Dipetalonema</i> taxonomy and highlights the risk of parasitic infections in captive primates due to wildlife trade.