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

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